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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.

Our objective was to evaluate the reproductive performance of Holstein nulliparous heifers carrying the SLICK1 mutation and half-sisters not carrying the mutation. Heifers were born between November and March of 2020 to two Holstein sires heterozygous for the dominant SLICK1 allele and raised in four dairy farms in the San Joaquin and the Tulare basins of the California Central Valley. Heifers were bred from January to September of 2021 according to farm protocols. Data were obtained via farm records and analyzed with the MIXED and LOGISTIC procedures of SAS; proportions were obtained via the FREQ procedure. Models included the fixed effects of genotype, sire, and farm; animal was considered a random effect. Response variables included overall pregnancy rate, age at first breeding, services per conception, pregnancy rate to first insemination, calving rate and pregnancy length. As shown in Table 1, pregnancy and calving rates were similar between slick and non-slick heifers. Overall, services per conception were similar between slick and non-slick heifers (1.8±0.2 and 2±0.2 services for slick and non-slick heifers, respectively; P = 0.3); however, pregnancy to first service tended to be greater in slick heifers (P = 0.07). Age at first breeding was not affected by genotype or sire, but there was an effect of farm due to one dairy starting the breeding program at an older heifer age. Pregnancy length tended to be longer for slick heifers (P = 0.08). This is the first study to evaluate the reproductive performance of slick Holstein females, although it is limited in sample size. Results indicate that the presence of the SLICK1 allele could provide an advantage to reproductive efficiency of Holstein heifers by improving the rate of pregnancy to first service. The authors thank the participating dairy farms. Support: Holstein Association USA Research Grant Program.

The SLICK1 mutation in the prolactin receptor (PRLR) results in a short-hair coat and increased ability to regulate body temperature during heat stress. It is unclear whether the mutation affects capacity for sweating. The objective of this observational study was to evaluate whether the SLICK1 mutation in PRLR alters characteristics of skin related to sweat gland abundance or function. Skin biopsies from 31 Holstein heifers, including 14 wild-type (SL

Cattle productivity in tropical and subtropical regions can be severely affected by the environment. Reproductive performance, milk and meat production are compromised by the heat stress imposed by the elevated temperature and humidity. The resulting low productivity contributes to reduce the farmer’s income and to increase the methane emissions per unit of animal protein produced and the pressure on land usage. The introduction of highly productive European cattle breeds as well as crossbreeding with local breeds have been adopted as strategies to increase productivity but the positive effects have been limited by the low adaptation of European animals to hot climates and by the reduction of the heterosis effect in the following generations. Gene editing tools allow precise modifications in the animal genome and can be an ally to the cattle industry in tropical and subtropical regions. Alleles associated with production or heat tolerance can be shifted between breeds without the need of crossbreeding. Alongside assisted reproductive biotechnologies and genome selection, gene editing can accelerate the genetic gain of indigenous breeds such as zebu cattle. This review focuses on some of the potential applications of gene editing for cattle farming in tropical and subtropical regions, bringing aspects related to heat stress, milk yield, bull reproduction and methane emissions.

The objectives of this study were to evaluate physiological responses to heat stress of Holstein heifers carrying the SLICK1 allele of the PRLR, i.e., the slick mutation. Slick and non-slick females were produced in central CA (n = 3 farms) and south FL (n = 3 farms) by inseminating cows with semen from two heterozygous slick Holstein sires. In July 2020, a subgroup of heifers of both genotypes (slick=93; non-slick=110) and two age groups (Group 1: 6–8 months old; n = 131; Group 2: 9–51 days old; n = 72) in both states were evaluated for rectal temperature (RT), surface temperature (ST) and sweating rate (SR). Dry bulb temperature, relative humidity and dew point were recorded every 15 min during testing for temperature humidity index (THI) calculation. Statistical models included the effects of genotype, state, farm within state, group, sire, THI, and interactions. Significant effects were considered as those with P < 0.05. Although the THI in CA was lower than FL (80 ± 0.1 vs 84 ± 0.2; P < 0.01), both were above 77 (estimated heat stress threshold for young animals). Slick heifers raised in FL had lower RT compared to non-slick siblings (39.6 ± 0.1 vs 40.1 ±0.1; genotype P < 0.01); this difference was not observed in CA (39.1 ± 0.04 vs 39.1 ± 0.05; genotype P = 0.5; state x genotype P < 0.01). In both states, slick heifers tended to have lower ST (34.7 ± 0.2 vs 35.1 ± 0.2; P = 0.07); CA heifers had lower RT and ST and higher SR (P < 0.01) regardless of genotype. Current results show that presence of the SLICK1 allele can improve the ability of Holstein heifers to regulate body temperature, particularly in high humidity conditions. Next steps will include analysis of performance as study animals enter the reproductive phase. Funding sources: Holstein Association USA and L.E. “Red” Larson Endowment.

The slick-hair phenotype in cattle is due to one of a series of mutations in the prolactin receptor (PRLR) that cause truncation of the C-terminal region of the protein involved in JAK2/STAT5 activation during prolactin signaling. Here we evaluated whether the inheritance of the SLICK1 allele, the first slick mutation discovered, is inherited in a fashion consistent with Hardy-Weinberg equilibrium. It was hypothesized that any deleterious effect of inheriting the allele on embryonic or fetal function would result in reduced frequency of the allele in offspring. A total of 525 Holstein and Senepol cattle produced from matings involving one or both parents with the SLICK1 allele were genotyped. The observed frequency of the SLICK1 allele (0.247) was not significantly different than the expected frequency of 0.269. These results support the idea that inheritance of the SLICK1 allele does not act in the embryo or fetus to modify its competence to complete development to term.

Herbivory by the specialist herbivore Exyra semicrocea on the carnivorous plant Sarracenia alata results in loss of nutrients and photosynthetic tissue (direct losses) and diminished prey capture (indirect losses). Using a combination of field surveys in a bog in Leon County, TX USA, and laboratory assays, we examined the losses of tissue and nutrients to herbivory in a population of S. alata. In a field experiment in the same bog, we manipulated herbivore access, prey capture, and supplemental (compensatory) prey to examine the relative effects of direct losses, indirect losses, and their combination on plant growth. We hypothesized that the combined effect of direct and indirect losses would be greater than the effects of either direct or indirect losses alone. Approximately 86% of pitchers in the study population had evidence of herbivory by E. semicrocea. On average, 15% of each damaged pitcher was consumed. In the field manipulation experiment, both direct and indirect losses significantly reduced growth in S. alata, but there was no significant interaction effect. As predicted, pitcher production was lowest in plants experiencing both direct and indirect losses. These results demonstrate that herbivory by E. semicrocea can be widespread and have a significant negative effect on growth of S. alata. Future studies should examine the effects of herbivory on nutrient limitation, storage in rhizomes, and sexual reproduction.

Objectives of this study were to evaluate birth weight (BW), weaning weight (WW), and average daily weight gain (ADG) of female calves carrying the SLICK1 allele, i.e., the slick gene. Holstein cows in four dairy farms located in central California were inseminated with semen from two heterozygous slick Holstein sires to produce slick and non-slick calves. Calves were born during the cool season (November 2019-March 2020). BW was recorded for 125 calves in four farms within 24 h of birth; WW was recorded for 92 calves in three farms within one week of weaning. Weaning age was recorded at day of weighing. ADG was calculated as the weight difference between birth and weaning divided by days of age at weaning. Only female calves were used in the analysis. Statistical analyses were performed using the GLIMMIX procedure of SAS version 9.4. The model for BW included the effects of genotype, farm, sire, and the interaction between genotype and farm. The model for WW and ADG included the effects of BW, genotype, farm, weaning age, sire, and interaction between genotype and farm. Significant effects were considered as those with P < 0.05. There was no difference in BW or WW between genotypes (BW: slick=40.1 ± 0.7 vs non-slick=39.7 ± 0.6 kg; P = 0.7 and WW: slick=82.5 ± 2.8 vs non-slick=80.9 ± 2.8 kg; P = 0.6). The mean age at weaning was 64.8 ± 0.4 and was similar for both genotype groups (P = 0.8). As a result, ADG was similar between genotypes (P = 0.7). There was a main effect of farm on BW, WW and ADG. Results indicate that slick heifer calves born in the cool season perform similarly to non-slick calves in regards to birth weight, average daily weight gain, and weaning weight. Funding provided by the Holstein Association USA Research Program and L.E. “Red” Larson Endowment.

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