Effect of sex and dietary energy concentration on feed conversion ratio, growth and carcass characteristics in Merino X Border Leicester lambs.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 16 EFFECT OF SEX AND DIETARY ENERGY CONCENTRATION ON FEED CONVERSION RATIO, GROWTH AND CARCASS CHARACTERISTICS IN MERINO X BORDER LEICESTER LAMBS N.A. AHMAD and H. LLOYD DAVIES SUMMARY Four Merino X Border Leicester rams, 4 wethers and 4 ewes were given a high energy diet (HE) ad lib. and 4 rams, 4 wethers and 4 ewes were given a low energy diet (LE) ad lib. and were grown to a final full live weight of 35 kg. HE lambs had significantly higher dressing percentage, lower feed conversion ratio, grew faster, had a greater amount of kidney channel and pelvic fat, more dissectable subcutaneous fat, less bone, a higher percentage of lipids and a lower percentage of water than LE lambs. Rams had a significantly faster rate of growth, better feed conversion ratio and their carcasses had a larger percentage of water than ewes. Rams had significantly lower dressing percentage, less omental fat and lower fat thickness than wethers and ewes. Ewes had significantly more kidney, channel, pelvic and mesenteric fat and a lower percentage of dissectable bone `than rams and wethers. Ram carcasses had significantly higher percentage of dissectable muscle, lower percentage of dissectable fat, a higher percentage of protein and a lower percentage of lipids than wether and ewe carcasses. There was no significant interaction between dietary energy concentration and sex. Sex, energy concentration, carcass composition.) (Keywords: INTRODUCTION Carcass composition within a genotype is mainly a function of empty body weight (Burton and Reid 1969). Composition may be altered by nutrition at the same body weight (Usborne et al. 1961, Soeparno and Davies 1982). Rams grew faster, had a lower feed conversion ratio, produced leaner carcasses with more protein and less fat than wethers and ewes (Oliver et al. 1967). The interaction between the sex and dietary energy concentration upon growth and carcass characteristics has rarely been investigated. This experiment was undertaken to determine the effect of dietary energy concentration and sex on the feed conversion ratio, growth and body composition in Merino X Border Leicester lambs. MATERIALS AND METHODS Animal manaqement and diet Twenty-four Merino X Border Leicester lambs (8 rams, 8 wethers and 8 ewes) were randomized into 24 individual pens. The initial live weights were 22.5, 22 . and 19.7 kg for rams, wethers and ewes respectively. Also 2 rams, 2 wethers and 2 ewes from the same flock were slaughtered at the beginning of the experiment to determine the initial composition of the group. They were grown to a terminal full live weight of 35 kg. Four of each sex were given a high energy (pelleted) diet and four of each sex were given a low energy diet. The high energy diet (as fed basis) consisted of 690g/kg wheat, 240g/kg lucerne chaff, 50g/kg soyabean meal and 20g/kg of a complete mineral mixture. The low energy diet was 7lOg/kg lucerne chaff, 230g/kg oaten chaff, 40g/kg soyabean meal and 20g/kg of the same mineral mixture used in the HE diet. Both diets were isonitrogenous and offered ad libitum. All sheep were fed three times a day and were weighed weekly. The chemical composition and energy concentration of the diets are given in Table 1. School of Wool and Pastoral Sci.ences, The University of New south Wales, P.O. Box 1, Kensington, N.S *w., 2033, Australia, 119 Proc. Aust. Soc. Anim. Prod. Vol. I6 Table 1 Dietary chemical composition Slaughtering and body composition measurements When animals attained a full live weight of 35 kg, they were fasted for 24 h, weighed, shorn, and slaughtered. Empty body weight and the weights of omental and mesenteric fat were recorded. After chilling the carcasses for 48 hours, kidney, kidney fat and channel and pelvic fat were removed. The carcasses were split down the midline and the fat thickness between the 12th and 13th ribs measured. The right sides were physically separated into lean, fat and bone and the left sides were chopped, ground, subsampled and subjected to chemical analysis. Statistical analysis The data formed a factorial experiment (2 diets x 3 sexes) and were analysed by standard analysis of variance (Harvey 1972). One way diet by sex interaction was evaluated. Means were then compared using Duncan's new multiple range test. RESULTS The initial body composition of the lambs of each sex is given in Table 2. Two animals of each sex were used for this part of the study and at this age (1620 weeks) and weight (22 kg rams and wethers, 20 kg ewes) differences in either dissectable tissue or chemical composition were small and of no biological significance. Table 2 Means and standard errors of dissected tissue and chemical components of the initial slaughter group (2 individuals per group) Means in the same row with different superscripts are significantly different (P < 0.05). 120 Proc. Aust. Soc. Anim. Prod. Vol. 16 Means and standard errors for the effect of dietary energy concentration and sex on performance and carcass characteristics are given in Table 1. Table 3 Means and standard errors for the effect of dietary energy concentration and sex on feed conversion ratio, growth and carcass characteristics of Merino X Border Leicester lambs For both sex and diet means in the same row with different superscripts are significantly different (P < 0.05). Dietary effect The HE lambs had significantly higher dressing percentages, lower feed conversion ratios, grew faster and deposited more fat at the kidney, channel and pelvic regions than LE lambs (P < 0.05). The IE lambs had 14% less omental fat, 16% less mesenteric fat than the HE lambs and 16% reduction in fat thickness but these differences were not statistically significant. The percentage dissectable subcutaneous fat was higher (18%) for HE lambs. The HE lamb carcasses had higher percentages of fat and lower percentage of water than LE lamb carcasses (P < 0.05). The % crude protein was not different between the two groups. 121 Proc. Aust. Soc. Anim. Prod. Vol. 16 Sex effect Rams had a significantly faster rate of growth, a lower feed conversion ratio than ewes (P < 0.05). Differences between rams and-wethers, and between wethers and ewes for the growth rate and feed conversion ratio were not significant. Dressing percentage, fat thickness and omental fat were higher for wethers and ewes than rams (P < 0.05). Ewes had significantly more kidney, channel, pelvic and mesenteric fat than wethers and rams, while wethers and rams contained more dissectable bone than ewes (P < 0.05), but these traits did not differ between rams and wethers. Ram carcasses had significantly more dissectable muscle and a lower percentage of dissectable fat than wether and ewe carcasses (P < 0.05). Ash and protein proportions were higher for the ram carcasses. Wethers and ewes had significantly (P < 0.05) more fat than rams. Interaction There was no signifi cant interact ion statistical ly between the diet and sex nor was there any trend in the data to suggest the pos sibility of an interact ion. DISCUSSION The results on the effect of dietary energy concentration are in agreement with those of Soeparno and Davies (1982). In this work, the investigation was extended 'to determine whether those findings applied to entire males and females as well as to wethers and particularly whether or not there was an interaction between sex and diet. We found that animals on a high energy concentration diet were fatter than those on a low energy diet regardless of sex. In none of the studies was there any suggestion of a significant interaction between these two variables. REFERENCES A.R.C. (1980). The Nutrient Requirements of Ruminant Livestock,(Farnham Royal, U.K., C.A.B.) BURTON, J. H. and REID, R. T. (1969). J. Nutr. 97: 517. HARVEY, W. R. (1972). U.S. Dept. Agr. Econ. StatyCoop. Serv. ESCS - 15. OLIVER, W. M., CARPENTER, 2. L., KING, G. T. and SHELTON, J. M. (1967). J. Anim. Sci. 26: 307. S SOEPARNO and DAVIES, H. Lloyd (1982). Proc. Aust. Soc. Anim. Prod. 14: 503. USBORNE, W. R., BRIEDENSTEIN, B. C., SOKOLOWSKI, J. H., GARRIGUS, U. S. and HATFIELD, E. E. (1961). J. Anim. Sci. 20: 921. C 122