The effect of dietary crude protein level on growth, carcass and meat composition of male goat kids in Tunisia

Abstract

Effects of concentrate protein content on growth performances and body composition were studied on fifteen local goat kids. All kids were male with an average body weight of 23.3 kg (S.D.=2.1 kg) at the beginning of the experiment. Animals were randomly divided into three groups of five kids each. Goats in each group received individually oat hay ad-libitum and one of three concentrates containing low, medium or high crude protein level. Low, medium, and high crude protein levels were 100, 130, and 160 g/kg of dry matter, respectively. All concentrates were isocaloric. The growth experiment lasted 12 weeks. In the following 2 weeks, digestibility was measured and then all kids were slaughtered. During the first 6 weeks of the experiment, kids fed low and medium crude protein diets gained less weight ( P<0.05) than those fed the highest protein level. In the rest of the experimental period, animals receiving the medium diet had the highest growth rate ( P<0.05). Digestibility of dry matter, organic matter, and crude protein was similar for the high and medium protein diets and was higher ( P<0.05) than that for the low diet. This same trend was found for the nitrogen balance except for the nitrogen retention. Diet content in crude protein seemed not to affect empty body and carcass weights, dressing percentage, and external (skin, head and feet) and thoracic organs (lungs and heart). However, goats fed medium protein level had the heaviest ( P<0.05) liver and gut among all animals. Muscle, bone and adipose tissue mean weights did not follow the increase of crude protein level in the diet. However, animals given medium crude protein diet had relatively more muscle ( P<0.01) and less fat ( P<0.05) than those fed high diets. Bone proportion was comparable among animals receiving the three diets. Animals fed high protein diet had more omental and mesenteric fat ( P<0.05) and total body fat in absolute ( P<0.05) and relative value ( P<0.01) than those offered the medium level, while values found for the low diet kids were intermediate. Meat of kids receiving the medium diet crude protein level was juicier than meat from other kids. It contented more protein ( P<0.05) and less fat ( P<0.01). Results from this work suggest that the optimum crude protein level in growing goats’ concentrate is approximately 130 g/kg DM and that any increase above this level seems no to improve meat production.