Effect of Polyethylene Glycol:Condensed Tannin Ratios On in Vitro Fermentation of Warm Season Herbaceous Legumes.

Our goal was to assess the effects of addition of different levels of polyethylene glycol (PEG) on nutrient in vitro disappearance (IVD) of two warm season herbaceous legumes containing condensed tannins (CT) compared to a legume without CT. Samples of 0.5 g of Acacia angustissima var. hirta (AA), Desmodium paniculatum (DP) and Medicago sativa (MS; as a control) were weighed into Aknom bags and placed in the Daisy^II-200/220 incubator for 48 hr. Each jar included a different proportion of CT:PEG based on the estimated amount of total CT present in the jar as a contribution of each plant evaluated. The proportions of CT:PEG included: 1:0 (control); 1:1, 1:2 and, 1:16. Addition of PEG affected (P<0.01) the dry matter IVD of each species differently. Dry matter IVD increased with the 1:16 proportion for AA compared to the no-PEG control; by contrast, it decreased for DP, regardless of CT:PEG proportion. The 1:2 proportion of CT:PEG increased phosphorus IVD 11.1 and 12.8% for AA and DP, respectively. Crude protein IVD increased 4.1 and 22.3% for AA and DP, respectively, with the 1:16 proportion of CT:PEG compared to the no-PEG control. Increments of nutrient IVD due to the addition of PEG illustrate the positive influence of CT inactivation on nutrient rumen disappearance. It also suggests differences in PEG effect for different species that could be related to CT concentration or molecule type present.