Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht 3584 CL, the Netherlands.
J Dairy Sci. 2010 Dec;93(12):5809-17. doi: 10.3168/jds.2010-3544.
The aims of this study were to estimate milk yield (MY) losses associated with subclinical intramammary infection (IMI) in dairy goats and to assess if somatic cell count (SCC) can be used to estimate such MY losses. We used 2 data sets to study these questions. The first data set consisted of 5 herds. Milk production and SCC were recorded during 1 lactation. From approximately 100 does in each herd, milk samples were collected on 3 occasions during lactation for bacteriological culture. Linear mixed regression was used to estimate the effect of IMI on MY. The second data set consisted of 6 large herds, in which some of the goats had an extended lactation (≥2 yr). Milk yield and SCC data were recorded without bacteriological culture. The data showed that bacterial infection was related to an increase in SCC. Infections with major pathogens were rare and associated with a decreased MY; infection with coagulase-negative staphylococci did not affect MY, whereas infection with Corynebacterium bovis was associated with increased MY. A negative correlation was observed between SCC and MY, but the data suggested that this negative correlation was attenuated rather than caused by IMI. Furthermore, SCC seemed to be affected by MY via a dilution effect. Hypotheses about biological mechanisms behind these observations are discussed. This paper shows that MY losses caused by subclinical udder infections are limited in goats, and that SCC cannot be used to estimate the magnitude of these losses.
本研究旨在评估隐性乳房炎对奶山羊产奶量的影响，并评估体细胞计数（SCC）是否可以用于估计这种产奶量损失。我们使用了 2 个数据集来研究这些问题。第一个数据集由 5 个牛群组成。在 1 个泌乳期内记录了产奶量和 SCC。从每个牛群中的约 100 只母羊中，在泌乳期的 3 个时间点采集奶样进行细菌培养。线性混合回归用于估计 IMI 对 MY 的影响。第二个数据集由 6 个大型牛群组成，其中一些母羊的泌乳期延长（≥2 年）。记录了产奶量和 SCC 数据，而没有进行细菌培养。数据表明，细菌感染与 SCC 增加有关。主要病原体感染很少见，与产奶量减少有关；凝固酶阴性葡萄球菌感染不会影响产奶量，而牛分枝杆菌感染与产奶量增加有关。SCC 与 MY 之间存在负相关，但数据表明这种负相关是减弱的，而不是由 IMI 引起的。此外，SCC 似乎通过稀释效应受到 MY 的影响。讨论了这些观察结果背后的生物学机制假说。本文表明，隐性乳房炎对奶山羊产奶量的影响有限，并且 SCC 不能用于估计这些损失的程度。
