key: cord-0721137-3um07feu
authors: Godden, Sandra M.; Lombard, Jason E.; Woolums, Amelia R.
title: Colostrum Management for Dairy Calves
date: 2019-10-04
journal: Vet Clin North Am Food Anim Pract
DOI: 10.1016/j.cvfa.2019.07.005
sha: 03f0238e1cd5e29cb5436e669ffa219369036ddc
doc_id: 721137
cord_uid: 3um07feu

Colostrum management is the single most important management factor in determining calf health and survival. Additional benefits of good colostrum management include improved rate of gain and future productivity. Successful colostrum management requires producers to provide calves with a sufficient volume of clean, high-quality colostrum within the first few hours of life. This article reviews the process of colostrogenesis and colostrum composition, and discusses key components in developing a successful colostrum management program. In addition, the article discusses approaches for monitoring and proposes new goals for passive immunity in dairy herds.

improved first and second lactation milk production, and reduced tendency for culling during the first lactation. [5] [6] [7] [8] Benefits from colostrum may be attributed to protective Ig as well as high levels of nutrients and bioactive compounds that stimulate postnatal growth and development. 9 Calves have historically been defined as having failure of passive transfer (FPT) if the serum IgG concentration is less than 10 g/L when sampled between 24 and 48 hours of age, based on increased mortality risk below this threshold. [10] [11] [12] However, this definition of FPT needs to be reevaluated, given that recent studies have described reduced morbidity in calves to be associated with incrementally higher serum IgG levels ( Fig. 1) . 4, 12, 13 Although the US dairy industry has shown steady improvement in colostrum and calf management over the past few decades, a recent national dairy study reported FPT to affect 15.6% of calves tested, 14 indicating a need for continued efforts to improve colostrum management. This article reviews the process of colostrogenesis and colostrum composition, and discusses the key components of developing a successful colostrum management program. In addition, it discusses methods for monitoring and presents new goals for passive immunity in dairy herds.

Bovine colostrum consists of a mixture of lacteal secretions and constituents of blood serum, most notably Ig and other serum proteins, which accumulate in the mammary gland during the prepartum dry period. 15 This process begins several weeks before calving, under the influence of lactogenic hormones including prolactin, and ceases abruptly at parturition. Important constituents of colostrum include Ig, leukocytes, growth factors, hormones, nonspecific antimicrobial factors, and nutrients. Concentrations of many of these components are greatest in the first secretions harvested after calving (first milking colostrum), then decline steadily over the next 6 milkings (transition milk) to reach the lower concentrations routinely measured in saleable whole milk ( Table 1 ). 15 Fig. 1 . Nondiseased probability for preweaned heifer calves by days of age and serum IgG concentration categories. Corresponding with serum IgG levels of greater than or equal to 25.0 g/L, 18.0 to 24.9 g/L, 10 to 17.9 g/L, and less than 10.0 g/L were serum total protein categories of greater than or equal to 6.2 g/dL, 5.8 to 6.1 g/dL, 5.1 to 5.7 g/dL, and less than 5.1 g/dL, and Brix score categories of greater than or equal to 9.4%, 8.9% to 9.3%, 8.1% to 8.8%, and less than 8.1%, respectively. 131 Immunoglobulins IgG, IgA, and IgM account for approximately 85% to 90%, 5%, and 7%, respectively, of the total Ig in colostrum, with IgG 1 accounting for 80% to 90% of the total IgG. 16 Although levels are highly variable among cows, one study reported that mean colostral concentrations of IgG, IgA, and IgM were 75 g/L, 4.4 g/L, and 4.9 g/L, respectively. 17 IgG, and IgG 1 in particular, is transferred from the blood stream across the mammary barrier into colostrum by a specific transport mechanism; receptors on the mammary alveolar epithelial cells capture IgG 1 from the extracellular fluid, and the molecule undergoes endocytosis, transport, and eventually release into the luminal secretions. 16 The alveolar epithelial cells cease expressing this receptor, most likely in response to increasing prolactin concentrations, at the onset of lactation. 18 Smaller amounts of IgA and IgM are largely derived from local synthesis by plasmacytes in the mammary gland. 16 Although not well understood, colostral transfer of IgE also occurs and may be important in providing early protection against intestinal parasites. 19 After absorption into the calf's circulation, the duration of passive immunity from maternal Ig is highly variable and depends to a great extent on the total mass of Ig consumed and absorbed within the first 24 hours of life. The rate of decay of colostral antibodies can be influenced by multiple factors, including active viral infections or vaccination. [20] [21] [22] Maternal Leukocytes

Fresh colostrum contains leukocytes of maternal origin; in cattle, macrophages and lymphocytes (mononuclear cells) make up the largest proportion of maternal colostral leukocytes. 23 Maternal colostral leukocytes enter the tissues of neonates following ingestion or enteral delivery in a variety of species, including rats, sheep, swine, and cattle, [24] [25] [26] and feeding colostrum containing maternal leukocytes has been associated with modified neonatal immune responses. [27] [28] [29] [30] [31] Blood mononuclear cells from calves fed colostrum containing maternal leukocytes developed the ability to activate cell-mediated immune responses by the time calves were 1 week of age, compared with 3 weeks of age for calves fed leukocyte-free colostrum. 27 Significant differences in percentage and degree of blood mononuclear cell activation were measured in calves receiving colostrum containing maternal leukocytes, compared with calves fed leukocyte-free maternal colostrum or frozen colostrum. [29] [30] [31] Both freezing 28 and heat treatment (Godden, unpublished, 2010) of colostrum kill most if not all colostral leukocytes. Blood mononuclear cells from 1-day-old calves fed colostrum containing maternal leukocytes were significantly more responsive to bovine viral diarrhea virus, compared with day-old calves that received frozen colostrum or leukocyte-free colostrum. 28 In contrast, there was no difference between treatment groups in the response to a mycobacterial antigen that the calves' dams had not encountered, suggesting that antigen-specific responses measured in a calf following ingestion of maternal colostral leukocytes are related to specific immune memory in the dam. In support of this, cell-mediated immune responses in piglets that nursed maternal colostrum containing leukocytes were significantly higher if their dams had been vaccinated against the tested antigen than if their dams had not been vaccinated. 32 Although research has not evaluated the degree of difference in responses induced by colostral leukocytes from a calf's own dam versus colostral leukocytes from another cow, cross-fostering experiments in piglets suggest that effects of colostral leukocytes on neonatal cell-mediated immunity are greatest when the colostrum contains leukocytes from the neonate's dam. 33 Although multiple studies have confirmed that colostral leukocytes modify immune responses in calves in ways that seem relevant to protective immunity, to date research has not clearly shown an unequivocally beneficial effect of colostral leukocytes on practical outcomes such as calf respiratory or enteric morbidity, or induction of specific and measurable protective immunity following vaccination. Colostral leukocytes fed alone are not sufficient to protect calves from fatal disease in the neonatal period, 34 and recent studies comparing proportions of calves affected by naturally occurring diarrhea or respiratory disease after calves consume fresh maternal colostrum containing leukocytes, or frozen colostrum from their own dam 31 or other cows, 35 have shown small or variable differences in disease between the groups. Regarding the effect of colostral leukocytes on vaccine responses, Meganck and colleagues 36 evaluated humoral and cell-mediated responses to tetanus toxoid vaccination at 2, 5, or 10 days of age in calves fed pooled colostral whey with maternal leukocytes added, or calves fed only pooled colostral whey; this work suggested that colostral leukocytes influenced both tetanus toxoid-specific cellmediated and humoral responses in calves, but the number of calves tested was small, and the effects measured varied substantially for calves vaccinated at 2, 5, or 10 days of age. Langel and colleagues 37 evaluated total (ie, not antigen-specific) monocyte and lymphocyte responses by measuring relative numbers and activation state of calf blood mononuclear cell subsets after routine calfhood vaccination; these investigators found significant differences between groups at certain time points over the months following vaccination. However, the clinical relevance of these differences for immunity against specific pathogens, or resistance to disease, was not defined. In summary, colostral leukocytes modify calf immune responses, and these effects may affect cow health and immunity months or years later. However, to date, effects of colostral leukocytes on practically important health outcomes have not been unequivocally identified, which may in part because it is logistically challenging and expensive to conduct research to measure effects of colostral leukocytes on calf immunity and health, so trials to date may not have included enough calves to provide adequate statistical power to identify small but important health differences.

In addition to Ig for passive immunity, colostrum also contains high amounts of nutrients and nonnutritive biologically active factors that stimulate maturation and function of the neonatal gastrointestinal tract (GIT). 9 The total solids content (percentage) in first milking colostrum and whole milk in Holstein cows was reported to average 23.9% and 12.9%, respectively (see Table 1 ). Much of the increase in colostrum solids content is attributed to a more than 4-fold increase in protein content of colostrum versus milk, this being caused by significant increases in both Ig and casein content. 2 The crude fat content of first milking Holstein colostrum (6.7%) is also significantly higher than for milk (3.6%). 15 Energy from fat and lactose in colostrum is critical for thermogenesis and body temperature regulation. Certain vitamins and minerals, including calcium, magnesium, zinc, vitamin A, vitamin E, carotene, riboflavin, vitamin B12, folic acid, choline, and selenium, are also found in increased concentrations in bovine colostrum. 15, 38 Nonnutritive factors found in increased levels in colostrum include, but are not limited to, growth factors, hormones, cytokines, and nonspecific antimicrobial factors. Trypsin inhibitor, a compound found in colostrum in concentrations nearly 100 times greater than in milk, serves to protect Ig and other proteins from proteolytic degradation in the intestine of the neonatal calf. Bioactive components with antimicrobial activity include lactoferrin, lysozyme, and lactoperoxidase. [39] [40] [41] Oligosaccharides may provide protection against pathogens by acting as competitive inhibitors for the binding sites on the epithelial surfaces of the intestine. 38 It has also been suggested that certain oligosaccharides in colostrum may contribute to gut microbiome development by serving as a substrate to beneficial microorganisms such as Bifidobacterium, although this hypothesis requires further study. 42 Growth factors in bovine colostrum include transforming growth factor beta-2, growth hormone, and insulin. Colostral insulinlike growth factor I and II may be key to regulating development of the GIT of bovine neonates, including stimulation of mucosal growth, brush-border enzymes, intestinal DNA synthesis, and increased villus size, resulting in enhanced absorptive capacity and glucose uptake. 9, 43 Another intriguing and potentially beneficial factor found in high levels in colostrum may be microRNAs (miRNAs). MiRNAs are short, noncoding RNA molecules that can regulate gene expression at the posttranscriptional level, and could represent one possible method of postnatal signaling from the mother to the neonate. Although studies are needed to describe their functional significance in calves, early research in other species suggests that, once absorbed by the neonate, MiRNAs from colostrum may be important in the differentiation and functional development of the intestinal epithelium, 44 and could also play an important role in the maturation of the neonate's immune system. 45 These nutrients and nonnutritive factors, combined with benefits of disease protection from Ig, may contribute to the short-term and long-term benefits from improved colostrum intake, including improved rate of gain, reduced age at first calving, improved first and second lactation milk production, and reduced tendency for culling during the first lactation. [5] [6] [7] [8] Further research is needed to investigate the concept of epigenetic programming or imprinting effects of colostrum on both short-term and long-term health and performance. 9

To achieve successful passive transfer, calves must consume a sufficient mass of IgG in colostrum, and then successfully absorb a sufficient portion of IgG into their circulation. In order to achieve acceptable passive transfer (APT) in greater than or equal to 90% of calves fed, using the traditional definition of APT (serum IgG >10 g/L), it has been estimated that a minimum of 150 to 200 g of IgG needs to be delivered to the calf shortly after birth. In order to achieve the more ambitious goals for excellent passive transfer, presented later in this article, the authors estimate that producers need to deliver greater than or equal to 300 g of IgG shortly after birth. The 2 major factors affecting the mass of Ig consumed are the quality and volume of colostrum fed. Factors affecting the absorption of Ig molecules into circulation include the quickness with which the first colostrum feeding is provided after birth, bacterial contamination of colostrum, and metabolic status of the calf. This article next discusses these key factors, strategies for minimizing bacterial contamination of colostrum, the use of colostrum supplements (CSs) and replacers, benefits of multiple feedings, and benefits of extended colostrum or transition milk feeding after intestinal closure.

Although it is recognized that colostrum contains a wide spectrum of important immune and nutritional components, the concentration of IgG in colostrum has traditionally been considered the hallmark for evaluating colostrum quality, with high quality defined as IgG levels greater than 50 g/L. Colostrum IgG levels can vary dramatically among cows; in an observational study that tested 2253 colostrum samples from 104 farms in 13 states, mean colostral IgG level was 74.2 g/L, with the 5th and 95th percentiles ranging from 24.9 to 130.2 g/L. A total of 77.4% of samples had colostrum IgG level greater than 50 g/L. 46 Factors affecting colostrum quality and yield are reviewed next and methods for testing colostrum quality are discussed.

Comparative studies have reported that there can be a breed effect on colostrum quality. 47, 48 In one study, Holstein cows produced colostrum with total Ig content (5.6%) that was lower than for Guernsey (6.3%), Brown Swiss (6.6%), Ayrshire (8.1%), or Jersey (9.0%) breed cows. 48 Breed differences could be caused by genetics and/or dilutional effects.

Most, but not all, studies report a tendency for older cows to produce higher-quality colostrum, presumably /because of older animals having had a longer period of exposure to farm-specific pathogens. 46, 49, 50 In a study by Shivley and colleagues, 46 colostrum from first and second lactation cows had similar colostrum quality (73.2 and 71.7 g/L of IgG), whereas colostrum from third lactation and older cows was of higher quality (83.3 g/L IgG). Producers should test and record the quality of all colostrum fed. Producers should not automatically discard colostrum from first calf heifers without first testing, because it may be of very good quality.

Studies have generally reported that Ig content of colostrum is not greatly affected by restricting prepartum maternal nutrition. [51] [52] [53] Mann and colleagues 54 reported that feeding a controlled energy diet that met, but did not exceed, energy requirements during the dry period increased colostral IgG but did not affect colostrum yield, compared with diets that offered increased energy. Lacetera and colleagues 55 reported that cows supplemented with injections of selenium and vitamin E in late pregnancy produced a greater volume of colostrum than unsupplemented cows, when all cows were fed a prepartum diet that was deficient in vitamin E and selenium. Aragona and colleagues 56 reported that supplementation with nicotinic acid for 4 weeks prepartum increased IgG concentration in colostrum from 73.8 to 86.8 g/L. More research is needed to investigate whether and how nutrition of the dam during the preparturient period may affect colostrum yield and quality. Producers should feed rations balanced according to National Research Council 2001 guidelines. 57

The relationship between season and colostrum quality or volume remains unclear. Although some studies have reported that exposure to high ambient temperatures during late pregnancy is associated with poorer colostrum composition, including lower mean concentrations of colostral IgG and IgA, 49, 58 others have reported the opposite. 46 It has been suggested that any negative effects of heat stress on colostrum quality might be associated with reduced dry matter intake or reduced mammary blood flow resulting in impaired transfer of IgG and nutrients to the udder. 58 Season may also have an impact on colostrum yield, although this is less well described. In a year-long study of a 2500-cow Jersey dairy in Texas, colostrum yield was highest in June but declined during the fall and winter months. 59 A low-temperature humidity index and a shortened photoperiod 1 month before and at calving were both highly correlated with reduced colostrum yield. The investigators hypothesized that shortened photoperiod may reduce colostrum production because of its impact on melatonin and prolactin, hormones known to be involved with colostrogenesis. However, a study that experimentally manipulated photoperiod reported no effect of photoperiod during the dry period on colostrum Colostrum Management for Dairy Calves quality or yield. 60 Producers should adopt heat-abatement strategies for prepartum cows and heifers and are advised to bank frozen colostrum to meet needs during low colostrum production months. 59 

Although vaccination is not likely to increase total IgG in colostrum, a large body of research has established that vaccinating pregnant cows and heifers during the final 3 to 6 weeks preceding calving results in increased concentrations of antigen-specific protective colostral antibodies, and increased passive antibody titers in calves of vaccinated dams, specific for some common pathogens including Pasteurella haemolytica, Salmonella typhimurium, Escherichia coli, rotavirus, and coronavirus. [61] [62] [63] [64] Dry Period Length Cows with excessively short dry periods (<21 days) produce colostrum with lower IgG concentration. 65 Furthermore, cows with shorter dry periods produce lower yields of colostrum. 59, 66 One controlled field study reported cows with a short (40-day) dry period produced 2.2 kg less colostrum than did cows with a conventional (60-day) dry period. 67

Pritchett and colleagues 68 observed that cows producing less than 8.5 kg of colostrum at first milking were more likely to produce high-quality (>50 g/L) colostrum than higher-producing cows, presumably because of dilutional effects. However, more recent studies report that there is no strong predictable relationship between colostrum IgG concentration and weight of colostrum produced at first milking. 67, 69, 70 

Most studies report that the concentration of Ig in colostrum is highest immediately after calving but begins to gradually decrease over time if harvest is delayed. 60, 71 In an experimental study, Morin and colleagues 60 reported that colostral IgG concentration decreased by 3.7% during each subsequent hour that milking was delayed after calving, because of postparturient secretion (dilution) by the mammary glands. In another study, delaying harvest of colostrum for 6, 10, or 14 hours after calving resulted in a 17%, 27%, and 33% decrease in colostral IgG concentration, respectively. 72

It is difficult to predict, based on such factors such as visual consistency, which colostrum collected will be of high (>50 g/L IgG) versus low quality. 69 The colostrometer, a hydrometer instrument that estimates IgG concentration by measuring specific gravity, can be useful to differentiate high-quality from low-quality colostrum (specific gravity >1.050 approximates IgG >50 g/L). However, factors such as content of fat and colostrum temperature affect the hydrometer reading. 73 More recently, several studies have validated use of the Brix refractometer, an instrument that measures percentage solids in a solution, to indirectly estimate IgG level in colostrum. The Brix refractometer is less affected by temperature and more durable than the glass colostrometer. Studies have reported that a value between 18% and 23% Brix is an appropriate cut point for determining good-quality colostrum (IgG >50 g/L). [74] [75] [76] [77] An achievable herd-level goal is to harvest high-quality colostrum (IgG 50 g/L or Brix 22%) in greater than or equal to 90% of samples tested.

It is recommended that calves be fed 10% to 12% of their body weight (BW) of colostrum at first feeding (3-4 L for a Holstein calf). In one study, mean serum IgG level at 24 hours was significantly higher for calves fed 4 L of colostrum at 0 hours and a further 2 L at 12 hours (serum IgG 5 31.1 g/L) compared with calves fed only 2 L of high-quality colostrum at 0 hours and a further 2 L at 12 hours (serum IgG 5 23.5 g/L). 78 Another study reported that Brown Swiss calves fed 3.8 L (vs 1.9 L) of colostrum at first feeding experienced significantly higher rates of average daily gain and greater levels of milk production in both the first and second lactations. 8 The method of delivering colostrum deserves consideration. Suckling the dam is the least preferred approach, because delays in suckling and failure to control quality and volume ingested can result in higher rates of FPT. 79 When colostrum is delivered with an esophageal tube feeder, the esophageal groove reflex is not triggered, resulting in fluid being deposited into the forestomachs. However, this is not a significant limitation because outflow of colostrum from the forestomachs to the abomasum and small intestine occurs for the most part within 3 hours. 80 As such, equal and acceptable levels of passive transfer are achieved when colostrum is delivered by nipple bottle or esophageal tube feeder, provided that a sufficient volume of colostrum is delivered. 81, 82 One study reported that calves drinking from a nipple bottle consumed an average of only 2.2 L (range, 1-4 L). 83 As such, producers feeding colostrum by nipple bottle should be prepared to deliver any remaining colostrum using a tube feeder, or provide a second bottle feeding within 6 hours, for those calves that do not voluntarily consume their whole allotment. Veterinarians should train staff on how to safely administer colostrum using tube feeders. Equipment sanitation and maintenance are important for both bottles and tube feeders.

The term open gut refers to the unique ability of the neonatal enterocyte to nonselectively absorb intact large molecules, such as Ig, by pinocytosis. 84 From there, Ig molecules are transported across the cell and released into the lymphatics by exocytosis, after which they enter the circulatory system through the thoracic duct. 85 In a process referred to as closure, the absorption of Ig across the intestinal epithelium decreases linearly with time from birth to completely close at approximately 24 hours. 11 Factors affecting the apparent efficiency of absorption (AEA) of Ig for the first colostrum feeding are discussed here, as well as the value of extended colostrum feeding and feeding colostrum or transition milk after gut closure.

The efficiency of Ig transfer across the gut epithelium is optimal soon after birth, with a progressive decline in Ig absorption over time until gut closure. 86, 87 Delaying the first colostrum feeding can only slightly postpone gut closure (36 hours). 88 In a study that randomized newborn calves to provide the first feeding of colostrum (7.5% BW; approximately 200 g of IgG) at different times, higher efficiency of absorption and maximum serum IgG levels were achieved for calves fed at 45 minutes of age (AEA 5 51.8%; IgG 5 25.5 g/L), compared with calves fed at 6 hours (AEA 5 35.6%; IgG 5 18.2 g/L) or 12 hours (AEA 5 35.1%; IgG 5 18.5 g/L). 87 Earlier feeding also resulted in more rapid bacterial colonization of the intestine with organisms such as Bifidobacterium spp. Producers should aim to feed all calves within 1 to 2 hours after birth.

High levels of bacteria in colostrum, and particularly coliform bacteria, may bind free Ig in the gut lumen and/or directly block uptake and transport of Ig molecules across intestinal epithelial cells, thus interfering with passive transfer. 89 Strategies to minimize bacterial contamination of colostrum are discussed next.

Decreased colostral Ig absorption in the first 12 hours has been reported in calves with postnatal respiratory acidosis, associated with prolonged parturition. 90, 91 Hypothermia may also be responsible for a delay in Ig absorption. 92 Although hypoxic calves may have delayed IgG absorption initially, studies have reported that there is no difference in overall absorptive capacity between hypoxic and normoxic calves, and that there is no difference in serum IgG concentrations by the time of gut closure. 93, 94 Producers should provide adequate supportive care to newborns, including warming and drying calves born during cold weather, and providing supplemental heat, blankets, and deep straw bedding. Pain management, through the provision of a nonsteroidal antiinflammatory, has been shown to improve calf vigor and enhance IgG absorption for low-vigor calves following difficult calvings. [95] [96] [97] Presence of the Dam Ig absorption was improved when calves were housed with the dam. 98 However, considering that acceptable levels of serum IgG can be achieved without housing the calf with the dam, and given that the latter practice may increase the calf's risk of exposure to pathogens in the dam's environment, it is currently recommended that the calf be removed from the dam within 1 to 2 hours of birth and hand-fed colostrum. 3

Although it is well recognized that maximal efficiency of absorption of IgG is achieved when the first colostrum feeding is provided within 2 hours after birth, the neonatal intestine is still permeable to IgG past 12 hours. Providing a second feeding sometime after the first postnatal meal can further increase passive transfer of IgG. In a recent study in which calves were randomly assigned to be fed a second feeding (5% BW) of either colostrum, a 1:1 colostrum/milk mixture, or milk at 12 hours of age, calves achieved a higher maximum serum IgG concentration if they were fed either colostrum (30 g/L) or mixture (25.0 g/L) at the second feeding, compared with milk (22.4 g/L). 99 

Feeding colostrum after the gut has closed still offers benefits, even though Ig absorption no longer occurs. One benefit may be that bioactive compounds, such as hormones or oligosaccharides, may stimulate development of the GIT. 42, 100 In one recent study, calves that were transitioned directly onto milk after the first colostrum meal had less overall gastrointestinal mass and less development of villi in the small intestine compared with calves fed either colostrum or transition milk for the first 3 days of life. 100 This improved GIT development could be beneficial for nutrient absorption and gut health. Another benefit may be local protection of the GIT by colostral antibodies. Challenge studies and field trials have reported health and growth benefits from supplementing the milk diet with colostrum for the first 14 days of life. One controlled field trial that added 70 g of colostrum powder containing 10 g of IgG into milk replacer twice daily for 14 days reported improved growth, reduced diarrhea days, and reduced antimicrobial use in treated calves. 101 In another field trial, supplementation of milk replacer with 150 g of bovine colostrum powder containing 32 g of IgG, for the first 14 days, resulted in reductions in diarrhea, respiratory disease, umbilical enlargement, and antibiotic therapy in treated dairy calves. 102 Producers feeding pasteurized whole milk are encouraged to include transition milk in the pool.

Although it is an important source of nutrients and immune factors, colostrum can also represent one of the earliest potential exposures of dairy calves to infectious agents, including Mycoplasma spp, Mycobacterium avium subsp paratuberculosis, and Salmonella spp. 103, 104 Furthermore, high levels of bacteria in colostrum may interfere with Ig absorption. 89 A negative association between colostrum bacteria levels and Ig absorption has been described in several studies. [105] [106] [107] Fresh/raw colostrum fed to calves should contain less than,100,000 colony-forming units (cfu)/mL total plate count (TPC) and less than 10,000 cfu/mL total coliform count. 3 However, bacteria levels in colostrum frequently exceed these goals in dairies. In an observational study that tested 827 colostrum samples from 67 farms in 12 states, almost 43% of samples had TPC greater than 100,000 cfu/mL and 17% of samples had greater than 1 million cfu/mL. 104 Strategies for minimizing bacterial contamination of colostrum are discussed next.

Producers should avoid feeding colostrum from known infected cows (eg, Johne disease) and should avoid pooling raw colostrum. Contamination during colostrum harvest, storage, or feeding processes can be reduced by properly cleaning and sanitizing udders before harvesting colostrum; milking into a clean, sanitized bucket; and transferring colostrum into clean, sanitized storage or feeding equipment.

Bacteria can multiply rapidly if colostrum or milk is stored at warm ambient temperatures. Unless colostrum is to be fed right away, it should be frozen or refrigerated within 1 hour after collection. Colostrum may be frozen for up to 1 year, provided repeated multiple freeze-thaw cycles do not occur. When thawing frozen colostrum, producers should avoid overheating colostrum (avoid temperatures >60 C) or some denaturation of Ig can occur. 108 Options for storing fresh colostrum include refrigeration with or without the use of US Food and Drug Administration-approved preservatives such as potassium sorbate (0.5% final solution in colostrum). In one study, average bacterial counts in raw refrigerated colostrum reached unacceptably high levels (TPC >100,000 cfu/mL) after 2 days of refrigeration. By comparison, average colostrum TPC remained less than,100,000 cfu/mL for 6 days of refrigeration when colostrum was preserved with potassium sorbate. 109

Although pasteurization at higher temperatures can damage Ig, colostrum may be safely heat treated (HT) using a lower-temperature, longer-time approach (60 C [140 F] for 60 minutes), maintaining IgG levels and fluid characteristics while eliminating important pathogens, including E coli, Salmonella enteritidis, and Mycoplasma bovis, and significantly reducing risk of exposure to M avium subsp. paratuberculosis. 108, 110, 111 Calves fed HT colostrum have improved efficiency of IgG absorption, presumably caused by reduced bacterial interference with IgG absorption. 105, 112 In a field study of 1071 newborn calves in 6 Midwest dairy herds, calves fed HT colostrum had higher serum IgG level (18.0 g/L) and reduced risk for diarrhea (30.9%) compared with calves fed fresh colostrum (15.4 g/L; 36.5%). 106 Possibly contributing to these health benefits, Malmuthuge and colleagues 113 reported that feeding HT colostrum enhanced GIT colonization with Bifidobacterium but reduced colonization with E coli within the first 12 hours. If refrigerated in a clean covered container, the shelf life of HT colostrum is at least 8 days. 114 Goals for bacteria levels in HT colostrum are TPC less than 20,000 cfu/mL and coliform count less than 100 cfu/mL, respectively.

Although feeding high-quality, clean maternal colostrum is considered the gold standard, the use of high-quality CSs or colostrum replacements (CRs) may be attractive to producers for a variety of reasons, including availability, consistency, convenience, and as a means of breaking the transmission cycle of pathogens such as M avium ssp. paratuberculosis. 115 Supplements typically contain less than or equal to 60 g of IgG per dose and are intended to supplement (not replace) existing colostrum. There is no added benefit of feeding CS if already feeding 3 to 4 L of high-quality maternal colostrum. 116 By comparison, CR products are designed to completely replace maternal colostrum. They should provide a minimum of 100 g of IgG per pack and should also provide sufficient levels of nutrients to the calf to support metabolic needs in the first day of life. In Canada and the United States, CS and CR products may be licensed through the Canadian Food Inspection Agency, Canadian Center for Veterinary Biologics (Ottawa, ON), or through the US Department of Agriculture (USDA) Center for Veterinary Biologics (CVB; Ames, IA), respectively. In addition to other requirements, licensed products must originate from bovine colostrum; must be processed using accepted protocols to guarantee efficacy, safety, purity, and potency (minimum IgG content); and every serial made for sale and distribution must be tested for purity and potency. 117, 118 Many products that are not CVB-licensed are produced in the United States, using a variety of manufacturing techniques, and with Ig sources including spray-dried bovine colostrum, milk, whey, bovine serum, or plasma. Nonlicensed products are not legally able to claim to supply IgG or to purport to be used for the prevention of FPT, although their use for this purpose is widespread in the United States.

A major consideration when feeding CR products is delivering an adequate dose of IgG to the calf. Many products provide only 100 to 150 g of IgG per pack, although some products provide label directions that suggest feeding increased masses of IgG, at the discretion of the producer. Although not true of all products, studies have shown that several commercially available CR products, when administered at a high enough IgG mass (150-200 g of IgG) within a few hours after birth, can provide acceptable serum IgG concentrations when using a conventional goal for APT (eg, 90% of calves with serum IgG 10 g/L). [119] [120] [121] [122] However, if producers hope to achieve the more ambitious goals for passive transfer that are proposed in relation to monitoring, the authors suggest that they may need to deliver at least 300 g of IgG in a CR product. Research is required to investigate this hypothesis. Apart from dose, there can also be differences among CR products in Ig absorption, with studies generally reporting greater AEA percentage for lacteal-derived CR compared with serum-derived or plasma-derived CR. 123, 124 Because of variable performance among products, veterinarians should review results of peer-reviewed controlled trials when recommending CR products to producers.

A dairy's colostrum management program is one of very few processes in the animal health world that can be easily evaluated and should be routinely reviewed by veterinarians. Although serum IgG measured via radial immunodiffusion (RID) assay is considered the gold standard for evaluating passive transfer in calves, 11 it is expensive and generally requires that samples be tested at a laboratory. Other analytes, such as serum total protein (STP), have been extensively validated, are easily measured at the farm level, and are more economical than measuring IgG directly. 125, 126 STP levels in healthy calves should be evaluated from blood samples collected from 24 hours after the first colostrum feeding to 10 days of age. 127 The earlier in this sampling window that samples are collected, the more accurately the results reflect true IgG absorption and the less likely it is for results to be influenced by IgG distribution/decay or dehydration. The use of a standard optical refractometer to measure STP or an optical or digital Brix refractometer, both of which are field friendly, is becoming more common.

Optical refractometer values of 5.0 to 5.5 g/dL and Brix readings of 8.1% to 8.5% have been used as the cutoff for FPT. 3, [128] [129] [130] [131] The individual calf standard for FPT (serum IgG <10 g/L) has been used for more than 35 years and is mainly based on a decreased risk of mortality when values are greater than or equal to 10 g/L. 7,10,12 Although strategies to evaluate colostrum management programs have traditionally been based on the individual calf standard, McGuirk and Collins 3 proposed sampling a minimum of 12 healthy calves and defined a successful program as one in which 80% of calves had an STP value of 5.5 g/dL or higher. From a study by Calloway and colleagues, 128 Tyler proposed (Personal Communication, 2002) that a successful passive transfer program was one in which 90% of sampled calves test 5.0 to 5.2 g/dL or higher. 132 However, one concern with this approach to setting goals includes the notion that "failure" should be used to describe calves with no measurable IgG, whereas "adequate" does not convey whether an optimal amount of IgG has been absorbed by the calf. In addition, a single cutoff that expresses failure versus adequate passive transfer is too simplistic, because it fails to recognize that increasing concentrations of IgG or STP are associated with reducing morbidity risk and improved calf performance. Studies by Furman-Fratczak and colleagues 13 and Windeyer and colleagues 12 showed that dairy calves with serum IgG levels greater than or equal to 15 g/L and STP greater than or equal to 5.7 g/dL, respectively, experienced lower rates of respiratory disease. In beef calves, Dewell and colleagues 133 reported lower morbidity rates when serum IgG level was greater than or equal to 24 g/L. Based on these and other studies, including the USDA National Animal Health Monitoring System's Dairy 2014 study, 4,46 a reevaluation of the FPT individual and herd-based cut points was conducted. A group of calf experts from the United States and Canada convened in 2018 to review and propose revised individual and herd-based evaluation standards. The proposed consensus standard is based on the association of lower morbidity and higher values of serum IgG, because mortality risk is associated with serum IgG values less than 10 g/L. The proposed standard includes 4 categories: excellent, good, fair, and poor. These categories can be applied to individual calves and to the operation for herd-based evaluation based on the percentage of calves that should be represented in each category ( Table 2) . Because serum IgG level is not commonly measured, equivalent STP and Brix levels are provided for the 4 categories. The proposed consensus standard is meant to set higher goals for calf health in the US dairy industry.

Producers feeding CR products should be aware that the relationship between STP and serum IgG can vary dramatically for calves fed different CR products, depending on manufacturing techniques, the Ig source, level of inclusion, and level of absorption of Ig and non-Ig proteins. As such, the STP and Brix cut points suggested for monitoring passive transfer in calves fed maternal colostrum are frequently inaccurate for calves fed CR. Veterinarians are encouraged to use STP or serum Brix measures to monitor the effectiveness of a CR feeding program only if independently conducted studies are available describing the relationship between STP or serum Brix measures and serum IgG for the specific commercial CR product in use on the farm. If this information is not available for specific CR products, veterinarians are advised to periodically submit frozen serum samples for laboratory analysis of IgG using direct methods such as RID.

Colostrum management is the single most important management factor in determining calf health and survival. Although good progress has been made in the past 20 years, there remains a considerable opportunity for many dairy producers to improve their colostrum management practices, resulting in improved short-term and long-term health and performance of the animals. Producers should provide calves with a sufficient volume of clean, high-quality colostrum within the first few hours of life. Additional benefits may be captured by providing multiple feedings and by extended feeding of colostrum or transition milk after gut closure. Colostrum replacers are useful tools if clean, high-quality maternal colostrum is not available. Ongoing monitoring helps producers to more quickly identify and correct problems within the colostrum management program. 

The development of the conceptus

The development, nutrition, and management of the young calf

Managing the production, storage and delivery of colostrum

Preweaned heifer management on US dairy operations: Part V. Factors associated with morbidity and mortality in preweaned dairy heifer calves

Effects of passive immunity on growth and survival in the dairy heifer

Effects of passive immunity on subsequent production in dairy heifers

Factors associated with mortality to 21 days of life in dairy heifers in the United States

Case study: Effects of colostrum ingestion on lactational performance

Lactation Biology Symposium: Role of colostrum and colostrum components on glucose metabolism in neonatal calves

Failure of passive transfer of colostral immunoglobulins and neonatal disease in calves: a review

Passive transfer of colostral immunoglobulins in calves

Factors associated with morbidity, mortality, and growth of dairy heifer calves up to 3 months of age

The influence of colostral immunoglobulin concentration in heifer calves' serum on their health and growth

Preweaned heifer management on US dairy operations: Part I. Descriptive characteristics of preweaned heifer raising practices

Availability, storage, treatment, composition, and feeding value of surplus colostrum: A review

Immunoglobulin production and transport by the mammary gland

Immunological activities of milk

Effect of prolactin on in vitro expression of the bovine mammary immunoglobulin G 1 receptor

Colostral transfer of bovine immunoglobulin E and dynamics of serum IgE in calves

Passively transferred immunity in newborn calves, rate of antibody decay, and effect on subsequent vaccination with modified live virus vaccine

Effect of age at the time of vaccination on antibody titers and feedlot performance in beef calves

Comparison of levels and duration of detection of antibodies to bovine viral diarrhea virus 1, bovine viral diarrhea virus 2, bovine respiratory syncytial virus, bovine herpesvirus 1, and bovine parainfluenza virus 3 in calves fed maternal colostrum or a colostrum-replacement product

Distribution of T and B lymphocytes in mammary dry secretions, colostrum and blood of adult dairy cattle

Intestinal uptake of intact maternal lymphocytes by neonatal rats and lambs

Intestinal absorption of colostral lymphoid cells in newborn piglets

Update of colostral leukocytes in the intestinal tract of newborn calves

Effects of the ingestion of whole colostrum or cell-free colostrum on the capacity of leukocytes in newborn calves to stimulate or respond in one-way mixed leukocyte cultures

Effect of maternal cells transferred with colostrum on cellular response to pathogen antigens in neonatal calves

Transfer of maternal colostral leukocytes promotes development of the neonatal immune system I. Effects on monocyte lineage cells

Transfer of maternal colostral leukocytes promotes development of the neonatal immune system Part II. Effects on neonatal lymphocytes

Effect of feeding whole compared with cell-free colostrum on calf immune status: The neonatal period

Colostral antibody-mediated and cell-mediated immunity contributes to innate and antigen-specific immunity in piglets

Effect of cross-fostering on transfer of maternal immunity to Mycoplasma hyopneumoniae to piglets

The influence of colostral leukocytes on the immune system of the neonatal calf. IV. Effects on bactericidity, complement and interferon; synopsis

Effect of maternal cells transferred with colostrum on the health of neonate calves

Maternal colostral leukocytes appear to enhance cell-mediated recall response, but inhibit humoral recall response in prime-boost vaccinated calves

Effect of feeding whole compared with cell-free colostrum on calf immune status: Vaccination response

Antioxidants in bovine colostrum

Growth factors and antimicrobial factors of bovine colostrum

Effects of milk-derived bioactives: an overview

Immunoglobulins, growth factors and growth hormone in bovine colostrum and the effects of processing

Short communication: The effect of heat treatment of bovine colostrum on the concentration of oligosaccharides in colostrum and in the intestine of neonatal male Holstein calves

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: Role in the newborn

Porcine milk-derived exosomes promote proliferation of intestinal epithelial cells

Time-dependent expression profiles of mi-croRNAs and mRNAs in rat milk whey

Preweaned heifer management on US dairy operations: Part II. Factors associated with colostrum quality and passive transfer status of dairy heifer calves

Regulation of colostrum formation in beef and dairy cows

Colostral immunoglobulin concentrations among breeds of dairy cattle

Factors associated with colostral specific gravity in dairy cows

Colostrum immunoglobulin concentrations in Holstein and Guernsey cows

Effects of prepartum protein restriction in the beef cow on immunoglobulin content in blood and colostral whey and subsequent immunoglobulin absorption by the neonatal calf

Influence of nutritional restriction during late gestation on production measures and passive immunity in beef cattle

The impact of cow nutrition in the dry period on colostrum quality and immune status of calves

Effect of dry period dietary energy level in dairy cattle on volume, concentration of immunoglobulin G, insulin, and fatty acid composition of colostrum

Effects of selenium and vitamin E administration during a late stage of pregnancy on colostrum and milk production in dairy cows, and on passive immunity and growth of their offspring

Prepartum supplementation of nicotinic acid: Effects on health of the dam, colostrum quality, and acquisition of immunity in the calf

Nutrient requirements of dairy cattle

Composition of colostrum from dairy heifers exposed to high air temperatures during late pregnancy and the early postpartum period

Low colostrum yield in Jersey cattle and potential risk factors

Effect of colostral volume, interval between calving and first milking, and photoperiod on colostral IgG concentrations in dairy cows

Passive protection of calves against experimental infection with Salmonella typhimurium

A field trial to evaluate the efficacy of a combined rotavirus-coronavirus Escherichia coli vaccine in dairy cattle

Preparturient vaccination to enhance passive immunity to the capsular polysaccharide of Pasteurella haemolytica A1

Effect of vaccination of the dam on rotavirus infection in young calves

Metabolism and mammary secretion of proteins in the cow

Reducing dry period length to simplify feeding transition cows: Milk production, energy balance and metabolic profiles

Shortening the dry period from 60 to 40 days does not affect colostrum quality but decreases colostrum yield by Holstein cows

Management and production factors influencing Immunoglobulin G 1 concentration in colostrum from Holstein cows

Use of mammary gland and colostral characteristics for prediction of colostral IgG 1 concentration and intramammary infection in Holstein cows

Mass transfer of immunoglobulin G1 into colostrum

Factors associated with the concentration of immunoglobulin G in the colostrum of dairy cows

Effect of delayed colostrum collection on colostral IgG concentration in dairy cows

Evaluation of the hydrometer for testing immunoglobulin G 1 concentrations in Holstein colostrum

Refractometer assessment of colostral and serum IgG and milk total solids concentrations in dairy cattle

An evaluation of Brix refractometry instruments for measurement of colostrum quality in dairy cattle

Evaluation of the Brix refractometer to estimate immunoglobulin G concentration in bovine colostrum

Evaluation of on-farm tools for colostrum quality measurement

Effects of quality, quantity, and timing of colostrum feeding and addition of a dried colostrum supplement on immunoglobulin G 1 absorption in Holstein bull calves

The period between birth and first suckling in dairy calves

The failure of the oesophageal groove reflex, when fluids are given with an oesophageal feeder to newborn and young calves

Improving passive transfer of immunoglobulins in calves II: Interaction between feeding method and volume of colostrum fed

The effect of tube versus bottle feeding colostrum on immunoglobulin G absorption, abomasal emptying, and plasma hormone concentrations in newborn calves

Comparison of colostrum feeding by nipple bottle versus oroesophageal tubing in Holstein dairy bull calves

Electron microscopic studies of the jejunal epithelium from neonatal pigs fed different diets

The ultrastructure of neonatal calf intestine and absorption of heterologous proteins

Effect of colostral immunoglobulin G1 and immunoglobulin M concentrations on immunoglobulin absorption in calves

Effect of delaying colostrum feeding on passive transfer and intestinal bacterial colonization in neonatal male Holstein calves

Colostral immunoglobulin transfer in calves I. Period of absorption

Influence of administered indigenous microorganisms on uptake of [iodine-125] gamma-globulin in vivo by intestinal segments of neonatal calves

Decreased colostral immunoglobulin absorption in calves with postnatal respiratory acidosis

Energy metabolism and thermoregulation in the newborn calf; Effect of calving conditions

The effects of cold stress on neonatal calves II. Absorption of colostral immunoglobulins

Hypoxia in neonatal calves: Effect on intestinal transport of immunoglobulins

Effect of high arterial carbon dioxide tension on efficiency of immunoglobulin G absorption in calves

A field study to evaluate the effects of meloxicam NSAID therapy and calving assistance on newborn calf vigor, improvement of health and growth in pre-weaned Holstein calves

The effect of Meloxicam NSAID therapy on the change in vigor, suckling reflex, blood gas measures, milk intake and other variables in newborn dairy calves

Effect of implementing a novel calf vitality scoring system and early intervention program on pain management in newborn calves

Studies on dairy calves allowed to suckle their dams at fixed times post-partum

Effect of extended colostrum feeding on serum IgG in newborn calves

The effects of extended colostrum feeding on gastrointestinal tract growth of the neonatal dairy calf

Evaluation of the effects of oral colostrum supplementation during the first fourteen days on the health and performance of preweaned calves

Evaluation of the effects of colostrum replacer supplementation of the milk replacer ration on the occurrence of disease, antibiotic therapy, and performance of pre-weaned dairy calves

Isolation of Mycobacterium paratuberculosis from colostrum and milk of subclinically infected cows

Otitis media in preweaned Holstein dairy calves in Michigan due to Mycoplasma bovis

The effect of feeding heat treated colostrum on passive transfer of immune and nutritional parameters in dairy calves

Heat-treated colostrum and reduced morbidity in preweaned dairy calves: Results of a randomized trial and examination of mechanisms of effectiveness

Nationwide evaluation of quality and composition of colostrum on dairy farms in the United States

Heat-treatment of bovine colostrum I: Effects of temperature on viscosity and immunoglobulin G

Preventing bacterial contamination and proliferation during the harvest, storage and feeding of fresh bovine colostrum

Heat-treatment of bovine colostrum II: Effects of heating duration on pathogen viability and immunoglobulin G

Heat treatment of colostrum on commercial dairy farms decreases colostrum microbial counts while maintaining colostrum immunoglobulin G concentrations

Heat-treated (in single aliquot or batch) colostrum outperforms non-heat-treated colostrum in terms of quality and transfer of immunoglobulin G in neonatal Jersey calves

Heat-treated colostrum feeding promotes beneficial bacteria colonization in the small intestine of neonatal calves

Improving cleanliness and shelf-life of refrigerated colostrum using heat-treatment and chemical preservatives

Minnesota Dairy Health Management Conference

Efficacy of feeding a plasma-derived commercial colostrum replacer for the prevention of transmission of Mycobacterium avium subsp. paratuberculosis in Holstein calves

Serum immunoglobulin concentrations after feeding maternal colostrum or maternal colostrum plus colostral supplement to dairy calves

Evaluation, and Licensing -Reviewer's Manual

Center for Veterinary Biological Products

Improving passive transfer of immunoglobulins in calves. I: Dose effect of feeding a commercial colostrum replacer

Anionic salts in the prepartum diet and addition of sodium bicarbonate to colostrum replacer, and their effects on immunoglobulin G absorption in the neonate

Serum IgG and total protein concentrations in dairy calves fed two colostrum replacement products

Efficacy of colostrum replacer versus maternal colostrum on immunological status, health and growth of preweaned dairy calves

Relationship between serum total protein and serum IgG in Holstein calves fed either a plasma-or lacteal-derived colostrum replacer

Effect of feeding maternal colostrum, a plasma-derived, or a colostrum-derived colostrum replacer on passive transfer of immunity, health, and performance of preweaning heifer calves

Systematic review and meta-analysis of diagnostic accuracy of serum refractometry and Brix refractometry for the diagnosis of inadequate transfer of passive immunity in calves

Using serum and plasma samples to assess failure of transfer of passive immunity in dairy calves

Technical note: Serum total protein and immunoglobulin G concentrations in neonatal dairy calves over the first 10 days of age

Comparison of refractometers and test endpoints in the measurement of serum protein concentration to assess passive transfer status in calves

Evaluation of digital and optical refractometers for assessing failure of transfer of passive immunity in dairy calves

Evaluation of a Brix refractometer to estimate serum immunoglobulin G concentration in neonatal dairy calves

Brix refractometry in serum as a measure of failure of passive transfer compared to measured immunoglobulin G and total protein by refractometry in serum from dairy calves

Colostrum management for dairy calves

Association of neonatal serum immunoglobulin G1 concentration with health and performance in beef calves