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Prediction of Daily Total Digestible Nutrient Requirement of Beef Cows in Northern Climates¹

South Dakota State University^,4, Brookings 57007

Abstract

Calculated energy consumed in 284 cow yr by individually fed Angus, Charolais and reciprocal cross cows was partitioned into maintenance, weight change and milk production requirements. Total digestible nutrient (TDN) consumed in 94 heifer yr was partitioned into maintenance and weight change requirements. The cow year was subdivided into midgestation, late gestation and lactation periods that were 69 ± 1, 90 ± 0 and 203 ± 1 d long, respectively. Variables affecting TDN intake (P<.25) in all periods studied were mean body weight (MWT), weight change and age of dam. Previous parity influenced TDN consumption during midgestation and milk production influenced TDN consumption during lactation. Mean body weight was evaluated by three methods as one of the variables influencing TDN consumption; MWT^1.00, MWT to a fractional exponent (MWT^x) calculated from the data and MWT with the regression line forced through the origin (zero intercept) were substituted in the multiple regression model. Equations were used to predict daily TDN for cows over a range of weights. Results indicate that method of analysis influenced predicted daily TDN requirements. Use of MWT^1.00 and MWT^x resulted in similar predictions, while the zero intercept technique underestimated energy requirements for small cows and overestimated energy requirements for large cows. Inclusion of an intercept allowed the best fitting regression line to intersect the Y axis at the point determined by the data. Quadratic effects of weight were nonsignificant in all periods. Total energy requirements of cows and heifers in this study exceeded previously published recommendations because of environmental influences.

¹ Published with the approval of the Director of the South Dakota Agr. Exp. Sta. as Pub. No. 1762 of the Journal Ser. Cooperative with and a contribution from Regional Project NC-1.

² Present address: Irrigation Station, Box 219, Carrington, ND 58421.

³ Present address: USDA, ARS, Box 225, Stone-ville, MS 38776.

⁴ Dept. of Anim. Sci.