Effects Of Ruminal Nicotinic Acid On Heat Stress And Production Performance Of Holstein Cow In Northern Region

The heat stress is one of the major factors leading to the great economic loss of the dairy industry. Therefore, the heat stress issue has already aroused wide concern in the industry. Some domestic and foreign researches indicate that the niacin can alleviate the heat stress and improve the dairy performance, which shows important significance in improving the production level of the dairy cattle. In the Northern China with the severe heat stress, the niacin poses some effect on the heat stress. However, in the Eastern China, there are so few reports relating to this issue.Thermal environment evaluating test are carried out in Daqing, Mudanjiang and Mishan meanwhile, which located in West, South and East of Heilongjiang. This three places have representativeness both in climatic conditions, cultivation, pasture scale and other elements. The test time is July 2014 to August 2014, 62 days, determining humiture of cowshed in four timing points of a day( 7:00、10:00、14:00 and 17:00), and evaluating the thermal environment through humiture level. The result indicates that: most temperature-humidity indexes were between 72 and 79, which showed that the cattle in the summer in Northern region were mostly under the environment with slight heat stress. Although the average temperature in the northern area is lower than that in the southern area, the annual temperature different in the northern area is relatively big. The summer climate and temperature still can lead to the heat stress for the dairy cattle.According to the test result of thermal environment, we can confirm the experiment environment condition and study the influence of high-yield cow to thermal and production performance through adding different level of rumen bypass niacin into daily food of Holstein high-yield cow. This experiment use single element random design, which will begin in Heilongjiang cow farm in July and August(hottest month) 2015 It selected 30 healthy cattle with similar body condition, parity, and milk production, and randomly divided them into three experimental treatment groups. They were added with rumen bypass niacin 0 g·d-1(the control group), 6 g·d-1(Group I), and 12 g·d-1(Group II) respectively. Test period in 70 days, among them 10 days is advanced feeding time. Testing the humiture of cowshed in experiment time in 2015.It measured the constant physiological indexes, production performance indexes, and blood biochemical indexes, and compared the difference between the experimental groups and disposal groups.Test shows out:(1) Compared with the experimental group and control group, the temperature and respiratory rate have no significant difference in thermal period(P>0.05).(2) The difference in hind led, shoulder of experimental group and control group are both not remarkable(P>0.05). The rumen skin temperature of experimental group has a little bit decline, but not remarkable.(3) Compared with the experimental group and control group, the cow milk composition not changed significantly(P>0.05).(4) Different levels of rumen bypass niacin have no significant effect on milk production of Holstein cows(P>0.05).(5) The rumen bypass niacin in experimental group no significant difference to the control group(P>0.05). The glutamic-pyruvic transaminase of experimental group decreased significantly than the control group(P<0.05). Different levels of adding niacin to cow serum thyroid hormone(T3, T4) and cortisol(COR) had no effect(P>0.05). And 20 days in the experimental group has downturn in the T3, T4 compare with the control group but the difference was not significant(P>0.05).(6) Calcium and phosphorus levels in experimental group have no significant difference than the control group(P>0.05), with a trend of fluctuations. In the 20 th and 60 th days, the triglycerides in test group Ⅱ decreased compared with the control group(P<0.05). In the later test, urea levels in test group were significantly lower than the control group(P<0.05).This research confirms the production environment of the dairy cattle in the high-temperature seasons in the Northern China(Mudanjiang River, Mishan, and Daqing) through the temperature and humidity. It systematically evaluates the influence of the rumen bypass niacin on the heat stress and production performance of the dairy cattle in Northern China. This experiment proves that, under the slight heat stress that the cattle suffers in the summer in the northern region, to add 6 g·d-1 and 12 g·d-1 rumen bypass niacin separately relieves the cellular damage, improves the lipid metabolism and absorptivity of the nitrogen. However, the rumen bypass niacin does not have significant impact on the dairy performance of the cattle in summer in Northern China.