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Effects of ruminal protein degradability and frequency of supplementation on site and extent of digestion and ruminal fermentation characteristics in lambs fed low-quality forage

Department of Animal Science, University of Wyoming, Laramie 82071

ludden{at}uwyo.edu

Abstract

Four ruminally and duodenally cannulated Suffolk wether lambs (34.5 ± 2.0 kg initial BW) were used in a 4 x 4 Latin square designed experiment to examine the effects of ruminal protein degradability and supplementation frequency on site and extent of digestion in lambs consuming a low-quality forage diet. Wethers were fed a basal diet of mature crested wheatgrass hay (4.2% CP) for ad libitum consumption plus 1 of 4 supplements: 1) a high ruminally degradable protein (RDP) supplement provided daily (RDP-D), 2) the high RDP supplement provided on alternate d (RDP-A), 3) a high ruminally undegradable protein (RUP) supplement provided on alternate d (RUP-A), or 4) a 50:50 mixture of the RDP and RUP supplements, provided on alternate d (MIX-A). Forage OM, N, NDF, or ADF intakes were not affected by treatment. True ruminal OM digestibility was greater (P < 0.001) for MIX-A lambs compared with other treatments. True ruminal N digestibility was lower (P < 0.01) in RUP-A lambs compared with other treatments. Ruminal digestibilities of NDF and ADF were greater (P 0.01) for MIX-A lambs compared to other treatments. There was a treatment x hour interaction (P < 0.001) with a delay in peak concentrations within the RDP-A lambs. However, lambs supplemented with RUP had lower (P < 0.001) ruminal ammonia concentrations compared to RDP-D lambs, with RUP-A lambs exhibiting the lowest concentrations and least variation over time. Ruminal urease activity was not affected by treatment. Microbial N flow was not affected by treatment; however, there was an increase (P = 0.004) in microbial efficiency for RDP-D lambs. Alternate day protein supplementation with a mixture of RDP and RUP may improve digestibility in lambs consuming low-quality forage, which may be related to decreased fluctuation in ruminal ammonia concentrations as a result of greater endogenous N recycling.

Key Words: growing lambs • low-quality forage • nitrogen metabolism • ruminal protein degradability • supplementation frequency