The detrimental impact of using natural service, even in a clean-up situation, cannot be overemphasized. AI has been integral in reducing disease transmission, allowing for genetic selection and increasing the milk yield of dairy cattle.  Nevertheless, after a few as one or two AI services, many dairy producers and heifer ranch operators use clean-up bulls on the heifers.

Here are six reasons why you should NOT use clean-up bulls on your heifers.

Reason 1 - Clean-up bulls cannot provide the genetic advancement possible with proven AI sires.

No information regarding production, physical conformation or calving ease is available for natural service bulls. Dairy producers must recognize that any natural service bull used on the farm is the offspring of 99 percent of all cows that were NOT considered to be potential bull mothers by the USDA and the AI industry. In addition, it is important to remember that for every 10 bulls sampled in an AI progeny test program, only one or two will make it to active service. Therefore, the odds of selecting a natural service sire that will compare with a proven AI sire are insurmountable.

Reason 2 - First lactation heifers represent the greatest potential contribution to your herd's genetics.

Why? Because first lactation heifers represent the highest number of calvings per lactation group on most farms. For example, with an average annual replacement rate of 35 percent, a minimum of 35 heifers (per 100 cows) must calve each year to maintain herd size. In reality, more that 35 heifers (per 100 cows) must calve each year, as you must consider death loss, infertility, and selection within the heifer pool. If you assume a 15 percent increase is necessary to cover death loss, infertility and selection within the heifer pool, then 41 heifers (per 100 cows) must calve each year (35 heifers minimum x .15 = 6; 35 + 6 = 41 heifers).

Reason 3 - Open heifers after one or two AI services are not necessarily subfertile, but rather victims of "chance" (profitability).

If you achieve a 55 percent conception rate in your heifers, only 80 percent of your heifers wil conceive after two or fewer service (see table 1). If heifers are limited to two AI services, the clean-up bull wire sire 20 percent of the offspring in this scenario. This is unacceptable as open heifers after two AI services are not necessarily subfertile, but rather most likely haven't conceived due to "chance" (probability).

Reason 4 - Clean-up bulls cost more than most producers realize.

Management must recognize the costs of natural service, which include: a) the purchase price of the bull; b) daily feed costs; c) veterinary costs; d) lost income because the offspring of the clean-up bull will produce less milk than the offspring of a proven AI sire.

Reason 5 - Clean-up bulls can introduce veneral disease into a herd, whereas AI bulls are free from disease.

Venereal diseases such as campylobacteriosis (previously called vibriosis) and trichomoniasis can be devesting to your herd's profitability as heifers may become infected during natural service, abort, and become either temporarily or permenently infertile. In contrast, health, semen quality and fertility of AI bulls are routinely monitored by the AI industry.

Reason 6 - Bulls pose a health risk to you, your employees and the entire herd.

Bulls are dangerous and unpredicatable. AI eliminates the risk of catastrophic injury or death to you and your employees.