Maîtrise des points critiques dans l''élevage des génisses laitières : quel impact sur la production laitière ?

Context

An initial project studying critical points showed that most milk producers could envisage an early first calving for their heifers at the age of 24 months. Even though the results suggested room for improvement in some areas such as housing conditions or parasite control, the physical development results assessed on the basis of girth showed that most of the animals monitored were sufficiently formed for insemination at 15 months. In practice, however, the average age of first calving in Wallonia is 29 months. That means that farmers probably keep the young cattle too long, thus extending the rearing phase and causing a considerable economic loss. Reasons mentioned by farmers include group management of young animals, on the one hand, and fears of lost production due to too-early calving, on the other.

Objectives

The main aim of the project is to establish the correlation between the physical development of dairy heifers, measured in the previous project, and their milk performance at the first lactation.

Results obtained

The results showed that steady heifer growth during the rearing phase enabled farmers to bring forward the average age of first calving. For a more robust analysis the impact on milk performance was studied in cooperation with the Walloon Livestock Farming Association (AWE), which gave us data on more than 60,000 animals comprising first and second lactation milk performance, date of calving and milk composition. Analysis of the data showed that calving in the 22-26 months age bracket did not adversely affect first lactation milk performance (Figure 1). The subjects’ milk performance was in fact shown to have improved by the second lactation compared with heifers whose first calving was later. This effect may be attributed to the farmer, as the farmers who managed calving most efficiently were no doubt also the top performers in terms of productivity.
The results also showed that animals who first calved in autumn produced more milk than those whose first calving fell in spring. This difference may be explained by seasonal differences in feeding patterns at the start of lactation.
In a future programme of work the effects of first calving age on life performance, longevity and reasons for culling will be studied in cooperation with AWE.
A program called Opticroît, developed in cooperation with AWE, will shortly be available to help farmers manage their dairy heifers. The program will also be used to collect data on dairy heifer growth and subsequent performance.