Angel Wing

This article is not meant to be a scientific study, but only the personal observation and experience of one breeder.

Slipped wing, also known as angel wing, is a condition in which the extremity of the bird's wing, weakened by it's own weight during the early stages of the primaries' development, folds at an unnatural angle to the body.

The majority of Muscovy breeders have, at one time or another, been faced with this problem. This in turn has given rise to a variety of theories as to it's causes and numerous approaches to its correction. These hypothetical causes cover a wide spectrum of concepts ranging from the accidental stretching of the bird's undeveloped wing tip to the presence of problematic genes. The most popular, by far, seems to be the notion that the wing is deformed by the young bird's accelerated growth, due to an overabundance of protein in it's diet. Unfortunately, most of these ideas have never been verified.

Alleged cures also vary quite significantly. Some more colorful than others, but most offering some degree of success, depending on the severity of the case and at what stage the corrective manipulation is started. These procedures, which usually call for the use of strings or tape, are meant to immobilize the wing until the bone and cartilage have developed sufficiently to hold a more or less natural position without assistance. For those who believe that nutrition is the culprit, a reduction in the amount of protein fed to the young birds seems to be the preferred course of action.

Personally, I am convinced that the problem is genetic; at least at it's base. By that I mean, in order for a bird to develop slipped wing, it must first have the genetic predisposition for it. Then, and only then, if the duckling is fed a diet high in protein, will it develop the symptoms.

I make it a point of maintaining very accurate records and pedigrees (all my birds are mated in pairs, making clutches genetically distinct from one another); this in turn greatly simplifies the task of tracing the exact source of a problem. At first, amongst my original Muscovies, the incidence of slipped wing in any given clutch would range from 0% to 100%, depending on the strain. Since I have always offered my young birds homemade rations containing high levels of protein, several long time breeders led me to believe that the cause of my problem was strictly nutritional. But the fact that it's manifestation varied so greatly from one family to the next, made me question why some birds seemed resistant to the affliction, while others fell prey to it; even if all had been consuming the same diet and managed in the same way.

I soon began to notice obvious patterns within my breeding program. The most important observation was that clutches in which all the young had slipped wing, usually came from matings in which both parents had developed the condition as youngsters, but had their wings "repaired." Another very important fact was that when a clutch was totally free of slipped wing, the parents, if mated together in future seasons would rarely, if ever, produce youngsters with the problem. There had to be something more than just nutrition controlling the occurrence of this
deformity. Although I never got around to conduct any in depth experimental breeding, I did however try quite a few test matings using birds that were either afflicted or normal, but coming from clutches where only one parent showed the condition. I also used birds from parents that had always produced normal offspring.
The results were pretty much predictable and consistent. Based on those tentative findings, I would guess that the predisposition for slipped wing is caused by one or possibly several recessive genes acting in unison. Hopefully, in the near future, someone will be able to confirm this hypothesis.

As far as I'm concerned, repairing the wing of an affected bird, and using it as a breeder, only whitewashes the problem. If Mendel's theory serves, all of that bird's offspring will be, in some way, influenced by the condition...regardless of what you mate with it.

Based on the theory that a simple recessive gene is responsible for the predisposition to slipped wing, the following mating results can be expected, when using an affected or "repaired" bird (the outcome would not necessarily be the same should more than one gene be involved.)

1). When mated to a non-carrier of the gene -- all offspring appear normal but all, without exception, are carriers.

2). When mated to a bird, which appears normal but is a carrier -- 50% of the offspring are affected and the remaining 50% appear normal, but are carriers (the percentage figures only reflect the odds of producing these results.)

3). When mated to an affected bird -- all the offspring are affected.

Naturally, these figures no longer apply if the bird's diet is altered during the early stages of development. In fact, many breeders firmly believe that holding the ducklings back nutritionally, by reducing the amount of protein ingested is a prerequisite to proper wing formation. They will argue that a high protein diet is unnatural, and that a slower rate of growth relieves the wing of excessive weight before it is fully formed. I remain very skeptical about the validity of this argument.
Consider, for one moment, what wild Muscovies eat in their natural habitat; you will notice that fish, small amphibians and insects are way up there on the menu, making the consumption of large quantities of protein an integral part of their lives. My personal experience has been that, ultimately, restricted birds don't quite achieve their full potential. I am persuaded that resorting to diet tampering in order to produce birds free of slipped wing, only perpetuates the camouflaging of an abnormality, which can easily be eradicated by judicious breeding and record keeping.

Again, I must emphasize that these are only my personal views and observations. A qualified geneticist would be quick to point out many oversimplifications in this text. I am a hobbyist writing for other hobbyists, and in no way am I urging anyone to adopt a breeding or feeding program in lieu of another.

As I once commented to a friend; "Saying that high protein rations cause slipped wing in waterfowl can be compared to saying that strobe lights, so widely used in the 70's at the height of the disco era, cause epileptic seizures in humans. Sure, strobe lights do cause epileptic seizures, but only if you're epileptic to begin with."

The genes load the gun, nutrition pulls the trigger.