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The effects of heat stress on milk yield milk composition and major mineral content in milk of dairy cows during early lactation

Kume, S.; Takahashi, S.; Kurihara, M.; Aii, T.

Japanese Journal of Zootechnical Science 61(7): 627-632

1990


Accession: 007895771

The objective of this study was to clarify the effects of heat stress on milk yield, milk composition, and major mineral content in milk during early lactation in Holstein cows. Milk yield, milk composition, and major mineral content in milk were measured by using 8 cows calved from Jul. to Sep. (summer group) and 9 cows calved from Feb. to Mar. (winter group). Milk yields during early lactation were significantly lower for the summer group than the winter group. Total solid, fat, protein, calcium (Ca), phosphorus (P), and magnesium (Mg) content in milk during early lactation in each group tended to decrease until 5 weeks after parturition and then increase gradually, whereas they tended to be lower for the summer group than the winter group. Total solid, fat, protein, Ca, P, and Mg content in milk during mid to late lactation in the winter group, which were reduced by heat stress, were higher than those during early lactation in the summer group. However, sodium (Na) and potassium (K) contents in milk during early lactation tended to be higher for the summer group. There were close relationships between total solid, fat, protein, Ca, P, and Mg content in milk, since there were positive correlations between those of the winter group during the lactation period. Thus, heat stress in summer may reduce milk yields drastically and also reduce fat, protein, Ca, P, and Mg content in the milk of dairy cows during early lactation.

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