ABSTRACT:The objective was to evaluate the effects of genetic group and age on growth, carcass, and meat traits of rabbits. A total of 144 straightbred Botucatu and White German Giant × Botucatu crossbred rabbits were involved. Rabbits were weaned at 35 d and sequentially slaughtered, four per genetic group × sex combination, at: 42, 49, 56, 63, 70, 77, 84 05) were heavier in crossbreds than in straightbreds, but these differences were attributed to differences in SW. Uncorrected weights of head, kidneys, liver and thoracic viscera were higher in the crossbred group, but only head (116.6 vs. 113.6 g; P=0.06) and thoracic viscera (30.4 vs. 28.6 g; P=0.01) were, in fact, proportionately heavier in crossbreds than in straightbreds. No effect of genetic group was detected on meat to bone ratio, muscle ultimate pH and chemical composition of the Longissimus dorsi muscle. All traits, except for ash and fat contents of the Longissimus muscle, showed age effects (P<0.01). Crossbreeding may be recommended for the production of whole commercial carcasses, but it is not clearly advantageous for the production of retail cuts. Slaughter should take place between 63 and 70 d of age for both genetic groups.

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 3 2 (genetic groups 3 genders) factorial arrangement. Young rabbits were weaned at 35 days of age and sequentially slaughtered, four per genetic group 3 sex combination, at 42, 63 and 84 days of age. The flexor carpi radialis muscle was dissected, histological sections (10 mm) 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 3 sex 3 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.

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RESUMO -Esta pesquisa avaliou o efeito da separação mãe-ninhada sobre o desempenho reprodutivo de coelhas lactantes e ponderal das ninhadas até aos 70 dias de idade. Examinaram-se 415 exposições ao macho de 157 fêmeas lactantes distribuídas em dois grupos: controle, com livre acesso ao ninho, e tratado, cujo acesso bloqueou-se entre o sétimo e o nono dias pós-parto, durante as 39 horas que precederam a cobrição. Das 415 exposições ao macho, 387 resultaram em cobrições e 264 em partos. As fêmeas tratadas, de quinta lactação em diante, apresentaram receptividade e taxa de parição, respectivamente, 6,7% e 10,8% maiores em comparação às fêmeas do grupo controle. Não se constatou efeito da interação tratamento x ordem de lactação, ou do tratamento, com respeito ao número de láparos/ ninhada à desmama e nos 70 dias de idade. Em ninhadas de primíparas, a taxa de mortalidade da separação até 70 dias de idade foi maior no grupo tratado, em relação ao controle (0,248±0,047 vs. 0,120±0,047). O peso total da ninhada à desmama foi inferior no grupo tratado, do que no controle (5.753±93 g vs. 6.222±89 g) em todas as ordens. Todavia, não se observou diferença no peso total ou médio da ninhada nos 70 dias de idade. O tratamento também reduziu o peso individual à desmama (912,4±4,9 g vs. 962,7±4,5 g) em todas as ordens de lactação, entretanto, elevou o ganho de peso médio diário pós-desmama (32,25±0,19 g/d vs. 31,44±0,17 g/d), proporcionando a ocorrência de ganho compensatório neste período. Pode-se recomendar a separação temporária mãe-ninhada para melhorar o desempenho reprodutivo de coelhas lactantes multíparas; mas deve ser evitada para as primíparas, devido à elevação da taxa de mortalidade das ninhadas.Palavras-chave: bioestimulação, coelhos, desempenho de ninhadas, manejo reprodutivo, receptividade sexual, taxa de parição Bioestimulation of the Reproductive Activity of Lactating Rabbit Does in a NaturalMating System ABSTRACT -The objective was to evaluate the effect of temporary mother-litter separation on the reproductive performance of lactating does and growth performance of their litters up to 70 days of age. A total of 415 presentations of 157 lactating does assigned to two groups: control, with free nest access, and treated, whose nest access was closed during the 39 hours that preceded mating, were analyzed. From the 415 presentations, 387 resulted in matings and 264 in parturitions. Does of the treated group, from fifth and further lactations, had sexual receptivity and parturition rate, respectively, 6.7% and 10.8% higher than those females of the control group. No treatment by lactation order interaction, or treatment effects, were detected on number weaned and number of young per litter at 70 days. In litters of primiparous does, mortality rate from separation up to 70 days of age was higher in the treated group (0.248±0.047 vs.0.120±0.047). Litter weaning weight was lower in the treated group compared to the control group (5,753±93 g vs. 6,222±89 g), for all lactation orders, but no differences were detected i...