Alternatives to Antimicrobial Growth Promoters Not As Effective As Traditional Antimicrobial Additives for Nursery Pigs

Livestock Update, May 2002

Allen Harper, Extension Animal Scientist ­ Swine and Mark Estienne, Swine Research Physiologist, Tidewater AREC

Pressure continues to mount against the use of antimicrobial growth promoters in livestock and poultry feeds. In March of this year the European Health and Consumer Protection Commission proposed a set of regulations that would essentially eliminate use of remaining antimicrobial feed additives in the European Union. Antimicrobial feed additive use is also facing criticism in the U.S. and Canada. Evidence of human and animal health problems associated with use of these products is very limited. But regulatory agencies, medical groups and consumer groups are expressing concern about the potential for development of resistant microbial populations and the potential for bacterial resistance to compromise human and animal disease treatment.

Because use of antimicrobial feed additives appears to face an uncertain future, some companies have attempted to develop alternative growth promoting products for the feed industry. One example includes mannanoligosaccharides such as Alltech's Bio-Mos^TM product. Mannanoligosaccharides are complex mannose sugars derived from the cell wall of yeast. They are proposed to reduce the ability of certain pathogenic bacteria to adhere to the intestinal lining. Although results have been inconsistent, some trials involving weanling and young starter pigs have shown improved performance with mannanoligosaccharide inclusion in the diet.

A second category of feed additive that potentially could serve as a replacement for antimicrobials is probiotics. Probiotics generally refer to live or dehydrated microbial cultures that are intended to increase the population of so-called beneficial bacteria in the gastrointestinal tract while competitively excluding bacteria that are negative to intestinal health and nutritional performance. Such products include Probios^TM, a dried culture of Lactobacillus acidophilus organisms, and Bioplus-2B^TM, a dried fermentation product of Bacillus licheniformis and subtilus organisms.

We recently evaluated two of these products in separate trials as single feed additives and in combination with the antimicrobial feed additive Mecadox^TM. Mecadox^TM is a widely used growth promoter that has been approved for use in weanling and starter pig diets since 1975. Each trial involved crossbred pigs ranging in age from 19 to 24 days at weaning. At the start of both trials the pigs had an average initial weight of 16.1 lbs. Pigs were housed in small pens in a conventional pig nursery room with 4 pigs (2 barrows and 2 gilts) in each pen. Both trials lasted for 5 weeks and pig weight and feed consumption were recorded weekly.

The first trial investigated BioMos^TM mannanoligosaccharide at the recommended feed inclusion rate of .3% during week 1 and .2% thereafter, alone and in combination with Mecadox^TM at the recommended inclusion rate of 50 grams per ton of feed. There were 5 pens of pigs per diet treatment. Table 1 shows pig performance results of this 5-week nursery trial. There was no response to the mannanoligosaccharide additive for any of the performance traits measured. In addition there was no interactive or additive effect of feeding the mannanoligosaccharide in combination with Mecadox^TM. However, use of the antimicrobial feed additive resulted in a significant increase of 10% in growth rate and a 9% increase in feed consumption.

Table 1. Performance of nursery pigs in response to a mannanoligosaccharide (BioMos^TM), an antimicrobial (Mecadox^TM) or both additives in the diet.

Item	Unsupplemented	BioMosTM	MecadoxTM*	BioMosTM + MecadoxTM
Daily Gain, lbs.	.98	.99	1.08	1.08
Daily Feed, lbs.	1.70	1.70	1.85	1.82
Feed/Gain	1.73	1.72	1.72	1.69

* Statistical improvement with Mecadox” for daily gain and daily feed intake.

The second trial investigated the probiotic BioPlus-2B^TM at the recommended inclusion rate of .1% of the diet, alone and in combination with Mecadox^TM at 50 grams per ton of feed. There were 7 pens per diet treatment. Results of this trial are shown in Table 2. Consistent with the first trial, Mecadox^TM was effective in increasing growth rate by about 8%. In this trial there was also a significant improvement in feed efficiency, with the Mecadox^TM supplemented pigs requiring less feed per unit of weight gain throughout the trial. However, dietary inclusion of the probiotic did not result in improved growth rate, feed intake or feed efficiency.

Table 2. Performance of nursery pigs in response to a probiotic (BioPlus-2B^TM), an antimicrobial (Mecadox^TM) or both additives in the diet.

Item	Unsupplemented	BioPlus-2BTM	MecadoxTM*	BioPlus-2BTM + MecadoxTM
Daily Gain, lbs.	1.06	1.01	1.15	1.11
Daily Feed, lbs.	1.72	1.67	1.80	1.75
Feed/Gain	1.62	1.66	1.57	1.58

* Statistical improvement with Mecadox^TM for daily gain and feed/gain ratio.

A recent comprehensive review of pig feeding trials involving these and other related products by researchers at Kansas State and North Dakota State Universities tends to support the findings of our two trials. This research review indicated that the response to the various types of potential replacement products for antimicrobial growth promoters is inconsistent and no response was observed in more cases than when a positive response was seen. It appears that the potential for currently available alternative feed additives to promote growth and maintain performance in the presence of sub-clinical disease is neither of the same consistency or magnitude as seen with the use of traditional antimicrobial growth promoters.

¹ Use of product trade names is for example purposes. No particular endorsement or exclusion is implied by use of these trade names.

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