EFFECT OF ULTRASONICALLY-GUIDED FOLLICLE ASPIRATION ON ESTROUS-CYCLE AND FOLLICULAR DYNAMICS IN HOLSTEIN COWS

Two experiments were conducted to test the effect of ultrasonically-guided follicle aspiration on estrous cycle and follicular dynamics in Holstein cows. The objective of the first experiment was to determine if aspiration of all visible follicles would influence the estrous cycle. All visible follicles greater than or equal to 5 mm in diameter were punctured and the oocytes aspirated once during the second and fourth cycle, with no aspirations occurring during Cycles 1, 3 and 5 in 4 Holstein cows. Between aspirations the follicles were scanned ultrasonically every 2 to 3 d to monitor follicular waves. Estrus was monitored twice daily and plasma progesterone concentrations were measured daily. The inter-estrus periods were significantly longer when aspiration was performed than in the 3 cycles in which aspiration did not occur (25.0 vs 21.1 d; P<0.01). To determine the maximum number of follicles harvestable on a continuing basis, a second experiment was conducted to contrast unstimulated cows subjected to ultrasonically-guided oocyte collection twice-weekly with animals from which oocytes were collected once a week after gonadotrophin stimulation. All visible follicles of multiparous Holstein cows were aspirated every 3 or 4 d (unstimulated group, n=4), and the total number of follicles was compared with the number of follicles in cows that were aspirated weekly after 400 mg FSH were administered over 2 d (stimulated, n=6). The study continued for 8 consecutive weeks. The weekly mean number of follicles available for aspiration in the unstimulated cows was 15.7 +/- 3.3 (mean +/- SEM), which was not different from the 14.2 +/- 1.9 follicles available for aspiration from the FSH-stimulated cows. Within the unstimulated cows, there was an increased number of follicles available for aspiration over time during the period of study (P<0.001). The number of follicles available for aspiration from the stimulated cows did not change, but plasma concentrations of progesterone increased over time as persistent luteal tissue developed on the ovaries.