Endocrine and ovarian response after a 2-daycontrolled suckling and eCG treatment inlactating rabbit does

Synchronization methods are used to obtain higher fertility when artificial insemination (AI) is applied tolactating rabbit does. The most common methods are eCG administration or temporary doe–litter separation.Nevertheless, drawbacks have been reported, such as negative side effects of hormonal treatment in the doeand low litter growth due to absence of suckling, respectively. Recently, improved reproductive performance(without visible consequences on young rabbit growth), has been obtained by applying a 2-day controllednursing method before AI, by allowing for a 10 min nursing of the litter 24 h of separation. The presentstudy was undertaken to examine the pituitary (PRL, LH, FSH) and the ovarian response (follicle size andnumber) to those methods. A total of 442 lactating does inseminated on day 11 post-partum were distributedin three experimental groups: 2CN (closing of nest box on day 9, controlled nursing on days 10 and 11),eCG (20 IU administered on day 9 post-partum) and CONTROL (untreated). Blood samples were obtainedfrom 10 does per group at 48, 24 and 0 h before AI, and 1 h after AI. Both 2CN and eCG treatments similarlyimproved sexual receptivity (76.3, 77.5 and 58.2%, respectively; P < 0.001) and fertility (63.1, 64.1 and48.4%, respectively; P < 0.05) in lactating does, compared to the CONTROL group. Similar plasma FSHlevels in all groups of does and sampling times were observed. Due to the absence of suckling, plasmaconcentration of PRL on day 10 post-partum in the 2CN group was lower than in the CONTROL group(P < 0.05); this endocrine change in PRL levels could explain the better reproductive performances obtained with 2CN treatment. At 1 h after exogenous administration of GnRH (at the moment of AI) a high LHresponse was observed in all groups (P < 0.001).Ovaries from 20 rabbits treated in the same way but uninseminated (2CN, n = 10; eCG, n = 5; CONTROL,n = 5 does) were obtained on day 11 post-partum in order to check the morphometric status (weight, width andheight) and to make histological and immunohistochemical studies to detect growth hormone receptor (GHR).As a result, synchronization methods did not showany significant difference in relation to the CONTROLgroup. However, a small increase in the number of primary follicles was evidenced in the 2CN group withrespect to the eCG group, similarly to the CONTROL group (23.0±3.7, 9.4±4.9 and 14.8±4.92 primaryfollicles, respectively; P = 0.1). GH-R immunostaining-presence was more evident in the 2CN and the eCGgroups, including primordial follicles and oocytes themselves. Thus, there could have been some direct effectsofGHon follicular development, as described in other species. Some ovarian parameters described open newways to study intra-ovarian mechanism of follicular development in the post-partum period of rabbit does.