Data were collected on 476 spring-calving, primiparous cows at six locations in Louisiana over a 2-yr period. Objectives of the study were to evaluate changes in prepartum body condition score (BCS) and BW of heifers when fed varying energy levels and to determine the influences of prepartum BCS and BW changes and BCS at calving on postpartum traits. Heifers were allocated to one of three energy levels from approximately 90 d prepartum to parturition. The diets were formulated to provide low, recommended, and high energy levels based on TDN requirements. After calving, cows were placed on annual ryegrass pasture and managed similarly at each location. Weight and BCS at calving were greater (P < .05) for females with higher BCS at 90 d prepartum (IBCS) and for those assigned to higher energy levels. Calving and calf growth traits were not affected (P > .05) by IBCS, energy level, prepartum changes in BCS and BW, or BCS at calving. Prepartum changes in BCS and BW regulated by varying energy levels had no effect (P > .05) on postpartum reproduction; however, BCS at calving influenced (P < .03) pregnancy rate and days to pregnancy. Cows with BCS 6 and 7 at calving had higher (P < .05) pregnancy rates (87.0 and 90.7%) than those with BCS 4 and 5 (64.9 and 71.4%). Interval to pregnancy for cows with BCS 4 at calving was 10 to 18 d longer (P < .05) than for those with BCS > or = 5.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Carcass data from 1,494 straightbred and rotational crossbred steers were collected over four generations. Mating systems included straightbreds (Angus [A], Brahman [B], Charolais [C], and Hereford [H]); two-breed rotations (A-B, C-B, and H-B); three-breed rotations (A-B-C, A-B-H, and B-C-H); and a four-breed rotation (A-B-C-H). Steers were randomly allocated to one of four postweaning treatments that varied in length of grazing and feeding periods. Treatment and breed group (four straightbreds and seven rotational combinations) significantly influenced hot carcass weight (HCWT), retail yield (RY), longissimus muscle area (LM), fat thickness (FT), marbling score (MS), USDA quality grade (QG), and Warner-Bratzler shear force (WBS). Feeding for longer periods resulted in greater (P < .05) HCWT, RY, FT, and MS, higher QG, and lower (P < .05) WBS values. Among the straightbreds, C was heavier and larger for HCWT, RY, and LM (P < .01), whereas A and H had greater (P < .01) FT and MS. The B was similar to H for HCWT, RY, and LM and to C for FT but ranked last (P < .01) for MS and WBS. Three- and four-breed rotational mating systems were superior (P < .05) to the two-breed rotation for HCWT, RY, and LM but were similar for FT, MS, and WBS. Rotational combinations exceeded (P < .05) the straightbreds for all carcass traits except MS.

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.

The cow‐calf operation is the primary beef cattle enterprise in the Southeastern USA. Cool‐season annuals can be used to improve forage production and quality with the long growing season that the Gulf Coast offers. The objective of this study was to determine the effect of supplemental grazing of cool‐season annuals, sodseeded on perennial Argentine bahiagrass (Paspalum notatum Flugge) pasture, had on cow‐calf productivity. Five hundred forty‐seven reproductive and calving records obtained over 8 yr from ISO purebred Angus cows (Bos taurus) were used to evaluate two pasture systems (PS). Stocking rates of 1 cow/2 acres were maintained for each PS. The two PS consisted of: (1) bahiagrass and (2) bahiagrass and bahiagrass sodseeded with cool‐season annuals [rye (Secale cereale L.) or wheat (Triticum aestivum L.) with crimson clover (Trifolium incarnatum L.) and arrowleaf clover (Trifolium vesiculosum Savi)]. The amount of winter feeding of hay and supplemental protein were lower (P < 0.01) for cows in PS 2 than those in PS 1. Calving rate, weaning rate, survival rate, culling rate, calving date, and calving interval were not affected (P > 0.05) by PS. A greater (P < 0.08) percentage of cows in PS 2, however, calved in the first month of the calving season than cows in PS 1 (28 vs. 14%) Weaning and 205‐d weights of calves from PS 2 were 6 to 7% heavier (P < 0.07) than those from calves in PS 1. Cows in PS 2 were 48 lb heavier (P < 0.07) at the time of weaning and produced 13 lb more (P < 0.07) calf per 1000 lb of cow weight. The primary benefits realized from the grazing of the cool‐season annual forages were reduced winter feeding of hay, protein supplement, and heavier calf and cow weights at weaning.