With more countries legislating against the prophylactic use of antibiotics, pig producers are looking for alternative strategies to maintain gut health and performance of weaned piglets. Inevitably, most are looking for a solution that involves the inclusion of alternative materials in the diet, such as organic acids, phytoceuticals, or probiotics.
The attraction of these alternatives is that they require little or no change to feeding practices. A more radical solution is to feed weaned pigs on liquid diets. Over the last twenty years, it has been shown that liquid diets can improve both the health and performance of weaned pigs.
Liquid feeding, gut health
So why do liquid diets support good gut health? First, liquid feeding helps overcome the transient starvation many pigs suffer at weaning. Pigs that have been growing at 300 grams per day while suckling, often grow at less than half that rate in the week following weaning.
When suckling, the piglets’ hunger and thirst are satisfied by sow’s milk, while their feeding regime is programmed by her nursing behavior. After weaning, the piglet has to learn to distinguish between the physiological drives of hunger and thirst, and then satisfy these drives by consuming water and solid food.
This can take some time. Some pigs require more than 24 hours to take their first feed, or drink, post-weaning. We found that weaned pigs can take more than a week to achieve a daily fluid intake equivalent to that on the day before weaning. This food and water deprivation has a dramatic effect on the digestive tract of the pig, reducing villus height and, consequently, absorptive capacity of the gut, which can then be a precursor to colibacillosis infection. Feed intake needs to be well above maintenance in order to maintain villus height and overall gut health.
Liquid feeding can help overcome this problem. In the study presented in Figure 1, villus height and microvillus surface area were respectively 34 and 31 percent greater when pigs were fed liquid diets. Many of the nutrients required for the growth of the gut epithelium come directly from the gut.
Consequently, it is likely that the improved nutrient intake on liquid feed has a direct influence on the growth of the gut. This in turn increases its absorptive capacity and facilitates greater growth of the pig. In the same study, feed intake was 55 percent and growth rate 38 percent greater on liquid feed.
In our studies at Plymouth University, feed (dry matter) intake has ranged from 20 to 80 percent higher in pigs fed liquid diets in the four weeks post weaning. Crucially, in the first week post weaning intake was 36-220 percent greater on liquid feed. A great number of published studies have reported post weaning growth rates 12-25 percent higher on liquid diets.
The second way that liquid feeding impacts health, is that it affects the balance of ‘good’ and ‘bad’ bacteria in the gut. The ratio of lactic acid bacteria to coliforms (Lab:Coli) in the gut can be used as an indicator of gut health. We found that coliform numbers increased rapidly post weaning when pigs were fed pelleted diets as shown in Table 2, but the numbers were similar to the pre-weaning level if the pigs were fed freshly prepared liquid diets.
If the pigs were fed fermented liquid feed, coliform numbers were reduced dramatically and the Lab:Coli ratio was similar to that found in pigs fed antibiotic growth promoters. This suggested that fermented liquid feed could be an alternative to antibiotic growth promoters.
Fermented liquid feed
Under experimental conditions, fermented liquid feed has produced extremely good results. The two factors primarily responsible for the beneficial effects associated with fermented liquid feed are the high numbers of lactic acid bacteria and the lactic acid that they produce. In an adult pig, the stomach produces a high concentration of hydrochloric acid. This is bactericidal and acts as a first line of defence in the gut, killing potentially harmful organisms like coliforms and salmonellae ingested with the food.
The stomach of the young pig does not produce enough acid to do this, so harmful bacteria can pass through and establish themselves in the gut. The faecal/oral route is the main mode of transmission of salmonella and while salmonellosis is not seen as a serious problem in pigs, it is very significant for human health.
Correctly prepared fermented liquid feed can significantly reduce the transmission of enterobacteria. These organisms cannot proliferate in fermented liquid feed containing 100-150 mmol lactic acid. Additionally, the fermented liquid feed can compensate for the low production of acid by the stomach; enhancing the barrier function of that organ. The increase in acidity also helps to improve protein digestion, which starts with hydrolysis in the stomach under acid conditions. In challenge studies, we found that fermented liquid feed both increased the pigs’ resistance to colonisation by salmonella and reduced faecal shedding in pigs previously infected with salmonella.
Two published studies suggest that feeding fermented liquid feed may also have a beneficial effect on another important disease organism, Lawsonia intracellularis. In one study, fermented liquid feed delayed faecal excretion of Lawsonia intracellularis when pigs were challenged with that organism and in the other, feeding fermented liquid feed for six weeks resulted in a lower prevalence of faecal Lawsonia intracellularis (15 percent vs. 26 percent).
Commercial applications
Although liquid feeding has proved extremely beneficial under experimental conditions, it has proved difficult to realise these benefits on commercial units. If liquid feed is going to be fed ad libitum it will inevitably ferment due to the presence of LAB and yeasts present in the feed.
Therefore many pig producers have been attracted to the idea of using fermented liquid feed. Unfortunately, spontaneous fermentation and the practice of inoculating fresh batches of feed with previously fermented feed (‘backslopping’) to speed up the fermentation process produces extremely variable and often poor quality fermented liquid feed.
To achieve bactericidal levels of lactic acid in fermented liquid feed requires skilful formulation of diets, the use of a LAB inoculant, and excellent hygiene throughout the feed preparation and distribution process. As this has proved beyond the capability of many units, the way forward may be to ferment a major portion of the feed components, using food industry production standards, before they are delivered to the farm.
