This study evaluated the effects of providing or not providing maternal access to shade and chromium (Cr) propionate supplementation for beef cows under heat stress conditions on cow-calf performance, thermotolerance and physiological responses. Seventy-two Angus-cross cows were stratified by body weight (BW; 566 ± 5.38 kg) and body condition score (BCS; 6.3 ± 0.5) and allocated to 1 of 12 bermudagrass pastures (3 to 5 ha pastures/5 to 7 cows per pasture). Treatments were randomly assigned to pastures in a 2 × 2 factorial arrangement: shade and Cr (SCr), no shade and Cr (NSCr), shade and no Cr (SNCr) and no shade and no Cr (NSNCr), from day 0 to 180 (on average 150 ± 20 d prepartum and 30 ± 10 days post-partum). Chromium propionate was added to the mineral mix at a rate of 1.8% of the total mineral mixture on a weight basis (Cr target intake of 6.3 mg/cow/d). Data was analyzed on SAS as a 2 × 2 factorial design with pasture considered the experimental unit. The SCr cows showed greater BW on days 90 and 120 compared to all other treatments (P = 0.04). Shaded cows had greater BCS on d 30, 60 and 120 (P < 0.001). Supplementation of Cr increased Cr liver concentration of cows (P = 0.05), but not in calves (P = 0.14). Calves born from no-shaded cows showed lower vigor score at birth (P < 0.02) and were lighter at birth and weaning (P < 0.001). Shaded cows had reduced respiration rate (RR) on d 45, 75 and 90, but cows supplemented with Cr showed increased RR on these days (P < 0.01). Shade reduced cows overall body temperature and rectal temperature (P < 0.001). Shade reduced overall intravaginal temperature (IT), but NSCr cows showed greatest IT from 0900h to 1800h between treatments on d 60 and 90 (P ≤ 0.04). No-shade cows tended to have increased glucose concentrations on d 30, d 90 and d 120 (P < 0.0001), and increased NEFA concentrations on d 90 and d 120 (P < 0.01). Cows supplemented with Cr had reduced total proteins, globulins and creatinine (P ≤ 0.03) and tended to have reduced glucose concentrations (P = 0.10). NSCr cows had greater serum urea N concentrations on d 30 and 60 compared to NSNCr (P < 0.001). Total protein, globulins and IgG tended to be greater for calves born from shaded cows (P ≤ 0.10). Shade improved dam performance, thermotolerance and calf vigor, immunity and growth. Chromium enhanced pre- and postpartum body weight, but only when shade was provided. Chromium supplementation did not improve thermotolerance but enhanced physiological responses.
Ferreira et al. (Thu,) studied this question.