The effect of repeated follicular puncture on ovarian function in dairy heifers.

Three dairy heifers were examined during three consecutive oestrous cycles (control period, CP). Subsequently, the animals were subjected to 4 and then 5 weeks of twice-weekly ovum pick-up (OPU) (FPP1 and FPP2, respectively) with a recovery period (RP) of two consecutive oestrous cycles between FPP1 and FPP2. After FPP2, the animals were slaughtered and the ovaries were macroscopically examined. Throughout, ovarian activity was monitored by transrectal ultrasonography and concentrations of plasma progesterone. During CP, all the heifers showed normal cyclicity. During FPPs, the heifers occasionally presented oestrous activity. Corpus luteum (CL)-like structures developed from punctured follicles with diameters and life-spans varying from smaller and shorter than those in the CP (P > 0.05) to equal to those in the CP. There was a tendency for a lower number of emerging and punctured follicles in the presence of a CL-like structure. Subsequently to FPP1, all heifers regained normal cyclicity. A thickening of the ovarian tunica albuginea and a slight hardening of the ovaries were found postmortem. In conclusion, dairy heifers can occasionally show cyclic activity and form CL-like structures during twice-weekly OPU. Further, OPU did not seem to cause any major negative effects on ovarian structure and subsequent ovarian function.