Changes in milk yield in dairy cows associated with metabolic and reproductive disease and lameness

Abstract

A study was undertaken of 1594 lactations occurring in 732 British Friesian, Ayrshire and Holstein crossbred cows. One thousand two-hundred of these lactations were used to consider the association between the occurrence of hypocalcaemia, ketosis, hypomagnesaemia, dystocia, retained placenta, endometritis and lameness and changes in milk yield. A statistical technique was applied which used the relationship between pairs of consecutive lactations in the same cow to assess losses in milk yield associated with disease relative to an individual's own potential. Seven hundred and seventy-two pairs of consecutive lactations from the 1200 lactations were available for this purpose. Average significant reductions of 6–7% in peak milk yield occurred in lactations in which the cow had a retained placenta or ketosis. Cows which had ketosis showed a slower decline in milk yield in later lactation and there was no overall significant difference in 305-day milk yield, However, for cows which had a retained placenta, there was no corresponding reduction in rate of decline, and 305-day milk yield was on average 7% lower. There were no significant associations between hypocalcaemia, hypomagnesaemia, dystocia or endometritis and milk yield. Cases of lameness, which occurred during a 20-week period following peak yield and were mainly associated with lesions involving the interdigital cleft and sole or white line sites of the claw, were more common in cows which had higher than average peak milk yields. Heel lesions appeared to be associated with lower than average 305-day yields, but this may have been due to variations in incidence with season.