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Lactating Holstein cows carrying the SLICK1 allele of the prolactin receptor gene have demonstrated increased thermotolerance during periods of heat stress in tropical and subtropical climates. We aimed to evaluate Holstein heifers heterozygous for the SLICK1 allele for their (1) preweaning growth, (2) physiological responses to heat stress in low and high humidity climates at pre- and postweaned ages, and (3) reproductive performance as nulliparous heifers. Upon evaluation of 35 slick and 36 non-slick half-sister calves born in California during the cool season, birth weights of slick calves averaged 40.0 ± 0.9 kg while non-slick calves averaged 38.0 ± 1.0 kg (P = 0.08); however, weaning weights and average daily gain did not differ between slick and non-slick calves. In July 2020, 50 calves in Florida (21 slick and 29 non-slick half-sisters) and 222 calves in California (80 slick, 81 non-slick half-sisters, and 61 unrelated cohort control) were evaluated for physiological responses under environmental conditions where the average THI was 90 in Florida and 72 in California. Data were collected midday in Florida and at three times in California: morning and afternoon for all animals, and at an additional timepoint at midday for the pre-weaned calves. Two separate data analyses were performed. The first analysis combined the data from the measurements obtained in slick and non-slick heifer calves in Florida with the measurements obtained in the afternoon in the slick and non-slick heifer calves in California. Slick calves in Florida had rectal temperatures that were 0.4ºC lower than the non-slick calves in Florida while no difference between genotypes was detected in the calves in California. Regression analysis to test for a correlation between rectal temperature and THI revealed a stronger correlation between rectal temperature and THI of non-slick calves (Adj. R2 = 0.36) compared to slick calves (Adj. R2 = 0.06). Moreover, the calves in Florida had greater rectal temperature, respiration rate, and sweating rate than those in California regardless of genotypes. The calves in Florida experienced more severe heat stress conditions, under which the presence of the SLICK1 allele was advantageous to improve thermotolerance in the calves. The second analysis was performed on the data obtained from slick, non-slick, and unrelated control cohort heifer calves in California in the morning, midday, and afternoon. Here again, regression analyses to test for a correlation between rectal temperature and THI during the afternoon when THI is highest, revealed a weaker correlation in slick calves (Group 1 Adj. R2 = 0.01; Group 2 Adj. R2 = -0.04) compared to non-slick (Group 1 Adj. R2 = 0.12; Group 2 Adj. R2 = 0.19) and control calves (Group 1 Adj. R2 = 0.10; Group 2 Adj. R2 = 0.07). This indicates that the slick heifers maintained a more consistent body temperature as THI rose compared to the non-slick and control animals. However, we did not detect differences between genotypes in the morning, midday, or afternoon. The preweaned calves began the day with lower rectal temperature, respiration rate, skin temperature, and sweating rate than the postweaned heifers, yet by the afternoon, preweaned calves had comparable or slightly higher measurements on all physiological parameters evaluated. We also evaluated the age at first breeding, pregnancy success, pregnancy success to first service, services per conception, age at calving, calving success, and pregnancy length for a subgroup of heifers in California. There were no differences in these reproductive parameters between heifers carrying the SLICK1 allele and their non-slick half-sisters. This project is the first to evaluate the preweaning growth of slick Holstein calves in a climate with low humidity. Additionally, this is the first evaluation of physiological responses to heat stress in relation to presence of the SLICK1 allele in young cattle (< 1 year of age) and cattle raised under heat with low humidity. Finally, this is the first report on the reproductive performance of nulliparous Holstein heifers carrying the SLICK1 allele.

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.

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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