Physiological responses of Holstein calves and heifers carrying the SLICK1 allele to heat stress in California and Florida dairy farms

Abstract

Inheritance of the SLICK1 allele of the prolactin receptor gene improves thermotolerance of lactating Holstein cows under humid heat stress conditions. The aim of this study was to investigate whether pre-and postweaning Holstein heifers carrying the SLICK1 allele would show physiological responses indicative of higher tolerance to heat stress in high-and low-humidity climates. A total of 101 heifer calves of two age groups heterozygous for the SLICK1 allele and 103 wild-type half-siblings were evaluated during July 2020 in 3 dairy farms in central California and 2 in south Florida. Dry bulb temperature and relative humidity data were recorded during evaluation and used to calculate the temperature-humidity index (THI). Physiological measurements were obtained between 1600 and 1900 h in California, and 1200 and 1400 h in Florida and included rectal temperature, respiration rate, skin temperature, and sweating rate. Data were analyzed via Generalized Linear Mixed Models including the main effects of genotype, state, group, sire, farm within state, and interactions, with THI included as a covariate. The correlations between THI and dependent variables were analyzed via linear regression. The average 24-h THI was higher in Florida compared with California (90 vs. 72, respectively); the main driver of the higher THI in Florida was the high relative humidity (average 85.6% in Florida vs. 36.7% in California). In Florida, the rectal temperature of slick calves was 0.4°C lower than non-slick calves (39.5 ± 0.1 vs 39.9 ± 0.1°C); no differences were detected between slick and non-slick calves in California. Regardless of genotype, heifer calves in Florida had higher respiration rate, higher rectal and skin temperatures, and lower sweating rate than in California. This study is the first to evaluate physiological responses of calves carrying the SLICK1 allele under heat stress conditions in different climates. Our findings demonstrate that the presence of this allele is associated with lower rectal temperatures in pre-and post-weaning Holstein females. According to the physiological parameters evaluated, calves raised in Florida appeared to be under more severe heat stress; in those conditions, the SLICK1 allele was advantageous to confer thermotolerance as evidenced by lower rectal temperature in slick animals.

Effects of the bovine SLICK1 mutation in PRLR on sweat gland area, FOXA1 abundance, and global gene expression in skin

“…In some experiments during heat stress, slick Holsteins had greater sweating rates than wild-type Holsteins (Dikmen et al, 2008(Dikmen et al, , 2014, whereas no difference was found between genotypes in another experiment (Carmickle et al, 2022). Angus × Senepol heifers inheriting the slick mutation experienced greater transepidermal water loss than wild-type animals (Eisemann et al, 2020).…”

“…The gene is also frequent in the Senepol breed located on the Caribbean island of St. Croix; presumably, some founder animals possessed the gene. Crossbreeding has also been used to deliberately introduce the SLICK1 mutation into other breeds such as Holstein by crossbreeding (Olson et al, 2003;Dikmen et al, 2008Dikmen et al, , 2014Carmickle et al, 2022).…”

“…Cattle inheriting slick mutations in PRLR exhibit increased thermotolerance with respect to regulation of body temperature during heat stress (Olson et al, 2003;Dikmen et al, 2008Dikmen et al, , 2014Eisemann et al, 2020;Landaeta-Hernández et al, 2021;Carmickle et al, 2022) and production of milk in the summer (Olson et al, 2003;Dikmen et al, 2014). Much of the increased thermotolerance of slick cattle can be ascribed to the short-hair coat.…”

Genes and models for estimating genetic parameters for heat tolerance in dairy cattle

“…Dikmen et al (2014) indicated that rectal temperature, respiration rates and sweating rates were lower in slick cows than wild-type cows. Carmickle et al (2022) reported that the presence of SLICK1 allele of the prolactin receptor gene was associated with low rectal temperature rates in pre and post-weaning Holstein females. Moreover, heat tolerance has a negative genetic correlation with milk production parameters (Aguilar et al, 2009).…”

Perspectives of gene editing for cattle farming in tropical and subtropical regions

“…Slick-haired Criollo Limonero non-pregnant heifers had lower rectal temperature and respiratory rates than normal-haired heifers ( Landaeta-Hernández et al, 2021 ). Pre-weaned Holstein calves and growing heifers carrying the SLICK1 allele also maintained lower rectal temperature when exposed to high-humidity heat during summer ( Carmickle et al, 2022 ). Criollo Limonero cattle slick females had larger sweat glands (more consistent with those of B. indicus cattle) compared to wild-type females ( Landaeta-Hernández et al, 2011 ).…”