Reproduction efficiency in a dairy herd has the largest long-term effect on gross revenue of any other management area of a dairy operation. Consistent cash flow for a dairy farm is dependent on the number of cows becoming pregnant and freshening throughout the year. As pregnancy rates decline, the average days-in-milk for the herd increases resulting in fewer fresh cows rotating into the milking herd with new, high-producing lactations. Reproduction efficiencies on a dairy farm are affected primarily by two factors: (1) fertility health and (2) reproduction and breeding management.
On all commercial dairy herds, the primary function of a cow is to produce milk about 10 to 11 months of every year, giving birth to a calf and repeating the cycle the following year. This reproduction cycle is a natural phenomenon for both domesticated and nondomesticated ruminants. For many of today’s high-producing dairy cows, however, poor fertility is common, making it difficult to conceive and carry calves to full term. Fertility is one of the first things to be negatively affected in cows with chronic health challenges such as poor body condition or nutrition. Obstacles to conception and full-term pregnancies can be caused by both metabolic health problems as well as environmental challenges. Even if cows conceive in a timely manner, unexpected stress or disease factors later in the pregnancy may cause the cow to abort the pregnancy.
Dairy heifers must be pregnant and give birth to a calf before they can produce milk. Older cows must continue to produce calves during their lifetime to remain productive. Breeding and conception are a necessary part of competent and effective dairy management. To maximize cash flow and profitability on dairy farms, cows must become pregnant on a regular basis and reproductive programs on a dairy farm must be a high management priority.
In the commercial dairy industry, natural insemination with bulls has been largely replaced by artificial insemination in an effort to improve genetics. Although better functioning feet and legs and improved udder conformation has significantly improved milk production in all the dairy breeds, fertility has been declining in all breeds. There are several reasons for this decline including inbreeding, increasing milk production, nutrition and time management.
According to Dr. Erin King, DVM, of Tufts University, two significant factors affecting fertility for dairy cows are environmental heat stress and nutrition, with the two often being interrelated. Although heat stress occurs primarily during the summer months when heat and humidity are high, decreases in fertility during that time period can result in cash flow challenges for the entire year due to increased days-in-milk.
Heat stress essentially overheats a cow, preventing her from adequately cooling herself, which diverts energy that’s needed for necessary metabolic functions such as milk production, ovulation and fetal growth. A delay in conception means the cow must wait for the next time she ovulates before breeding again, which adds additional days to her lactation and a decrease in daily milk production.
King said heat stress is often overlooked in the Northeast. As cows become more uncomfortable during heat stress they spend greater amounts of energy in an attempt to cool themselves. Heat from excessive body temperature damages the eggs in the ovaries along with the follicles that are going to produce eggs. It takes 40 to 50 days from the time a follicle is formed to when it ovulates – meaning a heat-damaged follicle will affect conception many weeks after a hot spell has passed.
Embryos are also more susceptible to heat stress in the initial days of life, resulting in early embryonic death. Cooling of the cow is critical to avoid the metabolic issues that can result in the termination of an early pregnancy or decrease a cow’s ability to ovulate with a healthy egg.
Many dairy farms are hesitant to install fans or evaporative cooling systems in their barns and milking parlors and over feeding areas where cows must spend extended periods of time. Evaporative cooling systems with fans and misters are priced relatively low based on the results that can be attained in just one extended summer heat wave in which a cow’s estrus activity is decreased or there are aborted pregnancies.
King noted that an emerging management strategy is the timing of embryonic transfers during periods of cooler temperatures. This doesn’t necessarily improve fertility per se, but reduces the chances of early embryonic death in seasons and locations that experience high heat and humidity. As ET technology becomes more affordable and widespread, this could become another management tool.
The estrus cycle of dairy cows is fairly straightforward. On average, cows and heifers ovulate every 21 days (range: 18 to 24 days) and are capable of conceiving all year. The process begins with the “bulling” activity and “coming in heat” as she allows both a bull and other cows to mount her. For dairy farms using artificial insemination or timed AI programs, King explained that cows should be bred in a window of about 12 hours before ovulation. Ovulation generally occurs about 24 to 28 hours after the standing heat. For artificial insemination programs on dairy farms to be successful, timing is everything.
The vast majority of poor conception in dairy herds can be traced back to poor reproduction management and heat detection on the dairy farm or improper insemination techniques rather than fertility problems in the cow. In some cases, barn or barnyard conditions that make bulling and heat detection more difficult to monitor may have an impact on effective heat detection. The key to successful breeding programs is the heat detection and knowing when to breed the cow or heifer.
Every dairy must devise its own heat detection and breeding protocols that are best suited for its management. If semen does not find its way to the egg, the egg expires. Vaginal discharges containing blood a day or two after standing heat indicates that it’s too late for conception. For healthy cows, the estrus cycle repeats on a regular basis until a pregnancy is attained. However, for cows that go for extended periods (many months) without becoming pregnant, the estrus cycle often becomes more erratic and the chances for pregnancy are reduced.
Cows may have undiagnosed uterine infections that will affect their fertility. Monitoring post-calving body temperatures is an effective means of diagnosing infections that may lead to fertility problems. Cystic ovaries, which prevent ovulation, are an increasing problem in many dairy herds and should be evaluated with the veterinarian in finding and implementing solutions. Retained placentas have been linked to both nutrition and hypocalcemia along with difficult calving (dystocia) and should also be evaluated with the help of the nutritionist and veterinarian. Cows that are experiencing respiratory diseases at the time of insemination or come down with them after conception can abort an early pregnancy.
King also said that proper nutrition at the time of transition and a properly functioning immune system are key to improving and maintaining fertility in dairy cows. Cows undergo a lot of stress at the beginning of the lactation with the demand of high milk production that is placed upon them.
Transition diets that maintain energy levels and high levels of vitamins and antioxidants such as vitamin E have been shown to improve fertility. Fatty acids that are high in omega 3 and omega 6 are needed for the synthesis of important reproductive hormones such as prostaglandin, estrogen and progesterone.
She also noted that for many dairies, hypocalcemia and over-body conditioning continue to be a challenge in getting cows bred. Hypocalcemia (milk fever) slows the muscle function, leading to higher incidence of metritis (uterine infections) along with poor rumen function and nutrient absorption.
Cows that enter the dry period and go through the dry period over-conditioned (or fat) will have more difficulty with fertility as their bodies dispose of the excess body fat and fight off ketosis while going through that negative energy balance that nearly all cows experience at the start of lactation. Again it falls on the dairy farmer to avoid over-feeding energy (aka, calories) prior to drying off or getting them excessively fat while in the dry period.
The proper nutrition of replacement heifers also will have an impact on the lifelong fertility of cows as they age. The generally accepted management goal for most dairy farms is to have replacement heifers freshening at about 2 years of age. This means they must become pregnant at 15 months of age and should be exhibiting normal estrus cycles and activity by the time they are 1 year old.
Puberty in dairy heifers is highly dependent upon weight and size – generally occurring at about 700 to 800 pounds or about half of their mature weight. Attaining adequate stature and weight so as to conceive at 15 months or earlier requires aggressive and appropriately balanced nutrition during the entire growth period, starting when the calf is born.
According to King, the area of genomics shows promise in improving fertility in herds with the heritability of fertility in genes being greater than once thought. Genomic selection of heifers with high fertility indices offers the potential for improved reproduction efficiencies in herds.
Many of the challenges of poor fertility in modern dairy herds can be mitigated with more aggressive herd management. The solution for combating declining fertility and the improvement of reproduction efficiencies on dairy farms will come primarily from more aggressive management of cows during the breeding and calving cycles, cow comfort and a higher plane of nutrition – improving energy and immune status – as well as focusing on the selection of genotypes for improved fertility traits.