Abstract
In rabbits, progesterone (P4) levels have to be sufficient for maintenance of pregnancy particularly in does which gestate at first time. Hence, lack of P4 in pregnant does may result in detrimental influence on embryo development. Therefore, the goal of this study was to quantify the effect of single long-acting progesterone dose (SLA P4) injected i.m. 2 days post-mating in the first pregnancy of pubertal does on some productive and reproductive traits at first and second kindling. A total of 12 virgin female New Zealand White rabbits of 6 months of age with mean body weight 2.59 ± 0.43 kg were used in this study and divided randomly into 2 groups of 6 does/each. The first group was considered the control and injected i.m. by saline solution, while the second group was injected i.m. by 1.0 mg/kg SLAP4 (P4, hydroxy-progesterone caprote, Cidolut Depot). Does were naturally mated by fertile bucks and re-mating interval was fixed at 10 days after kindling. Does were individually weighed, fed ad libitum on maintenance ration and reared indoor in individual cages equipped with an automatic drinker and a manual feeder. Blood samples were withdrawn from all does during pre-mating, d 7 post-mating and mid-pregnancy. Data of productive and reproductive traits with treatment were analyzed statistically by two and three-way analysis of variance using GLM procedure of SPSS software. Measures of does development (live body weight (BW) during first and second pregnancy and moment of kindling) and reproductive traits (number of mating/conception, conception rate (CR), gestation length (GL), abortion, litter size (LS) and total litter weight (TLW) at birth, and litter size and mortality rate (MR) at weaning) were recorded in this experiment. Also, the correlation between mean P4 concentration and these traits was recorded. Present findings showed that does BW was not significantly differed between the two groups during the first gestation, and significantly (p<0.05) in the first 10 days of gestation during the second gestation. Furthermore, BW gain was significantly higher in the group injected by SLA P4 (0.20 kg) than in the controls (0.02 kg) particularly during the transition from d 10 post-mating to d 20 of first pregnancy.. While, the transition from d 20 of pregnancy to moment of second kindling, the treatment with SLA P4 resulted in significantly (p<0.05) increased BW (0.26 kg) compared with the controls (-0.04 kg). After first kindling, the drop in doe BW was not differed significantly between the two groups. No significant differences in GL between the two groups of both two kindling. Despite absence of significance, the treatment with SLAP4 resulted in GL slightly lower at first and second kindling than in the controls. Numbers of mating per first and second conception were significantly lower in the does treated by SLAP4 than the control. CR at first and second parity was significantly (p <0.05) higher in the does injected by SLAP4 (88.88 ± 11.12) than the controls (55.53 ± 14.06). Abortion was significantly (p<0.05) lower in the does inject by SLAP4 than the controls of both kindling. LS and kit weight at birth and MR at weaning of both two kindling were not significantly differed between the two groups, while TLW at birth of first kindling was significantly (p<0.05) higher in the SLAP4 group than the controls. P4 concentrations were significantly higher at first week and mid- pregnancy of does injected by SLAP4 than the controls (4.97 ± 1.27 and 12.45 ± 2.79 ng/ml blood serum vs. 1.69 ± 0.66 and 5.11 ± 1.96 ng /ml blood serum). Also, the overall mean of P4 concentration from mating to mid pregnancy was significantly higher in the does treated by SLAP4 than the controls. Otherwise, levels of P4 at mating were insignificantly < 1.0 ng/ml blood serum in all does. The correlation between mean p4 concentration and TLW at birth was significantly positive (r = 0.90; p<0.05) of does injected in the first pregnancy by SLAP4 compared with the control group. Conclusively, the SLAP4 improved doe BW, numbers of service/conception and CR of both two kindling, reduced abortion of two kindling, and increased TLW at first kindling. Otherwise, SLAP4 had no significant effect on GL, MR and LS of both two kindling.