Rumplessness

 

There is an old wives’ tale about crossing ‘tail’ to ‘rumpless’ every few generations to increase fertility. Maybe this does help fertility but what this really does, is serves to encourage the reproduction of tail birds or part tail due to the fact that some recessive tail modifier genes can accumulate to the point of even taking over the homozygote Rumpless.

The Rumpless genes are: Dominant Rumplessness “Rp” & Recessive Rumplessness “rp-2” The latter condition commonly known as the “Roach Back” is not usually found in our Araucana. The rumpless genetic normally found in our Araucana is of the Dominant Rumplessness “Rp” form. It is commonly accepted that there are 3 types of rumplessness: complete, intermediate and accidental. I will expand on what really concerns us and our Araucana: the complete and the intermediate types.

In “Poultry Breeding and Genetics”, R. D. Crawford, editor, the research published on this subject is summarized by Ralph G. Somes, Jr as follows:

 

Dunn (1925) Landauer (1928)

Complete & Accidental form:  Appeared outwardly the same. The posterior of their bodies is round, and they lacked an oil gland and tail feathers. Examination of the vertebrae, however, showed that they were different.

The complete rumplessness condition is characterized by a lack of all but the last two pygostyle vertebrae, all the free caudal vertebrae, and one or two vertebrae from the centre of the five synsacrocaudal vertebrae.

Du Toit (1913)

The intermediate rumplessness differed from both of the others in that all the free caudal vertebrae were present although they were fused together irregularly. As with complete rumplessness, the pygostyle was lacking except for the last two vertebrae, and one or two vertebrae were missing from the centre of the synsacrocaudal vertebrae, Rudimentary oil glands appeared on about 25 percent of this type, and varying numbers of tail feathers (2-17) were usually present.


The genetic basis of the intermediate or modified rumplessness was studied by Dunn and Landauer (1934, 1936) after it appeared following the mating of rumpless to normal. Additional outcrosses as well as selection for the intermediate type resulted in all heterozygotes and some homozygotes of the intermediate type. This phenotype appeared to be due to multiple recessive modifying genes which are carried by normal birds and which tend to suppress abnormal development.

Dunn and Landauer (1934)

The rumpless condition also had an influence on viability and fertility. The proportion of rumpless embryos dying between the l7th to 21st days of incubation was always higher than expected, and the proportion of rumpless chicks that hatched was lower than expected. This applied to both the complete and intermediate types. For the complete type, this reduction in viability was about five percent. They were unable to determine if viability was better in the intermediate type. Increased mortality continued post hatch with 12.1 percent of rumpless and intermediate chicks dying during the first two months as opposed to 7.2 percent of the normal chicks. Fertility problems resulted from purely mechanical reasons. Lack of tails which act as balancers in the copulation act resulted in incomplete copulations. Also very heavy fluff about the cloacae was an additional handicap. Fertility was as low as 17 percent for rumpless x rumpless, and as high as 71.2 percent for normal female x intermediate male. Fertility was always better when the females were normal.

So, in short, the use of tail or part tail in our breeding program will only help reproduce and integrate the tail gene and its modifiers. This can easily be seen today in many Araucana, probably because of the old wives’ tale mentioned above.  I know that our breed is rare in this country and that sometimes one must deal with what he has as best as possible but we should avoid the use of tail or part tail or even single retrice birds when breeding our Araucana. This is the only way we can hope to have true rumpless birds.

Rumplessness is also cause for a little higher mortality in chicks but it is not a lethal gene. As far as low fertility is concerned some birds will have lower fertility while others will not. Personally I have experienced fertility rates much higher than the 17 percent noted above. Fertility is also influenced by weather and season etc. It should be understood that fertility is different than hatchability, since other genetics such as the tuft gene can and will affect the end result.