Energy and nitrogen metabolism of broilers selected over ten generations for increased growth rate, food consumption and conversion of food to gain

Abstract

Energy and nitrogen (N) metabolism were studied in 6-week-old male birds taken from 4 lines of chickens selected for 10 generations for increased weight gain (line W), increased food consumption (line F), increased conversion of food to gain (line E) or at random (controls, line C). Calorimetric measurements were made 8 times on each line while fed ad libitum in large open-circuit respiration chambers for 3 d, and 11 to 13 times without food in smaller closed-circuit respiration chambers for 24 h. The F line ate 60% more food, produced 90% more excreta and 34% more heat and retained 80% more energy and 35% more N in their bodies than lines E and C. Line W was intermediate. When differences in body weight were taken into account, the E and W lines had lower heat production than the C line, while the F line ate 40% more food, produced 30% more heat and retained 70% more energy and 30% more N than the E line. In lines W, F, E and C respectively, the mean metabolisability of dietary energy (%) was 69.4, 62.9, 70.1 and 67.8; the fasting heat production (mean +/- SE) was 481 +/- 9, 569 +/- 10, 485 +/- 9, and 508 +/- 9 kJ/kgW d; the net availability of metabolisable energy (NAME) was 0.68 +/- 0.05, 0.76 +/- 0.04, 0.85 +/- 0.06 and 0.73 +/- 0.04; the estimated daily maintenance energy requirements were 671 +/- 15,866 +/- 14,701 +/- 13, and 742 +/- 11 kJ ME/kgW; and the proportion of N retained per unit increase in N intake was 0.38 +/- 0.08, 0.50 +/- 0.06, 0.56 +/- 0.10 and 0.53 +/- 0.06. The contribution of line differences in the above traits to large line differences in efficiency of food utilisation is discussed.

Effect of the slow (K) or rapid (k+) feathering gene on body and feather growth and fatness according to ambient temperature in a Leghorn × brown egg type cross

“…The results of Lowe and Merkley [10] showed that body weight gains/food consumption ratios tended to favour the K/k + genotype, which our results suggest at 10 weeks, although not significantly. The effects of the k + gene observed by Pym et al [15] seem to agree with our observations.…”

Breeding for efficiency in the broiler chicken: A review

“…However, it may seem unlikely, as an overarching factor on which energy use efficiency is dependant, that this would have remained suboptimal after natural selection. Elsewhere, protein turnover has been credited to account for anywhere up to 30 % of broiler heat production, prompting some research into the genetic potential of reducing it (Millward et al 1976;Muramatsu et al 1987;Pym et al 1984). There has been some indication that higher protein accretion rates are achievable through selection by lowering protein degradation rates (Tomas et al 1988(Tomas et al , 1991.…”

“…There have been attempts to quantify the differences in the metabolic heat production rate between different broiler breeds (e.g. Pym et al 1984), and it has been suggested that it is lower in breeds selected for high feed efficiency or high weight gain than birds selected for high feed intake. Pym and Farrell (1977) showed the fasting metabolic heat production, indicative of the basal metabolic rate (Noblet et al 2013), to be 19 % higher in lines selected for high feed consumption when compared to a control line by using respiration chambers to carry out feeding experiments; this led to an estimated 10 % decrease in the feed use efficiency (Carré et al 2008).…”

Opportunities to improve nutrient efficiency in pigs and poultry through breeding

“…Pym et al (1984) found no differences in net N retention efficiency between broilers that had been selected for traits such as growth, food intake or FCR. Fractional rates of protein turnover did not differ between a line selected for high breast yield and a random bred control line (Pym et al, 2004).…”

“…Poultry Differences in (energy) maintenance requirements have been reported both between breeds of broilers and between breeds of laying hens. Whereas Geraert et al (1990) and Buyse et al (1998) have reported few differences in maintenance between broiler strains that have been selected against fatness, Pym et al (1984) have reported large differences between broilers that have been selected for traits such as growth, food intake or FCR. However, these differences were mainly due to the increased energy maintenance requirements of birds selected for food intake.…”