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Effects of Dietary Potassium Supplementation for Growing Turkeys on Leg Weakness, Plasma Potassium Concentration, and Selected Blood Variables1
METABOLISM AND NUTRITION Effects of Dietary Potassium Supplementation for Growing Turkeys on Leg Weakness, Plasma Potassium Concentration, and Selected Blood Variables1 W. O. Reece,*,2 J. L. Sell,† D. W. Trampel,‡ and W. F. Christensen§,3 *Department of Biomedical Sciences, College of Veterinary Medicine, †Department of Animal Science, College of Agriculture, ‡Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, and §Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, Iowa 50011 By 12 wk, toms fed the High K diets weighed less (P = 0.018) than toms fed the control diets, and this difference was still evident at 18 wk (P = 0.013), even though the High K groups were changed to the control diets at 12 wk. Toms fed the Mod K diets also tended to weigh less at 16 and 18 wk than those fed the control diets, however, the diet effect at the latter time was not significant (P > 0.05). There were no consistent effects of dietary K on feed efficiency. Total incidence of leg weakness at 12 wk was greater (P = 0.015) among toms fed Mod K and High K diets than for those toms fed the control diets. These results show that dietary K concentrations greater than those usually present in corn-soybean meal based diets for growing turkeys should be avoided. Increases in dietary K concentrations were associated with increases in plasma K concentration. Storage of blood after sampling and before centrifugation decreases the plasma concentration of K. The decrease is minimized when ambient temperature of storage is decreased. Accordingly, blood should be centrifuged immediately after sampling for accurate measurement of plasma K concentration. Plasma creatine kinase activity is not a good indicator of associated leg weakness unless physical activity and stress can be controlled before blood sampling.
(Key words: dietary potassium, plasma potassium, leg weakness, blood sampling, creatine kinase) 2000 Poultry Science 79:1120–1126
INTRODUCTION Rapidly growing animals have a relatively high K requirement, and increase of the dietary protein level increases that requirement (Hays and Swenson, 1993). Ac-
Received for publication May 28, 1999. Accepted for publication March 22, 2000. 1 Supported by the Iowa Livestock Health Advisory Council. 2 To whom correspondence should be addressed: [email protected]. 3 Current address: Statistical Science Department, Southern Methodist University, Dallas, TX 75275-0332.
cordingly, NRC requirements (NRC, 1994) for turkeys range from 0.7 to 0.4% (start to finish) of the diet. As a major cation in intracellular fluid, K has an essential role in the maintenance of membrane potential and cellular fluid balance. Clinical signs of K deficiency in avian species are overall muscle weakness, characterized by weak extremities; poor intestinal tone with distention; cardiac weakness; and weakness of the respiratory muscles (Austic and Scott, 1997). Our interest in K relates
Abbreviation Key: CK = creatine kinase; High K = corn-soybean meal diets supplemented with 50% more K than the control diets; Mod K = corn-soybean meal diets supplemented with 25% more K than the control diets; PCV = packed cell volume; [PP] = plasma protein.
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ABSTRACT The objectives of this research were to observe the effects of increased K in the diets of growing tom turkeys from 6 to 18 wk of age on body weight, feedto-gain ratio, and leg weakness; to study the effects of time and temperature of blood storage after sampling and before centrifugation on plasma K concentration; and to evaluate plasma creatine kinase activity as an indicator of leg weakness. Male Nicholas White turkeys were fed corn-soybean meal based starter and grower diets from 1 d to 6 wk of age. At this time, each of three dietary treatments was assigned randomly to three pens of toms, 30 toms per pen. The dietary treatments consisted of 1) corn-soybean meal control (control) diets, 2) corn-soybean meal diets supplemented with 25% more K than the control diets contained (Mod K), and 3) corn-soybean meal diets supplemented with 50% more K than the control diets (High K). Potassium carbonate was used as the source of supplemental K for the Mod K and High K diets. Calculated K concentrations of the control diets fed from 6 to 9, 9 to 12, 12 to 15, and 15 to 18 wk were 0.84, 0.74, 0.57, and 0.54%, respectively. Results of laboratory analysis of the diets agreed closely with the calculated values.
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EFFECTS OF INCREASING DIETARY POTASSIUM
MATERIALS AND METHODS Thirty male Nicholas White turkeys obtained at 1 d of age from a commercial hatchery were placed in each of nine floor pens. The pens were equipped for brooding and rearing the turkeys, with a floor space allowance of approximately 0.3 m2 per tom. Continuous lighting was applied until birds were marketed. All toms were fed the same corn-soybean meal based starter and grower diets from 1 d to 6 wk of age. The dietary ingredients (corn, soybean meal, and feather meal) and the percentage of K and Na in each are shown in Table 1. The K concentration for the control diets was provided by the feed ingredients. The ingredient composition of the control diets was similar to those used in the turkey industry. Ingredient composition of the control diet fed from 6 to 9 wk is
TABLE 1. Diet ingredients and the percentage of K and Na in each Percentage Ingredients
Age when used (wk)
K
Na
Corn, batch 1 Corn, batch 2 Corn, batch 3 Soymeal, batch 1 Soymeal, batch 2 Feather meal
6 9 18 6 18
0.30 0.30 0.35 2.07 2.10 0.11
0.0035 0.0036 0.0073 0.032 0.0026 0.18
to to to to to
9 18 20 18 20
shown in Table 2. Control diets fed from 9 to 12, 12 to 16, and 16 to 18 wk differed only in the proportions of corn, soybean meal, methionine, and Ca-P sources that were necessary to achieve desired nutrient concentrations. Starting when toms were 6-wk-old, three dietary treatments, which differed in K concentration, were assigned randomly to three pens of toms. The three treatments and the K concentration present in the diet for each treatment at each age period are shown in Table 3. Six diet changes were made from starter through finisher. Moderately high K (Mod K) and high K (High K) diets were calculated to contain K concentrations that were 25 and 50% higher, respectively, than the control diets. So that all other dietary components and nutrient concentrations remained the same among treatments, the K increase
TABLE 2. Composition of the control diet fed to turkeys from 6 to 9 wk of age Ingredients and analysis Corn Soybean meal Feather meal Animal-vegetable fat Dicalcium phosphate Limestone Vitamin premix1 Mineral premix2 DL-methionine L-lysine HCl Sodium chloride BMD威,3 Solka Flock威,4 Calculated Analysis: MEn, kcal/kg Protein Total sulfur amino acids Methionine Lysine Ca Nonphytate P Na Cl K
(%) 50.837 35.490 4.000 4.540 1.940 1.420 0.300 0.300 0.096 0.236 0.076 0.025 0.740 3,050 24.00 0.90 0.45 1.45 1.10 0.50 0.14 0.23 0.84
1 Vitamin premix supplied per kilogram of diet: vitamin A (retinyl acetate), 8,065 IU; cholecalciferol, 1,580 IU; vitamin E (dl-α-tocopheryl acetate), 15 IU; vitamin B12, 16 µg; vitamin K (menadione sodium bisulfite), 1.98 mg; riboflavin, 7.8 mg; pantothenic acid, 12.8 mg; niacin, 75 mg; choline, 509 mg; folic acid, 1.62 mg; biotin, 270 µg. 2 Mineral premix supplied per kilogram of diet: Mn, 70 mg; Zn, 40 mg; Fe, 37 mg; Cu, 6 mg; Se, 0.15 mg; and NaCl, 2.6 g. 3 Bacitracin methylene disalicylate, A. L. Pharma, Inc., Fort Lee, NJ 07024. 4 Brown Co., Berlin, NH 03570.
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to its function in nerve impulse transmission, wherein hypokalemia causes hyperpolarization of nerve fibers, and greater stimuli are needed to depolarize and establish nerve impulses and subsequent muscle contractions. A first objective of this research was to study the effects of dietary K supplementation as a means of preventing hypokalemia and the leg weakness syndrome in turkeys and to study the effects of increased K in the diets on weight gain and feed-to-gain ratios. This objective was based upon a pilot study (W. Reece, unpublished data) with growing turkeys that indicated the presence of hypokalemia. Also, we were concerned that our observation of hypokalemia in the pilot study may have been misleading, in that serum was harvested from blood instead of plasma, and considerable delay was often encountered for blood coagulation. Work by others with pigeon and chicken blood demonstrated that a time delay between sampling and separation of cells from plasma resulted in a significant decrease in plasma potassium ion concentration [K+] (Lumeij, 1985). Therefore, a second objective was to establish true values for plasma [K+] by noting the effect of delaying the separation of cells and plasma following blood collection. Muscle weakness is the principal clinical sign of neuromuscular disorders, and the most widely used plasma enzyme determination in neuromuscular diseases of domestic animals is that for creatine kinase (CK) (Cardinet, 1997). Accordingly, a third objective was to determine the status of plasma CK activity associated with observed muscle weakness. Reluctance to move, a clinical sign of leg weakness, can be associated with the fatigue of anemia. Reduced activity deminishes erythropoiesis and results in a functional anemia. Assessment of the erythrocyte status by determining the packed cell volume (PCV) was the fourth objective. Finally, in addition to PCV, CK activity, and [K+], determinations for plasma protein concentration ([PP]), sodium ion concentration [Na+], and chloride ion concentration [Cl−] comprised a fifth objective of establishing reference values for these variables in growing turkeys, in that this information appears to be virtually nonexistent in the literature.
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REECE ET AL. TABLE 3. Calculated and analyzed K concentration of diets of tom turkeys Age in Weeks 0 to 3
3 to 6
6 to 9
Diet
C1
LA2
C
LA
C
Control Mod K3 High K4
1.03 1.03 1.03
1.10 1.10 1.10
0.92 0.92 0.92
0.96 0.96 0.96
0.84 1.05 1.26
9 to 12
LA
C
LA
12 to 16
16 to 18
C
LA
C
LA
0.57 0.71 0.57
0.62 0.76 0.62
0.54 0.68 0.54
0.57 0.65 0.57
(% dietary potassium) 0.88 1.09 1.28
0.74 0.92 1.11
0.86 0.94 1.14
C = calculated analysis on basis of National Research Council (1994) data. LA = results of analysis by a commercial laboratory. 3 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 4 High K = high K concentration, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed. 1 2
4
Brown Co., Berlin, NH 03570. CN Laboratories, Courtland, MN 56021. 6 Goldberg refractometer (TS meter), Cambridge Instruments, Inc., Buffalo, NY 14215. 7 Microhematocrit method. 8 Abbott Spectrum威 electrolyte method, Abbott Laboratories, USA, Diagnostics Division, Abbott Park, IL 60064. 9 Abbott Spectrum CK-NAC威 reagent, Abbott Laboratories, USA, Diagnostics Division, Abbott Park, IL 60064. 5
one. Appropriate dilutions were made when CK activity exceeded 2,000 IU/L. At 12 wk of age, clinical signs of leg weakness were noticeable, and the turkeys in each pen were evaluated by unbiased evaluators for their ability to walk and were scored as either mild, moderate, or severe. A mild score was characterized by a slight impairment and reluctance to walk, a moderate score was characterized by a marked reluctance to walk and an impaired gait, and a severe score was characterized by a crippled bird that walked with much difficulty or not at all. Feed consumption for each pen of turkeys was recorded throughout the experiment, and turkey weights were obtained at 3-wk intervals beginning at 3 wk of age and extending through the 18-wk feeding period (4-wk interval between 12 and 16 wk). These data were used to calculate a feed-to-gain ratio. Weight gain, feed-to-gain ratio, and leg weakness data were analyzed with the general linear models procedure of the Statistical Analysis System (SAS Institute, 1985) to determine the effects of dietary K concentration. Tukey’s test was used to detect differences among treatment means when dietary K effects were significant (P ≤ 0.05). Analysis of variance was performed to determine the significance of dietary K concentration, week, and diet by week interaction for each of the plasma variables ([K+], [Na+], [Cl−], CK activity, [PP]), and PCV. For these variables, type III sums of squares was used for all F-tests.
TABLE 4. Na and Cl concentrations (%) in diets of tom turkeys Na
Cl
Age period, wk
C
LA
C
0 to 3 3 to 6 6 to 9 9 to 12 12 to 16 16 to 18
0.145 0.144 0.143 0.143 0.142 0.141
0.13 0.15 0.14 0.15 0.13 0.13
0.227 0.225 0.225 0.224 0.223 0.222
1
2
C = calculated analysis on basis of NRC (1994) data. LA = results of analysis by a commercial laboratory.
1 2
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in the Mod K and High K diets was provided by the addition of K2CO3 in place of an equal weight of Solka Floc.威,4 The K concentration in the diets was formulated according to average values present within the various feed ingredients and according to the amount of K2CO3 added. To verify the actual amounts present (those shown in Table 3), samples representing each of the time-period diets within each treatment (six time-period diets × three treatments = 18 samples + 9 for duplicate checks = 27 samples) were submitted to a commercial analytical laboratory.5 The Na and Cl concentrations in the diets are shown for each age in Table 4. Because of inappetence, poor weight gain, and watery feces, it was apparent at 12 wk of age that the turkeys on the High K diet would not be able to tolerate a continuation of this treatment to 18 wk, and they were moved to the control diet at this time. Blood was sampled between 0900 and 1100 h biweekly from the ulnar vein beginning at 8 wk (2 wk after start of treatments) from five randomly selected turkeys in each pen; thus, each treatment was represented by 15 samples. Two 5-mL blood samples (lithium heparin anticoagulant) were obtained from each of the five turkeys. Time of collection was noted, and one of these samples (sample one) was centrifuged immediately. Sample two was used for the determination of [PP]6 and PCV7 soon after its collection and before centrifugation at 2 h. Samples were processed in an unheated location in the turkey house. The ambient temperatures for the 12-, 14-, 16-, and 18-wk collections were recorded. On the same day as blood collection, [K+], [Na+], and [Cl−] were determined8 for plasma harvested from samples one and two, and analysis for CK activity9 was performed only for sample
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EFFECTS OF INCREASING DIETARY POTASSIUM TABLE 5. Influence of dietary K concentration on the incidence of leg weakness in 12-wk-old tom turkeys Incidence of leg weakness, %1 Diet
Mild
Control Mod K2 High K3 SEM Diet effect4 P-value
Moderate
Severe
Total
4.8 9.2a 9.6a 0.8
0.4 2.8 2.8 1.5
15.0b 23.1a 25.0a 3.1
0.001
0.068
b
9.8 11.1 12.6 2.2 0.370
0.015
a,b
RESULTS AND DISCUSSION Leg weakness evaluation was completed at 12 wk of age because the High K diet was discontinued at this time and because leg weakness was noticeable. The results of this evaluation are presented in Table 5. Although leg weakness was present among turkeys fed any of the three diets, there was a significantly greater incidence for those showing moderate (P = 0.001) and severe (P = 0.068) weakness among those consuming the Mod K and High K diets. There was no significant difference among diets for those turkeys showing mild leg weakness. There were indications that feeding the High K diet from 6 to 9 wk of age adversely affected 9-wk body weight of the turkeys (Table 6). By 12 wk, weights of turkeys fed the High K diets were less than those of turkeys fed the control diets. Although turkeys fed the High K diets from 6 to 12 wk were changed to the control diets, toms previously fed the High K diets were considerably lighter at 18 wk than those continuously fed the control diets. Feeding the Mod K diets from 6 wk onward also seemed to decrease body weights of toms at 16 and 18 wk, al-
TABLE 6. Influence of increased dietary K on body weight and feed-to-gain ratios of tom turkeys Body weight, kg/tom
Feed-to-gain ratio
Diet
31
6
9
12
16
18
3
6
9
12
16
18
Cumulative
Control Mod K2 High K3 SEM Diet effect P-value
0.56 0.56 0.55 0.007
2.23 2.21 2.18 0.040
4.63ab 4.69a 4.57b 0.020
8.08a 7.85ab 7.57b 0.090
12.10a 11.68b 11.18c 0.110
13.50a 12.98ab 12.39b 0.180
1.52 1.50 1.57 0.050
1.62 1.61 1.61 0.020
2.06 2.06 2.11 0.030
2.57b 2.61b 2.75a 0.020
3.70 3.78 3.72 0.040
5.12 4.83 5.31 0.240
2.90 2.94 2.91 0.020
0.580
0.640
0.030
0.018
0.004
0.013
0.620
0.970
0.580
0.002
0.810
0.410
0.680
Means within a column with no common superscript letters differ significantly (P ≤ 0.05). Numerical values in row indicate age in weeks. 2 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 3 High K = high concentration of K, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed. a,b 1
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Percentage values within a column with no common superscript letters differ significantly (P ≤ 0.05). 1 Leg weakness was evaluated on the ability of toms to walk. Mild = slight impairment and reluctance to walk, Moderate = an obvious reluctance to walk and an impaired gait, and Severe = an obviously crippled tom that walked with much difficulty or not at all. 2 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 3 High K = high K concentration, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed to this group. 4 Arcsin transformations of data were done before statistical analysis.
though the diet effect at the latter time was not significant (P > 0.05). There were no effects of dietary K noted for feed-to-gain ratios except for the 9- to 12-wk period. In this instance, the feed-to-gain ratio of toms fed High K was poorer than that of toms fed control and Mod K diets. There was no effect of dietary K concentration on mortality. Little information is available on the effects of relatively high dietary concentrations of K on performance of turkeys. Research with 1- to 4-wk-old turkeys showed that feeding diets containing 1.3 or 1.7% K decreased weight gain (Smith et al., 1973). Chavez and Kratzer (1973) reported that weight gains and livability were adversely affected when a turkey starter diet contained 1.25% K. In the current study, the Mod K and High K diets fed from 6 to 9 wk contained 1.09 and 1.28% K, respectively. Although body weight was not adversely affected by these dietary levels of K from 6 to 9 wk, there was a trend toward decreased body weights as the experiment progressed for toms fed the Mod K diet to 18 wk (as noted above) and for toms fed the High K diet from 6 to 12 wk. These observations, together with an increased incidence of leg weakness among toms fed the Mod K and High K diets, indicate that dietary K concentrations greater than those usually present in corn-soybean meal based diets for growing turkeys should be avoided. In that K concentrations in the control diets ranged from 1.10 to 0.57% (start to finish; Table 3), in contrast to NRC requirements of 0.7 to 0.4%, there is a potential for some turkeys to develop hyperkalemia either from diminished renal excretion or excessive diffusion from cells to the extracellular fluid. Decreased renal elimination can result from acute renal failure and hypoadrenocorticism. Excessive diffusion of K from the intracellular to the extracellular compartment can be caused by metabolic acidosis or the rapid release of K from tissues following injury or acute catabolic states. The main clinical signs of the resulting hyperkalemia include weakness, muscle twitching, and characteristic cardiac arrhythmias that ultimately lead to ventricular asystole or to fibrillation (The Merck Veterinary Manual, 1991). Cardiomyopathies are frequently observed in growing turkeys, and, perhaps, hyperkalemia as a contributing cause should be investigated.
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REECE ET AL. TABLE 7. Comparison of plasma concentrations of K+, Na+, and Cl− of tom turkeys as determined when plasma was separated from cells immediately after blood collection or when separation was delayed 2 h Plasma concentration (mEq/L) +
Time from sampling Immediate 2-h delay Time effect P-value
Na+
K x 1
4.75 3.86
Cl−
SEM
x
SEM
x
SEM
0.032 0.031
154.3 154.5
0.162 0.161
118.0 116.6
0.138 0.126
<0.0001
<0.0001
0.0135
n = 270 for both immediate and 2-h delay sampling and includes all samples from birds on control, moderately high, and high K concentration diets for Weeks 8 through 18. 1
For both control and Mod K diets, plasma [K+] decreased from 5.09 and 5.23 mEq/L, respectively, at 8 wk to 4.47 and 4.66 mEq/L, respectively, at 18 wk. A similar decrease with age was not shown in the study by Vasicek et al. (1991), and values for toms tended to increase from 5.1 mEq/L at 53 d to 5.9 mEq/L at 131 d. Creatine kinase activity of healthy turkeys is comparable with that of chickens and is substantially higher than that of many mammals (Tripp and Schmitz, 1982). Also, it was found that plasma CK activity in healthy turkeys is extremely sensitive to physical activity and stress, and high values persist for an extended time beyond the physical activity and stress. However, in that study, elevations from baseline CK values were not apparent immediately after exertion but were apparent at 4 h postexercise that persisted for 29 h (study end-point). Therefore, the values shown in Table 9 should not have been influenced by the capture and restraint associated with our blood sampling because the sampling occurred simultaneously with capture and restraint. However, the physical activity and stress of weighing individual birds would also elevate CK activity that may persist. The highest values shown (Weeks 12, 16, and 18) do reflect increases associated with weighing that occurred prior to blood sampling during the same week. Blood samplings at Weeks 8, 10, and 14 were separated from weighing by 2, 1, and 2 wk, respectively, so that more time was permitted for return to baseline values. Even though our first notice of high values for CK activity seemed to coincide with noticeable leg weakness, no valid conclusions can be made because
TABLE 8. Effect of ambient temperature on stored blood,1 when coupled with a 2-h delay before separation of plasma from cells, on plasma concentrations of K+, Na+, and Cl− of tom turkeys Change in plasma concentration2,3 (mEq/L) K+
Na+
Cl−
Ambient temperature (C)
x
SEM
x
SEM
x
SEM
21 16.5 14.5 8.9
−1.30 −0.51 −0.43 −0.27
0.048 0.047 0.036 0.032
+0.07 +0.04 +1.02 −0.73
0.136 0.135 0.124 0.364
−1.71 −0.80 −0.43 −2.60
0.104 0.144 0.105 0.199
n = 45 for values within each recorded ambient temperature. Temperature effect, P < 0.0001 for all three variables. 3 Change represents the difference between the values determined 2 h after sampling from the value determined at the time of sampling. 1 2
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The comparison of plasma [K+] between samples of which plasma was separated from cells immediately after collection with those of which separation was delayed 2 h is shown in Table 7. There was a significant decrease in [K+] when separation was delayed (P < 0.0001). This result supports our assertion that our previous observation of hypokalemia in the pilot study, based on plasma [K+], was misleading. What appeared to be hypokalemia was most likely associated with a delay in separation of serum from cells. Also shown are values for [Na+] and [Cl−] that suggest ionic shifts associated with the [K+] decrease in plasma and its transport to the intracellular compartment. The effect of ambient temperature on blood storage before centrifugation and subsequent [K+] analysis is shown in Table 8. With ambient temperature decrease, plasma [K+] decrease was less (P < 0.0001), and the effect of the 2-h sample storage before centrifugation was less noticeable. The value for K+ at the 2-h delay (3.86 mEq/ L) in Table 7 does not account for the ambient temperature differences and would have been lower if ambient temperatures had not decreased. The effect of adding potassium to the diets on the plasma [K+] and CK activity is shown in Table 9. Whereas plasma [K+] is significantly increased (P < 0.0001) when dietary K is increased, no diet effect is noted for CK activity (P = 0.8189). An abrupt increase is noted, however, in plasma CK activity when turkeys were 12 wk of age in both the control and Mod K groups, and, with the exception of Week 14, the increase persisted to 18 wk.
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EFFECTS OF INCREASING DIETARY POTASSIUM + 2
1
TABLE 9. Effects of diet and age at sampling on the means for plasma [K ] and creatine kinase (CK) activity2 for the control and Mod K3 diets in tom turkeys from 8 through 18 wk Plasma concentration or activity +
K (meq/L)
CK (IU/L)
4
Diet4
Diet Control 5
Week
Mod K
SEM
8 10 12 14 16 18
5.09 5.06 4.42 4.21 4.43 4.47
0.070 0.113 0.074 0.057 0.069 0.051
Control
SEM 5.23 5.49 4.72 4.47 4.53 4.66
Mod K
SEM
0.082 0.133 0.090 0.120 0.090 0.096
1129 2465 10126 5129 11519 18020
73.7 365.3 2827.0 433.2 1159.6 3396.2
SEM 1170 2202 9730 5569 10990 13831
102.0 141.3 2384.3 664.2 1251.2 1675.2
n = 15 for each diet within a week. Values from samples where plasma separated immediately from cells after collection. 3 Mod K = moderately high potassium concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 4 Overall diet effect for K+, P < 0.0001; overall diet effect for CK, P = 0.8189. 5 Week effect for K+, P < 0.0001; week effect for CK, P < 0.0001. 1 2
16, 18) is shown in Table 10. With the exception of [K+], diet differences for these values were not significant, and the means shown represent turkeys from control and Mod K diets. Although value differences are apparent among the weeks, an overall x with its SEM and minimum and maximum values are meaningful for purposes of orientation.
ACKNOWLEDGMENTS The authors are grateful for the assistance of Arthur Anderson and Donald (Bud) Maakestad (both are presently retired; Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011) with blood sampling and processing, Debora Hoyt (Clinical Pathology Laboratory, Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011) for the clinical chemistry analyses, and Vern Hoyt (Department of Biomedical Sciences, College of Veterinary
TABLE 10. Mean values for plasma concentrations1 of Na+, K+, Cl−, plasma protein ([PP]),2 creatine kinase (CK) activity, and packed cell volume (PCV)2 at biweekly intervals beginning at 8 wk and overall for the period for tom turkeys Week Variable + 3
[Na ], mEq/L [K+],4 mEq/L [Cl−],3 mEq/L CK,3 IU/L [PP],3 g/dl PCV,3 % 1
8
10
12
14
16
18
Week effect P-value
Diet effect P-value
Overall x ± SEM
151.7 5.09 116.5 1,149 3.60 31.9
152.7 5.06 116.8 2,333 3.75 32.4
155.9 4.42 118.7 9,928 3.85 34.0
154.2 4.21 117.6 5,349 3.90 33.1
153.4 4.43 117.6 11,254 3.76 33.0
157.1 4.47 120.2 15,926 3.41 35.1
<0.0001 <0.0001 <0.0001 <0.0001 0.0004 0.0020
0.4882 <0.0001 0.2334 0.8189 0.4603 0.3270
154.2 4.61 117.9 7,657 3.71 33.3
± ± ± ± ± ±
0.20 0.05 0.17 602 0.03 0.19
Minimum
Maximum
149.0 3.8 113.0 569 2.8 27.0
161.0 5.9 123.0 63,940 5.5 41.0
Plasma separated from cells immediately after sampling. Plasma protein concentration and PCV determined from the hematocrit of a second sample immediately after sampling. 3 n = 30 and 180 for mean of each week and overall, respectively, and combined turkeys on the control and moderately high K concentration diets because of no significant diet effect. 4 n = 15 and 90 for mean of each week and overall, respectively, and included only turkeys from the control diets because of diet effect in which values for moderately high K concentration diets were higher. 2
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we lacked control of the physical activity and stress (same week weighing preceding sampling). An age relationship for the CK activity increases cannot be ruled out. Wilson et al. (1990) studied four lines of turkeys, representing two commercial breeders, that included one unimproved, primitive line. At 13 to 16 wk of age, three of the selected lines had significantly higher CK activities than the unimproved line, a reflection of the positive correlation between body weight and CK activity, wherein turkeys with greater body weights had higher CK levels. However, plasma CK activity was positively correlated with age within only one of the four lines (female; selected for reproductive traits). The erythrocyte status as determined by PCV is shown in Table 10. Because [PP] was obtained from the plasma portion of the hematocrit, these values are also shown. There were no diet differences, and it appeared that anemia was not a factor in the leg weakness observed, as may be caused by fatigue. A display of mean values for plasma [Na+], [K+], [Cl− ], and [PP]; CK activity; and PCV by week (8, 10, 12, 14,
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REECE ET AL.
Medicine, Iowa State University, Ames, IA 50011) for typing the manuscript.
REFERENCES
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Austic, R. E., and M. L. Scott, 1997. Nutritional diseases. Pages 47−73 in: Diseases of Poultry. 10th ed. B. W. Calnek, H. J. Barnes, C. W. Beard, L. R. McDougal, and Y. M. Saif, ed. Iowa State University Press, Ames, IA. Cardinet, G. H. III, 1997. Skeletal muscle function. Pages 407−440 in: Clinical Biochemistry of Domestic Animals. 5th ed. J. J. Kaneko, J. W. Harvey, and M. L. Bruss, ed. Academic Press, San Diego, CA. Chavez, E., and F. H. Kratzer, 1973. The potassium requirement of poults. Poultry Sci. 52:1542−1544. Hays, V. W., and M. J. Swenson, 1993. Minerals. Pages 517−535 in: Dukes’ Physiology of Domestic Animals. 11th ed. M. J. Swenson and W. O. Reece, ed. Cornell University Press, Ithaca, NY. Lumeij, J. T., 1985. The influence of blood sample treatment on plasma potassium concentrations in avian blood. Avian Pathol. 14:257−260.
National Research Council, 1994. Nutrient Requirements of Poultry. 95th rev. ed. National Academy Press, Washington, DC. SAS Institute, 1985. SAS User’s Guide: Statistics Version 5 Edition. SAS Institute Inc., Cary, NC. Smith, J. D., W. H. Burke, and G. M. Speers, 1973. The response of starting turkeys to moderate differences in dietary potassium concentration. Poultry Sci. 52:1344−1348. The Merck Veterinary Manual, 1991. Fluid therapy (hyperkalemia). 7th ed. C. M. Fraser, ed. Merck & Co., Inc., Rahway, NJ. Tripp, M. J., and J. A. Schmitz, 1982. Influence of physiological exercise on plasma creatine kinase activity in healthy and dystrophic turkeys and sheep. Am. J. Vet. Res. 43:2220−2223. Vasicek, V. L., I. Schwendenwein, and S. Voill, 1991. Chemische blutuntersuchung zur erstellung von richtwerten bei mastputen verschiedenen alters. Dtch. Tieraerztl. Wochenschr. 98:126−129. Wilson, B. W., P. S. Nieberg, R. J. Buhr, B. J. Kelly, and F. T. Schultz, 1990. Turkey muscle growth and focal myopathy. Poultry Sci. 69:1553−1562.
(Key words: dietary potassium, plasma potassium, leg weakness, blood sampling, creatine kinase) 2000 Poultry Science 79:1120–1126
INTRODUCTION Rapidly growing animals have a relatively high K requirement, and increase of the dietary protein level increases that requirement (Hays and Swenson, 1993). Ac-
Received for publication May 28, 1999. Accepted for publication March 22, 2000. 1 Supported by the Iowa Livestock Health Advisory Council. 2 To whom correspondence should be addressed: [email protected]. 3 Current address: Statistical Science Department, Southern Methodist University, Dallas, TX 75275-0332.
cordingly, NRC requirements (NRC, 1994) for turkeys range from 0.7 to 0.4% (start to finish) of the diet. As a major cation in intracellular fluid, K has an essential role in the maintenance of membrane potential and cellular fluid balance. Clinical signs of K deficiency in avian species are overall muscle weakness, characterized by weak extremities; poor intestinal tone with distention; cardiac weakness; and weakness of the respiratory muscles (Austic and Scott, 1997). Our interest in K relates
Abbreviation Key: CK = creatine kinase; High K = corn-soybean meal diets supplemented with 50% more K than the control diets; Mod K = corn-soybean meal diets supplemented with 25% more K than the control diets; PCV = packed cell volume; [PP] = plasma protein.
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ABSTRACT The objectives of this research were to observe the effects of increased K in the diets of growing tom turkeys from 6 to 18 wk of age on body weight, feedto-gain ratio, and leg weakness; to study the effects of time and temperature of blood storage after sampling and before centrifugation on plasma K concentration; and to evaluate plasma creatine kinase activity as an indicator of leg weakness. Male Nicholas White turkeys were fed corn-soybean meal based starter and grower diets from 1 d to 6 wk of age. At this time, each of three dietary treatments was assigned randomly to three pens of toms, 30 toms per pen. The dietary treatments consisted of 1) corn-soybean meal control (control) diets, 2) corn-soybean meal diets supplemented with 25% more K than the control diets contained (Mod K), and 3) corn-soybean meal diets supplemented with 50% more K than the control diets (High K). Potassium carbonate was used as the source of supplemental K for the Mod K and High K diets. Calculated K concentrations of the control diets fed from 6 to 9, 9 to 12, 12 to 15, and 15 to 18 wk were 0.84, 0.74, 0.57, and 0.54%, respectively. Results of laboratory analysis of the diets agreed closely with the calculated values.
1121
EFFECTS OF INCREASING DIETARY POTASSIUM
MATERIALS AND METHODS Thirty male Nicholas White turkeys obtained at 1 d of age from a commercial hatchery were placed in each of nine floor pens. The pens were equipped for brooding and rearing the turkeys, with a floor space allowance of approximately 0.3 m2 per tom. Continuous lighting was applied until birds were marketed. All toms were fed the same corn-soybean meal based starter and grower diets from 1 d to 6 wk of age. The dietary ingredients (corn, soybean meal, and feather meal) and the percentage of K and Na in each are shown in Table 1. The K concentration for the control diets was provided by the feed ingredients. The ingredient composition of the control diets was similar to those used in the turkey industry. Ingredient composition of the control diet fed from 6 to 9 wk is
TABLE 1. Diet ingredients and the percentage of K and Na in each Percentage Ingredients
Age when used (wk)
K
Na
Corn, batch 1 Corn, batch 2 Corn, batch 3 Soymeal, batch 1 Soymeal, batch 2 Feather meal
6 9 18 6 18
0.30 0.30 0.35 2.07 2.10 0.11
0.0035 0.0036 0.0073 0.032 0.0026 0.18
to to to to to
9 18 20 18 20
shown in Table 2. Control diets fed from 9 to 12, 12 to 16, and 16 to 18 wk differed only in the proportions of corn, soybean meal, methionine, and Ca-P sources that were necessary to achieve desired nutrient concentrations. Starting when toms were 6-wk-old, three dietary treatments, which differed in K concentration, were assigned randomly to three pens of toms. The three treatments and the K concentration present in the diet for each treatment at each age period are shown in Table 3. Six diet changes were made from starter through finisher. Moderately high K (Mod K) and high K (High K) diets were calculated to contain K concentrations that were 25 and 50% higher, respectively, than the control diets. So that all other dietary components and nutrient concentrations remained the same among treatments, the K increase
TABLE 2. Composition of the control diet fed to turkeys from 6 to 9 wk of age Ingredients and analysis Corn Soybean meal Feather meal Animal-vegetable fat Dicalcium phosphate Limestone Vitamin premix1 Mineral premix2 DL-methionine L-lysine HCl Sodium chloride BMD威,3 Solka Flock威,4 Calculated Analysis: MEn, kcal/kg Protein Total sulfur amino acids Methionine Lysine Ca Nonphytate P Na Cl K
(%) 50.837 35.490 4.000 4.540 1.940 1.420 0.300 0.300 0.096 0.236 0.076 0.025 0.740 3,050 24.00 0.90 0.45 1.45 1.10 0.50 0.14 0.23 0.84
1 Vitamin premix supplied per kilogram of diet: vitamin A (retinyl acetate), 8,065 IU; cholecalciferol, 1,580 IU; vitamin E (dl-α-tocopheryl acetate), 15 IU; vitamin B12, 16 µg; vitamin K (menadione sodium bisulfite), 1.98 mg; riboflavin, 7.8 mg; pantothenic acid, 12.8 mg; niacin, 75 mg; choline, 509 mg; folic acid, 1.62 mg; biotin, 270 µg. 2 Mineral premix supplied per kilogram of diet: Mn, 70 mg; Zn, 40 mg; Fe, 37 mg; Cu, 6 mg; Se, 0.15 mg; and NaCl, 2.6 g. 3 Bacitracin methylene disalicylate, A. L. Pharma, Inc., Fort Lee, NJ 07024. 4 Brown Co., Berlin, NH 03570.
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to its function in nerve impulse transmission, wherein hypokalemia causes hyperpolarization of nerve fibers, and greater stimuli are needed to depolarize and establish nerve impulses and subsequent muscle contractions. A first objective of this research was to study the effects of dietary K supplementation as a means of preventing hypokalemia and the leg weakness syndrome in turkeys and to study the effects of increased K in the diets on weight gain and feed-to-gain ratios. This objective was based upon a pilot study (W. Reece, unpublished data) with growing turkeys that indicated the presence of hypokalemia. Also, we were concerned that our observation of hypokalemia in the pilot study may have been misleading, in that serum was harvested from blood instead of plasma, and considerable delay was often encountered for blood coagulation. Work by others with pigeon and chicken blood demonstrated that a time delay between sampling and separation of cells from plasma resulted in a significant decrease in plasma potassium ion concentration [K+] (Lumeij, 1985). Therefore, a second objective was to establish true values for plasma [K+] by noting the effect of delaying the separation of cells and plasma following blood collection. Muscle weakness is the principal clinical sign of neuromuscular disorders, and the most widely used plasma enzyme determination in neuromuscular diseases of domestic animals is that for creatine kinase (CK) (Cardinet, 1997). Accordingly, a third objective was to determine the status of plasma CK activity associated with observed muscle weakness. Reluctance to move, a clinical sign of leg weakness, can be associated with the fatigue of anemia. Reduced activity deminishes erythropoiesis and results in a functional anemia. Assessment of the erythrocyte status by determining the packed cell volume (PCV) was the fourth objective. Finally, in addition to PCV, CK activity, and [K+], determinations for plasma protein concentration ([PP]), sodium ion concentration [Na+], and chloride ion concentration [Cl−] comprised a fifth objective of establishing reference values for these variables in growing turkeys, in that this information appears to be virtually nonexistent in the literature.
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REECE ET AL. TABLE 3. Calculated and analyzed K concentration of diets of tom turkeys Age in Weeks 0 to 3
3 to 6
6 to 9
Diet
C1
LA2
C
LA
C
Control Mod K3 High K4
1.03 1.03 1.03
1.10 1.10 1.10
0.92 0.92 0.92
0.96 0.96 0.96
0.84 1.05 1.26
9 to 12
LA
C
LA
12 to 16
16 to 18
C
LA
C
LA
0.57 0.71 0.57
0.62 0.76 0.62
0.54 0.68 0.54
0.57 0.65 0.57
(% dietary potassium) 0.88 1.09 1.28
0.74 0.92 1.11
0.86 0.94 1.14
C = calculated analysis on basis of National Research Council (1994) data. LA = results of analysis by a commercial laboratory. 3 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 4 High K = high K concentration, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed. 1 2
4
Brown Co., Berlin, NH 03570. CN Laboratories, Courtland, MN 56021. 6 Goldberg refractometer (TS meter), Cambridge Instruments, Inc., Buffalo, NY 14215. 7 Microhematocrit method. 8 Abbott Spectrum威 electrolyte method, Abbott Laboratories, USA, Diagnostics Division, Abbott Park, IL 60064. 9 Abbott Spectrum CK-NAC威 reagent, Abbott Laboratories, USA, Diagnostics Division, Abbott Park, IL 60064. 5
one. Appropriate dilutions were made when CK activity exceeded 2,000 IU/L. At 12 wk of age, clinical signs of leg weakness were noticeable, and the turkeys in each pen were evaluated by unbiased evaluators for their ability to walk and were scored as either mild, moderate, or severe. A mild score was characterized by a slight impairment and reluctance to walk, a moderate score was characterized by a marked reluctance to walk and an impaired gait, and a severe score was characterized by a crippled bird that walked with much difficulty or not at all. Feed consumption for each pen of turkeys was recorded throughout the experiment, and turkey weights were obtained at 3-wk intervals beginning at 3 wk of age and extending through the 18-wk feeding period (4-wk interval between 12 and 16 wk). These data were used to calculate a feed-to-gain ratio. Weight gain, feed-to-gain ratio, and leg weakness data were analyzed with the general linear models procedure of the Statistical Analysis System (SAS Institute, 1985) to determine the effects of dietary K concentration. Tukey’s test was used to detect differences among treatment means when dietary K effects were significant (P ≤ 0.05). Analysis of variance was performed to determine the significance of dietary K concentration, week, and diet by week interaction for each of the plasma variables ([K+], [Na+], [Cl−], CK activity, [PP]), and PCV. For these variables, type III sums of squares was used for all F-tests.
TABLE 4. Na and Cl concentrations (%) in diets of tom turkeys Na
Cl
Age period, wk
C
LA
C
0 to 3 3 to 6 6 to 9 9 to 12 12 to 16 16 to 18
0.145 0.144 0.143 0.143 0.142 0.141
0.13 0.15 0.14 0.15 0.13 0.13
0.227 0.225 0.225 0.224 0.223 0.222
1
2
C = calculated analysis on basis of NRC (1994) data. LA = results of analysis by a commercial laboratory.
1 2
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in the Mod K and High K diets was provided by the addition of K2CO3 in place of an equal weight of Solka Floc.威,4 The K concentration in the diets was formulated according to average values present within the various feed ingredients and according to the amount of K2CO3 added. To verify the actual amounts present (those shown in Table 3), samples representing each of the time-period diets within each treatment (six time-period diets × three treatments = 18 samples + 9 for duplicate checks = 27 samples) were submitted to a commercial analytical laboratory.5 The Na and Cl concentrations in the diets are shown for each age in Table 4. Because of inappetence, poor weight gain, and watery feces, it was apparent at 12 wk of age that the turkeys on the High K diet would not be able to tolerate a continuation of this treatment to 18 wk, and they were moved to the control diet at this time. Blood was sampled between 0900 and 1100 h biweekly from the ulnar vein beginning at 8 wk (2 wk after start of treatments) from five randomly selected turkeys in each pen; thus, each treatment was represented by 15 samples. Two 5-mL blood samples (lithium heparin anticoagulant) were obtained from each of the five turkeys. Time of collection was noted, and one of these samples (sample one) was centrifuged immediately. Sample two was used for the determination of [PP]6 and PCV7 soon after its collection and before centrifugation at 2 h. Samples were processed in an unheated location in the turkey house. The ambient temperatures for the 12-, 14-, 16-, and 18-wk collections were recorded. On the same day as blood collection, [K+], [Na+], and [Cl−] were determined8 for plasma harvested from samples one and two, and analysis for CK activity9 was performed only for sample
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EFFECTS OF INCREASING DIETARY POTASSIUM TABLE 5. Influence of dietary K concentration on the incidence of leg weakness in 12-wk-old tom turkeys Incidence of leg weakness, %1 Diet
Mild
Control Mod K2 High K3 SEM Diet effect4 P-value
Moderate
Severe
Total
4.8 9.2a 9.6a 0.8
0.4 2.8 2.8 1.5
15.0b 23.1a 25.0a 3.1
0.001
0.068
b
9.8 11.1 12.6 2.2 0.370
0.015
a,b
RESULTS AND DISCUSSION Leg weakness evaluation was completed at 12 wk of age because the High K diet was discontinued at this time and because leg weakness was noticeable. The results of this evaluation are presented in Table 5. Although leg weakness was present among turkeys fed any of the three diets, there was a significantly greater incidence for those showing moderate (P = 0.001) and severe (P = 0.068) weakness among those consuming the Mod K and High K diets. There was no significant difference among diets for those turkeys showing mild leg weakness. There were indications that feeding the High K diet from 6 to 9 wk of age adversely affected 9-wk body weight of the turkeys (Table 6). By 12 wk, weights of turkeys fed the High K diets were less than those of turkeys fed the control diets. Although turkeys fed the High K diets from 6 to 12 wk were changed to the control diets, toms previously fed the High K diets were considerably lighter at 18 wk than those continuously fed the control diets. Feeding the Mod K diets from 6 wk onward also seemed to decrease body weights of toms at 16 and 18 wk, al-
TABLE 6. Influence of increased dietary K on body weight and feed-to-gain ratios of tom turkeys Body weight, kg/tom
Feed-to-gain ratio
Diet
31
6
9
12
16
18
3
6
9
12
16
18
Cumulative
Control Mod K2 High K3 SEM Diet effect P-value
0.56 0.56 0.55 0.007
2.23 2.21 2.18 0.040
4.63ab 4.69a 4.57b 0.020
8.08a 7.85ab 7.57b 0.090
12.10a 11.68b 11.18c 0.110
13.50a 12.98ab 12.39b 0.180
1.52 1.50 1.57 0.050
1.62 1.61 1.61 0.020
2.06 2.06 2.11 0.030
2.57b 2.61b 2.75a 0.020
3.70 3.78 3.72 0.040
5.12 4.83 5.31 0.240
2.90 2.94 2.91 0.020
0.580
0.640
0.030
0.018
0.004
0.013
0.620
0.970
0.580
0.002
0.810
0.410
0.680
Means within a column with no common superscript letters differ significantly (P ≤ 0.05). Numerical values in row indicate age in weeks. 2 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 3 High K = high concentration of K, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed. a,b 1
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Percentage values within a column with no common superscript letters differ significantly (P ≤ 0.05). 1 Leg weakness was evaluated on the ability of toms to walk. Mild = slight impairment and reluctance to walk, Moderate = an obvious reluctance to walk and an impaired gait, and Severe = an obviously crippled tom that walked with much difficulty or not at all. 2 Mod K = moderately high K concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 3 High K = high K concentration, and from 6 to 12 wk of age, this diet contained 50% more K than the control diet. From 12 to 18 wk, the control diet was fed to this group. 4 Arcsin transformations of data were done before statistical analysis.
though the diet effect at the latter time was not significant (P > 0.05). There were no effects of dietary K noted for feed-to-gain ratios except for the 9- to 12-wk period. In this instance, the feed-to-gain ratio of toms fed High K was poorer than that of toms fed control and Mod K diets. There was no effect of dietary K concentration on mortality. Little information is available on the effects of relatively high dietary concentrations of K on performance of turkeys. Research with 1- to 4-wk-old turkeys showed that feeding diets containing 1.3 or 1.7% K decreased weight gain (Smith et al., 1973). Chavez and Kratzer (1973) reported that weight gains and livability were adversely affected when a turkey starter diet contained 1.25% K. In the current study, the Mod K and High K diets fed from 6 to 9 wk contained 1.09 and 1.28% K, respectively. Although body weight was not adversely affected by these dietary levels of K from 6 to 9 wk, there was a trend toward decreased body weights as the experiment progressed for toms fed the Mod K diet to 18 wk (as noted above) and for toms fed the High K diet from 6 to 12 wk. These observations, together with an increased incidence of leg weakness among toms fed the Mod K and High K diets, indicate that dietary K concentrations greater than those usually present in corn-soybean meal based diets for growing turkeys should be avoided. In that K concentrations in the control diets ranged from 1.10 to 0.57% (start to finish; Table 3), in contrast to NRC requirements of 0.7 to 0.4%, there is a potential for some turkeys to develop hyperkalemia either from diminished renal excretion or excessive diffusion from cells to the extracellular fluid. Decreased renal elimination can result from acute renal failure and hypoadrenocorticism. Excessive diffusion of K from the intracellular to the extracellular compartment can be caused by metabolic acidosis or the rapid release of K from tissues following injury or acute catabolic states. The main clinical signs of the resulting hyperkalemia include weakness, muscle twitching, and characteristic cardiac arrhythmias that ultimately lead to ventricular asystole or to fibrillation (The Merck Veterinary Manual, 1991). Cardiomyopathies are frequently observed in growing turkeys, and, perhaps, hyperkalemia as a contributing cause should be investigated.
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REECE ET AL. TABLE 7. Comparison of plasma concentrations of K+, Na+, and Cl− of tom turkeys as determined when plasma was separated from cells immediately after blood collection or when separation was delayed 2 h Plasma concentration (mEq/L) +
Time from sampling Immediate 2-h delay Time effect P-value
Na+
K x 1
4.75 3.86
Cl−
SEM
x
SEM
x
SEM
0.032 0.031
154.3 154.5
0.162 0.161
118.0 116.6
0.138 0.126
<0.0001
<0.0001
0.0135
n = 270 for both immediate and 2-h delay sampling and includes all samples from birds on control, moderately high, and high K concentration diets for Weeks 8 through 18. 1
For both control and Mod K diets, plasma [K+] decreased from 5.09 and 5.23 mEq/L, respectively, at 8 wk to 4.47 and 4.66 mEq/L, respectively, at 18 wk. A similar decrease with age was not shown in the study by Vasicek et al. (1991), and values for toms tended to increase from 5.1 mEq/L at 53 d to 5.9 mEq/L at 131 d. Creatine kinase activity of healthy turkeys is comparable with that of chickens and is substantially higher than that of many mammals (Tripp and Schmitz, 1982). Also, it was found that plasma CK activity in healthy turkeys is extremely sensitive to physical activity and stress, and high values persist for an extended time beyond the physical activity and stress. However, in that study, elevations from baseline CK values were not apparent immediately after exertion but were apparent at 4 h postexercise that persisted for 29 h (study end-point). Therefore, the values shown in Table 9 should not have been influenced by the capture and restraint associated with our blood sampling because the sampling occurred simultaneously with capture and restraint. However, the physical activity and stress of weighing individual birds would also elevate CK activity that may persist. The highest values shown (Weeks 12, 16, and 18) do reflect increases associated with weighing that occurred prior to blood sampling during the same week. Blood samplings at Weeks 8, 10, and 14 were separated from weighing by 2, 1, and 2 wk, respectively, so that more time was permitted for return to baseline values. Even though our first notice of high values for CK activity seemed to coincide with noticeable leg weakness, no valid conclusions can be made because
TABLE 8. Effect of ambient temperature on stored blood,1 when coupled with a 2-h delay before separation of plasma from cells, on plasma concentrations of K+, Na+, and Cl− of tom turkeys Change in plasma concentration2,3 (mEq/L) K+
Na+
Cl−
Ambient temperature (C)
x
SEM
x
SEM
x
SEM
21 16.5 14.5 8.9
−1.30 −0.51 −0.43 −0.27
0.048 0.047 0.036 0.032
+0.07 +0.04 +1.02 −0.73
0.136 0.135 0.124 0.364
−1.71 −0.80 −0.43 −2.60
0.104 0.144 0.105 0.199
n = 45 for values within each recorded ambient temperature. Temperature effect, P < 0.0001 for all three variables. 3 Change represents the difference between the values determined 2 h after sampling from the value determined at the time of sampling. 1 2
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The comparison of plasma [K+] between samples of which plasma was separated from cells immediately after collection with those of which separation was delayed 2 h is shown in Table 7. There was a significant decrease in [K+] when separation was delayed (P < 0.0001). This result supports our assertion that our previous observation of hypokalemia in the pilot study, based on plasma [K+], was misleading. What appeared to be hypokalemia was most likely associated with a delay in separation of serum from cells. Also shown are values for [Na+] and [Cl−] that suggest ionic shifts associated with the [K+] decrease in plasma and its transport to the intracellular compartment. The effect of ambient temperature on blood storage before centrifugation and subsequent [K+] analysis is shown in Table 8. With ambient temperature decrease, plasma [K+] decrease was less (P < 0.0001), and the effect of the 2-h sample storage before centrifugation was less noticeable. The value for K+ at the 2-h delay (3.86 mEq/ L) in Table 7 does not account for the ambient temperature differences and would have been lower if ambient temperatures had not decreased. The effect of adding potassium to the diets on the plasma [K+] and CK activity is shown in Table 9. Whereas plasma [K+] is significantly increased (P < 0.0001) when dietary K is increased, no diet effect is noted for CK activity (P = 0.8189). An abrupt increase is noted, however, in plasma CK activity when turkeys were 12 wk of age in both the control and Mod K groups, and, with the exception of Week 14, the increase persisted to 18 wk.
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EFFECTS OF INCREASING DIETARY POTASSIUM + 2
1
TABLE 9. Effects of diet and age at sampling on the means for plasma [K ] and creatine kinase (CK) activity2 for the control and Mod K3 diets in tom turkeys from 8 through 18 wk Plasma concentration or activity +
K (meq/L)
CK (IU/L)
4
Diet4
Diet Control 5
Week
Mod K
SEM
8 10 12 14 16 18
5.09 5.06 4.42 4.21 4.43 4.47
0.070 0.113 0.074 0.057 0.069 0.051
Control
SEM 5.23 5.49 4.72 4.47 4.53 4.66
Mod K
SEM
0.082 0.133 0.090 0.120 0.090 0.096
1129 2465 10126 5129 11519 18020
73.7 365.3 2827.0 433.2 1159.6 3396.2
SEM 1170 2202 9730 5569 10990 13831
102.0 141.3 2384.3 664.2 1251.2 1675.2
n = 15 for each diet within a week. Values from samples where plasma separated immediately from cells after collection. 3 Mod K = moderately high potassium concentration, and beginning at 6 wk of age, this diet contained 25% more K than the control diet. 4 Overall diet effect for K+, P < 0.0001; overall diet effect for CK, P = 0.8189. 5 Week effect for K+, P < 0.0001; week effect for CK, P < 0.0001. 1 2
16, 18) is shown in Table 10. With the exception of [K+], diet differences for these values were not significant, and the means shown represent turkeys from control and Mod K diets. Although value differences are apparent among the weeks, an overall x with its SEM and minimum and maximum values are meaningful for purposes of orientation.
ACKNOWLEDGMENTS The authors are grateful for the assistance of Arthur Anderson and Donald (Bud) Maakestad (both are presently retired; Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011) with blood sampling and processing, Debora Hoyt (Clinical Pathology Laboratory, Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011) for the clinical chemistry analyses, and Vern Hoyt (Department of Biomedical Sciences, College of Veterinary
TABLE 10. Mean values for plasma concentrations1 of Na+, K+, Cl−, plasma protein ([PP]),2 creatine kinase (CK) activity, and packed cell volume (PCV)2 at biweekly intervals beginning at 8 wk and overall for the period for tom turkeys Week Variable + 3
[Na ], mEq/L [K+],4 mEq/L [Cl−],3 mEq/L CK,3 IU/L [PP],3 g/dl PCV,3 % 1
8
10
12
14
16
18
Week effect P-value
Diet effect P-value
Overall x ± SEM
151.7 5.09 116.5 1,149 3.60 31.9
152.7 5.06 116.8 2,333 3.75 32.4
155.9 4.42 118.7 9,928 3.85 34.0
154.2 4.21 117.6 5,349 3.90 33.1
153.4 4.43 117.6 11,254 3.76 33.0
157.1 4.47 120.2 15,926 3.41 35.1
<0.0001 <0.0001 <0.0001 <0.0001 0.0004 0.0020
0.4882 <0.0001 0.2334 0.8189 0.4603 0.3270
154.2 4.61 117.9 7,657 3.71 33.3
± ± ± ± ± ±
0.20 0.05 0.17 602 0.03 0.19
Minimum
Maximum
149.0 3.8 113.0 569 2.8 27.0
161.0 5.9 123.0 63,940 5.5 41.0
Plasma separated from cells immediately after sampling. Plasma protein concentration and PCV determined from the hematocrit of a second sample immediately after sampling. 3 n = 30 and 180 for mean of each week and overall, respectively, and combined turkeys on the control and moderately high K concentration diets because of no significant diet effect. 4 n = 15 and 90 for mean of each week and overall, respectively, and included only turkeys from the control diets because of diet effect in which values for moderately high K concentration diets were higher. 2
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we lacked control of the physical activity and stress (same week weighing preceding sampling). An age relationship for the CK activity increases cannot be ruled out. Wilson et al. (1990) studied four lines of turkeys, representing two commercial breeders, that included one unimproved, primitive line. At 13 to 16 wk of age, three of the selected lines had significantly higher CK activities than the unimproved line, a reflection of the positive correlation between body weight and CK activity, wherein turkeys with greater body weights had higher CK levels. However, plasma CK activity was positively correlated with age within only one of the four lines (female; selected for reproductive traits). The erythrocyte status as determined by PCV is shown in Table 10. Because [PP] was obtained from the plasma portion of the hematocrit, these values are also shown. There were no diet differences, and it appeared that anemia was not a factor in the leg weakness observed, as may be caused by fatigue. A display of mean values for plasma [Na+], [K+], [Cl− ], and [PP]; CK activity; and PCV by week (8, 10, 12, 14,
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REECE ET AL.
Medicine, Iowa State University, Ames, IA 50011) for typing the manuscript.
REFERENCES
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Austic, R. E., and M. L. Scott, 1997. Nutritional diseases. Pages 47−73 in: Diseases of Poultry. 10th ed. B. W. Calnek, H. J. Barnes, C. W. Beard, L. R. McDougal, and Y. M. Saif, ed. Iowa State University Press, Ames, IA. Cardinet, G. H. III, 1997. Skeletal muscle function. Pages 407−440 in: Clinical Biochemistry of Domestic Animals. 5th ed. J. J. Kaneko, J. W. Harvey, and M. L. Bruss, ed. Academic Press, San Diego, CA. Chavez, E., and F. H. Kratzer, 1973. The potassium requirement of poults. Poultry Sci. 52:1542−1544. Hays, V. W., and M. J. Swenson, 1993. Minerals. Pages 517−535 in: Dukes’ Physiology of Domestic Animals. 11th ed. M. J. Swenson and W. O. Reece, ed. Cornell University Press, Ithaca, NY. Lumeij, J. T., 1985. The influence of blood sample treatment on plasma potassium concentrations in avian blood. Avian Pathol. 14:257−260.
National Research Council, 1994. Nutrient Requirements of Poultry. 95th rev. ed. National Academy Press, Washington, DC. SAS Institute, 1985. SAS User’s Guide: Statistics Version 5 Edition. SAS Institute Inc., Cary, NC. Smith, J. D., W. H. Burke, and G. M. Speers, 1973. The response of starting turkeys to moderate differences in dietary potassium concentration. Poultry Sci. 52:1344−1348. The Merck Veterinary Manual, 1991. Fluid therapy (hyperkalemia). 7th ed. C. M. Fraser, ed. Merck & Co., Inc., Rahway, NJ. Tripp, M. J., and J. A. Schmitz, 1982. Influence of physiological exercise on plasma creatine kinase activity in healthy and dystrophic turkeys and sheep. Am. J. Vet. Res. 43:2220−2223. Vasicek, V. L., I. Schwendenwein, and S. Voill, 1991. Chemische blutuntersuchung zur erstellung von richtwerten bei mastputen verschiedenen alters. Dtch. Tieraerztl. Wochenschr. 98:126−129. Wilson, B. W., P. S. Nieberg, R. J. Buhr, B. J. Kelly, and F. T. Schultz, 1990. Turkey muscle growth and focal myopathy. Poultry Sci. 69:1553−1562.