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Goat Grazing Effects on a Native Grassland Overseeded with Stylo (Stylosanthes Guyanensis HBK)
Thesis Abstract:
The effects of goat grazing on a grassland located at the University of the Philippines Los Baños (UPLB) Upland Hydroecology Program Main Site at Putinglupa, Calamba, Laguna, Philippines were studied for six months, covering the dry and wet seasons.
Results showed that grazing did not affect soil pH. Soil compaction tended to show some initial effects of the grazing animals with the increase of bulk density (from 1.01 g/cc to 1.14 g/cc) after six months. Total nitrogen and organic matter content of the soil was significantly higher in the ungrazed than in the grazed area during this period. Stylo composed 71 percent of the total dry matter yield of the area before grazing was started. After six months, the legume dropped to a very low eight percent of the total yield in the grazed site. On the other hand, Imperata cylindrica and Saccharum spontaneum increased from the initial 29 percent to 92 percent in the same site after the same period.
The net primary productivity of the area was 0.23 tons/ha/month for the ungrazed plot and 0.68 tons/ha/month for the grazed site. There was no significant difference in crude fiber content of the forage found between the two treatments. However, crude protein and in vitro dry matter digestibility were observed to be higher in the ungrazed plot than in the grazed area after six months.
Average monthly forage consumption was 55 kg dry matter/goat during the first two months, with a corresponding liveweight gain of 1.25 kg/month. In the following months, consumption was greatly reduced to 2.5 kg/goat/month such that the animals lost weight by an average of 0.875 kg. The grazing goats extremely affected the performance of Leucaena leucocephala saplings inside the grazing area. After three months, all the plants were totally defoliated and debarked owing to the browsing characteristic of the animals.
The amount of seeds collected from the grazed area was relatively lower than those from the ungrazed plot. It was found that 1 gm of stylo pure live seeds is composed of about 290 pieces.
Significant changes in various parameters throughout the six-month study period and the differences between the two treatments were discussed and possible explanations were offered.