PSIII-3 - Effects of milk replacer composition on beef x dairy calf growth and muscle fiber cross-sectional area

Abstract: Increased availability of female-sexed semen for the generation of replacement heifers within the dairy industry has expanded the opportunity for production of crossbred beef x dairy (BxD) calves. However, data evaluating feeding strategies for BxD calves are limited. The objective of this study was to determine the effects of two different milk replacers on muscle growth of BxD calves compared with dam-reared Angus calves. We hypothesized that both male and female BxD calves fed added fat and protein through milk replacer would have muscle fiber cross-sectional area (CSA) similar to that of purebred Angus calves. SimAngus x Holstein calves (n=40) were assigned to one of two treatments: a) Additional 32.0% Crude Protein (CP), 30% Crude Fat (CF) milk replacer (ADD, n=10 males, 10 females), or b) Control 22% CP, 20% CF milk replacer (CON, n=10 males, 10 females). BxD calves were fed milk replacer 3 times daily from 0 to week 8 of age. BxD calves received starter grain and hay ad libitum at ±3 days of age. Twenty Angus calves (n=10 males, 10 females) were group housed in cow-calf pairs with ad libitum access to maternal milk. Calves were weighed within 24 h of birth. Longissimus muscle biopsies were performed at week 2 and 8. Samples were cryosectioned, stained with wheat germ agglutinin, and analyzed for muscle fiber CSA. Body weight and CSA were analyzed with PROC MIXED of SAS with animal as the subject and fixed effects of treatment, breed, age, sex, and their interactions. Repeated measures analysis was used for CSA. At birth, Angus calves were 24% lighter than BxD (P < 0.0001). Females were 8% lighter than males for both breeds (P≤0.02). At week 2 of age, CSA of ADD BxD calves was 16% smaller than Angus or CON BxD calves (P≤0.07). At week 8 of age, relative to CON, Angus calves had 22% larger CSA (P=0.02) and ADD BxD calves had 17 % larger CSA (P=0.07). There was no difference detected in CSA between Angus and ADD calves (P=0.54). In conclusion, feeding milk replacer with additional CF and CP may increase muscle growth in BxD calves.