Effect of increasing progesterone concentration from Day 3 of pregnancy on subsequent embryo survival and development in beef heifers

摘要

Higher systemic progesterone in the immediate post-conception period is associated with an increase innembryonic growth rate, interferon-tau production and pregnancy rate in cattle. The objective of this study was to examinenthe effect of increasing progesterone concentration on Day 3 on subsequent embryo survival and development. Oestrusn(Day 0) was synchronised in beef-cross heifers (n=210) and approximately two-thirds of the heifers were inseminatednwith semen from a proven sire, while the remainder were not inseminated. In order to produce animals with divergentnprogesterone concentrations, half of the animals received a progesterone-releasing intravaginal device (PRID) on Day 3 ofnthe oestrous cycle, which was left in situ until slaughter. The four treatment groups were: (i) pregnant, high progesterone;n(ii) pregnant, normal progesterone; (iii) non-pregnant, high progesterone; and (iv) non-pregnant, normal progesterone.nAnimals were blood-sampled twice daily from Days 0 to 8 and once daily thereafter until slaughter on Days 5, 7, 13 or 16,ncorresponding to the 16-cell stage, the blastocyst stage, the beginning of elongation and the day of maternal recognition ofnpregnancy, respectively. Embryos were recovered by flushing the tract with phosphate-buffered saline and characterisednby stage of development and, in the case of Days 13 and 16, measured. Data were analysed by mixed models ANOVA,nChi-square analysis and Student’s t-testwhere appropriate. Insertion of a PRID on Day 3 increased (P <0.05) progesteronenconcentrations from Day 3.5 onwards. There was no difference between treatments in the proportion of embryos at thenexpected stage of development on Days 5 or 7 (P >0.05). While not significantly different, the proportion of viablenembryos recovered was numerically greater in the high progesterone group on both Day 13 (58 v. 43%) and Day 16 (90 v.n50%). Elevation of progesterone significantly increased embryonic length on Day 13 (2.24±0.51mm v. 1.15±0.16 mm,nP =0.034) and Day 16 (14.06±1.18 cm v. 5.97±1.18 cm, P =0.012). In conclusion, insertion of a PRID on Day 3 ofnthe oestrous cycle increased serum progesterone concentrations on subsequent days, which, while having no phenotypicneffect on embryonic development on Days 5 or 7, was associated with an increase in embryonic size on Days 13 and 16.