Kananub Suppada, Jawjaroensri Wassana, VanLeeuwen John, Stryhn Henrik, Arunvipas Pipat
Department of Large Animals and Wildlife Clinical Sciences, Faculty of Veterinary Medicine, Kasetsart University, Bangkok, Thailand.
Laboratory Unit, Kasetsart University Veterinary Teaching Hospital, Nong Pho, Ratchaburi Province, Thailand.
Vet World. 2018 May;11(5):642-648. doi: 10.14202/vetworld.2018.642-648. Epub 2018 May 18.
The study was to determine seasonal fluctuations and non-nutritional factors associated with bulk tank milk urea nitrogen(BTMUN).
A total of 58,364 BTM testing records were collected from 2364 farms in Central Thailand during September 2014-August 2015. Using square root BTMUN as the outcome, other milk components, farm effect, and sampling time were analyzed by univariable repeated measures linear regression, and significant variables were included in multivariable repeated measures linear regression.
The average BTMUN (standard deviation) was 4.71 (±1.16) mmol/L. In the final model, BTM fat and protein percentages were associated with BTMUN as quadratic and cubic polynomials, respectively. BTM lactose percentage and the natural logarithm of somatic cell counts were negatively linearly associated with BTMUN. At the farm level, the BTM lactose association was negatively linear; herd BTMUN decreased following an increase of herd lactose average, and BTM lactose slopes were quite different among farms as well. Sampling time had the highest potency for the estimation of BTMUN over time, with lows and highs occurring in August and October, respectively. The variation in test level BTMUN was decreased by 18.6% compared to the null model, and 6% of the variance could be explained at the farm level.
The results clarify seasonal variation in BTMUN and the relationships among other BTM constituents and BTMUN, which may be useful for understanding how to manage lactating dairy cattle better to keep BTM constituents within normal ranges.
本研究旨在确定与奶罐乳尿素氮（BTMUN）相关的季节性波动和非营养因素。
2014年9月至2015年8月期间，从泰国中部的2364个农场收集了总共58364条BTM检测记录。以平方根BTMUN作为结果变量，通过单变量重复测量线性回归分析其他乳成分、农场效应和采样时间，显著变量纳入多变量重复测量线性回归。
BTMUN的平均值（标准差）为4.71（±1.16）mmol/L。在最终模型中，BTM脂肪百分比和蛋白质百分比分别与BTMUN呈二次多项式和三次多项式相关。BTM乳糖百分比和体细胞计数的自然对数与BTMUN呈负线性相关。在农场层面，BTM乳糖关联呈负线性；随着牛群乳糖平均值的增加，牛群BTMUN下降，且不同农场的BTM乳糖斜率也有很大差异。采样时间对BTMUN随时间的估计影响最大，8月和10月分别出现低值和高值。与空模型相比，测试水平BTMUN的变异减少了18.6%，6%的方差可在农场层面得到解释。
研究结果阐明了BTMUN的季节性变化以及其他BTM成分与BTMUN之间的关系，这可能有助于更好地理解如何管理泌乳奶牛，使BTM成分保持在正常范围内。
