Monthly and seasonal evaluation of dietary nutrients and their relationships with blood and milk parameters in lactating dairy cows.

Monthly and seasonal variations among dietary, blood and milk parameters and their interrelationships were investigated during the lactation period in Holstein dairy cows in order to determine reliable dietary indices that could be useful in the studies related to milk yield improvement. Samples were prepared monthly, up to 11 months of lactation and were analyzed by the current laboratory methods using appropriate kits. Mean monthly and seasonal comparison of the dietary, blood and milk values were different among sampling times (p<0.05). The overall mean for dietary energy (ME), crude fiber (CF), moisture, ash, phosphorus (DP), calcium (DCa), ether extract (EE) and crude protein (CP) were 1.38 Mcal/KgDM, 20.4%, 42.8%, 5.5%, 0.34%, 0.76%, 2.39% and 10.2%, respectively. Correlations were found between dietary DP/Ca (r=-0.73), DP/EE (r=0.67), DP/ash (r=0.79), DP/moisture (r=0.84), DP/ME (r=0.60), Ca/ash (r=0.95), Ca/moisture (r=-0.64), and DCa/moisture (r=-0.93). Correlations among dietary, blood, and milk parameters revealed different relationships with the most important correlations between DP and blood parameters, and CP with blood and milk parameters. Among blood parameters glucose, BHB, SK, AST, GGT, neutrophils and lymphocytes. Milk parameters: Mg, Ca, and lactose showed the strongest relationships with dietary parameters. In conclusion, the dietary, blood and milk values were different during the lactation months and seasons. Dietary CP, Ca and DP could be applied as relevant indices in studies related to milk production improvement in dairy herds.