Exposure to teratogens during gestation or lactation can lead to congenital defects
This webpage was last updated on February 3, 2003 by Sheila Schmutz firstname.lastname@example.org
In terms of disease, teratogenic inheritance implies a genetic predisposition in the fetus and an environmental trigger during gestation. Sometimes the lactation period is included under this category because the triggers or teratogens are still under maternal influence.
Since teratogenic inheritance is due to in utero exposure of a teratogen, it is a mammalian phenomenon. Gestation in cattle, like humans, is 9 months. Therefore the calf fetus is developing on approximately the same timescale as a human fetus.
If there is teratogenic exposure early in pregnancy up to the blastocyst stage, there is more likely abortion than a congenital defect. This is typically the first 7 days post-copulation in the cow. Organogenesis occurs during the first trimester of pregnancy and is the most critical period during which teratogens should be avoided. Histogenesis occurs during the middle trimester. Subtle changes in the the types of cells in the gut lining, etc. happen during this period. The third trimester is primarily growth of the fetus so teratogenic exposure at this time is more likely to lead to stunting than to specific congenital defects.
Teratogens fall into several categories and include fever, drugs, chemicals, viruses, specific plants, etc. Keep in mind that most cows are pregnant or lactating or they wouldn't be on your ranch. Avoiding drug treatments completely is therefore impossible but one must try to pick the least dangerous time to administer vaccinations, etc.
Most ranchers are very familiar with BVD or bovine virus diarhea. If a heifer contracts this disease early in pregnancy she is likely to abort. Later, the calf is often left with central nervous system damage.
Most medications and vaccines have warnings about use in pregnancy for a reason. Wormers such as parbenzol should not be used during pregnancy. Anury or tailessness is one of the defects that can result. The calf at the left has a shortened tail but also contracted vertebrae in its spine.
Pollutants can be teratogens to cattle also. These could be in dugouts from runoff and become especially concentrated in drought years. Conifer resin from the accumulation of pine needles in puddles can be toxic to cattle who drink this water source.
Sour gas wells near pastures can be teratogenic also. Sulfur occurs in high amounts near such wells and the plants growing nearby take up this sulfur and not the rarer selenium. Although plants do not need selenium, animals do. Calves who suckle cows grazing on selenium deficient pastures can develop white muscle disease.
The calf at the right has arthrogryposis or twisted legs. One teratogen that has been known to cause this type of defect is lupines. Lupines tend to bloom in years of relatively high moisture on the prairies and may attract cattle to graze them heavily during such blooms. Loco weed is another prairie plant that can be a teratogen for cattle.
Twinning in cattle and humans usually puts the pregnancy into the "high risk" category. About 5% or less or pregnancies in cattle result in twins. 30-40% of twin pregnancies in cattle result in abortion. Twins are usually born about 2 weeks premature and should not be expected to be more than 75% of the birthweight of a single born calf.
Position defects, such as arthrogryposis, are higher in twins than singleton calves. The other problem with twins of unlike sex is that the heifer calf is a freemartin. Both twins exchange cells due to placental anastomosis as is shown in early (left) and late pregnancy (right). These cells and the hormonal exchange, cause the gonads and genitalia of the female to not develop properly. The fertility of the bull co-twin may be subtlely lowered, but this is not usually noticable.
All cattle twins potentially harbor cells of the other twin. It is possible that a bull might literally sire his brother's calves! Parentage testing and other DNA testing can reveal more than 2 alleles in twins.
Twins require extra management during the pregnancy and thereafter but they are desired by some ranchers. Dr. Brian Kirkpatrick publishes a
for further information contact:
Department of Animal and Poultry Science
University of Saskatchewan
Saskatoon, Canada S7N 5A8
phone: (306)966-4153 fax: (306)966-4151
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