Everyone is getting ready for breeding season at this time. Are your bulls ready to go? Bulls are very important to the herd. A good bull can change your calf crop very quickly and make or break you. The wrong bull can produce too big of calves, too small of calves (dinks) or not get any of your cows pregnant.
I highly recommend having your bull tested prior to turn out. This involves a breeding soundness exam. This is not just a semen test, but determines if your bull is in good enough health for the breeding season. The Society of Theriogenology and Bovine Practitioners and the breed association got together back in the 90’s and developed the standards for this examination.
There are four parts to this breeding soundness examination. The first part is physical exam. Is he sound to breed cows in the pasture and in good health? Is his body condition score where he can withstand the stress of breeding the cows you want? Is he sound of feet and leg? All of these can be seen as the bull walks into the chute and/or checked out in the chute. Normally, I like bulls to have a body condition score of around 5 or 6 on the beef scale. This would be a 3.0 on the dairy scale.
The next step is measuring the scrotal circumference. As a minimum the bull has to measure 30 cm around the largest circumference of his scrotum. This is a minimum for a bull under 15 months of age. If they do not measure at least this big, they fail immediately. Scrotal circumference is directly correlated to how big the factory is and how early your heifers will reach maturity. It is obvious; we need a big enough factory to produce the spermatozoa to breed multiple cows. And we do not want our heifers not reaching puberty at 24 months of age. On bulls over 24 months of age this scale is up to 34 centimeters. The scale goes up 1 centimeter every 3 months until 24 months of age.
The next step is collecting an ejaculate and grading the motility of the live sperm. In other words, how fast are they swimming? I like to see motility greater than or equal to 70 percent, but minimum is 30 percent for passing. Generally this will correlate directly to the morphology of the spermatozoa.
The next step is the morphology of the spermatozoa. This is what they look like under a microscope. I normally count 100 sperm and at the same time I will count how many defective sperm I see. 70 percent is passing. There is a whole list of defects from bent tails, headless sperm, misshapen heads, to medusa heads. These spermatozoa can not fertilize an egg from your cow. We used to put a score on the bulls 19 years ago. This procedure does not put a score on the bull. He either passes or fails. The way I always have looked at it is “What is the difference between a bull scoring 76 and a bull scoring 90 in the pasture?” Not a thing!
Now to finish the test, we either mark satisfactory potential breeder or not. We do have the right to defer classification at this time. This means neither fail nor pass. It means the bull may have problems right now and may get better in time. Generally this is where I will see spheroids under the microscope. Spheroids are immature spermatozoa and the bull has had a problem and may be getting better. The spermatozoa I look at today are actually 60 days old. This is how long it takes to grow spermatozoa up to maturity.
Remember that it can cost you as much as $1,000.00 in 6 weeks if your bull is shooting blanks, let alone an entire calf crop if not caught.
Dr. Tim O'Neill owns Country Veterinary Clinic in Farmington, Ark.
