Effect of heat load on shade use and panting score in Holstein dairy and Belgian Blue beef cattle on pasture

We evaluated the effect of heat load on shade use and (preliminarily) the effect of heat load and shade on visual indications of heat-stress, for Holstein dairy cows (HD) and adult (ABB) and juvenile (JBB) Belgian Blue cattle on pasture. During the summer of 2012, no shade was available (NS). During the summers of 2011 (HD, ABB, JBB) and 2013 (AHD, ABB; no JBB in trial) each herd was divided into a group with (S) and a group without (NS) access to a fenced shade-area (with trees and shade-cloth). The Panting Score (PS), range 0-5, assesses heat stress based on the degree of panting and drooling. On several days during the three summers (ADH: ntotal=35, ABB: ntotal=41, JBB: ntotal=20), it was scored hourly (10h-15h) for individuals inside and outside shade. During the same days, individual shade use was determined per 15min. Mixed logistic regressions evaluated the effect of six different climatic heat-stress-indices (combining temperature, humidity, solar radiation and wind speed) on shade use. Increasing Heat Load Index (HLI; range 45-90) was the best predictor for increasing shade use (P<0.0001 for HD, ABB, JBB). In 2011, there was a high threshold for shade use, probably due to high motivation for herd cohesion. At HLI=90, shade use probability reached 17%, 27% and 25% for HD, ABB and JBB, respectively. In 2013, (at HLI=90) shade use probability reached 48% for HD and 41% for ABB. When all data were pooled, in hot conditions, shade use reduced the prevalence of PS≥2 for HD and ABB (Chi2-test, P<0.001). For JBB it eliminated PS≥2 and reduced the prevalence of PS≥1 (Chi2-test, P<0.001). These results indicate that, even in Belgium, heat load may evoke thermal discomfort (shade use increases despite the apparent ‘cost’ of leaving the group) and that shade use lessens visual indications of heat-stress (PS).

Publication year:2014