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Grazing behavior and energy expenditure by sheep and goats co-grazing grass/forb pastures at three stocking rates

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

A study was conducted to assess effects of stocking rate (SR) on grazing behavior and energy expenditure (EE) by growing sheep and goat wethers co-grazing grass/forb pastures. Grazing was for 16-wk periods in 2002 and 2003. Pastures consisted of various grasses, primarily bermudagrass (Cynodon dactylon) and johnsongrass (Sorghum halepense), and forbs (e.g., ragweed; Ambrosia spp.). Sheep (Khatadin) and goats (≥ 75% Boer) averaged 21 0.7 and 21 0.5 kg initial BW, respectively, and were 4 to 5 mo of age when grazing began. Stocking rates were four (SR4), six, (SR6), and eight (SR8) animals per 0.4-ha pasture, with equal numbers of sheep and goats. The nine pastures (three/treatment) were divided into four paddocks that were rotationally grazed in 2-wk periods. In wk 3, 8, and 13 of both years, EE was determined for one goat and one sheep in each pasture via heart rate. Grazing behavior using IGER Grazing Behavior monitoring system units was measured over 24-h periods on the same animals. The number of steps increased linearly (P < 0.05) with increasing SR (2,279, 2,707, and 2,788 for SR4, SR6, and SR8, respectively (SE = 96.4)), but was similar for the two species (2,633 and 2,550 for sheep and goats, respectively (SE = 69.9)). As SR increased time spent eating increased (7.4, 8.4, and 9.6 h) and time spent lying (11.0, 10.2, and 8.9 h), ruminating (7.9, 7.7, and 6.8 h), and idle (8.6, 8.0, and 7.6 h for SR4, SR6, and SR8, respectively) decreased (P < 0.05). Goats spent less time eating (1.1-h difference) and more time idle (0.7 h-difference) than did sheep (P < 0.05). SR, species, and year interacted (P < 0.05) in EE of wethers (year 1, sheep: 510, 569, and 572 kJ/kg BW0.75; year 2, sheep: 572, 597, and 648 kJ/kg BW0.75; year 1, goat: 524, 524, and 640 kJ/kg BW0.75; year 2, goat: 499, 496, and 551 kJ/kg BW0.75 for SR4, SR6, and SR8, respectively (SE = 17.0)). In summary, influences of SR on grazing time and EE can vary with grazing season. With forage conditions of this study, SR had similar effects on grazing behavior of sheep and goats when co-grazing. Effects of SR on EE may contribute to impact on ADG by small ruminants.


 

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