Breeding soundness exams often disrupted by droplets
Cattle producers often question the appearance of lots of droplets on the semen evaluation forms of their young bulls.
These droplets cause frustration because the bulls have to be retested.
Droplets are probably the most common defects that veterinarians see when performing breeding soundness exams in the spring.
We see many more droplets in immature bulls that are just reaching sexual maturity. They are less active, and droplets are a frequent occurrence, especially when not housed close to cycling females.
It is important to know that the sperm that matures in the testicles’ epididymis starts with a proximal droplet near the head of the sperm.
This is wiggled or shook off as the sperm matures and travels through the canals within the epididymis. Fertility is affected because sperm with droplets is essentially not mature.
There are two types of droplets:
- Severely affected (pathologic) droplets are called proximal because they are near the head of the sperm.
- Droplets that will be shaken off later (physiological) are called distal and are in the middle of the tail.
Dr. Jacob Thundathil of the University of Calgary’s veterinary medicine school found that the percentage of droplets in ejaculated sperm goes down in the time it is chilled to be frozen and put into straws for artificial insemination.
This time interval is only three hours, and the same thing must happen with natural breeding.
A number of these distal droplets shake off and are left behind as the sperm swims up the vagina and into the uterus. As a result, the distal droplets aren’t as serious a defect as the proximal ones.
All sperm start with a proximal droplet and become distal droplets as they mature in the canals of the epididymis. Lots of proximal droplets are often associated with other sperm defects, such as head defects.
Droplets are the main reason why many young bulls fail their first semen evaluation, especially if done at a young age. It’s why testing a beef bull before it’s 12 months old is not recommended.
It’s also why only half of 12-month-old bulls pass. Many young bulls that fail on initial semen tests pass in subsequent tests a month or two later.
Indeed, 75 percent of bulls 14 to 15 months pass the test.
Veterinarians can’t predict which bulls will improve, so retesting is the only option.
I believe semen improvement can be sped up by housing young bulls close to cycling females so that they ejaculate off the senescent semen.
Veterinarians include morphological defects on their semen forms, so producers can see over time if the situation is improving.
The most dramatic improvement I have seen was in a young bull with 100 percent proximal droplets. The percentage kept decreasing over time, and the bull had excellent semen by the time it was two years old.
The animal was a show bull, which prompted questions about whether it was too fat or inactive, factors that could have affected the situation.
Large numbers of droplets in mature bulls aren’t as common.
Producers who evaluate semen forms of young bulls should know there is a good chance the defects will lessen with maturity and use if most of them are distal droplets and the animal passes its semen test with overall defects of less than 30 percent.
The testing of younger bulls has become more common, partly because bull sale dates have remained the same while purebred producers are calving later.
Producers who sell bulls off the farm should postpone testing until their animals are as mature as possible.
It’s easier to evaluate sperm in the spring, when the weather is warm and cows are cycling close by, than it is in the dead of winter when the bulls are too young. Even one to two weeks makes a big difference.
The pass rate will be higher if semen evaluation is done later. It will also be easier on everyone, including the bulls.
via The Western Producer http://www.producer.com/2013/05/breeding-soundness-exams-often-disrupted-by-droplets/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+westernproducer+%28The+Western+Producer%29