Genetic Component of Heat Stress in Dairy Cattle, Development of Heat Index Function

Abstract

Production data obtained from AIPL USDA included 119,337 first-parity, test-day records of 15,012 Holsteins from 134 Georgia farms collected in 1990 to 1997. Weather information was obtained from the Georgia Automated Environmental Monitoring Network and included daily minimum, average, and maximum temperatures and humidity for 21 stations throughout the state. Each test-day record was augmented with weather information from the closest weather station. Analyses were based on models that included effects of herd-year-season, age, test day, milking frequency, and several types of heat and humidity. The best model used a temperature-humidity index. With this model, the average test-day yield for milk was about 26.3 kg for a temperature-humidity index <72 and decreased at about 0.2 kg per unit increase in the temperature-humidity index for a temperature-humidity index > or =72. For fat and protein, the test yield was 0.92 and 0.85 kg at a temperature-humidity index <72, respectively, and declined at a rate of 0.012 and 0.009 kg per degree of the temperature-humidity index, respectively. The temperature-humidity index calculated with the available weather information can be used to account for the effect of heat stress on production.

Physiological and behavioural response of two dairy cows&#8217; genotypes during summertime in the central region of Chile

“…Bernabucci et al (2014) also reported a reduction in milk production at THI from 65 to 76 depending of the parity of cows. There are other reports showing a range of multiple values of THI thresholds ranging from 69 to 78.2 (Bohmanova et al 2007, Bouraoui et al 2002, Dikmen and Hansen 2009, Johnson et al 1962, Ravagnolo et al 2000. However, it is important to mention that most of those reports are associated with the same genetic (Holstein Friesian).…”

Influences of breed, sex and age on seasonal changes in haematological variables of tropical goat kids

“…The values of the morning and afternoon temperature-humidity index (THI) were used to evaluate the level of heat stress induced by the environment. The formula reported by Ravagnolo et al (2000) was used to calculate THI:…”

Influence of seasonal changes on physiological variables, haematology and serum thyroid hormones profile in male Red Sokoto and Sahel goats

“…The AT and RH were recorded daily during the morning (08:00-10:00 h) and afternoon (13:00-16:00 h) hours in each season of study. The temperature-humidity index (THI) was used to evaluate the level of heat stress induced by the environment and was calculated using the equation reported by Ravagnolo et al (2000):…”