Serum Growth Hormone Concentrations after Growth Hormone or Thyrotropin Releasing Hormone in Cows

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Abstract
A single s.c. injection of 10, 50, or 100 mg bovine growth hormone [GH] into lactating Holstein cows increased concentrations of GH, insulin and glucose in serum above preinjection baselines for at least 16 h. GH concentrations in serum after injection of GH or thyrotropin-releasing hormone were greater in cows during early (2-4 mo.) as compared with cows during late (8-12 mo.) lactation. Stage of lactation did not affect rate of metabolic clearance of GH in 8 cows, but larger cows cleared GH more rapidly than smaller cows. Data of these experiments may help to explain how injections of GH every 3 days stimulate milk yields.