Lay Summary Feeding studies indicate dairy cattle and other livestock grow faster and produce more milk when consuming pasture or freshly cut forage of birdsfoot trefoil (BFT). This response is attributed to condensed tannins (CT), which partially shift crude protein (CP) digestion from the rumen (the first compartment of the stomach) to the intestine where it can be more efficiently utilized by livestock. Dairy cattle are usually less responsive to BFT fed as hay or silage, and this might be related to CT making a large proportion of CP completely resistant to digestion. To investigate this, we prepared hay and silage from alfalfa lacking tannin and BFT containing an average of 19.7% CP and up to 3.1% CT on a dry matter basis. The forages were sequentially incubated in the rumen of cows and in glass flasks with gastric and intestinal enzymes. We found each unit of CT protected 0.62 units of CP in BFT from ruminal degradation, but only 40% of the CP complexed with CT could be degraded by gastrointestinal enzymes. This suggests CT are not an efficient means for increasing the quantity of plant protein digested in the gastrointestinal tract of livestock fed BFT conserved as hay or silage.
Grabber et al. (2026) studied this question.