No information was reported as to whether cows actually suffered heat stress during treatment. A short-term metabolism trial showed production responses to be of smaller magnitude with BST during heat stress. In that trial, BST cows under heat stress did not increase in feed intake. No long-term studies comparing BST supplementation of cows under cool and hot conditions in the same experiment have been reported. Sustained Release Injections Use of sustained-release BST would be desirable to reduce frequency of administration and labor requirements.
Several studies are in progress on use of sustained-release products.
Dry matter intake increased in studies where BST was given as daily injections. The magnitude of response initially increased and then decreased with time after the injection. These sustained-release products show promise and are likely to be improved. Implications of BST Use on Management Most experiments with BST have been conducted in well-managed herds. It is probable that positive responses in poorly managed herds will be smaller and short-lived.