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Forage Intake by Lactating Beef Cows Differing in Potential for Milk Production^1,2,

University of Nebraska⁵, North Platte 69101

Abstract

Two feeding trials (early and late lactation) were conducted to measure ad libitum forage intake by beef cows from three breed groups of similar mature weight, but with different milk production potential. Twenty-four cow-calf units, eight from each milk production level (low, medium and high) were grouped (two/pen) based on similarity of cow weight and previous weigh-suckle-weigh and calf weaning weight data. Each pair of cow-calf units was confined to separate pens and allowed ad libitum access to chopped native Sandhills meadow hay. Dry matter intake, cow and calf BW and calf milk consumption were determined. Daily DMI (kg/hd) and milk consumption showed a positive linear response (P < .05) among low, medium and high milk-producing cows. When cow DMI was expressed as g/unit mean cow BW during the trial, both a positive linear (P < .05) and a quadratic response (P < .01) expressed the relationship among production levels during early and late lactation. Calf forage intake, birth weight and adjusted 181- and 205-d weaning weight had no linear or quadratic relationship (P > .10) to milk production levels. However, June 1 calf weight, actual calf weaning weight and calf rate of gain (birth to weaning) had a positive linear (P < .07) relationship. Best fit regression models with DMI as the dependent variable were developed for each trial based on R² and CV values of the potential models. The best fit model (R² = .94, SE = .33) for early lactation included production level as a class variable with cow BW^.75 and calf birth weight as independent variables. The best fit model (R² = .92, SE = .53) for late lactation included actual weaning weight in addition to the variables used during early lactation.

¹ Journal paper no. 8790, Univ. of Nebraska Agric. Res. Div.

² Contributing to Regional Res. Project W-151.

³ Present address: U.S. Sheep Exp. Sta., HC 62, Box 2010, Dubois, ID 83423.

⁴ Biometrics Center, Univ. of Nebraska, Lincoln 68583-0712.

⁵ West Central Res. and Ext. Center.