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Effects of stocking rate on grazing behavior of sheep and goats co-grazing mixed pastures

G. Animut1,2, A. L. Goetsch1, G. E. Aiken3, R. Puchala1, G. Detweiler1, C. R. Krehbiel2, R. C. Merkel1, T. Sahlu1, L. J. Dawson4, and Z. B. Johnson5

1E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK, 2Animal Science Department, Oklahoma State University, Stillwater, 3USDA ARS Dale Bumpers Small Farms Research Center, Booneville, AR, 4 College of Veterinary Medicine, Oklahoma State University, Stillwater, 5Department of Animal Science, University of Arkansas, Fayetteville

Differences among ruminant species in forage selectivity offer potential for efficient utilization of pastures with a diverse array of plant species. Therefore, this experiment was conducted to determine effects of stocking rate (SR) on grazing behavior of growing sheep and goat wethers co-grazing mixed pastures. Grazing was for 16-wk periods in 2002 and 2003. Pastures consisted of various grasses, such as bermudagrass (Cynodon dactylon) and johnsongrass (Sorghum halepense), and forbs (e.g., ragweed; Ambrosia spp). Sheep (Katahdin) and goats ( ≥ 75% Boer) averaged 21 ± 4.8 and 21 ± 3.7 kg initial BW, respectively, and were 4 to 5 mo of age when grazing began. Stocking rates were four (4), six, (6), and eight (8) animals per 0.4-ha pasture, with equal numbers of sheep and goats. The nine pastures (three/treatment) were divided into four paddocks, which were sequentially grazed in 2-wk periods. In wk 3, 8, and 13, behavioral observations were made on two goats and two sheep in each pasture every 30 min of daylight (i.e., 27 observations) for position (standing vs lying) and activity (grazing, ruminating, or idle). Observations were averaged over time of the day to determine percentages of total daylight. There were interactions (P < 0.05) between year and the linear effect of SR in time spent grazing (yr1: 57.3, 57.8, and 62.3%; yr 2: 48.0, 56.4, and 60.5% (SE = 1.54)) and idle (yr 1: 18.7, 20.9, and 16.3%; yr 2: 29.7, 21.4, and 15.5% for 4, 6, and 8, respectively (SE = 1.95)). Standing time increased linearly (P < 0.05) as SR increased (61.1, 66.3, and 69.8% for 4, 6, and 8, respectively). Grazing time was similar between species (56.1 and 58.0% for sheep and goats, respectively (SE = 0.97)), although idle time was greater (P < 0.05) for goats vs sheep (23.6 vs 17.21%; SE = 1.36). Time ruminating was similar among SR but differed between species (25.0 and 17.0% for sheep and goats, respectively; SE = 1.22). Year and species interacted (P < 0.05) in time standing (yr 1: 69.8 and 66.6%; yr 2: 60.2 and 66.3% (SE = 1.26)) and ruminating (22.3 and 19.0%; yr 2: 27.8 and 15.1% for sheep and goats, respectively (SE = 1.41)). In summary, these results suggest that influences of SR on grazing time and presumably energy expenditure may vary with grazing season. With forage conditions of this study, it appears that SR has similar effects on grazing behavior of sheep and goats when co-grazing.


 

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