Effects of zinc deficiency per se and of dietary zinc level on urinary and endogenous fecal excretion of 65Zn from a single intravenous dose by ruminants

Reducing mineral usage in feedlot diets for Nellore cattle: I. Impacts of calcium, phosphorus, copper, manganese, and zinc contents on microbial efficiency and ruminal, intestinal, and total digestibility of dietary constituents

This study evaluated intake, microbial efficiency, and ruminal, small and large intestinal, and total digestibility of DM, OM, CP, and NDF, as well as availability of Ca, P, Mg, Na, K, Cu, Mn, and Zn in Zebu cattle fed with or without supplemental sources of Ca and P or a micromineral premix. Five rumen- and ileum-cannulated Nellore bulls (BW = 200 ± 10.5 kg; 9 mo) were used in the experiment, distributed in a 5 × 5 Latin square design. The experiment was developed in a 2 × 2 + 1 factorial design to measure the effects of mineral supplementation on intake, digestibility, and site of nutrient absorption. The factors consisted of 2 Ca and P levels (macromineral factor; CaP+ or CaP-) and 2 microminerals levels (micromineral factor; CuMnZn+ or CuMnZn-). In addition, a treatment with alimentary restriction (REST) was evaluated at 1.7% of BW. Nutrient fluxes were measured in the omasum and ileum, in addition to intake and fecal excretion. Microbial efficiency was estimated using purine derivative excretion. Dry matter, OM, NDF, CP intake, and total digestibility were not affected ( ≥ 0.058) by the absence of Ca, P, Cu, Mn, and Zn supplementation. Intake of Ca, P, and Mg were reduced ( < 0.01) by CaP-. The absence of CuMnZn reduced ( < 0.01) Cu, Mn, and Zn intake. Ruminal recycling of P, Na, and K is significant for increasing the influx of these minerals to the digestive tract; however, influences of treatments were not observed. The small and large intestines contributed to mineral absorption in different proportions ( < 0.05), according to minerals and treatments. Because of the similarity ( > 0.05) of OM, NDF, and CP digestion sites and coefficients, we assume that omitting supplemental sources of Ca, P, Cu, Mn, and Zn may be an option in raising cattle on feedlots. If supplementation is viable, knowledge about the specific absorption site of each mineral could positively impact choices about the supplemental source.

Estimating mineral requirements of Nellore beef bulls fed with or without inorganic mineral supplementation and the influence on mineral balance

The objectives of this study were to quantify the mineral balance of Nellore cattle fed with and without Ca, P, and micromineral (MM) supplementation and to estimate the net and dietary mineral requirement for cattle. Nellore cattle ( = 51; 270.4 ± 36.6 kg initial BW and 8 mo age) were assigned to 1 of 3 groups: reference ( = 5), maintenance ( = 4), and performance ( = 42). The reference group was slaughtered prior to the experiment to estimate initial body composition. The maintenance group was used to collect values of animals at low gain and reduced mineral intake. The performance group was assigned to 1 of 6 treatments: sugarcane as the roughage source with a concentrate supplement composed of soybean meal and soybean hulls with and without Ca, P, and MM supplementation; sugarcane as the roughage source with a concentrate supplement composed of soybean meal and ground corn with and without Ca, P, and MM supplementation; and corn silage as the roughage source with a concentrate supplement composed of soybean meal and ground corn with and without Ca, P, and MM supplementation. Orthogonal contrasts were adopted to compare mineral intake, fecal and urinary excretion, and apparent retention among treatments. Maintenance requirements and true retention coefficients were generated with the aid of linear regression between mineral intake and mineral retention. Mineral composition of the body and gain requirements was assessed using nonlinear regression between body mineral content and mineral intake. Mineral intake and fecal and urinary excretion were measured. Intakes of Ca, P, S, Cu, Zn, Mn, Co, and Fe were reduced in the absence of Ca, P, and MM supplementation ( < 0.05). Fecal excretion of Ca, Cu, Zn, Mn, and Co was also reduced in treatments without supplementation ( < 0.01). Overall, excretion and apparent absorption and retention coefficients were reduced when minerals were not supplied ( < 0.05). The use of the true retention coefficient instead of the true absorption coefficient provided a better estimate of mineral requirements. Dietary mineral requirements were lower for P, Cu, and Zn and greater for Fe compared with previously published recommendations. This study provides useful information about mineral requirements and mineral supplementation to obtain adequate dietary mineral supply of Nellore cattle in tropical conditions.

The use of dysprosium to measure endogenous zinc excretion in feces eliminates the necessity of complete fecal collections

The secretion of endogenous zinc (Zn) into the gut and subsequent excretion in the feces is understood to play a major role in maintaining Zn homeostasis in humans. Therefore, the measurement of endogenous Zn losses in the feces (EFZ) can be an important aspect of the study of Zn metabolism and homeostasis. The methods currently used to measure EFZ have the disadvantage of requiring complete fecal collections over multiple days. We have investigated the use of dysprosium (Dy), a nonabsorbable rare earth metal, in a method of determining EFZ that does not require complete fecal collections and permits the measurement of EFZ from several fecal samples. The method was evaluated using data from a study of free-living adult females in which Dy was administered 3-4 times/d over a period of 5 or 6 d to monitor completeness of fecal collections. The results did not differ from those obtained using an established isotope dilution method. We found that the measurement of the sample Dy:Zn ratio was useful for selecting samples for measurement. We conclude that the Dy method of determining EFZ is a valid and less burdensome alternative to current techniques.

Zinc absorption, metabolism, and endogenous excretion in zinc-deficient and normal calves over an extended time

Zinc metabolism was studied in Zn-deficient and control Holstein calves over a 2-mo period following a single oral or i.v. 65Zn dose. In both orally and i.v. dosed animals, all gastrointestinal tissue sections from Zn-deficient animals contained more 65Zn than comparable tissues of controls. Contents of proximal small intestinal sections of Zn-deficient calves contained more 65Zn 8 to 10 wk after dosing than did those from controls; however, the reverse occurred in the distal small intestine, cecum, and large intestine. With both dosing methods, Zn-deficient calves retained more 65Zn throughout the study. Daily 65Zn excretion rate as a percentage of that retained declined for 6 wk after dosing, indicating a constantly increasing biological half-life. For deficient calves, the biological half-life was about 500 d in the later weeks of the experiments. In orally dosed, Zn-deficient animals, specific activity of fecal 65Zn exceeded that of serum Zn throughout the study. This shows a shortcoming in the basic assumption of measuring endogenous Zn loss from fecal and serum specific activities and total fecal stable Zn. Thus, endogenously excreted Zn is not representative of that remaining.

Absorption and secretion of 65Zn in the stomach and intestinal tract of sheep exchanging digesta via duodenal re-entrant cannulas

The absorption and secretion of 65Zn in the stomach and intestinal tract regions was studied in sets of two and three sheep which were exchanging digesta via re-entrant cannulas in the proximal duodenum. One sheep from each of the three three-sheep sets was dosed intraruminally with the radioisotope. One sheep from the three two-sheep sets received an intravenous dose. Measurements of 65Zn in blood plasma from intraruminally dosed sheep showed that there was no apparent absorption from the stomach region. Measurements from sheep receiving radioactive digesta intraduodenally showed that mean apparent absorption of 65Zn was 0.07 and mean true absorption was 0.103. There was a large variation in endogenous recycling of 65Zn into the stomach region. Secretion of 65Zn into the stomach and intestinal regions in the intravenously dosed sheep of the two-sheep sets was calculated on the basis of total recovery over 10 d in the digesta and faeces. The present study showed that for every 1 molecule Zn secreted into the stomach region, 2.1 molecules were secreted into the intestinal tract region.

A model for zinc metabolism in sheep given a diet of hay

1. Four pairs of Scottish Blackface ewes were given a basal diet of hay, providing 8 mg zinc/d, and one of four levels of supplementary Zn (0,75, 150 or 225 mg/d) continuously by intraruminal infusion. 2. 65Zn (59 microCi) was given intravenously after stabilization for 14 d and the changes in specific radioactivity (SR) of plasma and faeces were monitored for a further 10 and 13 d respectively. The faecal endogenous losses and absorption of Zn were estimated, using the principle of isotope dilution, by two methods using the whole or latter parts of SR:time curves. 3. Faecal endogenous losses were estimated by the part area method to be 4.9, 6.4, 5.1 and 6.3 +/- 0.35 mg/d at 0, 75, 150 and 225 mg supplemental Zn/d i.e. largely unaffected by Zn intake and averaging 0.11 mg/kg live weight (LW). The whole area method gave similar results. 4. Urinary excretion was negligible (probably less than 0.2 mg/d) for all sheep. 5. The amount of Zn absorbed was assumed to equal the irreversible loss of Zn under steady-state conditions and found to remain constant at 7.6 +/- 0.39 and 10.3 +/- 0.6 mg/d when calculated by "whole' and "part area' methods. Zn retention did not increase with Zn intake and homoeostasis was achieved primarily by control of Zn absorption which fell from 0.75 to 0.03 or from 0.96 to 0.05 of intake, depending on method of calculation, as intakes increased.

Effects of dietary aflatoxin on performance and zinc metabolism in dairy calves

Young dairy calves were fed diets containing 40 or 640 ppm zinc with 0 or 5 ppm aflatoxin for 3 wk. The aflatoxin mixture contained 80.5% B1, 19.5% G1, and less than .1% B2 and G2. The aflatoxin-fed calves exhibited characteristic signs of aflatoxicosis which included reduced feed intake, weight gains, nitrogen balance, pulse rate, and respiration rate. Feed intake and weight gains recovered some during the 3rd wk. No gross abnormalities were observed in the liver or other organs at autopsy. Addition of 600 ppm zinc to diets containing aflatoxin did not alleviate the toxic conditions. Effects of aflatoxin or zinc metabolism were investigated during the 3rd week of treatment through oral dosing of zinc-65. Absorption of zinc-65 was slightly lower in aflatoxin-fed calves. However, the aflatoxin effect on absorption of zinc-65 was less than that of high dietary zinc. Retention of zinc-65 in small intestinal tissue was increased in aflatoxin-fed calves, but concentrations in other tissues were not affected. Stable zinc was reduced in liver and increased in kidney and three sections of the small intestine. Further research is needed to define more clearly the relationship of zinc to aflatoxin in dairy calves.

Intestinal absorption of zinc: a role for a zinc-binding ligand in milk

This study examined the proposal that a low molecular weight, zinc-binding ligand (ZBL) in certain milks is important for zinc absorption in the neonatal period. Ten-day-old rats, in which intestinal ZBL is absent, fed (by stomach intubation) 65Zn-labeled ZBL from rat milk, absorbed significantly more 65Zn than those fed free 65ZnCl2 or bovine milk fractions. ZBL from human milk appeared to have an intermediate effect, possibly due to species specificity. 65Zn was found in the ZBL fraction in intestinal mucosa of 10-day-old rats fed rat or human milk fractions, but not in those fed bovine milk or free 65ZnCl2. In contrast, in 18-day-old rats, which have an endogenous intestinal ZBL, there were no differences in zinc absorption, and any of the labeled milk fractions or free 65Zn caused localization of 65Zn in the ZBL fraction of intestinal mucosa. These results support the hypothesis that the intestinal ZBL plays a role in zinc absorption and that in the neonatal period before its development the milk ZBL is valuable for this function. This mechanism may be important in normal human infants as well as in acrodermatitis enteropathica patients.

[Effect of zinc deficiency on the digestibility and utilization of nutrients]

Weaned male rats were used in a metabolic trial to investigate the digestibility of dry matter, crude protein, ash and energy, the energy and N balances and the rates of zinc absorption and zinc retention under conditions of zinc deficiency. 2X8 experimental animals were kept in separate metabolism cages for 6 periods each lasting 5 days. The animals received a semisynthetic zinc-deficient diet (casein + starch + sucrose) containing only 1.0 mg Zn per kg of dry matter (zinc-deficient group fed ad libitum) or plus 49 mg Zn per kg of dry matter (pair-fed control group). The mean intake of dry matter was 2-3 g per day/animal. 2.9 g of food were necessary to produce 1 g of weight increase in the deficient animals and 1.4 g in the controls. The rate of apparent zinc absorption was always clearly negative in the Zn-deficient group. In the control group apparent zinc absorption decreased from 60% to 27% in the course of the trial while zinc retention decreased from 51% to 10%. During zinc deficiency the rates of both faecal and absolute renal Zn excretion were found to be greatly reduced. The proportion of renal zinc excretion relative to total excretion averaged 60% in the experimental group as compared to 17% in the controls. No significant differences were found in the digestibility data of gross energy. Nutrient digestibility (%) was significantly reduced under conditions of Zn deficiency (data for the control group given in brackets): 92,6 (94.0) for dry matter; 93,2 (94.1) for organic matter; 93.3 (96.2) for crude protein and 76.6 (90.8) for crude ash. Similarly, N retention data, in Zn-deficient animals, declined from 30.5% to 14.7%, and metabolizable energy decreased from 88.7% to 85.6%. The differences obtained are not sufficient, however, to account for the clearly increased food requirements observed in zinc-deficient animals. Thus, considerable disturbances have to be assumed to occur in the processes of intermediary nutrient utilization.

[Effect of zinc deficiency and varying zinc supplements on resorption and retention in dairy cows]

5 lactating cows were used in a trial to investigate the process of Zn absorption and Zn retention under conditions of Zn deficiency and variations in Zn supplementation. The apparent Zn absorption was found to be markedly increased if the animals were fed a Zn deficient semisynthetic diet containing 6 mg Zn per kg of dry matter during the depletion period. Apparent Zn absorption continued to rise with continuing Zn depletion. Over a period of 6 weeks of Zn depletion the mean rate of Zn absorption was 58% with increases from 51% to 64% between the 1st and 6th week of experiment. After 19 weeks of Zn depletion 75% of the supplemented zinc were absorbed. With a Zn supply of 22 ppm and 54 ppm the rate of apparent Zn absorption decreased to 51% and 44% while still higher Zn supplements, up to 436 ppm, produced only a slight further decline down to 40%. The absolute Zn balances were shown to be directly associated with the level of Zn supply, all the more so because a linear relationship was found to exist between the levels of alimentary zinc supplementation and absolute Zn retention. Under conditions of Zn deficiency the cows exhibited a negative Zn balance, where animals with the highest milk yields showed the most negative Zn balances and remained for the longest period in the negative phase. With increasing periods of Zn depletion a homeostatic mechanism of Zn regulation in the organism of the animals became more and more pronounced so that at advanced stages of Zn depletion Zn retention of some extent occurred.

[Excretion of zinc in lactating cows receiving various supply of zinc]

Studies were carried out with 5 lactating cows receiving a semisynthetic diet to trace the pattern of zinc excretion in the faeces, urine and milk under conditions of Zn depletion and repletion. Faecal Zn concentrations were found to be drastically reduced during a 6-week period of Zn depletion. The Zn supply to the animals at different levels of Zn repletion (varying between 22 mg and 436 mg Zn per kg) was well reflected in the corresponding faecal Zn concentrations. Similarly, faecal Zn excretion expressed as the percentage of Zn supplied with the diet was shown to change with the level of Zn supply. In the range between 6 mg and 54 m Zn per kg of dietary dry matter the level of relative faecal Zn excretion increased from 42% to 56% whereas with higher Zn supplements (up to 436 mg/kg) only slight increases (up to 60%) were observed. This indicates that the organism exhibits a strong tendency to maintain a physiological balance; this tendency is all the more pronounced with increasing Zn depletion; thus after 19 weeks of Zn depletion as little as 25% of the administered amount of Zn was excreted in the faeces. The average minimum of urinary Zn concentrations was 0.25 mg Zn per litre. The Zn concentrations in urine were not found to be dependent on the Zn supply. The level of relative Zn excretion in the milk was markedly increased despite the reduced concentrations of milk Zn during the periods of Zn deficiency. At the beginning of Zn depletion rather more zinc was released with the milk than was taken up with the Zn deficient diet. The mean proportion of milk Zn in the total amount of dietary Zn over the 6-week depletion period was 91%. With Zn amounts of 22 mg, 54 mg, 87 mg, 108 mg, 130 mg and 436 mg per kg of diet 23.7%, 13.1%, 12.9%, 5.7%, 4.3%, and 1.7% of the dietary Zn were excreted with the milk. Thus, a relative decrease of Zn excretion in the milk was observed, i.e. relative to the level of Zn supplementation.

New concepts and developments in metabolism and homeostasis of inorganic elements in dairy cattle. A review

Major routes of homeostatic control animals use to adapt to widely variable intakes of minerals and the necessity of keeping tissue content of functional forms relatively constant are changes in: (1) percentage absorbed, (2) urinary excretion, (3) tissue deposition in harmless or mobilizable reserve forms, (4) secretion into milk, and (5) endogenous excretion via feces. The importance of each varies greatly among elements. Changes in absorption are of major importance with calcium, iron, zinc, and manganese but not with cadmium or iodine. Urine is a major control route for magnesium, fluorine, selenium, iodine, sodium, chlorine, and potassium. Milk iodine varies almost directly with intake. Tissue deposition and withdrawal are key routes for iron, copper, fluorine, and calcium. Endogenous (metabolic fecal) excretion is crucial in manganese homeostasis. Biochemical details of most homeostatic control mechanisms have not been established. Apparently changes in body tissues control percentage absorption of several elements, including zinc, at the intestine which is the control site. Other major factors which may affect metabolism of several elements include chemical form, whether the elements include chemical form, whether the element is absorbed or injected, and genetic differences among animals. Several common pitfalls and special research problems are discussed. New research indicates that silicon, vanadium, nickel, tin, and fluorine are probably essential.

Effects of zinc, copper, and manganese supplementation of high-concentrate ration on digestibility, growth, and tissue content of Holstein calves

The effects of supplemental zinc, copper, and manganese alone or in combination in a high-concentrate ration were studied in 16 Holstein bull calves during a 10-wk feeding trial. Metabolism was studied after the feeding trial. Apparent digestibility of dry matter, nitrogen, and gross energy, and nitrogen retention and urinary excretion of zinc, copper, and manganese were determined. The calves were slaughtered after the experiment, and liver, heart, and kidney were taken for analyses of trace minerals. Supplementation of the basal ration with the trace minerals did not affect body weight gains, which averaged 1.42 kg daily. The addition of trace minerals did not affect apparent digestibility co-efficients. A zinc-manganese interaction in digestion of nitrogen and gross energy was significant. Higher dietary manganese caused increased zinc concentrations in the liver, kidney, and heart. The copper concentration of liver was decreased by dietary zinc and increased by dietary copper and manganese. Supplemental manganese increased its net retention. There was no evidence of deficiency of any trace minerals in the unsupplemented treatments.