Effects of Stocking Density on Milk Fatty Acids Composition and Oxidative Stability of Mid- and Late-Lactating Dairy Cows
Institute of Dairy Science, MoE Key Laboratory of Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou 310058, China
College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China
Author to whom correspondence should be addressed.
Received: 5 July 2018 / Revised: 4 August 2018 / Accepted: 20 August 2018 / Published: 21 August 2018
The ratio of unsaturated fatty acids (UFAs)/saturated fatty acids (SFAs) of milk fat is known to play an important role in regulating milk oxidation capacity in lactating dairy cows. Recently, it was found that dietary antioxidant addition plays an important role in changing UFAs/SFAs ratio of milk fat and milk oxidation capacity in dairy cows, indicating the role of oxidative stress status in regulating milk oxidation capacity. Although stocking density can affect stress level in lactating dairy cows, whether stocking density may affect milk oxidation capacity remains to be answered. In the current study, we stocked the cows with different physiological stages (mid- and late-lactating) under different stocking density (100% vs. 75%), respectively. The plasma variables, milk fatty acids compositions, and oxidative index in the milk were further evaluated to clarify if stocking density can regulate the oxidation capacity of the milk. The results showed that, in mid-lactating cows, milk produced by low stocking density animals had lower oxidation stability due to the higher UFAs levels, compared with those of high stocking density cows. Milk oxidation capacity of late-lactating dairy cows did not differ when they were blocked under different stocking density. Our results suggested that stocking density did affect milk oxidation capacity but in a physiological-stage dependent manner. Nutritional strategies should be developed to improve the milk oxidation capacity of cows managed under a low stocking density.