影响北京地区荷斯坦牛牛奶尿素氮的环境及生理因素分析

Analysis of Environmental and Physiological Factors Influencing MUN of Holstein Cows in Beijing

为探究北京地区荷斯坦牛牛奶尿素氮(MUN)的影响因素及夏季热应激相关指标对MUN的影响,实测北京地区7个牛场2016年7、8月的荷斯坦牛直肠温度和体况评分(BCS),收集北京地区68个牛场生产性能测定数据,利用固定模型分析环境和生理因素,以及4%乳脂校正乳(FCM)、乳蛋白量和体细胞分(SCS)对MUN全年测定值的影响,并重点分析夏季MUN随BCS和直肠温度的变化趋势。结果表明:数据测定月份和产犊季节对MUN影响极显著(P<0.01),冬季MUN水平偏低,夏季普遍较高,春季产犊的牛MUN高于其他产犊季节;泌乳121~180 d MUN水平最高;MUN随胎次的增加显著降低(P<0.05);SCS、FCM和乳蛋白率分别与MUN夏季测定值呈极显著的回归关系(P<0.01);BCS对夏季MUN影响显著(P<0.05),但直肠温度对MUN无显著影响(P>0.05)。综上,利用产犊季节和测定月份可以预估群体MUN的水平,夏季则可通过奶牛体况变化及泌乳性能预测个体MUN,及时调整饲养管理,管控夏季奶牛健康和牛奶品质。

In order to explore the influence factors of milk urea nitrogen（MUN） of Holstein cows in Beijing area and the effects of dairy cow heat stress related indicators in summer on MUN, rectal temperature（RT） and body condition score（BCS） were assessed in 7 dairy farms in Beijing area from July to August, 2016, and DHI data from 68 dairy farms in Beijing area was collected as well. The effects of environmental and physiological factors, and 4% fat corrected milk（4%FCM）, milk protein yield and somatic cell score（SCS） on MUN were analyzed using a fixed model. The changing pattern of MUN in summer together with changes of BCS and RT were analyzed emphatically. The results showed that testing month and calving season had extremely significant influence on MUN（P〈0.01）. The level of MUN was the lowest in winter and relatively higher in summer in general. Cows calved in spring had a higher level of MUN compared with cows calved in other seasons. The highest MUN in the whole lactation shows up during 121~180 d in milk, and MUN decreased significantly with the increase of parity. SCS, 4%FCM and milk fat percentage showed extremely significant regression relationship with MUN respectively（P〈0.01）. There was significant influence of BCS on MUN in summer（P〈0.05）, however, RT has no significant effect on MUN（P〈0.05）. Above all, MUN level could be predicted by combining calving season and testing month information, and in summer, changes in BCS and milk performance could also be used to estimate MUN level of individual cows so that herd managers could adjust feeding management in time and control health condition of dairy herds in summer as well as good milk quality.