UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE RELATIVE EFFICIENCY OF SPAYED, OPEN, AND BRED HEIFERS IN THE FEED LOT G. H. HART, H. R. GUILBERT, and H. H. COLE BULLETIN 645 December, 1940 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE The 1938 feeding trial 4 The 1939 feeding trial 10 Discussion 15 Conclusions 18 Acknowledgments 19 THE RELATIVE EFFICIENCY OF SPAYED, OPEN, AND BRED HEIFERS IN THE FEED LOT 2 G. H. HAKT, 3 H. R. GUILBEET, 4 and H. H. COLE 5 In cattle-feeding operations, opinions have differed on the relative efficiency of spayed, open, and bred heifers. Interest was stimulated by Cole's 8 demonstration of superfecundity and superfertility in rats treated with mare gonadotropic hormone. Success was not attained with adult females so treated, although the average size of their litters was larger than in the normal colony. When young rats 21 to 31 days old were treated and bred, the number of implanted fetuses was extraor- dinary, reaching in one case 28. Among the 288 immature rats used in these experiments, 38 per cent of those sacrificed had more than 20 fe- tuses implanted, while the largest number of living young born was 17. The excessive pregnancy burden placed on these very young female rats was carried with an apparent increase in body growth. Cole and Hart 7 studied further the effect of pregnancy and lactation on growth in the rat. According to their data, pregnancy stimulates skeletal and tissue growth in this species beyond that found in nonbred littermate controls. This occurred even during the first pregnancy in females precociously matured by the injection of mare gonadotropic hormone. These enhanced gains continued at a fairly constant rate for the first six pregnancies. Nursing litters of four to six young did not retard the rate of gain over the nonbred controls. The increased growth rate of these immature animals during preg- nancy was accompanied by and dependent upon an increased food con- sumption, which was evident by the second day after conception. In continuing similar studies on pseudopregnant rats, Hart and Cole 8 found 1 Eeceived for publication June 17, 1940. 2 The investigational work reported herein, being financially supported under a Bankhead- Jones project, became cooperative with the Bureau of Animal Industry, United States Department of Agriculture. 3 Professor of Animal Husbandry and Animal Husbandman in the Experiment Station. 4 Associate Professor of Animal Husbandry and Associate Animal Husbandman in the Experiment Station. 5 Associate Professor of Animal Husbandry and Associate Animal Husbandman in the Experiment Station. 6 Cole, H. H. Superfecundity in rats treated with mare gonadotropic hormone. Amer. Jour. Physiol. 119:704-12. 1937. 7 Cole, H. H., and G. H. Hart. The effect of pregnancy and lactation on growth in the rat. Amer. Jour. Physiol. 123:589-97. 1938. 8 Hart, G. H., and H. H. Cole. Studies on the cause of increased growth during pregnancy. Soc. Exp. Biol, and Med. Proc. 41:310-13. 1939. [3] 4 University of California — Experiment Station that the gains caused by repeated pseudopregnancies were at nearly the same rate as secured in animals going through normal pregnancy. The long-established practice of spaying heifers has been gradually declining. Breeding heifers to prevent the disturbance in feed lots inci- dent to heat periods has become widely practiced. Ostertag 9 at Stuttgart, Germany, reported experiments showing that bulls up to two years of age produced meat more efficiently than castrates of the same breed. Gramlich 10 and Gramlich and Thalman 11 reported data on spaying, sex, and age as factors in cattle feeding. They concluded that heifers made the most desirable beef carcasses at 8 to 15 months of age and that if the animals were marketed at these earlier ages there was little oc- casion for spaying. In three direct comparisons with spayed and open heifers, two with yearlings and one with calves, the average daily gain was 2 pounds for the open against 1.8 pounds for the spayed. The food required for 100 pounds of gain was 10 per cent greater for the spayed groups. There was also a difference in the dressing percentages — 59.1 per cent for the open against 57.3 per cent for the spayed groups. The conclusion was reached that spaying, while not highly important for the feeder, may still be of some value to the ranchman, in managing his herd, by preventing pregnancy in heifers that are to be sold for slaughter. The desire to obtain further data on the questions discussed in the foregoing paragraphs, particularly in relation to feed-lot operations, resulted in the experiments discussed in this paper. Over a period of years, about one fourth to one half of the heifers are required for re- placement, and the remainder are available for slaughter. THE 1938 FEEDING TRIAL It was planned to carry concurrently in the feed lot, spayed, open, and bred heifer groups. Despite some difficulty in locating open heifers in the fall, when the animals were purchased, 37 head of yearlings were obtained in October, 1938. Most of these originated in northern Arizona as calves; the others were natives. The purchase weight after a 3 per cent shrink averaged 571 pounds per head. At purchase the heifers were on wheat stubble containing little or no grain ; and their food supply 9 Ostertag, E. von. Veterinary science in relation to public health with special reference to the production and distribution of meat. Keports for the General Meet- ings, 11th Internatl. Vet. Congress, London 2:257-72. 1930. 10 Gramlich, H. J. The effect of spaying in beef production. Amer. Soc. Anim. Prod. Proc. 1926-27:213-16. 11 Gramlich, H. J., and E. E. Thalman. Sex and age as factors in cattle feeding. Nebraska Agr. Exp. Sta. Bui. 252:1-55. 1930. Bul. 645] Relative Efficiency of Heifers in the Feed Lot 5 was probably lacking certain dietary essentials, notably vitamin A, pro- tein, and total energy intake. They had been losing weight and were very thin on arrival at the University Farm on October 15, 1938. As a group they received 300 to 400 pounds of chopped barley straw containing 30 per cent molasses with alfalfa hay. They did not eat well on arrival and lost additional weight. A tuberculin test was given ; and at the time of reading the test on October 20, they were weighed individually and divided according to weight and grade as follows : Lot 1: To be bred; 13 head (5 good, 4 low good, and 4 medium) ; average weight, 537 pounds. Lot 2: To remain open; 11 head (4 good, 4 low good, and 3 medium); average weight, 540 pounds. Lot 3: To be spayed; 13 head (6 good, 3 low good, and 4 medium) average weight, 536 pounds. At this time they were also numerically branded, with a caustic brand- ing fluid, for identification. One animal was removed because rectal ex- amination showed her to be pregnant. The following day, October 21, the cattle were started on the pre- liminary feeding period. The straw was omitted, and they were grad- ually brought on feed by increasing the percentage of concentrates. At the end of the 24-day preliminary period they were averaging 14 pounds daily of a combination containing 60 per cent of alfalfa molasses meal and 40 per cent of concentrate mixture. The alfalfa meal contained 25 per cent of molasses ; and the concentrate mixture consisted of 50 per cent of rolled barley, 40 per cent of dried molasses beet pulp and 10 per cent of hot pressed cottonseed meal. The changes in proportion of alfalfa molasses meal and the concentrate mixture during the 118-day experi- mental period are shown in table 3. The first alfalfa available was pre- pared on the University Farm. It was coarsely chopped into about 1-inch lengths and mixed with molasses. On January 25 a new source of this part of the ration became necessary, which consisted of much finer-chopped alfalfa molasses meal, passed through a hammer mill with a ^-in.-mesh screen. The lot-3 animals were spayed on October 25. All recovered in normal time and were gaining weight at the end of the preliminary period. The animals tentatively placed in lots 1 and 2 were carefully paired with respect to grade and weight in order to breed whichever one of a pair that came into estrum first. This arrangement resulted in getting the required number of animals for lot 1 pregnant in the shortest time. Breeding began on November 1, and all animals for lot 1 became preg- 6 University of California — Experiment Station nant except no. 24. This heifer did not again manifest heat after the first breeding on November 28 and her nonpregnant condition was not ascertained until time of slaughter. Table 1 gives the weight of the uterus with contents, and the weight and crown-rump length of the fetus of each animal at the varying stages of gestation. During the preliminary period four heifers in each lot were trained to be enclosed in individual pens at feeding time. The remainder of the animals in each lot were fed as a group. Individual feeding was planned in order to more accurately record the time of increase in appetite of TABLE 1 Breeding and Pregnancy Data of Lot-1 Animals, 1938 Trial* Animal no. Date bred Date rebred Days pregnant Weight of uterus and contents, pounds Weight of fetus, pounds Crown- rump length of fetus, centimeters 5 Nov. 12 Nov. 7 Nov. 1 Jan. 17 Nov. 2 ' Nov. 14 Nov. 14 Nov. 28 Nov. 11 Nov. 5 Dec. 4 Nov. 1 Nov. 2 None None None Feb. 4 None None Dec. 7 None None None None None None 131 136 142 47 141 129 106 Not pregnant 132 138 109 142 141 17.3 17.8 21.8 1.3 20.3 17.7 7.2 0.5 16.0 20.2 8.0 20.0 13.9 2.7 3.7 4.4 3.6 2.8 1.1 2.7 4.2 1.0 3.4 2.1 28.5 8 32.0 9 23.0 10 2.3 15 33.0 16 30.0 18 21.5 24 25 28 29.0 33.5 32 21.5 34 32.5 39 25.5 The animals were killed on March 23, 1938. pregnant heifers compared with open and spayed, if this occurred. The concentrates and roughage were fed mixed in definite proportions and were the same for each lot. This procedure simplified feeding according to appetite, yet assured the same quality of feed for all animals. Individual feeding of cattle has its complications, and this trial proved no exception. In lots 1 and 2 the animals fed individually gained on the average less per day, consumed less food, and required more feed per 100 pounds' gain, than the group-fed animals. In lot 3 there was prac- tically no difference. Water was not provided in the individual pens, whereas animals in the group-fed lots frequently drank water during feeding. The cattle were weighed on three successive days at the beginning of and on two successive days at the close of the experimental period ; the averages of these weights were used as beginning and final weights. Table Bul. 645] Relative Efficiency of Heifers in the Feed Lot TABLE 2 Weights and Gains of Individual Animals, in Pounds; 1938 Trial Animal no. Beginning weight Final weight Total gain Average daily gain Lotl 25* 39* 9 10 15 16 18 24 28 32 34 Average 577 650 528 593 548 507 673 573 546 517 662 491 589 573 733 904 688 775 805 745 953 840 720 680 895 720 835 791 156 254 160 182 257 238 280 267 174 163 233 229 246 218 1.32 2.15 1.35 1.54 2.12 2.02 2.37 2.26 1.47 1.38 1.97 1.94 2.09 1.85 Lot 2 3* 563 516 750 730 187 214 1.58 12* 1.81 26* 569 604 638 672 725 755 888 925 156 151 250 253 1.32 40* 1.27 19 2.11 20 2.14 22 584 843 259 2.19 23 520 755 235 1.99 29 542 725 183 1.55 33 507 743 236 2.00 38 542 569 723 778 181 209 1.53 Average 1.77 Lot 3 11* #•■ 13* 511 592 567 627 508 549 551 573 657 506 520 594 453 554 715 855 795 815 695 698 868 780 900 653 780 868 625 773 204 263 228 188 187 149 317 217 243 147 260 274 172 219 1.73 2.23 14* 1.93 27* 1.59 2 1.59 6 1.26 7 2.68 17 1.84 21 30 2.06 1.24 35 2.20 36 2.32 37 1.46 Average. 1.86 The individually fed animals are marked with an asterisk. 8 University of California — Experiment Station 2 gives these weights, with total gain and average daily gain individually of the animals in all the lots. Table 3 shows the average weights for each 30 days and the entire 118 days, including average daily gain and ration TABLE 3 Weights, Daily Gains, and Feed Consumption, in Pounds, of All Lots in 1938 Trial Feeding period Average initial weight Average final weight Average daily gain Average daily ration Alfalfa molasses meal Concen- trates Feed per 100 pounds gain Alfalfa molasses meal Concen- trates Total Lot 1 (13 head) 573 654 2.70 10.0 6.7 322 248 654 704 1.64 12.0 8.0 734 490 704 743 1.32 9.8 9.8 742 742 743 792 1.72 9.0 10.0 531 587 573 792 1.85 10.3 8.6 556 467 568 799 1.96 10.6 9.0 542 456 587 775 1.60 9.4 7.9 607 507 First 30 days Second 30 days Third 30 days Last 28 days Entire period (118 days). .. Group-fed (118 days) Individually fed (118 days) 620 1,224 1,484 1,118 1,023 998 1,114 Lot 2 (11 head) First 30 days Second 30 days Third 30 days Last 28 days Entire period (118 days).. . Group-fed (118 days) Individually fed (118 days) 569 648 2.65 10.0 6.7 379 253 648 702 1.78 11.6 7.8 653 435 702 738 1.21 9.7 9.7 801 801 738 778 1.43 9.1 10.1 641 703 569 778 1.77 10.0 8.6 572 482 572 800 > 1.93 10.7 9.0 554 470 563 740 1.49 9.2 7.7 618 519 632 1,088 1,602 1,344 1,054 1,024 1,137 Lot 3 (13 head) First 30 days Second 30 days Third 30 days Last 28 days Entire period (118 days)... Group-fed (118 days) Individually fed (118 days) 554 633 2.63 10.1 6.7 385 257 633 692 1.96 12 3 8.1 627 418 692 727 1.17 9.9 9.9 •849 849 727 773 1.62 9.4 10.3 578 639 554 773 1.86 10.4 8.8 565 475 546 763 1.84 10.6 8.9 576 485 574 795 1.87 10.1 8.4 553 448 642 1,045 1,698 1,217 1,040 1,061 1,001 with the feed consumed per 100 pounds' gain. Corresponding data are given for the group-fed and the individually fed animals. The animals were sold on March 14, 1939 ; but actual slaughter was delayed until March 23. Table 4 gives the data on individual live weight, the carcass weight, warm and cold, together with the dressing percentage figured on the cold-carcass weight. Bul. 045] Relative Efficiency of Heifers in the Feed Lot TABLE 4 Slaughter Data, 1938 Trial Animal no. Final weight, pounds Selling weight, pounds Warm -carcass weight, pounds Cold-carcass weight, pounds Dressing percentage, cold Lot 5 8 9 10 15 16 18 24 25 28 32 34 39 Average 733 904 805 745 953 840 720 680 688 895 720 835 775 791 703 867 773 715 691 653 660 859 691 802 744 760 436 483 455 418 523 463 401 388 400 508 405 452 460 421 465 439 404 504 447 388 376 387 486 389 445 443 430 53.6 56.8 56.5 55.1 55.4 56.1 57.6 58.6 56.6 56.3 55.5 59.5 Lot 2 3 750 730 888 925 843 755 725 725 743 723 755 778 720 701 852 888 809 725 696 696 713 694 725 747 434 403 502 525 480 406 426 419 412 400 458 442 417 388 483 507 464 392 403 403 399 387 442 426 57.9 12 55.3 19 56.7 20 22 23 57.1 57.3 54.1 26 57.9 29 57.9 33 56.0 38 55.8 40 60.9 57 Lot 3 2 695 698 868 715 855 795 780 900 815 653 780 868 625 773 667 670 883 686 821 763 749 864 782 626 749 833 600 742 403 410 463 404 473 450 463 516 479 360 429 474 366 438 392 396 445 390 456 432 442 494 465 350 411 454 356 422 58.8 6 59.1 7 53.4 11 56.8 13 55.5 14 56.6 17 59.0 21 57.2 27 59.5 30 55.9 35 54.9 36 54.5 37 59.3 Average 56.9 10 University of California — Experiment Station At the end of the trial the slaughter animals graded somewhat lower than the feeders, as follows : Lot 1 : 1 good, 4 low good, and 8 medium. Lot 2 : 2 good, 2 low good, and 7 medium. Lot 3 : 1 good, 5 low good, and 7 medium. The carcass grades were comparable with those of the finished animals, although five were removed from the cooler before they had been graded. THE 1939 FEEDING TRIAL In 1939 the experiment was repeated, using 40 head of yearling heifers from a different source. These animals came from New Mexico as calves and had been on a Madera County range for about one year. The range was dry, and the animals were even thinner than those purchased the previous year, though of considerably better breeding. They arrived at the University Farm on August 12, 1939 ; as a group they were given, between arrival and August 15, 1,790 pounds of alfalfa hay and 160 pounds of concentrates. As in the first experiment, each of the animals was branded. On Au- gust 13 and 15, when individual weights were taken, the average weight was 482 pounds. On the latter date the heifers were graded and divided into three lots as nearly equal as possible on the basis of both weight and grade, as follows: Lot 1: To be bred; 14 animals (4 good, 6 low good, and 4 medium); average weight, 477 pounds. Lot 2: To remain open; 13 animals (4 good, 4 low good, and 5 medium) ; average weight, 485 pounds. Lot 3: To be spayed; 13 animals (3 good, 6 low good, and 4 medium); average weight, 484 pounds. The lot-3 animals were spayed on August 19, and all recovered from the operation in normal time. Ten had a recently formed corpus luteum in one ovary, showing that they were having estrual periods, whereas the ovaries in the other three were inactive. It was desired to have the animals in lot 1 as far advanced in preg- nancy as possible at the time of slaughter. Breeding was therefore started at once, no. 1 being bred on August 23. This animal, like no. 24 in the 1938 trial, did not become pregnant to this service, never came in heat again, and her nonpregnant condition was ascertained at time of slaughter. Some difficulty was experienced in getting all the animals bred. They had been paired with animals in lot 2 for breeding, as in the previous year, but no exchange of animals was made. It was felt that the early appearance of estrum might be evidence of more thrifty condition Bul. 645] Relative Efficiency of Heifers in the Feed Lot 11 and thus give advantage to lot 1 if transfers were made. At the time of slaughter, 9 animals were pregnant 150 days or more ; 4 varied from 75 to 125 days ; and 1 was open (table 5) . The average weight of the uteri and ovaries of the open heifers in lot 2 was 0.57 pound, whereas that of the uteri alone in the spayed heifers in lot 3 was 0.15 pound. The same concentrate mixture was fed throughout the trial, made up as follows : rolled barley, 50 per cent ; dried molasses beet pulp, 40 per cent; hot pressed cottonseed meal, 10 per cent. A good quality of baled alfalfa hay produced on the University Farm constituted the sole rough- TABLE 5 Breeding and Pregnancy Data of Lot-1 Animals, 1939 Trial* Animal no. Date bred Date rebred Days pregnant Weight of uterus and contents, pounds 1 5 9 Aug. 23 Aug. 23 Sept. 17 Sept. 17 Sept. 5 Aug. 25 . Aug. 31 Sept. 17 Aug. 31 Aug. 27 Sept. 2 Sept. 4 Sept. 17 Sept. 17 None None None Dec. 1 None None None Nov. 5 None None None None Oct. 13 Nov. 12 Not pregnant 175 150 75 162 173 167 101 167 171 165 163 124 94 0.5 26.0 25.0 12 19 20 2.5 25.5 28.5 21 26.0 22 6.5 28 22.0 29 30.5 31 23.0 33 36 21.5 10.0 37 4.5 * The animals were killed on February 14, 1940. age. This change was made because evidence from the previous year indicated that the very fine-chopped roughage might have influenced rumination and appetite. No animals were fed individually, because of difficulties encountered in this procedure the previous year. Throughout the trial, concentrates and roughage were fed separately. The latter was always in excess, the hay mangers being cleaned out at regular intervals to remove coarse stems of alfalfa and foreign material ; and the weigh- back was recorded. The concentrates were increased very gradually, to avoid throwing the animals off feed. It was desired not to have the ani- mals overfinished at the end of the trial, the length of which was fixed by the desire to have gestation well advanced. During the preliminary period the concentrates were gradually raised from 1 to 4 pounds per head daily. Bringing animals to full feed from dry range feed when they are very thin is necessarily slower than when they come from green pastures in reasonably good feeder condition. 12 University of California — Experiment Station TABLE 6 Weights and Gains of Individual Animals, in Pounds ; 1939 Trial 13 3 14 2 35 38 30 23 8 11 32 24 Average Lot 1 19 578 572 612 553 556 543 528 537 510 537 515 513 508 468 538 777 933 973 835 915 865 883 873 832 883 807 825 802 788 857 199 361 361 282 359 322 355 336 322 346 292 312 294 320 319 1.33 20 2.40 12 2.40 28 1 88 31 2.39 5 2.15 9 2.37 36 2.24 22 2.15 33 2.31 1 1.95 21 2.08 29 1.96 37 2.13 2.12 Lot 2 10 598 603 565 578 555 573 510 530 525 510 483 512 473 540 922 968 882 917 855 832 873 862 828 712 723 817 712 839 324 365 317 339 300 259 363 332 303 202 240 305 239 299 2.16 18 2.43 4 2.11 39 2.26 27 2.00 16 15 1.73 2.42 40 2.21 25 2.02 17 1.35 7 1.60 26 2.03 34 1.59 Average 1.99 Lot 3 Bul. 645] Relative Efficiency of Heifers in the Feed Lot 13 On September 11, 12, and 13, the animals were weighed individually for average weights. The final period started on September 12 and con- tinued for 150 days to February 9, 1940. At the beginning of the final period the animals in lot 1 averaged 538 pounds ; lot 2, 540 pounds ; and lot 3, 531 pounds. The slightly reduced average of the lot-3 animals at TABLE 7 Weights, Daily Gains, and Feed Consumption, in Pounds, of All Lots in 1939 Trial Feeding period Average initial weight Average final weight Average daily gain Average daily- ration Alfalfa hay Concen- trates Feed per 100 pounds, gain Alfalfa hay Concen- trates Total Lot 1 (14 head) First 30 days Second 30 days Third 30 days Fourth 30 days Fifth 30 days Entire period (150 days) 538 616 2.60 13.9 5.5 534 212 616 663 1.60 13.5 7.6 860 486 663 715 1.73 12.4 9.0 721 521 715 794 2.63 10.4 10.9 395 416 794 857 2.09 6.5 13.4 313 644 538 857 2.12 11.4 9.3 535 438 746 1,346 1,242 812 957 973 Lot 2 (13 head) First 30 days Second 30 days Third 30 days Fourth 30 days Fifth 30 days Entire period (150 days) 540 612 2.40 14.3 5.5 593 229 612 672 1.99 14.2 7.6 712 383 672 713 1.36 12.2 9.0 900 663 713 771 1.94 9.8 10.9 503 565 771 839 2.26 9.3 13.4 410 594 540 839 1.99 12.0 9.3 600 467 1,095 1,563 1,069 1,005 1,067 Lot 3 (13 head) First 30 days Second 30 days Third 30 days Fourth 30 days Fifth 30 days Entire period (150 days) 531 605 2.40 13.8 5.5 562 226 605 656 1.71 13.1 7.6 767 447 656 694 1.27 11.9 9.0 935 711 694 743 1.64 9.6 10.9 584 667 743 799 1.88 4.3 13.4 226 716 531 800 1.79 10.5 9 3 588 521 788 1,214 1,645 1,251 943 1,109 this time was probably caused by the spaying operation. Table 6 gives the beginning and final weights, with total gain and average daily gain of the animals in all the lots. Table 7 gives the average weights and daily gains for each 30 days and for the entire 150 days of the animals in each lot, including the average daily ration and feed consumed per 100 pounds' gain. The final period terminated February 9; and the animals were 14 University of California — Experiment Station TABLE 8 Slaughter Data, 1939 Trial Animal no. Final weight, pounds Selling weight, pounds Warm-carcass weight, pounds Cold-carcass weight, pounds Dressing percentage, cold Lot 1 1 5 9 12 19 20 21 22 28 29 31 33 36 37 Average 4 7 10 15 16 17 18 25 26 27 34 39 40 Average 2 3 6 8 11 13 14 23 24 30 32 35 38 Average 807 865 883 973 777 933 825 832 835 802 915 883 873 788 857 775 830 848 934 746 896 792 799 802 770 878 848 838 756 517 520 484 582 459 555 484 502 503 472 534 497 516 470 507 500 500 467 565 443 539 468 487 486 455 517 481 500 455 490 64.53 60.21 55.09 60.48 59.38 60.17 59.09 60.97 60.62 59.09 58.85 56.74 59.66 60.14 59.64 Lot 2 723 922 873 832 712 817 855 712 917 862 839 847 694 885 838 799 684 929 795 784 821 684 880 828 805 538 446 538 536 492 441 605 515 496 501 430 553 523 509 522 432 520 522 477 426 585 500 481 482 416 536 506 492 61.64 62.24 58.74 62.28 59.72 62.32 62.95 62.90 61.32 58 72 60.86 60.88 61.14 61.21 Lot 3 840 857 807 765 775 808 788 790 732 795 737 867 832 823 775 734 744 776 756 758 703 763 708 832 799 767 506 499 494 470 468 476 482 457 439 470 441 510 477 493 482 479 456 452 462 469 441 425 457 425 493 473 462 61.13 59.55 61.82 62.09 60.75 59.56 61.99 59.20 60.47 59.87 61.19 60.19 60.22 Bul. 645] Relative Efficiency of Heifers in the Feed Lot 15 weighed individually on February 8, 9, and 10, to secure the average final weights. The selling weight was taken in the morning before feed- ing, and a 4 per cent shrink allowed. Each group was hauled by truck to a nearby slaughterhouse and killed on successive days — lot 3 on February 12, lot 2 on February 13, and lot 1 on February 14. Table 8 gives the final weight and slaughter data of the individual animals. At the end of this second trial the slaughter animals were well finished and graded higher than the feeders, as follows : Lot 1 : 2 choice, 9 top good, 1 good, and 2 medium. Lot 2 : 4 choice, 4 top good, 2 good, 2 low good, and 1 medium. Lot 3 : 2 choice, 5 top good, 3 good, and 3 medium. The carcass grades, which compared reasonably well with those of the finished animals, were as follows : Lot 1 : 4 choice, 4 top good, 3 good, and 3 medium. Lot 2 : 4 choice, 2 top good, 2 good, 1 low good, and 4 medium. Lot 3 : 2 choice, 5 top good, 3 good, and 3 medium. DISCUSSION Nonpregnant heifers, no. 24 in the first trial (1938) and no. 1 in the second trial (1939), are included in the averages of their respective groups. If they were removed from the calculations the average daily gain of lot 1 in the first trial would have been 1.88 pounds instead of 1.85 pounds and the average weight of the uteri 15.1 pounds instead of 14.0 pounds. In the second trial the daily gain with no. 1 omitted would have been 2.14 pounds in place of 2.12 pounds and the weight of the uteri 19.4 pounds instead of 18.0 pounds. It is evident therefore that in- clusion of these two nonpregnant animals does not materially change the results and avoided the doubtful procedure of correcting feed consump- tion on the basis of the average consumption of the lots, had they been removed from the calculation. The breeding of the animals in the 1938 trial was not such as to make the most desirable quality of feeders. They were rather fine-boned and light-muscled. They went on feed fairly well, but after the first 60 days the gains were unsatisfactory. According to some unpublished observa- tions, animals as thin as these, especially those coming to the feed lot from dry ranges deficient in certain dietary essentials, must be brought to full feed slowly. During the third 30-day period, when gains were most unsatisfactory, the change from coarse to finely ground alfalfa was made. To judge from observations on the time, frequency, and dura- tion of rumination at this period, the heifers were not ruminating so 16 University of California — Experiment Station much as would have been expected in animals on whole alfalfa hay. The marked fineness of the alfalfa meal fed from January 25 to the end of the feeding period probably caused or enhanced this condition. Appe- tite was capricious, and slight increases in feed resulted in lower intake with considerable weigh-back. Thus the feed required per 100 pounds' gain in the third 30-day period was very high, and the individual daily gains were low. Parasitic infestation was also manifested at this time. With the change in the chopped alfalfa, some of the animals developed scours. Number 18 in lot 1 passed bloody feces for a week beginning January 27, and examination showed the cause to be infestation with coccidiosis. The feces of all the heifers were examined to determine the extent of this condition. Only a few animals were discharging coccidia, and no. 18 showed no further symptoms. Half of the animals showed slight infes- tation with the microscopic stomach worm Trichostrongylus. The ex- tent to which these parasites affected gains and feed utilization cannot be determined. Infestation was, however, distributed through all the lots. During the fourth 30-day period, feed intake and appearance indi- cated that the animals had attained about as much finish as economy and their quality justified. It was decided, therefore, to close the experi- ment although most of the animals had not attained more than medium slaughter condition. The slaughter data show no significant differences in the dressing percentages of the three lots. In the 1939 trial the animals were never off feed, and the concentrate mixture was finally raised to 15 pounds per head daily. They made satis- factory gains, finished well, and produced carcasses of high quality. The lower rate of gain during the third 30-day period was perhaps caused by a rather heavy infestation of warbles that were emerging from the backs of the animals at this time, with accompanying local irri- tation and swelling. The pregnant lot was further advanced in preg- nancy than in the previous year. This condition was desired in order to ascertain whether increased appetite and gains would be manifested by heifers more advanced in pregnancy than those of the 1938 trial. The concentrates consumed by all the lots were constant, although more would have been supplied to any group if the feed would have been consumed. Toward the end of the 150 days and at the time of feed in- creases earlier in the trial, 3 hours or more were required for all the con- centrates to be consumed, although the feed was always gone before the next feeding time arrived. To accomplish this result, hay consump- tion varied somewhat. A reduced quantity of fresh hay was placed in the mangers of any group when concentrates were slow in being cleaned Bul. 645] Relative Efficiency of Heifers in the Feed Lot 37 up. Excess hay, however, was always present in the mangers of all three groups. For the 150-day period, hay consumption was greatest in lot 2, averag- ing 0.6 pound per animal daily over the amount consumed by the ani- mals in lot 1, and 1.4 pounds more than in lot 3. These differences are not significant. The data confirm the findings of the previous year — namely, that pregnancy even in the more advanced stages does not increase ap- petite in cattle. Hay, concentrates, and total feed consumption per 100 pounds' gain were lowest in lot 1. Concentrates and total feed per 100 pounds' gain were lower in lot 2 than in lot 3, the latter being definitely the highest, though hay consumption per 100 pounds' gain was slightly higher in lot 2 than in lot 3. These data on live weights together with the accompanying higher average daily gain in the lot-1 animals, seemed to indicate somewhat bet- ter utilization of feed in the pregnant group. That there was no differ- ence, however, in carcass gain or efficiency of feed utilization is shown in the following paragraph. The average weight of the pregnant uteri of lot-1 animals in the first trial was 14 pounds (table 1) and in the second trial 18 pounds (table 5) . This constitutes approximately the difference in the average live weight of the animals at the end of the trials. The carcass weights of the lot-1 and lot-2 animals in each trial were about equal. The difference in live weight and apparent gains is therefore due to the weight of the gravid uteri. As the weight of the gravid uteri including the amniotic fluid, even in animals advanced as far as 175 days in pregnancy, is very largely made up of water, the extra weight of the pregnant animals on the same amount of feed is thereby explained. If the live-weight gain is corrected for the uterus and its contents, then the feed required for 100 pounds' gain in lot 1 becomes practically the same as for lots 2 and 3, in both trials. In the second trial the difference in daily gain between lot 2 (open) and lot 3 (spayed) approached statistical significance. In the first trial, however, the gains were similar and when both trials are con- sidered there are no statistically significant differences between any of the lots. The dressing percentage (calculated as in the first trial from the sell- ing weight and the cold weight as the carcasses were sold from the cooler after hanging 7 to 14 clays) was 59.64 per cent for lot 1, 61.21 per cent for lot 2, and 60.62 per cent for lot 3. The pregnant uteri and ovaries of lot 1, including the one open ani- mal, averaged 18.0 pounds against 0.57 pound for those of lot 2 and 0.15 18 University of California — Experiment Station pound for the lot-3 animals. This slight difference in dressing percentage of the three groups, compared with the considerable difference in weight of the uteri and ovaries, substantiates similar data of the previous year. Here, then, is evidence that, in well-finished heifers, advanced pregnancy (150 to 175 days) does not reduce the dressing percentage materially. Animals advanced in pregnancy show mammary gland development when a cross section is made of the udder. When pregnancy extends beyond the fifth month, a soft place is present over the milk cistern at the base of the teat. Leakage of secretion commonly extends down the carcass for a distance of 6 to 18 inches after 24 hours in the cooler, and this fact is used as a trading argument against the desirability of such carcasses. On open and spayed heifers no mammary development is noticeable on cross section of the udder, which appears to be a solid mass of fat. It is interesting that the only open heifer in lot 1 had the highest dressing percentage of the entire 40 animals, being 1.58 per cent higher than its nearest competitor, animal 18 in lot 2 with 62.95 per cent. This heifer was bred early and never came in heat again, though a bull was placed in the corral every afternoon until January 15. On the other hand, a very similar case, no. 24 of the pregnant lot the previous year, showed no such advantage in dressing percentage. The activity of unbred heifers in riding each other at estrual periods is particularly noticeable in the early stages of feeding in dry lot, no doubt because of the stimulating action of high food intake. As fattening progresses, this behavior becomes less marked; and toward the end of the feeding period the only evidence of a heifer's being in heat may be her failure, at times, to step up to the feed bunk with the other animals in the pen. CONCLUSIONS The data from these two feeding trials confirm those from other sources : no advantage accrues from spaying heifers that are going into the feed lot. Activity of open heifers in riding each other at estrual periods is not serious. It becomes reduced as finish approaches and is not involved in feed consumed or in cost per hundred pounds of gain. Pregnancy in cattle does not cause increased appetite or food con- sumption. Neither does its existence up to the fifth or sixth month seriously affect the dressing percentage in reasonably well-finished heifers. The slight increase in weight of pregnant over open ainmals is due to the increase in weight of the gravid uterus. This consists largely Bul. 645] Relative Efficiency of Heifers in the Feed Lot 19 of water, and the change can thus take place without significant differ- ences in food intake. ACKNOWLEDGMENTS The writers acknowledge the kind assistance of Dr. Morris Stewart, Division of Entomology and Parasitology, in making the parasite studies of the animals in the 1938 trial; and also that of Mr. Robert Squibb, technical assistant in Animal Husbandry, in carrying on so carefully the feeding operations in both trials. 13m-2, '41(8721)