昨年に札幌で行われた世界牛病学会の講演で、分娩初期の搾乳制限と乳房炎予防の研究を聞き大変感銘を受けた。そのとき発表していたグループの論文がJDSに出ていたので早速読んでみた。
乳牛における分娩後5日までの搾乳制限が繁殖成績に及ぼす影響のランダム化比較試験(10.3168/jds.2018-14713)についてだ。とても興味がある内容だ！！
分娩後初期（5日まで）の不完全搾乳により、高ケトン血症のリスクが下がることが報告(10.3168/jds.2017-13151)されている。
分娩後初期の不完全搾乳が黄体機能と妊娠に及ぼす影響を調べること。また、初期の高ケトン血症が黄体機能と妊娠に及ぼす影響を調べること。
The main objective of the current study was to measure the effect of incomplete milking on luteal activity and on pregnancy hazard. We also aimed to study the effect of early-lactation hyperketonemia (i.e., β-hydroxybutyrate blood concentration ≥1.4 mmol/L during the first 3 wk in milk) on those reproductive outcomes.
2産以上のホルスタイン種経産牛853頭のランダム化比較試験。不完全搾乳では分娩後5日間、搾乳量を10~14L/dayに限定した。分娩後1~3週で血中BHB（1.4 mmol/Lを高ケトン血症の閾値とした）を、分娩後5~7週で血中プロジェステロン（1 ng/mLを有効な黄体機能の閾値とした）を測定した。
Multiparous Holstein cows (n = 853) from 13 commercial herds were enrolled in a randomized controlled trial. Cows were assigned to a control or a treatment group, incompletely milked (10–14 L of milk collected/d) from 1 to 5 DIM. Blood samples were collected once a week during weeks in milk 1 to 3 for β-hydroxybutyrate blood concentration, and a threshold of 1.4 mmol/L was used to define hyperketonemia. During weeks in milk 5 and 7, cows were sampled for progesterone blood concentration, and a threshold of 1 ng/mL was used to define luteal activity. Reproductive information and culling dates were obtained through herd records. Logistic regression models and survival analyses were used to assess the effect of treatment on luteal activity and on pregnancy hazard, respectively. Analogous models were used to investigate the effect of early-lactation hyperketonemia on reproductive outcomes.
不完全搾乳が黄体機能の活動に寄与するオッズ比は1.1だった（P = 0.67）。2産目だけの牛に限ると、分娩後55日以内に繁殖を開始した牛では、繁殖開始後1~21, 22~43, 44~65, 66~87, >87日の受胎リスクが、通常の搾乳方法と比較してそれぞれ、576.3 (240.0–1,383.7), 36.9 (18.9–72.1), 6.8 (3.3–13.8), 2.5 (1.0–5.9), 0.13 (0.07–0.26)倍になった。分娩後55日以降に繁殖を開始した牛では不完全搾乳による妊娠リスクへの寄与は認められなかった。初期の高ケトン血症は黄体機能と妊娠には関係していなかった。
The odds of luteal activity for incompletely milked cows were 1.1 (95% confidence interval: 0.72–1.7) times those of conventionally milked cows. The effect of treatment on pregnancy hazard varied as a function of time, parity, and start of the breeding period. In second-parity cows that started the breeding period <55 d in milk, the pregnancy hazard (95% confidence interval) in incompletely milked cows was 576.3 (240.0–1,383.7), 36.9 (18.9–72.1), 6.8 (3.3–13.8), 2.5 (1.0–5.9), and 0.13 (0.07–0.26) times that of conventionally milked cows at 1 to 21, 22 to 43, 44 to 65, 66 to 87, and >87 d after the voluntary waiting period, respectively. The treatment did not have an effect on pregnancy hazard in cows in third parity or greater or in those starting the breeding period ≥55 d in milk. Early-lactation hyperketonemia was not associated with any of the reproductive outcomes.
分娩後初期の不完全搾乳は黄体機能への影響は認められなかったが、2産目の分娩後55日以内に繁殖を開始した牛では妊娠に好影響が認められた。また、初期の高ケトン血症が黄体機能と妊娠に及ぼす影響は認められなかった。
In conclusion, the incomplete milking protocol had no effect on luteal activity and had a positive effect on pregnancy hazard in second-parity cows in herds with a short voluntary waiting period (<55 d). We did not observe an effect of early-lactation hyperketonemia on luteal activity or on pregnancy hazard.
んーーーーーーーー～～？ほとんど影響ないの？不完全搾乳→ケトーシス予防→免疫機能改善により乳房炎予防までは成功しているけど、その先の繁殖性までの影響は大きくないようだ。でも、一つのアイデア（不完全搾乳とか）で多方面に研究を進め、そして効果がなかったこともしっかり報告する姿勢は見習わなくてはならない。