Factors affecting the fate of selenium (Se) in the gastro-intestinal tract and its excretion in faeces were examined in four experiments. Large quantities of Se were secreted into the anterior region of the small intestine and were absorbed from the posterior region. These processes were not affected by the infusion of arsenite or by tying off the pancreatic duct. Faecal and urinary Se excretion were increased in sheep of higher Se status; the increase in faecal excretion was evident for several weeks after a change in Se intake but was not significant because of high variability between animals; it was attributed to the release of Se when tissues were turned over as tissue Se concentration equilibrated with contemporary Se intake. The bile was a possible route for the entry of such Se into the gastro-intestinal tract, and relationships between biliary Se and whole blood and plasma Se concentrations are presented. Faecal Se excretion was more sensitive to an increase in the organic matter intake than to an increase in forage Se concentration in one experiment. It is postulated that Se excretion was increased because rumen microbial activity was stimulated by the increased nutrient intake, and this increased the quantity of dietary Se which was reduced to an unavailable form by rumen microbial action.
Cadmium (Cd) concentrations in 1663 liver, 1779 kidney and 2526 muscle samples were measured in a residue survey organised by the Australian Bureau of Rural Science at meatworks throughout Australia. Cadmium concentrations in livers and kidneys were also determined in sheep ranging in age from newly born to 112 months of age which had been grazed throughout life at high or low stocking rates on an improved pasture dressed annually with superphosphate. Concentrations of Cd in the residue survey averaged (with median) 0.30 (0.11), 0.96 (0.28) and 0.03 (0.01) mg/kg freshweight in ovine liver, kidney and muscle respectively; the corresponding values in cattle were 0.18 (0.08), 0.65 (0.24) and 0.03 (0.01) mg/kg. Concentrations in liver and kidney were greater in older than in younger animals, at high than at low stocking rates, and in South and Western Australia than in other States. Cadmium concentrations increase with age because ruminants are born with a low Cd burden, and much of the Cd ingested and absorbed thereafter is retained as Cd-metallothionein in the liver and kidney. It is postulated that differences in Cd levels between geographical regions, species and stocking rate are partially due to the consumption of soil that had been fertilised with superphosphate containing Cd. Hepatic and renal Cd concentrations were highly correlated and were assumed to reflect Cd intake; correlations with copper concentrations were generally small. Eight per cent of kidneys exceeded maximum permissible Cd concentrations for human consumption (2.5 mg/kg), but only 2% of liver and 1% of muscle samples exceeded the statutory maxima (1.25 and 0.2 mg/kg respectively).
Hepatic copper (Cu) storage was determined in grazing sheep and cattle supplemented with copper oxide powder, oxidized Cu particles or Cu-calcium EDTA. Cu storage was significantly increased when particles or the EDTA complex were given, but responses in hepatic Cu concentration were small in animals given copper oxide powder. Sheep dosed with copper oxide particles retained particles in the abomasum at 44 days from dosing, but those given copper oxide powder did not retain measurable quantities in the abomasum and excreted about half the dose in the faeces within 4 days of administration.
Fine wool Merino and Border Leicester x Merino ewes grazed improved pastures low in selenium (Se) for 4 years at 6.3 and 12.5 sheep/ha; half of the ewes were supplemented with Se given as an intra-ruminal pellet. Selenium status of the ewes was monitored from Se concentrations in whole blood and plasma, and wool production, fibre diameter and liveweight were recorded. The unsupplemented ewes showed no overt signs of Se insufficiency; Se status was consistently low; and Se supplementation increased wool production and fibre diameter. Selenium status was lower in unsupplemented ewes grazed at the higher stocking rate and in ewes supporting a lamb; it showed seasonal trends and was negatively correlated with rainfall. Selenium concentrations in whole blood but not in plasma were lower in Merino than in Border Leicester x Merino ewes. Data relating to reproductive performance and the productivity of the lambs are presented in accompanying reports.
Measurements were made of blood selenium (Se) concentrations and liveweights of Dorset Horn x (Border Leicester x Merino) and Merino lambs born in October to ewes which were supplemented or not supplemented with intra-ruminal Se pellets and grazed at 6.3 or 12.5 ewe/ha for 4 consecutive years. Lambs were not supplemented with Se and most observations were made between birth and weaning. In some years the Merino lambs were grazed as a single flock for a further 18 months after weaning, and liveweights and fleece characters were recorded at 10 and 22 months of age. Blood Se concentrations of lambs at birth varied with the Se treatment of their dams but were generally lower in the lamb and declined during lactation. In lambs born to unsupplemented ewes, concentrations were lower at the high stocking rate, and declined with increasing rainfall in the preceding January-June period. Selenium concentrations were reduced in twins and this was particularly evident in lambs born to supplemented ewes. Liveweights at birth, in mid-lactation and at weaning were significantly increased in lambs born to Se-supplemented and crossbred ewes, and in lambs born as singletons. The response in liveweight following Se supplementation was greater in lambs reared at the high than at the low stocking rate, and in Merino than in crossbred lambs. The response to Se supplementation was correlated with rainfall during the preceding February to July, and was greater in early lactation. Clean fleece weight at 10 months of age was increased by 9.5% and fibre diameter by 0.3 pm in lambs born to ewes which had received supplementary Se. Differences in fleece weight were not detected at 22 months.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.