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Associations between Body Weight Predicted from Heart Girth and Production^{1, 2,}

Department of Animal Science North Carolina State University at Raleigh

ABSTRACT

Relationships among body weights predicted from heart girth measurements taken the first test day after calving, and age, 90-, and 305-day milk yields, and the corresponding fat percentages were assessed for 3,168 lactations of 1,593 Holstein cows in nine North Carolina Institutional herds.

The partial linear regressions of 305-day milk yield on weight independent of age were significant, but they averaged only about 150 lb milk for each 100-lb change in weight and accounted for only 1% of the variance in milk yield. Weight was not closely associated with 90-day yield, and it had only a minor influence on the fat percentages.

Estimates of the genetic correlation between weight and 305-day milk for the paternal half sister and daughter-dam analyses were positive but small (0.15 ± .17 and 0.02 ± .13), whereas those for weight and fat percentage were even nearer zero.

Selection indices computed for a range of economic situations and genetic relationships showed that little, if any, benefit can be expected by jointly considering body size when selecting for increased milk yield. Under present economic situations, a slight negative emphasis should be placed against body weight.

¹ Published with the approval of the Director of Research, North Carolina Agricultural Experiment Station, Raleigh, as Paper no. 1906 of the Journal Series.

² The computing services for this investigation were provided by NIH Grant No. FR-00011.

³ Present address: Dairy Cattle Research Branch, ARS, USDA, Beltsville, Maryland.