Document Type : Original Article
Dep. of Animal science, Faculty of Agriculture, University of Tabriz
Department of Animal Science, Faculty of Agriculture, University of Tabriz, Tabriz, Iran
Department of Animal Science,Faculty of Agriculture, University of Tabriz
The aim of the present study was to determine the effect of CLA supplementation on milk yield and composition, blood metabolites and reproductive parameters in dairy cows. Twenty lactating Holstein dairy cows were randomly assigned to one of two dietary treatments: 1) 110 g/day of fat supplement (control) 2) 120 g/day of rumen-protected CLA supplement. The experimental diets were formulated as isocaloric and isonitrogenous. The experimental period started 21 d precalving and continued until 60 day in milk (DIM). Dry matter intake (DMI), body weight (BW) and body condition score (BCS) were not affected by dietary treatments. Supplementation with CLA increased milk yield (3.04 kg/d, P < 0.001) and milk lactose concentration (P < 0.048), but decreased concentration of milk fat (P < 0.001) and short and medium chain fatty acids (P < 0.05). Milk protein concentration, milk energy output and net energy balance were unaffected by CLA supplementation. In cows supplemented with CLA, serum concentration of glucose, cholesterol, triglyceride (TG) (P < 0.01), insulin, insulin-like growth factor-1(IGF-1), estradiol and progesterone were higher (P < 0.05), whereas serum beta-hydroxybutyric acid (BHBA) concentration tended to decrease (P < 0.032). Days to first service and days open did not differ between experimental diets. The conception rate of cows from the first service increased with CLA supplementation (P < 0.045). The results indicated that CLA supplementation decreased milk fat concentration whereas some related metabolic parameters with a reproductive response increased in blood serum resulting in an increased conception rate from the first service.