87 Milk Yield, Vaginal Temperature, and Solar Radiation Exposure in Slick and Wild Type-Haired Puerto Rican Holstein Cows

As heat stress limits dairy cattle performance in the tropics, selection for heat resistant cattle has been proposed as a possible alternative for these countries. Such cattle should be able to regulate their body temperature efficiently so grazing activity is not compromised by environmental conditions. This is particularly important for Puerto Rico’s dairy industry, which depends on grazing as the principal or unique source of dietary fiber. Even though Puerto Rican slick-haired dairy cattle (SLICK) have been associated with superior thermoregulation, empirical data about their capacity to withstand greater solar radiation exposure while maintaining lower body temperature is scarce. The current study aimed to compare the vaginal temperature, solar radiation exposure, and milk yield between SLICK and wild type-haired (WT) cows. Evaluated groups were balanced for lactation number (P = 0.8101) and days in milk (DIM: P = 0.9619). Eight SLICK (2.00 ± 0.33 lactations and 160.33 ± 11.39 DIM) and 8 WT Holstein cows (1.89 ± 0.31 lactations and 159.44 ± 14.34 DIM) were compared. Initially, experimental groups were selected visually, then a genomic test confirmed each the hair coat type of each cow. Vaginal temperature was recorded by means of a HOBO TidbiT v2 Water Temperature datalogger secured to a blank CIDR. Light intensity exposure was recorded using a HOBO Pendant MX Temperature / Light datalogger secured to the top of a neck collar, as an index of solar radiation exposure (previously validated by our group). Data were recorded in each cow every 15 seconds for 48 consecutive hours (August 4-5, 2022) and averaged by hour for statistical analysis using the GLIMMIX Procedure of SAS. The week before the study SLICK cows showed greater milk yields than their WT counterparts (20.76 ± 0.55 vs.8.60 ± 0.56 kg/d; P = 0.0073). No time by hair coat type interaction was observed for vaginal temperatures (P = 0.1396). However, time (P < 0.0001) and hair coat type (P = 0.0042) affected vaginal temperature. The SLICK cows presented lower vaginal temperatures than their WT counterparts, with daily averages of 39.08 ± 0.09 and 39.45 ± 0.10°C, respectively. A time by hair coat type interaction (P = 0.0293) was observed for the light intensity exposure of the cows. The SLICK cows had greater light intensity exposure than their WT counterparts at 1,000 h (15,467.00 ± 1,584.92 vs.10,057.00 ± 787.35 lx; P < 0.0001), 1,100 h (12,028 ± 1,660 vs. 8,571.11 ± 888.13 lx; P = 0.0078), and 1,200 h (13,191.00 ± 2,188.86 vs.10,923.00 ± 1,904.31 lx; P = 0.0801). No other differences in light intensity exposure were observed. Slick-haired cows were able to maintain a lower daily vaginal temperature, even with a greater exposure to direct solar radiation, further suggesting a superior thermoregulatory capacity. Concurrently, a greater milk production was observed in the slick-haired group. Future studies should evaluate grazing activity under direct solar radiation exposure in both hair coat groups.