One hundred 1-day-old Ven Cobb chicks were used to study the effect of supplementation with 0-2 mg chromium (Cr) per kg diet from potassium chromate (T1), chromium chloride (T2) and chromium-yeast complex (T3). The control group (C) received no supplemental chromium. Each experimental group consisted of five replicates of five birds each and the supplementation was continued for 35 days. The weekly live-weight gain, food conversion ratio and the live-weight gain: food intake ratio were unaffected by the treatments. Metabolizability of the organic nutrients increased in the Cr supplemented groups compared with the C group and significantly higher values were observed in the T3 group indicating beneficial effects of Cr-yeast complex. Intake of the trace elements (copper, zinc, iron and manganese) fulfilled the requirements specified for broiler chickens. Retention of all these trace elements was higher (P < 0-001 for Cu, Zn and Fe, P <0-01 for Mn) in all the Cr supplemented groups compared with that in the C group. Furthermore, in the T3 group the retention of copper, zinc, iron and manganese was higher (P < 0001) than that in the T1 and T2 groups. Two birds were slaughtered from each replicate at the end of 21 and 35 days of feeding to observe Cr in the liver; this was higher (P < 0-01) after 35 days feeding only. Despite supplementation, liver Cr was lower (P < 0-01) in T1 T2 and T3 groups. Cr concentration in the plasma was higher (P < 0-05) in the T3 and T3 groups than that in the C group although its concentration did not change with the age of the birds. Higher (P < 0-01) plasma concentrations of copper were observed in the T1 T2 and T3 groups titan those in the C group. The differences between the Cr supplemented groups in this respect were not significant, however. Liver copper was higher (P < 0-001) in C while liver iron was the lowest (P < 0-05) in that group. The concentrations of copper, iron (P < 0-01) and zinc in the liver (P < 0-05) were higher after 35 than after 21 days while those of manganese were not affected by slaughter age. Protein accretion in the meat tended to be increased in the Cr supplemented groups while deposition of fat in the meat was lower but these differences were not significant (P > 0-05). Other meat quality parameters including sensory evaluation scores improved due to Cr supplementation and Cr-yeast complex was found to have exerted significantly greater effects on these parameters. It was concluded that the supplementation of 0-2mg Cr per kg food dry matter would improve the performance of broiler chickens in terms of metabolizability of organic nutrients, retention of trace elements and meat quality.

Four diets were formulated to study the effect of a progressive substitution of grape pomace (GP) for alfalfa hay (AH) at the rates 0, 100, 200 and 300 g/kg total weight. The control diet contained 500 g AH and 192 g acid-detergent fibre per kg dry matter (DM). In experiment 1, 32 Californian × New Zealand White rabbits were used to determine dietary nutrient apparent digestibility. The inclusion of GP decreased the apparent digestibility of crude protein (P < 0·001) and energy (P < 0·05). However, the digestible energy (DE) contents of the diets were similar because GP had a greater gross energy content than AH. In experiment 2, 36 rabbits given the same diets as in experiment 1 were used to determine several digestive and productive traits and chemical body composition (at 20kg live weight). Dietary inclusion of GP linearly decreased ammonia (P < 0·01), total volatile fatty acid concentration (P < 0·001) and the molar proportion of acetate (P < 0·05) in the caecum. Starch content in the Heal and caecal contents was low but linearly increased (P < 0·05) with increasing dietary concentration of GP. The average daily gain (from weaning at 30 days of age to 2·0 kg live weight) was not significantly affected (P > 0·10) by the diet, but the ratio gain: food linearly decreased (P < 0·001) with the GP inclusion. Dietary inclusion of GP linearly increased (P < 0·10) the fat content of the empty body of the rabbits. The efficiency of utilization of dietary DE and protein for growth were calculated by the comparative slaughter method, using the chemical body composition data of 22 suckling rabbits slaughtered at 30 days of age for the initial body composition. The efficiency of utilization of DE was not influenced by dietary GP inclusion, but GP linearly increased (P < 0·01) digestible crude protein utilization. The decrease in crude protein apparent digestibility may be the main reason that gain: food ratio was impaired in diets containing GP substituted for AH.

Food intake and body weight of 119 mice was measured from 3 to 18 weeks of age. Residual food intake was calculated for each week as the variation in food intake independent of variation in weight gain, weight maintained and sex. Growth efficiency and maintenance requirement were calculated by fitting curves to data from 3 to 18 weeks. The repeatability of residual food intake was low in young mice, but increased as they matured. Growth efficiency was correlated with residual food intake in very young mice. Residual food intake was not correlated with maintenance requirement in young mice, but as mice matured the correlation of residual food intake with maintenance requirement increased to 0·6. Body composition at maturity was correlated with residual food intake and maintenance requirement of mature mice, but a large proportion of the variation in residual food intake and maintenance requirement was independent of body composition. The results suggest that the age at which residual food intake is measured is important if it is to be used as a criterion for selection for efficiency.

Data on 3783 Yorkshire, 2842 Landrace and 937 Duroc littermate pairs of boars, station tested between 1976 and 1989, were used to measure genetic parameters of average daily gain (ADG) from 30 to 90 kg, live backfat at 90 kg (BF), estimated lean growth rate (LGR), average daily food intake, food conversion ratio (FCR) and lean food conversion ratio (LFCR), as well as measures of residual daily food intakes over and above requirements for growth and lean growth. A method was developed to obtain restricted maximum likelihood estimates of genetic variances and covariances under an animal model when observations are on the means of sib pairs. Heritabilities of ADG, BF, LGR, FCR and LFCR were 0·43, 0·59, 0·39, 0·28 and 0·34, respectively. Heritability of daily food intake was 0·45, and heritability of measures of residual daily food intake ranged from 0·30 to 0·38. About half of the variation in daily food intake was residual (0·48 to 0·56). Genetic correlations of ADG with daily food intake, FCR and LFCR were 0·80, −0·28 and −0·09, respectively, and were small and positive (0·18 to 0·34) with measures of residual daily food intake. Backfat had genetic correlations of 0·42, 0·24 and 0·52 with daily food intake, FCR and LFCR, respectively, and genetic correlations between backfat and measures of residual daily food intake ranged from 0·15 to 0·61. Selection against residual food intake may be a useful means of improving efficiency of food utilization.