18 Influence of Pregnant Cattle Grazing Endophyte-Infected Tall Fescue on Innate Immune Response of Male Offspring
Authors: Dunkel Sidney N , Hubbell Don S , Galloway Doug L , Looney Charles R , Powell Jeremy G , Littlejohn Brittni P 
Published: May 2023

The objective was to evaluate the influence of dams grazing endophyte-infected tall, toxic, fescue (E+) during gestation on innate immune response of male offspring to an endotoxin challenge. Crossbred pregnant multiparous cows (n = 36) bred to Red Angus sires were housed in replicated E+ or novel endophyte-infected, non-toxic, fescue (NE+) pastures before breeding and through the length of gestation. After parturition, cows and calves were moved to a common bermudagrass pasture until calves were weaned. From this calf-crop, a subset of post-weaned steers (E+ n = 8; NE+ n = 8) were selected for a lipopolysaccharide (LPS) challenge. Steers (302 ± 36 d of age; 261 ± 62 kg body weight) were fitted with jugular vein catheters &gt;7 h before sampling. Blood was collected every 30 min starting 2 h before (Pre-LPS) and 9 h following (Post-LPS) LPS administration (0.5 µg/kg body weight). Sickness behavior score (SBS), cortisol, and glucose were analyzed every 30 min. Complete blood count (CBC) and rectal temperature (RT) were analyzed hourly. Peak concentration, time at peak concentration, baseline, return to baseline, and area under the curve (AUC) were evaluated for cortisol and glucose. Cortisol and glucose were determined by radioimmunoassay and hexokinase colorimetric assay, respectively. The CBC data were analyzed using a Hemavet hemocytology analyzer. Pre-LPS and Post-LPS cortisol, glucose, SBS, RT, and CBC were analyzed using the MIXED procedure of SAS specific for repeated measures with treatment, time, and the interaction as fixed effects and dam sire breed as a random effect. Peak concentration, time at peak concentration, baseline, return to baseline, and AUC for cortisol and glucose were analyzed using the MIXED procedure of SAS with treatment as a fixed effect and dam sire breed as a random effect. There was a Pre-LPS treatment by time interaction for RT (P &lt; 0.05). Pre-LPS monocyte count was lower in offspring of dams grazing E+ relative to NE+ during gestation (P &lt; 0.05). Pre-LPS hematocrit was increased in offspring of dams grazing E+ relative to NE+ during gestation (P &lt; 0.05). There was a Pre-LPS effect of time on SBS (P &lt; 0.05). As expected, Post-LPS cortisol, glucose, RT, WBC, neutrophil count, lymphocyte count, lymphocyte percentage, eosinophils count, eosinophils percentage, hematocrit percentage, RBC, and platelets changed over time in response to LPS (P &lt; 0.05). Post-LPS lymphocyte count and monocyte percentage were decreased in offspring of dams grazing E+ relative to NE+ during gestation (P &lt; 0.05). Post-LPS eosinophils count, eosinophil percentage, and hematocrit were increased in offspring of dams grazing E+ relative to NE+ during gestation (P &lt; 0.05). There was a Post-LPS treatment by time interaction for monocyte count and neutrophil percentage (P &lt; 0.05). Preliminary results suggest an altered innate immune response of male offspring of dams grazing toxic relative to novel fescue during gestation.