Reproductive management of donkeys under productive programs

Domestic donkey (Equus africanus asinus) production programs for commercial purposes have gained special relevance in recent years, mainly due to clinical evidence proving that donkey milk is a natural alternative for food management of children with cow’s milk allergy (CMA). Donkey´s milk composition is similar to human milk, has a proven tolerability, palatability, and an adequate concentration of nutrients, as well as a large number of bioactive compounds (Sarti et al., 2019; Martini et al., 2021; Di Salvo E et al., 2022)). This led to a significant increase in scientific information flow regarding this species, historically relegated by science. Donkey milk production in the world is currently limited to a few countries, most of them in the Mediterranean area (Italy, Portugal, Spain, France, Serbia, Croatia; Greece), Asia (China) and very few in America (Chile, Mexico, Brazil, Argentina). Donkey milk production systems are mainly based on “semi-intensive” reproductive management, using natural breeding, with pregnancy rates between 85 and 90% (personal data). However, to implement genetic improvement programs and avoiding inbreeding risk, it is necessary to improve certain aspects of directional reproduction using assisted reproductive technologies (ART). Most ART applied to donkeys are adapted from horses (Oliveira, 2006), extrapolating information and knowledge and creating new information specific to donkeys. One of the first ART that can be applied is artificial insemination (AI) with fresh, cooled and frozen semen. Pregnancy rates/cycle with frozen semen (0-36%) are significantly lower than those obtained with fresh (86%) or cooled (78%) semen (Watson, 2000). Frozen semen induces a more severe inflammatory reaction in the uterus of the jenny than fresh semen (Kotilainen, 1994), and was hypothesize (Canisso, 2019), but not prove, that may be the cause of the low pregnancy rates obtained with frozen donkey semen in this species. In vivo embryo production by AI and subsequent uterine lavage for embryo recovery in donkeys shares numerous similarities with horses; uterine lavage is performed using the same technique, between 7 and 9 days post-ovulation, embryos are processed and transferred to synchronized recipient donkeys with pregnancy rates of 45-50%. Regarding in vitro embryo production, despite the fact that highly complex ART such as cloning, Intracytoplasmic Sperm Injection (ICSI), follicular aspiration and in vitro maturation have gained relevance and experience in horses in recent years, there are very few reports on this subject in donkeys and they are still in initial phases of development (Panzani, 2020; Flores Bragulat 2023). Although these complex biotechnologies may not be applied in milk production systems, they could be extremely important for the preservation of certain breeds of donkeys that are considered endangered.

Even though all aspects of a production system are important, such as genetics, reproduction and animal health; animal welfare and respect for the biological and behavioral aspects of this species are essential to work properly and obtain optimum results. Donkeys have been much less genetically manipulated by humans, so intensive management that entails changes in social groups, isolation, aggressiveness, and sudden changes in diets generate significant stress that negatively impacts reproduction and their productive health status, especially in milk production programs. So it is advisable to consider all these aspects when designing a reproductive program for donkeys and that changes or management guidelines such as serial ultrasounds, insemination, flushings, etc. are introduced sequentially and in a friendly manner.