ALLEVIATING HEAT STRESS IN COWS BY SHADE STRUCTURES

Dairy cattle originated in cool to cold climatic regions making them well adapted to colder rather than warmer conditions. In fact, the comfort zone for dairy cows varies between ‐5 and 21 °C indicating that at higher temperatures they will be sensitive to heat stress. Direct and indirect solar radiation is the cause of heat stress. As cows have limited means to reduce the effect of heat stress, environmental manipulation is required to help cows maintain production levels under hot conditions. Heat stress may be long term (seasonal) or short term (heat waves). Although there are different ways to alleviate heat stress on dairy cows, a shade structure could be the most simple and cost‐effective way to reduce the effect of heat stress. In this review by the authors cited below results on the effect of a shade structure on the production, physiological parameters and behaviour of Holstein‐Friesian cows are provided as well as the effect of heat stress on multi-lactation Holstein‐Friesian and Jerseys cows. Ways to alleviate the effect of heat stress are suggested. 

A summary of results showed: (1) the day‐time feed intake of cows with access to shade was higher than for cows without shade; (2) feed intake at night did not differ for shade and no‐shade cows; (3) water intake of cows without shade was higher, being 114 vs. 97 litres per cow per day; (4) the milk yield of cows with access to shade was 5.5% higher than for no-shade cows; (5) the difference in cumulative milk yield for shade and no‐shade cows increased, suggesting an increasing negative effect as summer progressed, which shows that heat stress has a long term effect; (6) the respiration rates and rectal temperatures of cows with access to shade were lower than for cows without shade; (7) blood cortisol levels were higher (indicating heat stress) in cows without shade; (8) cows with access to shade spent more time feeding during the day while lying down more than cows without shade; (9) heat stress affected Holstein‐Friesian and Jersey cows differently, i.e. rectal temperatures, respiration rates and heart rate of Friesian cows were higher than for Jersey cows from 11:00 to 19:00 when ambient temperatures exceeded 24 °C, suggesting that Jerseys should be more comfortable in the warmer regions of the country; (10) the rate of return on the capital outlay for the construction of a shade structure showed a positive return on investment within three summer seasons and since a well‐build shade structure has a lifetime of more than 30 years, the benefit is long term.                                                       

Apart from shade structures, other ways to reduce the effect of heat stress include forced air movement through fans, wetting cows before and after milking, evaporative cooling systems, diet adjustments, intensive housing systems, zone cooling and general air conditioning. 

Reference:

C.J.C. Muller & J.A. Botha, 2016. Heat stress in dairy cows and ways to alleviate it. In Proc. of the 49^th SASAS Congress, Stellenbosch, 4-7 July 2016.