Abstract
Genetic variation for more than 40 traits was assessed in 26 stocks of mature chickens reared together and fed ad libitum from hatching to slaughter at 507 days of age. There was greater genetic variation among males than among females. The intraclass correlation, t, was high (>.75) for measures of size and weight and moderate (.20 to .60) for most other traits (P<.05) including a measure of lean distribution (.37). Three main categories of stocks were studied, viz. outbred Leghorns, medium-sized stocks, and contemporary heavy meat chickens. Differences in lean distribution were not associated with category, but differences of 40 to 50 g/kg lean in the breast of some stocks may be caused by a single gene. Lean:bone ratios were similar in medium and heavy stocks but were greater (P<,05) in heavy meat-types compared with outbred Leghorns. Bone density was higher (P<.01) in females compared with males and in outbred Leghorns compared with heavier stocks (P<.01). Heavy meat-type males were leaner (P<.01) and had proportionately less fat in the abdominal cavity than outbred Leghorns. Carcass fatness was similar among stocks of females, but abdominal fat was lower in Leghorns selected for high egg production compared with unselected Leghorns (P<.05) and heavy stocks (P<.001).One resistant and two Marek's disease-susceptible stocks were replicated in a specific pathogenfree (SPF) environment. Spleen weight was larger (P<.001) in the conventional environment. Females were relatively smaller (P<.05) than males in the conventional than in the SPF environment. Resistant strain females had larger (P<.05) viscera in the conventional environment.Body temperature (t = .25, P<.05) and feed intake were assessed in males. Heavy meat birds had a lower (P<.01) body temperature than outbred Leghorns and medium-sized stocks. Differences among stocks for feed intake (t = .77) were significant (P<.05); however, they were greatly reduced when feed intake was expressed as g/kg liveweight (LW) (t = .49) or g/kg LW.75 (t = .25). Outbred Leghorns ate less in absolute terms but significantly more (P<.01) as a proportion of LW or LW.75 than the medium and heavy lines.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
