It should be simple: a bull, a cow, a pregnancy – it’s nature’s way, right? But dairy cow reproduction has become less about nature and more about human intervention as natural sire service – which accounts for roughly 30 percent to 50 percent of dairy breeding nationwide depending on who you ask – is being outpaced by artificial insemination (AI) and timed AI (TAI) protocols. A variety of breeding programs, varying in intensity, have been designed to get the job done, no bull required.

“AI is the simplest way that dairymen can improve their profitability. AI bulls are high in net merit and will improve profit over time,” said Bradley Heins, associate professor of dairy at the University of Minnesota. “All of the breeding protocols are used by dairymen to improve their herds’ profitability.”

Pregnancy rates

Keeping cows pregnant means money in the pocket. Because the reproductive cycle and milk production are interdependent, maximizing the dairy’s milk output means keeping cows pregnant as much as possible, while promoting cow health and keeping farm economics in mind.

“We know that herds that do better in reproduction can do better on a profitability basis,” Dr. Rob Lynch, Herd Health and Management, Cornell University, said in a recent PRO-DAIRY webinar. “When is it that we want to start breeding cows? What type of heat detection program are we looking at? What type of timed AI regiment are we considering?”

Ongoing research studies at Cornell University, via the Dairy Cattle Biology and Management Laboratory overseen by Dr. Julio Giordano, are examining the voluntary waiting period (VWP) and its effect on farm economics. The VWP is the time between calving and first service breeding and allows the cow’s reproductive system to recuperate. Typically, this is a 60-day period. Although some high-performance dairies work with a shorter VWP, Cornell research is looking at lengthening it to 88 days to measure the resulting impacts on conception, as well as long-term dairy economics and cow productivity.

Although it’s a complicated relationship between increasing pregnancy rates and economic benefits, increasing conception success rates above 20 percent is a goal for most dairy farmers.

The pregnancy rate measures the percentage of cows eligible to be bred that do get bred, multiplied by the conception rate, during any given 21-day period, as a cow’s estrous cycle is 21 days. The more cows in estrus that are inseminated, as well as an increase in conception rates, contribute to a higher pregnancy rate on the dairy.

Pregnancy reduces the days in milk (DIM) for a cow. The lower the DIM, the higher the milk production per cow. When the milking herd has more early lactation cows, dairy profitability increases. Enhancing reproductive performance through more successful breeding strategies increases that pregnancy rate.

“To see pregnancies established in a timely and efficient fashion to maximize milk production and maximize the number of offspring produced (are the primary goals of a dairy breeding system),” said Andrew Sandeen, Penn State University Extension dairy specialist.

There isn’t one right program for all dairies. Each reproductive program has its own limitations and its own costs to implement.

Artificial insemination

If a dairy herd is not being bred naturally, the dairy farmer should play a more active role in getting cows inseminated. But to do that, knowing when to inseminate so that conception is most likely to occur is key. Estrus is the period during the estrous cycle when the cow is fertile and receptive to being impregnated. Without a bull around to pick up on the hormonal and behavioral cues, dairy farmers need to do so.

Artificial insemination itself doesn’t just happen. Detecting that a cow is in heat, or estrus, and is patiently awaiting that sperm during this fertile period can be done in several ways and is normally the first step in any AI program.

“I don’t have true evidence, but I’d say the four common approaches for Northeast dairy farmers would probably be basic visual heat detection and using estrus detection aids followed by AI; using a herd bull for at least a portion of the herd or for problem breeders; timed AI or using an activity monitoring system,” Sandeen said.

Utilizing AI for first service breeding, combined with visual estrus detection or some low-key aids to get the timing right, is the least intensive method of dairy breeding, outside of that bull. Adding an activity monitoring system to assist with heat detection is the next step.

There are progressively intensive breeding programs that synchronize estrus, via hormone injections, so AI can occur systematically in the herd, making heat detection and insemination more efficient and less labor-intensive.

Other breeding protocols go further, synchronizing not only estrus, but ovulation, so that AI is more likely to cause conception. These more intensive, timed AI protocols don’t rely on or require estrus detection, although verifying heat can maximize any program’s success rate.

Estrus detection

When cows are in heat and ready to be impregnated, they will stand to be mounted. This standing heat indicates the most fertile period and is a good visual clue as to when conception would be most likely to occur upon insemination. Elevated estrogen levels and low progesterone levels in the blood cause the behavior. The duration of standing heat is about 15 to 20 hours and a cow will stand to be mounted between 20 and 55 times in this period.

“The ideal is to inseminate about 12 hours after the onset of standing estrus,” Sandeen said.

Many dairy farms rely on visual observation to detect heat. This visual observation requires cows to be observed at least once per day, for 30 minutes or more, for accurate detection. Other signs of heat include mounting, back rubbing, restlessness and increased bellowing. Physiological symptoms include an enlarged vulva and the presence of vaginal mucous. Environmental factors can interfere with these natural behaviors, making it less likely that heat can be visually detected in some herds.

Some farms, often due to time and labor constraints, use tailhead markings, which indicate when mounting behavior has occurred, or electronic mount detectors. Heat detector animals can also be used. Using cameras to record and observe cows can also increase the rate of estrus detection.

Another way to monitor for estrus is via activity monitoring systems. During heat, the cow’s activity level will change.

Activity monitoring systems “will monitor cows 24/7 and this technology can help to limit some of the problems we have with more traditional heat detection systems,” Giordano said during a webinar presentation.

Synchronizing the herd

Hormone injection protocols make it possible for the herd to be synchronized, so that groups of cows enter estrus simultaneously, increasing the chance of detecting heat and allowing for better time management and conception rates with AI. These estrus synchronization programs involve injecting one or more hormones on a specific schedule to induce heat. Prostaglandin (PG), progesterone (P) and gonadotropin releasing hormone (GnRH) can be used alone or in combination.

“Some systems termed estrous synchronization programs are designed to cause cows to come into heat over a short period of time so they can be inseminated in a timely manner. Heat detection is required for these programs. The newer systems, termed timed breeding or appointment breeding, are designed so both the onset of heat (estrus) and ovulation are induced so cows can be inseminated at a specific time without heat detection.”

Some common TAI protocols include Ovsynch or Presynch. Neither requires heat detection, although enhanced pregnancy rates can be achieved if estrus detection is also used. Combined protocols include Double Ovsynch and Presynch-Ovsynch programs.

Some cows show signs of heat but don’t ovulate. Some don’t show signs of heat but do ovulate. About 30 percent of cows will have some problems with conception, according to Giordano, whose PRO-DAIRY presentation provides detailed information on various synchronization programs. View the Cornell ProDairy YouTube page for Giordano’s presentation.

But success isn’t guaranteed, no matter how intensive the reproductive protocol. Most dairies today are showing average pregnancy rates of just below 20 percent, an increase from just a decade ago, with top herds showing rates of 30 percent to 40 percent, Giordano said.

There isn’t one right program for all dairies. Each reproductive program has its own limitations and its own costs to implement. Every dairy farmer must assess the benefits of any system and whether the probability of raising those pregnancy rates – and the resulting economic benefits from more milk – outweigh any obstacles. Finding the best reproduction management practice for your dairy and implementing it to the best of your ability is key to success.

“What reproduction program is the best for your system? What is important is to be aware of what reproductive programs are available,” Giordano said. “Outstanding reproductive performance is compatible with current production systems. There is not only one way.”