Arsenical feed additives have been used in poultry for control of coccidiosis and enhancement of growth since the discovery of activity in this group of compounds in the years after World War II and are still in use today. In particular, two compounds stand out. Nitarsone (4-nitro-phenyl arsonic acid) is used for prevention of histomoniasis in turkeys, and roxarsone (3-nitro-phenylarsonic acid) is used for improved coccidiosis control when given in combination with the ionophorous anticoccidial drugs.
Curiously, these applications are primarily in the US. The original roxarsone claim was for prevention of coccidiosis, and the product saw considerable use in the late 1940s and early 1950s. For this use it was quickly replaced by other products because of its limited spectrum of activity (principally against Eimeria tenella and E. brunetti).
In the 1950s another use was discovered, that of growth promotion in broiler chicks, which would keep it in use for several decades. By the 1980s many had come to doubt the value of roxarsone as a growth-promoting product and tended to discontinue its use (Dillworth and Day, 1985). This lapse was short-lived, as it was soon apparent that producers had received unexpected benefit as an adjunct to control of coccidiosis.
A test of field isolates in the US showed that roxarsone sometimes accounted for all of the control of coccidiosis caused by E. tenella when used in combination with ionophores (McDougald et al., 1992). According to surveys based on agricultural statistical services, the use of roxarsone in broilers continued unabated through the end of the century (Chapman and Johnson, 2002).
The use of arsenicals in the feed of poultry and livestock is not without controversy.
Recent attention has been focused on the accumulation of heavy metals in the environment and the potential for arsenic to build up in growing facilities and in soil where poultry litter is spread on the fields. Legal action by consumer groups and a growing climate of distrust by consumers has placed the future of such products in doubt.
Thus, it is no surprise that the food industries are seeking alternatives to the use of arsenicals and other products in poultry for control of disease and for enhancement of performance. Increasingly, products based on natural ingredients have gained favor, and considerable research has appeared in the scientific literature. One such product is Bio-Mos?(Alltech Inc.).
Faced with the urgency of finding a replacement for roxarsone in poultry diets, the present study was conducted to evaluate the potential of Bio-Mos?as an aid in controlling losses to coccidiosis and improving performance in comparison with roxarsone under simulated natural conditions in floor pens. Conventional medication with salinomycin was supplemented with bacitracin (BMD) as a base program, to which was added either roxarsone or Bio-Mos?for comparison.
Comparison of Bio-Mos?with roxarsone in a floor pen model Floor pen models for study of the effects of feed additives on performance of birds consist of numerous pens of similar size where broilers can be reared to market weight on normal litter materials.
In this study, the pens were 4 x 8 ft and were stocked with 48 birds. This allowed for removal of birds during the study for lesion score while maintaining a normal stocking density. Each treatment was replicated in six similar pens on pine shavings litter.
Day-old chicks from a commercial hatchery were stocked straight-run, but were sexed at final weighing. A commercial-type ration typical of that used in the US was fed throughout. The ration was formulated to meet or exceed NRC requirements for nutrients, vitamins and minerals.
The treatments consisted of (1) salinomycin (60 g/ton) + bacitracin methylene disalicylate (BMD, 50 g/ton), (2) salinomycin + BMD, + roxarsone 45.4 g/ton, or (3) salinomycin + BMD + Bio-Mos?2 lb/ton. These treatment groups were not directly exposed to coccidiosis and were allowed to have minor natural exposure by tracking from adjacent pens in which direct exposure was given.
The second set of treatments (4-6) were similar to 1-3, except that coccidiosis exposure was given by mixing a suspension of live oocysts in the feed. The inoculum consisted of E. acervulina, E. maxima and E. tenella, in dosages calculated on the basis of an assay to be sufficient to cause mild-moderate lesion scores and to reduce weight gain, while causing minimal mortality.
DATA COLLECTION
Birds were weighed by pen at 21, 35, and 42 days of age. At 42 days of age the birds were separated by sex for weighing. The feed issued was recorded, and any feed remaining at the end of any feeding period was weighed back and discarded. The mortality weights were added to live weights in the calculation of feed conversion to avoid skewing of the data. Four birds/pen were removed for necropsy and lesion scores on days 21 and 30.
The scores were subjective, based on the 0-4 scale of Johnson and Reid (1970), and were recorded for the upper intestine (E. acervulina), mid-intestine (E. maxima) and ceca (E. tenella). Dead birds were collected twice daily and examined for lesions of coccidiosis and for assessment of cause of death.
RESULTS
The performance data are summarized in Table 1 and the lesion scores are found in Table 2. The coccidiosis infection in treatments 4-6 was sufficient to reduce weight gains, negatively impact feed conversion, and to cause mild-moderate lesion scores.
There was some mortality (0.667-5.3%) as a result of E. tenella infections. Overall feed conversion for birds given Bio-Mos?or roxarsone was superior to feed conversion of birds given only salinomycin + BMD, whether exposed to coccidiosis or not. There was no significant difference in overall feed conversion between the Bio-Mos?and roxarsone treatments. Weight gains were improved in the Bio-Mos?treatment in coccidiosis-exposed birds compared with the roxarsone or base ration treatment.
Table 1. Performance and mortality of broilers given roxarsone or Bio-Mos?for 42 days.
Table 2. Lesion scores of broilers given roxarsone or Bio-Mos?for 42 days.
Lesion scores of directly exposed birds reflected the effects of the different treatments.
As expected, roxarsone had the best effect against E. tenella resulting in low cecal lesion scores and reduced coccidiosis mortality (treatment 5, Table 2). Although no direct anticoccidial effect is documented for Bio-Mos?(treatment 6), the lesions for the intestinal species were reduced in comparison with treatment 4.
Discussion
In the modern world of consumerism and public concern over the use of chemicals and antibiotics in food animals, it is prudent to investigate alternatives to the use of such products. At present, we are able to use roxarsone in the US, but in other countries the regulatory authorities have limited the use of many products and have announced plans to restrict the use of ionophores as well.
In the present study, it was observed that both roxarsone and Bio-Mos?had positive effects on performance of the chickens and aided in the control of coccidiosis. As could be expected, the products were not identical in their effects. The overall better growth of chickens directly exposed to coccidiosis and given Bio-Mos? while at the same time suffering some losses to E. tenella, suggests that this product has some beneficial properties other than those of roxarsone. Bio-Mos?also gave the best overall weight gain in birds not exposed to coccidiosis.
In the selection of products to use in commercial production there are many factors to consider. Naturally, one must evaluate the need for control of each of the species of coccidia as well as the overall effect of the product on performance. The results of this study suggest that the effects of Bio-Mos?differ in some ways from those of roxarsone.
The mechanisms involved in these effects have not been elucidated, but could involve direct antiprotozoal effects as well as indirect effects on primary resistance to disease.
The present results suggest that Bio-Mos?could be of significant value as a replacement for roxarsone for use in concert with other feed additives.
References
Chapman, H.D. and Z.B. Johnson. 2002. Use of antibiotics and roxarsone in broiler chickens in the USA: analysis for the years 1995-2000. Poultry Sci. 81:356-364.
Dillworth, B.C. and E.J. Day. 1985. Survey of the use of 3-nitro in broiler diets. Poultry Sci. 65: (Suppl 1):17 (Abstr).
Johnson, J. and W.M. Reid. 1970. Anticoccidial drugs: Lesion scoring techniques in battery and floor pen experiments with chickens. Experimental Parasitol. 28:30-36.
McDougald, L.R., J.M. Gilbert, A. Rotibi, M. Xie and G. Zhu. 1992. How much does roxarsone contribute to coccidiosis control in broiler chickens when used in combination with ionophores? J. Appl. Poult. Res. 1:172-179.