PSI-25 The effect of growth rate on the uterine environment in beef heifers

Abstract

Abstract Replacement heifers provide the foundation of breeding herds by incorporating new and improving genetics. Growth rate (GR) manipulation during heifer development may alter the uterine environment via immune response impacting reproductive function. Angus-crossbred heifers (n = 48) were blocked into 4 weight classes and randomly assigned to one of three treatments: 1) control (CON) fed to gain 0.68 kg/day for 120 d, 2) fast to slow (F/S) fed to achieve 1.25 kg/day for 57 d, then 0.11 kg/day for 63 d, and 3) slow to fast (S/F) fed to achieve 0.11 kg/day for 57 d, then 1.25 kg/day for 63 d. Heifers were supplemented (75% dry distillers grain and 25% corn) four times weekly to achieve desired GR and offered ad libitum forage and water. Blood, BW and BCS were taken every two wks beginning at the start of treatment (d 0) and supplements were adjusted following BW measurement. Uterine and vaginal flushes were taken at d 0, 57, and 120 to determine cytokine and hormone presence. Mixed model ANOVA utilized fixed effects of treatment, day, and their interaction to analyze influence of GR on BW, BCS, average daily gain (ADG), and feed:gain (F:G). All BW were similar until the GR switch; CON and S/F decreased for 3 samples and then returned to similarity (P=0.06). ADG was lower in CON and S/F immediately following GR switch; however, all treatments were similar before and after this event (P=0.0054). All maintained similar F:G until F/S decreased after GR switch (P=0.01). Total F:G was similar for all treatments (CON=18.3, F/S=26.5, S/F=22.7; P=0.25) In conclusion, altering GR during development will allow producers to hit growth thresholds but may impact the uterine environment. We plan to further elucidate the immune profile via cytokine and hormone concentrations from uterine and vaginal flushes.