Incidence of winter feeding, parasitism, and housing on the growth performances of dairy heifers in Wallonia.

With a replacement rate of 30 % in dairy herds, it is essential to ensure the best rearing conditions of young cattle for the development of future dairy cows. The aim of this study was to quantify the incidence of key management aspects such as housing, parasitism and winter feeding on growth performances of dairy heifers. Thirty farmers (774 heifers), located in the main dairy regions in Wallonia, participated to the survey. Development and growth were determined using Heart Girth (HG) measurements and compared with a French reference. Feed intake was estimated from the French Fill Unit System. A prediction equation of BW from HG, related to the genetic features of Walloon dairy herds (n = 256, BW = 0,0005 HG2.6161, r² = 0,96), was developed. The results suggested that 80 % of the breeders could pretend to an early calving, at 24 – 26 month of age. For half of the others, a lack of net energy supply in the diet could explain a growth delay. On the other hand, the protein supply was too high in 90 % of the diets compared to the animal’s requirement. This was due to the large utilization of grass silage. Ventilation efficiency, estimated by the difference of hygrometry inside and outside the barns, was not optimal in 40 % of the farms. This suggested that heifers were often accommodated in less adapted barns. The parasitism management did not differ fundamentally from one farm to another. Globally, heifers were treated systematically (1 to 4 treatments/year) and did not acquire a sufficient immunity at the end of the first grazing period (estimated by blood pepsinogen measurement). They should be treated again for the next grazing season. Knowing that the treatment cost varied between 5 and 21 € in drugs per heifer and per year, a better parasitism management in the future should improve the economical and ecological performance.