Post by cddexter on Oct 2, 2012 10:56:37 GMT -5
In England, where most of this started, you can ask different owners and get different answers as to how each of them tells if it's a 'shortleg' or 'longleg'. I'll include that info as well as the signs I identified and use, which ae effective probably about 98% of the time.
These guides depend on sex and age. I'll include that, too.
Some general guidelines. These must be taken collectively, not used as one-offs, or you will be misled. For every symptom, please add ‘most of the time’ in front of the description, because there are always exceptions.
First, you have to understand what chondro does, and everything else will fall into place. If you aren’t sure, check out the article on chondro on the ADCA website under Genetics Info. That article includes photos of the bone cells under a microscope, showing how the calcium chondrocytes are laid down in normal bone growth, and how they are (NOT) laid down in the bulldog. The former has no defective genes, the latter has both genes of the pair defective. A ‘carrier’ or ‘shortleg’ or ‘shortie’ or ‘true Dexter’ or ‘beef type’ is a half-way in between case. It has one normal gene, one defective gene. The bones are affected, but not to the point where the calf becomes unviable.
It isn’t just the legs that are affected. The spine, the nose, the shoulder and hip bones all show some degree of shortening/reduction. The legs show it most because of the growth plates at both ends of each of the bones. Between the wrist (pastern), forearm, and upper arm, there are SIX growth plates, making the effect SIX times as noticeable, hence the common incorrect assumption that only the legs are affected.
As more and more people move away from using height as THE breeding criteria, and start to use other desirable traits, better quality animals are being produced.
Another reminder: the chondro gene acts alone. It affects how bone grows. It does NOT affect muscle (meat) or organs. It may expose something else going on, but it doesn’t actually directly cause anything other than deformed bones. All the muscle and all the organs are normal size and have normal function.
What is not yet known is the cause of the variation in degrees of expression. My closest guess is that it’s sort of like (great grammar, huh?) how hormones work....people can have greater or lesser production of hormones which has nothing to do with anything else, it’s just part of the package. Think of some of the aging women you’ve seen: as the estrogen dries up, sometimes you’ll see coarser features, excess hair growth on the chin; sometimes even a fine moustache. When they were younger, a lesser degree of hormone production wasn’t apparent. It’s only as they get older that you notice it. I think maybe the degree of expression of chondro is caused by something like that: not actually related, but exposed by the change (in bone development).
If you don’t have a good imagination (or even if you do, this will help clarify areas), take any side-on cow photo and a pen and ruler. Draw vertical lines (1) just in front of the nose, (2) just where the neck separates from the head, (3) just in front of the point of the shoulder, (4) just behind the elbow (where a girth would go if it were a horse), (5) just in front of the hook (hip bone), and (6) just behind the pins, between the pins and the tail.
Face: remember I said the nose is affected? That’s because it’s cartilage, and all cartilage is affected.
This makes the whole face quite a bit shorter. Plus, the eye socket is made up of three different bones, the frontal (cranium), the zygomatic (side) and maxilla (upper jaw). With less development, the socket is slightly smaller than the eye that’s designed to fit in it, which results in that bug-eyed appearance often found in dwarfs, especially as they age. The cranium is composed of membranous bone, which is NOT affected by chondro because it’s a different type of bone, and doesn’t have ‘growth plates’. Instead, it starts out as separate plates, ‘fills in’ bone and then fuses solid. Sometimes a dwarf’s head appears to be more bulbous. This is caused by a combination of normal brain size (volume), reduced cartilaginous bone area (parts of the brain case which are affected by chondro) and membranous bone (brain case bone that can adjust its size). The brain grows as it should, part of the skull is smaller than expected, so the cranium, not being fused yet spreads and accommodates the brain and then fuses.
The lower jaw is made up of bone, too. It doesn't have the high volume of cartilage the upper jaw has, so this will often create a heavy appearing lower jaw (rear part of mandible), sometimes even producting an undershot result (projects in front of the upper jaw).
Neck: remember I said the spine is affected? That’s because cartilage is involved, and cartilage is affected.
The whole spine is shorter. This makes the neck shorter, because the neck is the start of the spine. You are seeing the cervical bones (the upper part of the spine). Some dwarfs appear to have almost no neck at all. It’s as though the head is attached directly to the shoulder. These are the extreme cases.
Shoulder: remember I said the leg bones are affected at both ends, and with three bones, that’s SIX times the effect?
Start at the top. The scapula (shoulder blade) has growth plates, and is affected. It will be a little shorter in length. Then you have the upper arm which goes from the point of the shoulder (in front) to the elbow (by the girth). This will be considerably shorter than it should. Then you have the forearm, which will also be shorter. Then the cannon bone, again shorter. Then the pastern, shorter again.
(SIDEBAR: horses are measured in ‘hands’ or four-inch intervals, because most people have a hand that is four inches in width across the knuckles. Put your hands sideways and stack one on top of the other from the ground up to the withers and you will get a pretty accurate height on the horse, and of course, a pretty accurate take on why horse measurement is done in ‘hands’.) Hands also work on cannon bones, just a little differently.
A. If you can put your hand around the straight part of the cannon bone and it fits comfortably between the knobbly bits (the joints) and maybe even still has room for another finger, it’s probably a non-dwarf.
If ditto, abut your hand just fits or even is a bit big (only room for three fingers) it’s probably a dwarf.
B When the animal trots, is the stride clean and free, moving from the shoulder? It probably is a non-dwarf.
If the stride is choppy and looks as though the action is all underneath and not from the shoulder, it probably is a dwarf (think of cartoon sheep with a flurry of legs to denote movement).
C If the full extension of the leg coincides with the hoof hitting the ground, it probably is a non-dwarf.
If the full extension of the leg occurs with the hoof still slightly above the ground, it probably is a dwarf. If you look closely, it almost looks as though the animal is too short to reach the ground and that’s why the hoof seems to hesitate in the air and then come down with a more ‘flat’ trajectory.
D If the animal looks as though the leg is right where it should be (in a front-to-back line), and the animal looks balanced, it probably is a non-dwarf.
If the animal looks as though the leg is a little back from where it should be, and you want to mentally unscrew it and move it forward just an inch or two, closer to the front of the brisket for better proportion, it’s probably a dwarf.
Barrel:
We’re back to the spine again. You noticed how much shorter the neck was compared to normal development. The barrel has the same issue. The problem here is that it’s only the bones that are affected by chondro. The organs still have the same volume they would have had without the bone mutation. Like the eyes, this means the organs must fit inside a smaller cavity than they were actually designed for. Since there is a rigid cage on three sides of the barrel (spine and ribs), the only real room for expansion is down. This is why a lot of dwarfs, especially those with severe symptoms, look pot-bellied. The only other place there is extra space is an area that can be compressed: the lungs. This is why it’s fairly common for dwarf cows to have breathing issues in the final trimester of pregnancy. You have all those organs tightly squeezed into a reduced space, and then you add a growing calf. Dwarfs often have a much wider spread of ribs....attributed to the need to accommodate everything. Non-dwarfs can look more ‘slab-sided’ when not pregnant compared to their dwarf counterparts.
Hindquarter:
The distance between the hook and pin is mostly a factor of other genetics, and not dwarfism. However, remember what I said about leg bones, and six times the affect? Now we get into one of the most reliable ‘tells’ for dwarfism. All the leg bones are shorter, so this affects the angle at the stifle. One of the best guides to type is to look at the back of the hock and just above the hock. The leg bones are shorter. This means the muscle that’s meant to be on a normal length bone is going to be compressed onto a shorter bone. This creates bulk. If you look at the approx. four inches starting from the hock and going up the leg, from the side, you will find two totally different profiles. The non-dwarf has a longer, flatter curve because the muscle is stretched out. The dwarf has a short, quite tight curve, much like a ‘C’ because the muscle is compressed. The combination of bulk and curve are usually a dead giveaway. And, of course, the pastern is again very small.
There are a lot of really bad, flat feet out there. Because of the deformity of the bones, often the foot angle on dwarfs is poor. Couple this with naturally flat feet, and you will often get skis.
Calves that look ‘mature’ right away are always dwarfs. Non-dwarfs usually retain a slab-sided look after calving. Dwarf bull calves will often have a crest by four months (it’s actually just bunched muscle, not sexual maturity); nons won’t.
Heifers at around two years can be really hard to identify as to type, especially if the expression of chondro is moderate—what some call a proportionate shortleg. Genebo got fooled by this terminology. Whenever you hear any words coupled with ‘short, you should be able to figure out what you are getting.
Mature bulls are often quite hard to tell, too, if you just look at leg length. Non dwarf bulls deepen a lot, which makes their legs appear short. That’s why it’s so important to scrutinize the whole animal, not just focus on one popular part of the skeleton.
A quick guide would be: face, neck, stride, hock curvature.
Animals severely affected are pretty easy to identify. It’s the more proportionate ones that are hard. It’s this group into which most of the errors fall.
Having said all that, you also need to know about developmental curves. All animals, us included, go through the same pattern: baby, juvenile, bone development, muscle development, fat development. There is an overlap between these groups, but on the whole, when one slows down, another starts up. Think of overlapping bell curves, looking rather like consecutive sine waves.
In my experience, the non-dwarf starts to grow serious bone at around 10-12 months, then at around 18-20 months starts to develop muscle. By around 28-30 months, regular feed gets converted to fat. On the other hand, in the dwarf, because of the effect of the mutation, bone growth seems to happen a lot sooner. It’s possible to get calves at just over a year that are already laying down fat. This gives an advantage at slaughter, because the meat will be marbled a lot sooner, even if the carcase is smaller (not because of the dwarfism, but because the animal will produce marketable beef much younger).
Dr. Piet Wilke, Dean of Agriculture, Orange Free State University, Blomfontein, SA, and long-time Dexter breeder (Pikinini herd), Wes Patton, Head, Department of Animal Science, California State U, Chico, CA, and breeder (Glennland herd), and Veronica Schofield, geneticist and DCS liaise on research, Carlisle, England, and long-time breeder (Harron herd) all found that a non-dwarf carcase produced a higher volume of saleable meat than a dwarf one, of the same age and genetic background. Patti Adams, breeder, KS, found no difference.
That's pretty well it for identifying the two types. None of this replaces the test, of course. But, it's fun to do, and helpful when you are looking at animals that others haven't tested, or you want a quick reference.
Barb makes a good point about terminology, and you've all read about Gene's problems with 'proportionate short'. Both got their start in Dexters in 2004. In eight years, Barb's had 87 head, Gene 19. Mike's just starting, but has fast-tracked his learning curve. Hans is in his third year and is working hard with nine so far. Let's look at some other numbers: for instance, the E+ red was discovered in 1997, chondro in 2001, brown in 2002, and PHA was identified in 2009. Sometimes we forget how recent is our knowledge base. thx. c.
These guides depend on sex and age. I'll include that, too.
Some general guidelines. These must be taken collectively, not used as one-offs, or you will be misled. For every symptom, please add ‘most of the time’ in front of the description, because there are always exceptions.
First, you have to understand what chondro does, and everything else will fall into place. If you aren’t sure, check out the article on chondro on the ADCA website under Genetics Info. That article includes photos of the bone cells under a microscope, showing how the calcium chondrocytes are laid down in normal bone growth, and how they are (NOT) laid down in the bulldog. The former has no defective genes, the latter has both genes of the pair defective. A ‘carrier’ or ‘shortleg’ or ‘shortie’ or ‘true Dexter’ or ‘beef type’ is a half-way in between case. It has one normal gene, one defective gene. The bones are affected, but not to the point where the calf becomes unviable.
It isn’t just the legs that are affected. The spine, the nose, the shoulder and hip bones all show some degree of shortening/reduction. The legs show it most because of the growth plates at both ends of each of the bones. Between the wrist (pastern), forearm, and upper arm, there are SIX growth plates, making the effect SIX times as noticeable, hence the common incorrect assumption that only the legs are affected.
As more and more people move away from using height as THE breeding criteria, and start to use other desirable traits, better quality animals are being produced.
Another reminder: the chondro gene acts alone. It affects how bone grows. It does NOT affect muscle (meat) or organs. It may expose something else going on, but it doesn’t actually directly cause anything other than deformed bones. All the muscle and all the organs are normal size and have normal function.
What is not yet known is the cause of the variation in degrees of expression. My closest guess is that it’s sort of like (great grammar, huh?) how hormones work....people can have greater or lesser production of hormones which has nothing to do with anything else, it’s just part of the package. Think of some of the aging women you’ve seen: as the estrogen dries up, sometimes you’ll see coarser features, excess hair growth on the chin; sometimes even a fine moustache. When they were younger, a lesser degree of hormone production wasn’t apparent. It’s only as they get older that you notice it. I think maybe the degree of expression of chondro is caused by something like that: not actually related, but exposed by the change (in bone development).
If you don’t have a good imagination (or even if you do, this will help clarify areas), take any side-on cow photo and a pen and ruler. Draw vertical lines (1) just in front of the nose, (2) just where the neck separates from the head, (3) just in front of the point of the shoulder, (4) just behind the elbow (where a girth would go if it were a horse), (5) just in front of the hook (hip bone), and (6) just behind the pins, between the pins and the tail.
Face: remember I said the nose is affected? That’s because it’s cartilage, and all cartilage is affected.
This makes the whole face quite a bit shorter. Plus, the eye socket is made up of three different bones, the frontal (cranium), the zygomatic (side) and maxilla (upper jaw). With less development, the socket is slightly smaller than the eye that’s designed to fit in it, which results in that bug-eyed appearance often found in dwarfs, especially as they age. The cranium is composed of membranous bone, which is NOT affected by chondro because it’s a different type of bone, and doesn’t have ‘growth plates’. Instead, it starts out as separate plates, ‘fills in’ bone and then fuses solid. Sometimes a dwarf’s head appears to be more bulbous. This is caused by a combination of normal brain size (volume), reduced cartilaginous bone area (parts of the brain case which are affected by chondro) and membranous bone (brain case bone that can adjust its size). The brain grows as it should, part of the skull is smaller than expected, so the cranium, not being fused yet spreads and accommodates the brain and then fuses.
The lower jaw is made up of bone, too. It doesn't have the high volume of cartilage the upper jaw has, so this will often create a heavy appearing lower jaw (rear part of mandible), sometimes even producting an undershot result (projects in front of the upper jaw).
Neck: remember I said the spine is affected? That’s because cartilage is involved, and cartilage is affected.
The whole spine is shorter. This makes the neck shorter, because the neck is the start of the spine. You are seeing the cervical bones (the upper part of the spine). Some dwarfs appear to have almost no neck at all. It’s as though the head is attached directly to the shoulder. These are the extreme cases.
Shoulder: remember I said the leg bones are affected at both ends, and with three bones, that’s SIX times the effect?
Start at the top. The scapula (shoulder blade) has growth plates, and is affected. It will be a little shorter in length. Then you have the upper arm which goes from the point of the shoulder (in front) to the elbow (by the girth). This will be considerably shorter than it should. Then you have the forearm, which will also be shorter. Then the cannon bone, again shorter. Then the pastern, shorter again.
(SIDEBAR: horses are measured in ‘hands’ or four-inch intervals, because most people have a hand that is four inches in width across the knuckles. Put your hands sideways and stack one on top of the other from the ground up to the withers and you will get a pretty accurate height on the horse, and of course, a pretty accurate take on why horse measurement is done in ‘hands’.) Hands also work on cannon bones, just a little differently.
A. If you can put your hand around the straight part of the cannon bone and it fits comfortably between the knobbly bits (the joints) and maybe even still has room for another finger, it’s probably a non-dwarf.
If ditto, abut your hand just fits or even is a bit big (only room for three fingers) it’s probably a dwarf.
B When the animal trots, is the stride clean and free, moving from the shoulder? It probably is a non-dwarf.
If the stride is choppy and looks as though the action is all underneath and not from the shoulder, it probably is a dwarf (think of cartoon sheep with a flurry of legs to denote movement).
C If the full extension of the leg coincides with the hoof hitting the ground, it probably is a non-dwarf.
If the full extension of the leg occurs with the hoof still slightly above the ground, it probably is a dwarf. If you look closely, it almost looks as though the animal is too short to reach the ground and that’s why the hoof seems to hesitate in the air and then come down with a more ‘flat’ trajectory.
D If the animal looks as though the leg is right where it should be (in a front-to-back line), and the animal looks balanced, it probably is a non-dwarf.
If the animal looks as though the leg is a little back from where it should be, and you want to mentally unscrew it and move it forward just an inch or two, closer to the front of the brisket for better proportion, it’s probably a dwarf.
Barrel:
We’re back to the spine again. You noticed how much shorter the neck was compared to normal development. The barrel has the same issue. The problem here is that it’s only the bones that are affected by chondro. The organs still have the same volume they would have had without the bone mutation. Like the eyes, this means the organs must fit inside a smaller cavity than they were actually designed for. Since there is a rigid cage on three sides of the barrel (spine and ribs), the only real room for expansion is down. This is why a lot of dwarfs, especially those with severe symptoms, look pot-bellied. The only other place there is extra space is an area that can be compressed: the lungs. This is why it’s fairly common for dwarf cows to have breathing issues in the final trimester of pregnancy. You have all those organs tightly squeezed into a reduced space, and then you add a growing calf. Dwarfs often have a much wider spread of ribs....attributed to the need to accommodate everything. Non-dwarfs can look more ‘slab-sided’ when not pregnant compared to their dwarf counterparts.
Hindquarter:
The distance between the hook and pin is mostly a factor of other genetics, and not dwarfism. However, remember what I said about leg bones, and six times the affect? Now we get into one of the most reliable ‘tells’ for dwarfism. All the leg bones are shorter, so this affects the angle at the stifle. One of the best guides to type is to look at the back of the hock and just above the hock. The leg bones are shorter. This means the muscle that’s meant to be on a normal length bone is going to be compressed onto a shorter bone. This creates bulk. If you look at the approx. four inches starting from the hock and going up the leg, from the side, you will find two totally different profiles. The non-dwarf has a longer, flatter curve because the muscle is stretched out. The dwarf has a short, quite tight curve, much like a ‘C’ because the muscle is compressed. The combination of bulk and curve are usually a dead giveaway. And, of course, the pastern is again very small.
There are a lot of really bad, flat feet out there. Because of the deformity of the bones, often the foot angle on dwarfs is poor. Couple this with naturally flat feet, and you will often get skis.
Calves that look ‘mature’ right away are always dwarfs. Non-dwarfs usually retain a slab-sided look after calving. Dwarf bull calves will often have a crest by four months (it’s actually just bunched muscle, not sexual maturity); nons won’t.
Heifers at around two years can be really hard to identify as to type, especially if the expression of chondro is moderate—what some call a proportionate shortleg. Genebo got fooled by this terminology. Whenever you hear any words coupled with ‘short, you should be able to figure out what you are getting.
Mature bulls are often quite hard to tell, too, if you just look at leg length. Non dwarf bulls deepen a lot, which makes their legs appear short. That’s why it’s so important to scrutinize the whole animal, not just focus on one popular part of the skeleton.
A quick guide would be: face, neck, stride, hock curvature.
Animals severely affected are pretty easy to identify. It’s the more proportionate ones that are hard. It’s this group into which most of the errors fall.
Having said all that, you also need to know about developmental curves. All animals, us included, go through the same pattern: baby, juvenile, bone development, muscle development, fat development. There is an overlap between these groups, but on the whole, when one slows down, another starts up. Think of overlapping bell curves, looking rather like consecutive sine waves.
In my experience, the non-dwarf starts to grow serious bone at around 10-12 months, then at around 18-20 months starts to develop muscle. By around 28-30 months, regular feed gets converted to fat. On the other hand, in the dwarf, because of the effect of the mutation, bone growth seems to happen a lot sooner. It’s possible to get calves at just over a year that are already laying down fat. This gives an advantage at slaughter, because the meat will be marbled a lot sooner, even if the carcase is smaller (not because of the dwarfism, but because the animal will produce marketable beef much younger).
Dr. Piet Wilke, Dean of Agriculture, Orange Free State University, Blomfontein, SA, and long-time Dexter breeder (Pikinini herd), Wes Patton, Head, Department of Animal Science, California State U, Chico, CA, and breeder (Glennland herd), and Veronica Schofield, geneticist and DCS liaise on research, Carlisle, England, and long-time breeder (Harron herd) all found that a non-dwarf carcase produced a higher volume of saleable meat than a dwarf one, of the same age and genetic background. Patti Adams, breeder, KS, found no difference.
That's pretty well it for identifying the two types. None of this replaces the test, of course. But, it's fun to do, and helpful when you are looking at animals that others haven't tested, or you want a quick reference.
Barb makes a good point about terminology, and you've all read about Gene's problems with 'proportionate short'. Both got their start in Dexters in 2004. In eight years, Barb's had 87 head, Gene 19. Mike's just starting, but has fast-tracked his learning curve. Hans is in his third year and is working hard with nine so far. Let's look at some other numbers: for instance, the E+ red was discovered in 1997, chondro in 2001, brown in 2002, and PHA was identified in 2009. Sometimes we forget how recent is our knowledge base. thx. c.
