Reproduction is economically important to a dairy herd. If cows don’t reproduce, they won’t become milk producers. Dr. José Santos, a professor at the University of Florida, delved into this vital factor as he reported on research that identified biological impediments to reproductive efficiency and strategies to improve reproduction during a workshop at the Vita Plus Dairy Summit Dec. 5 in Merrillville, Indiana.
Reproduction improves milk production by decreasing average days in milk of the herd, altering parity distribution and providing a faster transition of primiparous cows to a more productive second lactation.
It can increase the number of replacement heifers, which allows for greater genetic selection intensity and aids the sale of heifers and cows for milk production.
Better reproduction can facilitate adequate culling policies. “You no longer have to keep a problem cow just because she is pregnant,” Santos said.
In terms of milk gained or lost, Santos and his students recently looked at the lactation curve from different dairy herds. On average the curve peaked at 105 pounds of milk and extended to 15 months post partum. Based on this curve, he calculated that a change in calving interval by two months resulted in a loss of about 3 pounds of milk per day.
When he evaluated a farm producing 22,000 pounds of milk per year, Santos said the farm would see a major benefit of $4 to $5 profit per cow if it could move its 21-day pregnancy rate from 12.5 to 15 percent.
However the higher the pregnancy rate the farm has the harder it is to gain a significant benefit. For instance if it starts at 25 percent and increases to 28 percent there is less than $1 profit per cow.
“The only benefit of increasing this (at 25 percent pregnancy rate) is now you can make individual decisions on managing cows,” Santos said. “You don’t need to breed every cow. Having a very high pregnancy rate gives you flexibility.”
Biological impediments
For years it was thought that high milk production was an impediment to good reproduction, but producers have shown us they can achieve very high rates of reproduction with very high milk rates, Santos said.
Other biological impediments remain that can lead to delayed post-partum cyclicity, reduced intensity and duration of estrous expression, reduced fertilization and increased pregnancy loss.
A study he shared from Canada showed a huge variation (5 to 45) in the percentage of anovular cows in high producing dairy herds. The cows that are anovular don’t show estrus, he said, but can be helped with synchronization programs.
“Disease is the worst thing that happens to reproduction,” Santos said. He and his graduate students performed a study to see the incidence of health disorders in first 60 days in milk in high-producing Holstein herds.
Of the 5,719 postpartum dairy cows evaluated, 55 percent were healthy. Lameness was mostly under control, at less than 10 percent. The problems that affect the uterus – calving problem, metritis and clinical endometritis – were very prevalent, he said.
Blood samples were taken from these cows. In the healthy group, 84 percent of the cows had ovulated by 60 days in milk, compared to only 70 percent of the cows with a health disorder.
Cows with a disease had a pregnancy rate 16 percent less than the healthy group. Healthy cows averaged 9 percent for pregnancy loss, whereas cows with more than one health disorder lost 16 percent of pregnancies.
They also synchronized 1,000 cows, flushed them and collected 476 embryo-oocytes on day six after A.I. to evaluate fertilization, embryo quality and cell population. A smaller group was flushed on day 15 after A.I. to look for pregnancy, embryo shape and length and interferon-tau concentration.
Of the healthy cows, 86 percent achieved fertilization. Cows with one clinical disease or multiple diseases had 78 and 75 percent fertilization, respectively.
At day 15, 84 percent of healthy cows had elongated embryos. In the event of uterine disease, none of the embryos were elongated.
“We are losing in every step of the gestation period of cow once there is a disease problem,” Santos said.
Strategies to improve
Santos provided the following strategies to correct and reverse low reproductive efficiency.
• Improve the environment of the cow. “Industry standards for space and comfort of transition cows is often overlooked,” he said.
• Improve how employees deal with cows. Implement pro-active prevention and therapeutic programs to minimize and quickly correct disease incidence on the farm.
• Implement management practices that minimize disease.
One avenue is to focus on providing adequate nutrition for transition cows. High-producing cows have high requirements for energy intake. “If energy balance is a major drive of reproductive success then the focus should be on energy intake and not milk yield,” Santos said.
• Implement reproductive management that impact insemination rate and pregnancy per A.I.
“More than 20 percent of calves born from dairy cows in U.S. are sired by natural service bulls,” Santos said. “They do not improve reproductive performance…If you can handle A.I. there’s really no place for bulls on farms.”
To manage estrus, he recommended establishing a program that includes presynchronization; having a plan for a resynch program; and do not eliminate detection of estrus, unless fertility to timed A.I. is outstanding.
• Implement genetic selection program for improved health and fertility
“If I select for higher milk yield, in the long run I do a disservice to daughter fertility,” Santos said. “Today, if you spend a little time you can select for net merit, bull fertility and daughter fertility. They can be found in genomic proofs.”
To look at these strategies from a timeline perspective, Santos suggested during the pre-partum stage, group cows properly and give proper nutrition. For parturition, train personnel on how to handle calvings.
In early postpartum, train people to properly deal with problem cows. In the weeks after, monitor health and take proactive measures to diagnose and treat. Towards the end of the voluntary waiting period, use a reproductive program to prepare cows for breeding and maximize estrus detection for A.I.
By implementing these strategies to improve reproduction a dairy herd with benefit economically. PD
Karen Lee
Editor
Progressive Dairyman magazine
