The future productivity of a dairy herd hinges on the management of the replacement heifer calves.
A lot of effort goes into breeding high genetic merit replacement calves. Inadequate rearing results in poor milk production and poor reproductive performance causing high wastage rates. To avoid this wastage, adopt sound mating management and ensure that heifers are grown well.
The best way of monitoring is to check they are reaching their percentage of expected mature liveweight at specific ages:
If heifers do not reach their 30% target at six months of age they struggle to meet their 15-month target of 60% at mating, thus they are undergrown at calving. The period between six and 15 months of age coincides with summer in spring herds, during which the animal’s growth can suffer, especially if the season is dry. During such times a strong case could be made for buying in concentrates and/or roughages to keep animals growing at the required values.
Smaller heifers do not compete as effectively in the herd plus they have to direct more energy away from milk production towards body growth. In contrast, large heifers are closer to their genetically determined size and need to grow less during their first lactation. This means they can divert more energy and protein towards milk production and regaining body condition and less towards growth. Such ability to regain body condition could result in improved fertility as well as second lactation performance.
Regular three-monthly weighs and condition scoring are paramount as they ensure you know your heifers are reaching targets. This allows for management changes to be made based on recorded data well in advance of mating and calving. Another means of monitoring are growth rates. Growth rate is measured in kilograms gained per day and is a means of monitoring how fast or slow the heifers are growing. We recommend the following targets:
Target growth rates before 15 months of age should be maintained at a constant rate to avoid fluctuations or excesses as this can negatively affect mammary tissue growth. Once the heifers have been mated, an increased growth rate of 0.8-0.9kg/day during the first seven months of pregnancy can be used to increase milk yield at calving. However, in the last two months of calving the diet should be restricted to the tabulated targets to maintain a body condition score of 5.5 as to avoid fat heifers at calving.
Heifers are inherently fertile; however, you should be focusing on their second calving. This is because a heifer will easily get pregnant as a maiden as there are no extra pressures apart from growth. Once she is in the herd the added pressure of growth and production often leads to poor fertility in the future. By ensuring they meet their target growth weights and rates you provide your heifers with the best chance of remaining in the herd and maximising their productive performance.