EFFECTS OF A PARASYMPATHOMIMETIC AGENT, SLAFRAMINE, ON RETICULOOMASAL ORIFICE FUNCTION

Three nonlactating, nonpregnant, ruminally cannulated Holstein cows (680-732 kg) fed chopped brome hay ad libitum once daily were used to study effects of slaframine (SF) on rumen function in a 3 x 3 Latin square design. Animals were injected intramuscularly with 0, 20 or 40-mu-g kg BW-1 SF, allowing for 1 d between trials. At 0, 40, 180 and 360 min postinjection rumen contents were partially evacuated. Reticular contraction frequency (RCF) was determined using a balloon placed in the reticulum connected to a pressure transducer and physiograph and reticulo-omasal orifice opening duration (ROOD) was measured using palpation and endoscopy. RCF as a percentage of predose was decreased linearly by SF treatment (P < 0.01). SF affected ROOD, which was higher (P < 0.05) for both SF treatments. This pattern was also linear (P < 0.01). A characteristic change in reticulum pressure was identified that correlated with SF mediated variation in ROOD (r = 0.67; P < 0.01). Previous research has indicated that SF administration increased salivation and shifted site of digestion. The results presented herein are consistent with these observations and indicate that duration of reticulo-omasal orifice opening may be more highly associated with the rate of digesta passage than reticular frequency.