The effect of dietary protein on growth, carcass traits and some specific intestinal intestinal peptide and amino acid transporters in broiler chickens was studied. Birds received a common pre-test diet, and were subsequently fed either a standard positive control diet (PC) or a reduced CP diet (RCP) from 21 to 42 d of age. Growth was negatively impacted with feeding of RCP as manifested by an increase in feed consumption and feed conversion ratio. Carcass traits also showed evidence of negative effects of feeding the RCP diet, leading to a reduction in carcass and breast meat yield and an increase in abdominal fat percentage. Blood plasma total protein was reduced when the broilers were fed the RCP diet. Expression of mRNA for one peptide (PepT1) and four AA intestinal transporters (b o,+AT; CAT2; y+LAT2; EAAT3) was measured from the jejunum. Quantified mRNA for the AA transporters y+LAT2 and EAAT3 showed that they were up-regulated in chickens fed the RCP-diet. The transport systems PepT1, b o,+AT, and CAT2, were not affected by the dietary treatment imposed. The live and processing data validated the in vivo portion of the study and elucidated the negative impact of feeding the RCP diet, while the responses observed with the expression of the various transporters may help provide some insight on the physiological consequences and adaptations that birds endure when provided diets too low in CP for abnormally extended periods of time.

Dietary lysine has been shown to impact the performance of broilers, particularly with aspect of breast meat accretion and yield. There have been studies that suggest that early dietary lysine has an effect on breast meat yield in male broilers. A study was designed to evaluate starter dietary lysine (1.20 vs 1.35% of diet as achieved by the addition of L-lysine at the expense of a filler) effect on performance of female broilers from three different genetic strain crosses, and monitor subsequent effects at 41 and 56 d of age. Body weight and feed consumption were higher for birds consuming the high lysine starter diet, but feed conversions were similar when compared to the low lysine diet. Body weight and feed conversion were similar among strains. Mortality was unaffected by lysine level and strain cross. Carcass and breast meat weight, but not yields, were higher in birds fed the high lysine diet. At 56 d differences in carcass yield, abdominal fat, and breast meat yield were seen among strains, such that the strain with highest yield had the least amount of abdominal fat in terms of absolute weight and percentage. No effect on processing yields by dietary lysine was observed at any time regardless of the growing characteristics of the broilers. However, for early slaughter ages, feeding high levels of dietary lysine during the starter phase could prove to be convenient when maximum live performance or breast meat absolute values are desiredin order to maintain the commercial quality of final products.