Development of a large commercial camel embryo transfer program: 20 years of scientific research☆
Introduction
Camel embryo transfer has seen tremendous development since 1990. This interest has been driven mainly by the camel racing industry and stems from several inherent and external factors that limit maximization of female genetic merit which is essential to the camel racing industry (i.e. the majority of racing animals and females). In the traditional rearing system, dromedary females have a long (18–30 month) calving interval (Tibary et al., 2005). In addition, the top racing females retire from competition at a relatively advanced age limiting the number of offspring they can have in their reproductive career. Multiple ovulation and embryo transfer (MOET) and associated reproductive biotechnologies allow shorting of generation interval, optimization of mating plans (i.e. more male choices during one season) and the potential of using females for reproduction while they are still in competition. In our laboratory, the production of calves by embryo transfer increased from 30 per year in the early 90s to >300 in 2010.
The objective of this paper is to describe the scientific program behind the development of a leading center for camel reproductive biotechnology. We describe contributions of our research team as well as others in this area, and discuss the development of reproductive biotechnology in the camels.
Section snippets
Follicular dynamics
Management of donors for MOET depends on understanding the follicular cycle, ovulation and early embryo development. Until the mid 1980s, most of our knowledge on the reproductive process in the female camel was based on clinical studies (mainly behavioral and per rectum palpation) and on postmortem observations (mostly slaughterhouse specimens; El Wishy and Hemeida, 1984, Musa and Abu Sineina, 1976, El Wishy and Ghoneim, 1986). Studies to characterize endocrine aspects of the reproductive
Donor management
Although our donor females are predominantly retired racing animals, show and dairy animals have been increasingly presented by owners for embryo transfer in recent years. All donors undergo a thorough health screening before they are admitted to the facility. Donors are kept in quarantine for 4 weeks, during which they are screened for major contagious diseases (trypanosomiasis, camel pox, brucellosis). All animals receive prophylactic antiparasite and a trypanicide (quinapyramine sulfate)
Embryo collection and evaluation
Camelid embryos enter the uterus 6–6.5 days after ovulation. For maximum embryo recovery, flushing is performed 7–8 days after mating. Embryo recovery rates (embryos recovered/ovulations) are highly variable and depend on many factors including superovulation treatment, fertility of the donor and the male, management, collection date and technician experience (McKinnon et al., 1994, Tibary and Anouassi, 1997a, Tibary, 2001a). Recovery rate from the dromedary is 85% in single ovulators and 165%
Recipient selection and management
There are two contracts used for the programs. For resident donors embryos are transferred into females selected from our own herd of recipients which includes 800–1000 females. For visiting donors, owners are requested to provide at least 10 recipients per donor. All animals are identified and screened as describe above for the major contagious diseases before introduction to the center.
Embryo yield
Embryo recovery rates are highly variable and depend on several factors. Embryo recovery rates in the dromedary vary from 114% to 384% and are affected by several factors such as superovulation treatment, fertility, management, collection date and experience (McKinnon et al., 1992, McKinnon et al., 1994, Tibary and Anouassi, 1997a). In non stimulated females embryo recovery rate is 85% in single ovulators and 165% in double ovulators (Table 2).
The type of superovulation treatment can have a
Embryo quality
Embryos recovered from the uterus are at the hatched blastocyst (Cooper et al., 1990, Anouassi et al., 1992, Cooper et al., 1992, McKinnon et al., 1992, Skidmore et al., 1992, McKinnon et al., 1994). The embryos recovered from the dromedary camel 7 days after mating are extremely variable in size and have a diameter ranging from 175 to 500 μm (Skidmore et al., 1992). This variability of the stage of development is probably due to the wide spread of ovulations in superovulation animals. Hatched
Embryo preservation
With the exception of a few trials most of the transfers in the dromedary and particularly in commercial embryo transfer operations are done with fresh embryos. In our laboratory, MOET has been practiced since 1990. During the period between 1992 and 1998, a total of 2653 fresh embryos were transferred, resulting in an overall pregnancy rate of 62% at 35 days. Pregnancy rates improved steadily from 30% to 70% over that period. It is not uncommon to achieve a pregnancy rate of 100% with some
Effect of recipient synchrony of success of ET
Because of the small window of opportunity to transfer hatched blastocysts before initiation of luteolysis, we focused mainly on using asynchronous recipients for our program. Preliminary results in our laboratory between 1990 and 1994 showed that the best pregnancy rates are achieved when recipients ovulated one or two days after the donors. Later we observed that pregnancy rate were similar for synchronous and asynchronous females (-1 or -2 days). Similar results have been reported recently (
Overall embryo transfer program performance
Transfers at the center are performed from September until April. The mean gestation length after transfer is 379.4 days (SD = 10.72; range = 349–420 days). Factors influencing pregnancy length are still under study.
The number of calves produced by embryo transfer per year in our transfer program is shown in Fig. 2. Although the number of calves produced is increasing, the efficiency of the embryo transfer program in terms of weaned claves per transfer remains relatively low compared to other
Conclusion
Dromedary commercial embryo transfer presents several challenges due to the peculiar reproductive physiology of the species. The knowledge gained since 1990 has allowed development of MOET programs but these are still not very efficient. Ovarian stimulation treatment merits more studies. In our conditions, the most challenging aspect of a large scale embryo transfer operation is dealing with the infertile recipient and donor. In addition, results of MOET in term of number of calf production
Conflict of interest statement
No conflict.
Acknowledgements
The authors wish to thank both founders of the Veterinary Research Center at Sweihan for their vision, financial and moral support for the last 20 years. We also thank all the technical staff and workers for their care for the animals. Without their hard work we would not have been able to achieve this program.
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This paper is part of the special issue entitled: International Conference on Camelid Genetics and Reproductive Biotechnologies, Guest Edited by Gregg P. Adams and Ahmed Tibary.