Does it take antibiotics to preventively reduce the existence of E. coli in the porcine gastro-intestinal tract? Not at all – there are several natural ways to fight the pathogen's existence. Two recent field studies, using live yeast, resulted in a promising reduction of both mortality and morbidity due to pathogenic E. coli in newborn and weaned pigs.
By Dr Romain D’Inca, Lesaffre Feed Additives swine R&D manager, France
Over the past decades, various living micro-organisms such as yeasts and bacteria have been tested with success as probiotics. Firstly dedicated to human digestive comfort, their use progressively reaches livestock production. Indeed, probiotics feed additives have proven their efficacy in animals by improving zootechnical performances in many species, including monogastrics such as pigs.
As a consequence, various registrations of live yeasts have been validated by the EU for their contributions to pig performances in field conditions. The modes of action contributing to the increase of animal performances have been largely studied (particularly for live yeasts) using in vitro screening, development of rodent models or human clinical trials. Over the past years, laboratory trials have demonstrated live yeasts’ ability to stabilise gut microflora and capacity to reduce impact of many pathogenic bacteria, including Escherichia coli, therefore proving some potential health benefits of live yeasts. On the other hand, laboratory works sometimes failed in demonstrating a beneficial impact of probiotics on the growth of large animals, because of wide variability in the results. Moreover, laboratory conditions are generally not representative of field conditions for these large animals.
Requirements of field trials
Therefore, field evaluation of live yeast effects remains essential. Because most of the live yeast effects are gut orientated, tests in species exposed to intestinal disorders and diseases such as pigs are highly relevant.
Around weaning, piglets are exposed to stressors (feed change, building transfer, crowding with unknown penmates etc.) that increase their susceptibility to intestinal disturbance and diarrhoea, generally involving pathogenic E. coli. This is particularly true when neonatal development has been suboptimal. To control E. coli-induced diarrhoea, use of antibiotics is generally required to prevent reduction of performances or death. As the use of antibiotics is more and more a matter of concern, particularly in Europe, we investigated to which extent use of probiotic live yeast may be effective to reduce diarrhoea before and after weaning in pigs at two farms with historical diarrhoea problems due to E. coli.
One experiment was performed in a farrow-to-finish farm with 500 sows during neonatal period. A total of 32 sows (348 piglets) received standard feed. Half of the sows and their piglets received Saccharomyces cerevisiae live yeast (Actisaf Sc 47, Lesaffre Feed Additives, France) at the dose of 1,000 ppm. Presence of E. coli, diarrhoea and mortality, prestarter consumption, piglets’ weight and ADG were followed up to weaning at 28 days. A second experiment was performed in a farrow-to-finish farm with 600 sows during the post-weaning period. A total of 486 piglets weaned at 25 days received standard mash liquid feed until 80 days.
Half of the piglets received Saccharomyces cerevisiae live yeast at the dose of 1,000 ppm. From each treatment, ten piglets were randomly selected, weighed at the beginning and end of the post-weaning period and subjected to daily diarrhoea scoring:
- Score 1: no diarrhoea signs;
- Score 2: pasty faeces, active piglets;
- Score 3: watery faeces, active piglets;
- Score 4: severe diarrhoea, apathic piglets.Identification of the pathogen responsible for the diarrhoea was performed. All data were evaluated by several statistical tests.
Effects in newborn piglets
Detection of E. coli strains in ‘control’ newborn animals at two and three weeks of life confirmed the implication of haemolytic E. coli in the mortality of newborn piglets observed in the farm.
Saccharomyces cerevisiae treatment (SC) in sows and their piglets completely prevented presence of pathogenic E. coli in the faeces of the piglets at two and three weeks of life (Figure 1). Animals in the SC group presented low or nil diarrhoea symptoms. As postulated, live yeast positively contributed to the establishment of a stable flora, reducing pathogenic E. coli colonisation and symptoms in the piglets’ gut. Reduced contamination of the piglets from the sow receiving live yeast probably also occurred, but this parameter was not investigated in the present study. At this farm, live yeast reduced ETEC pressure on piglets leading to an important reduction of the mortality among litters. Of high interest to farmers, one extra piglet per sow per litter was weaned in the SC group compared to the control group (Table 1).
Effects in post-weaning pigs
Similar protective effect was observed in post-weaning piglets. Detection of pathogenic E. coli strains in two piglets of the control group confirmed the origin of the diarrhoea. No pathogenic E. coli were found in the SC group. A strong protective effect was observed against ETEC-induced diarrhoea. Control animals exhibited severe diarrhoea from 10 to 13 days postweaning (reaching a maximum at 11 days) whereas in SC group almost low or no diarrhoea was observed (Figure 2).
These results confirm that the weaning piglets were protected from E. coli-induced diarrhoea via the action of the live yeast. No significant differences were observed in the daily growth of the weaned piglets (Table 2) but supplemented pigs had a slight numerical increase of ADG (8 g/day/piglet), shortening the duration of post-weaning period by one day (Table 2).
These two trials realised in field conditions confirm that live yeast can contribute to the improvement of pig health status both around birth and in the postweaning period, as demonstrated in humans or rodents. Due to the known action of live yeast on pathogens already proven, several modes of action can be identified, that have contributed to the reduction of both mortality and morbidity of the animals in the present two studies. Firstly, it is demonstrated that SC can improve colostrum and milk immune quality. In the study, increased IgG content of the milk improved the development of the immune system of the piglets. Moreover a direct ingestion of the live yeast via the sow’s faeces may have occurred, resulting in a direct immunomodulation of the gut cells of the piglets as it is demonstrated in vitro.
Secondly, the capacity of the live yeast to stabilise gut microflora and competition with the other microorganisms has prevented ETEC colonisation of the gut in postweaning animals and reduced the diarrhoea during this critical period. Combined together, all these mechanisms of action of live yeast on the flora and the gut have positively impacted on the health status of the litters and of post-weaning pigs.
In these experiments, no significant improvement of the animals’ growth was observed using live yeast, contrary to what can be observed in healthy animals. It can be safely assumed that in these challenged conditions with E. coli pressure on piglets, energy extracted from the feed has been redirected in priority for immune protection and health maintenance, whereas in healthy animals it can be redirected for growth purposes. This is of high importance because in field conditions, some of the trials can fail to demonstrate a positive impact of live yeast (and probiotics in general) because of underlying challenging conditions of the animals. PPReferences are available on request.