Influence of the postpartum day on plasma estradiol-17 β levels, sexual behaviour, and conception rate, in artificially inseminated lactating rabbits

The present study was designed to determine the influence of several parturition-insemination intervals on the conception rate (CR) and prolificacy in lactating rabbits, as well as the evolution of plasma estradiol-17 β (E2) mean levels and sexual behaviour (SB) during the lactation period. E2 levels and SB were measured daily in 12 lactating rabbits of the California × New Zealand breed with 7–10 pups per litter. E2 levels were determined by immunoassay (ELISA), and SB by means of the turgidity and colour of the vulva. Milk production was predicted in this group by means of the litter weight on Days 21 and 30 of the lactation period, respectively. prolificacy were recorded after parturition in 130 lactating rabbits (7–10 pups per litter) inseminated systematically on 1 postpartum day only, from Days 1 to 11 of the postpartum period (PP). Fresh diluted semen (skim milk + antibiotic) was used in each insemination. Ovulation was induced by administration of an intramuscular injection of 20 μg GnRH at the time of insemination. eans of plasma E2 concentrations were found on Days 1, 5–7, and 23–30 of the PP (P < 0.001), and low E2 levels on Days 13–23 of the PP (P < 0.05), when compared with the general mean E2 level (11.7 ± 0.3 pg ml−1) . Of the does, 75% showed high SB on Day 1 after parturition (P < 0.001). High and medium SB was observed in most of the females (80%) on Days 2, and 25–30 of the PP (P < 0.05). Mean plasma E2 levels differed in does with high SB compared with animals with medium or low SB (15.2 ± 0.13 pg ml−1 vs. 11.4 ± 0.10 pg and 11.5 ± 0.12 pg, respectively; P < 0.05). Correlation of plasma E2 levels with SB was not significant. erall mean CR obtained was 47.4%, suggesting an effect of the parturition-AI interval on the CR (P < 0.09). High CR were obtained on Days 1 and 8 (P < 0.05), and low CR on Day 6 of the PP (P < 0.05) when compared with the general mean. Prolificacy was not affected by the parturition-AI interval. neral litter size at birth was 7.9 ± 0.2, and the number of born dead per litter was 0.8 ± 0.1 pups. roduction measured 4228.3 g± 148.4 g and 4019.4 g ± 116.7 g on Days 21 and 30 of the lactation period, respectively. sults suggest the presence of at least three high plasma E2 concentration intervals, and two periods of increased SB in lactating non-pregnant rabbits during the postpartum period. Mean plasma E2 levels differed in rabbits with high SB compared with animals with medium or low SB. No correlation of plasma E2 levels with SB was found. Sexual behaviour and CR appeared to be influenced by the lactation period, probably via prolactin concentrations. Days 1 and 8 of the PP appeared as favourable Al days in lactating rabbits with 7–10 pups per litter.