Heifer nutrition and growth on short duration grazed crested wheatgrass

Abstract

Animal performance and nutrition under short duration grazing (SDG) and season-long grazing (SLG) were compared on spring-grazed crested wheatgrass [Agropyron desertorum (Fisch.) Schult. and A. cristatum (L.) Gaertn.] range to determine if SDG has the potential to improve livestock production on such rangelands. Livestock performance was evaluated by measuring weight gains twice per grazing season. Diet quality was assessed by determining crude protein concentration and in vitro organic matter digestibility of extrusa samples collected from esophageally fistulated heifers. Three variables of ingestive behavior were measured: ingestion rate, biting rate, and grazing time. Daily forage intake was calculated as the product of ingestion rate and grazing time. Animals in the SLG treatment gained significantly more than those under SDG in 1983 (1.07 vs. 0.81 kg/hd/d), but no statistical differences were detected in 1984 (1.13 vs. 1.07 kg/hd/d for SDG and SLG, respectively). In 1985, animals under SDG gained the most (1.03 vs. 0.87 kg/hd/d for SDG vs. SLG, respectively). No differences were detected in diet quality between SDG and SLG throughout the study. No treatment differences were detected in ingestive behavior during 1984, but ingestion rate was greater and grazing time less under SDG than SLG during 1985. Results indicate that forage intake was greater, while energy expenditures were lower under SDG than SLG in 1985. The hypothesis that SDG extends the season of nutritious forage was not supported.