FORAGE SELECTION BY RANGE SHEEP ON A BUFFELGRASS (CENCHRUS-CILIARIS) PASTURE

During 1989, six esophageally fistulated male lambs (Pelibuey X Rambouillet), weighing 38.8 +/- 1.8 kg, were used to collect monthly extrusa on a buffelgrass (Cenchrus ciliaris) dominated pasture. Sampling periods (January through December) lasted 9 days (5 days adaptation followed by 4 days for extrusa collection). Monthly extrusa were separated in two portions; one was subjected to micro histological analysis and the other to chemical analysis. Botanical composition of the study area (10 ha) was measured monthly. Preference indices of lambs for forage species were also determined. Vegetation of the covered area was composed of 71.7%, 27.7% and 0.6% grasses, shrubs and forbs, respectively, Plant contribution of grasses, shrubs and forbs to the annual diets averaged 85.2%, 14.0% and 0.8%, respectively, Major shrubs in diets were soap brush (Porlieria angustifolia), black brush (Acacia rigidula), pale verde (Cercidium macrum) and cenizo (Leucophyllum texanum). Soap brush was the main preferred shrub by lambs throughout the year. Preference indices for forbs were inconsistent. Buffelgrass was preferred by lambs during all months, comprising 85.1% of the annual diets. This study suggested that the presence of shrubs and forbs in diets of lambs increased the levels of crude protein and in vitro organic matter digestibility. Even though cell wall constituents (neutral detergent fiber and acid detergent fiber) in forage selected by lambs were variable (P < 0.05) among months, percentages of these fractions were in agreement with published values. Mixed palatable native shrubs and forbs with buffelgrass in the pasture could improve the nutritive value of the dry matter available in the forage.