PSIX-17 - Preliminary assessment of preweaning growth performance of Dexter and Mashona x Dexter calves

Abstract: Non-traditional cattle breeds are often considered by managers for niche’ beef production and marketing systems. Some of these alternative breeds are small-framed and thus desired by small-farm operators, but have received little research attention because they do not fit traditional commodity beef production systems. Very few of these small breeds also offer heat tolerance. This project was designed to evaluate preweaning performance of straightbred (n = 76) and F₁ crossbred calves (n = 81) produced by mature Dexter cows across three years and two TSU research farms. Spring-born calves were sired by Dexter (n = 7; DD) and Mashona bulls (n = 6; MD) in single-sire, natural service breeding groups following 60-d breeding seasons. Breed of sire was balanced across cow age and farm locations. Calves were weighed within 24-h of birth, at 4 months (125 d of age) of age, and at weaning (227 d of age). Calves were not creep-fed and bull calves were not castrated until after weaning. No cases of dystocia were observed as a result of crossbreeding. Calf performance traits were evaluated using MIXED models of SAS. Fixed effects included sire breed, sex, farm location, and the interaction of sire breed and sex. Random effect terms were production year and sire nested within sire breed. For all the traits evaluated, models were consistent in that the sire breed x calf sex interaction was not significant (P > 0.1), whereas sire breed and calf sex were consistently important (P < 0.01) sources of variation. Bull calves had higher weight and ADG values than heifer calves from birth to weaning. Mean weight was higher for MD than DD calves at birth (28.4 ± 0.8 vs. 23.9 ± 0.7 kg), at 4 months of age (120.6 ± 9.7 vs. 96.7 ± 9.6 kg), and at weaning (154 ± 8.6 vs. 124.4 ± 8.6 kg). The MD calves had higher ADG than DD calves from birth to 4 months of age (715.8 ± 36.1 vs. 599.1 ± 36 g/d), from 4 months of age to weaning (334 ± 44.3 vs. 256.8 ± 44 g/d), and from birth to weaning (547 ± 35.7 vs. 447.1 ± 35.7 g/d). Mean 205-d adjusted weight was higher for MD than DD (140.2 ± 7.6 vs. 114.7 ± 7.6 kg). Preliminary results indicated that crossbreeding with Mashona bulls significantly increased preweaning growth of calves produced by Dexter cows, while the F₁ calves maintained small statute. The spring-born MD F₁ calves likely benefited from heat tolerance provided by the Mashona influence and heterosis generated by crossbreeding.