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Divergent selection for residual feed intake in laying hens: effects on growth and fatness
Chapter 12
Divergent selection for residual feed intake in laying hens: effects on growth and fatness M. Tixier, A. Bordas and P. Merat
Introduction Divergent selection for adult residual feed intake, the 'R' criterion, has been undertaken in a Rhode Island population since 1976. The direct and correlated responses obtained after seven generations in the two lines R— and R+ have already been presented (Bordas and Merat, 1984). At that time, the R - females tended to be lighter than R+ females, while the reverse tendency appeared in the males. Furthermore, the proportion of abdominal fat tended to be higher in the R— dams of the seventh generation (67.1 g/kg against 58.6g/kg in the R+ dams), although this sample of hens did not show any difference between lines for body weight (Zein el Dein, Bordas and Merat, 1985). This result might indicate a change in relative fatness due to selection, since the hens in the first generation showed no significant difference between lines for that trait (63.9g/kg fat in the R+ females and 54.9g/kg in the R - females) (Merat, Bordas and Ricard, 1980). Following these preliminary observations, the present study is aimed at describing the correlated responses obtained on growth and body composition of young chickens from both lines.
Materials and methods A sample of 30 male chicks, representing the nine sire families of each line, was taken from the progeny of the tenth generation. Female chicks were not available for this study. Birds were housed in individual cages between 4 and 9 weeks of age and were fed ad libitum on a grower diet containing 11.7 MJ ME and 200 g crude protein/kg. Body weight was recorded at 35 days of age and 61 days of age while feed intake was measured over the same period. Birds were starved for 18 h before being slaughtered. Abdominal fat was dissected as described by Ricard and Rouvier (1967). The weights of liver and abdominal fat were expressed as proportions of slaughter weight. Phenotypic correlations were calculated between the measured traits. In the absence of a control line, selection response is estimated by the divergence between lines. The line effect was estimated by variance analysis. A specific analysis was made for abdominal fat and liver weight, including the body weight as covariate, in order to compare body composition at constant body weight. 129
130
Divergent selection for residual feed intake in laying hens: effects on growth and fatness
The results are presented in Table 12.1 together with the average performances of the adult birds from the tenth generation. The divergence on the selection criterion has become very important and is still increasing at each generation. The differences observed between the lines on the adult traits were also larger than in the previous generations and in the expected direction. As already noted, the adult body weight differed significantly between lines for the females but not for the males, the R - females being lighter. However the R - male chicks appeared to be significantly heavier than the R+ male chicks. Table 12.1 Average performances of young and adult males and females for both lines R+ and R—, at generation 10 RMale Adult Number of birds Body weight (g) Feed intake (g) Residual feed intake 'R' Egg weight (g) Egg mass/feed intake Wattle length (mm) Rectal temperature (°C) Comb temperature (°C)
40 3576 2409 -453 60.3 40.35 31.04
R+ Female
156
2313
2875 -222 54.2 0.40 24.8 40.01 31.46
Male
40 3621 3312
453
77.4 40.69 33.91
Female
161
2426 3510
222
55.2 0.34 33.4 40.06 33.21
Line effect
t Φ Φ t Φ Φ * Φ Φ
NS
Young Number of birds Body weight (g) 35 days 61 days Weight gain (g) Feed intake (g) Feed conversion Abdominal fat (g/kg body weight) Liver (g/kg body weight)
30 364 976 612
29 310 854 544
1864 3.08
1665 3.11
19.7
21.7
7.1
3.0
Φ Φ t Φ NS Φ Φ
*, P<0.05; t, P<0.01; φ, P<0.001; NS, P>0.05
They showed a higher proportion of abdominal fat in the carcass but the level of fatness remained low in both lines. The food conversion ratio was rather high and did not differ between lines. The proportion of liver was significantly lower in the R - chicks and appeared negatively correlated with the slaughter weight (-0.31, P<0.05). Abdominal fat was positively correlated in both lines with final body weight (+0.44, P<0.001), weight gain (+0.44) and food consumption (+0.43), as already found in broiler strains (Pym and Solvyns, 1979). Abdominal fat was negatively correlated with food conversion ratio (-0.33), but the partial correlation calculated at constant body weight was not significant (+0.08). The line effect on abdominal fat remained significant at constant body weight, as shown by the covariance analysis.
References
131
Discussion and conclusion These results clearly show that the selection on feed efficiency of the adult bird had no correlated response on efficiency growth. However, body weight has been changed both in the adult and in the young but in a different way, depending on sex. The R - laying hens appeared lighter, although no consistent difference was observed in the female chicks in the last three generations (unpublished data). The R - male chicks appeared heavier but no consistent difference was noted in adult males. This could suggest a change in growth rate in spite of a common final body weight in the males. As compared to previous results, the line effect on male chicks' body weight was greater when birds were housed in individual cages instead of in groups on litter (unpublished data). No clear explanation has yet been found for the difference in response between sexes. However, the selection criteria used in males and in females do not rely upon the same physiological basis: the R of the males deals mainly with the maintenance requirements, feed intake being only related to body weight and weight gain, whereas the R of the females also involves the efficiency of egg production. Furthermore, R is calculated independently of body weight on a phenotypic basis but a genetic correlation might still exist between R and body weight. Correlations between the R of the females and the 8-week body weight of the progeny have been calculated in the last two generations: they were very low except for the value obtained for male progeny in the eighth generation of the R - line, where it reached - 0 . 3 . A confirmation of this correlation would be in agreement with the present data on R - chicks. The results appear more consistent for abdominal fat. The R - male chicks showed a higher proportion of fat in the carcass; the same tendency was previously observed in R - laying hens. Furthermore, plasma level of triglycerides in the R selected sires was significantly higher than in the R+ selected sires at the ninth generation with 1.23g/litre against 0.82g/litre (P<0.05). These characteristics could be related to the lower body temperature and to the shorter wattle length of the R— line which indicate lower heat production and loss. Additional physiological characteristics, such as thyroid hormone plasma levels, should be measured. The more efficient line for egg production would thus appear to be the fatter: this would differ from the relationship found between feed efficiency and fatness in broiler strains (Pym and Solvyns, 1979; Leenstra, Vereijken and Pit, 1986). This conclusion should of course be confirmed by a further study including both lines and sexes at both ages. References BORDAS, A. and MERAT, P. (1984) Correlated responses in a selection experiment on residual feed intake of adult Rhode Island red cocks and hens. Annales Agriculturae Fenniae, 23, 233-237 LEENSTRA, F. R., VEREIJKEN, p. F. G. and PIT, R. (1986) Phenotypic and genetic variation in, and correlations between, abdominal fat, body weight and feed conversion. Poultry Science, 65, 1225-1235 MERAT, p., BORDAS, A. and RICARD, F. M. (1980) Composition anatomique, production d'oeufs et efficacite" alimentaire de poules pondeuses. Correlations ph£notypiques. Annales de Ginitique et de Silection Animate, 12, 191-200 PYM, R. A. E. and SOLVYNS, A. J. (1979) Selection for food conversion in broilers: body composition of birds selected for increased body weight gain, food consumption and food conversion ratio. British Poultry Science, 20, 87-97
132
Divergent selection for residual feed intake in laying hens: effects on growth and fatness
RICARD, F. M. and ROUVIER, R. (1967) Etude de la composition anatomique du poulet de chair. I. Variabilite de la repartition des differentes parties corporelies chez des coquelets Bresse Pile. Annales de Zootechnie, 16, 23-39 ZEIN EL DEIN, A., BORDAS, A. and MERAT, p. (1985) Selection divergente pour la composante 'residuelle' de la consommation alimentaire des poules pondeuses: effets sur la composition corporelle. Archiv für Geflügelkunde, 49, 158-160
Divergent selection for residual feed intake in laying hens: effects on growth and fatness M. Tixier, A. Bordas and P. Merat
Introduction Divergent selection for adult residual feed intake, the 'R' criterion, has been undertaken in a Rhode Island population since 1976. The direct and correlated responses obtained after seven generations in the two lines R— and R+ have already been presented (Bordas and Merat, 1984). At that time, the R - females tended to be lighter than R+ females, while the reverse tendency appeared in the males. Furthermore, the proportion of abdominal fat tended to be higher in the R— dams of the seventh generation (67.1 g/kg against 58.6g/kg in the R+ dams), although this sample of hens did not show any difference between lines for body weight (Zein el Dein, Bordas and Merat, 1985). This result might indicate a change in relative fatness due to selection, since the hens in the first generation showed no significant difference between lines for that trait (63.9g/kg fat in the R+ females and 54.9g/kg in the R - females) (Merat, Bordas and Ricard, 1980). Following these preliminary observations, the present study is aimed at describing the correlated responses obtained on growth and body composition of young chickens from both lines.
Materials and methods A sample of 30 male chicks, representing the nine sire families of each line, was taken from the progeny of the tenth generation. Female chicks were not available for this study. Birds were housed in individual cages between 4 and 9 weeks of age and were fed ad libitum on a grower diet containing 11.7 MJ ME and 200 g crude protein/kg. Body weight was recorded at 35 days of age and 61 days of age while feed intake was measured over the same period. Birds were starved for 18 h before being slaughtered. Abdominal fat was dissected as described by Ricard and Rouvier (1967). The weights of liver and abdominal fat were expressed as proportions of slaughter weight. Phenotypic correlations were calculated between the measured traits. In the absence of a control line, selection response is estimated by the divergence between lines. The line effect was estimated by variance analysis. A specific analysis was made for abdominal fat and liver weight, including the body weight as covariate, in order to compare body composition at constant body weight. 129
130
Divergent selection for residual feed intake in laying hens: effects on growth and fatness
The results are presented in Table 12.1 together with the average performances of the adult birds from the tenth generation. The divergence on the selection criterion has become very important and is still increasing at each generation. The differences observed between the lines on the adult traits were also larger than in the previous generations and in the expected direction. As already noted, the adult body weight differed significantly between lines for the females but not for the males, the R - females being lighter. However the R - male chicks appeared to be significantly heavier than the R+ male chicks. Table 12.1 Average performances of young and adult males and females for both lines R+ and R—, at generation 10 RMale Adult Number of birds Body weight (g) Feed intake (g) Residual feed intake 'R' Egg weight (g) Egg mass/feed intake Wattle length (mm) Rectal temperature (°C) Comb temperature (°C)
40 3576 2409 -453 60.3 40.35 31.04
R+ Female
156
2313
2875 -222 54.2 0.40 24.8 40.01 31.46
Male
40 3621 3312
453
77.4 40.69 33.91
Female
161
2426 3510
222
55.2 0.34 33.4 40.06 33.21
Line effect
t Φ Φ t Φ Φ * Φ Φ
NS
Young Number of birds Body weight (g) 35 days 61 days Weight gain (g) Feed intake (g) Feed conversion Abdominal fat (g/kg body weight) Liver (g/kg body weight)
30 364 976 612
29 310 854 544
1864 3.08
1665 3.11
19.7
21.7
7.1
3.0
Φ Φ t Φ NS Φ Φ
*, P<0.05; t, P<0.01; φ, P<0.001; NS, P>0.05
They showed a higher proportion of abdominal fat in the carcass but the level of fatness remained low in both lines. The food conversion ratio was rather high and did not differ between lines. The proportion of liver was significantly lower in the R - chicks and appeared negatively correlated with the slaughter weight (-0.31, P<0.05). Abdominal fat was positively correlated in both lines with final body weight (+0.44, P<0.001), weight gain (+0.44) and food consumption (+0.43), as already found in broiler strains (Pym and Solvyns, 1979). Abdominal fat was negatively correlated with food conversion ratio (-0.33), but the partial correlation calculated at constant body weight was not significant (+0.08). The line effect on abdominal fat remained significant at constant body weight, as shown by the covariance analysis.
References
131
Discussion and conclusion These results clearly show that the selection on feed efficiency of the adult bird had no correlated response on efficiency growth. However, body weight has been changed both in the adult and in the young but in a different way, depending on sex. The R - laying hens appeared lighter, although no consistent difference was observed in the female chicks in the last three generations (unpublished data). The R - male chicks appeared heavier but no consistent difference was noted in adult males. This could suggest a change in growth rate in spite of a common final body weight in the males. As compared to previous results, the line effect on male chicks' body weight was greater when birds were housed in individual cages instead of in groups on litter (unpublished data). No clear explanation has yet been found for the difference in response between sexes. However, the selection criteria used in males and in females do not rely upon the same physiological basis: the R of the males deals mainly with the maintenance requirements, feed intake being only related to body weight and weight gain, whereas the R of the females also involves the efficiency of egg production. Furthermore, R is calculated independently of body weight on a phenotypic basis but a genetic correlation might still exist between R and body weight. Correlations between the R of the females and the 8-week body weight of the progeny have been calculated in the last two generations: they were very low except for the value obtained for male progeny in the eighth generation of the R - line, where it reached - 0 . 3 . A confirmation of this correlation would be in agreement with the present data on R - chicks. The results appear more consistent for abdominal fat. The R - male chicks showed a higher proportion of fat in the carcass; the same tendency was previously observed in R - laying hens. Furthermore, plasma level of triglycerides in the R selected sires was significantly higher than in the R+ selected sires at the ninth generation with 1.23g/litre against 0.82g/litre (P<0.05). These characteristics could be related to the lower body temperature and to the shorter wattle length of the R— line which indicate lower heat production and loss. Additional physiological characteristics, such as thyroid hormone plasma levels, should be measured. The more efficient line for egg production would thus appear to be the fatter: this would differ from the relationship found between feed efficiency and fatness in broiler strains (Pym and Solvyns, 1979; Leenstra, Vereijken and Pit, 1986). This conclusion should of course be confirmed by a further study including both lines and sexes at both ages. References BORDAS, A. and MERAT, P. (1984) Correlated responses in a selection experiment on residual feed intake of adult Rhode Island red cocks and hens. Annales Agriculturae Fenniae, 23, 233-237 LEENSTRA, F. R., VEREIJKEN, p. F. G. and PIT, R. (1986) Phenotypic and genetic variation in, and correlations between, abdominal fat, body weight and feed conversion. Poultry Science, 65, 1225-1235 MERAT, p., BORDAS, A. and RICARD, F. M. (1980) Composition anatomique, production d'oeufs et efficacite" alimentaire de poules pondeuses. Correlations ph£notypiques. Annales de Ginitique et de Silection Animate, 12, 191-200 PYM, R. A. E. and SOLVYNS, A. J. (1979) Selection for food conversion in broilers: body composition of birds selected for increased body weight gain, food consumption and food conversion ratio. British Poultry Science, 20, 87-97
132
Divergent selection for residual feed intake in laying hens: effects on growth and fatness
RICARD, F. M. and ROUVIER, R. (1967) Etude de la composition anatomique du poulet de chair. I. Variabilite de la repartition des differentes parties corporelies chez des coquelets Bresse Pile. Annales de Zootechnie, 16, 23-39 ZEIN EL DEIN, A., BORDAS, A. and MERAT, p. (1985) Selection divergente pour la composante 'residuelle' de la consommation alimentaire des poules pondeuses: effets sur la composition corporelle. Archiv für Geflügelkunde, 49, 158-160