Comparison of two different synchronization programs in New Zealand dairy cattle
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The main objective of this research is to study the effect of removing a progesterone-releasing device out of the treatment of a regular GnRH-Prostaglandine-GnRH + P4 program, on follicular dynamics and oestrus synchronization in post-partum anoestrus cows, in the New Zealand situation. Animals included in the experiment were selected from one farm, comprising a total of 22 Friesian dairy cows. Animals used for the experiment were multiparous, were not observed in heat, had no sign of being cyclic after two ultrasonographic examinations, and had no palpable evidence of uterine or ovarian abnormalities. The cows were randomly allocated to receive a treatment following the GPG + P4 program or to receive a treatment following the same protocol but than without P4. Ultrasonography was performed from day 0 to 8 once a day, and twice daily on days 9, 10 and 11, to record the presence and diameter of the dominant follicle (DF), and further follicular dynamics. Blood sampling took place on a daily basis in the coccygeal vein to measure P4 and E2 concentrations, and on a hourly basis at day 9 of the program, to follow LH-level dynamics. Fixed time AI was performed on the 10th day, 16 hours after the second GnRH injection. No significant difference was found between the two treatment groups concerning the number of cows with a synchronised ovulation, although a trend showed a better synchronization after treatment with GPG+P4. The only significant difference (p=0.050) found in this experiment was the diameter of pre-ovulatory follicles after the first GnRH administration in the GPG+P4 group were (on average 3 mm) smaller than in the GPG group.