CONGENITAL DEFECTS IN CATTLE
Congenital is a descriptive term denoting a condition existing at birth; hence congenital malformations or congenital deformities are defined as abnormalities of structure present at birth. Developmental or congenital abnormalities, defects and anomalies, include functional as well as morphological imperfections. Abnormal phenotypes are products of the genetic constitution of an animal and the molecular, cellular, and histogenic environment in which they grow (Colin, 1988).There are many undesirable traits that show up in cattle. These range from poor performance and structural unsoundness to semi-lethal and lethal diseases. Congenital defects are present in all breeds of cattle. In most herds, they are rather uncommon; however, occasionally the frequency within a herd will be high enough to be of considerable economic importance. Congenital defects, also known as congenital abnormalities or birth defects, can impact the health and productivity of cattle. These defects are present at birth and may result from genetic, environmental, or a combination of factors. Understanding the causes, identifying signs, and implementing appropriate management strategies are crucial for maintaining the overall health and well-being of cattle herds. This article explores common congenital defects in cattle, their causes, and measures to manage and prevent their impact.
Causes
The cause of many congenital defects is unknown, but some are inherited. Inherited disorders in cattle are mostly caused by autosomal recessively inherited genes.It is characteristic that the action of autosomal recessive genes only becomes expressed as a diseased phenotype if present in both loci. Therefore, autosomal recessively inherited disorders are of greater concern in cattle breeding than are disorders with dominant inheritance or recessive X-linked inheritance. As dominant or recessive X-linked genes are expressed in the phenotype of males, sires carrying such genes are mostly omitted from breeding. However, if the defective allele produces a desirable phenotype in heterozygous individuals, such animals may be used for breeding (Jorgen, 2007). Included in the list of recognized environmental causes are maternal nutritional deficiencies, teratogenic drugs or chemical exposure, mechanical interferences with the fetus, some viral infections, toxic plant, radiology, rectal palpation for gestation diagnosis and toxic effects of any kind that dam would be exposed to during the early stage of organogenesis (Rafid, 2010).
Causes of Congenital Defects
- Genetic Factors:
- Some congenital defects have a hereditary basis, with certain genetic traits predisposing cattle to specific abnormalities. Selective breeding can influence the prevalence of these defects within a herd.
- Environmental Factors:
- Environmental factors, such as exposure to toxins, certain plants, or infectious agents during pregnancy, can contribute to congenital defects. Proper management practices help mitigate these risks.
- Nutritional Deficiencies:
- Inadequate nutrition during gestation can lead to congenital defects. Ensuring pregnant cows receive a balanced and nutritious diet is essential for fetal development.
- Hormonal Imbalances:
- Disruptions in hormonal balance during fetal development may result in congenital defects. Proper reproductive health management, including timely vaccinations, helps prevent such imbalances.
Identification and Diagnosis
- Visual Inspection:
- Many congenital defects are visually apparent at birth. Regular visual inspections of newborn calves are crucial for early identification of abnormalities.
- Diagnostic Imaging:
- Techniques like ultrasound and X-rays can provide detailed images, aiding in the diagnosis of internal congenital defects, such as skeletal abnormalities or organ malformations.
- Genetic Testing:
- Genetic testing helps identify hereditary factors contributing to congenital defects. This information informs breeding decisions to reduce the likelihood of passing on genetic abnormalities.
Congenital Defects
Though there are many congenital and inherited defects reported in cattle but some of the most commonly occurred are discussed below:
l. Dwarfism: There are several types of dwarfism caused by both environment and genetics. · Snorter dwarfism. Animals are short and compact at birth. The fore limbs are abnormally short, head may be overly square, lower jaw slightly protruding and frequently a bulging or prominent forehead. The tip of the tongue usually protrudes and the eyes are bulging. Inherited as a simple recessive trait (Figure 1). · Long head dwarfism causes small size but does not affect the bone growth in nasal passages. Inherited as a simple recessive trait. · Compress dwarfism is inherited as incomplete dominance. An individual with one compress gene and one normal gene has an extremely compressed body conformation. The individual with two compress genes is a dwarf and the calf dies at or soon after birth. Animals appear to be almost normal but head, body, neck and legs are slightly shorter than in normal animals. Its mode of inheritance was determined by the early 1950s (Baker et al., 1951, Pahnish et al., 1955) and the investigators set about identifying the source, the reason for its prevalence.
2.Water head (internal hydrocephalus): Excess fluid is present in the brain. Calves are usually born dead or die shortly after birth. Environmental factors can cause the disease, as well as being inherited as a simple recessive trait.
3.Marble bone (osteopetrosis): Calves born prematurely (10-30 days premature).Typically calves are born dead, but if born alive will die within 24 hours after birth. Calves possess a short lower jaw and impacted molars. Long bones are fragile and can be broken with ease (Figure 2). Inherited as a simple recessive trait.
4.Hairlessness (hypotrichosis): Abnormal hair development, resulting in a less than normal amount of hair. Occasional the hairless lesions may occur in multiple sites, however most commonly the disease is generalized, and the entire skin is affected. Inherited as a simple recessive trait.
5. Rigid joints (arthrogryposis): Affected calves are born at term but most calves are stillborn or die shortly after birth, probably due to respiratory failure. Live born calves have muscular hypotonia. Flexion of the forelimbs, particularly due to flexion of the metacarpophalangeal joints and the carpus, rotation of the digits, and hyperextension of the metatarsophalangeal joints are found, but most joints of the appendicular skeleton may show flexion or extension (Jorgen, 2007).
6. Extra toes (polydactyly): One or both front feet are usually affected, but all four may have the outer dew claw develop into an extra toe. At least two sets of genes are involved in the inheritance of this trait.
7. Mulefoot (syndactyly): The two toes are fused together to produce only one toe. The front feet are most often affected, but all four may be affected (Johansson et al., 2006). Inherited as a simple recessive trait (Figure 3).
8.Weaver calf (progressive bovine myeloencephalopathy): The disease occurs between six months and two years old and occasionally later. The main clinical signs are ataxia, progressive weakness of the pelvic limbs, difficulties to stand up, proprioceptive deficit and oscillatory hypermetric walking.The mental state is always alert and all the reflexes are always present and normal. Inherited as a simple recessive trait.
9. Photosensitivity (protoporphyria): Animals are sensitive to sunlight and develop scabs and open sores when exposed to sunlight (Figure 4). The liver is also affected and the animals may suffer from seizures (Haydon, 1975). Inherited as a simple recessive trait
10. Bulldog (achondroplasia): This trait is inherited as an incomplete dominant. The homozygous may be aborted dead at 6-8 months gestation and has a compressed skull, nose divided by furrows and shortened upper jaw, giving the bulldog facial appearance. The heterozygous calf is small and heavy-muscled.
11. Double muscling: It is the result of a defect in the myostatin gene, which is responsible for regulating the growth of muscle fibers during development. Without a functioning mysostatin gene, muscles will develop hypertrophy (increase in muscle fiber size) and hyperplasia (increase in number of muscle fibers), resulting in the appearance of a “double muscled” animal (Figure 5).Inherited as a simple recessive trait.
12. Parrot mouth (brachygnathia inferior): One type of parrot mouth (Figure 6) is inherited as a simple recessive trait. The more common cause of teeth and denture pads not meeting is a quantitative trait caused by several sets of genes. This can cause either an under or over shot jaw with varying degrees of expression.
13. Cryptorchidism: One or both testicles fail to descend into the scrotum. Inherited as a sex limited trait and probably involves at least two sets of genes.
14. Prolonged gestation: The fetus fails to trigger parturition. Parturition must be induced or the calf removed. The calf is often extremely large and often dies.
15. White eyes (Oculocutaneous Hypopigmentation): Hair coat is a bleached color and the iris is pale blue around the pupil with tan periphery.
Importance of Abnormal Development
The obvious impact of abnormal development is loss of the nonviable fetus. This presents two possible problems for the producer: first, financial loss, through loss of saleable animals and the cost of retaining the dam for another year, in the case of cattle; second, this abnormal fetus may herald an outbreak of similarly affected fetuses if the whole herd has been affected by an environmental teratogen or if an abnormal gene has entered the gene pool of the herd.
Management and Prevention
- Culling:
- Culling affected animals from the breeding herd helps prevent the transmission of congenital defects to future generations. Selective breeding based on genetic testing can reduce the prevalence of hereditary defects.
- Nutritional Management:
- Ensuring optimal nutrition for pregnant cows is vital for fetal development. Balanced diets with appropriate levels of vitamins and minerals contribute to the prevention of nutritional-related congenital defects.
- Environmental Control:
- Minimizing exposure to environmental factors known to cause congenital defects, such as certain plants or toxins, contributes to prevention. Proper pasture management and control of toxic substances are essential.
- Reproductive Health Monitoring:
- Regular veterinary care, including reproductive health monitoring and timely vaccinations, helps maintain hormonal balance and prevents infectious causes of congenital defects.
- Breeding Strategies:
- Implementing breeding strategies that consider the genetic background of the herd helps reduce the likelihood of hereditary defects. Controlled breeding practices and genetic selection contribute to herd health.
Conclusion
Congenital defects in cattle can pose challenges to herd health and productivity. Understanding the causes, implementing effective management practices, and employing preventative measures are crucial for minimizing the impact of congenital abnormalities. Through vigilant monitoring, genetic testing, and informed breeding decisions, cattle producers can work towards maintaining a healthy and resilient herd while reducing the occurrence of congenital defects over time.
The best control of genetic diseases is to avoid animals that carry these genes. Bulls or semen should be purchased from reputable breeders, produced by parents who are not known to carry undesirable genes. The elite purebred breeder or owner of Al bulls may wish to test for simply inherited traits before bulls or donor cows are heavily used. If the undesirable trait is dominant, no test is needed since the animal would show the trait even if only one dominant gene is present. Testing is usually useful only when the trait is inherited as a simple recessive trait. Carriers should be identified and prevented from producing calves which may be used for breeding purposes. Since mutations occur in every generation, genetic defects can never be completely eradicated. However, modern genetic technology can greatly speed up the process of identifying which cattle are carriers and provide techniques for elimination of the defective genes from the breeds.
Compiled & Shared by- This paper is a compilation of groupwork provided by the
Team, LITD (Livestock Institute of Training & Development)
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