Periodically over the years there have been those who advocated increasing the incidence of twinning in cattle as a means of improving profitability per cow. The idea was that double the number of calves per cow per year would double the financial return. As usual, when something appears too good to be true, it is.
As a practicing Veterinarian, in my second year after graduating in 1973, I felt obligated to address this false claim. My first article on the subject was published in the January 1975 issue of the Milking Shorthorn Journal. In the intervening 46 years, cows have not changed and twins still represent a significant threat to the health and wellbeing of both cows and calves. So, with some minor editing, that article is reproduced here.
In 1974, there appeared an article advocating selection of cattle for twinning written by the University of Wisconsin Extension Service which cited the work of J. J. Rutledge, a geneticist at the University of Wisconsin. After recounting stories of various cows who made a habit of producing multiple births over the past 150 years, he concluded with the statement that ". . . in a protein hungry world, another 350 to 400 pounds of calf weight per cow might out-weigh the extra trouble of twinning . . ."! That was not true in 1974 and remains a fallacy today.
Basically, there are two types of twins, monozygotic (identical) and dizygotic (non-identical). Identical twins arise when a fertilized ovum splits and develops into two separate individuals. Identical twins are always the same sex and possess much the same color patterns, hair coat characteristics and productive abilities. They account for four to six percent of all twins and the incidence of identical twins is not particularly influenced by heredity.
Non-identical twins develop when the female ovulates two fertile ova which are subsequently both fertilized. This type of twins accounts for the vast majority of all twins and it is influenced, to some degree, by heredity.
Cows who are themselves twins have daughters with a tendency to produce twins more frequently than daughters of non-twinning cows. The repetition of multiple births in a cow is an indication of multiple ovulations. That tendency is passed on to the daughters. Twins occur about 1% of the time in beef cattle and about 4% to 5% of the time in dairy cattle, although certain breeds of cattle can have somewhat higher percentages. Primiparous dairy heifers average about 1% while aged Holsteins can approach 10%. Controlled breeding strategies, popular in dairy herds today, have reduced the incidence of twinning which has confused estimates of heritability.
Heritability is assumed to be low at between 0.01% and 0.09%. Heredity for double ovulations is similarly low for a single estrus cycle but over multiple cycles rises to about 0.35%. While somewhat difficult to understand, it does suggest that the same cow is likely to ovulate more than a single ova over multiple cycles. By selecting for twinning, some herds have increased the incidence to as high as 29% so it is clear that if twinning is deemed desirable, genetic means for increasing the incidence are available.
However, twinning significantly increases the demands on management in addition to detrimental effects on the cows. Dr. S. J. Roberts, writing in Veterinary Obstetrics and Genital Diseases, published in 1971, made the following statement:
"Multiple births or twinning in uniparous animals (cattle and horses) is undesirable and in most cases pathological and often disastrous to the dam as well as the fetus. Twinning represents an economical waste or loss and is a reflection of genital disease rather than health."
Twin gestations are generally about 5 days shorter than for single births. Twins are smaller, being up to 45% lighter for bull twins and up to 50% lighter for heifer twins. Twin pregnancies are a significant cause of abortion, stillbirth, and dystocia, with many needing assistance during delivery. Twins are typically less vigorous at birth and three times as likely to die at a young age. Finally, half the twin births are of mixed sex and 92% of those heifers born twin to a bull are sterile. Some of the bulls also exhibit reduced fertility or even sterility.
The detrimental effects of twinning often begin at conception. Of 600 ovulations in a herd of cows that were studied, 13.1% were double ovulations however only 1.92% twins were born. This represents a 14.6% conception rate. Cystic ovarian disease is also associated with double ovulation and twinning. It is common for a cow recovering from cystic ovaries to conceive twins suggesting that selection for twinning might increase the incidence of cystic ovarian degeneration and impaired fertility, especially in older cows.
It is estimated that up to 50% of all twin pregnancies terminate in abortion, either as early embryonic death or delivery of stillborn calves prematurely.
Following twin births or abortions, delayed uterine involution, retained placenta, and septic metritis are common which adversely affects subsequent fertility or can cause outright sterility. Calving interval following twinning is often prolonged. In dairy cows, milk production is often reduced. Dam mortality is also increased. After nearly 50 years of personal observations, twinning cows have over 50% more problems than single birth cows.
After considering all of the negative effects, it is impossible to wean an additional calf, on average, for every cow that has twins. Statistically, in fact, the average number of calves weaned from twinning cows is less than one—this is not a useful economic proposition in any operation, not to mention the additional management headaches.
The primary goal in raising cattle—healthy calves.
Author Profile: Dr. Martin Lee
Martin Lee was raised on a small registered Milking Shorthorn dairy, and graduated from Colorado State University with a DVM degree in 1973. He was in general veterinary practice after graduating, but since 1978 he has operated Idalee Veterinary Services, specializing in Dairy Consulting in Jerome, Idaho. He was the owner of Idalee Milking Shorthorns, which was the highest producing Milking Shorthorn herd in the world for many years between 1996 and 2006, until the herd was dispersed in 2006. One of his cows, Idalee Garnet Topsy-EXP, still holds the record for highest lifetime production for a Milking Shorthorn, with 318,330 lb. milk over 11 lactations. He currently has a herd of Beef Shorthorns with approx. 30 cows plus young stock and bulls, but in addition he still has 2 Native Milking Shorthorns.
Martin and his wife Susan Lee have each served multiple terms on the AMSS Board of Directors, and have each been National Presidents of AMSS. Susan Lee has also been very involved with dairy improvement and she has served terms as Director and as President of the National Dairy Herd Improvement Association. She currently manages the Idaho DHIA. Martin and Susan have a son and a daughter, plus 5 grandchildren.