Model components of forage-fed cattle systems: energy expenditure of grazing cattle and prediction of intake in dairy cows

Abstract

The maintenance energy requirements of cattle should include the activity component when cattle are grazing. The prediction of the voluntary dry matter intake (DMI) is also a factor of importance for feed management of cattle. The objectives were to develop a procedure to account for energy maintenance requirement of grazing cattle, and to develop predictive equations for voluntary DMI by dairy cattle fed high-forage diets. A literature review of factors affecting maintenance energy requirements was conducted. It is concluded that the principal factors affecting the additional requirements for maintenance of grazing cattle are the activities of walking and eating. Paddock size is an important factor affecting walking distance and a quadratic equation to calculate walking distance from paddock size is proposed. Adjustments for activity of grazing cattle, walking, ascent, and eating ranged from 15% for cattle grazing small paddocks of high quality forage, and high forage availability, to 70% for cattle grazing large paddocks of low quality forage, with limited forage availability. Data from published experiments with dairy cows fed high- forage diets were used to generate and evaluate equations for the prediction of voluntary DMI . Equations were developed by multiple regression and variable selection procedures. Three equations were evaluated together with three published equations. The equations including only the linear terms of the selected variables resulted in a better sensitivity of the model. The models generated had a mean square prediction error from 4.24 to 4.56 kg2 , lower than that obtained with the published equations. The model selected for voluntary DMI prediction includes body weight, days in milk, production of 4% fat corrected milk, forage dry matter, and diet neutral detergent fiber as independent variables.