Intraruminal injection of urea and changes in secretion of parotid saliva in sheep

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Abstract
1. Sheep were injected with varying doses of urea into the rumen and changes in the amount of saliva secreted from one parotid gland were studied. When the dose of urea was 0.1–0.2 g/kg, the secretion under- went no change. When the dose was 0.3 g/kg. the secretion was inhibited. When the dose was 0.4 or 0.5 g/kg, there was a marked inhibition in the secretion.2. There was a close relationship between the ammonia level of the jugular blood and the inhibition of salivary secretion. When the ammonia level exceeded approximately 0.28 mmol/l, the secretion was inhibited abruptly.3. Salivary secretion and rumen movement were inhibited when the blood ammonia level exceeded 0.28 mmoljl, after injection of ammonium acetate into the jugular vein.4. Based on the results mentioned previously, the mechanism of inhibition on the secretion of parotid saliva is discussed in relation to the domestic ruminant in which urea had been injected into the rumen.