Ecological, Sustainable and Economic Impact of Legume-based Pasture Systems for Limited-Resource Small Ruminant Farmers in the Virgin Islands

Ecological, Sustainable and Economic Impact of Legume-based Pasture Systems for Limited-Resource Small Ruminant Farmers in the Virgin Islands

Summary

Objectives
1.) Compare productivity and profitability of grass-legume mixtures (i.e., Leucaena; Leucaena leucocephala Lam de Wit.)-(Guineagrass; Panicum maximum Jacq.) to N-fertilized guineagrass pastures for sheep production.
2.) Compare plant and animal response to grass-legume combinations (i.e., Neonotonia wightii) and native or guineagrass pastures when grazed by sheep and goats.
3.) Determine the milk production potential of goats stocked on grass-legume mixtures compared to alfalfa hay.
4.) Promote and facilitate the efficient adoption of forage-livestock systems and introduce concepts of sustainable agriculture.

Approach
Pastures typically account for the largest proportion of land use in the Caribbean islands (i.e., 82% of land use in the U.S. Virgin Islands). Adapted tropical grasses and legumes have multiple end uses and if properly managed can contribute to sustainable land use. Sensitivity of some pasture plants (i.e., guineagrass) to overgrazing and sensitivity of small ruminants to periods of insufficient forage is critical to sustainable land use. Previous research in St. Croix showed that intercropping shrub legumes (i.e., Leucaena leucocephala) increased grass dry matter yield during wetter periods of the year. Grazing methods effect on animal performance and distribution of yield of guineagrass-leucaena pastures is unknown. Investment needed for each method and their long-term effect on the sustainability of pasture systems are needed. The initial phase of this study compared grazing method (continuous and rotational stocking at 500 lb body weight acre/d) effects on dry season (March to August) liveweight gains of castrated, growing White-hair sheep and distribution of yield of guineagrass-leucaena overstory (25% of planted area).

Strips (approximately 6 ft) of established guineagrass pastures were mowed and sprayed with Glyphosate (Round-up) to suppress growth. Two weeks after, strips were planted with leucaena (September 1999). In March 2000, replicated pastures (three; 0.33 acre paddocks ) were assigned grazing methods and stocked with 4-6 month old lambs (approximately 30 lbs initial BW). Lambs were fasted for 18 hrs and weighed weekly. Pastures stocked continuously were sampled for dry matter yield (grass and legume component) every 28 d . Rotational stocked pastures were stocked in rotation and sampled for yield every 14 d, followed by 28 d rest periods.

Continuous stocking resulted in gains of 270 lbs/acre and was similar to the rotational stocking (265 lbs/acre). Mid-way through the dry season, forage dry matter yield decreased to <1,000 lb acre under continuous stocking. Leucaena regrowth was affected and contributed little forage yield. Guineagrass was enough to allow for selective grazing, but leucaena had to be supplied in a cut and carry system in order for lambs to gain similar weights as those on rotational stocking. Under rotational stocking, leucaena regrowth was adequate to supply 30% of forage dry matter. The grass component was over 1500 lb/acre and no supplementation was needed. A partial budgeting analysis indicated that the monetary gains from rotational stocking are positive but relatively small ($52/acre). These results are for one season only. In the long run, the monetary differences could become magnified, depending upon the relative influence of factors such as changes in pasture botanical composition, weed encroachment, and parasites. Over time, in the continuous system, guineagrass and leucaena is expected to decline due to selective grazing. Live weight gains from continuous stocking can be expected to decline, necessitating even more supplemental forage. Preliminary assessments also indicates higher parasite counts under continuous stocking. If weeds and parasites increase over time in a continuous system as hypothesized, then this would be associated with greater costs as well. The impacts of grazing methods on forage quality, legume persistence, and weed encroachment are presently being assessed. Changes in botanical composition in the long term can influence live weight gain and, therefore, relative profitability. A comparison of grazing methods during the rainy season is being conducted.