Moving horses to young pastures by Dr. Jim White

By Dr. Jim White
Ruminent nutritionist, MFA Incorporated

At the first sight of green grass, especially after a long winter; all sorts of thoughts run through one's mind: "no more feed bills!, will it rain in August? Is it OK for horses to get MFA Hi-Mag mineral or MFA MAG-ADE? (yes it is OK), when can I turn the horses out?, hopefully as soon as possible."

As tempting as it might be to contemplate the wonderfulness of turning horses out on grass- a bit of caution and restraint is warranted. Spring grazing should be introduced slowly. If the grazing is deferred until the pasture is 6-8 inches in height- the outcomes for both the horse and pasture are improved.

Path forward- when the pasture hits 6 to 8 inches in height, allow grazing for 15 minutes/day and increase the amount of time by 15 minutes a day for 2 weeks- after that you can allow unrestricted grazing time. When working them up to unrestricted pasture- for the first week- allow them access to their current hay/forage source prior to turning them out. The justification for this increased management is to preclude the rapid intake of pasture grasses- the principal problem being that cool season grasses are potentially very high in fructans. The rapid intake of young grass in non acclimated horses has been associated with grass founder. 

While pasture and hay are both forage, there are significant differences. Air dry hay is 10-20% moisture, fresh grass can be 70-85%. Young pasture is much more soluble than is dry hay; the soluble carbohydrates in the fresh pasture will be fermented in the hind gut to a much greater extent. The horse depends on the energy from the volatile fatty acids produced in the hind gut as an energy source- that fermentation is going to be done by a microbial population that needs time to adjust to the different substrate feed that is being eaten.

If you graze too early, pasture re-growth is compromised. The clever MFA agronomists counsel me not to get too greedy and turn out animals at the first sprig of green I see. They have tried, for any number of years, to remind me that: 1) since photosynthesis occurs mainly within the leaves of plants, 2) if I get greedy and graze the plants too early- say just when they cover the toe of my boot- 2-3" tall, 3) there are reduced leaves to fix energy, plants are weakened, roots are weakened, weeds invade, dry matter yield is reduced, animal performance is reduced.

After the grass is tall enough, and the horses are in on the pasture- the grazing should be stopped when the pasture is grazed down to 3-4 inches. The horses are moved to another sward/pasture/lot; they will go back on the pasture when the grass has grown to that 6-8 inches, which gives the common recommendation of- take half, leave half.