It is hard to overstate the importance of the role that artificial insemination (A.I.) has played in the genetic improvement of dairy cattle. Genetically superior dairy bulls have transformed from safety hazards covering only a few dozen females a year and taking the space in a producing herd to global powerhouses. Elite sires can now command multimillion dollar valuations by positively influencing dairies around the world.
Since the inception of this technology, it was soon recognized that its capacity to disseminate genetics was only matched by its capacity to disseminate pathogens if the proper control measures were not in place.
As David E. Bartlett, one of the pioneers in bull health, clearly articulated, “It is within the realm of reasonable possibility for one diseased bull’s frozen semen to spread any of several infectious diseases into thousands of herds located in all 50 states or several continents over a period of several years.” Historical reports confirm this as a real threat, not just a theoretical risk, with documented cases of A.I.-based transmission of pathogens tuberculosis, brucellosis, infectious bovine rhinotracheitis, trichomoniasis, campylobacteriosis, bovine viral diarrhea and leptospirosis. More recently, among many other cases, frozen semen was highly suspected to be the reason behind the 2015 outbreak of Bluetongue 8 in France and proved to cause reproductive problems in cows inseminated with straws containing viable Histophilus somni.
The role of Certified Semen Services (CSS)
Aware of these risks, the National Association of Animal Breeders created the Certified Semen Services (CSS) program in 1976, largely based on protocols developed earlier by American Veterinary Medical Association, United States Animal Health Association and some state regulations. The CSS protocols aim to provide specific pathogen-free frozen bovine semen, and after decades of work, it has built the reputation for safety and innocuity of bovine semen.
Naturally, a modern dairy producer doesn’t worry about disease transmission when using a straw of semen. Akin to dining out, most of us do not select the restaurant based on whether it passed a health inspection; we just assume it has. This assumption has led many to use non-CSS beef semen without knowing it.
Staying with the example of a restaurant business; consider a scenario where restaurants are not legally required to undergo health inspections – leaving no one to ensure basic standards of hygiene are met. A comparable situation exists for semen destined for the domestic market.
International trade of bovine semen is highly regulated. Most importing countries have established requirements based on CSS, World Organization for Animal Health, their own diseases of concern or elements from all the above. For the domestic market, however, it is quite different.
While CSS has become the de facto national standard and has been used as the basis for exporting semen through its collaboration with the USDA Animal and Plant Health Inspection Services (APHIS), it is a voluntary program. This means not all domestic semen is required to be CSS. Consequently, semen straws from bulls with unknown health status that may also be produced with less-than-ideal practices, abound. They cross state lines; they hop from one semen tank to another. To our knowledge, only the Texas Longhorn Breeders Association of America requires health testing of A.I. bulls for their progeny to be eligible for registry.
Potential consequences
So what are the risks? How much would a dairy producer stand to lose by using non-CSS semen? Well, we all know pathogens can survive the freezing process. We all know antibiotics in semen don’t kill every pathogen in semen, even when handled correctly. Fortunately, the incidence of tuberculosis and brucellosis in the U.S. has decreased considerably in the last decades. However, those of us who have been in any proximity to a dairy with a proven case are aware of the devastation it can bring to the business and the morale of everyone involved.
This discussion could expand to include numerous pathogens or even the semen quality element of the CSS program. For the sake of efficiency, however, let’s use trichomoniasis as an example. The regional herd level prevalence of this disease in beef herds was recently mapped by a group of researchers from Texas Tech and Texas A&M universities using multiple sources. It was illuminating to see values ranging from 2.17% in northern states to 20% and 30% in the Texas and Southeastern regions.
Many factors can influence the economic impact of this disease on a specific operation. Using theoretical and real life examples, a few studies have aimed at providing some perspective.
One of the most cited studies on this issue analyzed an epizootic event at a large dairy in California in 1986. The results showed an estimated loss per cow – adjusted by inflation to September 2025 – of $1,970. The analysis used replacement costs from 1984-85, when premiums from beef-on-dairy were quite different. This study also exemplified how poor hygiene practices can extend the impact of an initial introduction of trichomoniasis far longer after the infected animals are identified, and A.I. with semen from negative animals is introduced.
CSS collaborated with AbacusBio to estimate the economic impact a 1,000-cow dairy herd would have if a fraction of its inseminations used semen from bulls positive to Trichomonas foetus. The estimate for the first year was $45,000; however, it is important to mention that it assumed a prompt identification and removal of the affected cows, no spread beyond the initially infected animals and used beef-on-dairy premiums from 2022.
Today's application
Due to the magnitude of the outbreak of highly pathogenic avian influenza (HPAI) in dairies, it is also important to discuss some of the recent developments as they relate to A.I. Researchers from multiple institutions, including the University of Wisconsin and Cornell, reported a positive H5N1 RNA identification in semen from one bull. The samples were collected from bulls providing natural service to a herd in an active outbreak. While the environment of the collection, and the level of detection were more consistent with sample contamination than viral shedding, the addendum to the document articulates it very clearly: “… bovine semen collected at CSS certified facilities does not represent a significant risk for H5N1 influenza A disease transmission.”
Regardless of the methodology, or the disease, the conclusion as stated by the assessment of AbacusBio is clear: “Potential annualized impacts of acute infections do not justify potential modest savings in semen costs associated with the purchase of semen from sources outside the CSS program.”
