Effect of weaning age on growth, mammary gland development, and immune function in Holstein Friesian calves fed conserved alfalfa (FiberStart)

This study aimed to evaluate intake, body growth, and the development of the rumen, mammary gland and immune system in Friesian calves reared for 100 d on FiberStart and fed calf milk replacer (CMR) for either 49 or 84 d. Eighty calves were reared indoors in single-sex groups (n=5/pen). All calves were fed 4L of CMR twice daily for 10 d, then once daily until d 49 (earlier weaned group) or 84 (later weaned group). Calves were gradually weaned by d 56 (earlier weaned group) and 91 (later weaned group). FiberStart (Modified Bio-Fermentation alfalfa treated with Xanotyde, Fiber Fresh Feeds Ltd., Reporoa, New Zealand) was fed ad libitum as the only solid feed from d 1 till 100 of the study. All calves had similar body weight at d 0 (40.9±3 kg) and 49 (74.2±5.1 kg). Earlier weaned calves consumed 18% more solid feed, but had 16% lower body weight gain (28.9 vs. 38.5 kg, respectively) from d 56 to 100 relative to later weaned calves, indicating that earlier weaned calves were unable to compensate for the loss of nutrients from the CMR on growth by increasing solid feed consumption. Plasma β-hydroxybutyrate concentrations were 62% greater in earlier than later weaned calves at d 84, indicating greater metabolic activity of the rumen. There was no evidence of an effect of the duration of CMR feeding on immune function of calves. Earlier versus later weaned calves had 5% lower mammary gland mass, indicating increased total nutrient intake increases mammary mass. The results of this experiment demonstrates the ability to artificially rear dairy calves with forage fiber as the only solid feed. Furthermore, early weaning off CMR promotes rumen development, but increasing the duration of CMR feeding improves growth and mammary gland mass by d 100. The implications of these findings on lifetime growth, health and milk production in dairy heifers warrant further investigation.