Pregnancy losses are extensive in lactating dairy cattle. In fact, in many cases these losses are underestimated because of the challenges that exist on-farm to accurately determine conception early after insemination.
For most dairies, pregnancy losses are only noted and recorded after an initial pregnancy diagnosis is performed at approximately 30 to 45 days after insemination. But recent studies with reliable assessments of fertilization have led to the conclusion that more than 60 percent of all pregnancies are lost before term (birth) in lactating dairy cows.
The critical period is from fertilization until the end of the differentiation phase (generally the period from conception to day 42, when the embryo becomes the fetus), in which approximately 85 percent of those losses occur. And although fetal losses are minor (approximately 15 percent) compared with embryonic losses, those are more costly than embryonic losses; therefore, they cannot be overlooked.
There are a host of causes for pregnancy losses, which complicates the challenge for producers. Known risk factors include:
- Prolonged periods of follicular dominance
- Reduced or basal progesterone concentration during ovulatory follicle development
- Heat stress
- Postpartum diseases and disorders like dystocia, metritis, endometritis, mastitis, fever, ketosis and lameness
- Digestive problems
- Negative energy balance and excessive bodyweight loss
- Toxins found in feedstuffs such as gossypol, mycotoxins and ergot alkaloids
- Infectious agents such as Neospora caninum, Leptospira spp., Campylobacter spp., BVD virus and IBR virus
You can reduce the incidence of pregnancy loss with strategies that prevent or control these known risk factors.
For instance, the negative effects of prolonged follicle dominance on fertility of dairy cows have been associated with impaired embryo quality. An approach that has been shown to improve conception rates in lactating dairy cows is to reduce the interval between the first GnRH dose of the Ovsynch program and the prostaglandin F-2 alpha (PGF2α) dose from seven to five days to reduce the period of follicle dominance.
This approach increases pregnancy rate, although a second dose of PGF2α administered 24 hours after the first one is required.
In addition, high-producing dairy cows are particularly sensitive to heat stress because of high feed intake and metabolic rate, which challenges thermoregulation. Heat stress affects fertilization and, particularly, early embryo development, especially days 1 through 3 of pregnancy.
The best heat abatement plan is to provide adequate cooling. Successful cooling strategies are based on maximizing available routes of heat exchange, convection, conduction, radiation and evaporation.
Strategies should include:
- Air movement (fans)
- Wetting (soaking) the cow’s body surface
- High-pressure mist (evaporation) to cool the air in the cow’s environment
- Facilities designed to minimize the transfer of solar radiation
Another strategy that has been suggested, but needs further research, is the transfer of embryos collected during winter or the transfer of in vitro-produced embryos.
Fertility is strongly associated with a cow’s health status, especially regarding calving-related disorders and diseases that affect the reproductive tract.
Cows with dystocia, metritis or clinical endometritis are 50 to 63 percent less likely to resume ovarian cyclicity by the end of the voluntary waiting period, which has major implications for embryo development.
In addition, cows with at least one of the previously cited disorders were 25 to 38 percent less likely to become pregnant following the first postpartum A.I. compared with healthy cows and were 55 to 67 percent more likely to lose their pregnancy during the first 60 days of gestation.
Cows with uterine diseases have been found to have decreased dry matter intake prepartum and postpartum and decreased immune function postpartum. Therefore, strategies that maximize dry matter intake prepartum and postpartum are expected to have a positive impact on immune function, decrease the postpartum incidence of uterine diseases and decrease pregnancy losses.
Furthermore, taking measures – like managing ration dietary cation-anion difference (DCAD) – to reduce incidence of subclinical hypocalcaemia and improve immune function are also suggested.
Other diseases not directly associated with the reproductive tract also have been implicated in impaired embryo survival. Cows with fevers greater than 103ºF during the first two weeks postpartum were 40 percent less likely to conceive following the first postpartum A.I. and twice as likely to lose their pregnancies between the first and second months of gestation.
Metabolic status of the high-producing dairy cow is also closely related to fertility, especially during the second lactation and higher. Cows with reduced body condition score (BCS) either at calving or at the time of the first postpartum A.I. are at a greater risk of losing their pregnancies from day 30 to 58 of gestation.
Cows that maintained their body condition during the first 70 days postpartum and those that lost less than one unit of BCS were 62 percent and 48 percent less likely to lose their pregnancies between the first and second month of gestation. Furthermore, the negative effect of BCS loss is probably at least in part related to anovulation.
Therefore, implement nutrition management programs and protocols that prevent significant BCS losses during the transition period. Also, monitor feedstuffs for the presence of toxins and take appropriate measures to reduce the impact of these potential problems as needed.
Don’t forget to vaccinate
Lastly, infectious agents create considerable fertility challenges. For example, bovine viral diarrhea virus (BVD) remains an important cause of abortion. Its main means of prevention is to eliminate persistently infected animals from the herd combined with vaccination against BVD every six months.
Abortions (loss between 42 and 260 days of gestation) caused by these infectious agents represent only 15 percent of all pregnancy losses, but they are the most costly, so take steps to reduce their impact on your herd.
Ultimately, while there are a myriad of challenges that impact dairy cow fertility, there are also a number of measures producers can take to reduce the influence of these complications. Work with your veterinarian, nutritionist and dairy team to implement and monitor the strategies needed to reduce pregnancy losses and improve your dairy’s performance.
To learn more about improving dairy reproduction, visit the Dairy Cattle Reproduction Council website. PD
Klibs N. Galvao is an assistant professor and residency-internship coordinator at the University of Florida School of Veterinary Medicine. He is also a member of the Dairy Cattle Reproduction Council Education Committee.
What is pregnancy loss?
It may seem simple, but one of the first things is to define pregnancy loss so everyone is talking about the same event. Pregnancy loss is defined by when in gestation it occurs.
For example, losses of pregnancy before day 24 indicate early embryonic losses (usually associated with failure of maternal recognition of pregnancy), and those between days 24 and 42 days indicate late embryonic losses.
Pregnancy losses detected between 42 and 260 days of gestation are characterized as fetal losses or abortion. And a calf that is born dead between 260 days and full term (approximately 280 days) is defined as a stillbirth.