Exigência em proteína para cordeiras deslanadas em crescimento

Abstract

This thesis was composed of two studies. The first work was conducted to determine the net protein requirements for gain (NPg) of Santa Inês female lambs, and secondarily, evaluate five feed systems predictions for this characteristic. Fifty-seven female lambs were slaughtered following common procedures of comparative slaughter technique, being twenty-one slaughtered at the beginning of trial and the remaining animals were assigned in a completely randomized design with a 2 x 3 factorial arrangement (two nutritional planes, ad libitum or restricted, versus, three slaughter weights, 20, 28 or 36 kg, six animals per group). Animals body composition was assessed, and nutrients percentage and amount were modelled by means of Huxleys and von Bertalanffys mathematical functions. Besides, the predictions from AFRC (1993), CSIRO (2007), NRC (1985), NRC (2007) and SRNS (2010) were evaluated. The estimated asymptotes from fitted von Bertalanffy function were in a reasonable value for the evaluated animals. The net protein requirements derived from Huxleys function resulted in an average NPg of 12.5 g/100 g o EBW gain in animals with 30 kg of shrunk BW. The models evaluation showed that Santa Inês female lambs present a higher NPg compared to the feed systems predictions. Moreover, the SRNS (2010) presented the best accuracy for NPg estimative (CCC = 0.948, r = 0.985 , Cb = 0.963, RMSEP = 1.80 g). The second study aimed to evaluate the effect of slaughter weight and feeding management on carcass and body development of Santa Inês female lambs. The same animals from first study were used. Linear models were fit to assess nutritional and slaughter weight effects on body traits, carcass yields and composition. Also, a multivariate allometric study was performed to visualize the relationship between body parts associated to nutritional regimen during growth. Concurrent with an increase of slaughter weight body condition score, fat thickness, visceral fat depots, cold carcass weight, cuts and carcass composition also increased. Nutritional plane influenced hot and cold carcass weights (P 0.002), as well as hindlimb, blade, rib/flank and neck, which presented lower weights for restricted animals compared to ad libitum ones (P < 0.05). The allometric study revealed that body parts grow in different rates and nutritional plane influences some parts such as ribs/flank. Moreover, fat distribution among depots is not isometric, and a higher nutritional regimen may drive the energy intake to visceral fat rather than to carcass. Restricted animals presented a better balance on fat distribution, what indicates that common nutritional systems may overestimate nutrient demands for Brazilian sheep and possibly reduce livestock system efficiency.