Improving the reproductive efficiency of small stock by controlled breeding

[摘要] English: Three independent experiments were conducted in sheep and goats to compare the efficiency of synchronization on induction of oestrus and fertility following a synchronized oestrus and artificial insemination. In experiment 1, oestrous synchronization study was conducted on 224 Dorper ewes kept under extensive veld conditions during the transition period from the natural breeding season to anoestrous period. Two types of intravaginal progestagen sponges (MAP; 60mg and FGA; 40mg), time of PMSG administration relative to sponge withdrawal (24h before, at or 24h after), different routes of PMSG injection (intramuscular, subcutaneous) were evaluated, and the combination of all these factors were compared on oestrous synchronization efficiency (oestrous response, time to onset of oestrus and the duration of induced oestrus) and fertility (pregnancy, lambing and fecundity rates) following AI with 0.1ml fresh diluted semen. No significant differences in terms of oestrous response, time to onset of oestrus and the duration of induced oestrus were recorded due to differences in the type o.fprogestagen sponges used, time and route of PMSG administration or a combination of these factors. The overall pregnancy, lambing and fecundity rates were 72.3%, 91.1% and 126.0%, respectively, with no significant differences in pregnancy, lambing and fecundity rates between MAP and FGA primed ewes (70.6%, 85.3% and 120.8% vs. 74.0%, 97.0% and 131.1%, respectively). Pregnancy, lambing and fecundity rates were significantly (P<0.01) higher in ewes injected with 300ru PMSG 24h prior to (78.0%, 115.3% and 147.8%, respectively) or at sponge withdrawal (75.0%, 94.6% and 126.2%, respectively), compared to ewes injected 24h after sponge withdrawal (70.2%, 73.7% and 105.0%, respectively) or ewes not injected with PMSG (60.0%, 70.0% and 116.7%, respectively). The maximum pregnancy rate (93.3%) was recorded in ewes synchronized with FGA sponges plus 300ru PMSG administered intramuscular 24h after sponge withdrawal and FGA plus 300ru PMSG administered subcutaneous 24h before sponge withdrawal. In experiment 2, oestrous synchronization trial was conducted on Blackhead Ogaden (BRO) ewes, one of the lowland sheep breed in Ethiopia, maintained under traditional management conditions. MAP (60mg) and FGA (40mg) treatments with different durations of priming (9, 12 or 15-days), 300ru PMSG with different times of administration relative to progestagen withdrawal (24h before, at sponge withdrawal and controls) and the combined effect of all these factors were evaluated. Both MAP and FGA progestagen sponges were equally effective in inducing oestrus (90.2% vs. 93.0%, respectively). These progestagen sponges induced a similar response in the time to onset of oestrus (40.0±2.2h vs. 39.4 ±2.1h, respectively) and the duration of induced oestrus (46.1±2.4h vs. 43.9±2.3h, respectively). No significant differences were recorded between MAP and FGA sponges regarding the pregnancy, lambing and fecundity rates. Administration of 300ru PMSG significantly (P<0.01) increased the induction of oestrus and decreased the time to onset of oestrus relative to progestagen withdrawal. Regardless of the time of PMSG administration, oestrous response was higher (P<0.01) in PMSG administered ewes (100.0%), compared to the control (75.0%) ones. The time to oestrus relative to progestagen sponge withdrawal was also significantly (P<0.01) earlier in PMSG treated ewes, compared to the control ewes. Pregnancy and lambing rates were also significantly (P<0.05) higher in PMSG administered ewes, compared to control ewes. The duration of progestagen priming period significantly (P<0.01) affected the oestrous response in these ewes. The percentage of ewes, which exhibited overt oestrus, was significantly (P<0.01) higher in the 12 and 15-day (93.1% and 96.2%, respectively), compared to 9-day progestagen priming (86.2%). The duration of progestagen treatment, however, had no significant effect on time to onset of oestrus, the duration of induced oestrus, pregnancy and lambing rates. Pregnancy rate was higher (P<0.01) in ewes with a BCS of between 3.1 and 3.5 (82.6%), compared to ewes with a BeS of>3.5 (4l.7%). The lambing rate was also higher (P<0.01) in ewes with a BeS of between 3.1 and 3.5 (87%), compared to ewes with a BeS of>3.5 (4l.7%). From 18 synchronization treatment combinations compared in this trial, synchronization with FGA sponges for 9 days with no PMSG or MAP sponges for 12 days with no PMSG induced oestrus in a significantly (P<0.01) lower percentage of ewes (25.0% and 60.0%, respectively). Similarly the pregnancy rates were also lower (P<0.01) in ewes synchronized with FGA sponges for 9 days with no PMSG (0.0%) or MAP sponges for 12 days with no PMSG (40.0%). The best pregnancy rates (100.0%) were recorded in ewes synchronized with MAP sponges for 9 days and 300IU PMSG 24h before sponge withdrawal, MAP sponges for 15 days plus 300IU PMSG at sponge withdrawal, FGA sponges for 9 days plus 300IU PMSG 24h before sponge withdrawal and FGA treatment for 12 days plus 300IU PMSG at sponge withdrawal. In experiment 3, oestrous synchronization trial was conducted on 120 Somali does in Eastern Ethiopia. Synchronization efficiency in terms of oestrous response, pregnancy, kidding and fecundity rates of MAP (60mg) and FGA (40mg) progestagen sponges with 4 priming periods (9,12, 15 or 18 days), with or without administration of PMSG at different times were compared. Both MAP and FGA intravaginal sponges with 9, 12, 15 or 18-day treatment periods were recorded to be equally effective in inducing overt oestrus - with no significant difference in pregnancy, kidding and fecundity rates. The pregnancy rate was significantly (P<0.05) higher in control does (no PMSG) (39.5%), compared to does administered 300IU PMSG 24h prior to (25.7%) or at sponge withdrawal (28.6%). Besides oestrous synchronization treatment, age and body weight (BW) of the does at AI significantly (P<0.05) affected the pregnancy rates. Pregnancy and kidding rates were significantly higher in 6 year old does (60.9% and 60.9%, respectively), compared to 1 (25.8% and 27.9%, respectively) and 9 year old does (17.7% and 29.4%, respectively). Similarly, significantly (P<0.05) higher pregnancy and kidding rates were recorded in does with a body weight of above 20kg at AI, compared to does below 20kg body weight. Significantly higher pregnancy rates were recorded in does with a body condition scores (BCS) between 2.6 and 3.0 at AI (44.8%), compared to those with a BCS between 2.0 and 2.5 or 3.1 and 3.5 (25.4% and 37.5%, respectively). Therefore, the use of PMSG as an oestrous synchronizing agent in Somali does is not recommended, as it would seem to compromise fertility. An upper and lower reproductive age limit should be set for this breed. Maintaining an optimal pre-mating BW (21 to 30kg in this case) and BCS (2.6 to 3.0) is crucial for the success of a synchronized breeding program. In general, both MAP (60mg) and FGA (40mg) progestagen sponges were equally effective in inducing synchronized oestrus with no significant difference in subsequent fertility. Thus, either of the progestagen types can be used for controlled breeding. Unlike in Somali does, administration of 300IU PMSG either 24h prior to or at sponge withdrawal improved fertility in the Dorper and BHO ewes. Therefore, the use of 300IU PMSG as synchronization agent is recommended in Dorper and BHO ewes but not in Somali does. The duration of progestagen treatment did not affect subsequent fertility both in Somali does and BHO ewes. Maintaining an optimal BCS (3.1 to 3.5) prior to AI is recommended in BHO ewes. Reproductive maturity age and the maximum age limit for culling should be implemented in Somali female goats. In all cases, the effect of nutritional status, dose of PMSG and season of synchronization warrant further investigation. Early pregnancy diagnosis by use of ultrasonic equipment is important to identify possible embryonic resorption, as large differences exist between the non-return rate and the actual pregnancy rate in both Somali goats and BHO ewes in Ethiopia. Further studies on the response of African small ruminant breeds to assisted reproductive techniques under different nutritional management and during different seasons are recommended.

[发布机构] University of the Free State