EFFICIENCY OF ENERGY AND NITROGEN LOSS AND GAIN IN MATURE COWS

Our objective was to quantify the energy and nitrogen balances of matu re cows fed a fixed amount of forage. Six cows were assigned to each o f two treatments. At time 0, control cows received 83.55 +/- .52 g of chopped brome hay.(BWkg)(-.75).d(-1). Feed intake remained fixed (9,10 3 +/- 217 g/d) over the entire 224 d of the study. At time 0 treated c ows received 82.10 +/- 1.26 g of chopped brome hay.(BWkg)(-.75).d(-1) (9,083 +/- 113 g/d). After time 0, treated cows were offered 65% of th e time-0 feed intake for the first 112 d (Phase 1) and 135% of the tim e-0 feed intake for the last 112 d (Phase 2), Treatments were designed so that the total amount of feed received during the 224 d was the sa me for each treatment. Additional balance measurements were made on d 28, 56, 84, 112, 140, 168, 189, and 224. Although treatment groups dif fered within phases for cumulative heat production, control cows did n ot differ from treated cows in total heat produced during the 224-d st udy (P = .60). Net retained energy over the entire 224-d period did no t differ between treatments (P = .43). Treated animals retained more n itrogen than did control animals (P = .008). The increased efficiency of nutrient utilization during refeeding in cows allowed to fluctuate in weight offers the potential to develop feeding strategies that impr ove grazed forage utilization and reduce supplemental feed.