Michèle Theau-Clément

The relationship between rabbit semen characteristics and reproductive performance after artificial insemination

The relationships between several rabbit buck semen traits, concerning either the ejaculate or the dose inseminated (volume, mass motility, pH, percentage of motile sperm (PMS), concentration, number of total and motile sperm per ejaculate and per insemination dose) and the reproductive performance of does was investigated in 839 inseminations involving 54 bucks and 111 does. Four genetic types were involved: INRA1601 strain (A), INRA2066 strain (B) and the two reciprocal crossbreds (AB and BA). The mating design was A x A, B x B, (AB or BA) x (AB or BA). Semen was diluted (1:9) and a constant volume of 0.5 ml was inseminated 2-4h after collection. Therefore, the total number of spermatozoa per dose was variable and proportional to the initial concentration. Mass motility significantly influenced the kindling rate. Taken separately, volume, PMS and concentration did not influence the kindling rate but their product, the number of motile sperm per ejaculate, did. Litter size (total born) was significantly influenced by concentration and all variables depending on it, particularly the number of total and motile sperm per dose. However, reproductive performances were predominantly influenced by the physiological status of the does at insemination (lactation stage and receptivity).

Fertilisation rate and preimplantation embryonic development in two rabbit strains of different fecundity, in purebreeding and crossbreeding

Abstract Does ( n = 289) and males ( n = 82) from two INRA strains selected for litter size, A2066 and A1077, were mated in purebreeding and crossbreeding systems, in a diallel design. Females were killed 28 h (D1), 72 h (D3) or 114 h (D5) post-coitum to assess the fertilisation rate of ova shed and preimplantation embryonic survival. A2066 does shed significantly more ova than A1077 does (+ 1.2). The overall pregnancy rate of ovulating females was 92%, without any effect of dam strain and an unfavourable effect of A2066 sires. Among pregnant females (with at least one live embryo), the mating between A2066 males and females gave a fertilisation rate of ova shed significantly lower (82%) than the three other types of matings, which were not significantly different (93%). In contrast, there were no significant differences between the four types of matings in the survival rate of fertilised eggs at D3 (93%) and D5 (87%), although embryos from A2066 dams at D5 were significantly smaller than those from A1077 dams, whatever the sire. The mucin coat was significantly larger in the eggs of A2066 dams, whatever the sire and the stage of pregnancy. Thus, the superiority of A2066 females in the number of ova shed was completely lost in purebreeding by D1, and was retained only in crossbreeding. This was not due to a heterosis effect on embryo viability, but to some antagonism between A2066 male and female gametes in purebreeding. The reasons for this antagonism have to be studied further.