Goat kids of different genders change the proteic metabolism when subjected to feed restriction

Abstract Text: The objective of this study was to evaluate the effect of gender and feed restriction on proteic metabolism of 72 Saanen goat kids (24 intact males, 24 castrated males and 24 females) with initial BW of 15.8±0.17 kg. At the beginning of the experiment 6 animals of each gender were slaughtered with 15 kg of BW to estimate their initial body composition, these animals were considered baseline for the comparative slaughter technique. The remaining animals of each gender were distributed into 6 groups of 3 animals subjected to different levels of feed restriction (ad libitum, 25% and 50% feed restriction). A whole group was slaughtered when the kid fed ad libitum reached 30 kg BW. Protein retention was estimated by the difference between the final and initial body composition. Blood samples were collected from all animals every 10 days, in a total of 7 collections for blood metabolites and 5 collections for hormones profile. In these samples we evaluated total protein, albumin, urea, creatinine, gamma glutamyltransferase (GGT), creatine kinase (CK), triiodothyronine (T3) and IGF-I.  Data were analyzed as split plot design, using mixed model of SAS. The retention of body protein (kg) was not affected by gender, only showing a linear decrease with the increase of feed restriction (P<0.0001). The total protein, creatinine and CK seric levels increased with the increase of experimental time (P<0.05). When fed ad libitum, urea concentration was highest in females (58.1 mg/dl), followed by castrated males (54.3 mg/dl) and intact males (51.2 mg/dl; P=0.0154). When the goats were subjected to 25% of feed restriction, the difference between genders was no longer observed, however, when subjected to 50% of feed restriction castrated males showed the highest serum urea level (54.02 mg/dl). The GGT activity in intact males was higher (P<0.0001) when they were fed ad libitum (51.31±1.58 U/L) and decreased with the increase of feed restriction. Whereas castrated males fed ad libitumpresented lower activities of GGT compared to those fed restricted and females remained constant at all levels of feed restriction. IGF-1 plasmatic were similar between castrated males and females (81.3 ng/ml), and lower than found in intact males (106.20 ng/ml; (P<0.0001). Intact males showed lower concentrations of T3 compared to females (P<0.05). Despite goats of different gender show similar protein accretion, they act physiologically different when subjected to feed restriction. Males changed their proteic metabolism to keep the protein synthesis.

Keywords: metabolism, sex