Heat stress responses in calves and heifers to SLICK1 Allele
There are many studies about negative effects of heat stress in lactating dairy cows, and to a lesser extent in dry cows. But there is limited research of heat stress effects on dairy calves and heifers.
By Dr. Al Kertz, Andhil LLC
There are many studies about negative effects of heat stress in lactating dairy cows, and to a lesser extent in dry cows. But there is limited research of heat stress effects on dairy calves and heifers. I reviewed one study (Kertz 2009) done in California which found increased DMI and daily gain when heifers were shaded versus sprinkled without shade (Marcillac-Embertson et al., 2009). Yet, very often I find operations where heifers have no shade. Heifers on pasture usually have some shade provided by trees.
More recently I have become aware of dairy cattle which have a genetic variation called the SLICK1 gene. This gene is associated with a short, fine hair coat phenotype and no detectable lactation defects while animals with this mutation have been reported to have higher milk yield in the summer. Because these mutations act as dominant, heterozygous animals typically show the slick phenotype. The main measurable effect is that SLICK1 allele lactating cows maintained vaginal temperature approximately 0.6°C (1.1ºF) lower compared with their non-slick half-siblings and unrelated counterparts in summer (as reviewed by Carmickle et al., 2022). This led a major team to study the effect of SLICK1 in 3 herds in California and 2 in south Florida Okeechobee area (Carmickle et al., 2022).
“Lactating Holstein cows were bred by AI with frozen thawed semen from 2 registered Holstein sires heterozygous for the SLICK1 allele. Semen from sire A was X-sorted and semen from sire B was conventional. Inseminations were performed to yield 2 groups of calves: group 1 calves were born between November 2019 and March 2020, and group 2 calves between May and July 2020. Heifer calves were genotyped via Clarifide Plus test after the experiment (Zoetis) and classified as slick (carrying the SLICK1 allele) or non-slick (halfsiblings not carrying the SLICK1 allele). Therefore, at the time of data collection, the research team did not have information about the genotypes. Female calves were included in the cross-sectional study performed in July 2020 to test the physiological responses to environmental conditions associated with heat stress.”
Watch our interview with Dr. Kertz on this topic.
“At the time of testing, the median age of group 1 calves (postweaning) in California was 195 d (range: 108–244 d), and the median age for group 2 calves (preweaning) was 23 d (range: 4 to 48 d). In Florida, the median age of group 1 calves (postweaning) was 242 d (range: 159 to 265 d), and the median age for group 2 calves (preweaning) was 29 d (range: 10 to 55 d). None of the calves in group 2 were weaned at the time of testing. Group 1 calves were kept in dry lots with shade structures and were brought to a feeding area containing headlocks (California) or kept in pasture pens and brought to a chute (Florida) for testing. Group 2 calves were kept in individual wood hutches outside (2 locations) or individual pens in wood hutches outside (1 location) in California; in Florida, group 2 calves were kept in individual wire hutches with shade cloth.”
Daily temperature and humidity were recorded and used to calculate the Temperature Humidity Index (THI), Vaginal rectal temperatures, skin temperature, and respiration rates were recorded by trained dairy workers. “
“California. Postweaning heifers were in dry lot pens with shade and were restrained in headlocks during feeding. Animals were released as their measurements were completed. Preweaning calves had their measurements taken in their individual hutches or pens. Florida. Postweaning heifers were brought from their pasture pens in the morning to a holding pen and were given a minimum of 2 hours to settle before physiological measurements were taken. Animals had ad libitum access to water and partial shade in the holding pens. To obtain the physiological measurements, the animals were brought up to a chute. Preweaning calves were tested in their individual hutches.”
“The 24-h mean THI in California during the testing period was 72 ± 0.2 (range 61–82), whereas in Florida it was 90 ± 0.2 (range 83–100; P < 0.0001). Figure 1A depicts the 24-h variation of THI during testing days in both states; the boxes indicate the window of sample collection. The average temperature, relative humidity, and THI during the time of collection in California and Florida are depicted in Figure 1B, C. The THI was consistently higher in Florida compared with California, and in California, the animals experienced several hours of THI below 68 overnight.”
“The rectal temperature of slick animals was 39.3 ± 0.1°C, whereas for non-slick animals it was 39.5 ± 0.1°C (P = 0.01). This difference was only observed in Florida, where postweaning slick heifers had 0.31°C (P < 0.05) and preweaning calves had 0.55°C (P < 0.001) lower rectal temperature compared with their non slick counterparts. In California, rectal temperature was not different between slick and non-slick animals (Figure 2A). “
Regardless of genotype, California animals had lower rectal temperature than Florida animals (39.2 ± 0.04°C vs. 39.7 ± 0.1°C; P < 0.001). Overall, postweaning heifers had higher rectal temperature than preweaning calves (39.7 ± 0.05°C vs. 39.1 ± 0.09°C; P < 0.0001). Again, this effect was due to differences observed in Florida, where postweaning heifers had higher rectal temperature than preweaning calves; in California, no difference was detected (Figure 2A).
Genotype did not affect respiration rate (Figure 2B). Overall, postweaning heifers had higher respiration rate compared with preweaning calves (78 ± 2 vs. 66 ± 4 BPM; P < 0.01). Postweaning heifers in Florida had the highest respiration rate, whereas no difference was found between age groups in California (Figure 2B).
The temperature in the clipped skinwas not affected by genotype, state, or group (Figure 2C).
Skin temperature in unclipped areas was not affected by genotype, state, or group (Figure 2D).
Genotype had no effect on sweating rateregardless of presence of hair (Figure 2E,F). Overall, California heifers sweated more than Florida heifers in clipped (139.0 ± 6.0 vs. 63.6 ± 18.7 g/m2 /h; P < 0.001) and unclipped skin (113.5 ± 5.9 vs. 70.3 ± 17.4 g/m2 /h; P < 0.05). Postweaning heifers sweated more than preweaning calves in both clipped and unclipped skin (P < 0.01; Figure 2E,F).
Regardless of genotype, daughters of sire A had higher respiration rate (77 ± 3 vs. 68 ± 3 BPM; P < 0.01) and clipped skin temperature (35.1 ± 0.2 vs. 34.7 ± 0.2°C; P < 0.05) compared with daughters of sire B.
Slick animals kept a more stable rectal temperature as THI increased, whereas non slick animals experienced an increase in temperature in response to increasing THI (Figure 3A). Response to THI for unclipped skin temperature and clipped skin sweating rate was similar for slick and non-slick animals (Figure 3B,C).
Comments:
“The average THI experienced by the animals during data collection in California was 72 (range 61–80), whereas in Florida it was 90 (range 83–100), exceeding heat stress thresholds on a daily basis in both states (Dado-Senn et al., 2020a).”
‘California has a Mediterranean climate, characterized by high temperatures and low humidity during the day, often with a decrease in temperature accompanied by an increase in humidity overnight…….Another important difference between the two states was that in Florida, the animals experienced several more hours of more severe heat stress each day, and no relief at night.”
“Cattle dissipate excess heat load via evaporative heat loss by increasing sweating and respiration rates, and the efficiency of these processes is largely dependent on the humidity of the air.”
“Young cattle have generally been regarded as more resistant than lactating cows to heat stress. Recent data, however, show that preweaning calves can begin showing signs of heat stress at a THI of 65 to 69 (Dado-Senn et al., 2020a), that is, substantially lower than the previously estimated value of 77 (St. Pierre et al., 2003) and similar to the value of 68 established for lactating cows (Zimbelman et al., 2009).
The Bottom Line
“Presence of the SLICK1 allele resulted in lower body temperature in young Holstein cattle exposed to the subtropical heat conditions found in Florida, whereas no differences were observed in the Mediterranean heat conditions found in California. The presence of the SLICK1 allele seems particularly important when high THI is driven by high humidity, and the effects of the mutation on the physiological responses to heat stress can be detected in Holstein calves as early as the preweaning stage of life.”
References
Carmickle, Allie T., Colleen C. Larson, Froylan Sosa Hernandez, Jessica M. V. Pereira, Fernanda C. Ferreira, McKenzie L. J. Haimon, Laura M. Jensen, Peter J. Hansen, and Anna C. Denicol. 2022. Physiological responses of Holstein calves and heifers carrying the SLICK1 allele to heat stress in California and Florida dairy farms. J. Dairy Sci. 105:9216-9225.
Dado-Senn, B., V. Ouellet, G. E. Dahl, and J. Laporta. 2020a. Methods for assessing heat stress in preweaned dairy calves exposed to chronic heat stress or continuous cooling. J. Dairy Sci. 103:8587– 8600.
Dado-Senn, B., L. Vega Acosta, M. Torres Rivera, S. L. Field, M. G. Marrero, B. D. Davidson, S. Tao, T. F. Fabris, G. Ortiz-Colón, G. E. Dahl, and J. Laporta. 2020b. Pre- and postnatal heat stress abatement affects dairy calf thermoregulation and performance. J. Dairy Sci. 103:4822–4837.
Kertz, A. F. 2009. Effects of shade on heifers evaluated. Feedstuffs, July 13, 2009, p. 12-13.
Marcillac-Embertson, N.M., P.H. Robinson, J.G. Fadel and F.M. Mitloehner. 2009. Effects of shade and sprinklers on performance, behavior, physiology and the environment of heifers. J. Dairy Sci. 92:506-517.emperature humidity index (THI) and black
Zimbelman. R. B., R. P. Rhoads, M. L. Rhoads, G. C. Duff, L. H. Baumgard, and R. J. Collier. 2009. A re-evaluation of the impact of temperature humidity index (THI) and black globe humidity index (BGHI) on milk production in high producing dairy cows. Pages 158-169 in Southwest Nutrition & Management Conference, Tempe, AZ, University of Arizona, Tucson.
