During a farm visit, a dairy farmer asked me this question.
The reason was a marked increase in twin pregnancies on his dairy farm.
Twin pregnancies are of all times and therefore nothing special.
However, in recent years an increasing trend of twin pregnancies in cattle can be observed.
In almost all cases the cause of a twin pregnancy is a double ovulation.
A number of (animal related) factors that significantly increase the likelihood of a twin pregnancy are:
1. Genetic predisposition
Some "breeds" and/or "cow families" give birth to more twins than others.
2. The number of pregnancies of the individual cow
In the first pregnancy, the probability of a twin pregnancy in a cow is only 1%.
In subsequent pregnancies, this percentage can increase to more than 10%.
3. The production level of the individual cow
More than 35% of cows with a high milk yield, (at least 40 kg of milk per day within 14 days before natural ovulation), therefore have an increased chance of double ovulation.
In contrast, in dairy cows with lower daily production in the same period, this percentage is around 10%.
4. A disturbed cycle
In about 38% of cows with a disturbed cycle we see a double ovulation in the following cycle.
In cows with a normal cycle this percentage is around 16%.
Mainly stress related situations, such as (for the individual animal), insufficient nutrients in the ration, overcrowding, rough handling, heat stress, can negatively influence the cycle of the cow.
5. The liver is partly responsible for low progesterone levels
In case of higher feed intake combined with high milk production, the liver breaks down more progesterone.
This results in a weak Corpus luteum (better known as "yellow body").
6. Ovulation synchronization or "Ovsynch"
The Ovsynch protocol is a fertility program developed in the United States in 1997.
In an Ovsynch program, (which lasts ten days), the animal is given three injections intramuscularly at a well-defined time interval.
The first day, gonadotropin releasing hormone or follicle stimulating hormone is administered.
This is followed seven days later by an injection of prostaglandin.
On day nine, the first hormone is administered again.
Finally, Ovsynch-AI takes place as standard 17 to 24 hours after the last injection, with no heat detection.
Ovsynch treatment involves treating a sexually mature female animal after examining the ovaries for active follicles in such a way that insemination can occur at exactly the right time.
For successful insemination, the exact determination of the time of ovulation is one of the critical factors for good pregnancy outcomes.
7. The influence of an ovulation synchronization
Some think that hormone programs are at the root of many twin pregnancies.
In my opinion, it is often the "hard to get pregnant" cow that are treated with a hormone program.
The cause of "hard to get pregnant" is often an imbalance of hormones, resulting in a weak yellow body or even NO yellow body.
This combination increases the risk of double ovulation.
The oocytes of the follicle are activated by applying a single ovulation synchronization.
Because this follicle is formed when progesterone is deficient, the risk of double ovulation is increased.