Graduate Thesis Or Dissertation
 

Mathematical modeling of selection and crossbreeding in beef cattle

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z316q412b

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  • A mathematical model was developed to simulate alternative selection and crossbreeding strategies for commercial beef production. Biological and economic constraints were selected to represent typical pasture production of calves in the Northwest. The crossbreeding study evaluated the relative economic efficiency of different 1) mating plans when sire breeds of several sizes were used, 2) maximum cow replacement ages, and 3) cow culling strategies based on measures of reproductive failure. Replacing open cows in the fall with a heifer increased economic efficiency, as did replacing cows without a live calf at the end of the calving season. Replacing cows for failure to wean a calf decreased economic efficiency. The use of a very large terminal breed in the criss-out-cross or the three-breed terminal cross surpassed the three-breed rotational cross in economic efficiency. The criss-out-cross was superior to the three-breed terminal cross at cow replacement ages less than twelve years. The cow replacement ages which maximized gross margin per cow were five, nine, and twelve years for three-breed rotational, criss-out-cross and three-breed terminal crossbreeding, respectively. This reflected the average utilization of individual and maternal heterosis for the various mating plans. The selection study evaluated the economic efficiency and selection response of alternative bull and cow culling strategies. Selection was practiced for forty years to increase weaning weight while holding birth weight constant. The bull use strategy which maximized selection gains was to keep bulls for four years while culling 75% of the two-year old bulls based on a progeny test. Economic efficiency was maximized by keeping bulls for only one year. Culling cows for being open or for not having a live calf at the end of the calving season improved economic efficiency to a greater degree than did changing the maximum cow replacement age or the proportion of cows culled based on progeny performance, both of which also improved economic efficiency. Weaning weight was increased either by decreasing the maximum cow replacement age or by increasing the proportion of cows culled for poor progeny performance, but not both, simultaneously.
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