DNA sexing

DNA sexing in Genimal in a few words

DNA sexing is nowaday the best method to determine the sex of the birds. Therefore, Genimal Biotechnologies gives the opportunity to bird breeder to determine the sex of their birds with accuracy and short delay.

• Reliability : Near 100%. Possibility to get the result in 1 day with the express option
• Test turnaround : 1 – 3 days
• Samples : Feathers or Dry blood on paper or Eggshell
• Species : We can do DNA sexing on all bird species. However we cannot sexed ratites (Ostrich, Rhea, Emu) and some glossy starling.
• Conditions : Order a pack of DNA sexing now and then send your samples at different times within the limit of 2 years. For example, you can send 2 samples tomorrow, 3 other in two months etc.

Why do DNA sexings in birds

The sexing of birds is a major issue in breeding because it allows to form with certainty couples to reproduce them. Placing two individuals of the same sex in the same aviary also increases the risk of aggression and dominance of one bird over the other. Having a couple with certainty thanks to DNA sexing is therefore a time saver in obtaining chicks.
From a research point of view, DNA sexing of birds is often requested in population studies. Indeed, it makes it possible to study the sex ratio in bird populations (Conover & Hunt 1988; Parkes 1989; Olson & Arsenault 2000), to study the hypothesis of sexual selection (Møller 1993; Savalli 1995; Regosin & Pruett-Jones 2001), to study the mating systems (e.g. Poinani & Pagel 1997; Sorenson & Payne) or to study the ecological niche differentiation (e.g. Richman & Price 1992; e.g. Cicero & Johnson 1998).

The differences between males and females in birds

In birds many species show no visible difference between males and females. This is called an absence of sexual dimorphism. Thus, in passerines more than 60% of the species does not show sexual dimorphism (PRICE & BIRCH 1996). In non-passerines, more than 80% of the species have no sexual dimorphism. In some species the visual differences between males and females only appear several weeks after hatching. In this case the use of DNA sexing is compulsory.
In birds with a sexual dimorphism, the differences between males and females are of several types but are often unreliable:

• Difference in plumage color. The differences in plumage between the male and the female can be very important as it is the case for Eclectus for example. These differences can be very sligh as in the Lybius dubius and often justify the use of DNA sexing. The color differences in some species appear late, several months after hatching and therefore the use of DNA sexing is mandatory.
• Size difference. Generally speaking, males are generally larger and heavier than females. The most important example is found in the hornbill (for example Bycanistes brevis) with males weighing on average 1/3 more weight than females. On the other hand, in more than 99% of species the size difference is too small and more due to food and breeding conditions. In this case the use of DNA sexing is compulsory.
• Difference in standing. In some species a different standing is observed in the male and the female. The males stand upright and proudly on the perch. This difference remains subtle, unreliable and variable depending on the species. DNA sexing is therefore generally practiced.
• Singing. In some species, only the male sings, thus distinguishing the male from the female. In other species, both sexes sing or do not sing or very discreetly. This sexing method remains unreliable and it is necessary to wait until the birds are adults and during the breeding season to be able to sex them.

What are the different methods of sexing?

There are different veterinary and laboratory methods for sexing birds :

• Endoscopy is an ancient method that is rarely used today. This method is not recommended because it is invasive for the bird. Indeed it requires anesthesia of the bird and surgery on the coelomic cavity. This method is also considered unreliable in birds that have not reached sexual maturity (adult). Indeed, according to his experience, the veterinarian may have difficulties in differentiating the male and female genitalia.
• The hormonal dosage. Some publications demonstrate the possibility of sexing birds by measuring certain sex hormones such as DHEA and estradiol. This method requires the development of the average hormone concentration in each species. The concentration of hormone in the same bird also varies depending on its age and stage during its reproductive cycle. All these uncertainties make this method of sexing nonexistent.
• The karyotype. This method involves isolating and observing the chromosomes of birds. At the level of the sex chromosomes, the female has a Z chromosome and a W chromosome. The male, on the other hand, has two Z chromosomes and no W chromosome. This laboratory technique is long, tedious and expensive and therefore no longer practiced Nowadays.
• DNA-based method. Numerous methods based on the study of DNA have been developed historically. The most important were the analyzes based on southern blot, RFLP, the use of DNA minisatellite or even real-time PCR. These methods are reliable but often more complicated and more expensive than traditional DNA sexing and therefore they are rarely used.

Newer methods than DNA sexing have been developed in recent years, such as HRM PCR or isothermal amplifications. The very precise HRM PCR requires complex and costly development for each species of bird and is therefore rarely used. Isothermal amplifications require very little equipment and allow sexing in the field in the absence of a laboratory. This method remains expensive, however, and many adjustments are necessary for each species in order to make the test reliable.