EFFECTS OF DAYLIGHT AND SEASONAL FACTORS ON SERUM AND MILK IGF-1 LEVELS IN HOLSTEIN DAIRY COWS AT DIFFERENT LACTATION PERIODS

The research was carried out on 34 Holstein dairy cows in their first lactation period, which were determined to be healthy by general examination in a commercial dairy farm with 800 heads of Holstein and Simmental but predominantly Holstein dairy cows. These animals were fed the same ration and housed in the same environment during the experiment. These 34 Holstein pregnant heifers that will give calve for the first time were followed up and their development was monitored, blood samples were taken from the v. jugularis before the morning feeding on the 15th, 35th and 45th days following the calving, blood plasma and milk IGF-1 levels were determined by Enzyme Linked Immunoassay method and morning-evening change and seasonal changes were determined. According to the data obtained, the lowest plasma IGF-1 levels were determined in the samples on the 45th day in all periods; In addition, it was found that plasma IGF-1 values increased periodically in three different seasonal transition periods. It was observed that plasma IGF-1 levels showed the highest value (94.46 ng/ml) on the postnatal 35th day, and the lowest value (79.37 ng/ml) was obtained on the 45th day, with a difference at P<0.001 significance level. Plasma IGF-1 levels in morning samples were higher (P<0.01) compared to evening samples. Milk IGF-1 values in milk samples sampled on the 15th and 45th days reached the highest value in March (P<0.01); there was a decrease (51.61 ng/ml; 47.13 ng/ml) on the 45th day compared to the 15th day. Periodic increases (P<0.01) were observed in milk IGF-1 levels, like plasma ratios.