Feedlot performance of beef heifers implanted with Synovex-H: effect of melengestrol acetate, ovariectomy or active immunization against GnRH

The effects on anabolic steroid implantation on feedlot performance and carcass composition and quality were examined in control (CNTRL), ovariectomized (OVX) or melengestrol acetate-fed (MGA) beef heifers or heifers actively immunized against GnRH (Anti-GnRH). Heifers (n = 112) were assigned randomly to a 2 x 4 factorial experiment. The two classes were made up of heifers not implanted and those implanted with Synovex-H. The four treatments were 1) CNTRL, 2) MGA, 3) OVX and 4) Anti-GnRH. Heifers were housed in individual pens and fed a high-energy diet for the 4-mo study. Synovex-H increased final live weight (P less than .005), carcass weight (P less than .005), ADG (P less than .0001) and feed efficiency (P less than .005) but did not alter carcass quality and yield grade (P greater than .05). Synovex-H increased deposition of protein (P less than .0001) and reduced deposition of fat (P less than .0001). Oral administration of MGA had no significant effect on feedlot performance or carcass quality. For heifers not implanted, active immunization against GnRH, but not ovariectomy, depressed ADG (P less than .05) and increased fat deposition (P less than .05) while reducing protein deposition (P less than .05). These effects of active immunization were reversed by concurrent administration of Synovex-H. Feedlot performance and carcass composition of heifers were improved by administration of anabolic steroids. When heifers were housed singly, neither ovariectomy, active immunization against GnRH nor oral administration of MGA improved feedlot performance of heifers implanted with Synovex-H.     

Pregnancy rates of beef heifers bred either on puberal or third estrus

The objective of this study was to determine if pregnancy rates (PR) differed between beef heifers bred to fertile bulls on either their puberal (E1, n = 89) or third (E3, n = 67) estrus. Heifers were obtained from two lactations (Manhattan, L1; and Miles City, L2), and the experiment was conducted at Miles City. Heifers were assigned randomly within location to either E1 or E3. Heifers were fed to gain .56 kg.head-1 X d-1 and observed twice daily for estrus. After exhibiting first estrus (puberty) and breeding, each heifer in E1 was palpated rectally on d 6, 9 and 12 +/- 1 d (estrus = d 0) for the presence of a corpus luteum, and a venous blood sample was collected for assay of progesterone by radioimmunoassay. Heifers in E3 were palpated and bled on the same schedule as heifers in E1 after first estrus and after being bred to a fertile bull at third estrus. Pregnancy rates were determined by rectal palpation at approximately 38 d post-breeding. Location of origin did not affect (P greater than .10) weight at puberty or weight at breeding; however, heifers from L1 were younger (P less than .05) than heifers from L2 at puberty and breeding. Pregnancy rates were 57 and 78% for heifers in E1 and E3, respectively (P less than .05). Weight at breeding did not influence (P greater than .10) pregnancy rates. The probability of heifers in E1 becoming pregnant increased (P less than .05) with increasing age, while age was not a factor (P greater than .10) for heifers in E3. These results indicated that fertility of puberal estrus in beef heifers is lower than third estrus. Higher fertility of third estrus may be related to maturational changes associated with cycling activity.     

The effects of cattle sex on carcass characteristics and longissimus muscle palatability

Two experiments were conducted to determine the effects of sex on carcass traits and cooked beef steak palatability. In Exp. 1, steers (n = 99), heifers (n = 51), and intravaginally spayed heifers (n = 46) were fed a high-energy diet for 161 d. No implants were administered, and heifers were not fed melengestrol acetate to suppress estrus. In Exp. 2, 60 steers and 60 intact heifers from the same ranch source used in Exp. 1 were fed in 2 locations (sites 1 and 2). All management factors were equal across experiments except that intact heifers were fed melengestrol acetate to suppress estrus in Exp. 2. Steers in Exp. 1 were 25 kg heavier (P < 0.01) in HCW than heifers at comparable (P = 0.39) carcass fat thickness. Spayed heifers (Exp. 1) had a 5.7% smaller (P < 0.05) LM area compared with steers and intact heifers, which were similar. In Exp. 2, there was no difference (P = 0.2) in carcass weight, and heifers had greater (P < 0.01) 12th rib fat thickness compared with steers. Calculated yield grades were similar (P = 0.21) among treatments in Exp. 1 and tended (P = 0.08) to be greater for heifers compared with steers in Exp. 2. In Exp. 1, USDA quality grades and marbling scores were lower (P < 0.01) for steers compared with intact and spayed heifers, which were similar. The effects of sex on tenderness were examined at a common level of fat-thickness and marbling by covariate analysis. Steaks from steers, compared with those from nonimplanted, intact heifers, in the 2 experiments combined were: (a) superior (P < 0.05) in 2 of 9 palatability assessments when subcutaneous fat thickness (at the 12th rib) was adjusted to a common level, and (b) superior (P < 0.05) in 6 of 9 palatability assessments when marbling score was adjusted to a common level. In Exp. 1, steaks from nonimplanted steers compared with those from nonimplanted spayed heifers were: (a) superior (P < 0.05) in 0 of 8 palatability assessments when subcutaneous fat thickness (at the 12th rib) was adjusted to a common level, and (b) superior (P < 0.05) in 3 of 8 palatability assessments when marbling score was adjusted to a common level. These findings suggest that sex should be added to the list of antemortem factors contributing to variation in cooked beef steak tenderness. However, more research is needed to precisely identify those factors contributing to the lower tenderness observed for steaks from heifer carcasses.     

Reproductive response of yearling beef heifers to a melengestrol acetate-prostaglandin F2 alpha estrus synchronization system.

A study was designed to evaluate estrus response and fertility after treatment with melengestrol acetate (MGA) and prostaglandin F2 alpha (PGF2 alpha) in yearling beef heifers. Three hundred four heifers at three locations were allotted to one of two treatments: Treatment 1 served as a nonsynchronized control (CON); and heifers in Treatment 2 received .5 mg of MGA.animal-1.d-1 for 14 d and 25 mg of prostaglandin F2 alpha (PGF2 alpha) 17 d after MGA (MGA-PGF). Heifers in CON and MGA-PGF groups were artificially inseminated 12 h after observed estrus for 21 and 6 d after PGF2 alpha, respectively. Blood samples were collected from each heifer 10 d before and on the day MGA feeding began and 10 d before and on the day PGF2 alpha was administered. Heifers with concentrations of serum progesterone greater than 1 ng/mL on either date before administration of MGA or PGF2 alpha were considered pubertal. More (P = .02) prepubertal heifers that received MGA attained puberty by initiation of breeding than did CON heifers (72 vs 45%, respectively). The proportion of heifers that displayed estrus within 6 d after PGF2 alpha was greater (P less than .001) for MGA-PGF than for CON heifers (77 vs 25%, respectively) but was also influenced by location (P = .03). Conception rate at first service for MGA-PGF heifers that attained puberty during MGA feeding and before PGF2 alpha was not different (P = .50) from that of CON that attained puberty during the same period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prenatal testosterone treatment and postnatal steroid implantation on growth performance and carcass traits of heifers and steers

Two experiments were conducted to evaluate the effect of prenatal testosterone treatment in combination with postnatal steroid implantation (Exp. 1) and to assess the effect of time of prenatal testosterone treatment in conjunction with postnatal steroid implantation (Exp. 2) on animal performance and carcass characteristics. In Exp. 1, seventy-six pregnant cows were assigned randomly to a control group or implanted with testosterone propionate (TP) silastic implants between d 40 and 80 of gestation. Half the heifer calves were selected randomly to be implanted with 200 mg TP plus 20 mg estradiol benzoate (EB); the other half of the steer calves were implanted with 200 mg progesterone plus 20 mg EB on d 1 and 85 of the feedlot trial. Daily gain of heifers was increased 10.4% (P less than .08) due to prenatal testosterone treatment (P) and 16.4% (P less than .05) by postnatal steroid implantation (I). Feed efficiency was 12.9% greater (P less than .05) due to P and 9.5% greater (P less than .05) due to I. Prenatal testosterone treatment decreased (P less than .05) kidney, pelvic and heart fat and final yield grade but increased (P less than .05) ribeye area of heifers. Heifers had greater (P less than .07) liver weights per unit of carcass weight due to P. In Exp. 2, one hundred seventy-four pregnant cows were assigned randomly to a control group or implanted with TP silastic implants on d 42, 63, 84 or 105 of gestation. Half the heifer and steer calves were selected randomly to be implanted on d 1 and 112 of the feedlot trial. Time of P caused a quadratic effect (P less than .08) on birth weight of heifers. There was a quadratic effect (P less than .05) of time of P on daily gain and final weight per day of age of heifers. Feed efficiency of heifers was improved (P less than .05) due to P. Postnatal steroid implantation increased (P less than .05) daily gain and feed efficiency of heifers by 9.6% and 8.6%, respectively. No changes were observed in growth performance of steers due to P. Results from these two trials suggest that the combination of prenatal testosterone treatment and postnatal testosterone and estradiol implantation produced an additive improvement of daily gain, feed efficiency and carcass merit of heifers.     

Heifer development systems: dry-lot feeding compared with grazing dormant winter forage

Two hundred ninety-nine Angus-based, nulliparous heifers (253 ± 2 kg initial BW) from 3 production years were utilized to compare traditional postweaning dry lot (DL) development with a more extensive winter grazing system utilizing a combination of corn residue and winter range (EXT). Heifers developed in the DL were offered a common diet after the weaning period for 208 d in yr 1, 194 d in yr 2, and 150 d in yr 3 until breeding. Heifers developed in EXT grazed corn residue for 135 d in yr 1, 106 d in yr 2, and 91 d in yr 3, and then fed in the DL until breeding (yr 1) or grazed dormant winter grass for approximately 60 d before being fed in the DL (yr 2 and 3). All 3 years, heifers were estrus synchronized, with timed AI performed in yr 1. In yr 2 and 3, estrus was detected and those detected in estrus were artificially inseminated approximately 12 h later. Heifers were exposed to bulls 10 d after the last AI for 60 d while grazing summer pasture. During the winter grazing period, EXT heifers gained less (P = 0.01) BW than DL heifers and EXT heifers had lighter (P = 0.02) BW at breeding. Fewer (P < 0.01) EXT heifers reached puberty before breeding. Conception to AI was not different (P = 0.23); however, AI pregnancy rate tended (P = 0.08) to be less in EXT heifers. Final pregnancy rates were not different (P = 0.38) between treatment groups. Although EXT heifers had lighter (P = 0.02) BW at pregnancy diagnosis; however, they did compensate with greater (P = 0.05) ADG after breeding, resulting in similar (P = 0.22) precalving BW. Winter development system did not influence (P > 0.10) percentage of calving in the first 21 d, calf birth date, and calf birth BW, or dystocia score. Pregnancy rate after the second breeding season was not different (P = 0.56) between treatments. Heifer development using extended winter grazing reduced (P < 0.01) the cost of producing a pregnant heifer by $45 compared with DL.     

Conception rate in Bos taurus and Bos indicus crossbred heifers after postweaning energy manipulation and synchronization of estrus with melengestrol acetate and fenprostalene

Conception rate in heifers after synchronization of estrus with melengestrol acetate (MGA) and fenprostalene (a prostaglandin F2 alpha analogue; PGF) was determined in pubertal Bos taurus and Bos indicus crossbred yearling heifers. Angus x Hereford (AH, n = 137) and Brahman x Hereford (BH, n = 97) heifers were sorted by body weight after weaning into light (LW) and heavy (HW) weight blocks. Heifers were assigned by age to diets to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weight by the start of breeding. Heifers that exhibited estrus and had serum progesterone greater than or equal to 1 ng/ml (0 or 10 d before estrous synchronization treatment) were assigned randomly within breed and nutritional groups to either an estrous synchronization (S) or control (C) group. Heifers in the S group were fed .5 mg of MGA for 7 d and injected s.c. with 2 mg PGF on d 7 of MGA. All heifers were inseminated 12 h after first detected estrus. A greater proportion of AH (P less than .01) than of BH heifers were in estrus within 6 d after PGF, and more S heifers than C heifers (P less than .01) were in estrus. Conception rate at first service was proportionately higher (P less than .001) in AH than in BH heifers and lower (P less than .02) in S than in C heifers. There was a breed x energy level interaction (P less than .01) for conception rate at first service. Stage of the estrous cycle at the time treatment with MGA was initiated influenced (P less than .05) conception rate at first service in the S, AH heifers, with lower conception rates among heifers beginning treatment late in their estrous cycles (greater than or equal to d 12). Pregnancy rates after 21 d were higher (P less than .01) in AH than in BH heifers and higher (P less than .01) in HW than in LW heifers. More HE than LE heifers (P less than .02), and more AH than BH heifers were pregnant after 45 d. Pregnancy rates at the end of 21 d were higher among HE, BH heifers than among LE contemporaries. A higher (P less than .02) percentage of HE, HW, BH heifers were pregnant at the end of 45 d compared with other BH groups. Results indicated that a 7-d MGA-PGF treatment reduced conception rates at first service in pubertal yearling heifers. Pregnancy rate was affected by prebreeding nutrition in BH yearling heifers at the end of 45 d.     

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW > or = 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-beta (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.     

The effects of spaying and anabolic implants on the average daily weight gain of heifers on pasture

Two studies were carried out to determine the effects of spaying and implanting on the growth of heifers and compare Ralgro and Synovex-S for spayed heifers. In the first study, 121 crossbred heifers were randomly allocated to four groups: intact and no implant; intact and progesterone and estradiol benzoate (Synovex-S); spayed and no implant; and spayed and Synovex-S. The average daily gain (ADG) and body weight (BW) data were analyzed as a 2 × 2 factorial experiment with a pasture effect which was considered as a block. Based on ADG for days 0-120, the response to implanting was 17.6% for spayed heifers and 1.8% for intact heifers. In the second study, 31 spayed heifers implanted with zeranol (Ralgro) were compared with 30 spayed heifers implanted with Synovex-S. The data were analyzed as a one-way analysis of variance. The ADG for spayed heifers on Ralgro did not differ significantly (p>0.05) from those implanted with Synovex-S over a period of 92 days, suggesting that both implants produce similar growth responses.     

Influence of insulin and energy intake on ovulation rate, luteinizing hormone and progesterone in beef heifers

Ovarian and gonadotropin responses to insulin and energy restriction were investigated in a 2 X 2 factorial experiment using 2-yr-old Brangus heifers. Thirty heifers were paired by weight and body condition, then assigned to treatment groups receiving 75 (LE) or 180% (HE) of NRC recommendations for dietary energy for maintenance. Diets were adjusted weekly to maintain daily .25 to .5 kg weight loss or 0 to .25 kg weight gain, respectively. On d 10 of the first estrous cycle subsequent to the initial 45 d of feeding, heifers within each dietary group were allocated to receive twice daily infusions of either 40 U insulin (I) or saline (C). Infusions began at 5 and 10 h postprandial and were given in six boluses, 20 min apart. Infusions continued daily until d 20 or estrus, whichever occurred first. On d 11, blood samples were collected at 15-min intervals for 12 h to determine luteinizing hormone (LH) and insulin concentrations. On d 16 to 20, twice daily im injections of 1 mg follicle stimulating hormone (FSH) were administered. Heifers were ovariectomized on d 11 after estrus. Number of corpora lutea (CL) in LE-I heifers was greater (P less than .05) in LE-C, HE-C or HE-I. Total CL weight (g) per heifer was greater (P less than .05) in HE-C and LE-I heifers than in LE-C. Individual CL wt was heavier in HE than in LE heifers (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Camelina meal and crude glycerin as feed supplements for developing replacement beef heifers

Angus × Gelbvieh rotationally crossbred yearling heifers (n = 99, yr 1; n = 105, yr 2) were used in a 2-yr randomized complete block design experiment with repeated measures to determine the effect of feeding camelina biodiesel coproducts (meal and crude glycerin) on serum concentrations of triiodothyronine, thyroxine, insulin, β-hydroxybutyrate, and glucose, as well as on growth and reproductive performance. Heifers were assigned to 1 of 15 pens, and pens were assigned initially to receive 7.03 k·?heifer(-1)·d(-1) of bromegrass hay plus 0.95 kg·heifer(-1)·d(-1) of 1 of 3 supplements for 60 d before breeding: 1) control (50% ground corn and 50% soybean meal, as-fed basis); 2) mechanically extracted camelina meal; or 3) crude glycerin (50% soybean meal, 33% ground corn, 15% crude glycerin, 2% corn gluten meal; as-fed basis). Preprandial blood samples were collected via the jugular vein on d 0, 30, and 60 of the feeding period. A 2-injection PGF(2α) protocol (d 60 and 70 of the study) was used to synchronize estrus. Heifers were artificially inseminated 12 h after estrus was first detected. Heifers not detected in estrus within 66 h received a GnRH injection and were artificially inseminated. Dietary treatment × sampling period interactions were not detected (P = 0.17 to 0.87). Dietary treatment did not affect BW (P = 0.44 to 0.59) or serum concentrations of thyroxine (P = 0.96), β-hydroxybutyrate (P = 0.46), glucose (P = 0.59), or insulin (P = 0.44). Serum concentrations of triiodothyronine were greater (P = 0.05) in heifers fed camelina meal. Additionally, dietary treatment did not affect the percentage of heifers detected in estrus before timed AI (P = 0.83), first-service pregnancy rates of those heifers detected in estrus (P = 0.97), or overall first-service pregnancy rates (P = 0.58). Heifers fed camelina meal, however, had greater (P = 0.05) first-service pregnancy rates to timed AI than did heifers fed the control and crude glycerin supplements. The cost per pregnancy was similar for heifers fed the crude glycerin or the control supplement, whereas the cost per pregnancy was the least for heifers fed camelina meal. We conclude that camelina coproducts can replace conventional corn-soybean meal supplements in the diets of developing replacement beef heifers.     

The effect of estradiol, trenbolone acetate, or zeranol on growth rate, mammary development, carcass traits, and plasma estradiol concentrations of beef heifers.

The effect of a single implantation (on d 1) with one or two long-acting, biodegradable estradiol implants (1E or 2E) on plasma estradiol concentrations in beef heifers was determined. The growth rates of these (2E) heifers, and of heifers repeatedly implanted with trenbolone acetate (TBA) or zeranol (Z) on d 1, 84, 168, and 252 of the trial, were compared to growth rates of controls. Trenbolone acetate alone was compared to TBA + 2E, and 2E was compared to 1E. At a mean age of 84 d (d 1 of experiment), 81 Hereford x Friesian heifers were allocated at random to the following treatments: Control (n = 15); TBA (n = 15); 1E (n = 12); 2E (n = 15); Z (n = 13); or TBA + 2E (n = 11). Mean live weight (kg) prior to slaughter on d 368 and hot carcass weight (kg) for heifers assigned to treatment Groups 1 to 6, respectively, were 366 and 200, 391 and 212, 374 and 201, 386 and 207, 387 and 210, and 391 and 208 (residual SD = 30.3 and 20.2). Heifers assigned to both the 2E and Z treatments were heavier on d 368 (P less than .05) and had longer teats on d 279 (P less than .05), less pelvic fat (P less than .05), and heavier kidneys (P less than .005) than control heifers. Heifers assigned to the TBA treatment had shorter teats on d 279 (P less than .001) but greater final live weight (P less than .05) and carcass weight than control heifers. Heifers given TBA alone had more pelvic fat (P less than .05) and lighter kidneys (P less than .05) than those given TBA + 2E. Mean estradiol concentrations in both the ipsilateral and contralateral jugular veins of heifers assigned to the 2E and TBA + 2E treatments, and in the ipsilateral jugular veins of heifers given 1E, were greater (P less than .05) than those in control heifers; concentrations did not decline during the experiment.     

Effects of breed and wintering diet on heifer postweaning growth and development

Fifteen spring-born Angus (AN) and 25 Brangus (BN) weanling heifers were used in a 2x5 factorial arrangement of treatments to evaluate the effects of breed and postweaning winter diet on heifer growth and development. Dietary treatments were warm-season perennial grass hay (H), ammoniated H (AH), H plus .68 kg/d cottonseed meal (HP), H plus .45 kg/d cottonseed meal plus 1.37 kg/d ground corn (HPE) and HPE plus 200 mg/d monensin (HPEM). Mean initial weight and age for the 107-d feed trial were 207 kg and 270 d. Brangus had .06 kg greater (P less than .05) ADG than AN during the trial. Although digestible DM intake (DDMI) relative to body weight was greater (P less than .10) for AN than for BN, ADG:DDMI was greater (P less than .05) for BN than for AN. Heifers fed H and AH lost weight, but heifers fed AH had 50% (P less than .05) less daily weight loss than those fed H. Daily gain increased (P less than .05) incrementally in response to sequential supplement additions of cottonseed meal (AH vs HP; -.10 vs .17 kg), ground corn (HP vs HPE; .17 vs .29 kg) and monensin (HPE vs HPEM; .29 vs .39 kg). Hay DM intake relative to body weight and DDMI were increased (P less than .01) by ammoniation. Intake did not differ between HPE and HPEM. Diet affected age at puberty (P less than .05), which decreased with increased dietary components. Weight differences among diet groups following the winter feed trial were largely eliminated prior to breeding. Nevertheless, H- and AH-fed heifers collectively weighed less (P less than .01) prior to breeding than did heifers of supplemented diet groups. Reproductive development tended to be adversely affected by weight loss during the postweaning period.     

Reproductive performance and profitability of heifers fed to weigh 272 or 318 kg at the start of the first breeding season

Reproductive performance and weaning weight of the first calf was determined in 221 Brahman crossbred heifers fed to weigh either 272 (TW1) or 318 kg (TW2) at the start of their first breeding season (target weight). Heifers were divided into light- (below average) and heavyweight (above average) groups on the basis of initial weight. Within each target weight, heifers were fed in three lots. One lot contained lightweight heifers, the second contained heavy heifers and the third was composed of one-half heavy- and one-half lightweight heifers. Heifers were fed for 200 d before the start of the first breeding season. More heifers in TW2 showed estrus and became pregnant in the first 20 d of the breeding season and more were pregnant at the end of the first breeding season. These same differences in reproductive performance were also noted the second year. Each heifer exposed in TW2 weaned 43.4 kg more calf than those in TW1. An average heifer in TW2 was fed 220 kg more corn and 100 kg less hay than a corresponding heifer in TW1. Estrus and pregnancy rate for lightweight heifers in TW1 and TW2 were not improved by sorting and feeding them separately.     

Effects of dam nutrition on growth and reproductive performance of heifer calves

A 3-yr study was conducted with heifers (n = 170) whose dams were used in a 2 x 2 factorial arrangement of treatments to determine the effects of late gestation (LG) or early lactation (EL) dam nutrition on subsequent heifer growth and reproduction. In LG, cows received 0.45 kg/d of a 42% CP supplement (PS) or no supplement (NS) while grazing dormant Sandhills range. During EL, cows from each late gestational treatment were fed cool-season grass hay or grazed sub-irrigated meadow. Cows were managed as a single herd for the remainder of the year. Birth date and birth weight of heifer calves were not affected (P > 0.10) by dam nutrition. Meadow grazing and PS increased (P = 0.02; P = 0.07) heifer 205-d BW vs. feeding hay and NS, respectively. Weight at prebreeding and pregnancy diagnosis were greater (P < 0.04) for heifers from PS dams but were unaffected by EL nutrition (P > 0.10). There was no effect (P > 0.10) of LG or EL dam nutrition on age at puberty or the percentage of heifers cycling before breeding. There was no difference (P > 0.10) in pregnancy rates due to EL treatment. Pregnancy rates were greater (P = 0.05) for heifers from PS dams, and a greater proportion (P = 0.005) of heifers from PS dams calved in the first 21 d of the heifers' first calving season. Nutrition of the dams did not influence (P < 0.10) heifers' average calving date, calving difficulty, and calf birth weight during the initial calving season. Weight at the beginning of the second breeding season was greater (P = 0.005) for heifers from PS dams but was not affected by maternal nutrition during EL (P > 0.10). Dam nutrition did not affect (P > 0.10) heifer ADG or G:F ratio. Heifers from PS dams had greater DMI (P = 0.09) and residual feed intake (P = 0.07) than heifers from NS cows if their dams were fed hay during EL but not if their dams grazed meadows. Heifers born to PS cows were heavier at weaning, prebreeding, first pregnancy diagnosis, and before their second breeding season. Heifers from cows that grazed meadows during EL were heavier at weaning but not postweaning. Despite similar ages at puberty and similar proportions of heifers cycling before the breeding season, a greater proportion of heifers from PS dams calved in the first 21 d of the heifers' first calving season, and pregnancy rates were greater compared with heifers from NS dams. Collectively, these results provide evidence of a fetal programming effect on heifer postweaning BW and fertility.     

Use of recombinant gonadotropin-releasing hormone antigens for immunosterilization of beef heifers

The objectives of this study were to evaluate the effects of immunization against recombinant GnRH fusion proteins and growth promotants on onset of puberty, feedlot performance, and carcass characteristics of beef heifers. Heifers were immunized against an ovalbumin fusion protein containing 7 GnRH peptides (oGnRH, n = 12), a thioredoxin fusion protein containing 7 GnRH peptides (tGnRH, n = 12), a combination of oGnRH plus tGnRH (otGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant injected into the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk -2. Weekly blood samples were collected from wk -2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH-immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second booster injection, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from otGnRH heifers. During the 26-wk study, ovulation was prevented (P < 0.05) in 10 out of 12, 12 out of 12, 11 out of 12, and 0 out of 11 tGnRH, oGnRH, otGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH-immunized heifers than control heifers. Synovex H-implanted heifers had greater (P < 0.05) ADG from wk -2 to 26, greater LM area, and lesser percentages of KPH, yield grade, and quality grade than nonimplanted heifers, regardless of the immunization treatment. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented ovulation in 92% of the heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.     

Time of zeranol implantation on growth, reproduction and calving of beef heifers

Zeranol implants were administered to 250 crossbred heifer calves at 1, 6 or 9 mo of age to evaluate growth, reproduction and calving performance. Heifers were assigned to eight treatment groups with 25 animals per group. Two additional groups of 25 heifers each were used to study the effects of multiple implants at two levels of nutrition on heifer performance. Implants at 1 mo of age (branding) increased heifer weights at 6 mo of age (weaning) by 5 kg (P = .08). Heifers receiving a combination of two implants gained faster (P less than .05) from weaning to breeding (6 to 13 mo) than controls or heifers implanted three times. Implants at either 6 or 9 mo increased (P less than .05) precalving pelvic areas (247 vs 241 cm2 and 248 vs 240 cm2 over controls, respectively). Implants did not affect the percent of heifers reaching puberty prior to breeding season. Conception rates in 62 d of breeding were comparable for implanted and control heifers (93 vs 96%), with the exception of heifers receiving implants at both 1 and 6 mo of age (56%). Calf birth weight, dystocia score, cow rebreeding rate and calf weaning weight were not affected by implant treatments. Heifers that received three implants and were fed at a high nutritional level (gained .62 vs .49 kg/d for regular level after weaning) tended (P greater than .10) to reach puberty at a higher rate prior to breeding and to have a higher total conception rate than implanted heifers on the regular nutrition level.     

Nonpuberal estrus in beef heifers

The frequency of occurrence of behavioral estrus without subsequent development of functional luteal tissue (termed nonpuberal estrus, NPE), was determined in 43 Simmental X Hereford-Brahman heifers. Blood samples were collected weekly from the start of the study to first behavioral estrus and then daily from d 1 (d 0 = estrus) through d 14 following first and subsequently observed estrous behaviors. All blood samples were analyzed for serum progesterone (P4) concentrations by radioimmunoassay. More heifers (62.8%) exhibited NPE than had luteal development after their first behavioral estrus (37.2%). There was a tendency for fewer light-weight heifers (less than or equal to 240 kg at the start of the experiment) to exhibit a puberal first estrus compared with the heavy-weight (greater than 240 kg at the start of the experiment) heifers (31.2% vs 68.8%, respectively; P = .12). Heifers that had a puberal first estrus were older (376 +/- 12 d vs 334 +/- 9 d, P less than .05) compared with heifers that had NPE. Weight at first behavioral estrus was similar between heifers that had a puberal first estrus and those that had NPE (298 +/- 8 kg and 289 +/- 6 kg, respectively). More heifers that had a puberal first estrus also had an elevation in serum P4 concentrations before that first estrus (64.3% vs 20.0%, P less than .05), and the serum P4 elevation was greater (2.5 +/- .4 ng vs 1.2 +/- .1 ng, P less than .05) than heifers that had NPE. We have concluded from these results that NPE is a common occurrence in heifers approaching puberty.(ABSTRACT TRUNCATED AT 250 WORDS)     

Forage mineral concentration, animal performance, and mineral status of heifers grazing cereal pastures fertilized with sulfur.

Thirty yearling Santa Gertrudis-sired heifers (average initial weight 238 kg) were continuously grazed (five heifers/pasture) on six 2-ha oat-wheat small grain pastures for 112 d to determine the effect of fertilization of pastures with urea (U) vs ammonium sulfate (AS) on mineral status and performance of heifers. Pastures were fertilized with either U, at 200 kg/ha, or AS, at 438 kg/ha, to provide 92 kg of N/ha in November 1987 and March 1988. Ammonium sulfate provided 107 kg of S/ha. Forage samples were collected during each month. Heifers were initially weighed following an overnight fast and at the end of four consecutive 28-d intervals (Periods 1 to 4). Serum and ruminal fluid were collected on d 56 and 112. Pastures fertilized with AS had a greater (P less than .10) in vitro dry matter disappearance during Periods 2 and 3. Ammonium sulfate-fertilized pastures had greater than (P less than .05) S concentrations from January 29 through termination of the trial. There were no differences in ADG (P less than .28) or gain/ha (GPH; P less than .43) over 112 d; however, heifer ADG was greater (P less than .08) in Period 3 and tended to be greater (P less than .16) in Period 2 for those animals grazing U-fertilized pastures. Pastures receiving AS produced less (P less than .04) GPH during Period 2. Ammonium sulfate fertilization in this trial had no effect on forage K, Ca, P, Mg, Cu, or Mo mineral concentrations or on serum mineral and ruminal VFA concentrations, but it did result in an increase in IVDMD and a trend for decreased ADG apparently associated with a decrease in forage intake.     

Plasma metabolites of receiving heifers and the relationship between apparent bovine respiratory disease, body weight gain, and carcass characteristics

Six hundred sixty-five crossbred beef heifers initially weighing 225 kg were used in a completely randomized design to measure plasma glucose, lactate, and urea N concentrations at time of initial processing, determine the incidence of apparent bovine respiratory disease (BRD) in receiving cattle, and evaluate the effect of apparent BRD on subsequent cattle growth and carcass characteristics. Heifers were processed within 24 h of arrival, and processing included vaccination against common viral and clostridial diseases, recording rectal temperature, and sampling whole blood for subsequent measurement of plasma glucose, lactate, and urea concentrations. Heifers were monitored for clinical signs of apparent BRD, including depression, lethargy, anorexia, coughing, rapid breathing, and nasal or ocular discharge. Heifers exhibiting signs of apparent BRD received antibiotic therapy, and the number of times a heifer was treated for apparent BRD was recorded. Following the 36-d receiving period, heifers were transported to native grass pastures and allowed to graze for 136 d. At the end of the grazing season, heifers were transported to a commercial feedlot where they were adapted to a common finishing diet offered for ad libitum consumption. Following the 124-d finishing period, heifers were slaughtered and carcass data were collected. Heifers treated for apparent BRD had decreased plasma glucose (linear, P < 0.01), lactate (linear, P < 0.01), and urea N concentrations (linear, P < 0.06) measured at time of initial processing. Rectal temperature measured at time of initial processing tended to be greater (linear, P < 0.11) for heifers treated for apparent BRD. Heifers treated for apparent BRD during the receiving period had decreased overall ADG (linear, P < 0.10), final BW (linear, P < 0.01), HCW (linear, P < 0.01), fat thickness (linear, P < 0.01), and marbling score (linear, P < 0.03). These data suggest that initial plasma glucose and lactate concentrations might be affected by the health status of receiving cattle and that increased incidence of apparent BRD in cattle decreases ADG and carcass quality.