Estimating Livestock Forage Demand: Defining the Animal Unit

Authors

Tonya L. Meyer, University of Nebraska-LincolnFollow

Date of this Version

5-2010

Document Type

Article

Comments

A thesis presented to the faculty of the graduate college at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science, Major: Animal Science, under the Supervision of Professor Terry J. Klopfenstein, Lincoln, Nebraska, May, 2010 Copyright 2010 Tonya L. Meyer

Abstract

The objective of this experiment was to evaluate the effect of a beef animal’s physiological status on forage intake. The experiment was repeated over two years with six replications of three treatments per year: cow-calf pair (CC; BW = 629 kg), dry cow (DC; BW = 503 kg), and yearling steer (S; BW = 305 kg). The cow and calf were treated as one unit, with cow BW and calf BW comprising CC BW. Calves were approximately 42 d of age and weighing 73 kg at the start of each year. Animals were housed in individual pens and fed high quality (11.6% CP) meadow hay ad libitum daily. Daily diet samples were composited by week and analyzed for dry matter (DM), organic matter (OM), in vitro dry matter disappearance (IVDMD), neutral detergent fiber (NDF), and undegradable intake protein (UIP). Refusals were collected, composited by week per pen, and analyzed for DM, OM, IVDMD, and NDF. Refusals were also composited for each year by pen and evaluated for UIP. Data was analyzed using the MIXED procedure of SAS. The cow-calf pair had the largest DMI, followed by the dry cow, and then the yearling steer (P < 0.01). A year × treatment effect was present. In year 1, cow-calf pairs had the highest intake as %BW, followed by dry cows, and then yearling steers (P < 0.01). In year 2, DMI as % BW was different between the cow-calf pairs and dry cows (P < 0.01). Cow-calf pairs and yearling steers were the same (P = 0.31), as were the dry cows and yearling steers (P = 0.12). Dry matter intake as % metabolic BW was the same for cow-calf pairs and dry cows (P = 0.51). Results indicate intake differences among cattle of different physiological states or classes should be considered when calculating forage demand for stocking rate or feeding purposes.