9 April 1999

Value of growth enhancers not apparent in trial

INITIAL results from Easton Lodge looking at the effect of removing antibiotic growth promoters and growth enhancers from pig diets has shown no difference in growth rate and feed use, but results are far from conclusive.

Unit manager Jasper Renold had removed AGPs and growth enhancers from diets fed to half the pigs passing through both weaner and grower stages. Differences in weight gain and feed conversion have been recorded for both groups.

In the flat-deck house oloquindox (Enterdox) – a growth enhancer used at 100mg/kg feed – was removed from half the pen diets. Growth rates for the 66, 7kg weaners on each ration were almost identical over the 18-day test at 384g/pig/day.

But feed conversion was different; weaners fed rations containing oloquindox had a 7% higher feed use for the same weight gain. Feed conversion with oloquindox was 1.104 and 1.036 without.

"It costs £5/t to add Enterdox to rations – equivalent to £257/year for a unit finishing 8000 pigs annually – and yet it appears were getting no benefit from it," says Mr Renold.

Other feed trials added to the uncertainty over benefits of using growth enhancers. In the grower trial batches of 80 pigs were fed either standard diets or those containing tylosin (Tylamix) – a growth promoter banned from use after July – at 40mg/kg feed.

Tylosin has been used by the units feed supplier as the standard growth enhancer in diets and will be replaced by avilamycin (Maxus) in future. This will be used at Easton Lodge despite growers being healthy having been vaccinated for EP and fed tilmicosin (Pulmatil) for two weeks in the flat-decks to combat APP.

Each group of four pens – a total of 80 pigs – was exposed to the same environment and management. Pigs had an average start weight of 43kg liveweight and finish weight – after 39 days on trial – of 74kg liveweight.

"There is a marginal difference in performance between the two groups," says Mr Renold. As expected, growth rate for pigs fed rations containing tylosin were slightly better; 782g/pig/day compared with 775g/pig/day. Likewise feed conversion was also better for pigs fed rations containing tylosin; 2.56 versus 2.60 for pigs on rations without the AGP.

But does this result in feed savings? The 1% improvement in feed efficiency for pigs fed AGPs is worth 20.5p/pig for the period of the trial. However, the cost of including tylosin, at 21p/pig, in rations outweighs the benefit by 0.5p/pig. "If the improvement in feed use had been 2% then wed have got a clear 41p/pig return for the 21p/pig cost of tylosin use."

Mr Renold was interested to see whether feed use and growth rate figures were significant or not. The trial is not intended to be scientific; more a look to see what happens when these products are removed. "But Im curious to know how many pigs wed have to run through the trial to get a significant result," he says.

PIC, who supplies breeding to Easton Lodge, analysed the results. But PICs Mark Wilson says to have enough trial data to analyse for significant results, given the 1% difference in feed conversion achieved in trials, Easton Lodge would have to run 770 individually tagged and recorded pigs on each ration.

According to Mr Renold, extensive tagging and recording would be impractical on a commercial unit. If Easton Lodge trial results had shown a 4% improvement in feed conversion, the number of pigs needed to find significant results would fall dramatically to just 52 individually tagged and recorded animals on each ration.

Similarly, without individual pig recording and with a 1% difference in feed use, 300 pens would need monitoring on each treatment to get a statistically proven result. Where a 4% difference is recorded, the number of pen results needed falls to just 20 pens for each ration.

But the complexity of on-farm trials is becoming apparent, says Mr Renold. "Elanco, who supplies tylosin, had to conduct large scale trials to establish that a dose of 20mg tylosin/kg feed gave pigs of 25-85kg liveweight an increase in growth rate of 33g/pig/day and an increase in feed conversion of 0.17.

Large numbers

"The problem for producers is finding out how much of this is achieved on an individual unit given the large numbers needed to get a sound result," he says.

The initial results indicate little advantage is achieved using AGPs and growth enhancers at Easton Lodge, but theres a reluctance to stop using them. "Its a complex exercise to see whether we can do without AGPs and growth enhancers should a full ban take effect," Mr Renold admits.

"But an independent, detailed examination of alternatives to AGPs would give us confidence. This should encompass their mode of action and how they relate to problems on-farm, such as poor hygiene. Sadly, nobody has got to grips with it."

Following the trial, rations at Easton Lodge will be supplemented with a growth enhancer supplied by the units compound feed supplier as and when required, he says. &#42

&#8226 Minimal benefit found.

&#8226 Numbers insignificant.

&#8226 No boost for healthy pigs.