Richard J. Rasby

Age at weaning and the endocrine response to stress

Seventy-five Angus x MARC II crossbred heifers were used to assess the effects of age at weaning on calf performance and blood constituents. Calves were weaned at 150, 210, or 270 days of age with comparisons made to their non-weaned counterparts. Changes in blood chemistry and hematology (cortisol, glucose, T3, total proteins, packed cell volume and the differential white blood cell count) were recorded on the day of weaning (day-0), and at 2, 7, 14, and 28 days post-weaning. Calves weaned at 210 days of age presented the highest plasma cortisol, glucose, and total protein concentrations during their early post-weaning period. Calves weaned at 150 days of age had significantly lower plasma T3 values. Packed cell volume and differential white blood cell counts showed no relationship to age at weaning. Calves weaned at 210 days of age presented the most rapid post-weaning growth performance, relative to the 150 or 270 days of age weaned calves.

Heifers sired by bulls with either high or low expected progeny differences (EPDs) for marbling do not differ in age at puberty

Abstract Selection for carcass traits such as deposition of intramuscular fat (marbling), which is a primary trait used as an indicator of meat quality, may incur additional effects such as younger age at puberty. Therefore, a trial was conducted for 2 years to determine age of puberty for two groups of crossbred heifers ( n = 124) sired by purebred Angus bulls selected for either low (Low, n = 6) or high (High, n = 6) expected progeny differences (EPDs) for marbling. Our working hypothesis was that age at puberty would be reduced in heifers sired by bulls with high EPDs for marbling in comparison to those heifers sired by bulls with low EPDs for marbling. Puberty was determined by collecting weekly blood samples and assaying for concentrations of progesterone. Mean age at puberty for heifers during the study did not differ (392 ± 5 and 387 ± 5 days, Low and High respectively). Of the 124 heifers, 79% reached puberty within the 145 days allotted for the study. We conclude that use of sires that produce daughters with increased ability to marble does not result in decreased age at puberty.

The effects of supplementing beef cows grazing cornstalk residue with a dried distillers grain based cube on cow and calf performance1

ABSTRACT Multiparous beef females (n = 832) were used to study the effects of supplementing cows grazing cornstalk residue with a dried distillers grain based cube on cow and calf performance. Cows were blocked by age, BCS, BW, and calving date and assigned randomly to 1 of 2 treatments: 1) supplemented with protein and energy using a dried distillers grain based cube or 2) not supplemented (control) during the last trimester of pregnancy. Cow BW was similar at initiation and at the end of cornstalk grazing, and at the initiation of the breeding season. Supplementation did not affect BCS at the start of breeding (5.4 ± 0.1) or at the initiation of cornstalk grazing the subsequent year. Body condition score of supplemented cows was greater (P = 0.02) at the end of cornstalk grazing compared with that of control cows (5.6 vs. 5.4 ± 0.1). Calving interval, calf birth weight, and calf weaning weight were not different. Percentage of cows cyclic before breeding and final pregnancy rates did not differ. Heifer progeny (n = 306) retained as replacements were similar in initial weight (277.5 ± 10.2 kg), final weight (351 ± 11.5 kg), initial and final BCS, and ADG (0.45 ± 0.04 kg/d). Age at puberty, response to synchronization, AI conception and pregnancy rates, and final pregnancy rates were not different. Supplementation of a dried distillers grain based cube to cows grazing cornstalks improves BCS in the last trimester without affecting reproduction, calf performance, or reproductive performance of heifer progeny.