5 Effect of Soy co-Products in Supplements for Grazing Cattle on Growth, Complete Blood Cell Counts, and Inflammatory Response Following a Lipopolysaccharide Challenge

Abstract

The objective was to determine the effect of soy co-products (soybean meal and soy oil) in the diet on the growth and hemocytology of cattle during a 56-day growing phase and the physiological/behavioral response to an endotoxin challenge. Angus crossbred steers (n = 36; 289 ± 31 kg, initial body weight ± SD) were stratified by body weight and sire; and assigned randomly to pastures (n = 9; 0.45 ha/mixed-grass pasture). Pastures were assigned randomly to of 3 dietary treatments: 1) a control supplement containing no soy co-products, 2) a supplement containing soybean meal, or 3) a supplement containing soy oil. All supplements were isonitrogenous and isoenergetic. Cattle were fed supplements (2.45 kg DM/day) for a period of 56 days during which weight and blood samples for complete blood count (CBC) were taken every 14 days. At the conclusion of the growing phase, cattle were assigned randomly to of 2 challenge groups (conducted 6 days apart) for a lipopolysaccharide (LPS) challenge (i.v. infusion of 0.5 µg LPS/kg of body weight). A minimum of 18 hours before sampling, cattle were fitted with jugular vein catheters and placed into stanchions. Sickness behavior scores and rectal temperatures were collected every 30 minutes for a duration of 8 hours following LPS infusion. Body weights were analyzed using pen means and the MIXED procedure of SAS specific for repeated measures with treatment, day, and the treatment × day interaction as fixed effects and replicate as a random effect. CBC were analyzed using the MIXED procedure of SAS specific for repeated measures with treatment, day, and the treatment × day interaction as fixed effects, replicate as a random effect, and pen specified as the subject. Rectal temperatures and behavior scores were analyzed using the MIXED procedure of SAS specific for repeated measures with treatment, time, and the treatment × time interaction as fixed effects and challenge group as a random effect with calf as the subject. Dietary inclusion of soy co-products did not affect the body weights of steers for the 56-day growing phase (treatment and treatment × day, P ≥ 0.20), nor were any hemocytology measurements affected (treatment and treatment × day, P ≥ 0.12) during the growing phase. Following the endotoxin challenge there was no effect of treatment or treatment × time (P ≥ 0.57) for rectal temperatures or sickness behavior scores. Therefore, preliminary results indicate that inclusion of soy co-products in cattle diets did not affect growth or complete blood counts during a 56-day growing phase, neither did diet affect body temperature or sickness behavior in response to an endotoxin challenge.