22 Influence of Cell-Mediated Immune Response Classification on Performance of Heat-Stressed Dairy Cattle

Abstract The objective was to evaluate the influence of cell-mediated immune response classification on performance of dairy cattle experiencing conditions of heat stress on pasture. On d 0, pregnant, lactating dairy cows (n = 27; 18 Holstein and 9 Jersey) received a subcutaneous sensitization dose of killed Candida albicans (CA; 0.5 mg) with Quil-A adjuvant (0.75 mg) in 2.5 mL of PBS. Tail skin fold thickness (SFT) was measured with a Harpenden caliper on d 14 immediately following an intradermal injection of killed CA (0.1 mg in 0.5 mL of PBS) in the right tail skin fold and a control injection (PBS) in the left tail skin fold. On d 15, change in SFT was measured and used to assign cell-mediated immune response classifications (CMIR) as High (HR; >0.5 SD above the mean; n = 9), Intermediate (IR; within 0.5 SD above or below the mean; n = 10), or Low (LR; >0.5 SD below the mean; n = 8). Cows from each CMIR were assigned to 1 of 3 environmental conditions (EC): No Abatement (no heat abatement provided; n = 9), Shade (portable shade structure; n = 9), or Sprinklers (polyvinyl chloride sprinkler system; n = 9) for a 38-d period (July 1, 2019 to August 8, 2019). Daily Milk Yield (DMY), Reticulorumen Temperature (RT), Heat Stress Score (HSS; 0 = respiration rate of < 80 breaths/min to 4 = moribund, labored breathing), and instances of Mouth Open (MO), Tongue Out (TO), and Drool were recorded daily. Respiration rate (RR; breaths/min) was recorded 3 times/day (morning, midday, and late afternoon) and averaged on Monday, Wednesday, and Friday weekly. Body Condition Score (BCS; 1 = emaciated to 5 = obese) was recorded weekly. Data were analyzed using MIXED procedures of SAS specific for repeated measures with CMIR, EC, Breed, Time and 2-way interactions as fixed effects and Pen as random. Low exhibited the lowest HSS and BCS, but the greatest MO and TO instances (P < 0.02). High exhibited the greatest instances of Drool (P < 0.02). Heat stress score, MO, and Drool were greatest in the No Abatement group (P < 0.01). Respiration rate was greatest in the No Abatement and Shade groups relative to Sprinklers (P < 0.01). Daily milk yield, RT, and Drool were increased whereas HSS and RR were decreased in Holstein relative to Jersey cows (P < 0.01). Interactions (P < 0.05) included: CMIR by EC for DMY, HSS, RR, MO, TO, and Drool; CMIR by Breed for RT, DMY, and BCS; EC by Breed for RT, DMY, HSS, and RR; and EC by Time for DMY, HSS, BCS, RR, MO, and TO. There was an effect of Time for all variables (P < 0.05). Preliminary results suggest an influence of cell-mediated immune response classification on performance of dairy cattle experiencing conditions of heat stress and warrant future studies with an increased number of animals.