Impact of the amount of milk replacer offers to Holstein dairy heifers on pre- and postweaning growth

The whole milk or milk replacer (MR) intake by dairy heifers during their preweaning period is known to have an impact on their early and long-term development, growth, and productivity. The objective of this study was to assess whether providing ad libitum access to MR in comparison to the Canadian milk feeding recommendation would impact growth performance during the preweaning period, and if those impacts would be maintained in the postweaning period, near puberty at around 11 months of age. On a commercial farm located in Quebec, Canada, 179 Holstein heifers were randomly assigned to two treatments where they were offered (1) ad libitum access to MR (AdLib, n = 93) or (2) a maximum amount of MR corresponding to 20% of their birth weights as currently recommended by the Canadian Code of Practice for the Care and Handling of Dairy Cattle (ReCan, n = 86). Weaning started at 52 and 64 d of age for AdLib and ReCan, respectively, and was completed at 76 d of age for both treatments. Milk replacer (28% CP, 16% fat, 15% DM) was offered using an automated feeding system, and the amount of MR was gradually reduced at weaning, over 24 and 12 d for AdLib and ReCan, respectively, with an identical program for the last 12 d. Data were collected for individual heifers to obtain live BW, heart girth circumference, withers height, hip height, and hip width during the preweaning (55 d) period and around puberty (around 11 mo). Mean MR intake at peak consumption between 46 d and 52 d was 11.8 L/d for AdLib vs 8.3 L/d for ReCan. Our results show that heifers on the AdLib treatment had significantly higher BW at 55 d of age and around puberty compared to heifers on the ReCan treatment. At weaning, no significant differences were observed for heart girth circumference, withers height, hip width, or average daily gain (ADG). Near puberty, the BW and hip height are significantly higher for the AdLib heifers and, when considering only heifers consuming a minimal amount of 7.5 L/d at the peak of consumption for the analysis, heart girth circumference, and ADG are significantly higher as well. Our results indicate that preweaning body conformation gains associated with an AdLib feeding program are maintained until puberty and this is even when compared to the current Canadian milk feeding recommendation of 20% of live weight in MR.