The effect of plane of nutrition on the growth and development of the east african dwarf goat III. The effect of plane of nutrition and sex on the carcass composition of the kid at two stages of growth, 16 lb. weight and 30 lb. weight

Abstract

1. Comparisons were made between the two sexes and the various treatments of kids at the 16 lb. stage and the 30 lb. stage. Kids were killed in such a manner that their fatless empty body weights were as uniform as possible at each dissection stage. This was achieved by slaughtering fat H-plane kids at somewhat heavier live weights than the less fatty L-plane kids. The experiment was successful in achieving uniformity of fatless empty dead weights at 16 lb., but not so successful at 30 lb. where significant differences existed between certain subclasses in the male series, the HH and LH having heavier fatless empty body weights than L.L and HL.2. The dry-matter percentages were in all cases highest for kids on H or eventual H planes of nutrition. On the basis of the total fatty bodies the differences were highly significant at both dissection stages, chiefly due to the larger amounts of fat, with very high dry-matter percentages, in the H-plane kids. On the basis of fatless bodies the differences were only significant at the 30 lb. stage. There were no differences in dry-matter percentages between the two sexes. The order of treatments with increasing dry-matter percentage was LL, HL, LH and HH.3. The proportions of the joints of the body were very uniform between sexes and the treatments. Male heads were larger than female heads, the difference being just significant at the 16 lb. stage only. Conversely, female hindlegs were significantly larger than male hindlegs at both stages studied. The effect of treatment on body proportions was that H kids had larger hindlegs than L kids, and significantly smaller heads. The female kids thus differed from male kids in body form in a similar fashion to the way H kids differed in body proportions from L kids.4. The effect of treatment on the carcass composition was greatest for the fatty tissues, H-plane kids in all cases having significantly larger amounts of fat. The treatment effect on all other tissues, that is on the fatless body, was very slight. H kids had slightly more muscle than L kids, but this difference was only statistically significant at the 16 lb. stage. This slightly larger amount of muscle in H-plane kids was offset by smaller amounts of bone, the differences in this case not being statistically significant at either dissection stage, and by smaller weights of alimentary canal, the difference again being significant only at the 16 lb. stage.The overall picture was one of great similarity in body composition between all the treatments employed in the experiment. The small differences which existed were only statistically significant at the 16 lb. stage when the heterogonic changes in body composition were most apparent. This picture of the effect of plane of nutrition on the body composition is very dissimilar to that claimed by other workers analysing their results on the basis of equal total weight of animal. The results confirm the provisional findings of the present writer using the chicken as the experimental material, and using a different design of experiment.5. The sex differences in body composition were larger and of greater statistical significance than the treatment differences discussed above. The females contained greater amounts of fat than males, the difference being greatest at the 30 lb. stage. In regard to the composition of the fatless body, the females differed from males in similar manner to the way H-plane kids differed from L kids. Females contained 2% more muscle and 1·5% less bone than males at 30 lb. Males possessed a greater proportion of skin, and a smaller proportion of visceral organs. The males had a much greater percentage of urinogenital organs, due to the basic differences in these structures between the sexes.6. The division of the body into total saleable percentage and non-saleable percentage showed that the only statistical differences existed between H and L treatments at 16 lb., when H kids had higher total saleable percentages than L kids at this stage, the difference being as great as 8%. Females tended to have a higher total edible carcass percentage than males, due to the larger amount of meat and edible offals in the female sex, but this difference was never statistically significant. The treatment difference demonstrated at 16 lb. is of no agronomic importance, since kids would not normally be slaughtered at this immature stage. By the time maturity was reached, the carcasses of the four treatments were remarkably uniform with regard to their economic composition.7. Sex and treatment differences were demonstrated by certain of the bone measurements. Male kids possessed thicker leg bones than females, and H kids had larger leg-bone diameters than L. At the 30 lb. stage the order of increasing minimum bone diameters was LL, HL, LH and HH. An identical picture was revealed by the series of data for bone volumes, but statistical differences could not be demonstrated for bone lengths or weights.8. Significant treatment differences were found in the weights of the rumen, reticulum, omasum, abomasum and in the lengths, but not the weights, of the small intestine. H-plane kids had larger abomasums than L, and L-plane kids had very much larger rumens, reticulums, omasums and bigger large intestines at the 16 lb. stage. These differences were related to the functional requirements of kids on different diets at the 16 lb. stage.9. Treatment differences were shown to exist in the weights of the heart, pancreas, kidneys and spleen at the 16 lb. stage, and in the liver weights at the 30 lb. stage. In all cases the H-plane kids contained larger visceral organs than L. Sex differences were significant for the heart, spleen and the pancreas. Females had larger hearts and smaller pancreas at 16 lb. than males, and females had bigger spleens at 30 lb. than males. It is suggested that these apparent sex differences may be due to greater amounts of fat contained in the structures of the female viscera.10. The only head structures to reveal sex and treatment differences were the eyes and tongue, which, like the total weight of the head itself, were larger in the L plane and the male sex.11. Male kids had significantly heavier skins than female kids at the 30 lb. stage. There were no treatment differences in the weight of the skin, and skins from all treatments alike were placed in the first grade by an experienced dealer.12. The thymus and abdominal lymphatic glands were significantly heavier in the female than in the male, and treatment exerted a significant effect in favour of the H-plane kids at the 16 lb. stage.13. The treatments exerted no effect on the early maturing ovaries or female genitalia, but the male kids which were initially on the L plane of nutrition had significantly heavier testes and penes than those which commenced growth on the H plane. The male gonads were the only organs studied in which the effect of initial plane of nutrition persisted at the 30 lb. dissection stage. In all other cases, the effect of initial plane of nutrition was masked or reversed by the nutritional level followed prior to sexual maturity.