The effect of reducing or omitting the dry period on the performance of dairy cows.

The milk quota policy has profoundly changed the economic context of dairy farming. Dairy farmers have now the possibility to focus more than before on factors such as ease of herd management and health conditions. As a result this idea of reducing or even omitting the dry period is attracting particular interest. This article summarizes some of the consequences of this management style. Reducing the length of the dry period below the standard 6-8 weeks decreases the amount of milk secreted in the following lactation. This decrease is about 10 % after a dry period of 1 month and slightly more than 20 % after a complete omission of the dry period. The shape of the lactation curve, however, is not modified. When the additional quantity of milk produced during the extended milking period is taken into account, the actual decrease in the volume of the milk secreted over the entire lactation is less than 5 % or slightly more than 10 % for the above conditions, respectively. A reduction in the length of the dry period increases the levels of protein and fat contents in the milk over the entire lactation period, to such an extent that their amount in the milk decrease less than the overall milk volume itself. At the end of pregnancy the milk becomes richer in components that are detrimental to its quality (free fatty acids, immunoglobulins, plasmin and plasminogen, lipase). This tendency increases as the calving date approaches. The large decrease in milk production does not seem to be accompanied, at least during the first weeks of lactation, by a reduction in the ingestive capacity of the animals. This maintained level of food intake and the reduction of milk secretion improve dramatically cows' energy balance. The cows lose less weight during early lactation, or may even not lose any weight at all, and the incidence of nutritional and metabolic disorders decreases. A reduction in the length of the dry period and certainly its omission, tend to increase the number of somatic cells in the milk, if no specific treatment is applied. It may be, although this remains to be tested, that reducing the length of the dry period will make it possible to feed modern, high milk producing cows with diets that are richer in forage than those currently in use, without inducing the usual concurrent health risks.