PSXIV-29 - Seminal plasma uterine priming in embryo-recipient beef cows alters preweaning offspring growth but not indices of body composition.

Abstract: Seminal plasma primes the uterus for pregnancy through the recruitment of cells aiding in microbial clearance, tissue remodeling and angiogenesis, and embryo implantation and growth. Less is known about the effects of seminal plasma uterine priming in practices devoid of seminal plasma, specifically evaluating offspring growth in embryo-recipient beef cows. In the present study, we sought to determine the effects of seminal plasma uterine priming on postnatal body weights, carcass ultrasound measures, and indices of body composition. To realize these objectives, embryo-recipient cows randomly received 0.5mL of pooled seminal plasma or no treatment (control) at estrus and underwent embryo transfer seven days later. Following parturition, offspring pre-weaning body weights were collected at 30, 90, and 180 days of age. Indices of body composition, carcass ultrasounds and bioelectrical impedance analysis (BIA), were collected pre-weaning at an average 209 days of age. Weaning weights and hip heights were collected at an average of 212 days of age. Ultrasound, BIA, and weaning weight data were analyzed using the MIXED procedure of SAS for fixed effects of treatment. Pre-weaning body weights were analyzed similarly with repeated measures for treatment, day, and their interaction. Covariates of sire, dam, sex, and age were included in all models if P ≤ 0.10. Correlations between carcass ultrasounds and BIA parameters of fat-free mass and fat-free soft tissue were analyzed using the CORR procedure of SAS. Significance is declared at P ≤ 0.05 and data are presented as means ± standard error. A treatment by day interaction was not observed for pre-weaning body weight. However, a main effect of treatment was observed for pre-weaning body weights, which was decreased (P = 0.0130) in seminal plasma calves compared with controls. Weaning weights and hip height were not different between treatments. There was not an effect of treatment on carcass ultrasound measures, including ribeye area, ribeye area adjusted by body weight, rib fat, intramuscular fat, or rump fat. Similarly, BIA measures of fat-free mass and fat-free soft tissue were not different between treatments. Ribeye area and rib fat ultrasound were moderately correlated (P < 0.05) with BIA measures of fat-free mass and fat-free soft tissue. Interestingly, previously reported data from this project show offspring from seminal plasma treated cows had decreased embryo size at days 35, 40, and 45 of gestation, and decreased birth weights. It appears seminal plasma uterine priming prior to embryo transfer negatively impacts offspring growth pre-weaning, however, by weaning this difference is diminished. It is less clear why pre-weaning weights differ due to similar body composition among treatment and control calves; however, these measures may have been collected after the period of compensatory gain occurred.