Digestibility, hormones and blood metabolites in dairy bucks subjected to underfeeding and refeeding

Sixteen mature dairy Alpine goat bucks (51±7 kg) were selected and fed a concentrate diet (2.9 Mcal/kg, DE) for 3 wk to maintain their body weight. They were then stratified by BW and randomly assigned to two treatment groups. Treatment 1 bucks (n = 8) were fed at maintenance for two consecutive periods of 21 d each while treatment 2 animals (n = 8) were fed at maintenance for 21 d followed by 21 d of feeding at 25% of maintenance. During the third 21-d feeding period, animals in both treatment groups were allowed ad libitum feed consumption. At the end of each dietary treatment period, body weights (BWs) were recorded, blood samples were collected and serumwas assayed for NEFA, plasma ureaN(PUN), LH, GH, and testosterone. Total feces were collected for 4 d to assess digestibility. Sub-maintenance feeding decreased fiber, OM, and EE digestibility and BW. Overall, bucks fed at 25% of maintenance intake had greater (P < 0.02) serum NEFA concentrations than when fed at maintenance, or during refeeding. During the refeeding period (ad libitum consumption), goats previously on the lowest plane of nutrition had lower (P < 0.011) plasma NEFA than those previously fed at maintenance levels (402 mg/dl vs. 632 mg/dl). Also, sub-maintenance feeding elevated (P < 0.002) PUN. Plasma urea N level when intake was ad libitum, was also affected (P < 0.003) by the previous level of feeding. BWgain was greater (P < 0.001) for bucks going from sub-maintenance to ad libitum compared to those fed from maintenance to ad libitum. Sub-maintenance feeding and the transition to ad libitum feeding did not affect LH, GH, or testosterone levels. These results suggest that undernutrition effects on digestibility disappear with refeeding and blood metabolites can be reversed by short-term refeeding. This can be used to maintain dairy bucks in temperate zones outside the breeding season. © 2007 Elsevier B.V. All rights reserved.