The objectives of this research were to determine the impact of grazing endophyte-infected tall fescue (E+) or novel non-toxic endophyte-infected fescue (NE+) on the immune response and performance of weaned fall (F) and spring (S) born calves, and to find the relationship between polymorphisms in the prolactin promoter and cytochrome P450 gene and the immune response measurements, and pre-, and post weaning performance for F and S calves weaned from NE+ or E+. A second objective of this research was to determine the effect of transport stress and specific gene polymorphisms on the prolactin promoter and cytochrome P450 gene expression and specific hormone production by steers weaned from NE+ or E+.

Based on these studies, the interaction between grazing treatments and specific gene polymorphisms may impact certain aspects of the immune response measurements and post-weaning performance. Pre-weaning performance was affected by pre-weaning grazing systems in the different seasons. Furthermore, transport stress influenced the expression of specific genes and hormone production, but there was no effect from grazing E+ or NE+ on the same measurements. Therefore, providing cattle a limited access to NE+ prior to weaning may enhance immune response and performance.