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Blood Composition of Hereford Steers. I. Levels of Certain Constituents at Weaning and Slaughter Ages¹

South Dakota State University, Brookings

Abstract

Several blood traits were measured on 84 and 74 Hereford steers in time- and weight-constant trials, respectively. Blood specimens were collected at an average initial age of 223 days and at slaughter. The weight-constant animals were slaughtered at 363, 408, 454, or 499 kg. and the time-constant animals were slaughtered after a 274-day post-weaning feeding period. All animals were maintained in the same lot during the same year. Average feedlot daily gains of all groups were quite similar indicating linear growth over the range of weights and ages involved. All blood traits were adjusted by regression for linear and quadratic effects of contemporary age and weight. The largest initial-final correlations in the time-constant phase (from 0.34 to 0.37, P<.01) were obtained for serum alkaline phosphatase, creatinine, plasma specific gravity, number of erythrocytes, hematocrit and percent eosinophils. The initial-final correlations were generally lower for the weight-constant data, probably a result of additional effects of climatic and behavioral variations. However, these results suggest that permanent environmental and genetic deviations of individuals significantly affect the levels of certain blood constituents. Changes in levels of certain blood traits from initial to final collections were decreased alkaline phosphatase, inorganic phosphorus, icteric index, number of erythrocytes, M.C.C., number of leukocytes and percent and number of monocytes and basophils and increased serum creatinine, plasma specific gravity, M.C.V., M.C.H., and percent and number of neutrophils.

¹ Department of Animal Science, published with the approval of the South Dakota Agricultural Experiment Station as Publication 783 of the Journal Series. Cooperative with A.R.S., U.S.D.A and a contribution from Regional Project NC-1, Improvement of Beef Cattle through Breeding Methods.

² Present address: Department of Animal Science, The Pennsylvania State University, University Park.

³ The authors express their appreciation to R. J. Emerick, Department of Biochemistry, W. L. Tucker, Station Statistician, and Mrs. Elizabeth Christianson, Department of Animal Science, for assistance in conducting this study.