The role of cholecystokinin in the expression of seasonal variation in thefeed intake and eating pattern of red deer (Cervus elaphus)

The role of cholecystokinin (CCK) in the expression of seasonal variation i n 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 o r 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 immuni sation on mean daily food intake. However, there was a significant interact ion (P < .01) between immunisation and month (season), with respect to rate of feed ingestion during meals, with animals immunised against CCK exhibit ing higher mean rates of ingestion during October to May but lower mean rat es during June to September. It is concluded that systemic CCK has a role i n 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 seaso nal change in daily feed intake. Since there was no evidence of differences with treatment in profiles of insulin, growth hormone (GH), thyroxine (T-4 ), triiodothyronine (T-3), insulin-like growth factor-1 (IGF-1) or prolacti n, it is unlikely that this effect is expressed through changes in the prof iles of these hormones. (C) 2001 Elsevier Science Inc. All rights reserved.