Título en español.

Milk produced during their first three lactations by nine Hoisteins fed exclusively on all-grass rations from steep tropical grass pastures in the humid mountain region of Puerto Rico was determined. The pastures, which received 1 ton of 15-5-10 per acre yearly, carried one cow per acre with no supplementary feed. Grass consumed by the grazing cows contained from 16.5 to 20.2 percent of protein depending on the season of the year. The cows produced an average of 4,497, 8,132, and 8,573 pounds of milk during their first, second and third lactations, respectively. The lactations averaged 263, 290, and 280 days in length, respectively, with an average calving interval of 12.3 months. The cows weighed an average of 929 pounds at first calving, increasing to 1,148 pounds at the third calving. An economic model based on these results shows that feeding cows on all-grass rations from intensively managed steep pastures can be highly profitable in the mountain region of Puerto Rico where the land has few alternative uses.