Interpretive Summary: Tannin-containing legumes and forage diversity influence foraging behavior, diet digestibility, and nitrogen excretion by lambs
By: Jackie Walling
A recent article published in the Journal of Animal Science investigated how tannin-containing legumes influence forage behavior, diet digestibility, and nitrogen excretion in lambs. Alfalfa (nontannin containing) is one of the most nutritious forages available but increases the risk of bloat and urinary nitrogen loss. Adding condensed tannins (CT), sainfoin, and birdsfoot trefoil to the diet diversifies feeding and may positively alter digestibility and nitrogen excretion.
Forty-two Columbia-Polypay Suffolk crossbred lambs were divided into seven forage treatments. Single forage species were sainfoin (SF), birdsfoot trefoil (BFT), and alfalfa (ALF). Two-way choice treatments were alfalfa-sainfoin (ALF-SF), alfalfa-birdsfoot trefoil (ALF-BFT), and sainfoin-birdsfoot trefoil (SF-BFT). The last treatment was all three forages (ALF-SF-BFT).
The chemical composition of forage and feces showed crude protein was highest in BFT and ALF. SF and SF-BFT were the only treatments with higher crude protein values in feces compared to ingested feed. Dry matter intake (DMI) and forage preference were highest for ALF followed by ST, and then BFT. Dry matter digestibility (DMD) was greater in SF, followed by BFT, and then ALF, but combining ALF with CT forages resulted in greater DMD compared to single species. On average, for DMI and DMD, two- or three-way species treatments were similar, but both were greater than single-species treatments. For fecal nitrogen, SF resulted in a higher ratio of feces to urine compared to BFT and ALF.
Overall, ALF was the most popular preference among lambs, but DMI was not significantly altered when paired with SF or BFT. SF, by itself, had the greatest fecal nitrogen output. Mixed forages resulted in a synergistic effect. When compared to ALF and other single species, mixed forages increased digestibility, and nitrogen excretion transitioned to a greater amount deposited in fecal matter. Adding tannin-containing legumes in lamb diets is associated with nutritional benefits.
For the full article, visit the Journal of Animal Science.