Effects of pasture inclusion of mimosa on growth by sheep and goats co-grazing grass/forb pastures
G. Animut, A. L. Goetsch, G. E. Aiken, R. Puchala, G. Detweiler, C. R. Krehbiel, R. C. Merkel, T. Sahlu, and L. J. DawsonSmall Ruminant Research. 2006. Revised.
Effects of mimosa alley-cropped in grass/forb pastures on growth performance of co-grazing sheep and goat wethers were determined. Eighteen sheep (Katahdin) and eighteen goats ( 75% Boer blood), with BW of 22 ± 0.3 and 21 ± 0.2 kg, respectively, and age of 4 to 5 mo were used. Wethers grazed 0.4-ha pastures consisting of grasses, such as bermudagrass (Cynodon dactylon) and johnsongrass (Sorghum halepense), and forbs (primarily ragweed, Ambrosia artemisiifolia), for 16 weeks. Three pastures with alley-cropped mimosa (W, 3 m between rows and 0.5 m within rows) and three without (WO) were divided into four paddocks for 2-week rotational grazing. Daily mimosa leaf mass removal averaged 47.4 g per animal, although mimosa leaf harvest was complete long before the end of 2-week grazing periods. Mimosa leaf samples averaged 2.81, 37.8, 24.6, and 85.9% N, NDF, ADF, and in vitro true DM digestibility (IVDMD), respectively. Forage mass (grass and forbs) was similar (P > 0.05) between treatments before (2928 and 2695 kg/ha; SE = 173.4) and after grazing (1507 and 1452 kg/ha for WO and W, respectively; SE = 140.4). Percentage of grass in forage determined by transect pre- (57 and 70%; SE = 8.3) and post-grazing (66 and 79% for WO and W, respectively; SE = 8.1) was not affected by treatment (P > 0.05). Pre-grazed forage concentrations of N (1.25 and 1.24%; SE = 0.031), NDF (64.5 and 63.8%; SE = 1.95), and IVDMD (52.9 and 56.2% for WO and W, respectively; SE = 1.44) were similar (P > 0.05) between treatments, as was also true post-grazing (N: 1.05 and 0.96%, SE = 0.054; NDF: 66.3 and 69.4%, SE = 2.68; and IVDMD: 49.0 and 48.0%, SE = 1.64, for WO and W, respectively). Overall ADG was numerically greater (P > 0.05) for W vs. WO (68 vs. 51 g/d; SE = 8.6). Species and period interacted in ADG (P < 0.05); ADG was greater for sheep than for goats in the first 4-week period but was similar in the other periods (first: 88 and 156 g/d; second: 89 and 105 g/d; third: 20 and 40 g/d; fourth: -6 and -16 g/d for goats and sheep, respectively (SE = 13.1)). In summary, alley-cropped mimosa increased quality of herbage available for grazing. Growth performance of co-grazing sheep and goats was only numerically enhanced, perhaps because of decreasing mimosa leaf availability as 2-week grazing periods advanced or overall relatively low intake of mimosa leaf. However, these findings do not suggest need for concern about potential anti-nutritional factors in mimosa and, thus, continuous inclusion of mimosa in low-quality diets at higher levels than in the present experiment should favorably impact performance of both sheep and goats.
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