[Show abstract][Hide abstract] ABSTRACT: The experiment was conducted with the objective of predicting the dry matter (DM) digestibility of rations for growing rabbits, by means of equations based on the concept of ideal nutritive entity. One hundred 42-day-old rabbits from the Botucatu Genetic Group were used. Sixteen rations were tested, containing roughage (paper, corn cobs, sugarcane bagasse or pine shavings), plus corn, soybean meal, soybean oil, kaolin and common salt. Roughages were included at four levels, to obtain 22, 28, 34 or 40% neutral detergent fiber (NDF) and 16% crude protein (CP). The experiment was accomplished in two periods, in a randomized block design. Positive linear effect of NDF on DM intake was observed. The means of DM digestibility varied between 60.10 and 80.78%. There was a negative linear effect of NDF, as well as of the NDF content × roughage interaction on the DM apparent digestibility. Both CP and cell contents behaved as ideal nutritive entity, but the fibrous components did not. To predict DM digestibility, three models were tested; the best model was based on the cell contents, with true digestibility fixed at 1; another on the NDF content, whose digestibility was predicted by means of an empiric equation; and the third one on the endogenous loss of cell contents. The main difficulty in the formulation of models for apparent DM digestibility prediction is to estimate, with precision, NDF digestibility and cell contents endogenous loss. Future studies evaluating higher fiber levels in the diets are needed. For diets with fiber content within the range tested in the present study, model 3, which includes, besides neutral detergent fiber, acid detergent fiber and lignin, is recommended.
Full-text · Article · Dec 2011 · Revista Brasileira de Zootecnia
[Show abstract][Hide abstract] ABSTRACT: The purpose of this experiment was to evaluate the effect of adding whole cottonseed to the diet of feedlot cattle over the performance and carcass traits. Thirty six Nellore bullocks were used, with an average age of 20 months and average initial weight of 333.5kg. The animals were raised on feedlot and fed diets with the following content of whole cottonseed: 0; 14.35%; 27.51%; or 34.09% on a dry matter basis. The daily weight gain, final weight and dry matter intake decreased linearly as the proportion of cottonseed increased. No effect of cottonseed on total weight gain adjusted for intake was observed. Carcass and ribeye weights decreased linearly as cottonseed content increased. No effect of cottonseed content was observed for ribeye area. In contrast, back fat and rump fat thickness decreased as cottonseed content increased. A correlation of .62 was observed between back fat and rump fat. Adding whole cottonseed to beef cattle diets did not prove advantageous because it reduced animal performance and carcass fat deposition.
Full-text · Article · Jun 2011 · Arquivo Brasileiro de Medicina Veterinária e Zootecnia
[Show abstract][Hide abstract] ABSTRACT: The objective was to evaluate the effects of genetic group and age on growth, carcass, and meattraits of rabbits. A total of 144 straightbred Botucatu and White German Giant x Botucatu crossbred rabbitswere involved. Rabbits were weaned at 35 d and sequentially slaughtered, four per genetic group x sexcombination, at: 42, 49, 56, 63, 70, 77, 84 and 91 d. A 2-2 factorial arrangement was employed in a completelyrandomized design with repeated measures for growth traits, and a split-plot for carcass and meat traits.Crossbred rabbits were heavier (2032 vs. 1962 g; P<0.01), consumed more feed (143.5 vs. 131.0 g/d; P<0.01),and presented higher slaughter weight (2169 vs. 2093 g; P=0.02) and dressing percentage (59.0 vs. 58.2%;P=0.07) than straightbreds throughout the experiment. No difference between genetic groups was detectedfor feed conversion and empty gastrointestinal weight corrected for slaughter weight (SW). Crossbredsshowed higher skin weight (308.2 vs. 299.7 g; P=0.06) and distal parts of leg weight (75.7 vs. 71.4 g; P<0.01),both corrected for SW. No genetic group effect was detected on dissectible fat and hind part weights. Chilledcommercial carcass (1284 vs. 1229 g; P=0.02), chilled reference carcass (1036 vs. 1000 g; P=0.06), fore part(297.9 vs. 283.3 g; P=0.01) and loin (308.7 vs. 295.5 g; P=0.05) were heavier in crossbreds than in straightbreds,but these differences were attributed to differences in SW. Uncorrected weights of head, kidneys, liver andthoracic viscera were higher in the crossbred group, but only head (116.6 vs. 113.6 g; P=0.06) and thoracicviscera (30.4 vs. 28.6 g; P=0.01) were, in fact, proportionately heavier in crossbreds than in straightbreds. Noeffect of genetic group was detected on meat to bone ratio, muscle ultimate pH and chemical composition of theLongissimus dorsi muscle. All traits, except for ash and fat contents of the Longissimus muscle, showed ageeffects (P<0.01). Crossbreeding may be recommended for the production of whole commercial carcasses, butit is not clearly advantageous for the production of retail cuts. Slaughter should take place between 63 and 70d of age for both genetic groups.
[Show abstract][Hide abstract] ABSTRACT: This study was designed to investigate the effects of the interaction among genetic group, sex and age on the frequencies and cross-sectional areas of myofiber types in rabbits. A total of 48 straightbred and crossbred Botucatu rabbits, males and females, were involved in a split plot design with a 2 × 2 (genetic groups × genders) factorial arrangement. Young rabbits were weaned at 35 days of age and sequentially slaughtered, four per genetic group × sex combination, at 42, 63 and 84 days of age. The flexor carpi radialis muscle was dissected, histological sections (10 μm) were obtained and the frequencies and cross-sectional areas of myofiber types: I, IIA and IIB/X were determined. An effect of the genetic group × sex × slaughter age interaction was found on the frequency distribution of myofiber types. A transition from type IIA to type IIB/X fibers was observed (P < 0.01) with advancing age, except in crossbred females, but the frequency of IIA fibers was already lower (57.3%) and of IIB/X fibers numerically higher (33.7%) in this group at 42 days. The proportions of IIA fibers in straightbred males, crossbred males and straightbred females decreased from 80.1%, 89.4% and 68.8% at 42 days to 43.9%, 52.3% and 40.1% at 63 days, respectively, whereas the proportions of type IIB/X fibers, in the same groups, increased from 10.3%, 1.6% and 22.3% at 42 days to 42.2%, 37.0% and 49.8% at 63 days, respectively. In all three age points, type IIA fibers showed the largest cross-sectional areas, followed by type I and IIB/X fibers. The cross-sectional areas of IIB/X fibers were larger in crossbreds, but no differences were found between genetic groups concerning fiber types IIA and I. All three types of fibers showed positive linear association with age, but relative to the initial area type IIB/X fibers presented a higher degree of hypertrophy (144% up to 84 days) than type IIA and I fibers (86% and 85%, respectively). The flexor carpi radialis muscle was, on average, heavier in crossbred than in straightbred females, but no difference was observed between crossbred and straightbred males. Differences in the weight of flexor carpi radialis muscle were attributed to the hypertrophy of type IIB/X fibers in the crossbreds.