Pre- and postweaning feeding strategies on growth and digestion of female Holstein calves

Abstract

This study evaluated the effects of pre- and postweaning feeding strategies on growth, digestibility, nitrogen metabolism, and ruminal fermentation in Holstein calves up to 5 mo of age. Eighty female calves were blocked by farm and week of birth and assigned to a 2 × 2 factorial arrangement: 10% (PRE10) or 20% (PRE20) of initial BW as milk replacer (MR) during preweaning, combined with postweaning feeding plans targeting an ADG of 500 (POST500) or 700 g/d (POST700). During preweaning, PRE20 calves consumed more MR and total DM, resulting in greater ADG, BW, and nitrogen intake per kilogram BW0.75; however, nitrogen efficiency and nitrogen retention were similar between preweaning treatments. Calves in PRE20 ingested less starter feed and accumulated less NFC, whereas PRE10 calves exhibited lower minimum daily ruminal pH. Contrary to our initial hypothesis, postweaning solid feed digestibility was not impaired. Both preweaning treatments surpassed the 15-kg cumulative NFC from starter feed threshold, supporting adequate digestive capacity after weaning. As expected, POST700 calves consumed more nutrients and achieved greater BW and BCS at 5 mo. No interactions among preweaning and postweaning feeding strategies were detected for body growth or diet digestibility. However, significant interactions were observed for nitrogen metabolism and ruminal fermentation shortly after weaning. Increased MR allowance enhanced nutrient supply and preweaning growth without compromising postweaning digestibility, reinforcing cumulative starter intake as the primary driver of digestive development. Restricted calves tended to retain more nitrogen and reached BW comparable to those fed greater MR when provided higher postweaning nutrition, highlighting compensatory growth. These results emphasize the importance of aligning pre- and postweaning feeding strategies to support physiological adaptation and optimize developmental outcomes of dairy heifers under postweaning forage-based diets.