Today is the day. You will find out if all of your hard work as paid off. You've been diligent in your preparations. You've followed the protocols to a T. You're excited and yet nervous. You hope for the best and, still, you prepare yourself for the worst. Then, the verdict comes in. The cow is ... open. Ugh! It's a moment of utter frustration! You shake your head in disbelief and wonder why, when, how?
Reproductive efficiency on a dairy is an important factor in overall profitability, and a sizeable amount of labor is involved in the synchronization or estrus detection and insemination of cows and heifers. That is why an open cow at pregnancy check is so frustrating. Time, money and other resources have resulted in a negative note on the checklist.
A frustration I have heard voiced several times is not knowing when or why cows lose pregnancies. Unfortunately, the list of possible whys is long and, more than likely, somewhat specific to your farm's location, climate, etc. What we can narrow down a bit is the WHEN.
Common Methods of Pregnancy Detection
The rate of pregnancy loss is variable among farms, as is the method of pregnancy detection used. There are several methods of pregnancy detection employed on progressive dairy operations including:
• Monitoring cattle for return to estrus
• Rectal palpation
• Blood or milk sample to test for pregnancy associated glycoproteins (PAG)
Cattle that have been bred but fail to become pregnant should return to estrus in approximately 21 days. The observation of a cow or heifer standing to be mounted during this timeframe post-insemination is the most basic method of determining pregnancy status. Observation of return to estrus, however, is not a reliable method of pregnancy detection as it does not prove the presence of a viable pregnancy, just the present of estrus behavior.
Palpation of the reproductive tract is a common, quick and accurate method of pregnancy detection when performed by a skilled practitioner. Palpation can accurately detect pregnancy at approximately 35 days post-insemination, and a highly skilled practitioner has the ability to accurately detect closer to 32 days.
Ultrasound of the reproductive tract is another method of pregnancy detection commonly employed on dairy farms across the country. There are several benefits of ultrasound compared with palpation, most evident in the information available to the practitioner. The embryo can be visualized and a heartbeat can be confirmed, ovarian activity can be monitored, uterine health can be examined and fetal sex can be determined, all with the use of ultrasonography (Fricke, 2002; DesCoteaux et al., 2009). Another advantage of ultrasound is that it can be used as early as 26 days of gestation for accurate pregnancy detection, although it is commonly used between 30-40 days (Romano et al., 2006).
The use of chemical pregnancy tests to detect PAGs has proven to be another reliable method of pregnancy detection. The presence of PAGs is pregnancy specific, and commercially available test kits are labeled to detect pregnancy at 28-29 days post-insemination. These tests have become increasingly sensitive with alterations, and studies have now shown PAGs can be detected in milk samples at quantities high enough to diagnose pregnancy comparable to PAG detection in blood (Leblanc, 2013; Gajewski et al., 2014; Lawson et al., 2014). The use of this technology is becoming more common, especially in areas with limited access to skilled veterinarians.
When are Embryos Most Likely to Die?
Timelines and reasons for embryonic loss are variable, with lactating dairy cattle representing a unique niche of cattle suffering from prolonged periods of embryonic and fetal loss.
Generally speaking, embryonic loss occurs from fertilization to day 42 of gestation, and fetal loss occurs from day 42 of pregnancy to calving (Nomenclature, 1972). The rate of embryonic loss id debated, but it has been estimated that up to 40% of embryonic loss occurs before day 15 of gestation (Thatcher et al., 2001; Berg et al., 2010). A recent study reports a 5-10% loss between 14 and 18 days of gestation, and an additional 5-10% loss from days 29 to 42 of gestation (Bondurant, 2007).
Late embryonic loss and fetal loss typically occurs at a lesser rate but is arguably more detrimental to dairy producers owing to the larger loss of investment in both capital and time. Several studies have investigated the occurrence of embryonic loss through day 42 of gestation, however, evidence indicates that in lactating dairy cattle, the rate of late embryonic and early fetal loss is still relevant through day 56 of gestation (Santos et al., 2004). In more than 4800 lactating dairy cattle examined between days 28 and 58 of gestation, on average 12.8% of the cattle experienced an abortion (Santos et al., 2004). This is greater when compared with the 10.8% reported for lactating beef cows during the same period (Stevenson et al., 2003).
When to Check for Pregnancy?
With those numbers in mind, the next question is, when is the best time to pregnancy check? The goal of an efficient pregnancy detection system is to identify open cows as soon as possible so they can be rebred in a timely manner. The strategic scheduling of pregnancy checks, and if applicable, the continued tail chalking of pregnant pens, can assist in locating open cows sooner.
The first pregnancy check is focused on detected the cows that are open following an insemination. We know that the majority of embryonic deaths occur before a pregnancy check is possible (less than 25 days), so the sooner the first pregnancy check occurs, the sooner cows can be re-inseminated. This typically means between 30-40 days post-insemination for a palpation or ultrasound herd but can be as quick as 28-29 days if chemical pregnancy tests are implemented.
The second pregnancy check should be focused on finding cows with embryos that were lost between the first pregnancy check and approximately 65 days post-insemination. Research shows that the rate of embryonic death is still continuing to decrease sharply between days 42 and 56 post-insemination, but levels off and decreases by only a few percentage points from days 56 to 98 (Santos et al., 2004). The placenta is also beginning to form functional placentomes (the placental connection between the fetus and the uterus) around day 42 of pregnancy, which is attributed to lower risk of embryonic loss.
These two time points for pregnancy detection are focused on the time period during which embryos are most susceptible to death. For most operations, an efficient estrus detection program should be sufficient to identify the remaining cows that require a pregnancy check for an abortion until dry off. The timeline suggested here is based on research data and landmarks in embryonic growth and can be shifted to accommodate veterinary schedules or management practices.
While gaining a better understanding of when cows and heifers experience pregnancy loss may note quite erase the frustration upon hearing the word "open" at pregnancy check, it may make you feel a little better knowing there's statistical analysis regarding when loss occurs and when pregnancy checks are most beneficial.