Digestibility Trials

Digestion Trials with Fresh Forage: Alfalfa, Birdsfoot trefoil, Tall Fescue and Reed Canarygrass

Based on previous experiments, Jake Owens designed a digestibility study to investigate how eating alfalfa or birdsfoot trefoil (BFT) before eating endophyte-infected tall fescue or reed canarygrass (RCG) might benefit livestock compared to livestock eating tall fescue or RCG alone.

Trial 1: Lambs were offered alfalfa for 30 min then fed either fescue or RCG for 3.5 h. In this study, fresh forage was actually cut and brought to each animal. Lambs ate more food, nitrogen and energy when they ate alfalfa prior to eating tall fescue or RCG compared to lambs fed only tall fescue or RCG. Lambs fed alfalfa ate slightly less tall fescue and RCG relative to animals that did not receive alfalfa.

Trial 2: Trial 2 was similar to trial 1 except lambs were fed BFT prior to receiving fescue or RGC. Trial 2 used a new group of lambs. Lambs fed BFT ate slightly less RCG, but much more fescue than animals that did not receive BFT.

Lambs ate less BFT than alfalfa, but lambs that ate BFT ate much more TF than lambs fed alfalfa. In both studies, feeding two forages had no affect on the digestibility of any of the forages.

The enhanced intake of fescue by lambs fed BFT, as well as the greater nutrient intake by lambs fed legumes and grasses is likely due in part to complementary profiles of alkaloids, saponins, and tannins.

Reference: Owens, J., F.D. Provenza, R.D. Wiedmeier, and J.J. Villalba. 2012. Supplementing endophyte-infected tall fescue or reed canarygrass with alfalfa or birdsfoot trefoil increases forage intake and digestibility by sheep. J. Sci. Food Agric. 92:987-992.


Digestion Trials with Purified Compounds: Tannins, Saponins and Alkaloids

In his second trial, Jake examined how eating a food containing saponins (SAP), or tannins (TAN) prior to foods containing one of two alkaloids (gramine (GRA) or 5-methoxy-N,N-dimethyltryptamine (TRP) ) would provide benefits not possible when the alkaloid-containing foods were eaten alone. All foods used in the study had the amounts of energy (3.3 Mcal/kg) and crude protein (14%).

In Trial 1, lambs were first offered a food with SAP for 30 min followed by food with one of two alkaloids for 3.5 h. Supplemental SAP did not affect digestibility or total intake.

In Trial 2, lambs were first offered a food with TAN for 30 min followed by food with one of two alkaloids for 3.5 h. Digestibility of dry matter, energy, and fiber were lower for lambs fed TAN plus alkaloid-containing foods than for animals fed only alkaloid containing diets. However, N digestibility, the amount of N retained in the body and the ratio of N retained/N consumed were higher for lambs eating alkaloid-containing diets plus TAN compared to animals not fed TAN.

Combinations of forages with complementary primary and secondary compounds may enable animals to maintain intake and improve nutrient utilization. It is interesting to note that results from Jake’s first and second trial do not mirror each other. Feeding trials with purified compounds and concentrated feeds can give us insight into the affects of secondary compounds on diet selection, but are no substitute for trials with fresh forage.

Reference: Owens, J., F.D. Provenza, R.D. Wiedmeier, and J.J Villalba. 2012. Influence of saponins and tannins on intake and nutrient digestion of alkaloid-containing foods. J. Sci. Food Agric. 92: 2373-2378.