205-d Weight Research Articles

Genetic evaluation of an index of birth weight and yearling weight to improve efficiency of beef production.

The CGC population is a stabilized composite of 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise germplasm. The objectives of this research were to estimate genetic parameters for weight traits of CGC and to evaluate genetic responses resulting from selection based on the following index: I = 365-d weight 3.2(birth weight). Phenotypes evaluated were birth weight (n = 5,083), 200-d weight (n = 4,902), 365-d weight (n = 4,626), and the index. In addition, there were 1,433 cows with at least one recorded weight, and 4,375 total observations of cow weight collected at the time their calves were weaned. In 1989, a randomly selected control line and a line selected for greater values of the index were established. Average generation intervals were 3.16 +/- 0.04 and 3.90 +/- 0.08 yr in the index and control lines, respectively. The index selection line (n = 950) accumulated approximately 212 kg more selection differential than the control line over three generations (n = 912). Heritability estimates for direct effects were 0.32 +/- 0.04, 0.49 +/- 0.05, 0.49 +/- 0.05, 0.30 +/- 0.04, and 0.70 +/- 0.04 for the index, birth weight, 365-d weight, 200-d weight, and cow weight, respectively. Heritability estimates for maternal effects were 0.05 +/- 0.02, 0.11 +/- 0.03, 0.04 +/- 0.02, and 0.19 +/- 0.04 for the index, birth weight, 365-d weight, and 200-d weight, respectively. In the control line, direct genetic changes for the index and its components were small. For the index selection line, direct genetic changes for the index, birth weight, 365-d weight, 200-d weight, and cow weight were 6.0 +/- 0.3, 0.45 +/- 0.09, 7.74 +/- 0.55, 3.42 +/- 0.25, and 6.3 +/- 0.9 kg/generation, respectively. Maternal genetic changes were generally small for both the control and index selection lines. Thus, selection for the index produced positive correlated responses for direct genetic effects on BW traits at all ages, with only minor effects on maternal genetic effects. Results demonstrate that despite a genetic antagonism that compromises selection response for decreased birth weight and increased postnatal growth, favorable genetic responses can be achieved with the selection index used in this study.

Dietary electrolyte balance for broiler chickens exposed to thermoneutral or heat-stress environments

Ross male broiler chicks (n = 480) on new litter were used in a randomized block design with two blocks (environmental rooms) and four treatments having four replicate pens (1.0 x 2.5 m; 15 chicks) each to evaluate dietary electrolyte balance (DEB; P < 0.05). Two rooms were 1) thermoneutral (Weeks 1 through 6, with decreasing maximum from 32 to 25 degrees C and minimum from 28 to 19 degrees C; relative humidity 49 to 58%) and 2) cyclic daily heat stress (Weeks 1 and 2, thermoneutral; Weeks 2 through 6, maximum temperatures 35, 35, 33, and 33 degrees C, respectively; and minimum temperatures 23, 20, 19, and 19 degrees C, respectively; relative humidity 51 to 54%). The DEB treatments (0, 140, 240, or 340 mEq Na + K - Cl/kg) had NaHCO3 plus NH4Cl, or KHCO3, or both added to corn-soybean meal mash basal diets with 0.30% salt (NaCl). In the thermoneutral room, DEB 240 increased 42-d weight gain and 44-d lymphocyte percentage and decreased heterophil percentage and heterophil to lymphocyte ratio compared to the DEB 40 treatment. The DEB 240 diets had 0.35 and 0.35% Na and 0.37% and 0.29% Cl in starter (0.75% K) and grower (0.67% K) diets, respectively. No DEB treatment differences were found in the heat stress room. For combined rooms, 42-d feed intake was higher for DEB 240 than for DEB 40. The 21-d weight gain was higher for DEB 240 than for DEB 40 or 140; and 21-d feed/gain was lower for DEB 40 than for DEB 340. The predicted maximum point of inflection for 21- and 42-d weight gains were DEB 250 and 201, with highest 42-d feed intake at 220.

Effects of supplementation with high linoleic or oleic cracked safflower seeds on postpartum reproduction and calf performance of primiparous beef heifers.

Primiparous Angus x Gelbvieh (n = 36) rotationally crossed beef cows (initial BW = 487.9 +/- 10.5 kg, body condition score = 5.5 +/- 0.02) were utilized to determine effects of supplemental safflower seeds high in linoleic (76% 18:2) or oleic (72% 18:1) acid on cow BW change, body condition score, milk production and composition, calf weight gain, cow serum metabolites, and metabolic hormones. On d 3 postpartum, cows were randomly assigned to one of three isonitrogenous dietary supplements with equal total quantity of TDN: corn-soybean control supplement (n = 12); high-linoleate safflower seeds (n = 12); or high-oleate safflower seeds (n = 12). Safflower-seed supplements were formulated to provide 5% DMI as fat. Supplements were individually fed from d 3 postpartum through 90 d postpartum. Cows had ad libitum access to native grass hay (7.8% CP), trace-mineralized salt, and water. Date of parturition was evenly distributed across treatments with all cows calving within 14 +/- 0.8 d. There were no differences (P = 0.65) in total OM intake among treatments. Although cow BW change did not differ (P = 0.33) by treatment, supplementation influenced cow body condition score (P = 0.02) with linoleate-supple-mented cows in higher (P = 0.005) condition overall than oleate-supplemented cows (5.1 +/- 0.06 vs 4.9 +/- 0.06). Twenty-four-hour milk production did not differ (P = 0.68) among treatments. Percentage milk fat was not different at d 30; however, at d 60 and d 90 percentage milk fat was greater (P ( 0.05) in control and oleate-supplemented cows than in linoleate-supplemented cows. Calf BW gains (P = 0.27) and adjusted 205-d weights (P = 0.48) were not affected by supplement treatment. Supplementation did not influence serum concentrations of glucose (P = 0.38), NEFA (P = 0.61), GH (P = 0.29), IGF-I (P = 0.81), insulin (P = 0.26), or IGF-I binding proteins (P > or = 0.11). Days to conception did not differ (P = 0.40) among treatments. Although overall productivity of the primiparous cows and their calves was not altered by safflower-seed supplementation, differential effects were noted between supplements. Oleate supplementation increased percentage milk fat at d 60, and cow body condition score was lower than in linoleate-supplemented cows. Linoleate-supplemented cows had greater body condition scores by 90 d postpartum than either corn-soybean- or oleatesupplemented cows.

Direct and maternal genetic effects on birth and weaning traits in multibreed cattle data and predicted performance of breed crosses.

Direct and maternal additive effects and heterosis were estimated using data from straightbred Angus, Brahman, Charolais, Hereford, and four generations of rotational crosses among these breeds. Traits of interest were birth weight, Julian day of birth, average daily gain from birth to weaning, 205-d weight, and weaning weight per cow exposed. Complete data were available on 3,445 calves produced from 4,733 matings. Discrete generations of 4-yr duration were produced from 1970 through 1988. Brahman was included in each rotational crossbreeding system. Genetic effects were estimated by regression. Direct and maternal additive effects of Brahman, Charolais, and Hereford were estimated as deviations from Angus. Direct and maternal heterosis effects were assumed proportional to expected heterozygosity. The Brahman direct additive effect resulted in later-born calves (P < 0.01). Brahman, Charolais, and Hereford direct additive effects increased birth weight, and the Brahman maternal additive effect decreased birth weight compared with Angus (P < 0.05). Charolais direct and maternal additive effects were greater than Angus for average daily gain and 205-d weight (P < 0.01). The Hereford maternal additive effects on average daily gain and 205-d weight were less than those of the other breeds (P < 0.01). Breed combinations including Brahman had greater direct heterosis for birth weight, average daily gain, and 205-d weight than other combinations (P < 0.01). Angus, Charolais, and Hereford direct additive effects on weaning weight per cow exposed were greater than Brahman (P < 0.05). Predicted average daily gain, 205-d weight, and weaning weight per cow exposed were, on average, greater in four-breed rotation systems than in three- and two-breed systems. Among two-breed rotation systems, predicted average daily gain and 205-d weaning weight were greatest for Charolais-Brahman and least for Angus-Hereford. Calves from the Angus-Charolais-Hereford system weighed less at weaning than any other three-breed combination. However, weaning weight per cow exposed from the Angus-Charolais-Hereford system was greatest among three-breed systems. Within three- and four-breed rotation systems, ranges in predicted birth and weaning weights among generations varied by up to 10.0 and 25.2 kg, respectively. The choice of breeds affects performance, and the sequence of their use may affect intergenerational variation in performance.

Genetic (co)variances for calving difficulty score in composite and parental populations of beef cattle: II. Reproductive, skeletal, and carcass traits.

There is limited genetic information relating calving difficulty and body weights to other productive and reproductive traits. Such information is useful for specifying selection criteria and for predicting economic consequences of selection. Genetic, maternal, and environmental covariances of six productive and reproductive measurements with calving difficulty, birth weight, 200-d weight, and 168-d postweaning gain were estimated in 12 experimental populations of cattle. Calf (direct) genetic effects resulting in longer gestation length were associated with increased calving difficulty and birth weight. Maternal genetic effects of increased gestation length and heavier birth weight were significantly associated. Lighter birth weight and reduced calving difficulty were associated with earlier heifer age at puberty. Increases in direct genetic effects of calving difficulty, 200-d weight, and postweaning gain were associated with a small increase in direct effect of scrotal circumference. Increased direct genetic effects of scrotal circumference were correlated with maternal effects decreasing calving difficulty and increasing 200-d weight. Direct effects of the skeletal measurements, yearling hip height, and heifer pelvic area were positively correlated with direct effects of calving difficulty, birth weight, 200-d weight, and postweaning gain, positively correlated with maternal effects for birth weight and 200-d weight, and negatively correlated with maternal calving difficulty. Percentage of retail product was positively associated with calving difficulty and negatively associated with 168-d gain. Predicted genetic change in calving difficulty resulting from one standard deviation of selection for either calving difficulty score or birth weight was much larger than for any other traits. Selection for 200-d weight, 168-d postweaning gain, hip height, pelvic area, or scrotal circumference was predicted to have opposite effects on direct and maternal calving difficulty. Estimated genetic correlations indicate some small to moderate relationships between calving difficulty and the measured productive and reproductive traits. However, selection for reduced calving difficulty should be based on calving difficulty score and(or) birth weight because of their superiority in predicted genetic change.

Genetic and phenotypic variance and covariance components for feed intake, feed efficiency, and other postweaning traits in Angus cattle.

Records on 1,180 young Angus bulls and heifers involved in performance tests were used to estimate genetic and phenotypic parameters for feed intake, feed efficiency, and other postweaning traits. The mean age was 268 d at the start of the performance test, which comprised 21-d adjustment and 70-d test periods. Traits studied included 200-d weight, 400-d weight, scrotal circumference, ultrasonic measurements of rib and rump fat depths and longissimus muscle area, ADG, metabolic weight, daily feed intake, feed conversion ratio, and residual feed intake. For all traits except the last five, additional data from the Angus Society ofAustralia pedigree and performance database were included, which increased the number of animals to 27,229. Genetic (co)variances were estimated by REML using animal models. Direct heritability estimates for 200-d weight, 400-d weight, rib fat depth, ADG, feed conversion,and residual feed intake were 0.17 +/- 0.03, 0.27 +/- 0.03, 0.35 +/- 0.04, 0.28 +/- 0.04, 0.29 +/- 0.04, and 0.39 +/- 0.03, respectively. Feed conversion ratio was genetically (r(g) = 0.66 ) and phenotypically (r(p) = 0.53) correlated with residual feed intake. Feed conversion ratio was correlated (r(g) = -0.62, r(p) = -0.74) with ADG, whereas residual feed intake was not (rg = -0.04, r(p) = -0.06). Genetically, both residual feed intake and feed conversion ratio were negatively correlated with direct effects of 200-d weight (r(g) = -0.45 and -0.21) and 400-d weight (r(g) = -0.26 and -0.09). The correlations between the remaining traits and the feed efficiency traits were near zero, except between feed intake and feed conversion ratio (r(g) = 0.31, r(p) = 0.23), feed intake and residual feed intake (r(g) = 0.69, r(p) = 0.72), and rib fat depth and residual feed intake (r(g) = 0.17, r(p) = 0.14). These results indicate that genetic improvement in feed efficiency can be achieved through selection and, in general, correlated responses in growth and the other postweaning traits will be minimal.

Milk production of crossbred daughters of high- and low-milk EPD Angus and Hereford bulls.

Milk yield from 273 Angus- and Hereford-sired cows and preweaning performance of their calves were used to determine how accurately milk EPD of Angus and Hereford sires predicted milk production of crossbred daughters and subsequent calf performance. Mean milk EPD (kg) for high Angus (HA), low Angus (LA), high Hereford (HH), and low Hereford (LH) bulls (n = 41) selected as sires were +8.7, -6.2, +7.6, and -4.8, respectively. Cows calved in spring or fall from 1992 to 1997 and yielded a total of 660 records. Twenty-four-hour milk production of the cows was estimated by two weigh-suckle-weigh measurements at monthly intervals. The statistical model included breed, milk EPD level, sire of cow within breed and milk EPD level, year, season, cow age, calf sire, sex, and all two- and three-way interactions. Means were obtained for monthly milk production, total milk production, time and yield of peak production, monthly calf weights, monthly cow weights and body condition scores (1 through 9), and calf birth and weaning data. The least squares means for 24-h milk production (kg) of HA, LA, HH, and LH with P-values for high vs low, across breeds, were, respectively, as follows: mo 1: 6.9, 5.9, 7.1, and 5.7 (P < 0.01); mo 2: 7.2, 6.1, 6.9, and 5.7 (P < 0.01); mo 3: 6.1, 5.1, 5.1, and 4.3 (P = 0.01); mo 4: 6.1, 4.9, 4.9, and 4.8 (P = 0.01); mo 5: 4.8, 4.0, 4.2, and 3.8 (P = 0.01); mo 6: 4.7, 3.4, 3.2, and 3.0 (P < 0.01); and mo 7: 3.7, 2.5, 3.0, and 3.0 (P = 0.05). Least squares means for total milk (kg) were 911.4, 729.6, 758.0, and 664.2 (P < 0.01); for yield at peak (kg/d) were 7.0, 5.7, 6.1, and 5.2 (P < 0.01); for birth weight (kg) were 37.1, 37.9, 38.3, and 38.8 (P = 0.31); for 205-d weight (kg) were 237.3, 218.2, 222.2, and 214.1 (P < 0.01); for final cow weight (kg) were 482.4, 505.4, 509.5, and 511.7 (P = 0.11); and for final cow BCS were 4.9, 5.3, 5.1, and 5.2 (P < 0.01). The correlations of total production with the monthly productions were 0.52, 0.56, 0.52, 0.54, 0.35, 0.37, and 0.31 (P < 0.01) and were 0.12 with birth weight, 0.45 with 205-d weight, -0.12 with final cow weight, and -0.26 with final cow body condition score (all P < 0.01). Daughters of high-milk EPD sires produced more milk and weaned heavier calves than those of low-milk EPD sires at the expense of body condition. These results suggest that sire milk EPD are sufficiently associated with milk yield and calf performance to be useful tools in genetic improvement of preweaning performance.

Genetic (co)variances for calving difficulty score in composite and parental populations of beef cattle: I. Calving difficulty score, birth weight, weaning weight, and postweaning gain.

Heritability of 2-yr-old heifer calving difficulty score was estimated in nine purebred and three composite populations with a total of 5,986 calving difficulty scores from 520 sires and 388 maternal grandsires. Estimates were 0.43 for direct (calf) genetic effects and 0.23 for maternal (heifer) genetic effects. The correlation between direct and maternal effects was -0.26. Direct effects were strongly positively correlated with birth weight and moderately correlated with 200-d weight and postweaning gain. Smaller negative correlations of maternal calving difficulty with direct effects of birth weight, weaning weight, and postweaning gain were estimated. Calving difficulty was scored from 1 to 7. Predicted heritabilities using seven optimal scores were similar to those using four scores. The predicted heritability using only two categories was reduced 23%. Phenotypic and direct genetic variance increased with increasing average population calving difficulty score. The estimated direct and maternal heritabilities for 2-yr-old calving difficulty score were larger than many literature estimates. These estimates suggested substantial variance for direct and maternal genetic effects. The direct effects of 2-yr-old calving difficulty score seemed to be much more closely tied to birth weight than were maternal effects.

Genotype x environment interactions in Angus, Brahman, and reciprocal-cross cows and their calves grazing common bermudagrass, endophyte-infected tall fescue pastures, or both forages.

Reproductive and preweaning data on 190 Angus (A x A), Brahman (B x B), and reciprocal-cross cows (A x B and B x A) and 434 two- and three-breed-cross calves managed on common bermudagrass (BG), endophyte-infected tall fescue (E+), or a combination of both forages (ROT) were used to evaluate the interaction of forage type with individual and maternal heterosis and maternal and grandmaternal breed effects. Cows were born from 1988 to 1991, and calves sired by 13 Polled Hereford bulls were born from 1995 to 1997. Heterosis for calving rate was larger on E+ than on BG or ROT (P < .05), whereas maternal effects were larger on BG than on ROT (P < .10). Maternal heterosis for birth weight was negative on BG (P < .11) but positive on E+ and ROT (P < .10). Grandmaternal effects were evident on BG (P < .10) and E+ (P < .01) but not on ROT. Forage effects were generally substantial for 205-d weight, calf weaning hip height, and calf weaning weight:height ratio; BG was highest, ROT was intermediate, and E+ was lowest. Maternal heterosis for these traits was generally greater on E+ than on BG (P < .10). Grandmaternal effects for 205-d weight, hip height, and weight:height ratio were not important on any forage. Heterosis for weaning weight per cow exposed was substantial on all forages (P < .01) and was significantly greater on E+ (P < .01) than on BG or ROT, but maternal effects were not significant. Thus, we observed more advantage to Brahman-cross cows over purebreds on E+ than on BG. We also observed that moving cows and calves from E+ to BG in the summer will alleviate some, but not all, of the deleterious effects of E+ on calf growth, although it may be more beneficial for reproductive traits in purebred cows.

ARPP-16 mRNA is up-regulated in the longissimus muscle of pigs possessing an elevated growth rate.

Selection for increased growth rate in farm and laboratory animals has been used to develop lines with increased body and muscle weights. However, very little is known about the underlying molecular pathways and how their constitutive genes influence this process. In this study, the differential display-reverse transcription PCR (DDRT-PCR) method was employed to identify longissimus muscle genes that are differentially expressed between a line of pigs selected for increased 200-d weight and a randomly selected control line. A 590-bp DDRT-PCR cDNA product was identified and isolated based on its greater abundance in the longissimus muscle of the select line relative to the control line animals. This DDRT-PCR product has 89% identity to the end of the 3'-untranslated region of the bovine 16-kDa cAMP-regulated phosphoprotein (ARPP-16) cDNA sequence. Reverse transcription PCR (RT-PCR) amplification of the porcine homologue of ARPP-16 and subsequent sequencing established that the DDRT-PCR product corresponds to the 3'-end of the porcine ARPP-16 transcript. Semiquantitative RT-PCR verified that ARPP-16 is up-regulated in the select line and determined that the relative expression level of ARPP16 mRNA is approximately fourfold higher (P < .01) in the select than in the control animals. The deduced amino acid sequence of ARPP-16 is highly homologous to the deduced amino acid sequences of bovine, human, and rat ARPP-16, and RT-PCR with ARPP-16-specific PCR primers indicated that this gene is expressed in many different porcine tissues. The porcine homologue of the 19-kDa cAMP-regulated phosphoprotein (ARPP-19) was also amplified by RT-PCR, cloned, and sequenced. The deduced amino acid sequence of ARPP19 differs from ARPP-16 only by the addition of 16 N-terminal amino acids. In all tissues studied, ARPP-19 mRNA was detected by RT-PCR amplification; however, the relative expression level of ARPP-19 mRNA was not differentially expressed between the select and control line animals (P > .05). The fourfold relative increase in ARPP-16 mRNA expression in the select line animals indicates that this gene may play an important role in the molecular pathway(s) that regulate postnatal skeletal muscle growth in the pig.

Estimates of direct and maternal genetic parameters for weight traits and backfat thickness in a multibreed population of beef cattle

Variance components were estimated for weight at birth, weaning, and 365 d of age, and yearling ultrasonic backfat thickness in a multibreed population of beef cattle. Data (n = 5880) were available on F1 animals and various crosses leading up to, and including, a composite breed (7/16 British, 1/4 Charolais, 1/4 Simmental, and 1/16 Limousin). Single- and two-trait analyses were conducted using an animal model and derivative-free REML procedures. Covariates representing fractional contributions of each of the four purebred groups and average heterotic effects, both direct and maternal, accounted for breed composition. Direct and maternal genetic, maternal permanent environmental, and residual effects were the random variables. Only minor differences existed between parameter estimates obtained from the various analyses. Mean direct heritabilities were 0.51, 0.33, 0.48, and 0.37 for weight at birth, weaning, and 365-d, and backfat, respectively, which, though well within the range of published estimates, seemed higher than average, indicating diversity in the founding purebreds. Mean maternal heritabilites were 0.09, 0.13, and 0.08 for the three consecutive weights. A likelihood ratio test showed maternal heritability and(or) the direct-maternal correlation was important (P &lt; 0.001) for 365-d weight. Averaged across weights, the direct-maternal correlation was 0.07, lacking evidence of genetic antagonism. No age of dam or random maternal effects on backfat were apparent. Phenotypic correlations between weight at birth and weaning and weight at weaning and 365-d were 0.46 and 0.76, respectively. Though moderate between birth and weaning weight, maternal genetic and permanent environmental correlations between weaning and 365-d weight approached unity, demonstrating maternal carryover effects. Phenotypic and genetic correlations of 0.19 and –0.13, respectively, implied a limited association between 365-d weight and backfat, which possibly would have been stronger had fat been measured later in life. Estimates of variance components suitable for general use can be obtained from data from multibreed animals by considering breed and heterotic effects. Key words: Beef cattle, crossbreds, genetic parameters, heritability, maternal effects

Variance components and breeding values for growth traits from different statistical models.

Estimates of genetic parameters resulting from various analytical models for birth weight (BWT, n = 4,155), 205-d weight (WWT, n = 3,884), and 365-d weight (YWT, n = 3,476) were compared. Data consisted of records for Line 1 Hereford cattle selected for postweaning growth from 1934 to 1989 at ARS-USDA, Miles City, MT. Twelve models were compared. Model 1 included fixed effects of year, sex, age of dam; covariates for birth day and inbreeding coefficients of animal and of dam; and random animal genetic and residual effects. Model 2 was the same as Model 1 but ignored inbreeding coefficients. Model 3 was the same as Model 1 and included random maternal genetic effects with covariance between direct and maternal genetic effects, and maternal permanent environmental effects. Model 4 was the same as Model 3 but ignored inbreeding. Model 5 was the same as Model 1 but with a random sire effect instead of animal genetic effect. Model 6 was the same as Model 5 but ignored inbreeding. Model 7 was a sire model that considered relationships among males. Model 8 was a sire model, assuming sires to be unrelated, but with dam effects as uncorrelated random effects to account for maternal effects. Model 9 was a sire and dam model but with relationships to account for direct and maternal genetic effects; dams also were included as uncorrelated random effects to account for maternal permanent environmental effects. Model 10 was a sire model with maternal grandsire and dam effects all as uncorrelated random effects. Model 11 was a sire and maternal grandsire model, with dams as uncorrelated random effects but with sires and maternal grandsires assumed to be related using male relationships. Model 12 was the same as Model 11 but with all pedigree relationships from the full animal model for sires and maternal grandsires. Rankings on predictions of breeding values were the same regardless of whether inbreeding coefficients for animal and dam were included in the models. Heritability estimates were similar regardless of whether inbreeding effects were in the model. Models 3 and 9 best fit the data for estimation of variances and covariances for direct, maternal genetic, and permanent environmental effects. Other models resulted in changes in ranking for predicted breeding values and for estimates of direct and maternal heritability. Heritability estimates of direct effects were smallest with sire and sire-maternal grandsire models.

Influence of prepartum body condition score change on reproduction in multiparous beef cows calving in moderate body condition.

Multiparous, spring-calving beef cows (n = 250) were used to determine whether large changes in body energy reserves during mid- to late gestation influenced subsequent reproductive performance of cows calving in moderate body condition. In three states, cows were blocked by BW and body condition score (BCS; 1 = emaciated to 9 = obese) then allotted to receive either a high or low plane of nutrition from late summer to early winter over a 3-yr period. This generated an array of BCS by the beginning of the last trimester of pregnancy when cows were grouped by BCS as follows: Group 1, BCS < or = 4; Group 2, BCS of 5 or 6; and Group 3, BCS > or = 7. Each group was managed so that individual cows would calve with a BCS of 5 to 6. At the time of group assignment, mean BW and BCS differed (P < .01) among groups and were 480 kg and 3.6, 541 kg and 5.5, and 594 kg and 7.1 for Groups 1 to 3, respectively. Within 28 d before calving, BW and BCS were similar (P > .20) among groups averaging 555 kg and 5.1. Prepartum BCS changes averaged 1.4, -.4, and -2.0 units for Groups 1 to 3, respectively (P < .01). Cows were managed as a single group after calving in each state. Location effect was significant for the prepartum and postpartum BW and BCS changes but not for postpartum reproductive performance. Significant location x BCS group interactions were found for the 90-d prepartum BW, BCS at calving, and prepartum changes in BW, but were caused by differences in magnitude among locations. The percentage of cows with luteal activity at the start of a subsequent breeding season was not affected (P > .20) by either location or BCS group, and averaged 66%. Mean pregnancy rates at 20, 40, and 60 d of a subsequent breeding season were 55, 76, and 89% for Group 1; 51, 67, and 82% for Group 2; and 64, 79, and 89% for Group 3 (P > .30). Mean days to conception were 89, 87, and 85 for Groups 1 to 3, respectively (P = .70). Neither calf birth weight (x = 38.6 kg) nor adjusted 205-d weight (x = 223.6 kg) were affected by prepartum BW and BCS changes. We conclude that reproductive performance of cows calving in moderate body condition is not influenced by large changes in body energy reserves during the last trimester of pregnancy.

Germplasm evaluation in beef cattle--Cycle IV: postweaning growth and puberty of heifers.

Postweaning growth, puberty, and pregnancy traits were evaluated for 783 F1 heifers sired by Angus, Hereford, Charolais, Shorthorn, Galloway, Longhorn, Nellore, Piedmontese, and Salers bulls and out of Angus and Hereford dams in Cycle IV of the Germplasm Evaluation (GPE) Program at the U.S. Meat Animal Research Center. The Hereford and Angus sires included a sample of bulls born from 1982 to 1985 (1980s HA) as well as reference sires born from 1963 to 1970 (REF HA) used in previous cycles of the GPE program. Breed group of sire had a significant (P<.01) effect on age and weight at puberty, on 200-, 400-, and 550-d weights, on ADG from 200 to 400 and from 400 to 550 d, and 550-d hip height, but it did not influence (P<.05) pregnancy rate. Mean age and weight at puberty were predicted from the cumulative distribution because of censoring of data in each tail of the distribution. Sire breed group rankings (and predicted means in days) for age at puberty were as follows: Piedmontese (332), Shorthorn (338), Charolais (348), REF HA (348), Galloway (351), 1980s HA (352), Salers (355), Longhorn (357), and Nellore (405). Sire breed group rankings (and predicted means in kilograms) for weight at puberty were Longhorn (283), Piedmontese (298), Galloway (305), REF HA (309), Shorthorn (329), 1980s HA (330), Salers (338), Nellore (341), and Charolais (345). Sire breed group rankings (and least squares means in kilograms) for 200-d weight were Charolais (229), Salers (225), Nellore (221), Shorthorn (220), Piedmontese (215), 1980s HA (215), Galloway (209), REF HA (206), and Longhorn (197), with differences >8.3 kg significant. Rankings for 400-d weight (kilograms) were Charolais (390), Shorthorn (384), Salers (380), 1980s HA (374), Nellore (364), REF HA (356), Piedmontese (353), Galloway (348), and Longhorn (321), with differences >11.5 kg significant. Rankings for 550-d weight (kilograms) were Charolais (445), Salers (430), Shorthorn (429), 80's HA (422), Nellore (420), Piedmontese (401), REF HA (398), Galloway (389), and Longhorn (371), with differences >11.7 kg significant. Rankings for 550-d hip height (centimeters) were Nellore (132.2), Charolais (131.9), Salers (129.9), Shorthorn (129.5), Piedmontese (126.7), 1980s HA (126.1), Longhorn (125.3), Galloway (121.7), and REF HA (121.5), with differences >1.35 cm significant. Breed of sire had significant effects on growth and puberty traits of heifers.

Germplasm evaluation in beef cattle-cycle IV: birth and weaning traits.

Gestation length, unassisted calving percentage, perinatal mortality, calf crop weaned (survival from birth to weaning), birth weight, and 200-d weaning weight of 2,597 calves born and 2,433 calves weaned are reported for F1 crosses resulting from matings of Angus, Hereford, Charolais, Gelbvieh, Pinzgauer, Shorthorn, Galloway, Longhorn, Nellore, Piedmontese, and Salers sires to Angus and Hereford dams (> or = 3 yr of age) in Cycle IV of the Germplasm Evaluation (GPE) Program at the U.S. Meat Animal Research Center. Hereford and Angus sires included 1) reference sires born from 1963 to 1971 used in previous cycles of the GPE Program, 2) sires born from 1982 to 1985 (1980s), and 3) sires born from 1983 to 1985 used in natural service clean-up matings. Effects of sire breed of calf were significant for gestation length, unassisted calving percentage, birth weight, and 200-d weaning weight. Gestation length was significantly longer for Nellore than for Charolais, Galloway, Longhorn, Piedmontese, and Salers, which were in turn longer than for Hereford-Angus and Shorthorn. Rankings for birth weight tended to be inversely related to those for calving ease, except for Shorthorn and Salers sires, which required low assistance relative to their heavy birth weights. Rankings for 200-d weight among AI-sired progeny were as follows: Charolais (231.3), Nellore (229.7), Salers (225.5), Shorthorn (223.8), 1980s Hereford-Angus (223.1), Piedmontese (220.0), Galloway (209.5), reference Hereford-Angus (210.1), and Longhorn (199.0); differences > or = 6.5 kg were significant.

Reproductive performance, calf growth, and milk production of first-calf heifers sired by seven breeds and raised on different levels of nutrition.

We evaluated heifers crossbred from seven breeds of sires (Hereford, Angus, Belgian Blue, Piedmontese, Brahman, Boran, and Tuli) and three breeds of dams (Angus, Hereford, and MARC III [four-breed composite]). Heifers were mated to Red Poll sires to calve at 2 yr of age. Heifers were placed in two treatments from weaning to breeding and raised on a high nutrition level (15.8 Mcal ME/d) or on 80% of the high nutrition level (12.6 Mcal ME/d). Breeds differed in the age of the heifers at parturition (P = .03). Birth weights of calves differed by maternal grandsire (P < .001) but not by heifer treatment (P = .91) or maternal grandam (P = .19). Heifers differed in their postpartum interval to estrus by sire breed (P = .001). Calf age at weaning (P = .02), calf ADG (P < .001), and 205-d weight (P < .001) differed between breeds of maternal grandsires. Milk production from 50 to 200 d of lactation was greatest for heifers of Belgian Blue (1,070 +/- 30 kg) and Brahman (1,029 +/- 38 kg) sires. Milk production did not differ with treatment group (P = .84). This study suggests that over a diverse group of breeds, accelerated rates of gain during the postweaning period within the ranges of this study do not result in increased production efficiency of the cows.

Genetic parameters for sex-specific traits in beef cattle.

Data from 3,593 beef heifers and 4,079 of their steer paternal half-sibs were used to estimate genetic parameters of and among female growth and reproductive traits and male carcass traits. Estimates of heritability for adjusted 205-d weight, adjusted 365-d weight, age at puberty, calving rate, and calving difficulty measured on females were .16, .38, .47, .19, and .18, respectively; estimates for calving rate and calving difficulty were expressed on a normal scale. Estimates of heritability for hot carcass weight; retail product percentage; fat percentage; bone percentage; rib eye area; kidney, pelvic, and heart fat percentage; adjusted fat thickness; marbling score; Warner-Bratzler shear force; taste panel tenderness; taste panel juiciness; and taste panel flavor that were measured on steers at an average age of 447 d (weaning age = 185, days on feed = 262) were .50, .66, .58, .54, .61, .48, .66, .71, .26, .31, .00, and .04, respectively. Genetic correlations were positive for heifer weights with hot carcass weight, fat percentage, rib eye area, adjusted fat thickness, marbling score, and Warner-Bratzler shear force, and they were negative with retail product percentage and kidney, pelvic, and heart fat percentage of steers. Age at puberty was genetically correlated with taste panel tenderness but not with other carcass traits. Calving rate had positive genetic correlations with fat percentage, rib eye area, adjusted fat thickness, and taste panel flavor, and it had negative genetic correlations with retail product percentage; bone percentage; and kidney, pelvic, and heart fat percentage. Calving difficulty had favorable genetic correlations with hot carcass weight, retail product percentage, and measures of carcass tenderness, but it was unfavorably correlated with traits that involve carcass fatness. These results indicate that selection for some traits expressed in one sex of beef cattle may result in undesirable responses in traits expressed in the opposite sex.

Preweaning Performance of Beefmaster- and Brahman-Sired Calves from Angus and Brahman Cows on Three Forage Systems

Three years of data from 42 purebred Angus (AA) and 50 Brahman (BB) cows bred to purebred Beefmaster (BM) and purebred Brahman (BB) bulls were used to evaluate both breed of sire effects and different forage systems. Cows and calves were managed on one of three forage systems: endophyte-infected tall fescue (E+E+), common bermudagrass and endophyte-infected tall fescue (E+CB), and common bermudagrass and endophyte-free tall fescue (E−CB). Data from 215 calves born and 197 calves weaned were used in this study. The calves were weighed and tagged at birth and were not creep-fed. They were weaned at an average of 195 d of age and their weights and hip heights were taken. There was little evidence of sire breed, forage effects, or interactions of the two on the birthweight of calves from the BM or BB sires, which averaged 39 and 37 kg, respectively. The calves from the AA cows were 7.7kg heavier at birth than those from the BB cows (P<0.01). There was evidence of a sire breed × dam breed × forage interaction (P<0.10) in calf 205-d weights. There was little evidence of any advantage in 205-d weight for calves on E+CB compared to those on E+E+ except for the BB × BB calves (P<0.10). Only the BB × AA calves seemed to benefit from the E−CB compared to E+CB (P<0.10), and 205-d weights were less for BB × BB calves on E−CB than on E+CB. Averaged over sire breed, the 205-d weights of calves on E−CB exceeded those on E+E+ by 15kg (P<0.05). Averaged over forages, there was little evidence of differences between BM and BB sires when bred to Angus cows, although predictable decreases in 205-d weights were observed in BM × BB and BB × BB compared to the Angus crosses (P<0.05). The means for hip height averaged over sire and dam breed suggest an advantage for E−CB compared to E+E+ (P<0.10). These data do not suggest any notable advantage for any of the breed groups on any particular forage system. A predictable trend for improved performance as E+ is removed from the forage system is evident as is a similar trend as heterozygosity is increased in the progeny.

Genotype x environment interactions in Angus, Brahman, and reciprocal cross cows and their calves grazing common bermudagrass and endophyte-infected tall fescue pastures.

Reproductive and preweaning data on 233 Angus (A), Brahman (B), and reciprocal-cross cows (AB, BA) and 455 two- and three-breed cross calves managed on common bermudagrass or endophyte-infected tall fescue were used to evaluate the interaction of forage type with individual and maternal heterosis and maternal and grandmaternal breed effects. Cows were born from 1988 to 1991 and calves from 15 Polled Hereford sires were born from 1991 to 1994. Heterosis for calving rate was similar and important on both forages (P < .01), but maternal effects were small on each forage. Maternal heterosis for birth weight differed between common bermudagrass and tall fescue (P < .10) and grandmaternal effects were evident on bermudagrass (P < .05) but not tall fescue. Forage effects were generally substantial for 205-d weight, weaning hip height, and weaning weight:height ratio (P < .01), and maternal heterosis for these traits was larger on tall fescue than on common bermudagrass (P < .01). Grandmaternal effects were in favor of Angus for 205-d weight, hip height, and weight:height ratio on common bermudagrass (P < .05) but not on tall fescue. Heterosis for 205-d weight per cow exposed was substantial on both forages (P < .01) and was numerically larger on tall fescue than on bermudagrass, but maternal effects were not significant. These results suggest more advantage for Brahman-cross cows over purebreds on endophyte-infected tall fescue than a similar comparison on common bermudagrass. They also suggest an advantage for Angus in grandmaternal effects on bermudagrass but not tall fescue.

Variation in Birth and Weight Traits of identical Calves Produced Through Nuclear Transplantation

The identical genetic makeup within groups of beef cattle produced through nuclear transplantation (NT) should reduce the number of animals required for statistically powerful research trials, assuming a lack of variability within genotypes. With this in mind, five groups of male, Brangus, second-generation NT pregnancies (seven to eight per group) being gestated in Holstein recipient females were obtained from Granada Biosciences (Wheelock, TX). Calving occurred from December 1991 to April 1992, and resulted in 24 live calves from 39 pregnancies. All animals were DNA fingerprinted to verify genotype within clone groups using restriction fragment length polymorphism analysis of genomic DNA. At birth, all calves were measured for head circumference (HC), shoulder width (SW), heart girth (HG), metacarpal circumference (MC), body length (BL), and birth weight (BW). All linear measures were positively correlated (P<0.01) to BW, and accounted for 84.5% of the variability observed in BW. Adjusted 205-d weaning weight (AWW) and adjusted 365-d yearling weight (AYW) were used to assess changes in variability within and among groups over time. Weight variability decreased 60% on average within genotypes as the animals matured. In one genotype, low variability (CV=6.3%) at birth with little change over time was observed. This uniformity may have been attributable to the surrogate dams being on a higher nutritional plane than earlier calving groups. These data indicate a reduction in observed weight trait variability within NT calves over time.