Thermoregulatory and productive-related comparisons between wild type and slickhaired Puerto Rican Holstein cows

Anecdotally, wild type (WT) Puerto Rican Holstein cows perform poorly in hot weather compared with their short-haired (SLICK) counterparts, but scientific evidence supporting this claim is limited. Thus, comparisons of their vaginal temperature (VT), sweat gland size (SGS) and milk production (MP) values were made. Data were analyzed by Proc GLIMMIX and REG (SAS). During the cool season (March 2014) VT was similar in WT and SLICK cows (38.71±0.09 and 38.71±0.08 °C, respectively; P=0.9634). However, in the intermediate air temperatures (AT) season (April 2014), WT cows presented VT values 0.25° C higher than their SLICK counterparts from 1900-2100h (P=0.0213). Moreover, in the hot season (August 2015) VT was greater in WT than in SLICK cows by 0.31° C from 1800-0700h and 0900-1600h (P=0.0032), and by 0.20° C at 0800h (P=0.0584) and 1700h (P=0.0619). The VT increased linearly until AT reached 30.5° C in both WT (0.10° C per 1° C of AT; P<0.0001) and SLICK cows (0.08° C per 1° C of AT; P<0.0001). After 30.5° C, no further VT-AT relationship was observed. The WT had smaller SGS (232±12 vs. 315±9 μm perimeter; P=0.0024) and smaller MP (17.11±0.63 vs. 20.26±1.28 kg/d; P=0.0288) than the SLICK cows. The SLICK cows demonstrated superior thermoregulatory capacity, which seems to depend directly on the severity of the AT.