Energy and nitrogen retention and loss in broiler chickens genetically selected for leanness and fatness

Abstract

1. A breeding programme based on the assessment of the body fat content of broilers by measurement of plasma very low density lipoprotein concentration has resulted in 2 lines with significantly different body fat contents. 2. Energy and nitrogen intake and retention were measured in 63- to 70-d-old females from each line during 5-d periods of indirect chamber calorimetry. Results obtained by this technique were compared with results from a previously published growth trial incorporating carcase analysis at 49 d. 3. Body weight, metabolisable energy intake, heat production, energy retention and efficiency of energy retention did not differ significantly between the fat and lean lines. 4. The proportion of energy retained as crude protein and the efficiency of crude protein retention were significantly greater in the lean line. 5. In terms of whole-body energy and nitrogen exchanges, the essential difference between the lines was therefore in the partition of the same quantity of retained energy between fat and protein deposition. 6. The results were consistent with a higher rate of breakdown of amino acids in the fat line; because heat production did not also increase, a greater proportion of retained energy therefore became available for storage as fat.

The Efficiency of Protein Utilization in Different Broiler Strains

“…Significant differences in protein utilisation have been reported between lines selected divergently for body fatness (McLeod et al, 1988;Geraert et al, 1987;Tomas and Pym, 1995) or for high appetite, feed efficiency or growth rate (Geraert et al, 1987;Tomas et al, 1988;Tesseraud et al, 2000). The genetic diversity between these lines in terms of protein utilisation, is due entirely to the effects of selection, since in each case the lines were derived from the same founder population.…”

“…The comparison between commercial strains is much more complex, since it includes the effect of the different founder populations in the different parental lines and the effect of selection within the lines. In regard to the latter comparisons of high and low fat lines, McLeod et al (1988) , Geraert et al (1987) and Tesseraud et al (2000) found a higher gross efficiency of protein retention in the lean lines. These line differences were due to differences in the partition of retained energy between fat and protein deposition.…”

Review: Energy partitioning in broiler chickens

“…Since, at a given body weight, fat tissue contributes little to heat production compared with that of muscle, it is suggested that maintenance energy requirements are lower in fat animals than in lean animals (Close 1990). MacLeod et al (1988) found significantly higher fasting heat production and N retention in broiler lines selected for leanness than those selected for fatness, suggesting an increased maintenance energy requirement in lean birds. Questions still remain whether fat animals have lower MEm or if animals with a lower MEm become fatter (Van Milgen et al 1998).…”

“…There are few estimates of maintenance energy requirements in poultry (MacLeod et al 1988;Sakomura et al 2003) and, in particular, growing broilers Lopez and Leeson 2005).…”

Evaluation of sunflower meal as a feed ingredient in broiler chicken diets: the effect of using supplemental fat or pelleting

“…However, energy efficiency was significantly improved with the inclusion of sunflower meal, irrespective of the form of diet. Improvement in the efficiency of energy utilization is typically associated with reduced metabolic rate (Brody, 1945), decreased MEn Intakes and/(or) changes in the composition of gain (Macleod et al, 1988).…”