AbstractFertility of lactating dair

Abstract
Fertility of lactating dairy cows is associated with reduced progesterone (P4) concentration compared with nonlactating animals.
The objective of the current study was to determine whether P4 during growth of the first follicular wave (FFW) affects embryo quality.
Lactating Holstein cows at 33G3 days post partum were allocated to one of three treatments. Cows in the FFW and FFW with P4 (FFWP)
treatments started the superstimulation protocol on day 1 of the estrous cycle and second follicular wave (SFW) cows started the
superstimulation protocol on estrous cycle day 7. Cows were superstimulated with 400 mg of NIH-FSH-P1 (FSH) given twice daily for
5 days, two prostaglandin F2a (PGF2a) injections given with the ninth and tenth injections of FSH, GNRH given 48 h after the first PGF2a
injection, and timed insemination 12 and 24 h after the GNRH injection. Cows in the FFWP treatment received two intravaginal P4
inserts during the superstimulation. Embryos were recovered 6.5 days after artificial insemination and excellent/good and fair
embryos were frozen and transferred. Blood was sampled daily from estrous cycle day 0 until insemination from donor cows. During
the superstimulation protocol, P4 was (P!0.01) greatest for SFW cows followed by FFWP and FFW cows respectively. The percentage of
embryos–oocytes from SFW and FFWP cows classified as excellent/good and fair embryos was (PZ0.02) greater than those of FFW cows.
Pregnancy per embryo transfer was not (PR0.73) affected by embryo donor treatment. Reduced embryo quality of cows induced to
ovulate the follicles from the first follicular wave is a consequence of reduced P4 during follicle growth.