The effect of amniotic fluid ingestion on the nociception of cows

The effect of the ingestion of the afterbirth on the nociception of cows was studied in two experiments. In both trials, the dependent variable was the thermal threshold of the animal, recorded as temperature and measured using nociceptive tests (NT). In the first experiment, 32 animals were randomly distributed in a 2 x 2 factorial design. The drug factor was an intravenous injection of morphine sulfate or of a saline solution. The fluid factor was the orogastric infusion of amniotic fluid or water. A pretreatment NT was considered as a baseline. Other NTs were performed after the drug injection and after the fluid infusion. In the second experiment, 28 multiparous Holstein cows were randomly assigned to 2 x 2 factorial treatments. The factors were amniotic fluid, either removed or not from the calves' surface immediately after delivery; and placenta, either left available or removed. A NT was performed before and 1, 6 and 36 h after the calf's delivery. In experiment 1, the morphine dose used did not produce an increase of the thermal threshold (p > 0.17) and neither did the amniotic fluid on the morphine-treated cows (p > 0.83). However, the amniotic fluid had an effect (p < 0.04) on the group injected with saline solution. In experiment 2, a linear rise occurred (p < 0.001) in the pain tolerance of the cows as parturition approached. Placenta ingestion and placenta and amniotic fluid ingestion had no effect (p < 0.26) on the thermal threshold of the cows. However, cows ingesting amniotic fluid had a significantly higher thermal threshold in the 1-h test than in the 6-h and 36-h tests (p < 0.004). The nociception of the cows not receiving amniotic fluid did not change across the same periods (p > 0.587). The results indicate that the ingestion of amniotic fluid enhances the ongoing opioid-mediated analgesia at parturition in bovines.