The effects of heat stress in Italian Holstein dairy cattle

Abstract

The data set for this study comprised 1,488,474 test-day records for milk, fat, and protein yields and fat and protein percentages from 191,012 first-, second-, and third-parity Holstein cows from 484 farms. Data were collected from 2001 through 2007 and merged with meteorological data from 35 weather stations. A linear model (M1) was used to estimate the effects of the temperature-humidity index (THI) on production traits. Least squares means from M1 were used to detect the THI thresholds for milk production in all parities by using a 2-phase linear regression procedure (M2). A multiple-trait repeatability test-model (M3) was used to estimate variance components for all traits and a dummy regression variable (t) was defined to estimate the production decline caused by heat stress. Additionally, the estimated variance components and M3 were used to estimate traditional and heat-tolerance breeding values (estimated breeding values, EBV) for milk yield and protein percentages at parity 1. An analysis of data (M2) indicated that the daily THI at which milk production started to decline for the 3 parities and traits ranged from 65 to 76. These THI values can be achieved with different temperature/humidity combinations with a range of temperatures from 21 to 36°C and relative humidity values from 5 to 95%. The highest negative effect of THI was observed 4 d before test day over the 3 parities for all traits. The negative effect of THI on production traits indicates that first-parity cows are less sensitive to heat stress than multiparous cows. Over the parities, the general additive genetic variance decreased for protein content and increased for milk yield and fat and protein yield. Additive genetic variance for heat tolerance showed an increase from the first to third parity for milk, protein, and fat yield, and for protein percentage. Genetic correlations between general and heat stress effects were all unfavorable (from -0.24 to -0.56). Three EBV per trait were calculated for each cow and bull (traditional EBV, traditional EBV estimated with the inclusion of THI covariate effect, and heat tolerance EBV) and the rankings of EBV for 283 bulls born after 1985 with at least 50 daughters were compared. When THI was included in the model, the ranking for 17 and 32 bulls changed for milk yield and protein percentage, respectively. The heat tolerance genetic component is not negligible, suggesting that heat tolerance selection should be included in the selection objectives.

Physiological and behavioural response of two dairy cows’ genotypes during summertime in the central region of Chile

“…The previous is in agreement with those reported by Markovich (2012) in New Zealand, where milk production began to decrease at THI of 65 for H and 75 for Jerseys. 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.…”

Effects of heat stress on serum insulin, adipokines, AMP-activated protein kinase, and heat shock signal molecules in dairy cows

“…THI is employed as an index, which is a single value combining effects of air temperature and humidity, and to evaluate the degree of heat stress in dairy cows (Bernabucci et al, 2014). THI has been used for more than four decades to assess heat stress in dairy cows.…”

“…Dairy cows are extremely sensitive to the hot environment (Bernabucci et al, 2014), and their alterations in the endocrine status (such as insulin) under heat stress have already been reported (Rhoads et al, 2009;O'Brien et al, 2010). In fact, heat stress does not only decrease milk yield by 35%-40% (West, 2003), but also leads to health problems and metabolic disorders (Wheelock et al, 2010;Bernabucci et al, 2014). Two adipokines secreted by adipose: leptin and adiponectin, are metabolically relevant in coordinating energy homeostasis (Ailhaud, 2006).…”

“…There is little information reported that shows serum HSF and HSPs can be biomarkers during heat stress. Traditionally, the temperature-humidity index (THI) is employed as the index to evaluate the degree of heat stress in dairy cows (Bernabucci et al, 2014). The advantage of THI is that it is easy to use in practice, but THI is only a rough estimation of heat stress and not a direct reaction of animal metabolism.…”

The global effect of heat on gene expression in cultured bovine mammary epithelial cells

“…Heat stress can be defined as a condition that occurs when an animal cannot adequately dissipate body heat in order to maintain thermal balance (Grover 2002, Bernabucci et al 2014. Some reports showed that Holstein milk yield decreased during HS; feed intake and management factors partly account for the decreased milk yield during heat stress (Rhoads et al 2010, Smith et al 2013, Hill and Wall 2014.…”