Ranking Dairy Sires by a Linear Programming Dairy Farm Model

Dairy sires were ranked for overall merit by an average daughter's contribution to farm net profit. Biological characteristics of sires and economic factors of a dairy farm were linked by linear programming. Availability and constraints of resources were in the model. Average daughter's returns over variable costs attributable to sire proofs for several traits was the measure of sire's net merit. The index of total economic merit for sires was the amount of change of net profit by milking progeny of different sires. Ranking considered sire's contribution to milk yield and feed intake of daughters caused by variations of proofs for milk, fat percent, and size, site's nonreturn rate, veal calf sales of the offspring, and labor costs of slow versus fast milking daughters. Size of quota for daily milk shipments, cow housing capacity, labor for milking, and milk tank capacity were critical in determining ranking and forced greater emphasis on traits other than milk yield. Correlations between sire ranking on returns over variable costs and sire proofs were highest for milk and significant for fat percent, milking speed, size, and nonreturn rate. These traits had high standard partial correlations with and explained most of the variation of the index of total ecReceived December 6, 1982. ~Animal Production Division, Malaysian Agricultural Research and Development Institute, P.O. Box 12301, General Post Office, Kuala Lumpur 01-02, Malaysia. This paper is based on the Ph.D. thesis of the first author, which was filed with the University of Guelph in 1979. 2 Department of Animal and Poultry Science. 3Department of Agricultural Economics and Extension Education. onomic merit. This method aims at maximizing farm profits and may be applied to rank dairy sires on a national basis or to select sires for specific dairy farm operations. Production dollar index ratings on the same sires were closely correlated ( .87 to . 9 6 ) with profit index ranking but are potentially misleading if constraints exist that limit maximum milk output per farm. I N T R O D U C T I O N High milk yield and high milk fat percent are important to the economic success of any dairy operation. However, profit derived from milk yield and fat percent may be influenced by other factors attributable to the herd's reproductive performance, milking speed, feed intake and efficiency, conformation, and susceptibility to common diseases such as mastitis. The goal in animal breeding is to improve total performance of the herd to maximize economic gains within the farm production unit. This requires the consideration of several animal attributes as well as other economic factors. The approach to multiple trait selection was discussed as early as 1935 by Lush. However, formulation of a selection index based on several traits was in 1942 by Hazel and Lush (11). Using profit as the aggregate genotype, Hazel (10) developed a selection index to measure net merit of young boars and gilts. Breeding values for each of several traits were weighted by relative economic weights which Hazel defined as the "amount by which profit may be expected to increase for each unit of improvement in each trait." No major strides in further development of multiple trait selection have been achieved since the inception of Hazel's (10) selection index approach. Several reports have been published (1, 5, 16, 19, 20, 22, 23, 25) that have dealth with 1) the influence of more than one trait on the net merit of an animal, 2) linear and nonlinear relationship 1984 J Dairy Sci 67:3015--3024 3015 3016 SIVARAJASINGAM ET AL. between net merit and individual traits, and finally, 3) importance of and association between net returns (as against gross returns) and several traits in selection goals. Everett (8) studied the influence of several variables on income over investment in semen and developed predictors of sire differences in income over investment for field application by a multiple regression approach. Andrus and MeGilliard (1) predicted profitability of cows as the difference between lifetime income and expense expressed per year. Burnside et al. (2), reported that gross returns for milk increased linearly as pedigree estimated transmitting ability (ETA) for milk of the cow increased. However, high producers with high ETA for milk gave greater gross returns only by having longer lactations and calving intervals. Miller and Pearson (15) reviewed the literature on selection criteria, profit equations, selection indexes, and other economic aspects of selection and concluded that there was overemphasis on single trait selection in setting out selection goals. They further attributed conflict of defining selection goals, difficulty of predicting economic traits, and lack of data to estimate profitability and economic efficiency as obstacles to using economics in defining breeding goals. Dairy producers are faced with the task of choosing sires for artificial insemination that will produce the most profitable offspring. When estimates of sires' breeding values for all economically important traits are available, it is then appropriate to evaluate sires on their average daughter's profitability within the production possibilities of a dairy farm. Objectives were 1) to estimate total economic merit and rank Canadian AI (artificial insemination) dairy sires within the framework of a dairy farm model, 2) to study the effect of certain production limitations on ranking of these sires, and 3) to measure variation of sire indexes of total economic merit caused by the sires' genetic merit for the different traits measured so as to ascertain the relative importance of these traits for determining profitability. MATERIALS AND METHODS