Animal Health Can Influence Embryonic Loss

Much has been written in agricultural and veterinary journals during the last few years regarding the challenges of reproduction in modern high producing dairy cattle. Many factors have been identified for the apparent reduction in fertility and there is no doubt the current problem is multi-faceted and not easy to resolve. Early embryonic loss (EEL) can be especially troublesome and frustrating. In these cases the fetus is lost after pregnancy recognition by the dam and approximately 18 to 40 days of gestation. This is especially frustrating to producers as they have successfully established a pregnancy in the cow but after all of that expense and effort, the fetus is lost. This loss can further complicate reproduction programs as early detection methods may indicate that animals are pregnant only to find them open later in lactation. Embryonic loss of this type can be caused by genetic, infectious, environmental, or toxic insults. This short piece will just deal with a couple of these causes that might be related to animal health and could be reduced on many farms.

While infectious agents (e.g., BVD infections) can cause EEL, on many herds control programs and effective immunization programs minimize these loses. Except for acute cases where specific infectious agents have been identified, EEL losses due to pathogens for which we have vaccines may be overstated. In herds as producers and veterinarians become frustrated with EEL the tendency is to add multiple boosters and more immunizations. There is mounting evidence that overzealous immunizations or the use of multiple products given in the early embryonic period may actually reduce embryonic viability or even in some cases promote embryonic loss. A reasonable immunization program should be in place and in most cases will prevent EEL due to common infectious diseases. Cooperation between the producer and the veterinarian can develop a program that is convenient, cost effective, and efficient. In most cases this entails (1) immunizations to key agents should be given at least 2-4 weeks prior to entering the breeding string (2)minimal or no immunizations given during the first 3 months of gestation (3)immunizations that contain large amounts of killed bacterial products or high levels of endotoxins should be avoided especially in the first few months of pregnancy (4) only truly necessary immunizations should be given in months 3-6 of pregnancy (5) immunization programs should be based on risk and timing to maximize effectiveness (6) label directions should be followed.

If producers or veterinarians suspect EEL due to infectious agents, some basic diagnostic procedures should be followed. Paired or cohort serum samples should be submitted along with any fetal tissues or whole small fetuses. Fetal tissues should be kept as clean as possible, chilled and submitted the same day or by over night shipment to a diagnostic laboratory. Repeat sampling is often necessary to ensure an accurate diagnosis is reached.

A number of studies have demonstrated that other animal health problems can influence embryonic viability. In a recent California study cows with modestly elevated somatic cell counts, had a much greater risk of EEL. Cows with a linear score (LS) of 4.5 prior to breeding were 2 times more likely to suffer embryonic loss than herd mates with a lower LS. Toxic insults and severe disease have been known for some time to increase embryonic loss; in this case even relatively mild mastitis cases reduced embryonic viability. This helps to further illustrate the importance of effective mastitis control programs even beyond the more obvious need to increase milk quality and reduce treatment costs. The producer and veterinarian should work closely together to develop broad ranging preventative health programs. Even modest infectious or toxic insults can increase EEL.

Future articles will deal with other issues and strategies that can influence and help to decrease EEL.

Additional information:
Moore, DA, et al., Evaluation of factors that influence embryonic loss in dairy cattle, JAVMA, 226(7): 1112-1117, 2005
www.das.psu.edu/pdf/ott_early_embryo_loss.pdf

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David R. Wolfgang, VMD
DABVP-Dairy Extension Veterinarian and Field Investigation Unit at Penn State University