[Endogenous secretion and reabsorption of 65zinc in ruminants as affected by zinc deficiency and feeding of ethylenediaminetetraacetate or cadmium]

Effect of Supplementation of Nano Zinc Oxide on Nutrient Retention, Organ and Serum Minerals Profile, and Hepatic Metallothionein Gene Expression in Wister Albino Rats

A study was conducted to validate the effects of nano form of zinc (NZn) on nutrient digestibility, zinc retention, organ and serum zinc profile, and hepatic metallothionein gene expression in Wistar albino rats (WAR). Nano zinc (NZn) was synthesized through chemical method, by using 0.45 M zinc nitrate [Zn(NO₃)₂.6H₂O] and 0.9 M sodium hydroxide (NaOH). The NZn particle in its oxide form was characterized by TEM-EDAX and XRD, and found to be in nano range (below 100 nm. Zinc was supplemented to the Wistar albino rats (WAR) through synthetic semi-purified diet either without Zn, or as inorganic zinc (IZn; 25 mg/kg), or as synthesized NZn (25, 12.5, 6.25, 3.125 or 50 mg/kg DM) for 60 days. The zinc content was observed to be significantly (P < 0.05) higher in liver, bone, kidney, and serum due to NZn supplementation where NZn-50 had highest zinc content and control had the least, without affecting Fe, Mn, and Cu. NZn at 12.5 mg/kg group rats were either comparable or better than IZn at 25 mg/kg in terms of zinc retention, CP digestibility, zinc level in serum, liver, bone, and kidney suggesting its better bioavailability simultaneously also reduced fecal excretion of zinc to the environment. Metallothionein mRNA expression was upregulated in NZn at 25 mg/kg and NZn at 50 mg/kg than IZn at 50 mg/kg. Thus, in WAR, NZn at half of the ICAR recommendation (25 mg/kg DM) is as effective as inorganic zinc at 100% of recommended dose.

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.

Studies on the flow of zinc, cobalt, copper and manganese along the digestive tract of sheep given fresh perennial ryegrass, or white or red clover

1. Sheep fitted with a rumen fistula and either a re-entrant cannula at the proximal duodenum or a re-entrant cannula at the terminal ileum were given twice daily 480-520 g dry matter as fresh perennial ryegrass, or white or red clover. Flows of digesta were corrected to 100% recovery of chronic oxide. 2. The quantities (g/24 h) of zince and cobalt leaving the stomach were significantly greater than those in the food. No significant change was found in the quantities of copper and manganese. Significantly smaller quantities of Co (all three diets) and Zn (all diets except red clover) left the small intestine than those which entered this region. No significant differences in the quantities of Cu and Mn entering and leaving the small intestine were found. Significantly smaller quantities of Zn, Co, Cu and Mn were excreted in the faeces than entered the large intestine. 3. From the flow results it was determined that there was a significant net secretion of Zn and Co in the stomach, and a significant net absorption of Zn (except with the red-clover diet) and Co from the small intestine, and of Zp Co Cu and Mn from the large intestine.