Cholecystokinin mediates depression of feed intake in dairy cattle fed high fat diets

Two experiments were conducted to investigate the effects of 1) different c oncentrations of dietary fat and 2) i.v. administration of a cholecystokini n receptor antagonist (MK-329) on feed intake and plasma concentrations of hormones and metabolites in dairy cattle. In Experiment 1, 4 lactating Hols tein cows were used in a 4 x 4 Latin square design. Treatments were diets w ith 1) no fat added, 2) 30 S fat/kg feed (calcium salts of long-chain fatty acids as fat supplement), 3) 60 g fat/kg, and 4) 90 g fat/kg added. Cows w ere fed once daily a diet of concentrate, corn silage, alfalfa haylage, and alfalfa pellets. Dry matter intake decreased linearly with increasing conc entrations of dietary fat (P ( 0.0001), Overall plasma concentrations of no nesterified fatty acids (P < 0.0001), triacylglycerol (P < 0.0006), and cho lecystokinin (P < 0.02), increased linearly with each level of dietary fat, but there was a linear decrease in plasma insulin (P < 0.0008). In Experim ent 2, 4 nonpregnant and nonlactating Holstein heifers were used in a cross -over design in a 2 x 2 factorial arrangement of treatments. Treatments wer e diet (fatty acids, 27 g/kg vs 103 g/kg diet dry matter) and i.v. injectio ns (MK-329 vs vehicle). Heifers were fed once daily a total mixed ration of corn silage, cracked corn and soybean meal with or without fat supplement. Diets were switched by period and either MK-329 (70 mug/kg body weight) or its vehicle was injected i.v. at 2 hr postfeeding. Daily dry matter intake was decreased by feeding the high fat diet (P < 0.02) but was not affected by injections. Injection of MK-329, however, increased dry matter intake b y 92% in heifers fed the high fat diet during the first 2 hr postinjection compared to vehicle injection, Plasma pancreatic polypeptide concentration was in creased by the high fat diet at 2 hr postfeeding (P < 0.02) but was towered by MK-329 at 1 hr postinjection (P < 0.001). Plasma insulin was low ered by the high fat diet (P < 0.01) but was not affected by injections. Th e elevated plasma cholecystokinin concentration may have mediated depressed feed intake of dairy cattle fed the high fat diets. (C) 2000 Elsevier Scie nce Inc. All rights reserved.