Production and composition of milk from cows grazing Siratro (Phaseolus atropurpursu) and greenleaf Desmodium (Desmodium intortus)

Abstract

The production and composition of milk were measured from 20 Jersey cows grazing unsupplemented pure stands of the tropical legumes Siratro (Phaseolus atropurpureus) and greenleaf Desmodium (Desmodium intortum) using a three period switch-back design. An abundance of feed was available for grazing so that herbage quality was evaluated in terms of production per cow. Preliminary and post-grazing on Pangola (Digitaria decubens) grass pasture allowed some comparison of production with grass swards to be made. A second experiment, of similar design, investigated the effects of feeding 4 kg of sorghum grain daily to cows grazing Siratro. Milk production from cows grazing Siratro and Desmodium was low, averaging 7.7 kg per cow per day. Milk production did not differ between the two legume treatments. The solids-not-fat percentage of milk produced on the Siratro pasture was lower than that produced on Desmodium, resulting in a lower production of solids corrected milk from cows grazing Siratro. Decreases in the yield and solid-not-fat content of milk and an increase in fat content were measured when cows grazed unsupplemented Siratro and Desmodium compared with their production on supplementd and unsupplemented Pangola. The mean casein : fat ratio of milk produced on Siratro swards was 0.47 : 1 compared with a mean ratio of 0.73 : 1 on Pangola pasture together with a 3 kg per cow per day of a balanced concentrate feed. Chemical composition, dry matter digestibility, and gross energy were poor indicators of potential milk production from Siratro and Desmodium pastures. Intake of digestible energy was considered to be the major factor limiting milk production. The addition of 4 kg per cow per day of sorghum grain increased daily milk yield, the S.N.F. content and the casein : fat ratio of milk produced on Siratro pasture.