泌乳牛の微量元素出納に及ぼす高温環境の影響〔英文〕

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Four lactating Holstein cows were housed in two independently controlled climatic rooms, each housing 2 open-circuit respiration chambers. Two of the cows were exposed to temperatures in the order 18°, 26°, and 30°Cand 60% RH for 2 weeks per treatment, while the other two were exposed to the same temperatures in reverse order.They were fed concentrate and Italian ryegrass hay in the chambers.Dietary levels of trace elements were almost adequate for lacatting cows. Except for Mo, there were no significant differences in trace element concentrations in milk between treatments, but Mo concentration in milk decreased at 30°C.Trace element intake and excretion decreased with higher temperatures.Iron absorption and retention decreased with higher temperatures, but there were no significant differences in the absorption and retention of Cu, Mn, and Co between treatment. Negative retention of Zn, Se, and Mo at 26°C may be partly due to ralatively high secretion in milk at 26°C.Since the ratio of secretion in milk to the intake of Zn, Se, and Mo was much greater than that of Fe, Cu, Mn, and Co, more attention must be paid to the Zn, Se, and Mo nutrition of lactating cows in relation to milk production. Results suggest that the Fe, Zn, Se, and Mo balance in lactating cows may be affected by heat stress, although it is not apparent whether the Cu, Mn, and Co balance are affected.
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