暑熱環境下における沼沢水牛の血液量変動による直腸-皮膚温度差の制御 : スイギュウとウシの体温調節に関する比較研究 Rectal-Skin Temperature Difference Regulated by Blood Volume in Swamp Buffaloes in Hot Conditions : Comparative Study of Thermo-Regulation in Buffaloes and Cattle

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夏季にスイギュウの血液量(BV)は増加し,ヘマトクリット(Ht)値が減少すること,暑熱環境でスイギュウの体表面温度がウシよりも高くなることが報告されてきた.このBVの増加は体深部から体表面への熱運搬に貢献しているという仮説に基づいて, Ht値が簡便なBVの指標となることを確認するために実験1を,直腸と皮膚の間の温度差(R-T差)に対するHt値の変動の貢献を調べるために実験2を行った.実験1では,スイギュウ•ウシ,各4頭を20から30°C,35°Cの環境に曝露し, BVとHt値を調べた.スイギュウは直腸温度が増加するとBVは増加し,Ht値は減少し,これらの相関はそれぞれ有意であったが,ウシはともに有意ではなかった.実験1から,スイギュウのBVの増加は主に血漿量の増加であり, Ht値がBVの指標となり得ることが示唆された.実験2では動物を20°Cから30°C,30°Cから35°Cおよび35°Cから20°Cと変動させた環境に曝露し, Ht値の変動とR-T差を対応させて調べた.ウシと比較してスイギュウは,環境温度の上昇に伴ってHt値は速やかに減少し,同時にR-T差も減少した.下降の場合は深部温度が下がるまでHt値の増加は遅れる傾向があり, R-T差も増加が遅れた.実験2から,スイギュウのBVの変動はR-T差を制御し,深部温度に影響を受けるにとが示唆された.本実験から,スイギュウのBV増加は暑熱曝露によって速やかに誘起され,体深部と体表面の温度差を縮めることに貢献することが示唆された.スイギュウのこの生理的特性は,水浴時の皮膚からの感放熱を促進させることに役立っと考えられる.

From previous findings that the physiological responses of buffaloes to hot conditions were characterized by an increase in blood volume, a decrease in hematocrit (Ht) and an increase in skin temperature, we hypothesized that an increase in blood volume in buffaloes contributes to heat transportation from the body core (rectum) to the surface (skin). To test this hypothesis, the first experiment was done to determine if Ht value, which is easy to measure, reliably alters with total blood volume. The second experiment was done to find the relationship between Ht value and the rectal-skin temperature difference. In experiment 1, four swamp buffaloes and four Holstein cattle were successively exposed to environments of 20, 30 and 35°C. Hematocrit value decreased and blood volume increased with the increase in rectal temperature in buffaloes, when they were exposed to hot conditions (30 and 35°C). Correlation coefficients between blood volume or Ht value and rectal temperature were significant for buffaloes. The respective correlations for cattle were not significant. In experiment 2, the animals were successively exposed to acute temperature changes from 20 to 30°C, from 30 to 35°C and from 35 to 20°C. With an increase in environmental temperature, Ht value rapidly decreased in buffaloes, but not in cattle. On the other hand, when environmental temperature decreased, Ht value gradually increased only in buffaloes and this change was associated with a significant decrease in rectal temperature. As a result, the rectal-skin temperature difference in buffaloes was small with the decrease in Ht value and was large with the increase in Ht value. From these results, it was concluded that an increase in blood volume in buffaloes was rapidly caused by the exposure to hot conditions and contributed to reduce the rectal-skin temperature difference and to increase the temperature difference between skin and environment. These characteristics of buffaloes may be advantageous to increase sensible heat loss from the skin surface during a wallowing.

収録刊行物

  • 日本畜産學會報 = The Japanese journal of zootechnical science  

    日本畜産學會報 = The Japanese journal of zootechnical science 69(2), 81-89, 1998-02-25 

    Japanese Society of Animal Science

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各種コード

  • NII論文ID(NAID)
    10021726721
  • NII書誌ID(NCID)
    AN00195188
  • 本文言語コード
    ENG
  • 資料種別
    ART
  • ISSN
    1346907X
  • データ提供元
    CJP書誌  J-STAGE 
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