Evaluation seasonal change on milk composition and production in Holstein dairy cows fed with flaxseed

This study evaluated the effects of seasonal change and diet on milk production, milk composition and related indices from 5 industrial dairy farms in Mashhad.
Samples in summer period (in 2014) and winter period (in 2015) were taken on each farm. Meteorological data were obtained from the Northeast Regional Climate Center of Iran, Mashhad. Dairy cows were fed with 2 diets, control diet and 10% flaxseed diet. In each farm, animals were divided into 3 groups based on their days in milk (early, middle and late). Diets were provided as TMR. Dry matter intake, daily milk yield, milk fat, milk protein, milk lactose and solids in milk were measured. Milk fatextraction and fatty acid separation were determined.
Increasing temperature-humidity index (THI) had decreased dry matter intake in summer (THI ≥72) against winter period (THI≤72; 21.8 vs. 24.0 kg DM d-1, respectively). Modification dry matter intake decreased milk yield and milk protein, but milk fat tended to increase. In addition, we observed the highest fat-to-protein ratio in winter (1.39 vs. 1.28). Milk yield, polyunsaturated fatty acids (PUFA), linolenic acids and monounsaturated fatty acids (MUFA) and linoleic acids for the cows were fed 10% flaxseed was significantly higher than for those fed control diet, but percentage of milk fat was significantly reduced when diets were supplemented with flaxseed. Feeding diets of flaxseed had no effect on dry matter intake, milk protein percentage, lactose and milk solids compared with control diet. The canonical correlation analysis of indices demonstrated that daily milk yield was negatively correlated with milk protein but no significant relationship was observed between daily milk yield and the other indices. Here, we found that milk solids was significantly correlated with milk fat (r= 0.795), milk protein (r= 0.770), and milk lactose (r= 0.477). Moreover, concentration of unsaturated fatty acids milk (18 carbons) was negatively correlated with milk fat.
The experiment demonstrated that the fed of flaxseed in winter was effective at increasing fat-to-protein ratio, indicating that cows mostly utilize their body fat. These results clearly demonstrate the possibility for sustainable production of organic omega-3 milk up to 2.3 times higher than typical levels in milk fat. Furthermore, it is necessary to investigate the factors that affect raw milk composition, which may improve the quality and yield of milk through temperate environmental conditions and management of nutritional supplementation.