高温感作に対する育成牛の体温調節性生理反応の日内変化について

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In order to better understand the character of thermoregulation in cattle, the variation of thermoregulatory responses during each of 4 phases; day, evening, night and morning were studied in four heifers (two Holstein and two Holstein and Japanese black cattle crossbred) that were exposed to environmental temperatures (Te) of 23 and 33℃ for 4 hours. One quarter of the daily feed ration was offered at 6 hr intervals to standardize heat production from feed ingestion. The rate of metabolic heat production (HP) was similar among the different phases of day and between the two groups of heifers. In spite of individual differences, a diurnal rhythm in vaginal temperature (Tv) and mean body temperature (Tb) both in Holstein and crossbred heifers at 23 and 33 PC was observed. However, a clear diurnal rhythm in mean skin temperature (mTs), respiration rate (RR) and heart rate (HR) could not be discerned. At 33℃ the level of Tb, Tv, mTS and RR was greater than that at 23℃ and the level of Tv and Th of Holsteins was greater than that of crossbred heifers. The results could be explained by using the concept of thermosensitivity. In the rhythm of Tv and Th, thermosensitivity was greater during the morning or day than the evening or night phase. Under high Te, increased thermosensitivity with an increased level of Th was necessary for the maintenance of heat loss. The different responses of the two groups against Te were related to differences in thermosensitivity. In this study, differences in thermoregulatory responses among phases of day, against Te and between breeds were observed, but the statistical evidence could not be shown. Jpn. J. Livest. Management, 32(3) : 83-89,1997. Received December 16,1996. Accepted February 12,1997.
1997-03-07

高温感作に対する育成牛の体温調節性生理反応の日内変化について

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