Tuesday, June 18, 2024

New internal parasite guidelines from AAEP

The American Association of Equine Practitioners (AAEP) has issued revised Internal Parasite Control Guidelines to help minimise the risk of parasitic disease and maintain the effectiveness of current drugs for as long as possible by delaying further development of anthelmintic resistance.

The guidelines, originally created in 2013 and last revised in 2019, account for recent advances in knowledge concerning increased anthelmintic resistance and optimisation of parasite control management practices. They also address common misconceptions and offer parasite control program recommendations for senior horses (over 15 years old), mature horses (between 5 and 15 years old), and young horses (under 5 years old).

The guidelines were reviewed and updated by the AAEP Internal Parasite Control Guidelines Task Force, chaired by Dr. Nielsen and comprised of 10 AAEP members predominantly board certified in veterinary internal medicine, veterinary parasitology and/or veterinary microbiology. 

“We have seen dramatic development in the field of equine parasite control over the past 10 years, since we first launched these guidelines, and we work hard to keep our recommendations up to date,” said Martin Nielsen, DVM, PhD, DVSc, DAVCM, DEVPC, Schlaikjer Professor of Equine Infectious Diseases at the University of Kentucky.

Important conclusions to be drawn from the revised guidelines are to:

  • Perform fecal egg count reduction tests annually to ensure that you are using effective dewormers in every herd or barn.
  • Recognize that no anthelmintic will eliminate all parasitic stages from a horse.
  • Continue using fecal egg counts once or twice per year to stratify horses into low, medium and high shedders to reduce pasture contamination.
  • Deworm all horses at a baseline rate and target selected horses more often based on fecal egg counts.
  • Not use fecal egg counts to diagnose disease in horses as there is no correlation between fecal egg counts and disease-causing parasite life stages.
  • Discontinue deworming all horses with fixed intervals year-round and stop blindly rotating anthelmintic classes.

View the guidelines at https://aaep.org/resource/internal-parasite-control-guidelines.

You can access the entire guidelines document by clicking the Download Resource button.

Monday, June 17, 2024

Memory for dung sniffing

Horse dung (c) Avrezn Dreamtime.com
 Horses sniff dung for several reasons - for communication, social behaviour, and environmental awareness.  

Dung contains chemical cues that can convey information about the individual who deposited it, such as their identity, sex, and reproductive status. By sniffing dung, horses can recognize and gather information about other horses in their vicinity. It may also help horses understand social structures and hierarchies within a group, allowing them to recognize dominant individuals and avoid potential conflicts.


Horses may form "stud-piles" where they deposit dung in specific locations to mark their presence. This behaviour can communicate territorial boundaries or indicate that a particular area is frequently used by certain individuals or groups


Research by Audrey EM Guyonnet, and Ian Q. Whishaw, at the Canadian Centre of Behavioural Neuroscience, University of Lethbridge, Alberta looked at how horses use location , odour, and memory related to their encounters with dung.


In their study, which is reported in Behavioural Processes, they assessed the response of horses when they were led, at varying time intervals, to objects chosen by the experimenter or to dung deposits, which they were allowed to sniff.


Twenty-two horses were included in the study. which was carried out in a total of six riding arenas—two indoor and four outdoor. – 


The research team took video recordings of the horses encountering the objects and the dung Frame-by-frame video analysis assessed several factors: the way the horses approached the objects or dung deposits, the duration of sniffing, nostril use, ear position, and blinking associated with dung investigation.


The researchers found that horses consistently approached and sniffed dung deposits for a longer time compared to non-dung objects.


While they were sniffing, horses moved their heads across the dung deposits. They showed no specific nostril or ear preference when investigating the target and they tended to blink as they disengaged from sniffing.


Horses showed a reduced likelihood of approaching and shorter sniff durations when revisiting dung deposits encountered earlier the same day, regardless of the location. The researchers suggest that this indicates a strong short-term memory for dung and its location.


However, horses showed poor memory for dung visited on the previous day, suggesting that their memory for dung is good on the same day but significantly diminishes by the next day. This pattern reflects adaptive forgetting, allowing horses to focus on current environmental cues. (“Adaptive forgetting” refers to the brain's mechanism of intentionally forgetting certain information to optimise memory function and cognitive efficiency. It helps individuals prioritise relevant and important information while discarding outdated, irrelevant, or redundant data. This process is thought to enhance learning, decision-making, and overall cognitive performance.)


The researchers suggest that this phenomenon of adaptive forgetting, where memory for dung visited the previous day fades, may be beneficial for horses. It optimizes risk assessment by preventing unnecessary interruptions in foraging caused by conspecifics and ensures that their attention remains focused on current and potentially more relevant environmental cues.



For more details, see:


Audrey EM Guyonnet, Ian Q. Whishaw,

Adaptive forgetting of place/object memory for dung in the domestic horse (Equus ferus caballus): Memory for a day.

Behavioural Processes,

Volume 217,



ISSN 0376-6357,


Friday, June 14, 2024

Do endocrine disorders affect anthelmintic performance?

Recent research indicates that insulin dysregulation may affect the performance of anthelmintics
like ivermectin. This suggests that horses with such endocrine disorders might be more prone to parasitic infections.

In a study conducted by Martin Nielsen and colleagues at the University of Kentucky, the response to ivermectin was evaluated in horses with insulin dysregulation (ID), pituitary pars intermedia dysfunction (PPID), or neither condition. 


The study population was part of a special herd at the University of Kentucky’s Department of Veterinary Science, which included horses with and without these endocrine disorders. These horses were kept in permanent paddocks without pasture rotation or enhanced hygiene practices and received routine anthelmintic treatments: ivermectin in March or April and July or August, and moxidectin/praziquantel in November.


The study focused on senior horses (aged 13 years and over) and those with or without PPID, ID, or both. Out of 47 horses in the research herd, 19 met the criteria for inclusion. These horses, all with positive faecal worm egg counts, were treated with ivermectin at the recommended dose of 200 mcg/kg. Faecal samples were collected before treatment, two weeks post-treatment (for the Faecal Egg Count Reduction Test, or FECRT), and then weekly until worm eggs reappeared in the faeces (Egg Reappearance Period, or ERP).


Two laboratory tests were employed to assess the response to ivermectin: the Faecal Egg Count Reduction Test (FECRT) and the Egg Reappearance Period (ERP). For the FECRT, a reduction of at least 99.7% in worm egg counts is considered effective two weeks post-treatment. The ERP for ivermectin is typically 8-10 weeks.


The study found no significant differences in the effectiveness of ivermectin between the groups. However, the small sample size may have made it difficult to detect any potential differences. Overall, ivermectin was highly effective, with all horses showing a greater than 99.7% reduction in worm egg counts at the two-week mark. 


Nonetheless, the researchers observed that the ERP was shorter in horses with ID and those with both PPID and ID, at six and seven weeks respectively, compared to eight weeks for both the PPID-only and healthy control groups.


They suggest that their findings indicate a need for further investigation of the possible influence of endocrine disorders on anthelmintic performance in horses.



For more details, see:


M.K. Nielsen, C.A. Finnerty, N.E. Ripley, A.E. Page, M.E. McClendon, A.A. Adams,

Ivermectin performance in horses diagnosed with equine endocrine disorders,

Veterinary Parasitology, (2024) Vol 328,110182,


Saturday, June 08, 2024

Effect of diet on strongyle infection and gut microbiome

Recent research from France suggests that the first step in controlling intestinal worm infections inanimals should be providing them with diets that maintain a healthy gut ecosystem. 

Horses’ intestines can harbour many different worms, some of which can cause severe disease. It's concerning that some of these worms are becoming resistant to deworming medications. This resistance has emerged through factors such as incorrect dosing or frequent use of the same medications.


It's clear that we need to adopt a more sustainable approach to managing equine  intestinal parasites.


To address this challenge, scientists are exploring different methods, including dietary changes. These diets might enhance the body's defences, regulate gut bacteria, or directly combat parasites. For example, certain foods containing plant compounds might hinder worm reproduction in the body.


A study by Noémie Laroche and colleagues, at Lab to Field, Dijon, and the University of Bourgogne Franche-Comté, investigated how diet affects strongyle infection in horses, focusing on immune-mediated, microbiota-mediated, or direct deworming mechanisms. The work is reported in PLos ONE.


They studied twelve adult French Trotter geldings naturally infected with strongyles. These horses were divided into two groups and fed either a high-fibre or high-starch diet, along with supplements containing polyphenol-rich pellets from dehydrated sainfoin or control pellets made from sunflower and hay.


The study revealed that horses on a high-starch diet had higher strongyle egg excretion compared to those on a high-fibre diet. However, adding sainfoin to the high-starch diet reduced egg excretion. What’s more, sainfoin supplementation decreased larval motility, regardless of the diet.


Moreover, the high-starch diet was associated with lower faecal bacterial diversity, changes in faecal microbiota structure, lower faecal pH, reduced blood acetate levels, and lower haematocrit compared to the high-fibre diet.


Overall, these findings suggest that dietary changes can be an alternative strategy for managing helminth infections. 


The study highlights the importance of considering broader ecological mechanisms in parasite management strategies. The researchers emphasize that eradicating helminth infections entirely is unrealistic and could have negative effects. 


They write: “… pursuing a goal of eradicating helminth infection (zero infection) is not only illusionary but also likely to produce more negative effects than benefits. Mammals have coevolved with helminths during millions of years, and in most cases, the infection does not produce severe symptoms.’


“We therefore suggest that a safer strategy to control helminth infection would be to improve host tolerance to the infection rather than pursuing a hopeless, environmentally toxic, strategy of drug-based eradication.”


For more details, see:


Laroche N, Grimm P, Julliand S, Sorci G (2024) 

Diet modulates strongyle infection and microbiota in the large intestine of horses. PLoS ONE 19(4): e0301920. 


Thursday, June 06, 2024

Ritual horse sacrifice in Baltic region in the Middle Ages

Artists impression. Credit: Miroslav Kuzma
 Research from Cardiff University indicates that during the Late Viking Age, horses were transported across the Baltic Sea in ships and sacrificed in funeral rituals. Published in the journal Science Advances, studies on horse remains found at ancient burial sites in Russia and Lithuania show that these animals were brought from Scandinavia via extensive trade networks connecting the Viking world with the Byzantine and Arab Empires.

Horse sacrifice was practiced in various parts of Europe during ancient and medieval times for religious, ceremonial, and symbolic purposes. While the practice varied across different regions and periods, it remained a significant aspect of ancient spiritual and cultural life.


Up to now, researchers had believed sacrificial horses were always locally-sourced stallions. But these results reveal some horses had travelled up to 1,500 km across the Baltic Sea from modern-day Sweden or Finland. The findings also show that the sex of the horse was not necessarily a factor in them being chosen for sacrifice, with genetic analysis showing one in three of these horses were mares.


The research team used a scientific technique called strontium isotope analysis on 74 horse teeth from ritual burial sites to identify their origins. 


Strontium, a naturally occurring element in rocks, soil, and water, has different isotope ratios in various geological formations. As plants absorb strontium and animals consume these plants, the strontium gets incorporated into their bones and teeth. The ratio of 87Sr to 86Sr in a sample reflects the geological signature of the area where the animal lived or fed.


Teeth are particularly valuable for this analysis because they form at specific periods in an animal's life and do not remodel after formation, preserving the strontium isotopic signature of the environment at the time of their formation. This allows archaeologists to trace the life journeys of animals hundreds of years later.


Horse sacrifices were highly visible and symbolic public rites across pagan prehistoric Europe, persisting the longest among the Baltic tribes, up to the 14th century AD. Offering pits might include multiple horses, single complete horses, or partial animals. In many Baltic cemeteries, horses were buried separately from humans, though there are numerous examples of horses buried with overlain human cremations.


In a press release, lead author Dr Katherine French, formerly of Cardiff University’s School of History, Archaeology and Religion, now based at Washington State University, said: “This research dismantles previous theories that locally procured stallions were exclusively selected for sacrifice. Given the unexpected prevalence of mares, we believe the prestige of the animal, coming from afar, was a more important factor in why they were chosen for this rite.


“Viking Age trade routes stretched from modern Iceland, Britain, and Ireland in the West all the way to the Byzantine and Arab Empires in the East. The presence of a trader’s weight in one horse grave points to the key role of horses in these vibrant trade networks.”


Co-author Dr Richard Madgwick, also based at Cardiff University’s School of History, Archaeology and Religion, said: “Pagan Baltic tribes were clearly sourcing horses overseas from their Christian neighbours while simultaneously resisting converting to their religion. This revised understanding of horse sacrifice highlights the dynamic, complex relationship between Pagan and Christian communities at that time.”


This project received funding from the EU Horizon 2020 scheme, Polish Ministry of Science and Higher Education, National Geographic Society, Society for Medieval Archaeology, Alexander von Humboldt Foundation, Deutsche Forschungsgemeinschaft, and Cardiff University.


For more details, see:


French, K. M., Musiał, A. D., Karczewski, M., Daugnora, L., Shiroukhov, R., Ropka-Molik, K., Baranowski, T., Bertašius, M., Skvortsov, K., Szymański, P., Mellin-Wyczółkowska, I., Gręzak, A., Wyczółkowski, D., Pluskowski, A., Andersen, M., Millet, M. A., Inglis, E., & Madgwick, R. (2024). 

Biomolecular evidence reveals mares and long-distance imported horses sacrificed by the last pagans in temperate Europe. 

Science advances, 10(20), eado3529. 



press release:  https://www.cardiff.ac.uk/news/view/2814957-pagan-christian-trade-networks-supplied-horses-from-overseas-for-the-last-horse-sacrifices-in-europe


video: https://www.youtube.com/watch?v=AbMbvXKv_AA

Saturday, June 01, 2024

Lyophilized colostrum: a viable alternative for foals?

 Colostrum is essential for a foal to have a good start in life. The first milk produced by mammals
after giving birth, colostrum is rich in antibodies, growth factors, and nutrients essential for newborn development. Foals require good quality colostrum in the first hours of life to ensure an adequate transfer of passive immunity.

Stud farms often maintain a supply of high-quality colostrum by collecting and freezing some from donor mares.

However, individual mare owners have more limited options. Commercial products like dried colostrum powder, usually made from processed cow colostrum, can provide some level of IgG to foals, but are generally not considered equivalent to mare colostrum in terms of quality and effectiveness.


Further research and development of equine-specific colostrum products, including lyophilized (freeze-dried) mare colostrum, may offer better alternatives for ensuring foal health and immunity.


Research by Thatyane Carla de Lima and colleagues, in Brazil, compared the quality of equine colostrum after freezing and lyophilisation, evaluating IgG concentration (using Simple Radial Immunodiffusion, SRID, and Brix refractometry) and the physicochemical characteristics of equine colostrum post-freezing and lyophilization. A report of their work is published in the Journal of Equine Veterinary Science


Thirty-one pregnant Quarter Horse mares participated in the study. Colostrum collected from these mares was divided into two samples: one for freezing and one for lyophilization. 


The research team measured the IgG concentration of both frozen and lyophilized colostrum by SRID, (the reference standard test), and Brix refractometry (a technique widely used for estimating colostrum quality in cattle.)   


Additionally, they evaluated properties such as pH, total protein (TP), fat, lactose, salts, total solids (TS), and density. They also tested the effect of reconstitution on the lyophilized colostrum.


They found no significant differences (P > 0.05) in IgG, fat, lactose, salts, TS, density, and pH between colostrum samples before and after lyophilization. Lyophilization resulted in a minor reduction (6.55%) in IgG concentration as measured by SRID.


 However, they did find a significant difference in the average Brix score and total protein, indicating that lyophilization alters some colostrum characteristics.


The results suggest lyophilization as a viable method for mare colostrum conservation, to ensure foals receive the essential nutrients and antibodies for a healthy start. It offers practical benefits, including long-term storage without refrigeration and easy transportation.


The authors suggest that further research, such as in vivo studies to evaluate the product's acceptance and the absorption of immunoglobulins, is recommended. 


For more details, see:

de Lima TC, de Sobral GG, de França Queiroz AES, et al.

Characterization of lyophilized equine colostrum. 

J Equine Vet Sci. 2024;132:104975.