84 Puerto Rican Slick-Haired Holstein Cattle Exhibit Enhanced Mammary Gland Hemodynamics Compared with Their Wild-Type Haired Counterparts

Abstract

Abstract A mutation of the prolactin receptor gene (PRLR) results in cattle with short and sleek hair coat and superior thermoregulatory capacity when exposed to heat stress conditions. This mutation, which is present in Puerto Rican Holstein cattle (SLICK) results in decreased vaginal temperatures and increased milk yield (MY) compared with wild-type haired Holstein cattle (WT) under tropical conditions. The superior performance of SLICK Holstein cows has been considered multifactorial in nature and physiological differences between genotypes still need to be elucidated. Thereby, the objective was to compare the mammary gland hemodynamics and udder skin temperature between SLICK (n = 7) and WT (n = 7) Holstein cows during the summer as possible contributors to such physiological differences. Animals were selected for differences in MY (23.77±1.24 vs.19.74±1.24 kg, SLICK vs. WT, respectively; P = 0.041) and stratified by body weight (BW), lactation number, and days in milk (DIM). At 160±3 DIM, left and right pudendoepigastric arteries were assessed transrectally via Doppler ultrasonography and the udder skin temperature was determined using a thermal camera. Data were analyzed by one-way ANOVA using the MIXED procedure of SAS with resistance index (RI), pulsatility index (PI), diameter, total mammary blood flow (MBF), MBF relative to BW, and udder skin temperature as dependent variables and hair coat as the independent variable. The CORR procedure of SAS was used to determine the correlation between MY and MBF. Statistical significance was declared at P ≤ 0.05 and tendencies were established at 0.05 ≤ P ≤ 0.10. The RI was less (P = 0.045) in SLICK Holsteins (0.56 ± 0.02) than WT (0.64 ± 0.02). The PI tended (P = 0.0589) to be less in SLICK Holsteins (0.94±0.07) compared with WT (1.15 ± 0.07). The average diameter of the left and right pudendoepigastric arteries was greater in the SLICK animals compared with WT (1.31 ± 0.07 vs..08±0.07 cm, respectively; P = 0.038). Total MBF was increased in SLICK cattle compared with WT (9.03 ± 1.11 vs. 5.14 ± 1.11 L/min; P = 0.0291). There was a tendency (P = 0.0577) for the MBF relative to BW to be greater in the SLICK Holsteins compared with the WT (16.75 ± 2.14 vs.0.38 ± 2.14 mL/min*kg). No differences were observed in udder skin temperature between SLICK and WT Holsteins (P ≥ 0.05). Lastly, a tendency for a positive correlation between MY and MBF was observed (r = 0.51, P = 0.066). In the current study, SLICK Holsteins had enhanced blood supply to the mammary gland which is indicative of greater amount of oxygen and nutrients available for milk synthesis. Therefore, the gene introgression of the PRLR mutation to a dairy herd may result in animals with superior physiological performance during heat stress conditions preventing economical losses in the dairy industry.