CORN SUPPLEMENTATION OF LAMBS GRAZING ALFALFA

We investigated the effects of supplementing Rambouillet x Suffolk wet her lambs grazing irrigated 'Cimarron' alfalfa (Medicago sativa L.) wi th three levels (0 [C-0], 123 [C-123], and 247 [C-247] g of DM.lamb(-1 ).d(-1)) of cracked corn. Each treatment group also received 190 g of a supplement designed to prevent bloat. Replicated pastures (three per treatment) grown on a fine, mixed, thermic Torretic Paleustoll soil w ere grazed rotationally (forage plus supplement allowance of 6.5% of B W/d) by lambs for 85 d during spring 1992. Supplemental corn levels we re analyzed as single degree of freedom contrasts for linear and quadr atic effects. At the start of the experiment, lambs weighed 30.7 +/- . 32 kg. Average daily gains for Co C-123, and C-247 were 141, 154, and 169 g/d, respectively. Lamb production per hectare increased quadratic ally (P<.01) with increasing corn level (C-0 [716 kg of lamb/ha], C-12 3 [816 kg of lamb/ ha], and C-247 [964 kg of lamb/ha]). Supplementatio n with C-247 vs C-0 increased carcass weights (11%), dressing percenta ge (6%), and backfat thickness (30%). Plasma urea N (PUN) concentratio ns did not differ (P>.10) between Co and C-123 after 27 d of corn supp lementation, but after 75 d PUN concentrations between C-0 and C-123 h ad decreased(P<.10) by 11%. For C-247, PUN concentrations after 27 and 75 d of corn supplementation had decreased(P<.10) by 17 and 18%, resp ectively, compared with C-0. Plasma urea N concentrations increased (P <.01) linearly (r(2) = .93) with an increase in digestible CP:DE ratio (DP: DE). Lambs with the greatest growth response had the lowest PUN and DP:DE levels. Feeding limited amounts of corn to lambs grazing alf alfa increased lamb production per hectare and per lamb, seemingly thr ough more efficient use of the alfalfa protein.