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NORWOOD-YOUNG AMERICA, Minn. - There's been a noticeable trend in the dairy industry over the last 50 years. While milk production per cow has steadily increased, fertility has done just the opposite.

In 1951, conception rate in dairy cows was around 62 percent; by 2007, it had dropped to around 35 percent. Meanwhile, milk production went from just over 8,818 pounds per year in 1951 to 22,046 pounds in 2007.

"As they milk more, cows are harder to breed," said John Zimmerman, DVM, owner of Liberty Veterinary Service, LLC in Cologne, Minn., and bovine practitioner of over 30 years.

This trend has become very costly for producers, who need to keep their cows bred to stay in business.

On Feb. 15, 2010, Zimmerman spoke on this topic during an educational session, "Basic Reproduction for the Advanced Dairyman," at the Carver County/University of Minnesota Dairy Expo in Norwood-Young America, Minn.

Maximizing reproduction in dairy cows

Pregnancies in dairy cattle are achieved through a combination of good heat detection and good conception, Zimmerman said during his session. In Minnesota, a pregnancy rate of 15 percent is considered acceptable. It is, however, possible to achieve a higher pregnancy rate through consistent evaluation and observation of the cows and their reproductive status.

There are several methods used to detect pregnancies in dairy cattle. Four of the most commonly used are ballottement (also known as bumping), rectal palpation, Biopryn blood testing and ultrasound imaging. Each method is effective and offers different benefits and information. Each also has its disadvantages. It is up to the producer to determine which method or combination of methods is right for his herd.

Zimmerman outlined four reproduction goals or benchmarks for producers to strive for on their dairies. The first goal was for a return to normal uterine environment by 50 days in milk (DIM). Secondly, cows should resume regular ovary function by 40 DIM. Heat detection within a herd should be greater than 60 percent, and conception rate should be greater than 50 percent. Unfortunately, many factors can affect the feasibility of reaching these goals.

Poor heat detection is one of the most common factors limiting pregnancy rates on dairies. In some instances, low heat detection is due to little or no visible signs of estrus. In other cases, heats are missed due to shorter heat periods; higher producing cows are known to have shorter duration of estrus. In any case, it is important to know the signs of heat and train all employees or family members to recognize those signs. Providing good cow comfort, including good footing throughout a cow's environment, will also help, as cows will be more likely to express signs of heat.

The percent of cows not cycling at 65 to 70 DIM, or anovular cows, will also affect pregnancy rate. Lack of ovulation is caused mainly by stress on the cows and inadequate nutrition during dry period and lactation, which can lead to a loss in body condition score (BCS).

Inadequate nutrition during dry period and lactation can also lead to poor conception rate in ovulating cows. Other health issues that can impact conception rate are excessive changes in BCS, metritis, sub-clinical ketosis and stress. Aside from health-related factors, insemination technique and semen quality can greatly influence conception rate. Always look at female fertility, bull fertility, accuracy of heats and A.I. efficiency.

Conception doesn't guarantee a full-term or healthy pregnancy. Embryonic loss can occur in 15 to 20 percent of pregnant cows between days 28 and 70. From day 70 to term, fetal loss rate drops to around five percent.

"Every cow deserves three pregnancy checks," Zimmerman said. "The first one should be done at 30 to 40 days. The second should be done between 60 and 80 days. This one can be done with Biopryn; if ultrasounding, you can determine the sex of the fetus at this check. The final check should always be done at dry-off."

The final factor Zimmerman discussed that can limit reproduction goals is multiple ovulations. The twinning rate has more than doubled since 1980, now close to five percent. Studies have shown that as milk production increases, the probability of conceiving twins also increases. Twin pregnancies can lead to increased risk of metabolic diseases and metritis.

With these factors in mind, many producers have turned to utilizing some sort of breeding program within their operation. In fact, a survey showed over 70 percent of dairymen use a breeding program. While all programs are slightly different, they all have one common goal: maximizing pregnancy rate.

"Any breeding program can be successful," Zimmerman said. "It just depends on your management and how compliant you are."

For any breeding program, timing is everything. Producers need to make sure they are giving the right shots to the right cows at the right time.

"With all programs you need to make sure the follicle is in the right stage," Zimmerman said.

For those using the Ov-Synch program, to achieve maximum conception all injections and breedings should be done in the mornings with the exception of the final GnRH shot, which should be given in the evening, Zimmerman said.

Whether on a breeding program or not, Zimmerman said producers should strive to have their cows pregnant by 87 DIM.

"You have to get your cows in heat, catch the heats early, keep the cows healthy and get them pregnant," he said.[[In-content Ad]]

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