Healthy cows, healthy hormones

MARSHFIELD, Wis. — Getting cows pregnant is a primary focus on dairy farms, and getting cows into a high-fertility cycle is one way to achieve reproductive success.

Megan Lauber, a University of Wisconsin-Madison Department of Animal and Dairy Science Ph.D. candidate, spoke at the Professional Dairy Producers Herdsperson Workshop Oct. 12 in Marshfield.

Lauber said that maintaining consistent body condition scores is one way to promote a high-fertility cycle.

“What I like to call the high-fertility cycle is having cows be fertile, not gaining excess body condition, having them calve in their subsequent lactation, not having transition issues, not losing a lot of body condition and reinstating the cycle,” Lauber said.

According to Lauber, cows that are calving with a body condition score of around 2.5 to 2.75 tend to lose less body condition early in lactation than their peers who calve with higher or lower scores. That leads to fewer health issues, which creates better fertility. These cows are more likely to be pregnant by 130 days in milk and tend to gain less body condition as they complete their lactation and enter their dry period, putting them at that optimum 2.5 to 2.75 body condition score to begin the next lactation.

“If we can minimize the amount of body condition score cows lose, we can have better fertility and keep our herds having better fertility,” Lauber said.

Lauber referenced a study that looked at how an early postpartum change in body condition score affected fertility to a timed breeding, where all cows were bred to a timed double ovsynch. Cows in the study were body-condition scored at calving and again at 21 days in milk. Cows were then grouped by whether cows lost, maintained or gained condition.

“You typically think that all cows lose condition during that time period,” Lauber said. “What is interesting in this study is that they didn’t. About 42% lost condition, 36% maintained and 22% gained. There was no real difference in production among those cows. So, cows that are gaining condition and still milking at the same level are eating more and getting energy that way, and having a full rumen in a ruminant is good.”

Looking at pregnancy outcomes, the study found that the differences in fertility between the groups was dramatic.

“The group that lost was 23%, while the group the gained was at 83%,” Lauber said. “It seems high, but it is so impressive to see how that condition loss, or lack of it, affects fertility. All of the protocols were the same, so the outcome was really driven by condition.”

Lauber said that, along with monitoring body condition scores, using timed breeding programs play a role in increasing fertility by increasing the conception rate.

“Research has found that, if we breed cows off a double ovsynch, we increase pregnancy per A.I. by about 10 percentage points,” Lauber said.

Developing an understanding of the cow’s hormonal cycle and how using hormonal protocols affects that goes hand in hand with getting cows into a high-fertility cycle, Lauber said.

“We have both lactating cows and heifers on our farms, and it is kind of interesting to look at the differences in their repro cycles,” Lauber said.

Lauber said that lactating cows typically have a shorter duration of estrus than heifers do. Conception rates for heifers are typically higher than those of lactating cows, and the occurrence of pregnancy loss is typically higher among lactating cows than among heifers. In addition, Lauber said that lactating cows are more likely to have multiple ovulations, which increases the incidence of twinning.

“These differences are something we have to try and manage our way through and better understand,” Lauber said.

Lauber also said that progesterone, produced in the corpus luteum, plays a role in these cycles.

She noted a UW-Madison research study that set out to determine why these differences occurred. During the study, Lauber said, researchers looked at the size of the CL, relative to the amount of progesterone produced. In that study, they learned that cows tended to have larger CLs than heifers.

Lauber said that one might think a larger CL would produce a greater amount of progesterone, but the study showed the opposite to be true.

“Lactation really increases the metabolic demands on cows,” Lauber said. “It seems that milk production is really impacting steroid concentration in our cows.”

As dairy farmers select for higher milk production, Lauber said, that correlates with increased feed intake, which leads to increased blood flow throughout the gastrointestinal tract and visceral to absorb those increased nutrients. Along with that, liver blood flow is increased.

“The liver is responsible for metabolizing steroids in the body, including these ovarian steroids,” Lauber said. “We have these high-producing cows with higher feed intake, more blood flow and greater metabolism of estrogen and progesterone, decreasing it in circulation.”

The protocols that have been established by the Dairy Cattle Reproduction Council have worked to address and compensate for these issues in lactating dairy cows, Lauber said.

In the normal hormone cycle of a lactating cow, Lauber said, GnRH would be released by the hypothalamus. The GnRH would stimulate gonadotrophs to produce luteinizing hormone and follicle-stimulating hormone, which play an important role in follicular development. As the follicle grows in size, it produces estrogen. When estrogen reaches the required threshold, the cow will be in estrus. The estrogen from the follicle will act on the brain, causing a GnRH surge which produces LH, causing the cow to ovulate.

During a hormonal treatment such as an ovsynch protocol, the cycle is manipulated by administering GnRH from an external source, to initiate a follicular wave.

“We have done a lot of management things over the years that have improved cow health and fertility in our herds,” Lauber said. “When we apply these management tools, we are taking what we understand about the cow, and her cycle, and using them to our benefit.”