Changes in the dry matter yield and rumen digestibility of forgae sorghum (Sorghum bicolor Moench) by bird injury

Changes in the dry matter yield and rumen digestibility of forage sorghum by bird injury were investigated on two types of sorghum including the grain type of variety, GS 401 (commercial release), and the dual-purpose type of two inbred lines (3 : 42-3-1 and 3 : 45-1-1) developed at Nagano Animal Industry Experiment Station, Japan. Forage sorghums tested, characterized of early maturation and high susceptibility to bird attack, were grown in experimental crop field with (covered plot) or without bird protection net (uncovered plot) and sampled to determine the effects of bird injury on the dry matter yield and rumen digestibility at dough stage. Grains of the three sorghums in the uncovered plot were not almost yielded, whereas dry matter yield and water-soluble content of follage in those sorghums were much higher than those or the covered plot. Consequently, loss of whole dry matter yield of the sorghums in the uncovered plot was compensated by increase of foliage parts, the values showing around 78.2 to 91.6% against each or the sorghum cultivars in the covered plot. Dry matter disappearance in the rumen or foliage in the uncovered plot was also increased by the average value of 12.2% unit as compared to those of the sorghums grown in the covered plot. However, the yield of the indigestible matter and digestible structural matter in foliage here similar in the covered and uncovered plot. It would be associated with grater translocation of photosynthate in leaves and culms after bird picking of young grains, because the increase in the yield and digestibility of the foliage in the uncovered plot was mainly caused by the excess storage of water-soluble matter. It was thus suggested in this study that grain type and dual-purpose type of sorghums injured by bird attack even can yield the digestible matter similar to sorgo type of sorghums