THE EFFECT OF DIETARY-PROTEIN CONTENT ON PERFORMANCE, CARCASS COMPOSITION AND ON CIRCULATING HORMONE LEVELS OF NAKED-NECK AND CONTROL BROILER-CHICKENS

The aim of this longitudinal study was to investigate the effects of a n isocaloric diet different in crude protein content (15% crude protei n, LP versus 20% crude protein, MP) on the performance, carcass compos ition and on plasma hormone levels of heterozygous Kabir naked-neck (N A/na+) and normal-feathered control (na+/na+) broiler chickens. Body w eight of na+/na+ chickens averaged higher compared to NA/na+ chickens. Decreasing the dietary protein content depressed live body weight in body lines to the same extent as no significant interaction between fe ed composition and line was observed. Cumulative feed intake was highe r for na+/na+ chickens but was not influenced by dietary composition. Cumulative feed conversion as well as abdominal fat content was not di fferent between lines but was higher for chickens of both lines when r eared on the LP diet. Chemical analysis of 56-day-old chickens reveale d a higher abdominal fat content of NA/na+ chickens but no significant line differences for dry matter, total fat and protein content. Feedi ng the LP diet increased abdominal fat, total fat and dry matter conte nt; an effect which was more pronounced for female than for male chick ens of both lines. Protein content was higher for males than for femal es and was decreased when chickens were reared on the LP diet. Feeding the LP diet significantly decreased plasma T4 and IGF-I levels wherea s plasma T3 and GH levels were increased. No significant differences b etween tines in hormonal status were observed.