PS8-11. Evaluation of Post-weaning Tissue Shrink in Beef Cow-calf Systems of the Southeastern United States.

Abstract Post-weaning shrink, defined as reduction in body weight following weaning-associated stress, represents a direct loss of saleable pounds, reducing revenue for producers and impacting the initial performance of calves in the beef supply chain. The objective of this study was to evaluate post-weaning shrink and subsequent weight recovery in weaned beef calves in order to demonstrate the value of retaining calves through preconditioning to maximize their market value. A total of 32 beef calves in two locations in the Southeastern US were included in the study. Body weights were monitored in Spring-born calves (n = 15) in Brooksville, Florida weaned in September and channeled through a preconditioning program for 45-60 days. Similarly, body weights were monitored in Fall-born calves (n = 17) in Hazel Green, Alabama weaned in March and subsequently preconditioned for 45-60 days. Periods of interest included day of weaning, 21 days postweaning, and 60 days after weaning. Calves in both locations were weaned on natural pastures and fed cracked-corn supplements at 1.0 kg/200 kg body weight/calf/day, adjusted biweekly throughout the preconditioning period. Blood samples were obtained periodically for serum collection and stored at −20°C for further physiological stress, immune and oxidative stress biomarker analyses. Data on bodyweight changes were evaluated by mixed procedures of SAS. The model statement included the interaction of period by location and significance declared at P < 0.05. Data are presented as lsmeans ± SEM, respectively. There was a significant (P = 0.0127) period by location effect on calf body weights. At weaning, calf body weights averaged 228.5 ± 8.1 vs. 314.2 ± 8.0 kg in Florida and Alabama, respectively. Post-weaning body weights averaged 206.6 ± 9.9 vs. 241.6 ± 7.7 kg in Florida and Alabama, respectively. After the preconditioning period, calf body weights averaged 238.6 ± 8.4 vs. 305.8 ± 7.7 kg in Florida and Alabama, respectively. Thus, a consistent pattern was seen in both locations, where calves body weight decreased immediately after weaning and then gradually increased 45 to 60 days later, reflecting the occurrence of post-weaning shrink. However, calves in Alabama remained significantly (P < 0.0001) heavier than calves in Florida across periods. This post-weaning dip in body weight occurred regardless of production location or season of weaning. These findings suggest that shrink is a consistent physiological response to weaning stress in beef calves. Therefore, great care must be taken in minimizing shrink when calves are marketed at the time of weaning. Calves sold immediately at weaning have the greatest risk of tissue shrink, potentially resulting in discounted market value. This study demonstrates occurrence of tissue shrink as late as 21 days after weaning and a recovery period of 45-60 days postweaning. Funded by NIFA CBG # 2021-38821-34599 and ALAX-012-0224.