Effect of the Antioxidant 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline on the Development of the Free-Living Stages of Some Nematode Parasites of Cattle

Abstract

The antioxidant used in commercial animal feeds, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline (ethoxyquin, Santoquin, or EMQ) had an inhibitory effect on larval nematode development. Increasingly fewer larvae were recovered from fecal cultures as the quantity of EMQ fed to infected calves, or mixed with feces from infected calves, was increased from the amount commonly used as a feed preservative (1/4 lb/ton) up to 100 times that amount. For example, the number of Cooperia pectinata larvae recovered from fecal cultures from a calf fed untreated chopped alfalfa hay was 40.4% as compared to 9.5% when 100 X EMQ was mixed with the hay. Similarly, 25 X EMQ resulted in reductions as follows: Trichostrongylus colubriformis from 33.2 to 13.5%, T. axei from 28.3 to 10.8%, and Oesophagostomum radiatum from 45.3 to 4.8%. Comparing commercial pelleted alfalfa hay with and without EMQ showed reductions, varying from 17% for C. punctata to 64% for T. colubriformis. Larval development in feces-vermiculite cultures treated with various concentrations of EMQ showed reductions as follows: T. axei from 27.9 to 0.0% with 500 X, C. pectinata from 22.8 to 0.8% with 30 X, and T. colubriformis from 24.6 to 15.3% with 4 x. Studies on the effect of host diet on the bionomics of the free-living stages of some cattle nematodes showed a reduction in the number of larvae recovered from cultures when the diet was changed from alfalfa hay to dehydrated alfalfa pellets. Further investigations indicated that inhibition of larval development could be due to the chemical preservative or antioxidant used in the preparation of commercial animal feeds. Of the antioxidants used in the food industry, 6-ethoxy1,2-dihydro-2,2,4-trimethylquinoline (known as ethoxyquin, Santoquin, or EMQ) is probably the most prevalent because of its high activity and desirable physical properies (Bickoff et al., 1954). According to Machlin et al., 1957, and Wilson et al., 1959, this chemical is rapidly absorbed and its metabolites are readily and nearly completely excreted in urine and feces. This paper considers the effect of EMQ on larval development when mixed with various feeds, and when added to feces obtained from donor calves monospecifically infected with various cattle nematodes. Received for publication 28 September 1966. * Resigned 13 August 1966. t In cooperation with the Georgia Agricultural Experiment Station. Station Journal Series Paper No. 546. MATERIALS AND METHODS Commercial dehydrated alfalfa pellets (16 or 17% crude protein) and alfalfa meal (17% crude protein) were compared with alfalfa hay and with chopped alfalfa hay, to which various amounts of EMQ (Santoquin-Mixture 6, Monsanto Company, St. Louis) had been added. The chopped hay was passed through a hammer mill with a 1/2-inch screen. The standard concentration of EMQ, designated as 1 X, was based on the amount commonly used in the manufacture of commercial pellets and other animal feeds (1/4 lb/ton, or 125 Mig/g). Higher dosages were in multiples of the standard dosage, and were designated, for the sake of brevity, from 1 X to 100 X. Dairy calves, monospecifically infected with various cattle nematodes, were used as experimental hosts. The species present were Cooperia punctata, C. pectinata, Trichostrongylus axei, T. colubriformis, and Oesophagostomum radiatum. Feces were collected from the hosts' rectums hourly during the day (8 AM to 4 PM) for various days while the particular host calf ate, ad lib., one of the rations. No collections were made 3 or 4 days following a change in diet in order to allow the elimination from the calf of all waste products of the previous diet and for the rumen flora to become adjusted to the new diet. The total daily output was mixed thoroughly, samples were taken for nematode egg counts, and the remainder was cultured in plastic pans. The cultures, each containing 1,000 g of feces, 166 g vermiculite, and any necessary water, were incubated for 9 days in constant temperature cabinets set at 25 C. All cultures were weighed daily and opened to aerate and to replace any water lost through evaporation. At the end of the incubation period, the cultured material was placed in Baermann funnels, left over-