Legumes are often grown with grasses in pastures to increase their protein content, and actually ruminants generally prefer forages high in protein. But how is forage preference affected when an increase in protein is accompanied by an increase in a toxic alkaloid? That’s exactly what happens when endophyte-infected tall fescue (TF-E+) is grown with alfalfa. Visiting scientist, Michael Friend, determined if sheep preferred TF-E+ grown near alfalfa (0.6 to 3 feet) (NEAR) or TF-E+ grown more than 15 feet away from alfalfa (FAR).
In his first experiment, lambs were offered a choice of freshly harvested TF-E+ NEAR and FAR for 12 days. Intake was measured each morning for one hour and at three more times during the day. As expected, NEAR contained more protein (8%) and the alkaloid ergovaline (360 ppm) than FAR (6% protein and 219 ppm ergovaline). Lambs preferred NEAR to FAR during the first hour of feeding, but not during feeding bouts later in the day.
In a second experiment, he examined the affect of odor on forage preferences by lambs. Lambs were offered TF-E+FAR in both feeders but one feeder contained the scent of freshly harvested alfalfa, the other the scent of freshly harvest TF-E+ FAR. Preference was greater for FAR with alfalfa scent than for FAR offered with FAR scent on two days of the eight-day experiment.
This research suggests that: 1) lambs initially preferred NEAR due to its higher protein content, but during the day the preference disappears due to the greater alkaloid content of NEAR compared to FAR, 2) olfactory cues influence preference, but to a lesser extent than the nutrients and alkaloids in TF-E+, 3) lambs adjusted their intake of forge and preference for forages during the day to balance their intake of nutrients and alkaloids.
Photo: Thomas Hawk / Foter / CC BY-NC