Development of divergent lines of lean and fat broilers using plasma very low density lipoprotein concentration as selection criterion; results over the fourth generation and lack of effect of dietary fat on performance and carcase fat content.

Comparisons were made of the performance and carcase composition of lean and fat broilers from the 4th generation of a breeding experiment which were fed diets containing 25 or 80 g fat/kg. Selection over the 4th generation resulted in continued divergence in the selection trait and the correlated responses of total body lipid and protein contents and the efficiencies of conversion of food and dietary protein. In both lines body weight, efficiency of food utilisation and total body lipid and protein contents were unaffected by dietary fat content. Tissue fatty acid composition was influenced by dietary and genetic factors: dietary fat increased the proportions of linoleic and oleic acids at the expense of palmitic, palmitoleic and stearic acids whilst greater body fatness increased the proportion of palmitoleic at the expense of linoleic acid.