Conjugated linoleic acids (CLA) moderate negative responses of heat-stressed cows

The objective of this study is to examine whether CLA would help to improve negative responses in lactating cows during heat stress. During a 2-week adjustment period, all cows were fed a control diet supplemented with 400 g of calcium salts of palm oil fatty acids. After the adjustment period, cows (n = 9 per group) were randomly assigned by block to one of four treatments: control or three diets containing 100, 200, or 400 g of CLA (70% of which were mixed isomers of CLA). Milk fat percentage and yield decreased by supplementation of CLA (P < 0.01), but milk yield and other nutrient components did not vary (P > 0.05). The concentrations of short and medium-chain fatty acids (C4–C14) decreased and long-chain fatty acids (C18) increased in milk fat for cows fed CLA. Moreover, the contents of cis9, trans11 and trans10, cis12-CLA in milk fat increased markedly (P < 0.01). Respiration rate was lower (P < 0.05) for cows fed 200 g of CLA and rectal temperature decreased (P < 0.01) in all CLA groups during day 15 to day 28. Contents of aspartate aminotransferase, creatine kinase, thyroxin, potassium, sodium, calcium and chlorine were altered by CLA supplements, whereas other plasma parameters were not affected (P > 0.05). Lower concentrations of aspartate aminotransferase and creatine kinase in blood for cows fed 200 g or 400 g of CLA suggested that CLA protected cows from muscle damage. In addition, higher concentrations of electrolytes and thyroxin in blood in these groups suggested that CLA could improve heat stress situations in cows. Overall, the results showed that supplementations with 200 or 400 g/day of CLA moderated the negative responses in heat-stressed cows.