In this Research Communication we describe the effect of temperature and humidity index (THI) on various physiological traits, the plasma heat shock protein 70 (HSP70), heat shock protein 90 (HSP90) and cortisol levels and other blood parameters in crossbred buffalo (Nili-Ravi × Murrah) and Mediterranean buffalo to compare their tolerance to heat stress. As expected, crossbred buffalo had a significantly higher rectal temperature (RT), body surface temperature (BT), respiratory rate (RR), HSP70 and HSP90 levels in summer compared to spring and winter. RT and BT were also significantly higher in spring compared to winter. A significant correlation existed between THI and RT (r = 0·81) and RR (r = 0·84). Importantly, in summer the crossbred buffalo had a significantly lower RT, BT and RR and higher HSP70, HSP90 and cortisol levels than the Mediterranean buffalo. In conclusion, higher THI was associated with significant increase in RT, RR, BT, HSP70, HSP90 and cortisol levels, and the crossbred buffalo were more heat tolerant than Mediterranean buffalo.

Buffalo are the second most valuable species in the world for milk production and their milk prices have been based on fat and protein composition. The aim of the paper was to compare the milk yield and composition of pure Egyptian buffalo (EB) and their crosses with the Italian buffalo and to investigate the impact of temperature humidity index (THI) on milk yield and composition under subtropical stressful conditions. 516 lactating buffalo were used (152 EB; 176 F1 crosses 50% EB and 50% Italian buffalo and 188 back cross (BC) 75% EB and 25% Italian buffalo). The results revealed that, milk yield (5·79 and 10·32%) and peak yield (6·36 and 7·67%) were significantly higher in F1 and BC than in EB, respectively. BC had 7·74 and 3·67% significantly higher daily yield when compared with EB and F1, respectively. EB were robust in the hot condition as the only reduction was in the peak of milk production from 15·02 in low THI to 13·72 kg in high THI, but fat and total solids%, were increased from 5·61 and 16·31 THI in low to 7·01 and 17·59 in high THI, respectively. BC was similar to some extent to EB as their milk was similar to EB under sever hot climate conditions (2331·92 and 2327·50 kg, respectively). A statistically significant reduction in the average daily milk yields was detected only in F1 from 10·33 to 8·38 kg in low and high THI level, respectively. The current study showed that BC produced a higher milk with higher daily average milk yield and peak yield with some evidence of robust under sever hot condition which were approximately similar to EB. Thus, it is recommended to encourage the producers to increase the number of BC animals in their farm for improving the milk production to fulfil the demand of Egyptian markets.

A better understanding of how livestock respond to weather is essential to enable farming to adapt to a changing climate. Climate change is mainly expected to impact dairy cattle through heat stress and an increase in the frequency of extreme weather events. We investigated the effects of weather on milk yield and composition (fat and protein content) in an experimental dairy herd in Scotland over 21 years. Holstein Friesian cows were either housed indoors in winter and grazed over the summer or were continuously housed. Milk yield was measured daily, resulting in 762 786 test day records from 1369 individuals, and fat and protein percentage were sampled once a week, giving 89 331 records from 1220 cows/trait. The relative influence of 11 weather elements, measured from local outdoor weather stations, and two indices of temperature and humidity (THI), indicators of heat stress, were compared using separate maximum likelihood models for each element or index. Models containing a direct measure of temperature (dry bulb, wet bulb, grass or soil temperature) or a THI provided the best fits to milk yield and fat data; wind speed and the number of hours of sunshine were most important in explaining protein content. Weather elements summarised across a week’s timescale from the test day usually explained milk yield and fat content better than shorter-scale (3 day, test day, test day −1) metrics. Then, examining a subset of key weather variables using restricted maximum likelihood, we found that THI, wind speed and the number of hours of sunshine influenced milk yield and composition. The shape and magnitude of these effects depended on whether animals were inside or outside on the test day. The milk yield of cows outdoors was lower at the extremes of THI than at average values, and the highest yields were obtained when THI, recorded at 0900 h, was 55 units. Cows indoors decreased milk yield as THI increased. Fat content was lower at higher THIs than at intermediate THIs in both environments. Protein content decreased as THI increased in animals kept indoors and outdoors, and the rate of decrease was greater when animals were outside than when they were inside. Moderate wind speeds appeared to alleviate heat stress. These results show that milk yield and composition are impacted at the upper extreme of THI under conditions currently experienced in Scotland, where animals have so far experienced little pressure to adapt to heat stress.

In the present study, the relationship between the temperature–humidity index (THI) and the incidence of medical treatments in lactating dairy cows in Lower Saxony, Germany, was investigated. Records of all veterinary-treated cases over 2 years (2003 and 2005) from eight Holstein–Friesian dairy herds raised in loose-housing systems (55 to 170 cows per herd) were evaluated. After exclusion of management-dependent and climate-independent cases, a total of 5547 treatments were analyzed. Treatments were clustered into the following groups: metabolism, fertility, udder and foot/leg. Meteorological data were compiled from the nearest weather station (average distance ± s.d. 39 ± 13 km). Hourly temperatures and relative humidity values were used to calculate the THI, which was divided into classes. Out of the total number of treatments, 37.4%, 32.9%, 21.6% and 8.1% belonged to metabolism, udder, fertility and foot/leg, respectively. Data were analyzed with a mixed model that included THI class, season and year as fixed effects and farm as random effect. In general, incidences were neither affected by the year (P > 0.05) and season (P > 0.05) nor by THI classes (P > 0.05). In tendency, incidences of metabolic treatments increased with increasing THI and incidences of udder treatments increased with decreasing THI. In conclusion, indications of moderate heat stress during summer months in Central Europe were found in the present study, although THI and season did not affect the different disease complexes significantly.