Boosting pre-weaning growth and feed efficiency in suckling calves: replacing starch with dry corn gluten feed.

This study examined how varying levels of by-product substitution for human-edible (HE) feed ingredients affected nutrient consumption, growth performance, feed conversion, skeletal characteristics, and nutritional behavior in Holstein calves. Forty-four calves (3 days old; initial body weight 40.1 ± 1.5 kg) were randomly assigned to one of four dietary treatments in a completely randomized design (n = 11 per group). Diets contained 0, 150, 300, or 450 g/kg dry matter (DM) of corn gluten feed (CGF), corresponding to 0, 15, 30, and 45% of DM, respectively. Growth performance indicators, including dry matter intake (DMI), average daily gain (ADG), and body weight (BW), improved in calves receiving 15% CGF, which consistently showed the highest intake and growth, particularly during the mid growth phase; BW and ADG responded quadratically to CGF level (P ≤ 0.01), whereas DMI and starter intake (SI) responded linearly (P ≤ 0.04), identifying 15% CGF as the optimal inclusion level. Skeletal measurements, including withers height, hip height, and heart girth, were likewise greatest in calves fed 15 and 30% CGF, with significant quadratic responses (P ≤ 0.05), although body length, body barrel, hip width, and pin width did not differ among treatments. Nutritional behavior, including eating, ruminating, and non-nutritive oral activities, did not differ significantly among treatments either before or after weaning (P > 0.05). In conclusion, moderate inclusion of CGF (15% of DM) provided the greatest benefits for calf growth, nutrient intake, and skeletal development, while higher inclusion levels (45%) resulted in diminishing returns, particularly in feed efficiency (FE). These findings suggest that incorporating CGF at optimal levels can enhance calf development without compromising feed quality.