SPRING LAMB PRODUCTION ON ALFALFA, SAINFOIN, AND WHEATGRASS PASTURES

Lamb (Ovis aries) weight gains from wheatgrass-sainfoin (Agropyron and Thinopyron spp.-Onobrychis viciifolia Scop.) mixtures suggest that gr azing sainfoin monocultures offers advantages over mixtures. Our objec tive was to determine levels of spring lamb production from irrigated 'Renumex' sainfoin, 'Cimmaron' alfalfa (Medicago sativa L.), 'Luna' pu bescent wheatgrass [T. intermedium subsp. barbulatum (Schur) Barkw. an d D.R. Dewey], and pubescent wheatgrass-sainfoin pastures. Replicated pastures grown on a fine, mixed, thermic Torrertic Paleustoll were rot ationally stocked (herbage dry matter [DM] allowance of 6.5% of body w t. d(-1)) by weaned Rambouillet x Suffolk wether lambs for an average of 88 d in spring of 1991 and 1992. Across Sears, cumulative weight ga in (CWG) ranged between 7.9 kg lamb(-1) for wheatgrass and 16.4 kg lam b(-1) for alfalfa. In 1991 (avg. 16.1 kg lamb(-1)) and 1992 (avg. 12.3 kg lamb(-1)) CWG for alfalfa and sainfoin was similar. Lamb productio n per hectare (PROD) was greatest for legumes (808 kg lamb ha(-1)) and least for wheatgrass (533 kg lamb ha(-1)). Including sainfoin with wh eatgrass increased PROD by 23% over wheatgrass, whereas sainfoin alone increased PROD by 25% over the mixture. Intake of sainfoin herbage (1 .5 kg DM lamb-unit(-1) d(-1)) was 29% greater than of alfalfa, wheatgr ass, or wheatgrass-sainfoin (1.2 kg DM lamb-unit(-1) d(-1), where 1 la mb-unit is a 35-kg lamb). Herbage crude protein concentrations (pregra zing) were highest for alfalfa (253 g kg(-1)) and lowest for wheatgras s (159 g kg(-1)). Sainfoin had the lowest organic matter digestibility (641 g kg(-1)), which did not reflect the high CWG or PROD obtained. Alfalfa or sainfoin offer greater opportunities for spring lamb produc tion than wheatgrass or wheatgrass-sainfoin pastures.