Metabolic and Endocrine Responses to Feed Restriction and Refeeding in Kacang Goats

Abstract

Background: The ability of ruminants to undergo metabolic and endocrine adaptation to feeding restrictions and refeeding varies depending on the species and physiological characteristics, the age at which the feed restriction and refeeding are imposed, the rate and length of the feed restriction and refeeding, the physiological responses of various body parts to the feed restriction and refeeding conditions, sex and breed. Objective: The objective of this study was to evaluate the metabolic rates and endocrine responses of Kacang goats, Indonesian-bred ruminants, during the restricted feeding and refeeding periods. Methodology: Nine 1.5-2.5 year-old male goats were subjected to feed adaptation for the first 60 days. Then, the goats were subjected to three-level feed restriction for the second 60 days. The goats received 40, 50 or 60% feed restriction of dry fodder. The goats allocated to the 40, 50 or 60% feed restriction groups were referred to as group 1, 2 and 3, respectively. For the final 60 days, the goats underwent 100% refeeding with dry fodder. The weights of the ruminants were measured and blood samples were obtained at the end of the feed adaptation, feed restriction and refeeding. Results: At the end of the 60-day restriction, the three goats in group 3 were less than the baseline of Average Daily Gain (ADG), while the six other goats in groups 1 and 2 were still greater than the baseline of ADG, although there were no significant differences among the groups (p>0.05). The feed restriction increased lipolysis in adipose tissue and protein mobilization, non-esterified fatty acids (NEFAs) and albumin as the carrier of NEFA, creatinine and total protein in serum. Nonetheless, there were no differences among the three groups (p>0.05). Thyroid hormones (T3 and T4) as lipolytic hormones were ignored because their rates were lower than the baseline. Lipolytic responses in the form of High Density Lipoprotein (HDL) occurred in the three groups and there were significant differences among the three groups (p>0.05), indicating that triglycerides exported as Low Density Lipoprotein (LDL) were also not different among the three groups (p>0.05). This finding showed that there were no LDL secretion differences among the three groups. The two metabolic ketogenic effects, namely, Blood Urea Nitrogen (BUN) and glucose showed that BUN decreased to less than the baseline in group 2, although there were no significant differences among the groups (p>0.05). The glucose rate in group 2 was the highest among the groups (p<0.05), likely because of the low catabolism of labile protein deposits in group 2. After the refeeding was completed, the ADG in groups 2 and 3 increased significantly (p<0.05). In contrast, the ADG in group 1 did not increase significantly (p>0.05). Lipolysis continued to occur after the refeeding, with high rates of NEFA and albumin in the three groups without any differences among the groups (p>0.05). The lipolysis of hormones T3 and T4 was ignored, with both hormones remaining low. The rates of HDL and triglycerides exported as LDL were also constant and were not different among the three groups (p>0.05). Creatinine decreased significantly in the three groups (p<0.05) and there were no differences among the groups. The total protein increased significantly (p<0.5), but there were no differences among the three groups. The BUN metabolite did not change after refeeding was imposed on the three groups (p>0.05), although the BUN metabolite in group 1 tended to be higher than that in group 2. The glucose rate increased significantly in all three of the groups (p<0.05), although none of them reached the baseline. The ruminants in group 2 possessed the lowest glucose rate (p<0.05). Conclusion: A group of goats with a 50% restriction level of dry fodder tended to use ketones as the source of energy by suppressing protein degradation during feed restriction. The responses of ruminants to refeeding took the forms of continued lipolysis and increased protein degradation.