Technical note: effects of forage protein-binding polyphenols on chemistry of dairy excreta

Forage chemistry can affect intake, digestion, milk production, and manure excretion. Although information is available on the effects of forage protein-binding polyphenols on small ruminant production and manure excretion, little information is available for dairy cattle. The objective of this study was to compare fecal and urinary N excretion of diets formulated with alfalfa (Medicago sativa L.) silage versus condensed tannin-containing birdsfoot trefoil (Lotus corniculatus) or o-quinone-containing red clover (Trifolium pratense L.) silages. Significantly higher concentrations of N were excreted in urine by lactating Holstein dairy cows fed red clover and low-tannin birdsfoot trefoil (8.2 g/L) than by cows fed high-tannin birdsfoot trefoil or alfalfa (7.1 g/L). Fecal N concentrations were similar (33.6 g/kg) among all diets. Dairy cows fed red clover had lower rates of urinary N excretion (5.0 g/h) compared with other forages (6.6 g/h). Fecal N excretion rates were lowest for red clover (4.1 g/h), intermediate for alfalfa (5.8 g/h), and greatest for cows fed high- and low-tannin birdsfoot trefoil (6.4 g/h). The ratio of fecal N to urinary N was highest for high-tannin trefoil, lowest for alfalfa and red clover, and higher in excreta collected in morning than evening. Concentrations of neutral detergent fiber (NDF) in feces, of N in NDF (NDIN) and acid detergent fiber (ADIN), and relative amounts of NDIN and ADIN excreted in feces were significantly higher from cows fed high-tannin birdsfoot trefoil than the other silage types. Study results imply that collection of excreta for environmental studies needs to consider forage polyphenol and diurnal effects on chemistry of dairy excreta.