title: Influence of different reproductive rhythms on serum estradiol and testosterone levels, features of follicular population and atresia rate, and oocyte maturation in controlled suckling rabbits.
abstract: The aim of the current work was to analyze the features of ovarian follicular population and their quality in New Zealand white rabbit does synchronized by 24-h controlled doe-litter separation before artificial insemination (AI) during all their reproductive cycles. Synchronized animals were allocated systematically in two groups. A total of 73 rabbit does (group A) were submitted to a 35-day intensive rhythm (AI on day 4 post-partum [pp] and weaning at 25 days of lactation), and 108 rabbit does (group B) were submitted to a 42-day semi-intensive rhythm (AI on day 11 pp and weaning at 35 days of lactation) during 9 months. At the mid-end of their reproductive life, a total of 26 does (5.4 parturitions), under intensive (n=15) or semi-intensive rhythm (n=11) were either treated in each group with 25 IU eCG 48 h before laparotomy to recover their ovaries (n=7 for group A and n=6 for group B) (according to the Bioethics Committee of the University) or not synchronized with the hormonal treatment (n=8 for group A and n=5 for group B). Blood samples were collected at the moment of ovary recovery; morphometrical parameters, number of total follicles and number of follicles >or=1mm in size in the ovarian surface were recorded. Oocytes from follicles of one ovary were recovered and matured in TCM 199 supplemented with 10 ng/ml EGF, 100 ng/ml IGF-I and 10% FCS. The counterpart ovaries were fixed in paraformaldehyde solution for histological studies. Detection of cell apoptosis was determined using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labelling (TUNEL) technique. Reproductive performance was affected by the rhythm used, with lower reproductive parameters in the intensive group. The average ovary height and width, the mean number of >or=1mm follicles and the number of total follicles were similar between groups. Serum concentrations of estradiol (E(2)) and testosterone (T) were significantly lower in group A vs. B (E(2): 232.4+/-56.1 vs. 399.7+/-53.0 pg/ml; P<0.05 and T: 1.07+/-0.10 vs. 1.68+/-0.23 ng/ml; P<0.05). No significant differences were found in follicular population or in the mean follicular apoptosis index between groups. Metaphase II rate was significantly lower in group A vs. B (48.5+/-3.3 vs. 67.6+/-3.7%; P<0.01), as well as the migration rate of cortical granules (12.7+/-2.7 vs. 38.2+/-6.6%; P<0.001). On the other hand, neither follicular population, nuclear maturation rate nor apoptosis rate were affected by the eCG treatment, but cytoplasmic maturation was higher in animals treated with eCG in group A (29.2% vs. 5.5%; P<0.01). In conclusion, rabbit does under transient litter separation during their reproductive life have both their serum estradiol and testosterone concentrations and oocyte quality influenced by the intensive rhythm, leading to a decrease in reproductive parameters. Also, both intensive and semi-intensive rhythms seem to be less receptive to eCG treatment than expected.
authors.affiliation: Departamento de Fisiología (Fisiología Animal), Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain. rosa.garcia@vet.ucm.es
authors.forename: R M
authors.initials: RM
authors.lastname: Garcia-Garcia
authors.forename: M
authors.initials: M
authors.lastname: Arias-Alvarez
authors.forename: P G
authors.initials: PG
authors.lastname: Rebollar
authors.forename: L
authors.initials: L
authors.lastname: Revuelta
authors.forename: P L
authors.initials: PL
authors.lastname: Lorenzo
mesh_terms: D000818:Animals; D000833:Animals, Suckling; D017209:Apoptosis; D006063:Chorionic Gonadotropin / Q000008:administration & dosage; D004958:Estradiol / Q000097:blood*; D004973:Estrus Synchronization; D005260:Female; D005496:Follicular Atresia; D007315:Insemination, Artificial / Q000662:veterinary; D008297:Male; D009865:Oocytes / Q000254:growth & development* / Q000648:ultrastructure; D006080:Ovarian Follicle / Q000033:anatomy & histology*; D011817:Rabbits / Q000502:physiology*; D012098:Reproduction / Q000502:physiology*; D013739:Testosterone / Q000097:blood*; D014886:Weaning
chemical_list: D006063:Chorionic Gonadotropin; D013739:Testosterone; D004958:Estradiol