Abstract
Abstract: As the seasonal alternation of herbage height, yak regulates its foraging behavioral pattern to achieve the best matching. The grazing behavior of yak is the best foraging pattern in summer, the browsing and grazing combined pattern is the sub-optimal way in spring and autumn, and the browsing behavior, as the retained incisor in yak's historical evolution, is adopted in winter. In order to find out how the foraging pattern adjustment caused by the incisors influenced the dry matter intake and enteric-fermentation methane seasonal micro-fluctuation, from September 2014 to September 2015 in Tianzhu County, Gansu Province, we tested 3 pattern (grazing, browsing, grazing + browsing combined pattern) alternation and their environmental influences. The analysis results showed that the yaks in July and August had the highest protein intake (10.70%±0.38%), the lowest crude fiber (18.68%±5.31%) and lignin intake (1.89%±0.49%), and the shortest ruminant interval (1.1±0.3 h), which adopted the grazing pattern. In April, the yaks adopted the grazing and browsing combined pattern, and hemicellulose (15.68%±5.17%) and crude fat intake (1.08%±0.09%) were the minimum; in May, the foraging ratio of yaks (1.15±0.16 bite/s) was the fastest; in June, the crude ash intake (18.29%±2.39%) was the highest and the fetal birth weight was also the biggest; in September, the foraging intake (1.97±0.27 g/bite), the fat intake (3.77%±0.08%), the average daily gain (97.43±5.18 g/d), and the enteric methane emissions (315.70±21.24 g/d) were the highest; in October, the total dry matter intake (9749.40±2783.66 g/d) and the ruminant ratio (1.24±0.15 chyme-mass/min) were the highest; in November, the hemicellulose intake (19.46%±2.58%) was the highest; in December, the ruminant interval (2.9±0.2 h) was the longest. In February, the yaks adopted the browsing pattern, the total intake (0.95±0.14 g/bite) was the lowest, and the browsing ratio (0.73±0.24 bite/s), the protein intake (2.72%±0.49%), and the crude ash intake (7.14%±3.25%) were the lowest; in March, the cellulose (39.25%±7.15%) and lignin (12.57%±0.46%) had the highest intake, and the daily browsing intake (4417.29±1114.56 g/d), the ruminant ratio (0.76±0.16 chyme-mass/min), the average daily gain (?48.87±3.56 g/d), and the enteric-fermentation methane emissions (237.57±22.39 g/d) were the lowest. The feed intake per chewing in October was the highest. The intake per chewing was the lowest in March. The speed of food intake reached the fastest in May and the browsing pattern was mainly adopted, with little "empty grazing", then the yaks were regulating to the browsing and grazing combined pattern from October to December And then the intake speed was accelerated. The total daily intake reached the peak in October, and the daily body weight gain was the fastest; then the daily intake sharply declined in November. The daily intake reached the lowest in February and March. The highest ruminated efficiency was in October, and the slowest was in March. The shortest ruminant interval was in July, and the longest interval was in December. From June to September, there was the highest grass protein growth, and yaks regulated to the grazing pattern; and there was lower protein in winter grass, so yaks changed to the browsing pattern. From January to March, grass had the highest cellulose, and yaks changed to the browsing pattern; and in lower cellulose season, yaks used the grazing pattern. From January to September, yaks adopted the grazing pattern, and the enteric-fermentation methane emissions also reached the annual peak; the vitamin and nutrient declined in the milk during yak's lactation; and for the browsing pattern from January to March, the methane emissions were the lowest.
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