PSXI-37 Differences in thermoregulation ability and genetic parameters of skin traits in Angus, Brahman and their Crossbreds

Abstract

Abstract Thermoregulation is important for beef cattle but tends to be negatively correlated with production traits. The objective of this study was to determine the variation in core body temperature and to estimate genetic parameters of skin traits in Angus, Brahman, and different levels of crossbred heifers (n = 337) reared in hot and humid conditions. Core body temperature was recorded as vaginal temperature every 15 minutes for 5 consecutive days. Dry bulb temperature and relative humidity in the pasture were also measured every 15 min and used to calculate a temperature-humidity index (THI). Five mm skin biopsies were collected from the right side of sixth thoracic bone of each heifer. Cross-sections of biopsy samples with a thickness of 7 µm were stained with Hematoxilin–Eosin technique. The number and area of sweat and sebaceous glands, and the thickness of dermis and epidermis were determined using the ImageJ program. Data were analysed using PROC MIXED in SAS 9.4 with a model including the effect of breed, year, and their interaction. Genetic parameters were estimated using WOMBAT. Average core body temperature of Angus, 25%, 37.5%, 50%,75% and 100% Brahman were 39.50±0.05, 39.30±0.04, 39.15±0.05, 39.2±0.0, 39.03±0.05, 39.04±0.05, respectively. Brahman heifers had lower core body temperature compared to Angus heifers (P = 0.0006). Heifers with smaller and more numerous sweat glands had higher (P < 0.01) and more variable core body temperature (P < 0.0001). Heritability of core body temperature under high and low THI was 0.44±0.006 and 0.61±0.003, respectively. Dermis and epidermis thickness had the lowest heritability (0.231±0.002) and the highest heritability (0.75±0.007), respectively. Heritabilities for the number of sweat glands and total sweat gland area were 0.375±0.02 and 0.432±0.006, respectively. In conclusion, thermoregulation was highly correlated with breed composition, number of sweat glands and the average size of sweat glands.