Alain Bourdonnais (pictured) of Novus Europe looks at the importance of copper in piglet diets
There are many challenges involved in successfully rearing pigs, but one of the most important is managing weaning, where piglet growth can be compromised by risks to gut health and nutritional imbalances. Due to high prices of feed materials, the use of alternative ingredients may result in disorders of the gut microflora, like diarrhoea, resulting in general suboptimal nutrition. In particular, mineral nutrition may be impaired, affecting animal immunity, welfare status, reproduction and carcase quality.
Among such mineral imbalances, copper (Cu) is particularly at stake in piglets because it’s typically used for its growth-promoting effects: at elevated levels, between 150-250ppm, and usually as inorganic copper (sulfate salt), it improves feed intake and feed conversion, while reducing scouring. But, these effects are highly variable and sometimes lacking.
Copper is a trace element essential to life. Involved in a number of enzymes and also in structural proteins, copper has many functions throughout the body such as iron metabolism, cellular respiration, cross-linking of connective tissue, pigmentation and keratinisation of hair and wool, central nervous system development, reproduction, immunity and lipid metabolism.
Research shows that copper efficiency is linked to its metabolism, but copper is poorly absorbed: typically, no more than 5-10% in adult animals, and younger animals are just able to absorb a bit more (15-30%) of dietary copper. Once absorbed through the intestine, copper is carried throughout the blood stream (incorporated into ceruloplasmine, mainly) and is primarily taken up by the liver.
The liver is the main storage and distribution organ for copper: it’s capable of storing approximately 20% of the body’s copper supply. If the body is in a negative copper balance, like during fast growth of weaned piglets, it can move copper from the storage pool of the liver to the blood to be used.
Liver cells (hepatocytes), responsible for the uptake and storage of copper, also regulate the excretion of this metal into the bile and this appears to be a key role of copper. About 80% of copper excreted through the body is excreted through the bile. It has been shown that under normal conditions, the amount of copper excreted in the bile is directly linked to the amount of copper stored into the liver itself: so if the copper in the liver is increased, the bile content of copper will be increased as well.
Early research in piglets showed that the dietary copper was able to inhibit the growth of enteric-disease causing microorganisms, thus eliciting an antibiotic-like effect, killing some Coliforms, potentially the pathogenic ones. It was also shown that this growth-promoting effect was more important for the most digestible sources of copper.
These elements support the fact that copper needs to be absorbed, to circulate in the body and ultimately be stored in the liver, and then excreted into the bile to exert growth stimulation. This may help us understand the inconsistent growth results that are seen in trials.
In feedstuffs, as well as in the gut, there are many antagonistic substances (phytate, molybdenum, sulfur, changes in pH, vegetable fibres, some large polypeptides and so on) that will bind copper and limit its absorption. If copper absorption is limited, then its excretion into the bile is modified and consequently the reliability of obtaining a final benefit on piglet growth and health is considerably reduced.
A new form of organic copper, Mintrex copper, has recently been approved by the EU and is now available in the feed market: it’s a chelate of copper in which the hydroxyl analogue of methionine (2-hydroxy-4-methylthio-butanoic acid) is the ligand, acting as a protection for the copper.
As part of the research done for the registration dossier, weaned piglets were allocated to one of three dietary treatments: 6mg/kg copper from CuSO4 (T1, control), 170mg/kg copper from CuSO4 (T2) and 170mg/kg copper from Mintrex copper (T3). Piglets fed T3 had a greater liver copper than pigs fed T2 and significantly greater liver copper than control pigs fed T1. Copper levels in liver tissues indicate that this new chelated copper was more bioavailable than the inorganic source!
To better understand where this improved bioavailability of copper, as Mintrex, might play a role in piglets at weaning, a trial was set up to measure the copper content of the bile, using various levels and sources of copper. It found piglets receiving Mintrex copper had a consistently higher concentration of copper in the bile than all other piglets, at all doses.
The EU registration trial also found that piglets fed the chelated source of copper grew 9% faster over a 42-day period than those fed the diets containing the inorganic copper source with average daily gain values of 346g/day, 346g/day and 378g/day for treatments T1, T2 ,T3 respectively. In the same period, feed intake was greater for piglets fed the chelated copper source (see Figure 1).
This research trial clearly illustrates the fact that higher absorption and deposition of copper in piglets improves growth, with improved feed intake, ADG and reduced FCR.
Mode of action
Another research trial was set up to look at the potential bacterial inhibition of biliary copper in piglets. It saw 120 weaned piglets allocated to four treatments, with each treatment made of six replicates of five piglets/pen. The four treatments consisted of a control group (no added copper), a Mintrex group (with 75ppm of copper as Mintrex) and two sulfate groups (at 75ppm and 250ppm of copper as sulfate).
Bile secretion samples were collected at 27-28 days post-weaning, after three weeks of experimental treatments. Microbial inhibition of the bile samples was tested on Salmonella, E coli, Citrobacter, Enterobacter, and Campylobacter (isolated from the control pig intestines) using agar assays.
After incubation at 37C for 36 hours, inoculated agar plates were read, by measuring the diameter of the growth inhibition zone. The test showed that the weaning piglet bile did have antimicrobial activity and this activity was similar when piglets received either 250ppm of copper as sulfate or 75ppm only of copper as Mintrex!
This has to be considered in relation to the fact that copper as Mintrex is more bioavailable than copper as sulfate, shown to be more deposited in the liver where, according to normal metabolism of copper, it’s then more excreted into the bile where biliary salt and other copper-related compounds are exhibiting their antimicrobial activities.
Mintrex Copper is a highly available mineral chelate. It avoids mineral antagonisms and ensures optimal supply of copper, essential to immune functions and gut morphology, which are keys to overcome pathogenous aggressions.
Research has proven that copper as Mintrex is more bioavailable than other copper sources, allowing for a better metabolism of this copper: in piglets, and in conditions allowed by EU legislation, this results is optimal performance, through better feed intake, better feed efficiency, better growth and better immunity.