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)     

Comparison of Charolais and Limousin as terminal cross sire breeds

Birth, weaning, feedlot and carcass traits were evaluated on 1,181 calves sired by Charolais and Limousin bulls out of eight crossbred dam groups (Hereford X Angus, Angus X Hereford, Simmental X Angus, Simmental X Hereford, Brown Swiss X Angus, Brown Swiss X Hereford, Jersey X Angus, Jersey X Hereford). Calves were born in the spring over a 4-yr period during which dams ranged from 3 to 8 yr of age. Charolais-cross calves were 2.7 kg heavier (P less than .01) at birth and had a 9.9% higher (P less than .01) incidence of difficult calvings and 4.6% greater (P less than .05) preweaning death loss than did Limousin crosses. Charolais-sired calves out-gained Limousin-sired calves by 31 g/d (P less than .01) from birth to weaning and were 9 kg heavier (P less than .01) at weaning. After weaning, calves were self-fed a finishing diet and slaughtered as each animal attained an estimated carcass grade of low Choice. Charolais-cross calves gained 60 g/d faster (P less than .01) than Limousin crosses, were fed 6.8 fewer d and were 17.3 kg heavier (P less than .01) at slaughter. Feed efficiency was similar for both sire breeds. On a grade-equivalent basis, Charolais crosses produced 7 kg heavier (P less than .01) carcass and had 22 g more carcass weight per day of age (P less than .01). Charolais crosses had slightly less internal and external fat. Dressing percentage was higher for Limousin cross calves (64.6 vs 63.9%, P less than .01). Longissimus muscle area and carcass cutability were similar for crosses of both sire breeds.     

Testicular development, daily sperm production and epididymal sperm reserves in 15-mo-old Angus and Hereford bulls: effects of bull strain plus dietary energy

Bull calves (n = 143) were obtained from two strains of Angus and two strains of Hereford cattle for which replacements were selected on the basis of superior feedlot growth performance on either high- or medium-energy diets. From weaning to slaughter at 15 mo of age, bulls were fed either the high-energy (80% grain + 20% forage) or medium-energy diet (100% forage) corresponding to their strain. Bulls in high-energy diet groups had a greater (P less than .05) scrotal circumference at 12 mo, but not 15 mo of age, than bulls in medium-energy diet groups. Compared with Hereford bulls, Angus had greater (P less than .01) scrotal circumference (36.1 vs 33.9 cm) and greater (P less than .05) paired testes weight (570 vs 464 g) at 15 mo of age. Daily sperm production per gram testicular parenchyma (DSP/g) was affected by strain-diet (P less than .01) but not by breed. Bulls in medium-energy diet groups had 12% greater DSP/g than did high-energy diet bulls (17.4 X 10(6) vs 15.5 X 10(6)). Daily sperm production (DSP) was 9% and 30% greater (P less than .01) for medium-energy diet bulls in 1980 (8.2 X 10(9) vs 7.5 X 10(9)) and 1981 (8.0 X 10(9) vs 6.2 X 10(9)), respectively, compared with high-energy diet bulls. The effect (P less than .01) of breed on DSP was attributed to breed differences in paired testes weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 traits and composition of two- and three-way-cross intact male progeny of Bos taurus and Bos indicus X Bos taurus dams

Feedlot traits, carcass traits and distribution of commercial cuts of crossbred intact male progeny (n = 556) from young and mature 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 bred to Red Angus bulls; Santa Gertrudis sires were used for each cow's second and third breeding seasons. Calves from these young dams were slaughtered at 13 mo. Calves of mature dams were all sired by Limousin bulls and slaughtered at 12 mo. Dam breed was a major source of variation in most bull traits. Progeny of Brahman-cross dams were inferior (P less than .01) in daily gain, final weight, carcass weight and in edible cuts/day of age compared with progeny from Bos taurus dams. Intact male progeny of Angus X Charolais dams ranked highest in longissimus area, cutability, and edible cuts/day of age. The range of dam breed means in percentage of steak, roast, bone-in cuts (chuck short ribs and back ribs), short plate and thin cuts, and lean trim was just over 1%. Greater variation among dam breeds existed in fat measurements. Analyses in which Hereford-Red Poll diallel data for young dams and mature dams were combined showed positive maternal heterosis for dressing percentage (P less than .05), carcass weight (P less than .05), carcass weight/day of age (P less than .05), estimated carcass fat (P less than .05), fat thickness (P less than .01) and marbling score (P less than .01). Reciprocal effects were inconsequential. Results illustrate the importance of dam breed-type effects in formulating breeding strategies for commercial beef herds.     

Postweaning growth and reproduction of beef heifers exposed to calve at 24 or 30 months of age in spring and fall seasons.

Angus and Angus x Hereford heifer calves born in spring or fall seasons were allotted by weight at weaning to be exposed to bulls for calving at either 24 or 30 mo of age. Comparisons were made 1) within birth season--heifers born in the same season were first exposed to bulls at either 14 to 16 or 19 to 22 mo of age and 2) within breeding season--heifers born in different but consecutive seasons (spring-fall or fall-spring) were exposed to bulls during the same season but at different ages. Spring-born heifers exposed for 30-mo calving were heavier (336 vs 302 kg) and taller (P less than .01) at breeding than those exposed for 24-mo calving. Also, more were observed in estrus and became pregnant (P less than .01) during a 21-d AI breeding period, but season-long (63 d) pregnancy rates were not different (86%). Fall-born heifers exposed for 24- or 30-mo calving were similar for weight, hip height, and body condition score (BCS) at breeding, but season-long pregnancy rates were 71 and 94%, respectively (P less than .01). Although fall-born heifers were heavier at weaning (P less than .01), spring-born heifers were heavier, taller, and had higher BCS at breeding (P less than .01), regardless of age. Within spring breeding seasons, breeding weight and initial reproduction were not affected by heifer age. Within fall breeding seasons, older heifers were larger (P less than .01) and had greater reproductive performance (P less than .05) than younger heifers. Age at breeding, irrespective of season, consistently affected (P less than .01) both hip height (116 vs 113 cm) and pelvic area (209 vs 178 cm2) for older vs younger heifers, respectively. These data indicate that heifers exposed for 30-mo first calving are heavier, taller, have larger pelvic area, and have greater reproductive performance than those exposed for 24-mo first calving.     

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)     

Growth and muscle development of feedlot cattle of different genetic backgrounds

The effects of crossbreeding, cattle type and dietary energy level on semitendinosus muscle (ST) development, feedlot performance, daily carcass protein and fat gain and serum anabolic hormone concentrations were studied. Over 3 consecutive years, 176 feedlot steers representing four cattle types - unselected Hereford (UH), selected Hereford (SH), Angus x Hereford x Charolais (AHC) and Angus x Hereford x Holstein (AHH) - were fed either an all-corn silage (HS) or a high grain (HG) diet. Steers were slaughtered on day 1 and at the end of the feedlot trial, and ST muscles were removed rapidly. During years 2 and 3, single blood samples were obtained from steers on days 1, 29, 57, 113 and 169, and analyzed for insulin and growth hormone (GH). Steers fed HG had a higher (P less than .005) average daily gain (ADG) than steers fed HS, and cattle type had an effect (P less than .005) on ADG. Cattle type and HG affected (P less than .005) daily carcass protein and fat gain. Weight of ST muscle and total muscle RNA, DNA and protein content increased with frame size, and HS steers had heavier (P less than .05) ST muscles than the HG steers. Steers fed HG had higher (P less than .01) serum insulin concentrations than steers fed HS, but there were no consistent cattle type effects. Serum GH concentrations were not affected by cattle type or diet. Serum insulin concentrations, combined across diet and cattle types, were correlated (P less than .01) with ADG; however, serum GH, assessed on the same basis, was not related to ADG. Average daily protein and fat gain were positively related to serum insulin and were negatively related to serum GH.     

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.     

Evidence that bovine growth hormone treatment increases the rate of extrathyroidal 5'-monodeiodinase activity in cattle

This study examined the influence of bovine growth hormone (bGH) on liver and kidney thyroxine-5'-monodeiodinase activity (TMA) in growing beef cattle. In a preliminary trial (trial 1), tissue samples were obtained at slaughter from two placebo-injected and two bGH-injected (29.2 IU/day for 14 days before slaughter) Hereford heifers (398 kg avg slaughter wt), with one heifer on each treatment fed at either 1.0 or 2.0 times maintenance energy requirement. In a second trial, tissue and plasma samples were obtained from six placebo-injected and six bGH-injected (29.2 IU/day for 19 days) Hereford steers (331 kg avg slaughter wt) fed at 1.8 times maintenance energy requirement. In a third trial, liver tissue and plasma samples were obtained from 14 Angus X Hereford steers (270 kg avg wt) fed either an 8% protein, 1.96 Mcal-metabolizable energy/kg diet (8 steers) or a 14% protein, 2.67 Mcal-metabolizable energy/kg diet (6 steers) in association with acute administration of bGH. Half the steers in each group were given two injections per steer of either placebo or 37.8 IU bGH at 24-hr intervals and slaughtered 24 hr after the second injection. Units of tissue TMA in all trials were measured at slaughter; one unit defined as 1 ng T3 generated/hr/mg protein during incubation with T4 (1.3 fM). In trial 1, TMA in liver and kidney was 2.86 and 1.21 times greater, respectively, for bGH than for placebo treatments. In trial 2, units of TMA in liver homogenates were higher (P less than .05) for bGH (4.14) than for placebo (2.83) treatments and higher (P less than .02) in liver microsomal preparations for bGH (32.7) than for placebo (27.3) treatments. Units of TMA in kidney homogenates were also higher (P less than .10) for bGH (1.48) than for placebo (.87) treatments and higher (P less than .02) in kidney microsomal preparations for bGH (23.0) than for placebo (16.4) treatments. Following acute injection of bGH (trial 3), units of TMA in liver homogenates were higher (P less than .01) for bGH (2.5) than for placebo (1.8) treatments. Plasma T4 (70.0 vs 73.5 ng/ml) and T3 (1.08 vs 1.18 ng/ml) concentrations appeared slightly higher in bGH-treated steers (trial 2) and increased by 20 and .5 ng/ml, respectively, (P less than .01) within 6 to 12 h after acute injection of bGH (trial 3). Concurrently, plasma TSH concentration increased following acute GH injection (trial 3).(ABSTRACT TRUNCATED AT 400 WORDS)     

Serum hormone and metabolite concentrations in fasted young bulls and steers.

The effect of dietary energy restriction on serum insulin, insulin-like growth factor I (IGF-I), growth hormone, (GH), cortisol, plasma urea nitrogen (PUN) and nonesterified fatty acid (NEFA) concentrations was examined. Angus bulls and steers (10 mo) were allotted to two groups of 12 animals and assigned a treatment order. In a switchback design, animals in order 1 were fed a high grain diet, then fasted, while order 2 animals were fasted, and then fed. Animals were allowed 60 hr to acclimate between treatments. Serum and plasma were obtained at 20 min intervals and 60 min, respectively, for 6 hr after feeding and for the last 6 hr of a 30 hr fast. Serum was assayed for insulin, IGF-I, GH, and cortisol (total and free). Plasma was assayed for PUN and NEFA. Mean insulin (ng/ml) differed between fed (.95 +/- .08) and fasted (.26 +/- .08) animals (P less than 01). Both mean total and free cortisol (ng/ml) were lower in fed (11.48 +/- .99) (1.06 +/- .12) than in fasted (17.10 +/- .93) (1.62 +/- .12) animals, respectively (P less than .01). Animals in order 1 differed in mean IGF-I (ng/ml) between fed (199.0 +/- 8.0) and fasted (116.5 +/- 7.2) treatments (P less than .01). Mean IGF-I for animals in order 2 was 146.7 +/- 7.2 in fed and 213.9 +/- 7.2 in fasted animals (P less than .01). Mean GH did not differ between treatments. Mean PUN and NEFA were higher in fasted than in fed animals (P less than .01). Except for % free cortisol (P less than .05), the hormones did not differ between bulls and steers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preweaning breed-of-sire comparisons involving the Senepol breed of cattle

Preweaning data collected at two locations (Kentucky, Louisiana) were utilized to evaluate breed-of-sire comparisons involving the Senepol breed of cattle. For the Kentucky study, calves sired by Senepol bulls were 1.3 kg heavier (P less than .05) at birth than calves sired by Hereford bulls; however, weaning weights were similar for the two sire groups. For the Louisiana study, calves sired by Longhorn bulls were 5.3 kg lighter (P less than .01) at birth, 20 kg lighter (P less than .01) at weaning and had weaning condition scores .5 unit less (P less than .01) than the average of calves sired by Red Poll and Senepol bulls. Also, heifers exposed to Longhorn bulls weaned 23 kg less (P less than .01) calf per heifer exposed than the average of heifers exposed to Red Poll and Senepol bulls. Calves sired by Red Poll bulls were 1.2 kg heavier (P less than .01) at birth and 12 kg heavier (P less than .01) at weaning than those sired by Senepol bulls; however, the Senepol-sired calves received higher (P less than .01) condition scores at weaning. Heifers exposed to Red Poll bulls weaned 20 kg more (P less than .05) calf per heifer exposed than did heifers exposed to Senepol bulls.     

Postweaning growth of unselected Hereford and Angus cattle fed two different diets

Two unselected herds of purebred Hereford and Angus cattle were created and their progeny evaluated during a 4-yr period (1964 to 1967) for 168-d postweaning gain when they were fed either a high- or medium-energy diet. Birth weight and 200-d adjusted weaning weight also were measured and the importance of sire x diet interactions for postweaning gain examined. Year effects were significant (P less than .001) for all traits in Herefords and for postweaning gain in Angus. Postweaning gain of both breeds increased in successive years, but no trend was observed for birth and 200-d weights. Bulls were heavier than heifers (P less than .05) for all three traits in both breeds. Hereford and Angus calves receiving the high-energy diet gained more (P less than .001) than their contemporaries fed the medium-energy diet. Sire differences were significant for birth weight in Herefords and for all three traits in Angus. Sire x diet interactions were not significant for postweaning gain in either breed. Genetic correlations were calculated by two methods: the two-way ANOVA approach using sire and sire x diet interaction variance components and the one-way ANOVA approach in which gains by progeny of each sire on each diet were considered to be two distinct traits. The genetic correlations for gain in Herefords could not be estimated by either method because of negative sire variance component estimates. The genetic correlations for gain in Angus were 1.08 for the two-way ANOVA method and 1.43 +/- .64 for the one-way ANOVA method. These results indicate that sires ranked the same based on progeny performance when fed either diet.     

Effect of energy intake after weaning on the sexual development of beef bulls. II. Age at first mating, age at puberty, testosterone and scrotal circumference

Simmental and Hereford bulls were individually fed varying levels of the same diet to determine the effect of energy intake after weaning on rate of sexual development. For 200 d, 29 Simmentals were fed an average of 14.6, 19.2 or 23.8 Mcal and 27 Herefords were fed 13.4, 17.5 or 22.2 Mcal metabolizable energy per bull daily. Higher energy did not hasten sexual development, as measured by serum testosterone, age at first mating or age at puberty. As energy level increased, weight at puberty increased (P less than .05) for both breeds, and scrotal circumference at puberty increased (P less than .05) for Simmentals. When adjusted for breed and energy level, bulls that were heavier at 1 yr of age had larger scrotal circumference (P less than .05) and were younger at puberty (P less than .01). Bulls that had higher serum testosterone at 1 yr of age reached puberty earlier (P less than .01). At a constant age there was no relationship between testosterone and scrotal circumference. Although higher levels of energy increased scrotal circumference of Simmentals, it did not hasten sexual development for either breed.     

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.     

Variation among twin beef cattle in maintenance energy requirements

The genetic variation in energy expenditures of cattle at fasting (FHP) and maintenance (MEm) was determined by using 12 pairs of monozygous twins at 20 mo of age. The pairs were of two breed types, eight Angus x Hereford (three steers, five heifers) and four Barzona x Hereford (three steers, one heifer). The heifers were 132 +/- 13 d pregnant at the time of measurement. The pairs were fed at 1.15 x maintenance energy requirements for a minimum of 30 d prior to heat production (HP) measurements in dual indirect respiration calorimetry chambers. The diet fed was cracked corn:alfalfa hay (45:55) with a determined ME of 2.47 +/- .02 Mcal/kg DM. This diet was fed individually for 7 d prior to and during two consecutive 22-h HP measurements. The animals then were fasted for 2 d and fasting heat production measurements (FHP) were made on d 3 and 4 of the fast. Metabolizable energy required for MEm was calculated iteratively by assuming a semi-log relationship between HP and metabolizable energy intake. There were no differences (P greater than .10) in measured energy expenditures due to different breed type. The FHP and efficiency of ME use for MEm (Km) were similar between sexes, although heifers had lower (P less than .025) MEm than steers. Twin pair effects were detected for FHP (P less than .005) and MEm (P less than .05) but not for Km. Broad sense heritability estimates were calculated as the intraclass correlation between members of monozygous twin pairs. Heritability estimates for MEm, FHP, and Km were .52 +/- .22, .75 +/- .13, and .34 +/- .27, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of breed and wintering diet on growth, puberty and plasma concentrations of growth hormone and insulin-like growth factor 1 in heifers

Twenty-five Brangus (BR) and 15 Angus (AN) heifers were used to study the effects of breed and wintering diet on average daily gain (ADG), onset of puberty and plasma concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Wintering diets (fed for 107 days beginning November 15) consisted of the following: 1) native grass hay (NGH), 2) ammoniated NGH, 3) NGH plus cottonseed meal, 4) Diet 3 plus corn and 5) Diet 4 plus monensin. After wintering, heifers were transferred to ryegrass pasture for 70 days. Mean ADG during the wintering phase were -.20, -.10, .17, .29 and .39 kg for heifers fed Diets 1 through 5, respectively (P less than .01). ADG was greater (P less than .05) for BR than for AN heifers. Plasma concentrations of GH were higher (P less than .05) in heifers fed Diets 1 and 2 than in heifers fed Diets 3, 4 or 5. Plasma concentrations of IGF-1 were lowest in heifers fed Diet 1 and highest in heifers fed Diets 4 and 5. During ryegrass grazing, GH concentrations were similar for all groups. However, concentrations of IGF-1 were higher (P less than .05) in heifers fed Diets 3, 4 and 5 than in heifers fed Diets 1 and 2. Age at puberty (onset of cyclic progesterone concentrations) was greatest in heifers fed Diet 1 and lowest in heifers fed Diet 5. Weight at puberty was not affected (P greater than .10) by wintering diet but was greater (P less than .01) in BR than in AN heifers. Therefore, negative ADG appears to be associated with elevated plasma GH concentrations in heifers, and plasma IGF-1 concentration appears to be a more accurate indication of nutritional status than plasma concentrations of GH.     

Effects of stair-step nutrition and trace mineral supplementation on attainment of puberty in beef heifers of three sire breeds.

A study was conducted to evaluate the influence of nutrition and sire breed on age at puberty and first lactation milk yield in crossbred beef heifers. After weaning, 208 heifers sired by Hereford, Limousin, or Piedmontese bulls were assigned to either a control (CG) or stair-step gain (SSG) dietary regimen plus a mineral supplement with or without Cu, Zn, and Mn top-dressed onto the feed. Heifers on the SSG regimen were fed a diet intended to supply energy to support gains at a rate of 120% of the CG diet for 55 d and then were switched to a diet formulated to produce an ADG at 70% of the rate of the CG diet for 84 d. They then switched back to the 120% diet for the last 30 d before breeding. Total weight gain and overall rate of gain did not differ among dietary treatments. Hereford- and Limousin-sired heifers gained at similar rates, and Piedmontese-sired heifers gained an average of .10 kg/d slower than the other two sire breed groups. During one period, Piedmontese-sired heifers on the CG diet gained .19 kg/d faster ( P < . 01) when supplemented with mineral than when not. During that same period, there was no influence of mineral supplementation on weight gains for Hereford- or Piedmontese-sired heifers on the high SSG diet, but Limousin-sired heifers tended (P = .07) to gain faster (1.00 vs .85 kg/d) when supplemented with Cu, Zn, and Mn than when not. Piedmontese-sired heifers reached puberty at the earliest age (P = .03), followed by Hereford- and then Limousin-sired heifers. There were no treatment effects on milk yield at an average of 70 d of lactation. However, at approximately 120 d of lactation, Piedmontese-sired heifers were producing less milk (P < .05) than Limousin- but not Hereford-sired heifers. Hereford-sired heifers had lower (P < .05) plasma Cu concentrations than Piedmontese-sired heifers. There were no treatment effects on plasma Zn concentrations. Heifers sired by bulls of breeds that differ in potential muscularity differed in growth, reproduction, milk yield, and plasma mineral concentrations, but dietary treatments resulted in little to no differences in these variables.     

Comparison of two- and three-way rotational crossing, beef x beef and beef x Brown Swiss composite breed production: postweaning growth and carcass traits

Data collected from steer and bull progeny, fed to a constant final feedlot weight over 11 yr, were used to estimate heterosis in post-weaning feedlot growth and carcass traits in two-way and three-way rotational crossing systems and a breed composite from crossing Hereford, Angus and Charolais breeds. Steer and bull progeny from matings of beef x Brown Swiss-cross sires and dams also were compared with the straight beef breeds and beef crosses. Growth traits evaluated were initial weight on test, 112-d weight, total feedlot average daily gain and total days from initial to final weight. Carcass traits included hot carcass weight, dressing percentage, rib eye area, 12th-rib fat thickness, kidney, pelvic and heart fat, yield grade and marbling score. Heterosis estimates for calves of all crossing systems were significant for initial and 112-d weight and for saving of days in the feedlot, but not for average daily feedlot gain. Heterosis estimates were small and nonsignificant for most carcass traits except for fat traits in specific crosses. Males from Hereford and Angus sires mated to Angus x Hereford dams had higher (P less than .10) backfat than did the parental average. Male progeny from Charolais ranked higher (P less than .10 to P less than .01) than calves from Hereford and Angus sires for most growth traits. Progeny from Charolais sires were more desirable (P less than .10 to P less than .01) for traits related to cutability, but they had less (P less than .05 to P less than .01) marbling than calves of Angus sires.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of zeranol implants on growth, behavior and carcass traits in Angus and Limousin bulls and steers

A 2(3) factorial arrangement of treatments was utilized to determine effects of postweaning zeranol implantation, breed (Angus vs Limousin) and castration (bull vs steer) on growth, behavior and carcass traits. An initial slaughter group was used to account for breed differences in composition and to determine fat and lean growth in the 9-10-11th rib section (NTE). The remaining cattle were fed a finishing diet to a fat end point of .76 cm, as determined by a backfat probe. Control bulls outgained (P less than .01) control steers both to the first kill date and over the entire test and did not require significantly more time to reach the fat end point. The implant did not influence gain in bulls but did increase gain in steers. Angus and Limousins were similar in growth rate for the first 126 d before the first slaughter date. Limousins required more (P less than .01) time to reach the fat end point. Bulls and Limousins produced heavier (P less than .01) carcasses and larger rib eyes (P less than .05; bulls; P less than .01; Limousins). Steers and Angus had higher (P less than .01) marbling scores and lower bone maturity. Implanting decreased (P less than .05) marbling and increased carcass maturity. Small but significant shifts in carcass wholesale cut weight distribution were found between breed and sex condition groups. Bulls and Limousins had greater lean growth in the NTE. Bulls and steers were similar in fat growth, but Angus exceeded Limousin in this trait. Zeranol reduced scrotal circumference (P less than .01) and testicle weight at slaughter (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)