Accumulation and depletion of liver copper stores in dairy cows challenged with a Cu-deficient diet and oral and injectable forms of Cu supplementation.
OBJECTIVE
To quantify the capacity of the liver to respond to a Cu-deficient diet and various forms of Cu supplementation in dairy cows with high Cu status.


METHODS
Sixty non-pregnant, non lactating mixed-age Friesian dairy cows were fed baled silage for 116 days, containing 5.8 mg Cu/kg dry matter (DM), that provided an inadequate Cu intake. They were either unsupplemented (Control); or treated thrice weekly orally with solutions containing the equivalent of 150 mg Cu/day as copper sulphate pentahydrate (CS), copper amino chelate (CAC), or copper glycinate (CG); 16 g Cu as CuO wire particles, administered in an intra-ruminal bolus on Day 0; or 100 mg Cu as calcium copper edetate, administered by S/C injection on Days 0 and 58. On Days -5, 14, 28, 58, 86 and 116, liver biopsies and blood samples were obtained for determination of Cu.


RESULTS
Mean initial concentrations of Cu in liver for all groups was 827 (SE 42) micromol/kg fresh tissue. In control cows, this decreased to 552 micromol/kg on Day 116, and averaged 670 micromol/kg over the length of the trial. Oral forms of Cu supplementation increased overall mean concentrations in liver to 960 (SE 79), 1,050 (SE 81) and 1,100 (SE 84) micromol/kg for CS, CAC and CG, respectively, but there was no difference between form of supplement. Mean concentrations were significantly increased by bolus treatment, but not by injection. Concentrations of Cu in serum in all groups decreased from 12.1 (SE 0.3) to 10.4 (SE 0.6) micromol/L by Day 116, with no differences due to treatments. The initial concentration of Cu in liver significantly affected the rate of accumulation of Cu among cows supplemented orally. In cows with an initial concentration <1,100 micromol/kg, the average increase was 4.1 micromol/kg fresh tissue/day, whereas rates were variable, even negative, when initial concentrations were >1,100 micromol/kg. Release of Cu over 116 days in cows given the bolus was calculated to be equivalent to an oral intake of CS of 106 mg Cu/day.


CONCLUSIONS
In dairy cows with a high Cu status fed a Cu-deficient diet, responses to supplementation with two chelated forms of Cu administrated orally were similar to those due to CS. Copper as CuO was about 77% as effective as oral supplementation with chemically similar inorganic Cu. Initial concentrations of Cu in liver influenced the rate of accumulation following oral supplementation.


CONCLUSIONS
Changes in concentrations of Cu in liver were readily observed following oral supplementation over a wide range of initial concentrations, whereas these changes could not be detected in serum. The liver is thus a good index of the Cu status of dairy cows.
Balemi
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Agvance Marketing Ltd, PO Box 38016, Howick, Auckland 2145, New Zealand.
Grace
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West
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Smith
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Knowles
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D000284:Administration, Oral; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy*; D003300:Copper / Q000008:administration & dosage / Q000172:deficiency / Q000378:metabolism / Q000627:therapeutic use*; D003612:Dairying; D004334:Drug Administration Schedule; D005260:Female; D007279:Injections, Subcutaneous; D008099:Liver / Q000737:chemistry* / Q000378:metabolism; D014131:Trace Elements / Q000032:analysis / Q000172:deficiency / Q000378:metabolism / Q000627:therapeutic use*
D014131:Trace Elements; D003300:Copper