U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Date of this Version


Document Type



Published in Physiology & Behavior 73 (2001) 211-216.


The role of cholecystokinin (CCK) in the expression of seasonal variation in feed intake and feeding activity in ruminants was investigated by active immunisation of castrated male red deer (Cervus elaphus). In April, animals of two groups (five animals per group) were immunised against either CCK or vehicle solution only and booster injections were administered at 2-month intervals for the following year. Measurements were conducted for a period of more than a year from July. There were no significant effects of immunisation on mean daily food intake. However, there was a significant interaction (P< .01) between immunisation and month (season), with respect to rate of feed ingestion during meals, with animals immunised against CCK exhibiting higher mean rates of ingestion during October to May but lower mean rates during June to September. It is concluded that systemic CCK has a role in the expression of seasonal variation in the rate of feed ingestion during meals in ruminants and that this, in turn, may affect the pattern of seasonal change in daily feed intake. Since there was no evidence of differences with treatment in profiles of insulin, growth hormone (GR), thyroxine (T4)' triiodothyronine (T3), insulin-like growth factor-l (IGF-l) or prolactin, it is unlikely that this effect is expressed through changes in the profiles of these hormones.