INVOLVEMENT OF OPIOID-PEPTIDES FROM CASEIN ON RETICULAR MOTILITY AND DIGESTA PASSAGE IN STEERS

Experiment 1 determined the effects of incremental abomasal casein infusion on reticular motility and digesta passage of mature steers in a 4 x 4 Latin square study. Casein solutions were infused at 0, 1.25, 2.5, and 5.0% (wt/vol) for 3 h at 16.7 ml/in. Steers were fed for maintenance every 2 h. Casein resulted in a linear decrease in frequency, duration, and amplitude of reticular contractions measured manometrically. Total area of reticular contractions from physiographic tracings decreased 10.4 to 18.5%. Ruminal DM contents decreased 4.5 to 7.5%. Experiment 2 characterized the effects of casein on reticular contractions to be mediated by opioid peptides. Steers were infused abomasally (4 h) with either a 5% (wt/vol) solution of casein or its hydrolysate with or without a predose of naltrexone as an opiate antagonist (.5 mg/kg of BW) in a 2 x 2 factorial. Both casein and hydrolysate reduced frequency and duration of reticular contractions. Hydrolysate decreased contraction frequency within 30 min of infusion and 60 . min prior to effects of casein. Naltrexone reversed the effects of casein and accentuated the effects of hydrolysate. Ruminal liquid outflow was decreased 19.7% with hydrolysate. Postruminal infusion of casein or its hydrolysate resulted in casomorphin-like activity on reticular motility and digesta passage.