159 Effects of artificial shade and chromium supplementation during mid and late gestation of beef cows under heat stress: cow performance and thermotolerance

Abstract

The objective of the study was to evaluate the effects of the provision of artificial shade and chromium (Cr) supplementation during mid and late gestation on the performance and thermotolerance of beef cows. At 150 ± 20 d days prepartum (day 0), 72 fall-caving Angus-cross cows were stratified by body weight (BW; 566 ± 5.38 kg) and body condition score (BCS; 6.3 ± 0.5) and allocated into 1 to 12 bermudagrass pastures (3 to 5 ha pastures/5 or 7 cows per pasture). Treatments were randomly assigned to pastures in a 2 × 2 factorial: shade and Cr (SC), no shade and Cr (NSC), shade and no Cr (SNC) and no shade and no Cr (NSNC), applied from day 0 to 150 days before calving. Shade was provided by artificial structures made from black polypropylene fabric, with 4.2 m² of shaded area per animal/pasture. Chromium (Cr propionate; KemTRACE Chromium 0.4%, Kemin Industries) was added to a free choice mineral mix (target intake of ~100 g/day/cow) to provide 0.5 mg Cr/kg of total diet. Body weight and BCS were measured on day 0, 30, 60, 90 and 120 pre-calving. Respiration rate and body surface temperature (BS) were measured every 15 days. Body surface temperature was collected individually using an infrared camera. On day 60 the intravaginal temperature of the cows was recorded every 30 minutes during 7 days through a data logger. Dry-bulb temperature and relative humidity were recorded through a data logger to obtain the temperature-humidity index (THI) throughout the study. The data was analyzed using the mixed procedure in SAS 9.4. The pasture was the experimental unit in all analyses, with the animal (treatment) included as a random effect. Significance was defined as P ≥ 0.05, and tendency when 0.05 > P ≤ 0.10. Interaction between Shade × Cr × Day was found for BW (P < 0.05), where cows from treatment Shade-Cr showed greater BW on 90 and 120 compared to the other treatments. An interaction between shade × day was found for BCS (P <.0001), where both shaded treatments had greater BCS from d 30 to 120 than treatments without shade. Interaction between shade and hours of day was found (P <.0001) where cows from shade treatment had reduced IT from 9:00 am to 7:00 pm. Shade reduced RR and BS (P <.0001). A Cr × day interaction (P < 0.01) was observed for RR, where Cr increased RR on days 30, 75, and 90. These results indicate that providing artificial shade helped beef cows under heat stress conditions maintain BCS and reduce IT and BS. The combination of artificial shade and Cr supplementation improved cows BW.