Effect of increasing progesterone concentration from Day 3 of pregnancy on subsequent embryo survival and development in beef heifers.
Higher systemic progesterone in the immediate post-conception period is associated with an increase in embryonic growth rate, interferon-tau production and pregnancy rate in cattle. The objective of this study was to examine the effect of increasing progesterone concentration on Day 3 on subsequent embryo survival and development. Oestrus (Day 0) was synchronised in beef-cross heifers (n=210) and approximately two-thirds of the heifers were inseminated with semen from a proven sire, while the remainder were not inseminated. In order to produce animals with divergent progesterone concentrations, half of the animals received a progesterone-releasing intravaginal device (PRID) on Day 3 of the oestrous cycle, which was left in situ until slaughter. The four treatment groups were: (i) pregnant, high progesterone; (ii) pregnant, normal progesterone; (iii) non-pregnant, high progesterone; and (iv) non-pregnant, normal progesterone. Animals were blood-sampled twice daily from Days 0 to 8 and once daily thereafter until slaughter on Days 5, 7, 13 or 16, corresponding to the 16-cell stage, the blastocyst stage, the beginning of elongation and the day of maternal recognition of pregnancy, respectively. Embryos were recovered by flushing the tract with phosphate-buffered saline and characterised by stage of development and, in the case of Days 13 and 16, measured. Data were analysed by mixed models ANOVA, Chi-square analysis and Student's t-test where appropriate. Insertion of a PRID on Day 3 increased (P<0.05) progesterone concentrations from Day 3.5 onwards. There was no difference between treatments in the proportion of embryos at the expected stage of development on Days 5 or 7 (P>0.05). While not significantly different, the proportion of viable embryos recovered was numerically greater in the high progesterone group on both Day 13 (58 v. 43%) and Day 16 (90 v. 50%). Elevation of progesterone significantly increased embryonic length on Day 13 (2.24+/-0.51 mm v. 1.15+/-0.16 mm, P=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 of the oestrous cycle increased serum progesterone concentrations on subsequent days, which, while having no phenotypic effect on embryonic development on Days 5 or 7, was associated with an increase in embryonic size on Days 13 and 16.
Carter
F
F
School of Agriculture, Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
Forde
N
N
Duffy
P
P
Wade
M
M
Fair
T
T
Crowe
M A
MA
Evans
A C O
AC
Kenny
D A
DA
Roche
J F
JF
Lonergan
P
P
D000818:Animals; D002417:Cattle; D047108:Embryonic Development / Q000187:drug effects*; D030762:Estrous Cycle / Q000502:physiology*; D005260:Female; D042341:Gonadal Hormones / Q000097:blood / Q000494:pharmacology*; D011247:Pregnancy / Q000502:physiology*; D011256:Pregnancy Outcome; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*
D042341:Gonadal Hormones; D011374:Progesterone