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Does Pulmonary Hypertension Syndrome (Ascites) Occur More Frequently in Broilers Medicated with Monensin?
Does Pulmonary Hypertension Syndrome (Ascites) Occur More Frequently in Broilers Medicated with Monensin? M. E. CHAPMAN,! H. D. CHAPMAN,* R. F. WIDEMAN,2 W. E. HUFF,3 A. H. HACKER,* N. C. RATH,3 and J. M. BALOG3 Department of Poultry Science and USDA, Agricultural Research Service, University of Arkansas, Fayetteville, Arkansas 72701
1995 Poultry Science 74:1591-1596
in blood pressure in the pulmonary circulation (hypertension) can cause enlargePulmonary hypertension syndrome ment of the right ventricle and eventually (PHS or ascites) is an important cause of congestive heart failure (Julian, 1993; mortality in broiler chickens that has been Wideman and Bottje, 1993). reported from many parts of the world Monensin (Coban®)4 is a carboxylic acid (Wideman, 1988). The fast-growing mod- ionophore or polyether antibiotic that is ern broiler is particularly susceptible to widely used for the control of coccidiosis PHS. It has been suggested that rapid in broilers (Ruff, 1982; Chapman, 1993). growth causes an increased demand for High concentrations of monensin have oxygen, which forces the heart to increase toxic effects on the cardiovascular system its output of blood. The resulting increase of chickens (Hanrahan et al., 1981; Wagner et al, 1983), and Julian (1993) has suggested that monensin toxicity may result in ascites. Received for publication February 7, 1995. Monensin acts as a mobile carrier of Accepted for publication June 23, 1995. department of Biology, Bassett Crescent East, The monovalent cations permitting their diffuUniversity, Southampton, S09 3TU, UK. sion across plasma and intracellular mem2 To whom correspondence should be addressed. branes. Monensin has a higher affinity for 3 USDA, Agricultural Research Service. + 4 for a Elanco Products Co., division of Eli Lilly and Na+ than for K and, in exchange proton, permits the diffusion of Na+ down Co., Indianapolis, IN 46285. INTRODUCTION
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ABSTRACT The performance of broilers reared in floor pens and given monensin in the feed at 121 ppm was compared with that of birds given no drug. Feed intake and BW gain of medicated birds was significantly lower than that of unmedicated birds from 0 to 22 d of age. Feed intake and feed conversion of medicated birds was significantly reduced, compared with unmedicated birds, from 22 to 53 and 0 to 60 d of age. Total mortality, and mortality due to leg abnormalities from 22 to 53 and 0 to 60 d, was significantly lower in birds given monensin. There was no difference in the incidence of tibial dyschondroplasia (TD) by 60 d. No differences in mortality due to pulmonary hypertension syndrome (PHS) were observed for any age period. Birds removed from pens at 28 d that had received monensin had lower hematocrit and percentage saturation of hemoglobin with oxygen in the blood than unmedicated birds. No differences in these variables were found at 54 d. There were no differences in the right ventricle weight: total ventricular weight ratios or electrocardiogram lead II values at 28 or 54 d. The results indicate that PHS does not occur more frequently in broilers medicated with monensin. (Key words: pulmonary hypertension syndrome, ascites, monensin, broiler, leg abnormality)
1592
CHAPMAN ET AL.
MATERIALS AND METHODS Day-old male broiler chicks (Cobb-500)5 were obtained from a local hatchery on June 23,1994 and assigned randomly to 32 equal sized pens (50 birds per pen) at a density of 1 bird per .093 m2. The chicks had been vaccinated against Newcastle, Infectious Bronchitis, and Marek's disease at the hatchery. Pens contained new rice hulls for litter and were equipped with two tubular hanging feeders and an automatic waterer. Thermostatically controlled gas brooders and ventilation fans were used to regulate temperature, and 23 h of light and 1 h of darkness was provided
sCobb-Vantress, Inc., Siloam Springs, AR 72761.
each day. Air temperature and relative humidity were recorded daily throughout the trial. Pens were randomly assigned to two treatment groups (16 pens per group). Birds in the first group were given monensin at a concentration of 121 ppm, and those in the second group were given no drug (unmedicated control). A sample of feed from each ration was assayed for monensin and analysis indicated that the levels of drug were within acceptable limits of the intended concentration. All birds were fed a corn-soybean basal ration formulated to meet the nutritional requirements of the broiler chicken (NRC, 1984). Diets consisted of starter feed (CP, 21.80%; ME, 3,152 kcal/kg), grower feed (CP, 20.17%; ME, 3,198 kcal/kg), and finisher feed (CP, 18.05%; ME, 3,250 kcal/ kg), given when the birds were 0 to 22, 22 to 53, and 53 to 60 d of age, respectively. Sodium chloride was included in the starter and finisher feeds at concentrations of .44 and .46%, respectively. A concentration of .6% NaCl was employed in the grower diet because high salt concentrations are known to increase the incidence of ascites in chickens (Julian, 1987a). Composite pen BW was obtained at 22, 53, and 60 d, and total feed consumed was recorded for each age period. Birds that died during the trial were necropsied and, if possible, the cause of death determined. The presence of fluid in the abdominal cavity, hydropericardium, or an enlarged heart with a dilated right ventricle were considered to be indications that death was due to PHS. Birds that could not eat or drink because of leg abnormalities were culled and the observations recorded separately. At trial termination (60 d), 6 to 10 randomly chosen birds from each pen were examined for leg abnormalities. Following a sagittal cut in the proximal aspect of the tibiotarsal bone, birds were scored for the presence and severity of tibial dyschondroplasia (TD) by visual examination as described by Huff (1980). Lesions were scored as follows: 1(+) TD lesions were not present, 2(+) lesions less than .5 cm, 3(+) lesions greater than .5 cm extending longitudinally at the margin of the metaphysis, and 4(+) lesions greater than .5 cm extending
Downloaded from http://ps.oxfordjournals.org/ at Columbia University Libraries on November 26, 2014
its concentration gradient into the cell (Pressman, 1973; Reed, 1982). Removal of Na+ from the cell is effected by a Na + / Ca2+ exchange system present in the plasma membrane of many cells and is accompanied by an influx of Ca2+. Calcium ions are involved in mediating the contraction-coupling process in muscle tissue (Naylor, 1967). It has been shown that, in mammals, high concentrations of monensin can increase the concentration of intracellular Ca2+ and enhance the contractility of cardiac muscle (reviewed by Reed and Bokoch, 1982). This results in increased aortic blood pressure and coronary blood flow (Pressman and Fahim, 1982, 1983). Increased contractility of cardiac muscle may accentuate pulmonary hypertension and increase the probability of congestive heart failure. Alternatively, increased cardiac muscle tone may delay or moderate the pressure-induced dilation of the right ventricle and subsequent evolution to congestive heart failure in broilers susceptible to PHS. In view of the potential effects of ionophores on the cardiovascular system it is conceivable that these drugs may play a role in the etiology of PHS in the fowl. In this study, we investigate the incidence of PHS in chickens given the maximum approved use level of monensin (121 ppm) via the feed and whether these birds show any hematological changes that might indicate a predisposition to this condition.
MONENSIN AND ASCITES IN CHICKENS
1593
TABLE 1. Effect (3c ± SEM) of monensin upon performance of broilers Body weight gain per bird
Feed intake per bird Period
Monensin
(d) 0 to 22 to 53 to 0 to
1,181 4,604 1,474 7,120
22 53 60 60
± 4» ± 53" ± 26 ± 60B
No drug M 1,228 4,868 1,494 7,381
Monensin
Feed conversion
No drug
Monensin
M ± 5A ± 36* ± 28 ± 38*
889 2,223 499 3,611
± ± ± ±
4B 13 15 18
928 2,222 478 3,629
± ± ± ±
4A 21 15 24
1.328 2.071 2.977 1.972
± ± ± ±
No drug
fr-H .003 1.324 .0228 2.191 .056 3.150 .014» 2.034
± ± ± ±
.003 .009* .068 .007*
A3Means for each variable in a row with no common superscript differ significantly (P < .001).
6
Biopac Systems Inc., Goleta, CA 93117. Criticare Systems, Inc., Milwaukee, WI 53226.
7
RESULTS Feed intake and BW gain of birds given monensin from 0 to 22 d were significantly lower than for the unmedicated controls (Table 1). Feed intake and feed conversion of medicated birds from 22 to 53 and 0 to 60 d were significantly lower than that of the controls (Table 1). Total mortality from 22 to 53 and 0 to 60 d was significantly lower in birds given monensin man in the unmedicated birds (Table 2). No differences in mortality due to PHS were observed for any age period. Mortality (including birds culled) attributable to leg abnormalities was significantly lower in the medicated birds from 22 to 53 and 0 to 60 d than in the controls (Table 2). There was no difference, however, in the incidence and severity of TD (control: 44 ± 3%, TD score 2.8 ± .2; monensin, 38 ± 4%, TD score 2.2 ± .3) or other leg defects by 60 d of age. Hematocrit was significantly lower and the percentage saturation of hemoglobin with oxygen in the blood significantly higher at 28 d in medicated birds than in the unmedicated controls (Table 3). No differences in these variables were found at 54 d. There were no differences in the RV:TV ratios or EKG lead II values at either 28 or 54 d. No oocysts of Eimeria were found in the litter (data not shown). DISCUSSION Body weight gain (0 to 22 d), feed intake (0 to 22,22 to 53 and 0 to 60 d), and feed conversion (22 to 53 and 0 to 60 d) were significantly reduced in birds medicated With monensin. Depression of BW of
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longitudinally and laterally throughout the entire metaphysis. Samples of litter were taken from five randomly chosen pens each week, and the presence of oocysts of Eimeria species determined (Chapman and Johnson, 1992). Eight birds were randomly selected from each pen at 7 d and tagged with a wing-band for identification. Three of these birds were taken from each pen at 28 and 54 d, and standard three limb electrocardiograms (EKG)6 recorded to evaluate lead-n R-S wave amplitudes as an index of cardiac hypertrophy (Owen et al, 1990). A pulse oximeter7 was used for noninvasive measurement of percentage saturation of hemoglobin with oxygen in arterialized capillary beds (Peacock et al, 1990). Blood samples (200 to 400 /*L) were taken by venipuncture for microhematocrit determination. Birds were then killed by cervical dislocation, the hearts were removed, blotted dry, and dissected to calculate right ventricle weight:total ventricular weight (RV:TV) ratios as an index of PHS. Means were compared by Student's t test using software of the SAS® Institute (1988). An average value was calculated for each variable from the three birds removed from pens at 28 and 54 d. The statistical unit for analysis was the pen (n = 16). Mortality data for each age period were transformed to square root prior to analysis.
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CHAPMAN ET AL. TABLE 2. Effect (x ± SEM) of monensin upon mortality of broilers Percentage mortality PHS1
Total Period (d) 0 to 22 to 53 to 0 to
Monensin
No drug
Monensin
4.1 6.8 4.2 13.6
± ± ± ±
No drug
Monensin
.5 5.6 1.3 6.6
.8 1.1 1.2 2.6
.,.
(o/\
22 53 60 60
Leg defects
.8 2.9 ± .9 .8b 12.4 ± 1.1« .8 5.0 ± .9 1.4b 18.1 ± l.2a
.5 3.8 2.4 5.9
± ± ± ±
.2 .6 .6 .8
± ± ± ±
.2 1.1 .5 1.0
± ± ± ±
.4 .3b .4 .4b
No drug (g) 1.0 3.1 2.6 5.3
± ± ± ±
.4 .6a .6 .9a
a b
chickens fed monensin (120 and 121 ppm) has previously been reported (Gard et ah, 1975; Weppelman et al., 1977) and is associated with a reduction in feed intake (McDougald and McQuistion, 1980; Metzler et ah, 1987; Harms et ah, 1989). Improved feed conversion following the use of monensin in broilers has also been reported (reviewed by Ruff, 1982) and is considered due to better control of coccidiosis. Overall mortality was lower in birds medicated with monensin than in birds given no drug. The improvement in feed conversion and reduced mortality found in this study was not due to control of coccidiosis as no oocysts of Eimeria species were found in the litter and lesions caused by Eimeria species were not seen in the intestines of birds that died. Mortality attributable to leg abnormalities (5.3% in unmedicated birds) was higher than expected for commercial broilers. This study was performed during June to August and leg problems are frequently high during the summer
months (Sullivan, 1994). Death attributable to leg defects was lower in medicated birds, but there was no difference in the incidence of TD or other leg abnormalities in birds surviving to the end of the study. Leeson and Summers (1988) have reported an increase in the incidence of leg problems in poultry when ionophores are used. Reduced mortality due to leg defects in chickens given monensin has not previously been reported. There was no difference in mortality due to PHS between medicated and unmedicated birds. Mortality was 6.6% in the unmedicated controls (5.6% during the grower phase). According to Julian (1987b) mortality due to ascites may occasionally be up to 5% in broiler flocks. The effects seen in this study may have been influenced by environmental conditions. It would be interesting to repeat this study during winter when environmental factors such as low temperature and high NH 3 and COz in the environment might predispose birds to a greater incidence of PHS.
TABLE 3. Effect (3c ± SEM) of monensin upon physiological measurements in broilers 54 d
28 d Variable Hematocrit, % Blood oxygen saturation, % RV:TVi EKG Lead n, mV2
Monensin 31.0 81.3 24.5 .11
b
± .6 ± 1.2* ± .9 ± .01
No drug
Monensin
No drug
34.0 74.3 26.0 .11
33.5 80.4 27.2 .10
34.3 81.6 26.9 .14
± ± ± ±
1.0» 3.0b 1.3 .01
±1.2 ±2.1 ± .9 ± .01
± ± ± ±
a^Means for each variable in a row with no common superscript differ significantly (P < .05). 1 RV:TV = right ventricle weighttotal ventricular weight ratio. 2 EKG = electrocardiogram.
.9 1.4 1.3 .02
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- Means for each variable in a row with no common superscript differ significantly (P < .05). Pulmonary hypertension syndrome.
1
MONENSIN AND ASCITES IN CHICKENS
cells. Horowitz et al. (1988) reported low levels of creatine phosphokinase in chickens fed 400 ppm monensin and suggested that this could result in a reduced ability to transfer high energy phosphate from adenosine triphosphate to creatine, which is needed for the heart to function normally. Although high concentrations of monensin may effect the cardiovascular system of broilers, there is no evidence that toxic effects upon this system occur in birds given the maximum approved use level of the drug. The results indicate that, under the environmental conditions of this study, pulmonary hypertension syndrome did not occur more frequently in broilers medicated with monensin. ACKNOWLEDGMENTS
We thank P. W. Waldroup for kindly providing the ration formulation, D. Bassi, K. McElyea, D. Horlick and S. Zornes for their technical assistance with parts of this study. REFERENCES Chapman, H. D., 1993. Twenty-one years of monensin for the control of coccidiosis—a review. Pages 37-44 in: Proceedings of the Vlth International Coccidiosis Conference, J. R. Barta and M.A. Fernando, ed. Ontario Veterinary College, University of Guelph, Guelph, ON, Canada. Chapman, H. D., and Z. B. Johnson, 1992. Oocysts of Eimeria in the litter of broilers reared to eight weeks of age before and after withdrawal of lasalocid or salinomycin. Poultry Sci. 71: 1342-1347. Gard, D. I., B. F. Schlegel, D. K. Weymouth, and R. P. Rathmacher, 1975. Effect of monensin and dietary protein on broiler growth, feathering, and anticoccidial efficacy. Poultry Sci. 54: 1764-1765. Hanrahan, L. A., D. E. Corrier, and S. A. Naqi, 1981. Monensin toxicosis in broiler chickens. Vet. Pathol. 18:665-671. Harms, R. H., N. Ruiz, and R. E. Buresh, 1989. Influence of monensin and salinomycin on the performance of broiler chicks. Poultry Sci. 68: 86-S8. Horowitz, C. T., Y. Avidar, E. Bogin, A. Schlosberg, I. Shkap, Y. Weisman, and M. N. Egyed, 1988. Enzyme profile in blood tissues of chickens fed various levels of monensin. J. Vet. Med. Ser. A 35:473-480. Huff, W. E., 1980. Evaluation of tibial dyschondroplasia during aflatoxicosis and feed restriction in young broiler chickens. Poultry Sci. 59:991-995. Julian, R. J., 1987a. The effect of increased sodium in the drinking water on right ventricular hyper-
Downloaded from http://ps.oxfordjournals.org/ at Columbia University Libraries on November 26, 2014
Chickens that develop PHS often show right ventricular dilation, elevated EKG Lead II R-S wave amplitudes, elevated hematocrit, and reduced percentage saturation of hemoglobin with oxygen, the latter reflecting generalized systemic hypoxemia (Wideman and Kirby, 1995). In this study no differences in RV:TV ratios or EKG values were found, but medicated birds had a lower hematocrit and higher blood oxygen saturation at 28 d than the unmedicated controls. Osborne et al. (1982) studied the effects of monensin, given in the feed at 121 ppm, upon arterial blood pressure, cardiac output, heart rate, and various EKG waveforms in the fowl. Plasma volume was significantly increased in medicated birds but no other differences were found. The authors concluded that monensin produced no cardiovascular liabilities in broiler chickens, a conclusion supported by the results of this study. Increased cardiac output might be expected to increase the susceptibility of broilers to PHS. Feed deprivation has been shown to decrease cardiac output in the chicken (Sturkie and Vogel, 1959). Although cardiac output of the fowl has not been shown to be affected by monensin, the drug apparently reduces feed intake and it could be argued that monensin may, therefore, reduce rather than enhance susceptibility to ascites. There have been a few reports indicating that toxic concentrations of monensin may effect the cardiovascular system of the fowl. Five of 10 chickens given a single oral dose of monensin (150 mg/kg of BW) showed cardiac enlargement and generalized congestion (Hanrahan et al, 1981). Histologic examination revealed intermyofibrillar vacuolation and fat droplets in ventricular myocardial tissue of all birds examined. Hydropericardium was occasionally seen in birds given high concentrations of drug. Wagner et al. (1983) found that 40% of chickens given twice the maximum approved use level of monensin (242 ppm) showed subepicardial hemorrhage and congestion in the wall of the right, and to a lesser extent, left ventricles of the heart. Lesions were characterized by widely dilated vessels and blood present between myocardial
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CHAPMAN ET AL. Pressman, B. C, and M. Fahim, 1983. Cardiovascular toxicity of ionophores used as feed additives. Adv. Exp. Med. Biol. 161:543-561. Reed, P. W., 1982. Biochemical and biological effects of carboxylic acid ionophores. Pages 185-302 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Reed, P. W., and G. M. Bokoch, 1982. Cardiovascular and renal effects of A23187 and monovalent polyether antibiotics. Pages 369-395 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Ruff, M. D., 1982. Veterinary applications. Pages 303-332 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. SAS Institute, 1988. SAS/STAT® User's Guide: Version 6. Fourth Edition. Vol. 1. SAS Institute Inc., Cary, NC. Sturkie, P. D., and J. A. Vogel, 1959. Cardiac output, central blood volume, and peripheral resistance in chickens. Am. J. Physiol. 197:1165-1166. Sullivan, T. W., 1994. Skeletal problems in poultry: estimated annual cost and descriptions. Poultry Sci. 73:879-882. Wagner, D. D., R. D. Furrow, and B. D. Bradley, 1983. Subchronic toxicity of monensin in broiler chickens. Vet. Pathol. 20:353-359. Weppelman, R. M., G. Olson, D. A. Smith, T. Tamas, and A. van Iderstine, 1977. Comparison of anticoccidial efficacy, resistance and tolerance of narasin, monensin and lasalocid in chicken battery trials. Poultry Sci. 56:1550-1559. Wideman, R. F., 1988. Ascites in poultry. Monsanto Nutr. Update 6:1-7. Wideman, R. F., and W. G. Bottje, 1993. Current understanding of the ascites syndrome and future research directions. Pages 1-20 in: Nutrition and Technical Symposium Proceedings. Novus International, Inc., St. Louis, MO. Wideman, R. F., and Y. K. Kirby, 1995. A pulmonary artery clamp model for inducing pulmonary hypertension syndrome (Ascites) in broilers. Poultry Sci. 74:805-812.
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trophy, right ventricular failure and ascites in broiler chickens. Avian Pathol. 16:61-71. Julian, R. J., 1987b. Are we growing them too fast? Ascites in meat-type chickens. Highlights Agric. Res. Ontario 10:27-30. Julian, R. J., 1993. Ascites in poultry. Avian Pathol. 22:419-454. Leeson, S., and J. D. Summers, 1988. Some nutritional implications of leg problems with poultry. Br. Vet. J. 144:81-92. McDougald, L. R., and T. E. McQuiston, 1980. Compensatory growth in broilers after withdrawal of ionophorous anticoccidial drugs. Poultry Sci. 59:1001-1005. Metzler, M. J., W. M. Britton, and L. R. McDougald, 1987. Effects of monensin feeding and withdrawal time on growth and carcass composition in broiler chickens. Poultry Sci. 66:1451-1458. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC. Naylor, W. G., 1967. Calcium exchange in cardiac muscle: A basic mechanism of drug action. Am. Heart J. 73:379-393. Osborne, M. W., J. Wenger, F. Kovzelove, R. Boyd, and M. Zanko, 1982. Effects of lasalocid and monensin on chickens. Pages 333-340 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Owen, R. L., R. F. Wideman, A. L. Hattel, and B. S. Cowen, 1990. Use of a hypobaric chamber as a model system for investigating ascites in broilers. Avian Dis. 34:754-758. Peacock, A. J., C. Pickett, K. Morris, and J. T. Reeves, 1990. Spontaneous hypoxaemia and right ventricular hypertrophy in fast-growing broiler chickens reared at sea level. Comp. Biochem. Physiol. 97A:537-541. Pressman, B. C, 1973. Properties of ionophores with broad range cation selectivity. Fed. Proc. 32: 1698-1703. Pressman, B. C, and M. Fahim, 1982. Pharmacology and toxicology of the monovalent carboxylic ionophores. Annu. Rev. Pharmacol. Toxicol. 22: 465-490.
1995 Poultry Science 74:1591-1596
in blood pressure in the pulmonary circulation (hypertension) can cause enlargePulmonary hypertension syndrome ment of the right ventricle and eventually (PHS or ascites) is an important cause of congestive heart failure (Julian, 1993; mortality in broiler chickens that has been Wideman and Bottje, 1993). reported from many parts of the world Monensin (Coban®)4 is a carboxylic acid (Wideman, 1988). The fast-growing mod- ionophore or polyether antibiotic that is ern broiler is particularly susceptible to widely used for the control of coccidiosis PHS. It has been suggested that rapid in broilers (Ruff, 1982; Chapman, 1993). growth causes an increased demand for High concentrations of monensin have oxygen, which forces the heart to increase toxic effects on the cardiovascular system its output of blood. The resulting increase of chickens (Hanrahan et al., 1981; Wagner et al, 1983), and Julian (1993) has suggested that monensin toxicity may result in ascites. Received for publication February 7, 1995. Monensin acts as a mobile carrier of Accepted for publication June 23, 1995. department of Biology, Bassett Crescent East, The monovalent cations permitting their diffuUniversity, Southampton, S09 3TU, UK. sion across plasma and intracellular mem2 To whom correspondence should be addressed. branes. Monensin has a higher affinity for 3 USDA, Agricultural Research Service. + 4 for a Elanco Products Co., division of Eli Lilly and Na+ than for K and, in exchange proton, permits the diffusion of Na+ down Co., Indianapolis, IN 46285. INTRODUCTION
1591
Downloaded from http://ps.oxfordjournals.org/ at Columbia University Libraries on November 26, 2014
ABSTRACT The performance of broilers reared in floor pens and given monensin in the feed at 121 ppm was compared with that of birds given no drug. Feed intake and BW gain of medicated birds was significantly lower than that of unmedicated birds from 0 to 22 d of age. Feed intake and feed conversion of medicated birds was significantly reduced, compared with unmedicated birds, from 22 to 53 and 0 to 60 d of age. Total mortality, and mortality due to leg abnormalities from 22 to 53 and 0 to 60 d, was significantly lower in birds given monensin. There was no difference in the incidence of tibial dyschondroplasia (TD) by 60 d. No differences in mortality due to pulmonary hypertension syndrome (PHS) were observed for any age period. Birds removed from pens at 28 d that had received monensin had lower hematocrit and percentage saturation of hemoglobin with oxygen in the blood than unmedicated birds. No differences in these variables were found at 54 d. There were no differences in the right ventricle weight: total ventricular weight ratios or electrocardiogram lead II values at 28 or 54 d. The results indicate that PHS does not occur more frequently in broilers medicated with monensin. (Key words: pulmonary hypertension syndrome, ascites, monensin, broiler, leg abnormality)
1592
CHAPMAN ET AL.
MATERIALS AND METHODS Day-old male broiler chicks (Cobb-500)5 were obtained from a local hatchery on June 23,1994 and assigned randomly to 32 equal sized pens (50 birds per pen) at a density of 1 bird per .093 m2. The chicks had been vaccinated against Newcastle, Infectious Bronchitis, and Marek's disease at the hatchery. Pens contained new rice hulls for litter and were equipped with two tubular hanging feeders and an automatic waterer. Thermostatically controlled gas brooders and ventilation fans were used to regulate temperature, and 23 h of light and 1 h of darkness was provided
sCobb-Vantress, Inc., Siloam Springs, AR 72761.
each day. Air temperature and relative humidity were recorded daily throughout the trial. Pens were randomly assigned to two treatment groups (16 pens per group). Birds in the first group were given monensin at a concentration of 121 ppm, and those in the second group were given no drug (unmedicated control). A sample of feed from each ration was assayed for monensin and analysis indicated that the levels of drug were within acceptable limits of the intended concentration. All birds were fed a corn-soybean basal ration formulated to meet the nutritional requirements of the broiler chicken (NRC, 1984). Diets consisted of starter feed (CP, 21.80%; ME, 3,152 kcal/kg), grower feed (CP, 20.17%; ME, 3,198 kcal/kg), and finisher feed (CP, 18.05%; ME, 3,250 kcal/ kg), given when the birds were 0 to 22, 22 to 53, and 53 to 60 d of age, respectively. Sodium chloride was included in the starter and finisher feeds at concentrations of .44 and .46%, respectively. A concentration of .6% NaCl was employed in the grower diet because high salt concentrations are known to increase the incidence of ascites in chickens (Julian, 1987a). Composite pen BW was obtained at 22, 53, and 60 d, and total feed consumed was recorded for each age period. Birds that died during the trial were necropsied and, if possible, the cause of death determined. The presence of fluid in the abdominal cavity, hydropericardium, or an enlarged heart with a dilated right ventricle were considered to be indications that death was due to PHS. Birds that could not eat or drink because of leg abnormalities were culled and the observations recorded separately. At trial termination (60 d), 6 to 10 randomly chosen birds from each pen were examined for leg abnormalities. Following a sagittal cut in the proximal aspect of the tibiotarsal bone, birds were scored for the presence and severity of tibial dyschondroplasia (TD) by visual examination as described by Huff (1980). Lesions were scored as follows: 1(+) TD lesions were not present, 2(+) lesions less than .5 cm, 3(+) lesions greater than .5 cm extending longitudinally at the margin of the metaphysis, and 4(+) lesions greater than .5 cm extending
Downloaded from http://ps.oxfordjournals.org/ at Columbia University Libraries on November 26, 2014
its concentration gradient into the cell (Pressman, 1973; Reed, 1982). Removal of Na+ from the cell is effected by a Na + / Ca2+ exchange system present in the plasma membrane of many cells and is accompanied by an influx of Ca2+. Calcium ions are involved in mediating the contraction-coupling process in muscle tissue (Naylor, 1967). It has been shown that, in mammals, high concentrations of monensin can increase the concentration of intracellular Ca2+ and enhance the contractility of cardiac muscle (reviewed by Reed and Bokoch, 1982). This results in increased aortic blood pressure and coronary blood flow (Pressman and Fahim, 1982, 1983). Increased contractility of cardiac muscle may accentuate pulmonary hypertension and increase the probability of congestive heart failure. Alternatively, increased cardiac muscle tone may delay or moderate the pressure-induced dilation of the right ventricle and subsequent evolution to congestive heart failure in broilers susceptible to PHS. In view of the potential effects of ionophores on the cardiovascular system it is conceivable that these drugs may play a role in the etiology of PHS in the fowl. In this study, we investigate the incidence of PHS in chickens given the maximum approved use level of monensin (121 ppm) via the feed and whether these birds show any hematological changes that might indicate a predisposition to this condition.
MONENSIN AND ASCITES IN CHICKENS
1593
TABLE 1. Effect (3c ± SEM) of monensin upon performance of broilers Body weight gain per bird
Feed intake per bird Period
Monensin
(d) 0 to 22 to 53 to 0 to
1,181 4,604 1,474 7,120
22 53 60 60
± 4» ± 53" ± 26 ± 60B
No drug M 1,228 4,868 1,494 7,381
Monensin
Feed conversion
No drug
Monensin
M ± 5A ± 36* ± 28 ± 38*
889 2,223 499 3,611
± ± ± ±
4B 13 15 18
928 2,222 478 3,629
± ± ± ±
4A 21 15 24
1.328 2.071 2.977 1.972
± ± ± ±
No drug
fr-H .003 1.324 .0228 2.191 .056 3.150 .014» 2.034
± ± ± ±
.003 .009* .068 .007*
A3Means for each variable in a row with no common superscript differ significantly (P < .001).
6
Biopac Systems Inc., Goleta, CA 93117. Criticare Systems, Inc., Milwaukee, WI 53226.
7
RESULTS Feed intake and BW gain of birds given monensin from 0 to 22 d were significantly lower than for the unmedicated controls (Table 1). Feed intake and feed conversion of medicated birds from 22 to 53 and 0 to 60 d were significantly lower than that of the controls (Table 1). Total mortality from 22 to 53 and 0 to 60 d was significantly lower in birds given monensin man in the unmedicated birds (Table 2). No differences in mortality due to PHS were observed for any age period. Mortality (including birds culled) attributable to leg abnormalities was significantly lower in the medicated birds from 22 to 53 and 0 to 60 d than in the controls (Table 2). There was no difference, however, in the incidence and severity of TD (control: 44 ± 3%, TD score 2.8 ± .2; monensin, 38 ± 4%, TD score 2.2 ± .3) or other leg defects by 60 d of age. Hematocrit was significantly lower and the percentage saturation of hemoglobin with oxygen in the blood significantly higher at 28 d in medicated birds than in the unmedicated controls (Table 3). No differences in these variables were found at 54 d. There were no differences in the RV:TV ratios or EKG lead II values at either 28 or 54 d. No oocysts of Eimeria were found in the litter (data not shown). DISCUSSION Body weight gain (0 to 22 d), feed intake (0 to 22,22 to 53 and 0 to 60 d), and feed conversion (22 to 53 and 0 to 60 d) were significantly reduced in birds medicated With monensin. Depression of BW of
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longitudinally and laterally throughout the entire metaphysis. Samples of litter were taken from five randomly chosen pens each week, and the presence of oocysts of Eimeria species determined (Chapman and Johnson, 1992). Eight birds were randomly selected from each pen at 7 d and tagged with a wing-band for identification. Three of these birds were taken from each pen at 28 and 54 d, and standard three limb electrocardiograms (EKG)6 recorded to evaluate lead-n R-S wave amplitudes as an index of cardiac hypertrophy (Owen et al, 1990). A pulse oximeter7 was used for noninvasive measurement of percentage saturation of hemoglobin with oxygen in arterialized capillary beds (Peacock et al, 1990). Blood samples (200 to 400 /*L) were taken by venipuncture for microhematocrit determination. Birds were then killed by cervical dislocation, the hearts were removed, blotted dry, and dissected to calculate right ventricle weight:total ventricular weight (RV:TV) ratios as an index of PHS. Means were compared by Student's t test using software of the SAS® Institute (1988). An average value was calculated for each variable from the three birds removed from pens at 28 and 54 d. The statistical unit for analysis was the pen (n = 16). Mortality data for each age period were transformed to square root prior to analysis.
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CHAPMAN ET AL. TABLE 2. Effect (x ± SEM) of monensin upon mortality of broilers Percentage mortality PHS1
Total Period (d) 0 to 22 to 53 to 0 to
Monensin
No drug
Monensin
4.1 6.8 4.2 13.6
± ± ± ±
No drug
Monensin
.5 5.6 1.3 6.6
.8 1.1 1.2 2.6
.,.
(o/\
22 53 60 60
Leg defects
.8 2.9 ± .9 .8b 12.4 ± 1.1« .8 5.0 ± .9 1.4b 18.1 ± l.2a
.5 3.8 2.4 5.9
± ± ± ±
.2 .6 .6 .8
± ± ± ±
.2 1.1 .5 1.0
± ± ± ±
.4 .3b .4 .4b
No drug (g) 1.0 3.1 2.6 5.3
± ± ± ±
.4 .6a .6 .9a
a b
chickens fed monensin (120 and 121 ppm) has previously been reported (Gard et ah, 1975; Weppelman et al., 1977) and is associated with a reduction in feed intake (McDougald and McQuistion, 1980; Metzler et ah, 1987; Harms et ah, 1989). Improved feed conversion following the use of monensin in broilers has also been reported (reviewed by Ruff, 1982) and is considered due to better control of coccidiosis. Overall mortality was lower in birds medicated with monensin than in birds given no drug. The improvement in feed conversion and reduced mortality found in this study was not due to control of coccidiosis as no oocysts of Eimeria species were found in the litter and lesions caused by Eimeria species were not seen in the intestines of birds that died. Mortality attributable to leg abnormalities (5.3% in unmedicated birds) was higher than expected for commercial broilers. This study was performed during June to August and leg problems are frequently high during the summer
months (Sullivan, 1994). Death attributable to leg defects was lower in medicated birds, but there was no difference in the incidence of TD or other leg abnormalities in birds surviving to the end of the study. Leeson and Summers (1988) have reported an increase in the incidence of leg problems in poultry when ionophores are used. Reduced mortality due to leg defects in chickens given monensin has not previously been reported. There was no difference in mortality due to PHS between medicated and unmedicated birds. Mortality was 6.6% in the unmedicated controls (5.6% during the grower phase). According to Julian (1987b) mortality due to ascites may occasionally be up to 5% in broiler flocks. The effects seen in this study may have been influenced by environmental conditions. It would be interesting to repeat this study during winter when environmental factors such as low temperature and high NH 3 and COz in the environment might predispose birds to a greater incidence of PHS.
TABLE 3. Effect (3c ± SEM) of monensin upon physiological measurements in broilers 54 d
28 d Variable Hematocrit, % Blood oxygen saturation, % RV:TVi EKG Lead n, mV2
Monensin 31.0 81.3 24.5 .11
b
± .6 ± 1.2* ± .9 ± .01
No drug
Monensin
No drug
34.0 74.3 26.0 .11
33.5 80.4 27.2 .10
34.3 81.6 26.9 .14
± ± ± ±
1.0» 3.0b 1.3 .01
±1.2 ±2.1 ± .9 ± .01
± ± ± ±
a^Means for each variable in a row with no common superscript differ significantly (P < .05). 1 RV:TV = right ventricle weighttotal ventricular weight ratio. 2 EKG = electrocardiogram.
.9 1.4 1.3 .02
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- Means for each variable in a row with no common superscript differ significantly (P < .05). Pulmonary hypertension syndrome.
1
MONENSIN AND ASCITES IN CHICKENS
cells. Horowitz et al. (1988) reported low levels of creatine phosphokinase in chickens fed 400 ppm monensin and suggested that this could result in a reduced ability to transfer high energy phosphate from adenosine triphosphate to creatine, which is needed for the heart to function normally. Although high concentrations of monensin may effect the cardiovascular system of broilers, there is no evidence that toxic effects upon this system occur in birds given the maximum approved use level of the drug. The results indicate that, under the environmental conditions of this study, pulmonary hypertension syndrome did not occur more frequently in broilers medicated with monensin. ACKNOWLEDGMENTS
We thank P. W. Waldroup for kindly providing the ration formulation, D. Bassi, K. McElyea, D. Horlick and S. Zornes for their technical assistance with parts of this study. REFERENCES Chapman, H. D., 1993. Twenty-one years of monensin for the control of coccidiosis—a review. Pages 37-44 in: Proceedings of the Vlth International Coccidiosis Conference, J. R. Barta and M.A. Fernando, ed. Ontario Veterinary College, University of Guelph, Guelph, ON, Canada. Chapman, H. D., and Z. B. Johnson, 1992. Oocysts of Eimeria in the litter of broilers reared to eight weeks of age before and after withdrawal of lasalocid or salinomycin. Poultry Sci. 71: 1342-1347. Gard, D. I., B. F. Schlegel, D. K. Weymouth, and R. P. Rathmacher, 1975. Effect of monensin and dietary protein on broiler growth, feathering, and anticoccidial efficacy. Poultry Sci. 54: 1764-1765. Hanrahan, L. A., D. E. Corrier, and S. A. Naqi, 1981. Monensin toxicosis in broiler chickens. Vet. Pathol. 18:665-671. Harms, R. H., N. Ruiz, and R. E. Buresh, 1989. Influence of monensin and salinomycin on the performance of broiler chicks. Poultry Sci. 68: 86-S8. Horowitz, C. T., Y. Avidar, E. Bogin, A. Schlosberg, I. Shkap, Y. Weisman, and M. N. Egyed, 1988. Enzyme profile in blood tissues of chickens fed various levels of monensin. J. Vet. Med. Ser. A 35:473-480. Huff, W. E., 1980. Evaluation of tibial dyschondroplasia during aflatoxicosis and feed restriction in young broiler chickens. Poultry Sci. 59:991-995. Julian, R. J., 1987a. The effect of increased sodium in the drinking water on right ventricular hyper-
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Chickens that develop PHS often show right ventricular dilation, elevated EKG Lead II R-S wave amplitudes, elevated hematocrit, and reduced percentage saturation of hemoglobin with oxygen, the latter reflecting generalized systemic hypoxemia (Wideman and Kirby, 1995). In this study no differences in RV:TV ratios or EKG values were found, but medicated birds had a lower hematocrit and higher blood oxygen saturation at 28 d than the unmedicated controls. Osborne et al. (1982) studied the effects of monensin, given in the feed at 121 ppm, upon arterial blood pressure, cardiac output, heart rate, and various EKG waveforms in the fowl. Plasma volume was significantly increased in medicated birds but no other differences were found. The authors concluded that monensin produced no cardiovascular liabilities in broiler chickens, a conclusion supported by the results of this study. Increased cardiac output might be expected to increase the susceptibility of broilers to PHS. Feed deprivation has been shown to decrease cardiac output in the chicken (Sturkie and Vogel, 1959). Although cardiac output of the fowl has not been shown to be affected by monensin, the drug apparently reduces feed intake and it could be argued that monensin may, therefore, reduce rather than enhance susceptibility to ascites. There have been a few reports indicating that toxic concentrations of monensin may effect the cardiovascular system of the fowl. Five of 10 chickens given a single oral dose of monensin (150 mg/kg of BW) showed cardiac enlargement and generalized congestion (Hanrahan et al, 1981). Histologic examination revealed intermyofibrillar vacuolation and fat droplets in ventricular myocardial tissue of all birds examined. Hydropericardium was occasionally seen in birds given high concentrations of drug. Wagner et al. (1983) found that 40% of chickens given twice the maximum approved use level of monensin (242 ppm) showed subepicardial hemorrhage and congestion in the wall of the right, and to a lesser extent, left ventricles of the heart. Lesions were characterized by widely dilated vessels and blood present between myocardial
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CHAPMAN ET AL. Pressman, B. C, and M. Fahim, 1983. Cardiovascular toxicity of ionophores used as feed additives. Adv. Exp. Med. Biol. 161:543-561. Reed, P. W., 1982. Biochemical and biological effects of carboxylic acid ionophores. Pages 185-302 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Reed, P. W., and G. M. Bokoch, 1982. Cardiovascular and renal effects of A23187 and monovalent polyether antibiotics. Pages 369-395 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Ruff, M. D., 1982. Veterinary applications. Pages 303-332 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. SAS Institute, 1988. SAS/STAT® User's Guide: Version 6. Fourth Edition. Vol. 1. SAS Institute Inc., Cary, NC. Sturkie, P. D., and J. A. Vogel, 1959. Cardiac output, central blood volume, and peripheral resistance in chickens. Am. J. Physiol. 197:1165-1166. Sullivan, T. W., 1994. Skeletal problems in poultry: estimated annual cost and descriptions. Poultry Sci. 73:879-882. Wagner, D. D., R. D. Furrow, and B. D. Bradley, 1983. Subchronic toxicity of monensin in broiler chickens. Vet. Pathol. 20:353-359. Weppelman, R. M., G. Olson, D. A. Smith, T. Tamas, and A. van Iderstine, 1977. Comparison of anticoccidial efficacy, resistance and tolerance of narasin, monensin and lasalocid in chicken battery trials. Poultry Sci. 56:1550-1559. Wideman, R. F., 1988. Ascites in poultry. Monsanto Nutr. Update 6:1-7. Wideman, R. F., and W. G. Bottje, 1993. Current understanding of the ascites syndrome and future research directions. Pages 1-20 in: Nutrition and Technical Symposium Proceedings. Novus International, Inc., St. Louis, MO. Wideman, R. F., and Y. K. Kirby, 1995. A pulmonary artery clamp model for inducing pulmonary hypertension syndrome (Ascites) in broilers. Poultry Sci. 74:805-812.
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trophy, right ventricular failure and ascites in broiler chickens. Avian Pathol. 16:61-71. Julian, R. J., 1987b. Are we growing them too fast? Ascites in meat-type chickens. Highlights Agric. Res. Ontario 10:27-30. Julian, R. J., 1993. Ascites in poultry. Avian Pathol. 22:419-454. Leeson, S., and J. D. Summers, 1988. Some nutritional implications of leg problems with poultry. Br. Vet. J. 144:81-92. McDougald, L. R., and T. E. McQuiston, 1980. Compensatory growth in broilers after withdrawal of ionophorous anticoccidial drugs. Poultry Sci. 59:1001-1005. Metzler, M. J., W. M. Britton, and L. R. McDougald, 1987. Effects of monensin feeding and withdrawal time on growth and carcass composition in broiler chickens. Poultry Sci. 66:1451-1458. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC. Naylor, W. G., 1967. Calcium exchange in cardiac muscle: A basic mechanism of drug action. Am. Heart J. 73:379-393. Osborne, M. W., J. Wenger, F. Kovzelove, R. Boyd, and M. Zanko, 1982. Effects of lasalocid and monensin on chickens. Pages 333-340 in: Polyether Antibiotics, Naturally Occurring Acid Ionophores. Vol. 1, Biology. J. W. Westley, ed. Marcel Dekker, New York, NY. Owen, R. L., R. F. Wideman, A. L. Hattel, and B. S. Cowen, 1990. Use of a hypobaric chamber as a model system for investigating ascites in broilers. Avian Dis. 34:754-758. Peacock, A. J., C. Pickett, K. Morris, and J. T. Reeves, 1990. Spontaneous hypoxaemia and right ventricular hypertrophy in fast-growing broiler chickens reared at sea level. Comp. Biochem. Physiol. 97A:537-541. Pressman, B. C, 1973. Properties of ionophores with broad range cation selectivity. Fed. Proc. 32: 1698-1703. Pressman, B. C, and M. Fahim, 1982. Pharmacology and toxicology of the monovalent carboxylic ionophores. Annu. Rev. Pharmacol. Toxicol. 22: 465-490.