Dietary Antagonists Research Articles

Feeding nanoparticles of copper oxide coated with lysine with or without added antagonists affects the copper status but not performance of Holstein dairy cows

The apparent absorption of copper (Cu) in ruminants is low, with between 0.01 and 0.07 g/g absorbed from sources such as copper oxide (CuO) under typical feeding conditions, resulting in high levels of excretion. Improving the bioavailability of Cu could reduce the supplemental amount required to maintain Cu status and reduce excretion, particularly in the presence of dietary antagonists such as sulfur (S) and molybdenum (Mo). The objective of our study was to determine the Cu status of cows when fed nanoparticle CuO coated with Lys compared with conventional CuO when fed without or in combination with antagonists to Cu absorption (S and Mo) in the diet of dairy cows. Fifty-six multiparous Holstein-Friesian cows that were 48 d ± 17.4 (mean ± SD) post calving and yielding 40.6 ± 6.9 kg milk/d were used in a 2 × 2 factorial design. The 4 treatment groups were; CuO (O-), CuO with added antagonists (O+), nano CuO with a lysine coating (N-), and nano CuO with a Lys coating with added antagonists (N+), fed for 16 wks. We formulated the diets to contain approximately 17 mg Cu/kg dry matter (DM) and diets with antagonists contained an additional 1 g S/kg DM and 6 mg Mo/kg DM, with Lys added to O- and O+ to provide the same daily supply as N- and N+. Blood samples were collected at wk 0, 2, 4, 6, 10 and 16, and liver biopsy samples at wk 0 and 16. We found no effect of dietary treatment on DM intake, milk yield, live weight or body condition score, with mean values of 23.3 kg/d, 40.1 kg/d, 646 kg and 2.68, but milk SCC was higher in cows fed conventional compared with non CuO, or with added antagonist. We also found no effect of treatment on blood activity of gamma glutamyl transferase, superoxide dismutase or ceruloplasmin, hematology profile, or plasma Cu and iron concentration. We found that plasma Mo concentration was increased from 0.36 µmol/L in cows fed O- or N- to 0.80 µmol/L in those receiving O+ or N+. Additional dietary antagonists also decreased the concentration of Cu in the liver of cows fed conventional CuO (C+) over the study period by 1.3 mg/kg DM/d, but in cows fed dietary antagonists and nano CuO coated with Lys (N+), liver Cu concentration was increased by 1.1 mg/kg DM/d. Our study is the first to demonstrate that reducing the particle size of CuO into the nano scale with a lysine coating improves the bioavailability of CuO in the presence of dietary antagonists in dairy cattle, and we did not observe any negative effects on performance or health.

163 Relative Bioavailability of Bis-glycinate Bound Copper in Beef Steers Fed a High Antagonist Growing Diet

Abstract To assess relative bioavailability of an organic Cu source, 90 Angus-cross steers (265 ± 21 kg) were blocked by body weight to pens with GrowSafe bunks and randomly assigned to dietary Cu treatments (14–18 steers/treatment): 0 mg Cu/kg dry matter (DM; CON), 5 or 10 mg Cu/kg DM as Cu sulfate (CS5; CS10) or chelated bis-glycinate Cu (GLY5; GLY10). Steers were fed a common high antagonist growing diet (0.48% S; 5.3 mg Mo/kg DM; 4.9 mg Cu/kg DM). Blood was collected from all steers on d 0, 28, 56, 84 and 124. Liver samples were collected at trial beginning (d -3/-2) and end (d 125/126). Data were analyzed using ProcMixed of SAS (experimental unit = steer; fixed effect = treatment; random effect = block). Plasma Cu was analyzed as repeated measures (repeated effect = day). Plasma and liver Cu concentrations were regressed against Cu intake using ProcGLM to calculate relative bioavailability of GLY. Initial liver Cu did not differ between treatments (P ≥ 0.63), but final liver Cu was lesser in CON versus steers supplemented 5 or 10 mg Cu/kg DM from either source (P ≤ 0.09). Final liver Cu was greater for CS versus GLY (P < 0.01). Plasma Cu for all treatments decreased through d 28; final plasma Cu was greatest for steers supplemented either source at 10 mg Cu/kg DM (treatment × day P < 0.01). Relative bioavailability of GLY was 82% compared to CS (P < 0.01) based on liver Cu but did not differ based on plasma Cu (P = 0.60). High concentrations of dietary antagonists and lower solubility of GLY (68.9% relative to CS) in rumen-like conditions (pH 5.2) may have resulted in free thiomolybdate absorption across the rumen wall and subsequent depletion of liver Cu stores in GLY supplemented steers.

Relative bioavailability of organic bis-glycinate bound copper relative to inorganic copper sulfate in beef steers fed a high antagonist growing diet

To assess the relative bioavailability of bis-glycinate bound Cu, 90 Angus-cross steers (265 ± 21 kg) were blocked by body weight (BW) to pens with GrowSafe bunks and randomly assigned to dietary treatments (14 to 18 steers/treatment): 0 mg supplemental Cu/kg dry matter (DM; CON), 5 or 10 mg supplemental Cu/kg DM as Cu sulfate (CS5; CS10) or bis-glycinate bound Cu (GLY5; GLY10). Steers received a high antagonist growing diet (analyzed 4.9 mg Cu/kg DM, 0.48% S, and 5.3 mg Mo/kg DM). Steers were weighed at the beginning (days 1 and 0) and end (days 125 and 126) of the trial to determine average daily gain (ADG) and gain:feed (G:F). Blood was collected from all steers on days 0, 28, 56, 84, and 126. Liver samples were collected on days −3 or −2 and day 123 or 124. Data were analyzed using ProcMixed of SAS (experimental unit = steer; fixed effect = treatment and block). Plasma Cu was analyzed as repeated measures (repeated effect = day). Plasma and liver Cu concentrations were regressed against total Cu intake using ProcGLM to calculate relative bioavailability of GLY. Final BW and overall ADG were greatest for CS5 and CS10 and least for CON and GLY5 (P = 0.01). Overall, DMI was not affected by treatment (P = 0.14), but overall G:F tended to be greatest for CS5, CS10, and GLY5 and least for CON (P = 0.08). Total and supplemental Cu intake was greatest for steers supplemented either source at 10 mg Cu/kg DM and least for CON (P < 0.01). However, total and supplemental Cu intake was greater for CS5 than GLY5 (P < 0.01). Final liver Cu concentrations were greatest for CS10, least for CON, CS5, and CS10, and intermediate for GLY10 (P < 0.01). Final plasma Cu was greatest for steers supplemented either source at 10 mg Cu/kg DM (P < 0.01). Relative bioavailability of GLY was 82% compared to CS based on liver Cu (P < 0.01) but did not differ based on plasma Cu (P = 0.60). The lesser bioavailability of GLY relative to CS could be due to a high concentration of dietary antagonists and lower solubility of GLY (68.9% relative to CS) in pH conditions (5.2) similar to the ruminal pH of a beef animal consuming a high concentrate diet. Future studies should examine the effects of bis-glycinate bound Cu fed in blended combination with inorganic Cu sulfate to determine the most effective blend of sources for feedlot cattle experiencing varying amounts of dietary Cu antagonists.

Route of administration determines effectiveness of single-use trace mineral products in beef cattle

An injectable trace mineral product increased plasma Mn, Se, and Zn concentrations within 8 h and liver Se concentrations through d 29. These products are an effective way to rapidly increase trace mineral status as they are delivered directly into the blood stream. Boluses did not increase liver mineral (Se) concentrations until 120 days after administration, suggesting these products may be an effective strategy to improve trace mineral status in the long-term. Products that were administered orally (drenches and pastes) had minimal effects on plasma and liver mineral concentrations, likely because interaction with dietary antagonists hindered trace mineral absorption. Beef cattle producers should select single-use trace mineral products based on how quickly a status change is needed.

393 Awardee Talk: Effect of trace mineral source on rumen fermentation and trace mineral distribution in the rumen

Abstract The role that Cu and Zn play in rumen microbial fermentation is not well understood. Microorganisms use small proportions of dietary Cu and Zn for catalytic, structural, and stabilizing functions. In order for microorganisms to acquire Cu and Zn, the elements must be soluble in the rumen environment. Data would indicate that practical diets fed to ruminants without Cu and Zn supplementation are able to meet the microbial Cu and Zn requirements. Therefore, rumen solubility of supplemental Cu and Zn can impact rumen microbial fermentation characteristics. Numerous factors can impact rumen solubility of minerals, such as the pH of the rumen, the concentration of dietary antagonists (Mo, Fe, S, fiber, etc.), and mineral source. Earlier research has indicated that high soluble concentrations of Cu and Zn in the rumen environment can become toxic to certain rumen microorganisms and decrease fiber digestion. Recent research from our laboratory has indicated that hydroxy trace mineral (HTM) forms of Cu and Zn are relatively insoluble in the rumen and that a greater proportion of HTM remained loosely bound to the insoluble fraction within the rumen when compared to sulfate trace mineral (STM) sources of Cu and Zn. We have also reported that supplemental sources of Cu and Zn that are highly soluble in the rumen environment (STM) can decrease fiber digestion, reduce total VFA concentrations, and can become more tightly bound to rumen solid digesta than HTM sources of Cu and Zn. The stronger binding of STM relative to HTM to the solid rumen digesta fraction may reduce absorption in the small intestine. Future research investigating the flow and passage rate of different trace mineral sources through the abomasum into the duodenum and duodenal absorption efficiency of Cu and Zn from different TM sources is needed.

Efficacy of l-glutamic acid, N,N-diacetic acid to improve the dietary trace mineral bioavailability in broilers.

Trace minerals are commonly supplemented in the diets of farmed animals in levels exceeding biological requirements, resulting in extensive fecal excretion and environmental losses. Chelation of trace metal supplements with ethylenediaminetetraacetic acid (EDTA) can mitigate the effects of dietary antagonists by preserving the solubility of trace minerals. Lack of EDTA biodegradability, however, is of environmental concern. l-Glutamic acid, N,N-diacetic acid (GLDA) is a readily biodegradable chelating agent that could be used as a suitable alternative to EDTA. The latter was tested in sequential dose–response experiments in broiler chickens. Study 1 compared the effect of EDTA and GLDA in broilers on supplemental zinc availability at three levels of added zinc (5, 10, and 20 ppm) fed alone or in combination with molar amounts of GLDA or EDTA equivalent to chelate the added zinc, including negative (no supplemental zinc) and positive (80 ppm added zinc) control treatments. Study 2 quantified the effect of GLDA on the availability of native trace mineral feed content in a basal diet containing no supplemental minerals and supplemented with three levels of GLDA (54, 108, and 216 ppm). In study 1, serum and tibia Zn clearly responded to the increasing doses of dietary zinc with a significant response to the presence of EDTA and GLDA (P < 0.05). These results are also indicative of the equivalent nutritional properties between GLDA and EDTA. In study 2, zinc levels in serum and tibia were also increased with the addition of GLDA to a basal diet lacking supplemental trace minerals, where serum zinc levels were 60% higher at the 216 ppm inclusion level. Similar to the reported effects of EDTA, these studies demonstrate that dietary GLDA may have enhanced zinc solubility in the gastrointestinal tract and subsequently enhanced availability for absorption, resulting in improved nutritional zinc status in zinc-deficient diets. As such, GLDA can be an effective nutritional tool to reduce supplemental zinc levels in broiler diets, thereby maintaining health and performance while reducing the environmental footprint of food-producing animals.

BILL E. KUNKLE INTERDISCIPLINARY BEEF SYMPOSIUM: Impact of mineral and vitamin status on beef cattle immune function and health.

The importance of optimal mineral and vitamin nutrition on improving immune function and health has been recognized in the preceding decades. In the southeast, beef cattle are raised predominantly on forages that may be limiting in nutrients for optimal health, especially trace minerals such as Cu, Zn, and Se. Clinical deficiencies of these nutrients produce classic symptoms that are common to several nutrient deficiencies (e.g., slow growth and unthrifty appearance); however, subclinical deficiencies are more widespread and more difficult to detect, yet may result in broader economic losses. Dietary mineral concentrations often considered adequate for maximum growth, reproductive performance, or optimal immune function have been found to be insufficient at times of physiological stress (weaning, transport, comingling, etc.), when feed intake is reduced. The impacts of these deficiencies on beef cattle health are not apparent until calves have been subjected to these stressors. Health problems that are exacerbated by mineral or vitamin deficiencies include bovine respiratory disease, footrot, retained placenta, metritis, and mastitis. Many micronutrients have antioxidant properties through being components of enzymes and proteins that benefit animal health. In dairy cattle, high levels of supplemental Zn are generally associated with reduced somatic cell counts and improved foot health, possibly reflecting the importance of Zn in maintaining effective epithelial barriers. Neutrophils isolated from ruminants deficient in Cu or Se have reduced ability to kill ingested bacteria in vitro. Supplemental vitamin E, in its role as an intracellular antioxidant has been shown to decrease morbidity in stressed calves. There is more understanding of the important biological role that these nutrients play in the functioning of the complex and multifaceted immune system. However, there is still much to be learned about determining the micronutrient status of herds (and hence when supplementation will be beneficial), requirements for different genetic and environmental conditions, understanding the bioavailability of these nutrients from feedstuffs and forages, quantifying the bioavailability of different supplemental sources of these nutrients, and identifying the impact of dietary antagonists on these nutrients.

A multielement trace mineral injection improves liver copper and selenium concentrations and manganese superoxide dismutase activity in beef steers1

Trace minerals (TM) are vital to health and growth of livestock, but low dietary concentrations and dietary antagonists may reduce mineral status and feeder cattle TM status is usually unknown at arrival. The objective of this study was to examine the effect of TM status on response to mineral injection in beef cattle. Forty steers were equally assigned to diets for an 84-d depletion period: control (CON; supplemental Cu, Mn, Se, and Zn) or deficient (DEF; no supplemental Cu, Mn, Se, or Zn plus Fe and Mo as TM antagonists). Lesser liver Cu and Se concentrations (79.0 ± 11.60 and 1.66 ± 0.080 mg/kg DM, respectively) in DEF steers compared with CON steers (228.8 ± 11.60 and 2.41 ± 0.080 mg/kg DM, respectively) on d 71 of depletion indicated mild deficiencies of these TM (P < 0.001). On d 1 of the 85-d repletion period, 10 steers within each dietary treatment were injected with sterilized saline (SAL) or Multimin90 (MM), containing 15, 10, 5, and 60 mg/mL of Cu, Mn, Se, and Zn, respectively, at a dose of 1 mL/68 kg BW. All steers were fed the same repletion diet supplemented with Cu, Mn, Se, and Zn to meet or exceed NRC recommendations. Blood was collected on d 0 and 1, and blood and liver biopsies were collected on d 8, 15, 29, 57, and 85 postinjection. Red blood cell lysate manganese-superoxide dismutase activity was greater in MM (P = 0.02), suggesting incorporation of injectable TM into a biological process. The increase in liver Se in response to MM was greater in CON vs. DEF (P = 0.02), suggesting TM from injection were used rather than stored in DEF steers. Liver Se and Cu (P < 0.05) were elevated through at least d 30 by MM. Dietary TM deficiency decreased neutrophil bacteria killing ability and increased myeloperoxidase (MPO) degranulation (P < 0.04) as measured on d 0, 1, 13, and 14 during the repletion period while injection had no impact. Within CON animals, total MPO was greater in animals that received TM injection, but injection did not affect MPO within DEF steers (P = 0.007). Overall, TM from an injectable mineral were used differently between TM adequate and mildly deficient steers.

Gestational exposure to the AhR agonist 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin induces BRCA‐1 promoter hypermethylation and reduces BRCA‐1 expression in mammary tissue of rat offspring: Preventive effects of resveratrol

Studies with murine models suggest that maternal exposure to aromatic hydrocarbon receptor (AhR) agonists may impair mammary gland differentiation and increase the susceptibility to mammary carcinogenesis in offspring. However, the molecular mechanisms responsible for these perturbations remain largely unknown. Previously, we reported that the AhR agonists 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CpG methylation of the breast cancer-1 (BRCA-1) gene and reduced BRCA-1 expression in breast cancer cell lines. Based on the information both the human and rat BRCA-1 genes harbor xenobiotic responsive elements (XRE = 5'-GCGTG-3'), which are binding targets for the AhR, we extended our studies to the analysis of offspring of pregnant Sprague-Dawley rats treated during gestation with TCDD alone or in combination with the dietary AhR antagonist resveratrol (Res). We report that the in utero exposure to TCDD increased the number of terminal end buds (TEB) and reduced BRCA-1 expression in mammary tissue of offspring. The treatment with TCDD induced occupancy of the BRCA-1 promoter by DNA methyltransferase-1 (DNMT-1), CpG methylation of the BRCA-1 promoter, and expression of cyclin D1 and cyclin-dependent kinase-4 (CDK4). These changes were partially overridden by pre-exposure to Res, which stimulated the expression of the AhR repressor (AhRR) and its recruitment to the BRCA-1 gene. These findings point to maternal exposure to AhR agonists as a risk factor for breast cancer in offspring through epigenetic inhibition of BRCA-1 expression, whereas dietary antagonists of the AhR may exert protective effects.

Abstract 1115: Epigenetic regulation of BRCA-1 by xenobiotic and dietary ligands of the aryl hydrocarbon receptor

Abstract Mutations of BRCA-1 account for only 5-10% of breast cancer cases, whereas sporadic breast tumors represent the remaining 90-95%. In sporadic breast cancers there is silencing of BRCA-1 in the absence of mutations. Factors contributing to this etiology may include environmental ligands of the aryl hydrocarbon receptor (AhR) such as dioxins (ex.2,3,7,8 tetrachlorodibenzene(p)dioxin, TCDD) and polycyclic aryl hydrocarbons (PAHs). Dietary ligands of the AhR with potential protective effects include the phytoalexin resveratrol found in grapes. In this study, we investigated the mechanisms responsible for repression of BRCA-1 expression by the activated AhR. The results of DNA binding studies in MCF-7 breast cancer cells documented that TCDD-induced the association of the AhR to xenobiotic responsive elements (XRE) harbored in the BRCA-1 promoter region. The cotreatment with resveratrol reduced AhR recruitment in a dose-dependent fashion, prevented the TCDD-dependent repression of BRCA-1 transcription and restored BRCA-1 protein expression. The treatment with TCDD induced the recruitment of histone deacetylase-1, DNA methyltransferase-1, methyl-binding protein-2, and reduced the association of acetylated histone-4 and acetylated histone-K9. These effects were abrogated by cotreatment with resveratrol. We propose that dietary antagonists of the AhR such as resveratrol may be useful in the prevention of epigenetic BRCA-1 silencing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1115.

Regulation of BRCA‐1 by Xenobiotic and Dietary Ligands of the Aryl Hydrocarbon Receptor

The BRCA‐1 protein is involved in repair of DNA damage and mutations of the BRCA‐1 gene confer a high risk of developing breast cancer. Interestingly, mutations of BRCA‐1 account for only 5‐10% of breast cancer cases, whereas sporadic breast tumors represent the remaining 90‐95%. In sporadic breast cancers there is silencing of BRCA‐1 in the absence of mutations. Factors contributing to this etiology include the environmental ligands of the aryl hydrocarbon receptor (AhR) 2,3,7,8 tetrachlorodibenzene(p)dioxin (TCDD) and polycyclic aryl hydrocarbons (PAHs). Dietary antagonists of the AhR with potential protective effects include the phytoalexin resveratrol and 3,3′‐diindolylmethane (DIM), the condensation product of indole‐3‐carbinol. The objective of this study was to investigate the mechanisms responsible for repression of BRCA‐1 expression by the activated AhR. Results of DNA binding studies in MCF‐7 breast cancer cells documented that TCDD‐induced the association of the AhR to xenobiotic responsive elements (XRE) harbored in the BRCA‐1 promoter region. The cotreatment with resveratrol (5, 10, 20µM) reduced AhR recruitment in a dose‐dependent fashion. We are investigating the chromatin modifications induced by the AhR at the BRCA‐1 gene and the preventative effects of resveratrol. These studies may have implications for the use of dietary AhR ligands in prevention of BRCA‐1 silencing induced by AhR agonists.Grant Funding SourceSusan G. Komen Breast Cancer Foundation and Arizona Biomedical Research Commission

Interaction between the aryl hydrocarbon receptor and its antagonists, flavonoids

Flavonoids have been reported to be dietary antagonists of an aryl hydrocarbon receptor (AhR). However, little is known about the molecular mechanism on their antagonistic effects. In this study, the inhibitory effect of flavonoids on ligand binding to the AhR and interaction between flavonoids and the AhR complex (AhRc) were investigated in each flavonoid subclass. Flavone, flavonol, and flavanone but not catechin inhibited the specific binding between the AhR and 3-methylcholanthrene dose-dependently, indicating that the former three subclasses possibly act as competitive antagonists of the AhR. However, catechin in addition to the former three subclasses directly interacted with the AhRc by surface plasmon resonance analysis. The dissociation constant values showed an inverse correlation with the suppressive effect on the DNA binding activity. These results suggest that flavone, flavonol, and flavanone act as competitive antagonists of the AhR, while catechin associates with the AhRc and indirectly exhibits its antagonistic effects.

Effect of Dietary Calcium Supplements and Amlodipine on Growth, Arterial Blood Pressure, and Cardiac Hypertrophy of Spontaneously Hypertensive Rats

It has been shown that calcium‐enriched diets cause a decrease in arterial blood pressure in hypertensive patients and animals. Moreover, it has been suggested that the combination of dietary calcium and calcium antagonists could paradoxically have a synergistic effect in order to decrease arterial blood pressure. The combination of these treatments may also have potential therapeutic benefit in the attenuation of cardiac hypertrophy. In this study, after being weaned at three weeks, male spontaneously hypertensive rats (SHR) were randomized in four groups of animals. Two of these groups were fed on a normal calcium diet (Ca 1%) and another two groups were fed on a calcium‐enriched diet (Ca 2.5%). One of the groups fed on each diet also received amlodipine (1 mg/kg/day) in the drinking water after being weaned. Body weight was measured weekly in all the groups, and arterial blood pressure was also measured in all the 10‐, 15‐, 20‐, and 25‐week‐old SHR by the tail cuff method. We established the ratio heart weight/body weight × 1000 (R), and we weighed the left ventricle in the 25‐week‐old animals at the end of the different treatments. The Ca 2.5% diet caused a delay in the development of hypertension in SHR. This effect could not be correlated with alterations in body weight since this diet improved growth in these rats. Amlodipine did not alter growth in SHR. This pharmacological treatment caused a decrease in the arterial blood pressure of the SHR and it intensified the antihypertensive effect of the Ca 2.5% diet. Nevertheless, this drug attenuated the effect of dietary calcium on body weight and when the treatment was prolonged, almodipine also antagonized the effect of dietary calcium on arterial blood pressure. At the end of the different treatments the ratio R and the left ventricular weight were similar in all the groups of animals. Therefore, the use of dietary calcium with a calcium antagonist to control arterial blood pressure seems not to be advisable, and the present data do not prove the usefulness of the mentioned antihypertensive treatments in preventing cardiac hypertrophy.

The application of an oral zinc tolerance test to assess zinc absorption from three different dietary sources in the dog

Zinc (Zn) is a key nutrient for dogs, playing an important role in many metabolic functions. It has been estimated that 91% of the minimum maintenance requirement for Zn is needed to support hair growth. Coat condition is perceived as being important by pet owners and is thus of fundamental concern when evaluating the adequacy of a diet for dogs.Zn absorption has been shown to vary as a function of the amount and source of the Zn in the diet and as a function of the presence of elevated calcium and / or phytate levels in the diet.It has been suggested that when dietary Zn is supplied in the form of a chelate with amino acids, rather than from inorganic sources, a greater proportion of Zn is absorbed an is thus available to the animal. Further, the undesirable effects that dietary antagonists, such as calcium, exert on Zn absorption may be negated

The application of an oral zinc tolerance test to assess zinc absorption from three different dietary sources in the dog

Zinc (Zn) is a key nutrient for dogs, playing an important role in many metabolic functions. It has been estimated that 91% of the minimum maintenance requirement for Zn is needed to support hair growth. Coat condition is perceived as being important by pet owners and is thus of fundamental concern when evaluating the adequacy of a diet for dogs.Zn absorption has been shown to vary as a function of the amount and source of the Zn in the diet and as a function of the presence of elevated calcium and / or phytate levels in the diet.It has been suggested that when dietary Zn is supplied in the form of a chelate with amino acids, rather than from inorganic sources, a greater proportion of Zn is absorbed an is thus available to the animal. Further, the undesirable effects that dietary antagonists, such as calcium, exert on Zn absorption may be negated

Zinc Source Influences Zinc Retention in Hair and Hair Growth in the Dog

Zinc absorption has been shown to vary as a func tion of the source of the zinc in the diet (Ho and Hdiroglou 1977, Ashmead et al. 1985, Wedekind and Baker 1990, Wedekind et al. 1990) and, in dogs, as a function of the presence or absence of dietary antag onists (Robertson and Burns 1963). Zinc absorption also varies as a function of the ac tual quantity of zinc in the diet (Mejborn 1990), the effect being with respect to the absolute amount of zinc absorbed with increasing dietary zinc, in contrast to the percentage absorption that may remain un changed. Problems may, however, arise as a result of increas ing the zinc content of a diet in an attempt to increase zinc absorption form the gut. The increase in zinc content of the diet may result in interaction with an other mineral causing a reduction in absorption of that mineral. Increasing dietary zinc above the minimum recommended, however, remains common practice to counteract antagonist effects on zinc absorption (NRC 1985) in many commercial diets. It has been suggested that when dietary zinc is sup plied in the form of a chelate with amino acids, rather than from inorganic sources, a greater proportion of zinc is absorbed. Depending on the amino acids used to chelate the zinc, the retention of zinc in tissues may be increased (Ashmead et al. 1989) and the undesirable effects that dietary antagonists exert on zinc absorp tion may be negated. Thus the inclusion of a zinc chelate in a diet for dogs may allow for the improvement of zinc absorp tion irrespective of the presence of dietary antagonists without the need to increase the total zinc supply in the diet. The purpose of this study was to compare two sources of zinc, zinc-amino acid chelate (2 mol metgly:l mol Zn) containing 20% Zn (ZM) and a zincpolysaccharide complex consisting of zinc sulphate complexed with alkali-modified brewers wort (the liq uid portion of malted grain), 16.7% Zn (ZP) as a re placement for Zn from zinc oxide when added to a commercial diet formulation. Materials and methods. Each zinc source was added to a typical commercial diet formulation (Table 1) that contained no added zinc. An equivalent of an additional 50 mg Zn • kg'1 as either ZO, ZM or ZP was

Role of selenium and vitamin E in mastitis and reproduction of dairy cattle

The literature would suggest that the selenium requirement for most species of livestock is between 0.05-0.3 ppm (mg/kg) of dietary dry matter. The current requirement for all classes of dairy cattle is 0.30 ppm. Selenium requirements are affected by dietary vitamin E intake, by disease process being prevented, and by the concentration of dietary antagonists including sulfur, iron, copper, and calcium.

Effect of dietary antagonists and corresponding nutrients on growth and reproduction of the flour mite (Acarus siro L.)

The flour miteAcarus siro L. (Acaridae, Astigmata) was reared on an axenic diet with the addition of various nutrient antagonists, with and without supplementation by the corresponding nutrients. The deficiency symptoms induced by dietary antagonists, and the reversibility of the former by nutrient administration, indicated that folic acid, riboflavin, thiamine, niacin, pyridoxine, biotin and a sterol are essential for the growth and reproduction of the flour mite. It was also demonstrated that the population density and generation sequence of this species can be suppressed to the level of acaristasis by nutrient antagonists, owing to inhibited nutrient utilization.

Trace elements in soils and pasture herbage on farms with bovine hypocupraemia

SummaryThe importance of molybdenum, sulphur, iron, zinc and cadmium dietary antagonists to ruminant copper metabolism was investigated at the farm level in an attempt to explain the widespread occurrence of bovine hypocupraemia in recent years.From 22 of the most severely hypocupraemic regions of England, six areas with as wide a range of geological, pedological and topological situations as possible were selected for detailed field work. This involved the collection of topsoil and herbage samples from approximately 15 farms per area with hypocupraemic stock. Possible causal factors of bovine hypocupraemia were then considered on the basis of three criteria: critical concentrations of copper, molybdenum, sulphur, iron, zinc and cadmium in pasture herbage; Cu:Mo ratios in herbage; and copper availability predictions for ruminants.Absolute copper deficiency and molybdenum-induced bovine hypocupraemia were clearly demonstrated at the farm level. The results also confirmed that dietary sulphur, in particular, plays a significant yet previously unrecognized role in the widespread incidence of bovine hypocupraemia in industrialized Britain. Antagonism due to iron orginating from soil-contaminated herbage was evident, but not common. No evidence was found to support the occurrence of zinc- or cadmium-induced hypocupraemia in the areas examined.