Xlll PANAMERICAN CONGRESS OF VETERINARY SCIENCES

(PANVET)

Richard Asquith, DVM

PANVET was held in Santiago, Chile on October 5-9, 1992. In addition to plenary sessions the congress con- sisted of symposia, conference, oral com- munications, poster sessions, video pre- sentatious and workshops.

Dr. R. P6rez from the School of Veterinary Medicine at the University of Concepcion described a trial utilizing 5 draft horses with body weights of around 650kg to determine the effect of continu- ous pulling of loads for 8 hours daily with 10 minutes rest intervals for each hour. A cart was used equipped with an odometer to measure distances and a hydraulic dynamometer to record the force. Results of the study demonstrated that all horses pulling loads which generate force levels between 0.57and0.59 kln while working at speeds of 1.60 to 2.11 m/s for the eight hour day with the resting intervals toler- ated the exercise. This toleration was analyzed by biochemical and physiologi- cal parameters. The study also showed that when the horses were subjected to prolonged periods of resting they lose their work fitness; ascertained by in- creases of serum activity of muscle-de- rived enzymes and also the blood lactate levels. The horses develop an adaptation to draft loads over a period of several days. Similar to observations described for race horses the determination of se- rum activity of enzymes, particular CK,

Author's address: Animal Science Department, University of Florida, Gainesville, FL 32611

an0 DIOO0 lactate levels appear to oe gooo indicators of fitness in draft horses.

Dr. L. C. Sa-Rocha and others from the Applied Pharmacology and Toxicol- ogy Laboratory at the Veterinary School at the University of Sao Paulo, Brazil reported the development of a test for plasma eholinesterase activity in horses subjected to organophosphate toxicity. Many eases of acute intoxication of orga- nophosphate compounds are reported in both human and animals in Brazil. Com- pounds such as trichlorfon (an anthelmintic in horses) and others such as parathion and ecktofos as pesticides were the main sources of poisoning.

Seventy-two horses were used and plasma was collected and evaluated for the activity of acetyleholinesterase using the spectrophotometric method of Ellman et al. (1961). Inhibition in vitro was achieved with 501d of plasma incubated at 36"C for 15 minutes. In general, there were no significant differences in activ- ity between male or female or age of the horse. However, trichlorfon showed the best safety correlation between dose and inhibition of homes acetylcholinestemse in vitro.

Dr. C. A. Robles from Bariloche, Argentina described an outbreak of"Mal seco" in the Patagonia region of Argen- tina. "Mal seco" is the local name given to a disease of horses that occurs season- ally during Spring and Summer in this geographic area. The cause of the disease remains unknown and empirical treat- ment has no effect. Botanic microhistological analysis of the stom- ach and intestinal contents revealed noth- ing, but species of grasses that the horses had consumed while grazing were Festuca pallecens, Festuca argentina and Stipa spp. Two different clinical mani- festation were defined. (a) hyperacute

with severe colies and swollen abdo- mens, Co) sub-acute or chronic with de- pression, "tucked up" abdomen and de- pression. Mortality rate was 100%.

This insidious condition occurs in a remote region of western Argentina where tractors cannot be used and horses are an important means of traction and trans- portation. The loss of horses can cripple the farm economy in this region. Many questions were asked by delegates in the audience and it appeared that veterinar- ians from other areas in the world have seen similar clinical signs. Because the findings alsoinchdeneuropathology such as myelin damage as well as neuronal lesions, it was suggested that the clinical picture was very much like the condition known as "grass sickness" in Europe. In addition, speculation that the cases in- volved were like mycotoxicoses, infec- tious disease, toxicity and metabolic con- dition were not entirely dismissed.

A welcome statement to the horse industry of Chile was brought to the attention of the Congress when Dr. A. Rivera revealed the success of the eradi- cation program for Equine Infectious Anemia. A decision to formalize this effort was announced in December of 1980 and after intense quarantine and isolation policies, along with monitoring and testing, has paid off in great divi- dends.

Dr. Rivera with the Servicio Agricola and Ganadero of Chile, concluded that with a high degree of certitude that the equine population of Chile has been freed of Equine Infectious Anemia. In addition to an educational program for horse own- ers, and a continual monitoring and test- ing program, this goal has been realized. This is not to discredit the unique geo- graphical situation. Chile is the only coun- try whose borders are dictated by nature.

Volume 13, Number 2, 1993 67

More specifically Antarctica, the Pacific Ocean, the infamous Atacama desert and the magnificent Andes Mountain Range contribute to the natural barriers that are formidable to illegal transport across and into Chile. This effort does complement the eradication program of a few years ago when the equine encephalitis virus was also eliminated from Chile.

Dr. Richard Asquith from the Horse Research Center of the University of Florida reported on the duration of effi- cacy for various anthelmintics tested for control of parasites in the young horse. The objective of this study was to deter- mine the length of time the efficacy of selected anthelminties was retained by demonstrating the eggs per gram (EPG) of common parasites in the young horse.

A total of 82 young horses, 4 to 13 months of age were used to include 8 different anthelmintics. The period of efficacy following treatment with ivermectin, febendazole, piperazine, pyrantel pamoate, febantel, eambendazole, piperazine/carbon disul- fide, phenothiazine and trichlorfoa/phe- nothiazine/piperazine was evaluated by weekly EPG's obtained after treatment.

Results showed EPG's averaged 1,345 per horse and they were reduced to 0 for up to 8 weeks after treatment in the ivermectin treated animals. Piperazine reduced EPG's to 0 for 2 weeks follow- ing treatment. The average EPG actually increased in 17 foals following treatment with febendazole. The other 5 anthelmintic compounds tested did re- duce the EPG within 1 week post-treat- ment but these EPG's were never re- duced to 0.

Controlling infection by parasites involves the therapeutic use of anthelminties whiell are design ed to elimi- nate the parasite existing in the horse at the time of treatment. The effectiveness of the treatment is reflected in the length of time the period of reduced egg output. The longer the period of a reduced egg output the more effective the treatment. In the present study, ivermectin was the

most effective anthelmintic in duration of efficacy when tested against 3 major parasite groups affecting young horses.

An update on Equine Rotavirus and senan antibody responses in infected foals was reported by Dr. L J. Sail from Ohio State University, Ohio Agriculture and Development Center. This research was in collaboration with workers from Gluck Equine Research Center at the University of Kentucky.

An outbreak of rotavirus infection was documented in 14 foals ranging in age from 6 to 136 days of age. Blood sampling was conducted on the foals and dams on day of the infection and approxi- mately 14 days after for serologic analy- sis. All dams and foals were seropositive to rotavirus and titer increases were evi- dent to suggest that 3 of the dams were subclinically infected. In 1988 a colos- trum fed, isolated-raised foal developed diarrhea and shed the rotavirus pointing out the potential infectivity of this virus and the difficulty of diagnosis without laboratory procedures.

So far only Group A rotaviruses, representing several strains, have been found in foals. Dr. Sail said that the strains may change from one year to the next to confuse the situation and some foals shedding the virus may not present with diarrhea.

Prevention has been suggested in several ways to create immunity. (1) Vaccinate dams with a modified live vaccine to produce active immunity in the mare and let the neonate nurse and receive passive immunity via the colos- trum, (2) hyperimmunize a bovine and feed the cow's colostrum to the neonate. No vaccine is being produced commer- cially as yet.

According to Saif this virus is very stable in the environment. The use of antibiotics does not have any positive effect and dehydration therapy has been the most effective means of treatment. Intense sanitation in the stable is a must and only a few disinfectants were effec- tive, with high pressure steam cleaning

preferred. Man may be the mechanical vector in the spread of the disease and change of clothing and footwear may be necessary when going from the sick to healthy animals. Isolation of new arrivals on the farm for 7 to 30 days would be ideal, but difficult to enforce at some breeding operations.

Members of the audience said that the rotavims has been recognized in Ar- gentina since 1989, and there were 2 papers on the disease in Chile last year.

AAEP CONVENTION

The American Association of Equine Practitioners held another s u ~ f u l con- vention last December, in Orlando, FL.

There was a lot of talk about the new injectable beta carotene product an- nounced by BASF. Some concerns were raised over the unsubstantiated claims made for the product by the manufac- turer. Nevertheless, preliminary field tri- als show the product to be helpful in improving equine pregnancy rates.

An entire session was devoted to equine nutrition. Dr. George Mundy said the basis for meetingthe nutritional needs of horses is ration balancing. He empha- sized that all stages of growth are suscep- tible to nutritional factors that may con- tribute to developmental orthopedic dis- ease (DOD), and that it is important to provide a total diet with adequate, but not excessive levels of nutrients known to contribute to DOD, such as copper and zinc.

Dr. Thomas Divers described a new equine motor neuron disease, the equiva- lent of the human Lou Gehrig's Disease. It is characterized by a progressive weak- ness, generalized muscle wasting and neuronal degenerative changes.

A new DNA test for the inherited hyperkalemic periodic paralysis prob- lem in horses was described by Dr. Sharon Spier. She said practicing veterinarians should advise clients with affected horses about the heritable nature of this disease.

68 JOURNAL OF EQUINE VETERINARY SCIENCE