Early selection and best management practice for dairy heifers to increase dairy farm profitability

Raising an excessive number of heifers has a direct impact on the cost of production because it increases raising costs and costs associated with premature culling. Genetic is often the only criteria used for selection. It is now known that other factors such as the immunity transfer, the milk consumption, and the average daily gain can also influence the future productivity of heifers. Those factors could also have a long term impact on metabolic functions. Up to now researchers working on the impact of heifer management on cow productivity have focused their work on the entire growth period. It is now needed to revisit those concepts in order to develop a selection tool to choose earlier, during the two first weeks of life, the heifers with the best potentials. In addition, weight gain is one of the main factor actually used to evaluate heifer management. The main tool use for this evaluation on farm is a tape for thoracic circumference measurements. The correlation between this measure and animal weight has been validated for animal weighting more than 100 kg. A validation of this tool is needed for young calves. Therefore, the aim of this study would be: 1) to develop a tool for early heifer selection; 2) to evaluate the impact of milk replacer management on heifer weight gain, cow productivity and gene methylation; 3) to validate or improve the use of a measuring tape used to evaluate the weight of young heifers. In order to fulfill these objectives, two experiments using 250 heifers each will be done on two farms with automatic calf feeders. The first experiment will investigate two program of milk replacers offered (limited quantity vs. ad libitum). The second experiment will investigate the feeding program of the automated calf feeder from day 10 to weaning (1 month ad libitum + 3 steps until weaning vs. 1 month as desired + 4 steps until weaning). For both experiments, heifers will be distributed randomly on treatments. Data will be collected three times each week for the first three weeks of life of each heifer. Afterward, data on heifers will be collected every two weeks until weaning. To evaluate the impact of feeding management on daily weight gain and cow productivity, heifers will be weighted before their first insemination and during the days following their calving. Milk production will be recorded during the three first month of lactation. Statistical analysis of these data will allow for the determination of the most important factors to include in the selection tool and the validation of the tape for weight evaluation. Finally, a subsample of heifers in each treatment will be used to evaluate the impact of feeding management on epigenetic.