Mastitis-metritis-agalactia complex in sows: effect of the dosage of oxytocin on intramammary pressure in lactating healthy sows.

The dose-response and time-response relationships between injected oxytocin and intramammary pressure were investigated in normal lactating sows. In less than 39 s after 20, 40, or 80 U of oxytocin was given (IM injection), there was a rapid initial increase in intramammary pressure (15 to 27 mm of Hg) which lasted 22 to 32 s. After this initial response, there were secondary oscillations in pressure which lasted approximately 40 minutes (20 U) and up to 60 minutes (40 or 80 U). Changes in intramammary pressure during each oscillation varied between 1 and 5 mm of Hg. Mean values for frequency and amplitude of oscillations and total work (area under the trace) were measured. Compared with response obtained after 20 U of oxytocin was given, responses obtained at the 40-U or 80-U dose level had an increased frequency (150.0% and 249.0%, respectively) and total work (36.6% and 104.4%, respectively), but not amplitude. Thus, there may be some clinical advantage in milk let-down effect when sows are given the larger doses of oxytocin (40 or 80 U). These results indicate that newborn pigs should be allowed to nurse at the same time in which oxytocin is injected.