High plasmatic progesterone levels at insemination depress reproductive performances of rabbit does

The aim of this experiment was to quantify the frequency of the high progesterone syndrome at the moment of insemination and to study the influence of progesterone level (P4) on receptivity and reproductive performances of primiparous and secondiparous rabbit does. A total of 422 primiparous INRA 0067 were inseminated twice at an interval of 42 days. Prior to artificial insemination (AI), sexual receptivity of the does was tested in the presence of a vasectomised buck and, just after AI, blood samples were collected to determine progesterone concentration by RIA. The mean plasma progesterone concentration was 1.8±3.4 ng/ml and significantly depended on parity (primiparous: 2.2±3.7 ng/ml, secondiparous: 0.9±2.2 ng/ml, P<0.001). At the following AI, 78% of pseudopregnant rabbit does returned to the basal level of oestrous condition, demonstrating that the pseudopregnancy is a reversible process. The overall percentage of pseudopregnant does (P4≥1 ng/ml) was 25.9%, but it was differently (P<0.001) distributed between primiparous (31.2%) and secondiparous does (12.2%). Moreover, primiparous lactating females were more frequently pseudopregnant than non-lactating ones (36.5 vs. 18.9% respectively, P<0.001). The progesterone level of primiparous does was related to the lactation status (2.5±3.8 vs. 1.5±3.2 ng/ml, respectively for lactating and non-lactating, P<0.001). The receptivity was highly related to the level of progesterone (P4<1: 74.1%, 1≤P4<6: 79.1% vs. P4>6: 56.3%, P=0.006). Also the kindling rate was significantly influenced by progesterone concentrations. Non-pseudopregnant does (P<1 ng/ml) had the highest fertility rate (79.0%) but when the progesterone concentration increased from 1≤P4<6 to P4>6 ng/ml, the fertility decreased from 68.1 to 37.4%, respectively (P<0.001). Consequently, the productivity at birth was highly depressed when the progesterone level was over 6 ng/ml (9.5 and 8.6 vs. 4.5 number of born alive rabbits/AI, for P4<1, 1≤P4<6 and P4>6 respectively, P<0.001). The productivity of pseudopregnant and nonreceptive females was very poor in comparison with pseudopregnant receptive does (0.4 vs. 9.5 born alive rabbits/AI). The productivity at birth was also highly (P<0.001) influenced by the physiological status of the does. Primiparous non-lactating does produced the highest number of born alive rabbits/AI, whereas primiparous lactating does had the lowest productivity at birth (9.9 vs. 5.6), secondiparous lactating being intermediate (7.1). In conclusion, the high progesterone syndrome evaluated at the moment of insemination occurred in 25.9% of females and had a strong negative impact on receptivity and reproductive performance of rabbit does.