- Email: [email protected]
Effects of Dietary Zinc upon Tissue Zinc and Percent Unsaturated Plasma-Zinc Binding Capacity1
Effects of Dietary Zinc upon Tissue Zinc and Percent Unsaturated Plasma-Zinc Binding Capacity I R. L. K I N C A I D and J. D. C R O N R A T H Washington State University Putlman 99164
ABSTRACT
Calves were fed 520 ppm zinc for 21 days, then placed on a low zinc diet (20 ppm zinc) for 35 days to determine the biological availability of zinc reserves of tissue. Concentrations of zinc in liver and kidney were elevated greatly by feeding high dietary zinc for 21 days and continued to increase with time. On the low zinc diet, the tissue burden of zinc decreased within 35 days to those comparable to calves initially fed low zinc. Likewise, both zinc in plasma and percent capacity o f unsaturated plasma for binding zinc were near negative controls 21 days after removal of calves from high zinc diets. Tissue stores of zinc will not maintain adequate zinc in blood for extended periods, and hence, they probably will not sustain optimal feed intakes and growth rates of calves on lowintakes of zinc. INTRODUCTION
Zinc is a required trace element for domestic livestock, and signs of a zinc deficiency, such as reduced growth, impaired sexual development, and parakeratosis, are documented (16, 18, 19, 21). In a recent survey of forages grown in Washington, the average concentration of zinc was approximately 20 ppm, with a range of 14 ppm to 28 ppm (12). These concentrations are below the dietary requirement of 40 ppm zinc for dairy cattle (17). Thus, zinc is a potential, practical problem for ruminants grazing forages in Washington. One of the first signs of zinc deficiency in an animal is reduction of feed intake (5, 6). However, moderate feed reductions, which are
Received September 25, 1978. Scientific Paper No. 5200. College of Agriculture Research Center, Washington State University. Project No. 0408. 1979 J Dairy Sci 62:572-576
difficult to detect under field conditions, may be indicative of many disorders in cattle. Blood data are of limited usefulness in detecting marginal zinc deficiencies because of the wide fluctuations of zinc in plasma. Many factors can affect the concentration of zinc in blood besides the dietary zinc intake; among these are fasting, infections, and stresses (4, 15, 22, 23, 24). Zinc concentrations in hair sometimes are used as an indicator of the zinc state of an animal (2). However, concentrations of zinc in hair do not appear to be sensitive enough of dietary amount to be a suitable indicator of zinc status. Another problem is the concentration of zinc in hair tells past intakes of zinc rather than current intake. Recent work by Evans (8) indicates zinc is absorbed from the basolateral membrane of the intestinal tract by apotransferrin. Apparently, apotransferrin has specific binding sites on its molecule for zinc. In the portal system, transferrin transports zinc to the liver where zinc is transferred to albumin. However, some zinc undoubtedly remains associated with transferrin. Thus, the relative number of free binding sites on transferrin in peripheral blood may be an indicator of the nutritional zinc status of an animal. Zinc has accumulated in large amounts in tissues of calves in response to high zinc intakes (13). Apparently, this effect is specific to age and species, not occurring in rats, chicks, or cows (1, 13, 14). However, feeding trials of calves were confined to 21 days, and no indications were made that further accumulation of zinc in tissues would occur if feeding trials were longer than 21 days. Likewise, the biological availability to the calf of this elevated burden of tissue zinc is not known. If this zinc is available for metabolism and released slowly from the tissues, the tissue burden of zinc could be a means of biological supplementation of zinc to calves on low-zinc diets. Accordingly, the objective was to evaluate the biological availability of zinc stores in tissue
572
ZINC RESERVES IN CALVES TABLE 1. Composition of basal diet. a
TABLE 2. Concentration of zinc in tissues of calves fed 0 and 500 ppm zinc for 21 days.
Ingredient
(kg/100 kg diet)
Barley Alfalfa Milk, dried whole Molasses Urea Dicalcium phosphate NaC1 Terramycin Vitamin A premix b Vitamin D premixC
67.825 10 10 8 1 2 1 .1 .05 .025
aThe diet, by analysis, contained 20 ppm Zn, 7 ppm Cu, and 250 ppm Fe (dry matter). bvitamin A premix contained 5,000,000 USP units/kg. CVitamin D premix contained 11,000,000 USP units/kg.
to calves on a low zinc diet. Zinc depletion from tissue and measure of blood were indexes of the nutritional state of zinc. MATERIALS AND METHODS
Twenty male early-weaned Holstein calves were in this experiment. These calves were 5 w old when placed on their respective diets. A practical ration formulated to contain inadequate zinc was fed (Table 1). Zinc was supplemented as ZnSO4. Heparinized samples of plasma were taken weekly from calves for determination of zinc in plasma and the percent capacity of unsaturated plasma for binding zinc. The procedure for the
2 ml add 3 ral ol , l S HC1
Plasma ]
2 ml add 2 ml 7nC12 s o l u t i o n (500 p l Z n / 1 0 0 ,hi)
l D~,termine Z i nc vtmcentration
;o** add 200 rag MgCO 3 | ~ mix 4x o v e r 30 rain. period
Amounts of added dietary zinc 500 SE
Tissue
0
Liver Kidney Heart Bonec Muscled
130a 68 a 64 59 78
Zn, ppm dry matter 307b 183b 65 64 69
30 47 9 24 2
a'bvalues not followed in the same horizontal line by the same letter are different at 5%. CCoccyx. dsemitendinosus.
percent binding-capacity is in Figure 1. Direct dilution of plasma with .1N HC1 was more suitable to determine zinc concentrations in our laboratory than wet-ashing. Differences in aspiration rates due to the relative viscosity between the plasma solution and the standard solutions made with .1N HC1 were only about 2%; this was insignificant. In the second part of the procedure magnesium carbonate aided removal of excess zinc not bound to protein. In blank samples, no measurable zinc remained in solution after addition of magnesium carbonate. The magnesium carbonate and excess zinc were discarded as a precipitate. The percent binding capacity is found by subtracting the amount of zinc in 1 ml of plasma from the amount of zinc in the spiked sample and dividing this by the a m o u n t of zinc in the spiked sample. This tells us the relative ability of the plasma to take up additional zinc, hence, is an indication of the number of free binding sites. Tissue samples were dry ashed, and zinc determinations were by atomic absorption spectrophotometry.
RESULTS AND DISCUSSION
Centrifuge
precipitate (d i s c a l'(t )
573
add 3 ml
,IN HCI
Detorttline
Zinc
concentra t ion
FIG. 1. Procedure for the percent capacity of unsaturated plasma for binding zinc.
The concentration of zinc in the liver and kidney increased significantly with elevated zinc intakes for 21 days (Table 2). Zinc of bone, heart, and muscle was not affected by feeding 520 ppm for 21 days. Further increases in zinc of the kidney, liver, Journal of Dairy Science Vol. 62, No. 4, 1979
574
KINCAID AND CRONRATH
TABLE 3. Effects of zinc depletion upon the concentration of zinc in tissues of calves previously fed 500 ppm added zinc. Amount of added dietary zinc Tissue
0 ppm for 56 days
Liver Kidney Heart Bone c Muscled
89 a 52a 63 36 59
500 ppm for 56 days
500 ppm for 21 days; 0 ppm for 35 days
SE
74a 66 a 66 42 71
36 84 27 27 27
Zn, ppm dry matter 479 b
391 b 56 80 65
a'bvalues not followed in the same horizontal line by the same letter are different at 5%. CCoccyx. dsemitendinosus.
and bone occurred with time of feed 520 ppm zinc (Table 3). When calves were fed 520 ppm zinc for 21 days, then placed on a low zinc diet (20 ppm zinc) for 35 days, large reductions in concentrations of zinc of kidney, liver, and bone occurred. Effects were similar when total organ zinc (in mg) was calculated: e.g., in the liver there were 86 mg of zinc in calves fed 520 ppm zinc for 21 days, 220 mg zinc in calves fed 520 ppm zinc for 56 days, and 36 mg zinc in calves fed 520 ppm zinc for the first 21 days, and 20 ppm zinc for the remaining 35 days. Zinc concentrations in plasma were slightly lower in calves fed 20 ppm zinc compared to 70 ppm zinc (Table 4). Zinc increased significantly (P <.05) in calves fed 520 ppm zinc. In general, the percent capacity of unsaturated plasma for binding zinc responded in a similar manner as plasma zinc to dietary zinc
intake except the differences in percent capacity among all treatment groups were statistically significant (P<.05). Thus, the percent binding capacity was superior to zinc of plasma for indicating the nutritional zinc status of calves. The potential of the percent capacity of unsaturated plasma for binding zinc as a clinical measure of the zinc status of an animal has not been evaluated effectively. Under experimental conditions, it did reflect realistically the nutritional zinc status of calves. However, the effect of factors, other than zinc intake, on this measure is not known. Chesters and Will (7) noted the uptake of 6 s Zn by the cells of whole blood in vitro was affected by low food intake, reduced dietary protein, and endotoxin administration. These factors reduce zinc in plasma and may have a
TABLE 4. Concentration of zinc in plasma and percent unsaturated plasma zinc-binding capacity of calves fed 0, 50, and 500 ppm added zinc. Amount of added dietary zinc Blood parameter Plasma zinc (tag zinc/ml) % Unsaturated plasma zinc-binding capacity
0 ppm .63 a 72a
50 ppm .72a 65b
500 ppm
SE
1.2ob
.05
41 c
a'b'CValues not followed in the same horizontal line by the same letter are different at 5%. Journal of Dairy Science Vol. 62, No. 4, 1979
2.1
ZINC RESERVES IN CALVES t
OletorI Zinc
f~PPM - - S 2 0 PPM f°, 3 . k , ~ "re
2
3
4
5
6
7
PP~
8
Weeks
FIG. 2. Concentration of zinc in plasma at w 1 through 8 in calves fed 0 or 500 ppm added zinc.
575
during zinc d e p l e t i o n ; however, this was n o t sufficient to maintain b l o o d contents. Thus, the large a m o u n t s o f zinc d e p o s i t e d in certain tissues of calves fed high dietary zinc m a y be part of a m e c h a n i s m to p r o t e c t cells f r o m zinc t o x i c i t y and not to serve as a source of reserve zinc. Accordingly, reliance u p o n tissue zinc to c o m p e n s a t e for low zinc intakes should n o t be e x p e c t e d to maintain m a x i m a l growth rates of calves. REFERENCES
similar effect on the p e r c e n t c a p a c i t y o f unsaturated plasma for binding zinc. When calves were switched f r o m high zinc to low zinc diets, b o t h zinc of plasma and percent binding capacity were reduced within 1 w (Fig. 2 and 3). Three weeks a f t e r transfer to l o w zinc diets, zinc of plasma and the percent binding capacity were nearly c o m p a r a b l e to negative control calves. T h e standard errors of t r e a t m e n t means were .05 for zinc in plasma and 2.1 for p e r c e n t capacity of unsaturated plasma for binding zinc. A similar r e d u c t i o n in blood zinc during zinc d e p l e t i o n has been r e p o r t e d (20). Tissue zinc burden, incurred f r o m previous high zinc intakes, will n o t maintain zinc in plasma effectively and m a y be o f marginal value to the calf. Several studies have r e p o r t e d the availability of bone zinc to the rat and Japanese quail during a zinc deficiency (3, 4, 9, 10, and 11). These findings suggest little availability of b o n e zinc under normal conditions; however, previous s u p p l e m e n t a t i o n o f large a m o u n t s of zinc appeared to cause storage of zinc in b o n e with s u b s e q u e n t m o b i l i z a t i o n to m a i n t a i n animal growth. In this study, zinc in b o n e decreased
OletOr~ Z~flc
60
~ z o ppM
4O - ~ z o PpM 2O
0
~ee~s
FIG. 3. The percent capacity of unsaturated plasma for binding zinc at w 1 through 8 in calves fed 0 or 500 ppm added zinc.
1 Ansari, M. S., W. J. Miller, J. W. Lassiter, M. W. Neathery, and R. P. Gentry. 1975. Effects of high but nontoxic dietary zinc on zinc metabolism and adaptations in rats. Proc. Soc. Exp. Biol. Med. 150:534. 2 Beeson, W. M., T. W. Perry, and T. D. Zurcher. 1977. Effect of supplemental zinc on growth and on hair and blood serum levels of beef cattle. J. Anita. Sci. 45:160. 3 Brown, E. D., W. Chan, and J. C. Smith. 1978. Bone mineralization during a developing zinc deficiency. Proc. Soc. Exp. Biol. Med. 157:211. 4 Calhoun, N. R., E. G. McDaniel, M. P. Howard, and J. C. Smith, Jr. 1978. Loss of zinc from bone during deficiency state. Nutr. Rep. Int. 17:299. 5 Chesters, J. K., and J. Quarterman. 1970. Effects of zinc deficiency on food intake and feeding patterns of rats. Brit. J. Nutr. 28:1061. 6 Chesters, J. K., and M. Will. 1973. Some factors controlling food intake by zinc-deficient rats. Brit. J. Nutr. 30:555. 7 Chesters, J. K., and M. Will. 1973. The assessment of zinc status of an animal from the uptake of 6 s Zn by the cells of whole blood in vitro. Brit. J. Nutr. 38:297. 8 Evans, G. W. 1976. Transferrin function in zinc absorption and transport. Proc. Soc. Exp. Biol. Med. 151:775. 9 Harland, B. F., M. R. Spivey Fox, and B. E. Fry, Jr. 1974. Changes in plasma zinc related to fasting and dietary protein intake of Japanese quail. Proc. Soc. Exp. Biol. Med. 145:316. 10 Harland, B. F., M. R. Spivey Fox, and B. E. Fry, Jr. 1975. Protection against zinc deficiency hy prior excess dietary zinc in young Japanese quail. J. Nutr. 105:1509. 11 Hurley, L. S. and H. Swenerton. 1971. Lack of mobilization of bone and liver zinc under teratogenic conditions of zinc deficiency in rats. J. Nutr. 101:597. 12 Johnson, R. J., L. van Nice, G. Williams, and T. H. Blosser. 1974. Mineral concentration of Washington forages as determined by activation analysis. Washington Agr. Exp. Sta. Tech. Bull. No. 76. 13 Kincaid, R. L., W. J. Miller, P. R. Fowler, R. P. Gentry, D. L. Hampton, and M. W. Neathery. 1976. The effect of high dietary zinc upon zinc metabolism and intercellular distribution in cows and calves. J. Dairy Sci. 59:1580. Journal of Dairy Science Vol. 62, No. 4, 1979
5 76
KINCAID AND C R O N R A T I t
14 Kincaid, R. L., W. J. Miller, L. S. Jensen, D. L. Hampton, M. W. Neathery, and R. P. Gentry. 1976. Effect of high a m o u n t s of dietary zinc and age upon tissue zinc in y o u n g chicks. Poultry Sci. 55:1954. 15 Kumar, S., and K. S. Jaya Rao. 1974. Blood and urinary zinc levels in diabetes mellitus. Nutr. Metabol. 17:231. 16 Miller, J. K., and W. J. Miller. 1960. Development of zinc deficiency in Holstein calves fed a purified diet. J. Dairy Sci. 43:1854. 17 National Research Council. 1978. N u t r i e n t requirem e n t s of dairy cattle. Nat. Acad. Sci., Washington, DC. 18 Neathery, M. W., W. J. Miller, D. M. Blackmon, F. M. Pate, and R. P. Gentry. 1973. Effects of long term zinc deficiency on feed utilization, reproductive characteristics, and hair growth in t h e sexually m a t u r e goat. J. Dairy Sci. 56:98. 19 O'Dell, B. L., P. M. Newberne, and J. E. Savage. 1958. Significance of dietary zinc for the growing chick. J. Nutr. 65:503.
Journal o f Dairy Science Vol. 62, No. 4, 1979
20 Ott, E. A., W. H. Smith, R. B. Harrington, H. E. Parker, and W. M. Beeson. 1966. Zinc toxicity in r u m i n a n t s . IV. Physiological changes in tissues of beef cattle. J. A n i m . Sci. 25:432. 21 Ott, E. A., W. H. Smith, M. Stob, and W. M. Beeson. 1964. Zinc deficiency s y n d r o m e in the y o u n g lamb. J. Nutr. 82:41. 22 Touillon, C., V. Bansillon, J. J. Vallon, A. Badimand, and J. J. Comtet. 1975. S t u d y of t h e zinc levels in serum and erythrocytes in b u r n patients. Clin. Chim A C T A 63 : 115. 23 Van Campen, D., and W. A. Iiouse. 1978. Effect of a low protein diet on retention of an oral dose of 6 S Zn and on tissue concentration of Zn, Fe, and Cu in rats. J. Nutr. 104:84. 24 Wannemacher, R. W. Jr., R. S. Pekarek, A. S. Klainer, P. J. Bartelloni, H. L. D u p o n t , R. B. Hornick, and W. R. BuseI. 1975. Detection of a leukocytic endogenous mediator-like mediator of serum a m i n o acid and zinc depression during various infectious illness. Infection and I m m u n i t y 11:873.
ABSTRACT
Calves were fed 520 ppm zinc for 21 days, then placed on a low zinc diet (20 ppm zinc) for 35 days to determine the biological availability of zinc reserves of tissue. Concentrations of zinc in liver and kidney were elevated greatly by feeding high dietary zinc for 21 days and continued to increase with time. On the low zinc diet, the tissue burden of zinc decreased within 35 days to those comparable to calves initially fed low zinc. Likewise, both zinc in plasma and percent capacity o f unsaturated plasma for binding zinc were near negative controls 21 days after removal of calves from high zinc diets. Tissue stores of zinc will not maintain adequate zinc in blood for extended periods, and hence, they probably will not sustain optimal feed intakes and growth rates of calves on lowintakes of zinc. INTRODUCTION
Zinc is a required trace element for domestic livestock, and signs of a zinc deficiency, such as reduced growth, impaired sexual development, and parakeratosis, are documented (16, 18, 19, 21). In a recent survey of forages grown in Washington, the average concentration of zinc was approximately 20 ppm, with a range of 14 ppm to 28 ppm (12). These concentrations are below the dietary requirement of 40 ppm zinc for dairy cattle (17). Thus, zinc is a potential, practical problem for ruminants grazing forages in Washington. One of the first signs of zinc deficiency in an animal is reduction of feed intake (5, 6). However, moderate feed reductions, which are
Received September 25, 1978. Scientific Paper No. 5200. College of Agriculture Research Center, Washington State University. Project No. 0408. 1979 J Dairy Sci 62:572-576
difficult to detect under field conditions, may be indicative of many disorders in cattle. Blood data are of limited usefulness in detecting marginal zinc deficiencies because of the wide fluctuations of zinc in plasma. Many factors can affect the concentration of zinc in blood besides the dietary zinc intake; among these are fasting, infections, and stresses (4, 15, 22, 23, 24). Zinc concentrations in hair sometimes are used as an indicator of the zinc state of an animal (2). However, concentrations of zinc in hair do not appear to be sensitive enough of dietary amount to be a suitable indicator of zinc status. Another problem is the concentration of zinc in hair tells past intakes of zinc rather than current intake. Recent work by Evans (8) indicates zinc is absorbed from the basolateral membrane of the intestinal tract by apotransferrin. Apparently, apotransferrin has specific binding sites on its molecule for zinc. In the portal system, transferrin transports zinc to the liver where zinc is transferred to albumin. However, some zinc undoubtedly remains associated with transferrin. Thus, the relative number of free binding sites on transferrin in peripheral blood may be an indicator of the nutritional zinc status of an animal. Zinc has accumulated in large amounts in tissues of calves in response to high zinc intakes (13). Apparently, this effect is specific to age and species, not occurring in rats, chicks, or cows (1, 13, 14). However, feeding trials of calves were confined to 21 days, and no indications were made that further accumulation of zinc in tissues would occur if feeding trials were longer than 21 days. Likewise, the biological availability to the calf of this elevated burden of tissue zinc is not known. If this zinc is available for metabolism and released slowly from the tissues, the tissue burden of zinc could be a means of biological supplementation of zinc to calves on low-zinc diets. Accordingly, the objective was to evaluate the biological availability of zinc stores in tissue
572
ZINC RESERVES IN CALVES TABLE 1. Composition of basal diet. a
TABLE 2. Concentration of zinc in tissues of calves fed 0 and 500 ppm zinc for 21 days.
Ingredient
(kg/100 kg diet)
Barley Alfalfa Milk, dried whole Molasses Urea Dicalcium phosphate NaC1 Terramycin Vitamin A premix b Vitamin D premixC
67.825 10 10 8 1 2 1 .1 .05 .025
aThe diet, by analysis, contained 20 ppm Zn, 7 ppm Cu, and 250 ppm Fe (dry matter). bvitamin A premix contained 5,000,000 USP units/kg. CVitamin D premix contained 11,000,000 USP units/kg.
to calves on a low zinc diet. Zinc depletion from tissue and measure of blood were indexes of the nutritional state of zinc. MATERIALS AND METHODS
Twenty male early-weaned Holstein calves were in this experiment. These calves were 5 w old when placed on their respective diets. A practical ration formulated to contain inadequate zinc was fed (Table 1). Zinc was supplemented as ZnSO4. Heparinized samples of plasma were taken weekly from calves for determination of zinc in plasma and the percent capacity of unsaturated plasma for binding zinc. The procedure for the
2 ml add 3 ral ol , l S HC1
Plasma ]
2 ml add 2 ml 7nC12 s o l u t i o n (500 p l Z n / 1 0 0 ,hi)
l D~,termine Z i nc vtmcentration
;o** add 200 rag MgCO 3 | ~ mix 4x o v e r 30 rain. period
Amounts of added dietary zinc 500 SE
Tissue
0
Liver Kidney Heart Bonec Muscled
130a 68 a 64 59 78
Zn, ppm dry matter 307b 183b 65 64 69
30 47 9 24 2
a'bvalues not followed in the same horizontal line by the same letter are different at 5%. CCoccyx. dsemitendinosus.
percent binding-capacity is in Figure 1. Direct dilution of plasma with .1N HC1 was more suitable to determine zinc concentrations in our laboratory than wet-ashing. Differences in aspiration rates due to the relative viscosity between the plasma solution and the standard solutions made with .1N HC1 were only about 2%; this was insignificant. In the second part of the procedure magnesium carbonate aided removal of excess zinc not bound to protein. In blank samples, no measurable zinc remained in solution after addition of magnesium carbonate. The magnesium carbonate and excess zinc were discarded as a precipitate. The percent binding capacity is found by subtracting the amount of zinc in 1 ml of plasma from the amount of zinc in the spiked sample and dividing this by the a m o u n t of zinc in the spiked sample. This tells us the relative ability of the plasma to take up additional zinc, hence, is an indication of the number of free binding sites. Tissue samples were dry ashed, and zinc determinations were by atomic absorption spectrophotometry.
RESULTS AND DISCUSSION
Centrifuge
precipitate (d i s c a l'(t )
573
add 3 ml
,IN HCI
Detorttline
Zinc
concentra t ion
FIG. 1. Procedure for the percent capacity of unsaturated plasma for binding zinc.
The concentration of zinc in the liver and kidney increased significantly with elevated zinc intakes for 21 days (Table 2). Zinc of bone, heart, and muscle was not affected by feeding 520 ppm for 21 days. Further increases in zinc of the kidney, liver, Journal of Dairy Science Vol. 62, No. 4, 1979
574
KINCAID AND CRONRATH
TABLE 3. Effects of zinc depletion upon the concentration of zinc in tissues of calves previously fed 500 ppm added zinc. Amount of added dietary zinc Tissue
0 ppm for 56 days
Liver Kidney Heart Bone c Muscled
89 a 52a 63 36 59
500 ppm for 56 days
500 ppm for 21 days; 0 ppm for 35 days
SE
74a 66 a 66 42 71
36 84 27 27 27
Zn, ppm dry matter 479 b
391 b 56 80 65
a'bvalues not followed in the same horizontal line by the same letter are different at 5%. CCoccyx. dsemitendinosus.
and bone occurred with time of feed 520 ppm zinc (Table 3). When calves were fed 520 ppm zinc for 21 days, then placed on a low zinc diet (20 ppm zinc) for 35 days, large reductions in concentrations of zinc of kidney, liver, and bone occurred. Effects were similar when total organ zinc (in mg) was calculated: e.g., in the liver there were 86 mg of zinc in calves fed 520 ppm zinc for 21 days, 220 mg zinc in calves fed 520 ppm zinc for 56 days, and 36 mg zinc in calves fed 520 ppm zinc for the first 21 days, and 20 ppm zinc for the remaining 35 days. Zinc concentrations in plasma were slightly lower in calves fed 20 ppm zinc compared to 70 ppm zinc (Table 4). Zinc increased significantly (P <.05) in calves fed 520 ppm zinc. In general, the percent capacity of unsaturated plasma for binding zinc responded in a similar manner as plasma zinc to dietary zinc
intake except the differences in percent capacity among all treatment groups were statistically significant (P<.05). Thus, the percent binding capacity was superior to zinc of plasma for indicating the nutritional zinc status of calves. The potential of the percent capacity of unsaturated plasma for binding zinc as a clinical measure of the zinc status of an animal has not been evaluated effectively. Under experimental conditions, it did reflect realistically the nutritional zinc status of calves. However, the effect of factors, other than zinc intake, on this measure is not known. Chesters and Will (7) noted the uptake of 6 s Zn by the cells of whole blood in vitro was affected by low food intake, reduced dietary protein, and endotoxin administration. These factors reduce zinc in plasma and may have a
TABLE 4. Concentration of zinc in plasma and percent unsaturated plasma zinc-binding capacity of calves fed 0, 50, and 500 ppm added zinc. Amount of added dietary zinc Blood parameter Plasma zinc (tag zinc/ml) % Unsaturated plasma zinc-binding capacity
0 ppm .63 a 72a
50 ppm .72a 65b
500 ppm
SE
1.2ob
.05
41 c
a'b'CValues not followed in the same horizontal line by the same letter are different at 5%. Journal of Dairy Science Vol. 62, No. 4, 1979
2.1
ZINC RESERVES IN CALVES t
OletorI Zinc
f~PPM - - S 2 0 PPM f°, 3 . k , ~ "re
2
3
4
5
6
7
PP~
8
Weeks
FIG. 2. Concentration of zinc in plasma at w 1 through 8 in calves fed 0 or 500 ppm added zinc.
575
during zinc d e p l e t i o n ; however, this was n o t sufficient to maintain b l o o d contents. Thus, the large a m o u n t s o f zinc d e p o s i t e d in certain tissues of calves fed high dietary zinc m a y be part of a m e c h a n i s m to p r o t e c t cells f r o m zinc t o x i c i t y and not to serve as a source of reserve zinc. Accordingly, reliance u p o n tissue zinc to c o m p e n s a t e for low zinc intakes should n o t be e x p e c t e d to maintain m a x i m a l growth rates of calves. REFERENCES
similar effect on the p e r c e n t c a p a c i t y o f unsaturated plasma for binding zinc. When calves were switched f r o m high zinc to low zinc diets, b o t h zinc of plasma and percent binding capacity were reduced within 1 w (Fig. 2 and 3). Three weeks a f t e r transfer to l o w zinc diets, zinc of plasma and the percent binding capacity were nearly c o m p a r a b l e to negative control calves. T h e standard errors of t r e a t m e n t means were .05 for zinc in plasma and 2.1 for p e r c e n t capacity of unsaturated plasma for binding zinc. A similar r e d u c t i o n in blood zinc during zinc d e p l e t i o n has been r e p o r t e d (20). Tissue zinc burden, incurred f r o m previous high zinc intakes, will n o t maintain zinc in plasma effectively and m a y be o f marginal value to the calf. Several studies have r e p o r t e d the availability of bone zinc to the rat and Japanese quail during a zinc deficiency (3, 4, 9, 10, and 11). These findings suggest little availability of b o n e zinc under normal conditions; however, previous s u p p l e m e n t a t i o n o f large a m o u n t s of zinc appeared to cause storage of zinc in b o n e with s u b s e q u e n t m o b i l i z a t i o n to m a i n t a i n animal growth. In this study, zinc in b o n e decreased
OletOr~ Z~flc
60
~ z o ppM
4O - ~ z o PpM 2O
0
~ee~s
FIG. 3. The percent capacity of unsaturated plasma for binding zinc at w 1 through 8 in calves fed 0 or 500 ppm added zinc.
1 Ansari, M. S., W. J. Miller, J. W. Lassiter, M. W. Neathery, and R. P. Gentry. 1975. Effects of high but nontoxic dietary zinc on zinc metabolism and adaptations in rats. Proc. Soc. Exp. Biol. Med. 150:534. 2 Beeson, W. M., T. W. Perry, and T. D. Zurcher. 1977. Effect of supplemental zinc on growth and on hair and blood serum levels of beef cattle. J. Anita. Sci. 45:160. 3 Brown, E. D., W. Chan, and J. C. Smith. 1978. Bone mineralization during a developing zinc deficiency. Proc. Soc. Exp. Biol. Med. 157:211. 4 Calhoun, N. R., E. G. McDaniel, M. P. Howard, and J. C. Smith, Jr. 1978. Loss of zinc from bone during deficiency state. Nutr. Rep. Int. 17:299. 5 Chesters, J. K., and J. Quarterman. 1970. Effects of zinc deficiency on food intake and feeding patterns of rats. Brit. J. Nutr. 28:1061. 6 Chesters, J. K., and M. Will. 1973. Some factors controlling food intake by zinc-deficient rats. Brit. J. Nutr. 30:555. 7 Chesters, J. K., and M. Will. 1973. The assessment of zinc status of an animal from the uptake of 6 s Zn by the cells of whole blood in vitro. Brit. J. Nutr. 38:297. 8 Evans, G. W. 1976. Transferrin function in zinc absorption and transport. Proc. Soc. Exp. Biol. Med. 151:775. 9 Harland, B. F., M. R. Spivey Fox, and B. E. Fry, Jr. 1974. Changes in plasma zinc related to fasting and dietary protein intake of Japanese quail. Proc. Soc. Exp. Biol. Med. 145:316. 10 Harland, B. F., M. R. Spivey Fox, and B. E. Fry, Jr. 1975. Protection against zinc deficiency hy prior excess dietary zinc in young Japanese quail. J. Nutr. 105:1509. 11 Hurley, L. S. and H. Swenerton. 1971. Lack of mobilization of bone and liver zinc under teratogenic conditions of zinc deficiency in rats. J. Nutr. 101:597. 12 Johnson, R. J., L. van Nice, G. Williams, and T. H. Blosser. 1974. Mineral concentration of Washington forages as determined by activation analysis. Washington Agr. Exp. Sta. Tech. Bull. No. 76. 13 Kincaid, R. L., W. J. Miller, P. R. Fowler, R. P. Gentry, D. L. Hampton, and M. W. Neathery. 1976. The effect of high dietary zinc upon zinc metabolism and intercellular distribution in cows and calves. J. Dairy Sci. 59:1580. Journal of Dairy Science Vol. 62, No. 4, 1979
5 76
KINCAID AND C R O N R A T I t
14 Kincaid, R. L., W. J. Miller, L. S. Jensen, D. L. Hampton, M. W. Neathery, and R. P. Gentry. 1976. Effect of high a m o u n t s of dietary zinc and age upon tissue zinc in y o u n g chicks. Poultry Sci. 55:1954. 15 Kumar, S., and K. S. Jaya Rao. 1974. Blood and urinary zinc levels in diabetes mellitus. Nutr. Metabol. 17:231. 16 Miller, J. K., and W. J. Miller. 1960. Development of zinc deficiency in Holstein calves fed a purified diet. J. Dairy Sci. 43:1854. 17 National Research Council. 1978. N u t r i e n t requirem e n t s of dairy cattle. Nat. Acad. Sci., Washington, DC. 18 Neathery, M. W., W. J. Miller, D. M. Blackmon, F. M. Pate, and R. P. Gentry. 1973. Effects of long term zinc deficiency on feed utilization, reproductive characteristics, and hair growth in t h e sexually m a t u r e goat. J. Dairy Sci. 56:98. 19 O'Dell, B. L., P. M. Newberne, and J. E. Savage. 1958. Significance of dietary zinc for the growing chick. J. Nutr. 65:503.
Journal o f Dairy Science Vol. 62, No. 4, 1979
20 Ott, E. A., W. H. Smith, R. B. Harrington, H. E. Parker, and W. M. Beeson. 1966. Zinc toxicity in r u m i n a n t s . IV. Physiological changes in tissues of beef cattle. J. A n i m . Sci. 25:432. 21 Ott, E. A., W. H. Smith, M. Stob, and W. M. Beeson. 1964. Zinc deficiency s y n d r o m e in the y o u n g lamb. J. Nutr. 82:41. 22 Touillon, C., V. Bansillon, J. J. Vallon, A. Badimand, and J. J. Comtet. 1975. S t u d y of t h e zinc levels in serum and erythrocytes in b u r n patients. Clin. Chim A C T A 63 : 115. 23 Van Campen, D., and W. A. Iiouse. 1978. Effect of a low protein diet on retention of an oral dose of 6 S Zn and on tissue concentration of Zn, Fe, and Cu in rats. J. Nutr. 104:84. 24 Wannemacher, R. W. Jr., R. S. Pekarek, A. S. Klainer, P. J. Bartelloni, H. L. D u p o n t , R. B. Hornick, and W. R. BuseI. 1975. Detection of a leukocytic endogenous mediator-like mediator of serum a m i n o acid and zinc depression during various infectious illness. Infection and I m m u n i t y 11:873.