Energy Status Related to Production and Reproduction in Dairy Cows Prevention of Decreased Fertility and Detection of Cows at Risk

Decreased fertility in dairy cows is widespread and economically undesirable. Current management strategies to prevent decreased fertility are exploiting the close relationship between negative energy balance in transition cows and subsequent decreased fertility. However, there is a continuous need for more information regarding the effects of different strategies on fertility. This thesis evaluated the effect of supplemental feeding with glycerol or propylene glycol, the usefulness of measuring metabolic indicators in blood samples to predict decreased fertility and investigated potential risk factors. In two field studies, the metabolic status, milk yield and fertility of cows in 17 herds, fed either a glycerol or propylene glycol supplement or no supplement (control) 0-21 days after calving, were evaluated. A separate study evaluated the accuracy of metabolic indicators when used to predict decreased fertility. The results were based on a single blood sample taken in early lactation and different test cut-off values were applied. Finally, potential risk factors for decreased fertility related to housing, feeding and the cow herself, were evaluated in approximately 750 Swedish herds. Cows fed glycerol produced significantly 1 kg more milk during the first 90 days in milk and cows fed propylene glycol tended to produce more milk without a subsequent decrease in metabolic status or fertility. The test performance of the metabolic indicators was in general low and was influenced by cow parity, cow breed and the prevalence of decreased fertility in the population studied. Cows experiencing a change in system (e.g. in housing or milking system or from conventional to organic production) had lower fertility than cows not experiencing such a change. In addition, cows with severe claw lesions and cows displaying a rise in somatic cell counts had a lower probability of pregnancy at first insemination. In conclusion, supplemental feeding with glycerol or propylene glycol, as a general strategy in a herd, does not seem to influence fertility or energy status and could increase milk yield. Measures to prevent a decrease in fertility could be more effective if applied to cows in physiological imbalance, rather than all cows in a herd. However, the use of metabolic indicators in a single blood sample may not be optimal for detecting cows at risk. The identified risk factors for decreased fertility could be used when devising preventive strategies.