Relationship of First Lactation Performance to Lifetime Production and Economic Efficiency

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Abstract
The relationship between yield in 1st lactation and lifetime performance and estimated economic return was studied on 933 Holstein cows to determine the marginal effects of increasing 1st lactation production. Polynomial regressions (3.degree.) on yield in 1st lactation accounted for 1.7 to 11.4% of the variation in traits of lifetime. Yield in first lactation accounted for 31.4 and 62.3% of the variations in milk/day of life and profit/day of life. Increases in daily yield of 1st lactation beyond a point do not lead to additional increases in total or daily lifetime production or economic return. Maximal total or daily lifetime performance occurred in the range of 19-22 kg milk/day during the 1st lactation. Profit/day of 1st accounted for more variation in profit for life (16.3 vs. 11.4%) and profit/day of life (42.9 vs. 31.4%) than did milk/day of 1st. Daily performance traits in 1st lactation accounted for only 1.7-3.5% of the variation in herdlife and 6.9-8.3% of the variation in milk for life. A significant positive linear trend existed between profit/day of first and lifetime traits. An estimated profit function may be important as an aid to economic evaluation among dairy cows.