Effects of creep feeding, zeranol implants and breed type on beef production: I. Calf and cow performance

A 2-yr study was conducted to evaluate the effects of a high-energy creep feed, preweaning zeranol implants and breed type on calf and cow performance. Two hundred calves sired by Brahman and Romana Red bulls out of Angus and Angus x Brown Swiss reciprocal crossbred (F1) dams were stratified by breed type and sex to three creep treatments: no creep feed (NC); long-term creep (LC), creep-fed from 56 to 210 d of age (weaning); and short-term creep (SC), creep-fed from 146 to 210 d of age. Alternate calves within sex, breed type and creep treatment were implanted with 36 mg of zeranol at an average of 56 d and reimplanted 90 d later. The LC and SC calves had heavier (P less than .001) 210-d weights than NC calves (264 and 257 vs 231 kg, respectively), and the LC calves were heavier (P less than .001) at 146 d than NC calves. The LC calves had higher (P less than .001) ADG from 118 to 210 d of age and higher 146 and 210-d condition scores than did NC calves. Pregnancy rate was not affected (P greater than .46) by creep treatment of calf. Zeranol implants increased (P less than .01) 146- and 210-d weights (184 vs 175 kg and 259 vs 243 kg) and ADG during all periods to weaning. Brahman-sired calves had higher (P less than .005) 146- and 210-d weaning weights and frame scores than Romana Red-sired calves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of growth-promoting agents and season on yearling feedlot heifer performance

Angus x crossbred heifers (270 per trial) were used in an experiment conducted over one 105-d summer and one 104-d winter feeding period. Treatments were identical for each trial and included: 1) control, 2) estrogenic implant (E), 3) trenbolone acetate implant (TBA), 4) E + TBA (ET), 5) melengestrol acetate (MGA) in the feed, and 6) ET + MGA (ETM). Each treatment was replicated in five pens, with nine heifers per pen in each season. Initial weights (mean = 384 kg, SE = 57) were the same for each season. There were no treatment x season interactions for final BW, ADG, G:F, water intake, or carcass characteristics. Heifers receiving a growth-promoting agent were 11.6 kg (SE = 4.08) heavier and gained 0.108 kg/d (SE = 0.04) more (P < 0.05) than control heifers. Heifers receiving ET gained 0.09 kg/d (SE = 0.032) more (P = 0.05) than heifers not receiving ET. Heifers receiving ET (with and without MGA) had greater G:F (P < 0.05) than control, E, and TBA heifers. Carcass weights of ET-treated heifers were greater (P < 0.05) than carcass weights for unimplanted heifers, those fed MGA only, and heifers receiving either E or TBA implants. Marbling scores were increased (P < 0.05) by feeding MGA to ET-treated heifers. Water intake was greater (P < 0.01) in the summer (31 L/d) than in the winter (18 L/ d), with no difference among implant treatments. Heifers fed in the winter had heavier carcasses, less 12th-rib fat, greater marbling scores, larger LM area, and a greater incidence of liver abscesses than heifers finished in the summer (P < 0.01). A treatment x season interaction (P = 0.07) was evident for DMI during the 35-d coldest and hottest portions of the year. Heifers fed MGA and implanted with ET tended (P = 0.07) to have greater DMI in the summer but lesser DMI in the winter. In general, differences among growth-promotant programs were relatively similar over the entire summer and in winter.     

Effects of nutrition, sex of calf and breed type on response to zeranol: preweaning growth

An experiment was conducted to evaluate the effects of breed, sex and plane of nutrition on the growth response to zeranol in Angus and crossbred calves prior to weaning. Eighty-eight heifers and 118 steers received either a high or low plane of nutrition using a first and last grazing technique. Half of the calves in each nutrition group received a zeranol implant (36 mg) at an average age of 3.4 mo. Both zeranol and the higher level of nutrition increased (P less than .001) growth rate prior to weaning (7.4 mo of age). Zeranol did not affect hip height at weaning (P greater than .1), but calves on the higher plane of nutrition were taller (P less than .01) than calves on the lower plane of nutrition. The zeranol x nutrition interaction was not significant (P greater than .1) for growth rate or hip height. Steers grew faster (P less than .01) preweaning and were taller (P less than .01) at weaning than heifers. Crossbred calves gained more rapidly (P less than .001) preweaning and were taller (P less than .001) at weaning than Angus calves were. Neither sex nor breed interacted with zeranol to influence any of the traits examined. Based on these results we conclude that preweaning growth was affected by zeranol and this effect was consistent across sexes, breeds and planes of nutrition tested.     

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.     

Effect of selection for growth traits on age and weight at puberty in bovine females

This 20-yr study, using 584 beef heifers born in the spring of 1984 or 1985, was conducted to determine whether selection for growth traits affected age and weight at puberty. Heifers were from three Hereford lines selected for weaning weight, final weight, and final weight plus muscling score, a control line and a line of Angus cattle. In addition, heifers from reciprocal crosses among the selection lines, control and Angus groups were evaluated. Intact bulls and androgenized heifers fitted with marking harnesses were used to aid in detection of estrus for heifers born in 1984 and 1985, respectively. The time of puberty was identified by the first behavioral estrus. During both years, heifers were weighed at 56-d intervals; these weights were used to calculate weight at puberty. Mean age at puberty was determined using survival analysis; percentages of heifers that were pubertal by the end of the study were transformed to logits for analysis. Heifers born in 1985 were heavier (P less than .05) at puberty than those born in 1984. Heifers in lines selected for growth traits were younger at puberty (P less than .05; 20 d) than were heifers in the control line because of combined direct and maternal genetic effects. Heifers from the final weight, control (P less than .05) and weaning weight lines (P less than .10) weighed less at puberty than Angus heifers; selection line x Angus crossbred heifers were heavier at puberty (P less than .05) than their respective pureline or purebred contemporaries due to heterotic effects. Selection for weaning weight, final weight or final weight plus muscling score did not have a detrimental effect on age at puberty in heifers.     

Maternal breed of sire effects on postweaning performance of heifer and steer progeny: postweaning growth and carcass characteristics.

Heifer and steer progeny of 2-yr-old first-cross (F1) heifers and 3- to 6-yr-old F1 cows, from Hereford dams and five sire breeds, were evaluated for postweaning feedlot growth and carcass composition. Breeds of sire of dam were Angus (A), Red Poll (RP), Tarentaise (T), Simmental (Sm), and Pinzgauer (P). Calves from 2-yr-old heifers were sired by Shorthorn, and calves from 3- to 6-yr-old dams were sired by Charolais. Breed of sire of dam was significant (P less than .05 to P less than .01) for total gain and final weight for female progeny from 2-yr-old dams. At all weights, Sm, P, and T ranked above A and RP. Progeny of A, P, Sm, and T F1 2-yr-old dams were not significantly different but were higher (P less than .05) than RP heifers in total feedlot gain. Breed of sire of dam was significant (P less than .05) for carcass weight and longissimus muscle area; T ranked highest and RP lowest. Breed was not significant for any growth traits of steer progeny of 2-yr-old dams. Breed was significant for marbling score; A ranked highest and exceeded (P less than .01) both RP and Sm steers. Breed was significant (P less than .05) for most growth traits in the heifer progeny of the 3- to 6-yr-old dams bred to Charolais sires. Heifer calves of the Sm group were heavier (P less than .05) than all other groups for most weights and total gain. For total gain, P and T were intermediate and A and RP lowest. For heifer carcass traits from 3- to 6-yr-old dams, breed was significant (P less than .05 to P less than .01) for carcass weight, longissimus muscle area, percentage of cutability, and estimated kidney, heart, and pelvic fat. Heifers from Sm-sired dams were heavier (P less than .05) than those from all other groups but ranked second to heifers from P for percentage of cutability. Marbling scores of RP heifer carcasses ranked highest of all groups. Breed was not significant (P greater than .05) for any of the weights or gains in steer progeny of 3- to 6-yr-old dams; however, the Sm and P groups ranked above A and RP for all feedlot test weights.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of reproductive traits in Bos taurus and Bos indicus crossbred heifers: effects of postweaning energy manipulation

Reproductive traits were evaluated in Bos taurus and Bos indicus crossbred heifers that were fed different diets during the postweaning period. The study was designed in a 2 x 2 x 2 factorial arrangement of treatments. Angus x Hereford (AH; n = 148) and Brahman x Hereford (BH; n = 148) heifers were sorted after weaning by body weight into light (LW) and heavy (HW) weight blocks. Heifers in each weight block were assigned to diets calculated to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weights by the start of the breeding season. Puberty was determined after a 160-d observation period and characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 6 to 10; estrus = d 0), and 3) rise in serum progesterone above 1 ng/ml (d 6 to 10). A higher (P = .01) proportion of AH heifers than of BH heifers reached puberty by the breeding season (93% vs 67%). Interactions of breed x weight block and energy level x weight block also contributed to this difference. Weight at puberty was heavier (P = .001) among HE than among LE heifers and greater for heifers in HW than for those in LW blocks (P = .02). Differences in prebreeding weight, body condition, average daily gain, hip height, and pelvic area were influenced selectively by breed, energy level, or weight block. Pregnancy rates were higher (P = .01) among AH than among BH heifers. Incidence and severity of dystocia was influenced by the breed x energy level interaction (P = .01). Brahman x Hereford heifers had less (P = .01) dystocia than AH heifers, HE heifers had less (P less than .02) dystocia than LE heifers, and HE-AH heifers had less (P less than .01) dystocia than LE-AH contemporaries. Subsequent duration of the postpartum interval to estrus was shorter (P = .002) among AH than among BH females. Pregnancy rates at the end of the 2nd yr were higher (P = .02) among LW than among HW females and weights were heavier (P = .001) at weaning among calves weaned from BH dams.     

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.     

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.     

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.     

Efficacy of vaginal spaying and anabolic implants on growth and carcass characteristics in beef heifers

Ninety crossbred beef heifers averaging 260 kg were blocked by weight and allotted randomly to 15 pens of six heifers each, with three replicates per treatment. The treatments were spayed heifers (S); intact heifers (I); S + Synovex-H7 (SH); I + Synovex-H (IH); and S + Synovex-S7 (SS). The heifers were spayed vaginally with a Willis instrument; intact heifers were rectally palpated for reproductive soundness. Heifers were fed a growing diet (55 d), re-implanted and subsequently fed a finishing ration (73 or 101 d). All heifers were observed for estrus daily at approximately 0600 and 2000 until d 69. A jugular vein blood sample was obtained from each heifer on d 48, 55, 62 and 69 for blood progesterone analysis. Results of blood progesterone analysis and reproductive tract examination indicated that two spayed heifers were incompletely spayed, a 96% success rate. The SH and SS heifers continued to exhibit estrous behavior despite being successfully spayed. Heifers implanted with Synovex-H had greater (P less than .01) ADG and were more efficient (P less than .03) than nonimplanted heifers. The SS heifers had greater ADG (P less than .05) during the finishing phase than SH heifers, but no advantage of SS over SH was apparent during the growing phase. The overall ADG response to implantation was fourfold greater (P less than .07) in the spayed heifers than in the intact heifers (32 vs 8%). Heifers implanted with Synovex-H had greater adjusted hot carcass weight (P less than .02) and ribeye area (P less than .002) than nonimplanted heifers. For adjusted live weight and ribeye area, the response to implantation was approximately threefold greater in the spayed heifer than the intact heifer. These results demonstrate that spaying and implanting heifers can increase rates and efficiency of gain even though behavioral estrus is not eliminated.     

Effects of recombinant DNA-derived somatotropin and dietary energy intake on development of beef heifers: II. Concentrations of hormones and metabolites in blood sera

The effects of somatotropin (STH) and energy intake on serum concentrations of glucose (GLU), insulin (INS), nonesterified fatty acids (NEFA), urea nitrogen (UN) and insulin-like growth factor-I (IGF-I) were determined in 40 Angus heifers. At 7 mo (208 +/- 8 d) of age heifers were assigned to four treatment groups: 1) vehicle (V) + high energy (HE; 2.68 Mcal ME/kg DM), 2) recombinant DNA-derived STH (20.6 mg/d; s.c.) + HE, 3) V + low energy (LE; 2.22 Mcal ME/kg DM) or 4) STH + LE. Animals remained on treatments until an average of 15.5 mo of age. Blood samples were taken every 30 min for 4 h at 9, 11, 13 and 15 mo of age to determine circulating concentrations of metabolites and hormones. Serum IGF-I was increased (P less than .01) by STH injections, but this effect appeared to diminish with age (STH x age; P less than .01). Energy intake did not influence IGF-I levels. Somatotropin increased (P less than .01) serum GLU in heifers fed the HE diet but only tended (P = .08) to increase GLU in those fed the LE diet (STH x energy; P = .05). Although STH increased (P less than .01) serum INS in both energy groups, the response in heifers fed the HE diet was greater (P less than .02) than that in heifers fed the LE diet (STH x energy; P less than .05). Heifers fed LE had higher (P less than .01) concentrations of NEFA than heifers fed HE.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and reproductive traits in beef heifers implanted with zeranol

Weaned replacement heifers were implanted with zeranol at 8 and 11 mo of age in two trials to evaluate growth and reproductive traits. Approximately 100 beef heifers were used in each trial, and the heifers were divided into categories of heavier than average (H) and lighter than average (L) weaning weight. Weight categories were further divided into control (HC and LC) and zeranol-implanted (HI and LI) groups. Heifers were kept in drylot from weaning to just before the start of the breeding season and were fed to reach a predetermined body weight by the start of the breeding season and were fed to reach a predetermined body weight by the start of the breeding season. Rates of gain in the drylot were greater in implanted than in control heifers in both trial 1 (.53 vs .48 kg/d; P less than .09) and trial 2 (.70 vs .63 kg/d; P less than .01). Pelvic areas were greater (P less than .01) in implanted than in control heifers of both trial 1 (175 vs 159 cm2) and trial 2 (175 vs 164 cm2). This increase in pelvic size was still present at the end of the summer pasture period, which followed the drylot period. Zeranol had no major effect (P greater than .10) on age of weight at puberty. Fall pregnancy rate was 16% lower in implanted heifers than in control heifers in trial 1 (62 vs 78%, P = .08) but did not differ in trial 2 (88 vs 87%, I and C, respectively).     

The effect of anabolic implants on intramuscular lipid deposition in finished beef cattle

Two experiments were conducted to determine the effects of anabolic implants on performance, changes in ultrasound measurements, carcass quality, cellularity of i.m. and s.c. adipose depots, and mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), and lipoprotein lipase (LPL) in i.m. adipose tissue of finished beef cattle. Angus heifers (experiment 1: n = 10; 411 kg of BW) and steers (experiment 2: n = 18; 279 kg of BW) were randomly allotted as control (C) or implanted with Synovex-Plus (SP) at d 0 and midway through the finishing period. The cattle were fed a high-concentrate diet and were weighed at approximately 28-d intervals. Heifers and steers were finished for 108 and 133 d, respectively. At slaughter, a section of the LM (sixth to ninth rib) was removed, and i.m. adipose tissue was dissected for mRNA analysis. Subcutaneous and i.m. adipose tissues also were collected for determination of cellularity. At 48 h postmortem, carcass data were collected, and a steak (12th rib) was removed for analysis of lipid and fatty acid composition. Body weight did not differ (P > 0.10) between treatments until after reimplanting of the heifers (d 55) or steers (d 73). Average daily gain was 36 and 16% faster (P < or = 0.01) for implanted heifers and steers, respectively, compared with their control counterparts. Implanting resulted in larger (P < or = 0.10) HCW and LM area for heifers and steers. However, implanting did not affect (P > 0.10) dressing percent, fat thickness, percentage of KPH, yield grade, or marbling score. Intramuscular lipid content and concentrations of major fatty acids did not differ (P > 0.10) between treatments. Percentage of SC adipocytes was greater at larger diameters ( > 150 microm), whereas the majority of i.m. adipocytes were at small to middle diameters (50 to 150 microm). The number of i.m. adipocytes per gram of tissue was greater (P < 0.05) for SP than C and also were greater (P < 0.05) than the number of s.c. adipocytes in SP heifers. In experiment 2, adipocytes per gram of tissue tended to be greater (P = 0.07) for SP than C and were greater (P < 0.01) for i.m. than s.c. In experiment 1, average cell diameter and volume did not differ (P > 0.10) between treatments and tissues, but in experiment 2 both cellularity traits were greater (P < 0.01) for s.c. than for i.m.. Implanting did not alter mRNA expression of ACC, SCD, or LPL in i.m. adipose tissue. This study shows that anabolic implants do not appear to have direct effects on i.m. lipid deposition.     

Maternal characteristics of young dams representing Bos taurus and Bos indicus x Bos taurus breed types

Reproductive traits and preweaning growth of progeny from young Hereford, Red Poll, Hereford X Red Poll, Red Poll X Hereford, Angus X Hereford, Angus X Charolais, Brahman X Hereford and Brahman X Angus dams were evaluated. First-calf heifers were mated with Red Angus bulls; Santa Gertrudis sires were used for each cow's second and third breeding season. Herefords, Red Polls and Hereford-Red Poll crosses were below average in percentage of calves weaned, whereas Angus-sired and Brahman-sired dams exceeded the overall mean. Angus X Charolais (P less than .10), Brahman X Hereford (P less than .01) and Brahman X Angus (P less than .10) dams weaned a higher percentage of calves than straightbred Herefords. None of these breed types differed from young Angus X Hereford females in reproductive performance. Angus X Charolais calves ranked highest in 180-d calf weight, exceeding progeny from both Hereford (P less than .01) and Angus X Hereford (P less than .10) dams. Brahman X Hereford dams weaned heavier (P less than .05) calves than Herefords, but their progeny did not differ at weaning from those reared by Angus X Herefords. Calves from Brahman X Angus dams weighed 12.7 kg less (P less than .01) than Angus X Hereford progeny. Analysis of the Hereford-Red Poll diallel showed evidence of (P less than .10) maternal heterosis in 180-d calf weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of recombinant DNA-derived somatotropin and dietary energy intake on development of beef heifers: I. Growth and puberty

The effects of dietary energy intake and somatotropin (STH) on growth and puberty were studied in 40 Angus heifers. At an average age of 7 mo (208 +/- 8 d), heifers were assigned to four treatment groups: 1) vehicle (V) + high energy (HE; 2.68 Mcal ME/kg DM), 2) recombinant DNA-derived STH (20.6 mg/d; s.c.) + HE, 3) V + low energy (LE; 2.22 Mcal ME/kg DM) or 4) STH + LE. Animals remained on treatments until 15.5 mo of age. Body weights (BW), hip heights (HH) and areas of pelvic openings (PA) were measured every 28 d and backfat thicknesses (BF) were measured every 56 d. Plasma progesterone was measured in blood samples taken three times per week beginning at 9 mo of age to determine age at first ovulation. Heifers fed HE were heavier (P less than .01), gained faster (P less than .01) and had greater BF (P less than .01) than those fed LE. Animals treated with STH gained faster (P less than .01) and were heavier (P less than .05) between 12 and 15 mo of age than V-treated heifers. Heifers treated with STH also had less BF (P less than .05) and a tendency for a greater (P = .08) increase in HH than in V-treated heifers. Somatotropin interacted with energy (P less than .05) and age (P less than .01) to influence PA. Somatotropin increased (P less than .01) PA in heifers fed the HE diet but not in those fed the LE diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Periparturient endocrine changes of conceptus and maternal units in Holstein heifers bearing genetically different conceptuses

Holstein heifers (n = 21) were balanced across sires and assigned to three service-sire-breed groups in which heifers were inseminated artificially to either purebred Angus (n = 7), Holstein (n = 7) or Brahman (n = 7) bulls. Semen from four bulls was used for each service sire-breed group. Blood samples were collected from a jugular vein thrice weekly from d 160 to 265 of pregnancy, daily thereafter until 15 d postpartum, and then thrice weekly until d 60 postpartum. Concentrations of progesterone, estrone, estradiol, and estrone sulfate from 23 d prepartum to parturition, and of 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) from 2 d prepartum to d 15 postpartum were measured by radioimmunoassay. Heifers within the Brahman-service-sire group had longer gestations (P less than .05) than those of Holstein- or Angus-service-sire groups (285.0 vs 278.7), 279.0 d). Calf birth weight was lower (P less than .05) in Angus- than Holstein- and Brahman-service-sire groups (30.6 vs 36.1, 43.4 kg). Daily trends of prepartum maternal progesterone concentrations were approximately 1 ng/ml lower (P less than .01) in Angus- than Holstein- or Brahman-service-sire groups until luteolysis occurred. Heifers bearing crossbred Angus conceptuses had lower daily trends of prepartum estrogens concentrations (P less than .01), whereas heifers of the Holstein- and, even more dramatically, of the Brahman-service-sire groups had a higher magnitude and greater rise of plasma estrogens concentrations between d -10 and -1 prepartum (less than .01). Postpartum mean concentrations (P less than .05) and response curves of PGFM were lower (P less than .01) in the Angus- than in the Holstein- or Brahman-service-sire groups. Calf birth weights were correlated with least-squares means for maternal concentrations of prepartum estrone (r = .57), estradiol (r = .59) and estrone sulfate (r = .64) and postpartum maternal concentrations of PGFM (r = .56). Functional responses of the conceptus (e.g., estrogens) and maternal units (e.g., progesterone and PGFM) were influenced by conceptus genotype during the periparturient period.     

Maternal breed of sire effects on postweaning performance of first-cross heifers and production characteristics of 2-year-old heifers.

Postweaning growth rates from weaning to 18 mo, fall condition score, pregnancy rates, and production to 2 yr of age were evaluated in a study of Angus (A)-, Pinzgauer (P)-, Red Poll (R)-, Simmental (S)-, and Tarentaise (T)-sired females from Hereford dams. First-cross heifers from the different sire breeds did not differ (P greater than .10) in initial weight. During a 140-d feed test, S gained 98.6 kg, exceeding (P less than .05) gains of P, 92.3; A, 91.4; and R, 87.3 kg but not T, 94.1 kg. Red Poll-sired heifers weighed less at the end of the 140-d test (P less than .05) than the other crosses, which did not significantly differ from each other. No breed of sire differences were found in gain from 140 d to fall weight. Simmental-sired heifers weighed more (P less than .05) than A- and R-sired heifers at 18 mo. Breed of sire and year interacted to affect pregnancy rate of the yearling heifers when mated to Shorthorn sires for 45 d. Percentage of dystocia varied from a low of 26.3 and 28.9% for T- and A-sired heifers, respectively, to 54.4 and 60.8% for P- and S-sired heifers, respectively (P less than .05). Age of dam of heifers affected (P less than .05) weight at the different period end points but not gains after weaning. Age of dam also affected incidence of dystocia. Two-year-old heifers from young dams had more dystocia than heifers from older dams. Shorthorn-sired calves from 2-yr-old heifers with different sire breeds differed in birth weight (P less than .05) but not survival from birth to weaning, ADG from birth to weaning, weaning age, or weaning condition score. Average 200-d weight of calves from P-, S- and T-sired heifers exceeded those from A- and R-sired heifers by 10.7 kg, or 5.7%.     

Growth, reproductive performance, and manganese status of heifers fed varying concentrations of manganese

An experiment was conducted to examine the effects of dietary Mn on growth, reproductive performance, and Mn status of beef heifers. Eighty Angus (n = 40) and Simmental (n = 40) heifers, averaging 249 kg, were stratified by BW within a breed and randomly assigned to 1 of 4 treatments providing 0 (control), 10, 30, or 50 mg of supplemental Mn/kg of DM from MnSO(4). Heifers were individually fed a diet containing cottonseed hulls, corn gluten feed, citrus pulp, and ground corn, and the control diet contained 15.8 mg of Mn/kg of DM by analysis. Average daily gain, DMI, and G:F for the 196-d period were not affected by Mn supplementation. Control heifers had reduced (P = 0.04) liver Mn when contrasted with the 3 levels of supplemental Mn. Serum cholesterol was greater (P = 0.001) in Angus compared with Simmental heifers over the course of the 196-d experiment but was not affected by treatment. Dietary Mn did not significantly affect measures of reproductive performance. Results of this study indicate that 15.8 mg of Mn/kg of diet DM should be adequate for growth, onset of estrus, and conception of beef heifers.