Crossbeak

[John W Blehm]

The problem is not with eliminating from SOME of the offspring, but in eliminating it from an entire line of birds for good.   I'm not sure anyone has accomplished that; it may have been done, but I haven't heard about it in the last 40 plus years of breeding.   The wheaten bantams are about the best success story I know of, but I'm pretty sure it still lurks in the genetics of individual birds.

The best we can do may be to really study the beaks of individual birds, in hand, before putting them in a breeding pen.  We all know we don't breed from birds with crossed beaks, but how close to being perfect are they?  Mike mentioned about them closing properly and that is one check point.  Proper length of both the upper and lower beaks is another.  Curvature is not just something that happens horizontally and viewed from the side, but also view the beak straight on and check that it isn't curved to the left or right of the face (both upper and lower beaks together).  Be critical when you can.

[Lee G]

^ Good advice John. Not all beaks are made the same, that is for sure. In fact, bearded and crested birds seem to be more prone to weak or ill fitting mandibles in general. And once the lower jaw goes wonky, the top is soon to follow. I've also seen curved beaks on adults that were so slight it's likely to be missed unless you're looking for it. Which is the exact reason I've added a ruler to my tool kit, and all beaks must pass the straight edge test before entering a breeding pen. I am very particular about heads, and nothing bugs me more than a bad head on a bird.

[Michelle Ogden]

I'm really impressed with all the information brought up here! I did see the post on FB, but nice to see it discussed here too.
Beth, the birds in question were the brown-red's sister and the smaller nice male (the one with wonky legs got attacked, and my friend sold my back-up, ugh!).
I've got a bunch of chicks I'm growing out, some of which are new, unrelated stock, so hopefully I'll have some good replacement males in there...
I'll go out tomorrow and inspect the adult and chick beaks to see if I can spot what you're talking about, John.

[Suki]

Morley Jull in 1950 says that twisted beak was found to be a simple autosomal recessive gene.    Hutt assigned it  the symbol is "su" and felt that it was a symptom of microphlathmia, a congenital birth defect that  can be chemically induced,  which the Merck Manual agrees and cites as a major cause of the condition in poultry.  See here. http://qurl.com/pldgs

Landauer described 4 types of crossbeaks


1)  the first type is present in chicks that have one eye missing and the upper beak is deviant
2)  upper or lower deformities that also have abnormal skulls.  This is homozygous condition.
3)  the beaks are normal at hatch but the crossbeak appears a month later.** this is most common according to Hutt
4)  cross-beaks that are developmental either before or at hatch which Landauer found only in White leghorns or Leghorn crossbreds, though Jull questions that point.

Types 3 and 4 are totally hereditary and are recessive to a normal beak.  If they are bred, they will produce progeny with normal beaks which has made tracing it difficult , as no statistical ratios were found in 1950, that could be easily replicated & verified.  It was found in a French experiment by Mercier and Poisson in 1925,  that if trimmed, the bird could live a normal life and not have crossbeaked progeny.  But when the upper beak is normal and the lower is twisted, that  bird has to be culled,  as trimming will not suffice,  as the tongue gets exposed and becomes hardened (cornified) with age and it will not be able to eat.


But there are lots of beak issues, short upper beaks, missing mandibles, short lower mandibles (half the length of the lower beak)  and missing maxillae (the upper beak is absent).  Also in the latter case the nasal bones were very small, so many of these die in shell, but not all.  All of these other cases are also autosomal (non sex linked) recessive and totally lethal in the homzygous state.  Beak issues happen a lot according to Prof Jull with Houdans (a crested breed).


~brownie

[Mike Gilbert]

I don't think I agree with Jull.    If it is simply a single recessive, why wouldn't it be possible to produce a line that throws all cross beaks?    And why do cross beaks and normal beaks come out of the same pair matings, even out of the same setting of eggs? (They do - I had a pair of buff bantams that did it this year).   No, I think it has to be a little more complicated than that. 

[Suki]

Well your first question Mike, that was done and it didn't happen which Hutt mentions so it does make Jull's comment suspect.
the second comment about breeding pairs, is taken up by Hill in 2001 where he studied that and the relationship of the egg yolk weight, age of the breeders and the incubator.   Hill did find a correlation early on in the incubation cycle but nothing later.  Others who have replicated this, Wolanski (2003, 2006) &  came to the same conclusion: there is a correlation early in the incubation cycle to the chick beak, (actually yolk length to beak) but we are talking really early, i.e.  day 7.  Here they they weighed them all against the metric of .057.  Since reading this a while ago,I've tested my eggs at day 7 but I don't have cross beaks so I haven't found anything....and of course that metric may not be the same for Ameraucanas.  You would need to weigh a lot of eggs at day 7 to get the proper weight -- something I am doing with Araucanas but not yet with any other breed I own.

[Tailfeathers]

I would tend to agree with Mike.  I'm not geneticist but, from what I do know, it is possible to get homozygous recessive genes.  For example the Straight Comb birds.  You know if you cross 2 SC birds you are going to get SC chicks.  So why wouldn't that be the case with recessive crossbeak genes?

The other question I have is how was it determined in 1950 "to be a simple autosomal recessive gene"?  Was the technology even available then?

Interestingly enough, I read a post on FB today from a local poultry group site that some gal got a chick that is a crossbeak and has NO eyes!

[Mike Gilbert]

It is possible to have the  homozygous condition for any type of gene, which means one of that particular gene was inherited from each parent, so there is a set of two.     The exception would be sex-linked genes, which are inherited only from the male parent in birds (just the opposite for mammals and humans), so the condition of that single gene in a female bird would be called hemizygous.     While they did not have the laboratory techniques available 65 years ago that we have today, the general principles of Mendel's laws were well known.   Jull would have made test matings to arrive at his conclusions, but I believe he interpreted the results in an oversimplified manner. 

[John W Blehm]

Study on LOC426217 as a candidate gene for beak deformity in chicken

Conclusions
To the best of our knowledge, this is the first time that LOC426217 was studied as an important candidate gene for beak deformity in birds. The over-expression of LOC426217 may be the cause of beaks malformation...

Background
The beak is an external structure of birds, consisting of the upper and lower mandibles covered with a thin keratinized layer of epidermis [1]. It is used for many important activities such as feeding, drinking, fighting, and preening. In addition to striking morphological differences between species, beak deformities of different forms (noticeably elongated, crossed, bent at right angles) have been documented in many wild birds [2, 3, 4, 5, 6, 7]. Frequencies of 1 % to 3 % of beak deformity (normally a crossed beak) were found in various indigenous chickens of China, such as Beijing-You (BJY) (studied here), Silkies, Qingyuan Partridge, and Huxu Chickens. Chickens with deformed beaks have reduced feed intake and growth rate. Therefore, beak deformity represents an economic as well as an animal welfare problem in poultry industry. According to our observations in a BJY population, in the absence of known environmental factors contributing to the malformation, birds with deformed beaks present consistently in each generation and cannot be eliminated from a population simply on the basis of the phenotype. This indicated the genetic effects underlying this trait...

Validation and tissue expression profile
...The results showed that the expression of LOC426217 in the deformed beaks was significantly higher than that in the normal beaks, which was in great agreement with DGE analysis. The result of tissue expression profile also revealed that this gene was specifically expressed in beak tissue. LOC426217 is a member of the keratin family [24]. Keratin is a key gene family for maintaining normal cell morphology [16]. Variation of keratin structure can lead to beak deformity [25]. It is also an intermediate filament protein that has essential functions in maintaining the structural integrity of epidermis and its appendages [26], presumably including the beak. In addition, keratin is the main composition of the chicken beak. This may be the main reason for its high expression in beak tissue. According to our early observation of beak anatomy, the lower mandibles of the beaks were abnormal/asymmetry. It was reported that avian keratin disorder could result in gross over growth of the rhamphotheca [7]. The beak deformity caused by the excessive growth of one side of the lower mandibles maybe a result of abnormal high expression of LOC426217.

[Mike Gilbert]

So, John, what conclusions do you draw from this study?    Did they identify what exactly would cause the overexpression of this gene as the likely causative agent in the variability of keratin?   I have long believed it is two or more different genes, likely on different chromosomes, working in concert with one another that cause the abnormality.    Or perhaps it could be something environmental along with the variable distribution of keratin?

[John W Blehm]

My understanding is they feel environment plays a role (without saying how) and other genes may be involved, but this keratin gene is the key player in deformed beaks. I don't remember them saying anything about it being a recessive or dominant gene and that in the Chinese chicken strain studied cross beaks show up.  I don't know of anyone that would breed from a bird with an cross beak and they seem to say the problem can't be eliminated by selective breeding.  If they mean obvious cross beaks (aka scissor beaks) I can agree, but I still believe the problem can be addressed by selecting against breeders with slightly curved beaks and even less than perfect ones.  We know from experience that some breeds/varieties/strains are more or less likely to have crossed beaks.