Cyathostomins resistant to macrocyclic lactones
This was more a question of when, not if, as resistance in equine cyathostomins to all the major classes of available anthelmintics has been reported previously. In the first report of macrocyclic lactone resistance in the UK, Bull et al (2023), faecal samples from four Thoroughbred studs in England were collected and faecal egg counts (FECs) were performed using the sensitive mini-Flotac method before and at intervals after treatment with ivermectin, moxidectin (each drug alone or in conjunction with the cestocide praziquantel) or pyrantel.
Yearlings in the largest stud had FEC reductions ranging from 36–81%, consistent with resistance to moxidectin, ivermectin and pyrantel. Yearlings on the other three studs did not appear to have resistance, but yearlings on all four studs had egg reappearance times of 4–6 weeks, shorter than the original published values of 9–13 weeks, an early indicator of developing resistance. Samples from mares on studs A and B also had a reduced strongyle egg reappearance time (7–10 weeks), but resistance was not confirmed by FEC reduction.
This report of resistance is of significant concern to the equine industry, which has relied heavily on the use of moxidectin and ivermectin to control burdens of cyathostomins and prevent disease, particularly in young horses. In the absence of new anthelmintics being developed for use in horses, the industry will have to concentrate more on non-drug strategies such as regular faecal removal from pasture which has been shown to reduce re-infection. The authors commented that ‘Poo-picking’ appears to have been adopted on many livery yards and private premises, but has not yet been so widely practised on studs – where vulnerable young horses are concentrated.
Responses of horses to drones
Small, unmanned aerial systems (sUAS), or drones, are increasingly being used for live-stock management, but there has been concern that horses may be disturbed by what could be perceived as a threat of predation. An American study by Howell et al (2022) examined the effects of this and developed an ethogram to classify and record horse behaviours and studied the effect of a 350mm quacopter drone approaching and hovering at 3, 15 and 33m above ground level. Drone pilots and take-off points were out of sight of the horses, and behavioural observations were made by spotters at a distance using binoculars and spotting scopes and video footage captured by the drone during flight.
Groups of 1–10 horses were studied, and behaviour categories recorded were walking, trotting, grazing, laying down, standing and vigilance. Control behaviours of horses ‘at ease’ were those exhibited before the drone was launched. Changes of behaviour when the horses first became aware of the drone included some behaviours characterised by vigilance and movement (referred to as ‘alarmed’). The two variables were analysed using the Chi-square test.
Horses did exhibit vigilant behaviours; grazing behaviour decreased or ceased, and walking, trotting and galloping were interpreted as fleeing. Horses were more alarmed when approached at low flight levels, particularly 3m. Fewer ‘alarmed’ responses were noted with 15m flights, and only half of horses approached at 33m changed behaviour to ‘alarmed’ vigilance or evasive walking or trotting. The authors concluded that drones may have effects on eating and other stress-related aspects of health and welfare. However, they also commented that drones may prove useful for surveying and managing free-roaming populations of horses.
Strangles: how effective is cleaning and sanitising?
Infection with Streptococcus equi causes concern about how to avoid further direct or indirect transmission. This paper by Ryden et al (2023) examined the effectiveness of cleaning and sanitising materials found around horses, and concluded that it is possible to effectively eliminate contamination.
A range of items in the equine stable environment, including outdoor tiles, wooden boards, water buckets, leather halters and gloves and polyester webbing halters, were inocculated with laboratory or clinical strains of S.equi. Following a 3-day incubation period, the items were sampled to confirm bacterial growth, and then half were subjected to cleaning and sanitation following recommendations from the Swedish National Veterinary Institutute. Additional pieces of polyester halter webbing were washed with an alkaline cleaner in a washing machine at 40°C or 60°C. The pieces were then air dried, except for half of the 40°C washed pieces which were dried in a tumble drier at 70°C. At the conclusion, all items were resampled for viable S.equi.
With one exception, results showed that most of the materials tested were effectively cleaned of S.equi. Polyester webbing halters proved more refractory to decontamination. Machine washing at 60°C was effective, but the cooler wash, even with tumble drying, was not effective in most cases. Even without cleaning, leather was a relatively poor medium for survival of S.equi.
It is reassuring for the industry to know that conscientious cleaning and disinfection can remove S.equi from most common stable surfaces, and crucial to understand that polyester webbing needs an effective hot wash to render it culture negative.