Early in the quest for great Texas Longhorn cattle DCC sold a bred cow to Jerry Cook of Colleyville, Texas. When the calf was born Jerry sent pictures of the calf's face, which clearly showed an eye in the middle of the forehead. Jerry was shocked, amazed and concerned. His first question was, "Does your bull sire this often?" I was gobsmacked to say the least. First thoughts were what if our herd started to have these extra eyes and no one would buy our cattle? Well, happy to say in 59 years I have not seen another with an extra eye. Yet it started a suspicious research of defects and their causes. There are hundreds of known defects or mutations and an equal number of reasons. Nearly every month I get a call from someone with some weird new wacko imperfection which scares the owner just like it scared me in 1965. Hopefully your next biological goof up, like mine, will never happen again.
Abnormalities are present in all species, including virtually all breeds of cattle. Some abnormalities can be identified visually because of the obvious differences between a normal animal and an abnormal one. Abnormalities in cattle may be caused by a variety of factors, including the environment, infectious agents and genetic mutations. Environmental factors, such as toxic plants, can cause an abnormal calf. Likewise, infectious agents (such as bacteria, viruses and fungi) may result in an abnormal calf. The following data relates to those abnormalities that are pathological (disease) conditions of genetic origin. These types of abnormalities have come to be known as “genetic defects.” Genetic defects include an impairment of health or a condition of abnormal function, due to a broken or mutated gene. Before designating a condition a genetic defect, it is important to give consideration to environmental and infectious possibilities.
The American Angus Association currently recognizes numerous genetic defects. These defects may result in either increased mortality, increased morbidity, decreased production, and/or decreased ability to market cattle. As such, their unchecked presence in the population is undesirable. The most known include Dwarfism, Osteopetrosis, Double Muscling, Syndactyly (mule foot), Arthrogryposis Multiplex, and Heterochromia Irides. Although these defects are undesirable, some of the most sought after Angus genetics are proven to possess these traits. When these defective traits are out-crossed to unrelated or non defective genetics their frequency can be managed to zero.
From a more scientific view, mutation, the process which produces errors during copying of DNA, is a fact of genetics. It is unavoidable and unfixable. This means that every calf born in all herds carries approximately 30 mutations that originated in the sperm and egg that created the calf. Only 3% of an animal’s DNA codes proteins, so most of these 30 mutations do not affect genes. But, a small number of these mutations will be within a gene and the protein coded by that gene will no longer function normally.
They sometimes refer to these genes which carry a loss of function mutation as broken genes. This means new broken genes are added to the pool of existing broken genes in the population every calving season. The mutations responsible for these broken genes usually disappear from the population simply due to random chance. Occasionally a mutation will rise to higher frequency and will be passed down through generations often as a result of inbreeding. Most of these broken genes carry recessive mutations; this means that two copies of the broken gene must be inherited for the animal to be affected. When only one copy of a recessive mutation is inherited from one parent the animal is normal because it uses the functioning copy inherited from the other parent. Many of these unusual scientific happenings are not documented or even noticed by the owners.
Seven days after cows are mated, 90 + - % of the matings result in pregnancies. But, when we observe cows 45 days after the mating, only 60 to 70% of the cows are still pregnant. Cows are aborting about 20% of the pregnancies during the first 45 days. While handling and nutrition influence these pregnancy losses, genetics also play a role. Twin pregnancies increase the abortion percentages.
On average, an animal will inherit 100 broken genes from its parents. Of these, 20 are lethal, meaning if two copies are inherited the embryo dies during pregnancy, usually early in Mutation, the process which produces errors during copying of DNA happens, and always will.
