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This study examined the effect of different crude protein (CP) levels in the diet on growth performance of broilers as well as the total aerobic mesophilic count (TAMC) and Escherichia coli count (ECC) isolated from chicken faeces. A total 150 day-old broilers (Hubbard) were allocated to three treatments with five replicates containing 10 birds. The dietary treatments consisted of three diets with different CP levels for 42 days: highprotein (HCP, 22.5%), medium-protein (MCP, 20.5%), and low-protein (LCP, 18.5%). Body weight and feed intake were determined and the feed conversion ratio was calculated. Faecal samples were collected at 14, 21 and 42 days. Dietary CP did not affect the growth performance of broilers. Reducing CP level was effective at beneficially modulating the composition of the faecal microflora, in particular TAMC and ECC concentrations (log 10 CFU g -1 ) were significant lower for the LCP birds. During hot temperature conditions (33°C and 70% relative humidity) a low protein diet may help to control the characteristics of the faecal microbial community without negative effects on broiler performance.

This study was conducted to investigate relationships between mitochondrial respiratory chain complex activities, feed efficiency, and carcass traits in sheep. A group of Ghezel male lambs sired by a single ram were randomly allotted to individual pens. The lambs were fed ad libitum with a fattening diet containing 30% roughage (corn silage and alfalfa hay) and 70% concentrate for 70 d to individually phenotype each lamb for feed conversion ratio (FCR), adjusted FCR (aFCR), and residual feed intake (RFI). The lambs were then humanely killed and the liver, abdominal fat, pelvic fat, cardiac fat, warm carcass weight, and cold carcass weight, as well as the cross-sectional area of the LM and the fat depth over the 12th rib, were determined. A portion of LM was obtained to determine mitochondrial protein and respiratory chain complex activities (complexes I to V). Statistical analysis was carried out based on lambs exhibiting high and low RFI (n = 8), FCR (n = 8), or aFCR (n = 8) phenotypes. The lambs exhibiting the high-RFI phenotype consumed 110 g more feed daily (P < 0.05) than did the phenotype exhibiting low RFI, with no difference in ADG. Conversely, there was no difference in feed intake between the low- or high-FCR groups, but sheep exhibiting the low-FCR phenotype gained 70 g more (P < 0.05) per day compared with those exhibiting the high-FCR phenotype. It was determined that all 5 respiratory chain complex activities were greater (P < 0.05) in sheep exhibiting the low-RFI phenotype compared with those exhibiting the high-RFI phenotype, with significant (P < 0.001) negative correlation coefficients between RFI and respiratory chain complex activity. When efficiency was assessed using FCR, only activities of respiratory chain complexes III, IV, and V were less (P < 0.05) in the low-FCR phenotype compared with the high-FCR phenotype, and there were no differences (P > 0.1) in respiratory chain complex activities between groups when FCR was adjusted for metabolic BW (aFCR). There were no differences (P > 0.1) in carcass traits among any of the feed efficiency phenotypes. The results suggest that the inclusion of respiratory chain complex activities in breeding programs may be helpful in selecting for sheep exhibiting the low-RFI phenotype.

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