|
404. Interest has been shown in extending the length of lactation. The term "extended lactation" means different things to different people. In all-year-round calving herds, extension of the period between calvings to 14 months may be acceptable. This may fit in with the management of the herd with some advantage to individual animals but with little effect on the number of calves born. In fact this is not too dissimilar from current, though not planned, farm practice. In the context of this report, extended lactation means calving once every 18 months or beyond.
405. The major expected benefit is the production of fewer progeny which are increasingly surplus to requirements. It is also expected that insemination costs and the number of dry days within the cow's lifetime would be reduced. Additionally, there could be benefits in reduced metabolic stress and increased longevity.
406. With high yielding dairy cows there have been a number of problems with extending the calving period to 18 months in terms of both production and welfare issues. There have been difficulties in getting cows back in calf at the desired time, (i.e. nine months post calving) and the lactation curve has remained the same as for a 12 month calving interval. This has resulted in cows becoming too fat and animals performing unsatisfactorily in subsequent lactations. There appear to be differences in the way that different cows and sire groups react to delayed breeding and the parameters that can be used to determine which cows will react beneficially to extended lactations need to be identified.
407. Another potential option is to alter the shape of the lactation curve in animals that do not fit into the system in order to produce flatter but prolonged lactations to overcome excessive liveweight gain. Diets would need to be developed to apportion feed differently after peak yield towards milk rather than body reserves.
408. Although some trial work is being undertaken, there is a great need for further research to identify those animals that would benefit from extended lactations and to develop diets that will alter the shape of the lactation curve and so reduce excessive liveweight gain later in the lactation.
409. Long-term trials should be undertaken to identify the effects of extended lactations on such parameters as udder conformation, longevity, breeding success, disease control and body condition.