Managing Heat Stress in Dairy Calves and Heifers: Housing Considerations
Dairy calves and heifers are often overlooked when considering not only cooling strategies, but housing in general. Providing housing with cooling in the summer for both young calves and older heifers could improve growth, subsequent lactation performance, and profitability for the dairy operation. While hutches for dairy calves have become fairly standard throughout the industry, providing a source of shade over the hutches has been shown to improve respiration rates and reduce skin temperature of calves (Spain and Spiers, 1996). Coleman et al., (1995) found a tendency for improve feed efficiency when calves were housed in shaded hutches along with lower rectal temperatures. Calves that were housed under metal roofing, with and without cooling, had lower temperatures, increased IgG, and lower mortality rates compared to those housed in hutches (with metal covers). Providing a source of shade over hutches during prolonged heat stress can improve calf performance, but cooling the shaded area may not result in further improvements. Similar trends have been noted in older heifers housed on pasture with different shade sources. Twenty-one yearling, Holstein heifers (n=7), were assigned to one of three paddocks, each with a different type of shade: 1) Natural shade from trees (T); 2) Hutches (H); 3) Shade cloth (SC). All heifers were fed a commercial grain mix, ryegrass hay, and grazed a grass-legume mix pasture. Body weight and frame measures, rectal temperatures, and blood samples were collected once per week. Heifer behavior was observed twice weekly for a total of 24 h. There was a tendency for decreased body weights in heifers housed under SC, but ADG, wither height, or hip height were not affected by shade type. Blood parameters were not affected by shade type. Time spent in the shade versus not was also not different with shade type, but time spent lying down was greater in both T and SC when compared to H (P < 0.05). Temperature was also lower in T and SC compared to H, which may have contributed to decreased time lying down.
Keywords: heat stress, dairy heifers, housing