The effect of growth rate on cytokine presence in uterine environment in beef heifers.

Heifer development is the foundation of performance in breeding herds. Growth rate during development may alter uterine immune responses impacting reproductive efficiency and, thus, productivity of that animal. Angus-cross heifers (n = 48) were blocked by BW [4 blocks; weight class (WC)], placed in pens (4 heifers per pen), and pens (n = 12) were randomly assigned treatments (4 pens per treatment): 1) control; targeted 0.68 kg/day, 2) high; targeted 1.25 kg/day, and 3) low; targeted 0.11 kg/day. A randomized complete block design with pen as the experimental unit utilized mixed model ANOVAs to determine if treatment influenced BW, BCS, and uterine cytokines. Beginning at the start of treatment (d 0) BW and BCS were taken every 2 weeks. Uterine flushes were performed at d 0 and d 57. Cytokine concentrations above the detectable limit were categorized into a quartiles (1=0-25%; 2=25-50%; 3=50-75%; 4=75-100%). Samples that were below the detection limit were assigned a category value of 0. At the end of the study high treatment pens had greater BW compared to control and low pens (P = 0.01). Concentrations of MCP-1, TNFa, IL-17A, IL-8, and VEGF-A decreased from d 0 to d 57 (P < 0.05). Pens on the high treatment tended to have IL-17A concentrations in the upper quartiles compared to control and low (P = 0.06). Pens in WC 1 and 2 tended to be in the lower quartile score for VEGF-A compared with WC 4 (P = 0.07) and WC 3 was intermediate. In conclusion, these data show that growth rate and size during heifer development may impact cytokine profiles in the uterine environment of nulliparous heifers. This may impact the ability to conceive early in the first breeding season, thus potentially altering long-term reproductive efficiency. [ABSTRACT FROM AUTHOR]