The University of Arizona

Free-choice grazing of native range and cool-season grasses.

J.F. Karn, R.E. Ries

Abstract


A grazing system which allows cattle to select a season-long diet more nearly meeting their nutrient requirements should facilitate optimal weight gains. A study was conducted near Mandan, N. D. comparing season-long weight gains of yearling steers free-choice grazing on composite pastures containing equal sized plots of 'Nordan' crested wheatgrass (Agropyron desertorum) (Fisch. Ex. Link) Schult.), 'Rodan' western wheatgrass (Pascopyrum smithii (Rydb.) Love), 'Lincoln' smooth bromegrass (Bromus inermis Leyss.), and native range, to pastures containing the individual pasture types alone. The study was initiated in mid-May and terminated in early October each year from 1995-1997. Pastures were grazed at a stocking rate of 1.9 ha per steer for 147 days or 1.7 AUM ha(-1). Steer behavior on composite pastures was recorded every 10 min. from dawn to dusk 2 days per week each summer. In 1997, forage samples were clipped for chemical analysis at 4-week intervals from all pasture types either within composite pastures or as individual pasture types. Only in 1996 were daily gains of steers on the free-choice treatment different (P < 0.10) from all other treatments. Over the 3-year study, daily gains for steers on the free-choice treatment (1.11 kg) were statistically equal to steers on smooth bromegrass (1.04 kg) and western wheatgrass (1.00 kg) and were significantly greater than daily gains on native range (0.98 kg) and crested wheatgrass (0.97 kg). Steers tended to spend a greater percentage of observation time grazing smooth bromegrass than the other 3 pasture types, especially early in the grazing season. The period of maximum grazing preference for the other pasture types was late in the season in 1995 and 1996 for crested wheatgrass, in mid-season in 1996 for native range, and late in the season in 1997 for western wheatgrass. Chemical analysis of forage samples collected in 1997 show that smooth bromegrass had the highest crude protein and in vitro dry matter digestibility, and the lowest neutral detergent fiber at all 3 summer grazing periods. Forage quality data and the preference of steers for smooth bromegrass help to explain why steers on this treatment had excellent daily gains, especially during early and mid-season.

DOI:10.2458/azu_jrm_v55i5_karn


Keywords


native range;Bromus inermis;Agropyron desertorum;protein content;liveweight gain;fiber content;chemical composition;pastures;Pascopyrum smithii;in vitro digestibility;botanical composition;grazing;beef cattle;feeding preferences;North Dakota

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