Protein, energy and mineral intake affects bone growth in young horses. Pasture forage may make up a large proportion of the diet and so can have a significant effect on the overall nutrient intake. Elaine Allen and others at Rutgers University, New Brunswick, examined the variability in protein and mineral content of pasture and turf grasses.
They followed horses at pasture and took samples from the same places they had been grazing. The samples were collected at 7-9am and 4-7pm. A second part of the study looked at samples taken from plots of individual grasses.
They found that the protein and mineral content of the pasture did not vary during the day. Non-structural carbohydrates (such as sugars and fructans) did increase after warm sunny days or after an overnight freeze.
There was a seasonal variation in mineral content. Calcium was lowest in August, copper lowest in October and November. The protein and mineral content exceeded the requirements for maintenance of body weight in adult horses. And the protein levels exceeded the requirements for growth. But the pasture did not provide sufficient minerals to meet the requirements for growth.
They concluded that growing horses raised only on pasture grasses as the main food, without any supplementary minerals, are at increased risk of developmental orthopedic disease because of the low mineral content. They advise that the mineral content of pasture should be evaluated.
For more details see: Variability in protein and mineral content of pasture and turf grasses.Elaine M Allen, William Meyer, Sarah L Ralston. Proceedings Equine Nutrition Conference. Pferdeheilkunde (2005) 21, 11 - 12.