OPTIMAL CULLING STRATEGIES FOR DAIRY-COWS OF DIFFERENT BREEDS

Dynamic programming models were developed to optimize culling decisions for Holstein, Jersey, Guernsey, and Ayrshire cows. Parameters of individual breeds for milk yield, milk fat percent, body weight, and disposal reasons were considered. Replacement heifers were allowed to vary in these traits by a probability distribution function. Maximum discounted returns over major variable costs were computed for 10-yr planning for each breed for five prices. Regardless of prices, Holsteins had the highest weighted average value of discounted returns over variable costs followed in decreasing order by Ayrshires, Guernseys, and Jerseys. Effects of the traits on these values were determined by response surfaces. Holsteins and, to a less extent, Ayrshires, would benefit from increased emphasis on milk fat percent as an effective method of increasing discounted 10-yr returns over variable costs. Values for the Jersey and Guernsey breeds would increase substantially if major emphasis were placed on milk yield. Little would be gained by increases in milk fat percent for these two breeds. These results were consistent over changes in prices of milk and feed. Within breeds, body weight had little effect on response surfaces and had only a slight positive effect on 10-yr discounted returns over variable costs. Body weight could be conveniently omitted from the models. © 1978, American Dairy Science Association. All rights reserved.