Sex Determination in Psittaciformes
Many avian species are considered sexually monomorphic, which means it’s difficult to tell their sex by looking at them. While most of these species probably have subtle physical characteristics that could be used to distinguish between the sexes, these differences are not readily visible.
Types of Sex Determination Tests
- Chromosomal analysis. In birds, the female is heterogametic (Z and W chromosomes) and the male is homogametic (two Z chromosomes). Cultured cells from a bird (most commonly cells derived from a developing feather) can be used as a source for chromosome isolation and karyotyping. Successful chromosome analysis by an experienced cytogeneticist can provide information that cannot be ascertained from any other technique. The primary disadvantage to chromosome analysis is the difficulty in obtaining viable cells for culture and a slow response time.
- Laparoscopy (endoscopic evaluation of the abdomen). Laparoscopic identification of the gonads by an experienced endoscopist is often used as the “gold standard” for sex determination. Laparoscopic sexing is particularly advantageous because it provides immediate results and evaluation of physical characteristics of the reproductive tract (as well as other organ systems). Gonadal tissue from a mature bird is easily visualized as compared to that of a juvenile, but an experienced endoscopist can determine the sex of chicks. The primary disadvantages of laparoscopy are the necessity of anesthesia and invasion of the coelomic cavity.
- DNA probe-based test (PCR) on whole blood. An increased number of birds are being sexed using DNA amplification techniques that differentiate between unique nucleic acid sequences found in the W and Z chromosomes. While these techniques offer the advantage of a non-invasive sexing method and do not require anesthesia, the only information provided is the sex of the bird.
DNA probe-based tests are subject to errors caused by contamination that is inherent with any DNA amplification and detection assay. The greatest potential for contamination occurs when blood samples are collected from a toenail or when feathers are used in lieu of blood. Washing the nail prior to sample collection, as is suggested, does not reduce the potential for contamination. For example, if the target segment of nucleic acid from the W chromosome, which is present in every cell in the heterozygous female bird, were to contaminate the feather of a male and the male’s feather was used for sex identification, the male bird could be incorrectly identified as a female. Contaminating a male’s sample with nucleic acid from another male would not effect the results.
- Generally, endoscopic evaluation of the reproductive tract and other internal organs by an experienced endoscopist is the best method for sex identification in birds that are being used for breeding purposes. Laparoscopy in conjunction with chromosome analysis would provide information about the condition of the reproductive tract and detect some chromosomal defects that could affect reproduction. Blood samples, collected by venipuncture, can be used in well-validated and controlled DNA amplification tests to determine the sex of many psittacine birds, if the convenience of this assay is more important than inherent inaccuracy as a result of sample contamination. The use of feathers for sex identification should be used only when some inaccuracies are acceptable.
- Careful examination of the interior of the cloaca.
- Blood feathers that are removed for chromosomal analysis should stop bleeding immediately after removal. If they continue to bleed, apply direct pressure to the feather follicle and call your avian veterinarian.
- Laproscopy is performed under general anesthesia and your bird may be groggy for several hours. The birds should be placed in a quite area to rest. Avoiding placing the bird on high perches over hard surfaces. There will be a small skin incision where the endoscope was inserted. This cut should heal within 4 to 5 days. If the cut is bleeding or becomes red or swollen, contact your avian veterinarian immediately.
- Knowing the sex of your companion bird can be important to help determine if problems that occur are related to specific disease syndromes that only affect males or females.
- There are some behavorial differences between male and female birds of some species and knowing your bird’s sex may help you better understand these behavoirs.