title: Effects of lactation length and an exogenous progesterone and estradiol-17beta regimen during embryo attachment on endogenous steroid concentrations and embryo survival in sows.
abstract: The hypotheses that short lactation lengths increase embryo mortality by altering endogenous post-weaning steroid concentrations, and that an exogenous steroid regimen during embryo attachment might increase embryo survival were tested using 36 s parity sows assigned randomly to a 2 x 2 factorial. Sows were subjected to either a short lactation (SL, 13.0 days, n = 25) or a long lactation (LL, 31.5 days, n = 11), artificially inseminated at first estrus and treated daily with 2 ml i.m. of either 25 mg progesterone (P4) and 1.25 pg estradiol-17beta (E2) (steroid treatment, ST, n = 17) or the vehicle alone (control treatment, CT, n = 17) on Days 14-20 post-insemination. Blood samples were collected by jugular venipuncture from weaning to 24 days post-insemination on alternate days. Sows subjected to the SL compared to the LL tended to have a longer weaning-to-estrus interval (WEI) (5.3 versus 4.6 days; P < 0. 10), but did not have a significantly reduced conception rate (CR) (71 versus 90%; P > 0.10). The SL and LL sows had a similar ovulation rate (19.9 versus 21.3 corpora lutea, CL; P > 0.05), but SL sows had fewer viable embryos than LL sows (11.5 versus 15.3; P < 0.05) when reproductive tracts were recovered 28-32 days post-insemination. In addition, even after correction for the difference in number of embryos between groups, viable embryos from the SL versus the LL group weighed less (1.63 versus 1.79 g; P < 0.05), had a decreased amnion volume (1.02 versus 1.22 ml; P < 0.05) and apparently produced less estrogens since estrone sulfate concentration was decreased at 24 days post-insemination in SL versus LL sows (4.3 versus 6.3 ng/ml; P < 0.05). Embryo survival (percentage of CL represented by a viable embryo) however, was not different between SL and LL sows (60 versus 74%; P > 0.05) and no differences in post-weaning P4 or E2 concentrations were apparent. Sows that received the ST only tended to have increased P4 concentrations at 16 days post-insemination compared to CT sows and neither the number of viable embryos, nor embryo survival, was increased in ST versus CT sows (14.7 versus 12.2; P > 0.05 and 66 versus 68%; P > 0.05, respectively). These data suggest that short lactations do not increase embryo mortality by inducing aberrant endogenous post-weaning P4 or E2 concentrations. It is unclear whether or not small, repeated doses of exogenous P4 and E2 during attachment can increase embryo survival.
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-1151, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Belstra
authors.forename: M A
authors.initials: MA
authors.lastname: Diekman
authors.forename: B T
authors.initials: BT
authors.lastname: Richert
authors.forename: W L
authors.initials: WL
authors.lastname: Singleton
mesh_terms: D000818:Animals; D010064:Embryo Implantation; D004622:Embryo, Mammalian / Q000502:physiology; D004958:Estradiol / Q000008:administration & dosage* / Q000097:blood; D004970:Estrone / Q000031:analogs & derivatives* / Q000097:blood; D004971:Estrus; D005260:Female; D005306:Fertilization; D006728:Hormones / Q000097:blood*; D007315:Insemination, Artificial / Q000662:veterinary; D007774:Lactation / Q000502:physiology*; D010060:Ovulation; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage* / Q000097:blood; D013552:Swine / Q000196:embryology*; D013997:Time Factors
chemical_list: D006728:Hormones; D004970:Estrone; D011374:Progesterone; D004958:Estradiol; C017296:estrone sulfate