Sixteen quarter horse yearling fillies were used in a 112-day feeding study to determine the comparative efficacy of alfalfa hay to soybean meal in supporting growth in young horses. The corn-based concentrate was supplemented with either protein from alfalfa hay or soybean meal. The yearlings were fed diets in a 60:40 grain-to-hay ratio. The fillies fed the soybean meal supplemented diet retained more nitrogen more efficiently than fillies fed the alfalfa diet. The soybean meal-fed fillies had higher concentration of osteocalcin. The researchers concluded that soybean meal and alfalfa proteins were equally effective in providing growth to young horses, however, the biological value of the absorbed nitrogen appeared to be higher in the fillies fed the soybean meal supplemented diet. Differences in osteocalcin concentration indicate that the soybean meal supplemented fillies were experiencing a greater amount of osteoblastic activity compared to the alfalfa-fed fillies.

Wall, L.H. and coworkers. 1998. Growth of yearling fillies fed alfalfa or soybean meal. J. Equine Vet.. Sci. 18(4):266-269.