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 grazing sainfoin monocultures offers advantages over mixtures. Our objective was to determine levels of spring lamb production from irrigated ‘Renumex’ sainfoin, ‘Cimmaron’ alfalfa (Medicago saliva L.), ‘Luna’ pubescent wheatgrass [T. intermedium subsp. barbulatum (Schur) Barkw. & D.R. Dewey], and pubescent wheatgrass-sainfoin pastures. Replicated pastures grown on a fine, mixed, thermic Torrertic Paleustoll were rotationally stocked (herbage dry matter [DM] allowance of 6.5% of body wt. d−1) by weaned Rambouillet ✕ Suffolk wether lambs for an average of 88 d in spring of 1991 and 1992. Across years, cumulative weight gain (CWG) ranged between 7.9 kg lamb−1 for wheatgrass and 16.4 kg lamb−1for 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 production per hectare (PROD) was greatest for legumes (808 kg lamb ha"1) and least for wheatgrass (533 kg lamb ha−1). Including sainfoin with wheatgrass 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, wheatgrass, or wheatgrass-sainfoin (1.2 kg DM lamb-unit−1 d−1, where 1 lamb-unit is a 35-kg lamb). Herbage crude protein concentrations (prograzing) were highest for alfalfa (253 g kg−1) and lowest for wheatgrass (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 production than wheatgrass or wheatgrass-sainfoin pastures.
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