Evaluation of the innate immune response of Angus heifers with genetic marker variation for intramuscular fat deposition following a lipopolysaccharide challenge

• Heifers with genetic markers for marbling may have an altered immune in response to an LPS challenge.
• Heifers possessing GeneStar® MVP QTL's, had an increase in vaginal temperature following LPS challenge.
• Heifers with 1+MVP may have greater energy reserves allowing a sustained increase in body temperature.

This study evaluated the effect of genetic selection for markers related to marbling deposition in Angus heifers on the immune response following a lipopolysaccharide (LPS) challenge. Fall-born heifers (n=19; ~7 months of age, 274±24 kg) with genetic variation for marbling were utilized including 10 heifers with no genetic markers (No-MVP) and 9 heifers with ≥1 markers (1+MVP). Genotypic variation for quantitative trait loci QG1 and QG2 heifers was determined. Twenty-four hour (h) prior to the LPS challenge, heifers were fitted with jugular catheters and vaginal temperature (VT) monitoring devices. Temperature monitoring devises were programed to record VT in 1 min intervals. On day (d) 0, 2 h prior to LPS challenge and 8 h post challenge, serum was collected in 0.5 h intervals (0800–1800 h). Serum was also collected at 12, 16, 20, and 24 h post LPS challenge. The LPS challenge was administered to the heifers at 1000 h via intravenous bolus (0.5 μg/kg BW). Serum was analyzed for cortisol, TNF-α, IL-6, IFN-γ, and haptoglobin (HAPT). A treatment×time interaction existed (P≤0.001) for VT; prior the LPS challenge, VT was similar. Vaginal temperature was elevated from 6 to 21 h post-LPS in 1+MVP compared to No-MVP. A treatment×time interaction (P=0.02) was observed for IFN-γ. Prior to the LPS challenge, IFN-γ concentrations were similar between the two groups. However, 3.5–7 h post-LPS concentrations of IFN-γ were greater (P≤0.05) for 1+MVP compared to No-MVP. There was no treatment effect (P≥0.17) for cortisol, TNF-α or IL-6. A treatment effect (P=0.02) was observed for HAPT; 1+MVP had decreased HAPT compared to No-MVP. Overall, results suggest that heifers selected based upon genetic markers for marbling may have an altered immune in response when challenged with LPS.