PSIV-13 - Influence of differing levels of concentrate on circulating cytokine concentrations in beef heifers

Abstract: Components of the immune system, such as cytokines and chemokines, can influence female reproductive efficiency. Recently, studies have begun to characterize the influence of nutrition on cytokines and reproductive function. Characterizing the influence of nutritional components on shifting circulating cytokine concentrations will allow for a better understanding of reproductive efficiency in cattle. The objective of this study was to determine the effect of diet composition on cytokine concentrations in blood plasma in beef heifers. Using a 3 x 3 Latin square design, fifteen rumen-cannulated, pubertal Bos taurus-influenced heifers were fed a diet based on ranging concentrate percentages. Their treatment period consisted of 28-day feeding periods with a washout interval of 21 days. The treatment groups were fed 100% grass hay (high forage; HF), 60% grass hay with 40% corn-based concentrate (intermediate; INT), and 25% grass hay with 75% corn-based concentrate (high grain; HG) within their respective treatment group. Heifers were offered 2% of their bodyweight daily. Blood was collected on days 0 and 28 of the treatment period for cytokine analysis. Plasma cytokine concentrations were quantified using RayBiotech Quantibody Bovine Cytokine Array Q1 kit according to manufacturer instructions. Data analysis was conducted using orthogonal contrasts (linear and quadratic) with day 0 as independent covariates and heifers as the experimental unit. There were no significant quadratic contrasts. Concentrations of interferon gamma-induced protein 10 (IP-10) linearly decreased with an increased concentrate diet (P = 0.04). Concentrations of IP10 significantly differed for heifers consuming the HF diet versus the HG diet (3069.5 ± 672.2 vs. 1001.8 ± 669.3 pg/mL, respectively) and heifers consuming the INT diet versus the HG diet (2886.8 ± 665.6 vs. 1001.8 ± 669.3 pg/mL, respectively); however, there were no significant differences in IP10 concentrations between the HF and INT heifers. Interferon-gamma (IFNg) concentrations significantly differed between feeding periods with period 2 having the lowest circulating concentrations when compared to periods 1 and 3 (5.2 ± 66.2 vs. 183.4 ± 68.4 and 221.3 ± 67.8 pg/mL, respectively; P < 0.05). Additionally, monokine induced by gamma interferon (MIG) significantly differed by period with period 2 having the lowest circulating concentrations compared to periods 1 and 3 (862.2 ± 285.4 vs. 1675.8 ± 283.4 and 1170.8 ± 286.9 pg/mL, respectively; P < 0.05). Interestingly, both IP10 and MIG are chemokines, or small cytokines with chemotactic functions, that are secreted by immune cells in response to IFNg. Results suggest that heifers consuming a high concentrate diet have lower concentrations of circulating cytokines, specifically IP10. Additionally, in the current study, cytokines that were influenced were associated with IFNg. Further research is necessary to better comprehend the dietary influence on the immune system in developing heifers and how this is associated with reproductive efficiency.