Interrelationships among ambient temperature, day length, and milk yield in dairy cows under a mediterranean climate

We examined the effect of calving month (CM) on the production of milk and milk protein by Israeli Holstein dairy cows located in the main climatic zo ne of Israel during their third and fourth lactations, and found it to be s ignificant. Cows that calved in December produced the highest milk and milk protein yields, and those that calved in June produced the lowest, 92.8% o f the maximum. The combined effect of the environmental average temperature and day length accounted for 0.96 of the variability in average milk produ ction during lactation and 0.93 of that in average protein production durin g lactation. Average milk production was reduced by 0.38 kg/degreesC and av erage protein production was reduced by 0.01 kg/degreesC. Elongation of day light increased average milk production by 1.2 kg/h and average protein pro duction by 0.02 kg/h of daylight. Analysis of the temperature pattern effec t on milk and protein yield during lactation indicated that cows at the sec ond month (the pike of their milk yield) are more vulnerable to the negativ e temperature effect than cows on the ninth month of lactation.