Forages containing plant secondary compounds can improve digestibility, rumen ammonia and rumen metabolites of pasture: an in vitro continuous culture case study

Authors: Christensen, Rachael; Halvorson, Jonathan; MACADAM, JENNIFER - Utah State University; Kronberg, Scott; Hendrickson, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2023
Publication Date: 5/1/2023
Citation: Christensen, R., Halvorson, J.J., Macadam, J.W., Kronberg, S.L., Hendrickson, J.R. 2023. Forages containing plant secondary compounds can improve digestibility, rumen ammonia and rumen metabolites of pasture: an in vitro continuous culture case study. Meeting Abstract. 1.

Interpretive Summary: Forages that contain various plant secondary metabolites (PSM) such as tannins and saponins can improve performance and reduce N waste from livestock. The use of such forages have been shown to reduce nitrogen (N) waste in feedlot and dairy cattle diets. But, their potential use as supplements to grazing beef cattle diets have not been investigated. They are a practical way to feed bioactive compounds consistently, with potential for waste reduction. Laboratory in vitro digestion methods were used to determine effects of hay containing PSM as supplements to grass pasture diets. The PSM-containing forages included birdsfoot trefoil, sainfoin, small burnet, and cicer milkvetch. Results showed that forages CMV containing saponin may improve forage utilization. Grass diets supplemented with forages containing tannins and saponin were more digestible and had less N waste. These results showed that feeding these supplements in cow-calf grazing programs may be promising for improving production and environmental sustainability of beef cattle production.

Technical Abstract: Forages containing plant secondary metabolites (PSM) have been investigated for use in reducing Nitrogen waste in feedlot and dairy cattle diets but use as supplements to grazing beef cattle to capture the positive effects of PSM is unclear. Here we investigate potential improvement in rumen digestibility and metabolome, rumen ammonia production and flow from feed protein due to PSM bioactivity in forages used to supplement pasture grass using in vitro methods. Can PSM-containing forages offer a practical way to improve range nutrition and delivery of pytochemical benefits? Phytochemical containing forages birdsfoot trefoil (BFT); sainfoin (SAN); small burnet (SMB) and cicer milkvetch (CMV) supplemented grass pasture diets (200 g/kg of DM). In vitro true dry matter digestibility was determined using 2-stage in vitro methods. Randomly assigned diets of PAS supplemented with one of the PSM-containing forage diets (PAS+X) or not supplemented (PAS) were randomly applied to in vitro dual flow continuous culture (CC) vessels inoculated with grazing beef cow rumen fluid as a metabolic host. For 2-stage digestibility, SMB digestibility exceeded that of CMV, followed by BFT and SAN. The grass diet (PAS) was the least digestible. Saponin was detected in CMV samples, which is a new finding. For CC, compared to PAS, minimum culture pH for PAS+CMV was highest (P<0.02) but no differences were observed in pH between PAS, and PAS+BFT and PAS+SAN. Compared to PAS, the molar proportion of the fatty acid propionate increased with PAS+CMV(P=0.03) in contrast to the acetate- to- propionate ratio found highest for PAS and decreased for all diets with supplementation of PSM forages. Concentration of rumen NH3–N flow to rumen fluid per gram of protein intake was lower (P<0.01) with PAS+CMV and PAS+SMB, compared to grass only. Feeding CMV and SMB to grazing cattle may improve nutrient utilization, metabolome, and environmental sustainability of beef cattle production by improving diet digestibility and reducing ammonia waste.