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  • Writer's picturePat Poletti

What’s stealing your weaner growth?

Recently, I attended a couple of Beef and Lamb field days on the subject of Management of weaner dairy & dairy beef stock. It was surprising and disappointing that the treatment of trace element nutrition by presenters was minimal. Advice ranged from merely stating that feeding stock well will mitigate trace element deficiencies (it does help, but depends on the severity of the deficiency) through to outright hostility to any specific recommendations of the use of trace elements.

Generalisations are not good enough

“Monitor trace elements” was as best as it got but no specific information on the how, when, where or why was forthcoming. Uncomfortably, explanations such as, “calves are born with high liver copper and as such there was no further requirement at weaning”, “copper deficiency is a winter issue only” and “there is no requirement for copper in calves” were bandied about without substantiation. This represents a grave disservice to farmers who gave up their time to be there.

Copper deficiency is the culprit

In Mineral Systems view, ensuring sufficient trace element nutrition is absolutely key to achieving anything like adequate weight gains and reduction in disease risk. Not to downplay the essential requirement for other trace elements, copper deficiency is the underappreciated thief of good weaner growth.

When we started our calf rearing operation (milking cows and feeding calves) our weaners experienced the usual lag before seemingly deciding that they were now fully fledged ruminants and getting stuck into the grass on offer. The calves had no reason not to kick on, pasture quality was good and meal was on offer. Thinking the problem through it appeared copper deficiency may be the culprit. The theory being that while milk is considered low in copper it is subject to rumen bypass and therefore the copper is 100% absorbed. Contrast this with less than 2% absorption on forage diets when copper is faced with the full brunt of rumen based sulphur, molybdenum, and iron antagonism.

Cold turkey effect

Therefore, at weaning the calf essentially has a supply of copper one day but then suffers the full force of copper deficiency the next. After giving copper supplementation (a 10g copper oxide bullet) the calves were quite simply different animals.

This outcome is well backed up by the numbers. A calf at the point of weaning will, depending on the rearing system, be consuming somewhere around 6-8 litres of milk (admittedly the range is large 4-12 litres?). This amount of milk will be providing well over half to three quarters of the calf’s copper requirement with the small requirement left over provided by the meals and forages on offer. However, once on grass only, if we assume average copper herbage content (10mg), and an average absorption of copper, the absorbed copper easily drops to a third of the calf’s requirement.

The figures add up

Despite the oversimplification, the numbers make it pretty obvious that at weaning with the cessation of rumen bypass milk there is a dramatic drop in copper intake. Meals fed over weaning will help. Not because they have a higher copper level – generally they have less (depending on the PKE and tapioca content) but meals, being low in sulphur and molybdenum, act to reduce antagonism and thus absorption increases across the diet. But, throw in a primary herbage deficiency, and a greater antagonism from the average figures used in this calculation and a significant copper deficiency very quickly becomes apparent.

Quite apart from the change of diet, the calculations also indicate that the copper requirement of a weaned calf exceeds that of a lactating cow. Once again using average figures, the copper content of the diet of a cow will be about 22 mg / kg of dry matter. With the same grass the calf requirement is 30mg / kg of dry matter – about 30% higher. Apart from indicating that growth rate has greater demand on copper than lactation it also suggests that if cows need supplementing with copper then calves on the same diet will also need supplementing.

What options do you have?

The clinical picture of such deficient calves is unsurprisingly ill-thrift and scour not to mention harbouring a greater parasite burden. The usual response is to enthusiastically drench these calves – but being so young the risk of drench toxicity is very real and not uncommon. It would also not be surprising if such calves were at greater risk of contracting yersinia and/or being nailed by BVD. All further reasons for disappointing weight gain .

Give up on the guesswork

Ensuring sufficient trace element nutrition is in place is an absolute necessity in achieving the weight gains expected in consideration of the feed on offer. Whether this is a specialist crop or high quality pasture that has taken skill and time to achieve. By feed sampling and accurate analysis trace element, and for that matter macro element, nutrition can be assured and required growth rates can be achieved. Bland and unsubstantiated generalisations are just not good enough.

#WeanerGrowth #Copperinsufficiency #Copperdeficiency #Drystockproduction #Dairyexpenditure #Drenching

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