Effects of a parasympathomimetic agent, slaframine, on reticulo-omasal 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 × 3 Latin square design. Animals were injected intramuscularly with 0, 20 or 40 μg 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. Key words: Slaframine, reticulo-omasal orifice, reticulum motility, cattle