The Effect of Supplemental Protein on the Uterine Environment during Heifer Development

Replacement heifer development is one of the most critical components of beef production. Nutrition affects development and reproductive success of replacement heifers. Our hypothesis was that different levels of protein supplementation would affect ULF of beef heifers, without altering the rate of development. Commercial Angus heifers (n=60) were blocked by BW into 4 weight classes. Within each weight class, heifers were randomly assigned to one of three treatment groups of supplemental protein (10% [CON], 20% [P20], and 40% [P40]) in a randomized complete block design with repeated measures. All heifers were allowed ad libitum access to mixed native grass hay. Bodyweight, BCS, and blood samples were collected every 2 weeks. Uterine fluid samples were collected monthly to evaluate components of ULF. Relative uterine pH was calculated by subtracting saline pH from the uterine flush pH. Separate mixed model ANOVAs via PROC GLIMMIX (SAS 9.4, Cary, NC) were used to determine if protein supplementation, time, and their interactions influenced BW, BCS, or ULF. Bodyweight of CON heifers was significantly lower (PP=0.002). At sample 2, the P40 group exhibited less change in pH compared to the CON group (0.33±0.1 vs. 0.74±0.1; PPP=0.05) at detection of puberty. Heifers in weight class 1 had a more acidic uterine environment at detected puberty (6.89±0.1) than weight classes 2, 3, or 4 (6.96±0.1, 7.18±0.1, 7.11±0.1; P<0.01). CON heifers had more Orn (0.12) than P20 (0.07) or P40 heifers (0.03; P=0.03). P40 heifers had more Trp (0.18) than CON (0.25) or P20 (0.19; P=0.03). In conclusion, protein supplementation increased heifer growth and altered the pH and AA content of uterine fluid but did not influence development from weaning to first breeding. All treatments were successful in developing replacement heifers with regards to industry standards.