Study of relationships between blood concentration in raw milk and milk quality and herd performance measures

Article

Previous methods for detecting blood in milk, including visual inspection and high-speed centrifugation, can only determine the presence or absence of blood in milk. However, inspection using a simple measurement device developed by Tokachi Zaidan enables quantification of blood in raw milk even at concentrations below the visual detection limit (0.01%). In this study, we used this device to determine the frequency of blood in the ordinary milk of individual cows and, based on herd performance, we investigated the relationships between blood concentration in milk and physiological factors such as month-age and breeding performance as well as the quantity and quality of milk. In total, 197 milk samples from individual cows were provided by two dairy farms (A and B) and analyzed in this study. Mean blood concentrations in milk (± standard deviation) were 0.0017±0.0009% (n=57) for Farm A and 0.0026±0.0008% (n=140) for Farm B. In both cases, the concentrations were substantially below the visual detection limit (0.01%). For both dairy farms (A and B), the blood concentration in milk tended to be higher for individuals with higher month-ages and calving numbers. On Farm B, the blood concentration in milk tended to be higher for individuals with a greater number of days after calving (i.e., individuals with lower breeding performance) and higher somatic cell counts in milk resulting from longer lactation periods. Nevertheless, in all cases, mean blood concentrations in ordinary milk were on the order of one-fifth the visual detection limit (0.01%) and were in a range that was not considered problematic.

今まで行われてきた血乳検査方法である目視検査や高速遠心分離では、血液混入の有無のみの判断しかできなかった。しかし、とかち財団が開発した簡易型血液混入検査装置を用いることによって、目視の検出限界（0.01％）以下であっても、生乳中の血液濃度を定量することが可能となった。そこで本研究では、同装置を用いて通常の個体乳に含まれる血液濃度を検査するとともに、牛群検定成績を用いて、乳牛の年齢や繁殖、乳成分や乳量などの生理的条件と、生乳中の血液濃度との関係を検討することを目的とした。本試験に用いた生乳は、２酪農場（Ａ・Ｂ）から提供を受けた、計197検体の個体乳とした。個体乳の血液濃度と標準偏差は、Ａ酪農場が0.0017±0.0009 (n=57）［％］、Ｂ酪農場は0.0026±0.0008［％］（n=140）であった。いずれも、目視で検出できる限界の血液濃度（0.01％）よりもはるかに低い値であった。Ａ・Ｂ両酪農場で月齢が長く産次数が多い、高齢な個体であるほど生乳中の血液濃度が高まる傾向がみられた。また、Ｂ酪農場では分娩後日数が長く（すなわち繁殖成績が良くなく）、搾乳日数が延びることで体細胞数が増えている個体乳の血液濃度が高まる傾向であった。いずれもごく微量で問題がないと考えられる値であり、通常乳に含まれる血液量の平均値は、目視で確認できる限界濃度（0.01％）の１/5程度であった。