Analysis of Hessian dairy herd improvement test results as a predictor of a risk for ketosis

The present study analysed 104,167 dairy herd improvement test results from 52 farms in Hesse (Breed German Holstein), collected between 2004 and 2007. Data were analysed to determine the effect of parity on the lactation curves for milk yield, milk fat percent, milk protein percent, and fat-to-protein ratio. The curves were then compared to a study based on data from the years 1977-1981. Additionally, it was analysed how often reference values commonly used for evaluation of energy status of dairy cows were exceeded and if lactation stage and parity had an effect on the frequency of exceeded reference values. The reference values chosen were milk fat content >= 4.8%, milk protein content <= 3.2%, and a fat-to-protein ratio >= 1.5. Results from the current study determined an improvement in lactation performance with an increase of 60% in milk yield and 4% in milk protein content, compared to the years 1977-1981. The progression of the lactation curve varies with parity. The milk yield curve of the first lactation is considerably flatter than in following lactations. Lactation curves from the third parity on were greater in milk yield than those of previous lactations and do not differ substantially from each other. Milk protein content is low for these parities, whereas milk fat content tends to be greater, especially at the onset of lactation. During the first 30 days in milk 31.4% of cows in third and following lactations have a milk fat content above 4.8%. Fat-to-protein ratio is also significantly greater for cows of third and following lactations (30.5%). These results indicate an increased risk of a negative energy balance and of ketosis for cows from the third lactation on.