In animals with a portosystemic shunt (PSS) there is abnormal blood flow in the liver. Blood should flow from the digestive tract to the liver via the portal system into the blood vessels of the liver, and then to the caudal vena cava which is the large blood vessel carrying blood back to the heart. In a portosystemic shunt, as the name implies, portal blood by-passes the liver and goes directly to the systemic venous circulation (caudal vena cava). One important function of the liver is to clear toxins, many of which are by-products of protein digestion, from the blood. In PSS, these toxins are not cleared, and circulate in the body. This causes the clinical signs associated with PSS, many of which are neurological. The complex of neurological and behavioral signs caused by liver dysfunction is called hepatic encephalopathy.
Portosystemic shunts may be acquired secondary to another disease, or they may be congenital - that is the animal is born with a shunt. A congenital shunt usually occurs as a single abnormal blood vessel that is a remnant of normal embryonic development. These shunts are defined as intra-hepatic or extra-hepatic depending on the location of the blood vessel in relation to the liver.
Most animals with congenital portosystemic shunts show clinical signs before 6 months of age. Where signs are subtle, the condition may not be diagnosed until much later.
The mode of inheritance is not known. Affected individuals and their parents should not be used for breeding.
Generally the diagnosis of congenital PSS is suspected based on the history, clinical signs, and laboratory features. Typically an affected dog is young, of a breed with a predisposition for PSS, with clinical signs and laboratory findings relating to liver dysfunction. A special radiographic tool, contrast portal radiography, is the best way to confirm the diagnosis. Contrast dye is injected into one of the blood vessels going into the liver. In a normal liver, the contrast material disperses into the many blood vessels in the liver, but in congenital PSS, a large portion of the contrast bypasses those vessels and goes directly to the caudal vena cava, the large blood vessel that carries blood to the heart. Contrast radiography also helps in assessing the chances of successfully tying off the shunt surgically. The more contrast that is apparent in the liver, the higher the likelihood of success. Contrast radiography will also identify whether the shunt is intra- or extra-hepatic.
Signs of portosystemic shunts include:
* poor weight gain
* sensitivity to sedatives (especially diazepam)
* pushing the head against a solid object
* poor appetite
* increased drinking and urinating
* balance problems
* frequent urinary tract disease or early onset of bladder stones.
* If these signs increase dramatically after eating, it is a strong supportive sign of a portosystemic shunt.
For more information visit Terri Shumsky Fanny Mae Liver Shunt Fund Dr. Tobias Back to Top
The normal retina lines the back of the eye. The retinal cells receive light stimuli from the external environment and transmit the information to the brain where it is interpreted to become vision. In retinal dysplasia, there is abnormal development of the retina, present at birth. The disorder can be inherited, or it can be acquired as a result of a viral infection or some other event before the pups were born.
There are 3 forms of retinal dysplasia
I) Folding of 1 or more area(s) of the retina. This is the mildest form, and the significance to the dog's vision is unknown.
II) Geographic - areas of thinning, folding and disorganization of the retina.
III) Detached - severe disorganization associated with separation (detachment) of the retina.
The geographic and detached forms cause some degree of visual impairment, or blindness.
In many breeds, inheritance has been shown or is suspected to be autosomal recessive. In others, the mode of inheritance has not been determined. The effect on vision of the mildest form (folding of the retina) is not known. The abnormal retinal folds may disappear with age in dogs that are only mildly affected. Back to Top
Mature Cataract ~ Immature Cataract
Like a camera, eyes have a clear lens inside them that is used for focusing. A cataract is any opacity within a lens. The opacity can be very small (incipient cataract) and not interfere with vision. It can involve more of the lens (immature cataract) and cause blurred vision. Eventually, the entire lens can become cloudy, and all functional vision lost. This is called a mature cataract. Most cataracts in dogs are inherited.
The cataract may develop rapidly over weeks, or slowly over years, in one or both eyes. Like humans, dogs also develop cataracts with age (often after 8 years of life).
Cataracts can also develop in dogs with diabetes mellitus or in orphan puppies on an artificial milk replacer diet.
Yearly CERF examinations are an important tool in diagnosing this condition. Proper treatment can be hastened by early diagnosis. Back to Top
Dry Eye (KCS) Keratoconjunctivitis Sicca
Keratoconjunctivitis sicca, or KCS, is a fancy way of saying the eye is dry. Kerato refers to the cornea or clear covering of the eye that faces the outside world. Conjunctivae are the moist pink membranes of the eye socket. "It is" means inflammation and sicca means dry. KCS means inflamed, dry cornea and conjunctiva. It occurs when there is a deficiency in the water portion of the tear film that normally accounts for 95% of the tear volume. Without the water, one is left with oil and mucus; hence, the gooey yellow eye discharge characteristic of this condition.
Tears are essential to the comfort of our eyes but they do more than just provide lubrication. Tears contain anti-bacterial proteins, salts, sugars, and even oxygen to nourish the eye. Tears flush away irritants and infectious agents that are constantly getting in our eyes. Since the outer portions of the eye does not have a blood supply, the tears must bring sugars and oxygen and must remove metabolic waste.
There are many causes of dry eye.
The most common cause of KCS appears to be immune mediated destruction of the tear-producing gland tissue.
Distemper infection attacks all body interfaces with the environment including the eyes. Dry eye is part of the constellation of symptoms that can occur with distemper infection.
There could be a congenital lack of tear producing gland tissue (as described in certain lines of Yorkshire terrier).
Exposure to sulfa containing antibiotics (such as Trimethoprim sulfa combinations) can lead to dry eye (which can be either temporary or permanent and occurs unpredictably).
Anesthesia will reduce tear function temporarily (thus eyes are lubricated with ointment by the attending nurse.)
A knock on the head in the area of one of the tear producing glands can lead to K
Artificial tears can be purchased in most drug stores. These can be combined with other therapies and are certainly very soothing. The problem is that they are typically recommended for use 4 to 6 times a day.
Antibiotic products are often needed especially when starting treatment for KCS as secondary infections are common when there are inadequate tears to wash infectious agents away. These products do not increase tear production but may be important, especially early in therapy.
Mucomyst® Eye Drops are made from a respiratory product used to dissolve thick mucus. In an eye formula, Mucomyst (active ingredient is Acetylcysteine) helps remove the thick eye discharge that accompanies dry eye. Back to Top
By 1 month of age, puppies generally start “erupting” their baby teeth and have all 28 deciduous teeth by the time they reach 1 ½ months of age. By the time a puppy is 6 to 7 months of age, generally all the baby teeth have been replaced with 42 adult or permanent teeth.
The body begins a process of resorption of the baby teeth as soon as the permanent teeth begin their formation. This process causes the teeth to loosen and fall out as the permanent teeth erupt. Occasionally, the normal resorption process fails, and the deciduous teeth do not fall out. This is commonly referred to as “retained deciduous teeth.” This situation leads to problems as two teeth try to occupy the same area causing the new permanent tooth to erupt at an abnormal angle or in an abnormal position. This can result in malocclusion or an "abnormal bite.” This seems to be more common in the small breed dogs.
The four “canine” teeth are most commonly retained. These two sets of canine teeth, one mandibular set on the lower jaw and one maxillary set on the upper jaw, are the sharp fang-like teeth that are just behind the front 6 central incisors.
Extraction of the retained deciduous teeth is recommended as soon as the problem is identified, since early removal allows the adult teeth to move into their normal positions preventing malocclusion problems. Special veterinary care is required during extraction of the baby teeth to prevent damage to the permanent tooth. Often, retained deciduous teeth are removed at the time of spay or neuter since anesthesia is recommended for both procedures.
Late diagnosis or late removal of retained deciduous teeth may result in severe malocclusion associated with pain or difficulty eating. These cases may require surgical removal and orthodontic dental work to reposition the teeth and improve the "bite," usually with the use of braces. Back to Top
Tracheal collapse is a narrowing of the inner diameter of the trachea, that fluctuates with the stage of the respiratory cycle. The rings of the trachea (made of cartilage) lose their ability to maintain their shape, and collapse when the dog breathes, causing a harsh cough. Most often this disorder is seen in middle-aged toy and miniature breeds. Chronic respiratory infection, obesity, and heart disease can all contribute to the development of the condition, but it appears that there is also a congenital deficiency (ie. a dog is born with it) in the make-up of the trachea itself.
How tracheal collapse is inherited is unknown. This disorder occurs almost exclusively in toy and miniature breeds.
Ideally, affected dogs should not be used for breeding. This is difficult in practice however, because many affected dogs do not develop signs of this condition until middle age, when they have already been bred. It is preferable not to use lines of dogs for breeding in which collapsing trachea is a problem. Back to Top
During development before birth, the testicles migrate from the abdomen into the scrotum. Normally this is complete by 10 days of age. Cryptorchidism means that one or both of a dog's testicles have not descended into the scrotum. If this does not happen by 8 weeks, the dog is generally diagnosed as cryptorchid, although the testicles may still descend up to 4 months or so.
This is a fairly common condition, which is seen most often in the toy and miniature. Although the condition is of course seen only in male dogs, both males and females can carry the gene for cryptorchidism. Heterozygous males and females, and homozygous females, will be physically normal, but can pass the gene on to their offspring. Homozygous males are cryptorchid. Thus cryptorchidism is thought to be a sex-limited autosomal recessive trait.
Dogs that are cryptorchid have a much increased risk of testicular cancer (approximately 10 times). Castration will of course eliminate this risk.
Affected dogs should be not be bred. It is best not to breed their parents as well, who carry the gene. Back to Top
A careful examination of puppies by a veterinarian is recommended at 6 weeks of age . Many puppies are born with a slight heart murmur (or puppy murmur) that clears up by itself after 4-6 months. In many cases, vets will simply recommend a later checkup, just to be sure that the condition has resolved itself. Congenital defects are those that have been present since birth. They are comparatively rare, accounting for only 5% of the cases seen by vets.
Chronic valvular disease can be thought of simply as 'leaky valves', caused when the moving parts of the heart valves thicken and harden with age. The result is more or less the same as when a valve in your central heating system starts to wear out: increasingly poor circulation. Valves may thicken or harden with age. This can either restrict bloodflow, or allow blood to 'leak' back past the valve. If any valve is affected in this way, it will compromise the heart's ability to pump blood. Although valvular disease can affect any dog, smaller breeds tend to be more prone.
Patent Ductus Arteriosus (PDA) At birth, mammals must adapt from living in a fluid environment (the amniotic fluid) and acquiring oxygen through the mother's blood, to breathing air and acquiring oxygen through their own lungs. The ductus arteriosus is very important in the adaptation process. This is a small communicating blood vessel between the pulmonary artery (which carries blood to the lungs), and the aorta (which carries blood to the rest of the body). Before birth, most of the blood from the fetal heart bypasses the fetal lungs via the ductus arteriosus. The lungs gradually become functional fairly late in fetal development. At birth, the blood supply from the mother is of course cut off, the dog (or other mammal) begins breathing on its own, and blood flow through the ductus arteriosus decreases dramatically. Within a few days, the ductus closes off completely.
Where the ductus does not close, the dog is left with a patent ductus arteriosus (PDA). The extent to which this affects the dog depends on the degree of patency, or opening, of the ductus. PDA is the most commonly diagnosed congenital heart defect in dogs. It occurs in many breeds and is seen more often in females. Yorkshire Terriers are one of the breeds with an increased risk for PDA. Back to Top
Reverse sneezing ~ Pharyngeal Gag Reflex
Reverse sneezing is a disconcerting event in which a dog makes unpleasant respiratory sounds that sound like it is dying. Reverse sneezing sounds similar to the honking noise made by a dog with a collapsing trachea, but reverse sneezing is a far simpler condition that usually does not need any treatment. It is called reverse sneezing because it sounds a bit like a dog inhaling sneezes. The most common cause of reverse sneezing is an irritation of the soft palate and throat that results in a spasm. During the spasm, the dog’s neck will extend and the chest will expand as the dog tries harder to inhale. The problem is that the trachea has narrowed and it’s hard to get the normal amount of air into the lungs. Small dogs are particularly prone to it, possibly because they have smaller throats.
Reverse sneezing itself rarely requires treatment. If the sneezing stops, the spasm is over. Oftentimes, you can massage the dog’s throat to stop the spasm; sometimes it’s effective to cover the nostrils, which makes the dog swallow, which clears out whatever the irritation is and stops the sneezing. Back to Top
Hypoglycemia is defined as abnormally low blood glucose (sugar) levels. The brain requires sugar for normal function, and unlike many other organs, the brain has a very limited ability to store glucose. The signs and symptoms of hypoglycemia are similar regardless of the cause. These include lethargy, weakness, incoordination, seizures, nervousness, tremors and hunger. Some puppies may only exhibit weakness or a wobbly gait. In severe cases the puppy may become unconscious. By giving a quickly absorbed source of sugar (syrup, honey, or jam) by mouth you may be able to controll the symptoms. If not treated it can result in death. Back to Top
What to do When You Suspect Poisoning
Pesticides, fertilizers, paints, antifreeze, household cleaners, and other chemicals can pose real dangers to your pet. It\'s best to prevent poisonings from happening in the first place by keeping containers tightly capped and stored out of reach.
If your pet should become poisoned despite your efforts to protect him, keep him warm and quiet. Don’t panic. Rapid response is important, but panicking can interfere with the process of helping your pet. Take 30 to 60 seconds to safely collect and have at hand any material involved. This may be of great benefit to your vet and/or APCC toxicologists, as they determine what poison or poisons are involved. In the event that you need to take your pet to a local veterinarian, be sure to take the product’s container with you. Also, collect in a sealable plastic bag any material your pet may have vomited or chewed.
If you witness your pet consuming material that you suspect might be toxic, do not hesitate to seek emergency assistance, even if you do not notice any adverse effects. Sometimes, even if poisoned, an animal may appear normal for several hours or for days after the incident.
Call the ASPCA Animal Poison Control Center ~ (888) 426-4435. There is a $55 consultation fee for this service.
Be ready with the following information:
* The species, breed, age, sex, weight and number of animals involved
* The animal’s symptoms
* Information regarding the exposure, including the agent (if known), the amount of the agent involved and the time elapsed since the time of exposure.
Have the product container/packaging available for reference.
If your animal is having seizures, losing consciousness, is unconscious or is having difficulty breathing, telephone ahead and bring your pet immediately to your local veterinarian or emergency veterinary clinic. If necessary, he or she may call the APCC.
Poisons and other toxins
Antifreeze is highly poisonous. Unfortunately, dogs actually like the taste of the stuff. Don't leave even a little on the driveway and never leave an open container where pets can reach it.
Aspirin, in appropriate doses is ok for dogs (not cats), but do not give Advil, Tylenol, or any other pain killer without specific instructions from a veterinarian.
Rattlesnake bites are rarely fatal to large dogs, but little dogs get a lot more venom in proportion to their size, and may die.
Mushrooms can cause severe illness or death. Try to keep them cleared away from places your dog can reach.
Chocolate can certainly be poisonous for dogs, not because it's highly toxic, but because dogs sometimes eat very large amounts in proportion to their size. If a big dog eats one or two candies, it won't do anything worse than add calories. When a beagle-sized dog eats half a box of chocolates, we have a problem. When a Chihuahua eats a whole box, we have an extremely serious and probably fatal problem.
Xylitol, a sugar substitute often found in dietetic candies and baked goods, can also be fatal to dogs.
Poisonous Plants - There are more than 700 kinds of plants that may be poisonous to your pet. Most plants make puppies pretty sick, but the quantities eaten are usually not life-threatening.--Mistletoe, Daffodils, Larkspur, Hydrangea, Lily of the Valley, Oleander and Foxglove are highly toxic.
Rhododendron and azaleas can be harmful to an animal's heart, intestines, and nervous system.
Philodendron and dieffenbachia are common houseplants which can prove fatal. Some flower bulbs are highly poisonous and dogs will occasionally be fatally poisoned by eating them. Even leaves and stems from tomato plants can be harmful.
It's best to keep pets out of vegetable and flower gardens altogether, but if you suspect your pet may have eaten a poisonous plant, watch for symptoms such as vomiting, diarrhea, loss of appetite, mouth swelling, and salivation. Take the animal to your vet and take along a leaf from the plant that was eaten. Treatment is based on the type of plant and amount swallowed.
If your dog drinks antifreeze or eats rat poison, immediate treatment is needed. You can induce vomiting by giving 1 teaspoonful of ipecac syrup per 10 lbs, or get him to a vet right away. Another good choice is hydrogen peroxide: give 1 teaspoonful per 20 lbs., if vomiting doesn't occur within ten minutes, this may be repeated once. Dogs usually look sad and drool just before they start vomiting. It is also possible to induce vomiting by pouring lots of very salty water down a dog's throat, but attempts are usually unsuccessful and merely waste time. Do not try to induce vomiting if petroleum distillates, caustics, or acids have been ingested, if a pet is having seizures, and/or is not fully conscious. Back to Top
Canine Parvovirus is a highly contagious and potentially fatal gastrointestinal disease in dogs. It was first identified in 1978. Infections occur most commonly in puppies less than20 weeks of age with inadequate or incomplete vaccination. Clinical signs vary in severity from mild to acute death. Clinical signs may include vomiting, bloody diarrhea, lethargy, depression, and anorexia.
Parvovirus is not the only disease that causes vomiting and diarrhea and therefore, should be evaluated by your veterinarian. Indirect transmission occurs by environmental contamination with fecal material or objects such as food/water bowls, bedding, and toys. Transmission may also occur by direct contact between dogs. In addition, the virus may be spread by caretakers by direct contact and on clothing and shoes. The virus is shed in large quantities in the feces for up to 14 days post infection.
The virus is very stable and survives in the environment for long periods of time. It has been known to survive months to even years. Vaccination is the key to prevention. Back to Top
Giardia are protozoans, tiny, one-celled parasitic life forms with the potential to cause serious illness. Some dogs are carriers who show no symptoms, but others get sick and need treatment. Like many disease organisms, Giardia mature in stages. Unlike many others, no time elapses between infestation with the dormant phase and activation of the disease. The cysts (the inactive form) are found in contaminated water and feces.
Once ingested by the dog, the cysts open and discharge the mobile form known as the trophozoite, a pear-shaped critter with whip-like flagella that propel it through the intestine. If the dog is healthy, the trophozoites may live in the lower digestive tract for years. If the dog has an immature or overburdened immune system, the trophozoites continue to multiply by dividing and can cause the debilitating disease. Cysts can remain viable for several weeks or months in cold, wet environments. Back to Top
Coccidia are single celled organisms that infect the intestine. They are microscopic parasites detectable on routine fecal tests in the same way that worms are but coccidia are not worms and they are not visible to the naked eye. Coccidia infection causes a watery diarrhea which is sometimes bloody and can even be a life-threatening problem to an especially young or small pet.
This is a common parasite and is not necessarily a sign of poor husbandry. Back to Top
Commonly mistaken for Parvovirus, but needs different treatment. It's a bacterial imbalance in the digestive tract. It is a disease that produces acute infectious diarrhea in puppies and kittens. This is not a new form of Parvo. Parvo tests will show a low positive & subsequent tests will continue to show low positives, will be inconclusive, or will give erratic results. This disease is so similar to Parvo, that some dogs have tested in the low positive for Parvo. But they do not have Parvo, and it has been recommended that three parvo tests are needed to exclude Parvo.
This disease can be tested for specifically, so if you have an affected dog that appears to have Parvo, but in your mind know that, that could not be possible, have them tested for "Camby". It is important to note that this disease can be transferred between humans, dogs, cats and other livestock. It starts with fecal mucus sheath & continues to get progressively softer until it is watery and contains blood. It then becomes explosive. Vomiting may accompany and may or may not also contain blood. Feces have a sweet/flowery aroma along with a "slaughterhouse on a summer day" smell (similar to parvo diarrhea but with a floral hint). Feces are usually mustard colored. Dogs dehydrate at an astounding rate. Some say that "Dog Show Crud" is the same as "Campy". Regardless of whether they are one in the same, the symptoms are the same and they both can be deadly if not treated properly. Back to Top
Heartworm (Dirofilaria immitis) is a fairly large worm up to 14 inches long that, in adulthood, lives in the heart and pulmonary arteries of an infected dog. Dogs acquire this infection through mosquito bites as mosquitoes readily pick up larval heartworms from infected dogs and carry them to new dogs. Some geographic areas have severe heartworm problems while other areas have none. In order for the parasite to establish its presence in an area, the following conditions must be met:
* Types of mosquitoes capable of carrying larval heartworms must be present
* The weather must be warm enough to allow heartworm larval development within the mosquito
* There must be infected dogs (or coyotes) in the area
* There must be vulnerable host dogs in the area
When these conditions come together, an area becomes endemic for heartworm disease.Monthly heartworm treatment is strongly advised. Back to Top
The adult tapeworm (Dipylidium caninum) lives in the small intestine of the dog or cat. It is hooked onto the intestinal wall by a structure called a rostellum which is sort of like a hat with hooks on it. The tapeworm also has six rows of teeth to grab on with. Most people are confused about the size of a tapeworm because they only see its segments which are small; the entire tapeworm is usually 6 inches or more. Once docked like a boat to the host intestinal wall, the tapeworm begins to grow a long tail. (The tapeworm’s body is basically a head segment to hold on with, a neck, and many tail segments). Each segment making up the tail is like a separate independent body, with an independent digestive system and reproductive tract. The tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it. Older segments are pushed toward the tip of the tail as new segments are produced by the neckpiece. By the time a segment has reached the end of the tail, only the reproductive tract is left. When the segment drops off, it is basically just a sac of tapeworm eggs. This segment is white and able to move when it is fresh and, at this time, looks like a grain of white rice. As the segment dries, it looks more like a sesame seed.
Tapeworms are acquired by the dog eating a flea. It takes 3 weeks from the time the flea is swallowed to the time tapeworm segments appear on the pet’s rear end or stool.
The hookworm (Ancylostoma caninum, Ancylostoma braziliense) is one of the classical internal parasites of puppies. Hookworm infection has several special features that are of interest to us as the caretakers of dogs:
* Hookworms suck blood.
* Hookworms can be transmitted to unborn pups.
* Hookworms can infect humans.
The adult hookworm lives in the small intestine of its host. It hangs on to the intestinal wall using its six sharp teeth and unlike other worms that just absorb the digested food through their skin as it passes by; the hookworm drinks its host's blood. The adult worm lives and mates within the host and ultimately, the female worm produces eggs. Hookworm eggs are released into the intestinal contents and passed into the world mixed in with the host's stool.
Infected puppies are commonly pale, weak, and have long-standing deficiencies. They may or may not have diarrhea. Back to Top
There are two species of roundworms affecting dogs and puppies: Toxocara canis and Toxascaris leonina. Both are treated with the same medication protocol so when eggs are seen on a fecal flotation exam, it is not necessary to determine which species is present. Roundworm infection can have numerous negative effects. It is a common cause of diarrhea in young animals and can cause vomiting as well. Sometimes the worms themselves are vomited up which can be alarming as they can be quite large which females reaching lengths of up to seven inches. The worms consume the host's food and can lead to unthriftiness and a classical pot-bellied appearance. Very heavy infections can lead to pneumonia as the worms migrate and, if there are enough worms, the intestine can actually become obstructed. Roundworms are long, white and described as looking like spaghetti. Back to Top
The whipworm of dogs (Trichuris vulpis) is substantially smaller than the other worms (a mere 30 to 50 mm in length, about a half inch maximum) and is rarely seen as it lives in the cecum (the part of the large intestine where the small and large intestine meet). The "head" (or more accurately the digestive end of the worm) is skinny vs. its stout tail (or reproductive end) which gives the worm a whip shape, hence the name.
A few whipworms generally do not pose a problem for the host but if large numbers of worms are present embedding themselves in the large intestine tissue, tremendous inflammation can result leading to a bloody, gooey diarrhea. Usually there is not enough blood loss to be dangerous but the diarrhea readily becomes chronic and hard to control.
Consult your Vet for the proper tretment of worms. Back to Top
Polygenic traits are controlled by an unknown number of genes. The gene expression is influenced by a variety of factors including gender, nutrition, breed, rate of growth, and amount of exercise. These traits are quantitative traits - that is, there is a wide range within the population. Such traits include height, weight, character, working abilities, and some genetic defects. Heritability varies within different breeds and within different populations of a particular breed.
Because it is virtually impossible to determine the exact genotype for such traits, it is difficult to control defects with a polygenic mode of inheritance. The best attempts at control are based on a grading scheme for identification of the defect and a breed policy of recording and publishing the results for as many dogs as possible. Back to Top
This is the most common mode of inheritance for genetic conditions in dogs. Progressive retinal atrophy (PRA), which causes blindness in many breeds, is such a trait. To be affected, the animal must inherit 2 copies of the gene (genotype pp), 1 from each parent. Dogs with the genotype PP (normal) or Pp (carrier) will be clinically normal but the carrier will pass the affected gene to approximately half the offspring. As long as carriers (Pp) are mated to normal animals (PP), the offspring will be unaffected but some will remain carriers. If 2 carriers are mated, some of the offspring (approximately 25%) will be affected.
As long as the frequency of a gene for a recessive disorder remains low in the population, the particular gene may be passed along for many generations before by chance 2 carriers are mated and affected individuals are born. However, the gene frequency may become unusually high due to breeding of close family members, or because of the "popular sire" effect where a sire with a harmful recessive gene is mated frequently because of desirable traits.
Because the recessive gene is carried in the population in outwardly normal animals, it is very difficult to eradicate these traits. However the incidence can be reduced by identification of carriers through test mating's or through various tests that have been developed, and the conscientious use of this information in breeding programs. Veterinarians, dog breeders, and breed associations must all work together for substantial progress to be achieved. Back to Top