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Selection Procedures for Altering Specific Nutrient Requirements in Poultry
SELECTION PROCEDURES FOR ALTERING SPECIFIC NUTRIENT REQUIREMENTS IN POULTRY S. P. WILSON
United States Department oj Agriculture1 (Received for publication February 27, 1967)
When selecting for lowered nutrient requirements by measuring growth (body weight at a given age or gain per unit of time) on a deficient diet, one assumes that the variation in the selected trait due to requirement differences among individuals is a sufficiently large portion of the total variation to allow for identification of those individuals with genetically lower requirements. However, this procedure allows all factors that affect growth, other than the nutrient being tested, to confuse the observable differences. In other words, heritability for a specific nutrient requirement most likely is quite low, even though heritability for growth is intermediate or even high. The obvious solution to the problem is to 1 Animal Husbandry Research Division, ARS, Beltsville, Maryland 20705.
devise a control system that maximizes the removal of differences in growth not attributable to the growth factor being studied. To do this on an individual basis, one would first establish the growth response of the chicks on a normal diet. Then, these same chicks would be switched to a deficient diet and their growth again measured. Length of feeding periods would depend somewhat on the specific nutrient carryover but could probably be hatching to three weeks and three weeks to six weeks, respectively. If lower specific nutrient requirement is desired, selection would be for those individuals that exhibit a minimum ratio of three week weight to six week weight (3 week wt./6 week wt.). The use of three week weight, established on a normal diet, removes a large segment of the variation in growth on the deficient diet not attributable to the nutrient under test; and, the use of a ratio of weights minimizes the inherent effect of three week weight on subsequent growth on the deficient diet. The key to this system is in the establishment, prior to the test on a deficient ration, of the individual bird's growth response to a normal ration and the utilization of this information to aid in identifying real differences in specific nutrient requirements. Also, with normal diets, it is assumed that the factors which control growth to a given age and subsequent growth are positively correlated. One drawback to the above described scheme is that it necessitates the establishment of the normal-diet growth response which eliminates beginning the test period at hatching. An alternative method which
773
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 19, 2015
Considerable effort has been and is now being expended in selecting for lowered specific nutrient requirements in poultry. Several reports have indicated the existence of genetic variance among lines, families and individuals for dietary utilization of specific nutrients or classes of nutrients (Griminger and Fisher, 1962; Harms and Waldroup, 1962; Nesheim and Hutt, 1962; Sibbald and Slinger, 1963; Davidson and Mathieson, 1965; and Enos and Moreng, 1965). However, Lepore (1965) failed to show a lower dietary requirement for methionine when selection was for body weight at three weeks on a methionine deficient diet. This report deals with the method of measuring such traits and suggests alternative systems that may enhance selection efficiency.
774
RESEARCH NOTES
Appetite or feed intake can be a problem in studies of nutrient utilization and may be a major source of error in identifying the real differences that exist. Certainly, those individuals with high intake would exhibit less depression when subjected to a specific deficiency and might be selected for this reason only. This problem can be minimized by controlling intake. However, if relative feed consumption for individuals or families is consistent over normal and deficient diets, the selection schemes de-
scribed in this report would effectively remove most of the bias associated with differential feed intake. It should be understood that the procedures outlined are proposed only as aids in identifying genetic differences in utilization of specific nutrients, provided such variation exists. Their efficiency, relative to uncontrolled selection, will vary with different nutrients. However, in cases where genetic variation exists, and, when compared to uncontrolled selection for body weight on a deficient diet, the described procedures should be more efficient in identifying genetic differences in nutrient utilization. REFERENCES Davidson, J., and J. Mathieson, 1965. Observations on the utilization of dietary energy by medium and fast growing strains of cockerels and on their arginine and methionine requirements. British Poultry Sci. 6: 225-233. Enos, H. L., and R. E. Moreng, 1965. Evidence of genetic variability for lysine utilization. Poultry Sci. 44:964-971. Griminger, P., and H. Fisher, 1962. Genetic differences in growth potential on amino acid deficient diets. Proc. Soc. Exp. Biol. Med. i l l : 754756. Harms, R. H., and P. W. Waldroup, 1962. Strain differences in the protein requirement of laying hens. Poultry Sci. 4 1 : 1985-1987. Lepore, P. D., 1965. Methionine and protein requirements of lines of chickens established by growth-rate selection on a methionine deficient diet. Poultry Sci. 44: 797-803. Nesheim, M. C., and F. B. Hutt, 1962. Genetic differences among White Leghorn chicks in requirement of arginine. Science, 137: 691-692. Sibbald, I. R., and S. J. Slinger, 1963. The effects of breed, sex, and arsenical and nutrient density on the utilization of dietary energy. Poultry Sci. 42: 1325-1332.
June 27-29. Annual Meeting of the Canadian Society of Animal Production, Macdonald College, Ste.-Anne de Bellevue, Quebec June 27-30. Annual Meeting, American Society of Agricultural Engineers, jointly with the Canadian Society of Agricultural Engineering, Saskatoon, Saskatchewan
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 19, 2015
would allow the test period to begin at hatching would involve a family selection system in which equal samples of each family, with sexes balanced between samples, would be tested concurrently on normal and deficient diets. The growth response of family samples on the normal diet would be used as an experimental control. Selection would be for those families that show minimum differences between the within-family, sample means on normal and deficient diets, respectively. In other words, those families with a lower specific nutrient requirement would exhibit less depression from being fed a specific nutrient deficient diet, and would show minimum differences between samples. The efficiency of this procedure is largely determined by the number of individuals tested per sample and the genetic relationship between within-family, sample means. Larger, more closely related samples should allow for increased efficiency in identifying genetic differences among families for utilization of a specific nutrient. Adequate numbers are imperative, and with full sibs more than one hatch might be necessary.
United States Department oj Agriculture1 (Received for publication February 27, 1967)
When selecting for lowered nutrient requirements by measuring growth (body weight at a given age or gain per unit of time) on a deficient diet, one assumes that the variation in the selected trait due to requirement differences among individuals is a sufficiently large portion of the total variation to allow for identification of those individuals with genetically lower requirements. However, this procedure allows all factors that affect growth, other than the nutrient being tested, to confuse the observable differences. In other words, heritability for a specific nutrient requirement most likely is quite low, even though heritability for growth is intermediate or even high. The obvious solution to the problem is to 1 Animal Husbandry Research Division, ARS, Beltsville, Maryland 20705.
devise a control system that maximizes the removal of differences in growth not attributable to the growth factor being studied. To do this on an individual basis, one would first establish the growth response of the chicks on a normal diet. Then, these same chicks would be switched to a deficient diet and their growth again measured. Length of feeding periods would depend somewhat on the specific nutrient carryover but could probably be hatching to three weeks and three weeks to six weeks, respectively. If lower specific nutrient requirement is desired, selection would be for those individuals that exhibit a minimum ratio of three week weight to six week weight (3 week wt./6 week wt.). The use of three week weight, established on a normal diet, removes a large segment of the variation in growth on the deficient diet not attributable to the nutrient under test; and, the use of a ratio of weights minimizes the inherent effect of three week weight on subsequent growth on the deficient diet. The key to this system is in the establishment, prior to the test on a deficient ration, of the individual bird's growth response to a normal ration and the utilization of this information to aid in identifying real differences in specific nutrient requirements. Also, with normal diets, it is assumed that the factors which control growth to a given age and subsequent growth are positively correlated. One drawback to the above described scheme is that it necessitates the establishment of the normal-diet growth response which eliminates beginning the test period at hatching. An alternative method which
773
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 19, 2015
Considerable effort has been and is now being expended in selecting for lowered specific nutrient requirements in poultry. Several reports have indicated the existence of genetic variance among lines, families and individuals for dietary utilization of specific nutrients or classes of nutrients (Griminger and Fisher, 1962; Harms and Waldroup, 1962; Nesheim and Hutt, 1962; Sibbald and Slinger, 1963; Davidson and Mathieson, 1965; and Enos and Moreng, 1965). However, Lepore (1965) failed to show a lower dietary requirement for methionine when selection was for body weight at three weeks on a methionine deficient diet. This report deals with the method of measuring such traits and suggests alternative systems that may enhance selection efficiency.
774
RESEARCH NOTES
Appetite or feed intake can be a problem in studies of nutrient utilization and may be a major source of error in identifying the real differences that exist. Certainly, those individuals with high intake would exhibit less depression when subjected to a specific deficiency and might be selected for this reason only. This problem can be minimized by controlling intake. However, if relative feed consumption for individuals or families is consistent over normal and deficient diets, the selection schemes de-
scribed in this report would effectively remove most of the bias associated with differential feed intake. It should be understood that the procedures outlined are proposed only as aids in identifying genetic differences in utilization of specific nutrients, provided such variation exists. Their efficiency, relative to uncontrolled selection, will vary with different nutrients. However, in cases where genetic variation exists, and, when compared to uncontrolled selection for body weight on a deficient diet, the described procedures should be more efficient in identifying genetic differences in nutrient utilization. REFERENCES Davidson, J., and J. Mathieson, 1965. Observations on the utilization of dietary energy by medium and fast growing strains of cockerels and on their arginine and methionine requirements. British Poultry Sci. 6: 225-233. Enos, H. L., and R. E. Moreng, 1965. Evidence of genetic variability for lysine utilization. Poultry Sci. 44:964-971. Griminger, P., and H. Fisher, 1962. Genetic differences in growth potential on amino acid deficient diets. Proc. Soc. Exp. Biol. Med. i l l : 754756. Harms, R. H., and P. W. Waldroup, 1962. Strain differences in the protein requirement of laying hens. Poultry Sci. 4 1 : 1985-1987. Lepore, P. D., 1965. Methionine and protein requirements of lines of chickens established by growth-rate selection on a methionine deficient diet. Poultry Sci. 44: 797-803. Nesheim, M. C., and F. B. Hutt, 1962. Genetic differences among White Leghorn chicks in requirement of arginine. Science, 137: 691-692. Sibbald, I. R., and S. J. Slinger, 1963. The effects of breed, sex, and arsenical and nutrient density on the utilization of dietary energy. Poultry Sci. 42: 1325-1332.
June 27-29. Annual Meeting of the Canadian Society of Animal Production, Macdonald College, Ste.-Anne de Bellevue, Quebec June 27-30. Annual Meeting, American Society of Agricultural Engineers, jointly with the Canadian Society of Agricultural Engineering, Saskatoon, Saskatchewan
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 19, 2015
would allow the test period to begin at hatching would involve a family selection system in which equal samples of each family, with sexes balanced between samples, would be tested concurrently on normal and deficient diets. The growth response of family samples on the normal diet would be used as an experimental control. Selection would be for those families that show minimum differences between the within-family, sample means on normal and deficient diets, respectively. In other words, those families with a lower specific nutrient requirement would exhibit less depression from being fed a specific nutrient deficient diet, and would show minimum differences between samples. The efficiency of this procedure is largely determined by the number of individuals tested per sample and the genetic relationship between within-family, sample means. Larger, more closely related samples should allow for increased efficiency in identifying genetic differences among families for utilization of a specific nutrient. Adequate numbers are imperative, and with full sibs more than one hatch might be necessary.