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Economic Efficiency of Lean Tissue Production through Crossbreeding: Systems Modeling with Mice. II. Reproduction-Growth Termination Alternatives¹

Purdue University and US Department of Agriculture, West Lafayette, IN 47907

Abstract

Culling alternatives based upon number of litters, age of parents and interval between litters were evaluated in 27 crosses from three random-mating, unselected strains of mice (S, J, P). Four hundred thirty-two mating cages were appraised over a 365-d production period for reproduction of parents and growth and carcass composition of progeny at 42 or 49 d of age. Simple single-factor rules were first tested by maximizing two of the three culling criteria (reproduction-termination rules) and varying the third. A particular rule was considered optimum at the point where minimum economic conversion (input/output) occurred. Each cross expressed differing economic conversion values for the various culling rules. Of all 27 crosses, P x PS expressed the smallest conversion value (.84154) for a culling procedure that would terminate a mating at eight litters or at 244 d of age (.84681). The cross P x SP expressed the smallest conversion value (.86438) for a termination rule of 20-d intervals between litters. Progeny growth to 42 d of age was more economical than to 49 d of age. The reproduction-termination rules were also evaluated by allowing all three criteria to vary (three-factor rule) rather than only one. For the three-factor rules, the number of litters, age of parents, or days between litters are those combinations of values at which minimum economic conversion was first reached. Of the 27 crosses tested, the cross P x PS was again the most efficient cross with a cost per unit of product of .84154 associated with a termination rule of eight litters or 305 d of age or 40-d intervals, whichever occurred first, with progeny growth to 42 d. The component traits of parent and offspring income, parent and offspring feed and labor and facility costs and cost per live weanling animal were studied. Conversion for the optimum three-factor rule was always equal to or less than conversion for the optimum single-factor rule. The optimum culling procedure depends upon the long-term reproductive capacity of the breeding parents and the feasibility of implementing the termination rule into the reproduction program.

¹ Journal Paper No. 9806, Purdue Agr. Exp. Sta. Joint contribution from USDA-ARS-NCR, Midwest Area and Dept. of Anim. Sci., Purdue Univ. The use of trade names in this publication implies neither endorsement by the Agricultural Research Service or Purdue Univ. of the products named nor criticism of similar products not mentioned. The authors acknowledge and appreciate the technical help in data collection for this study by Glenna Dee Redman, Mark Einstein and the staff of caretakers in the Purdue Animal Sciences Mouse Colony.

² Dept. of Anim. Sci., Purdue Univ.

³ Present address: Dept. of Meat and Anim. Sci., Univ. of Wisconsin, Madison 53706.

⁴ Research Leader, Animal Genetics Research Unit, USDA-ARS.