Abstract
Simple SummaryLiquid feed is produced by mixing dry feed ingredients with water, and sometimes liquid co-products from the food and beverage industry, at a defined ratio. Liquid feeding of pigs is popular, particularly in parts of northern and western Europe, and can be associated with lower feed costs, improved dry matter intake, growth rate and gut health, compared to dry feeding. However, spontaneous/uncontrolled fermentation upon mixing of feed with water or co-products can decrease the microbial and nutritional quality of the feed, resulting in poorer pig health and growth. For this reason, strategies aimed at optimising liquid feed microbial quality are frequently employed. These include: deliberate fermentation with/without the use of lactic acid bacteria starter cultures that produce lactic acid and lower the feed pH, thereby preventing growth of pathogens. Fermenting only the cereal component of the diet is preferred to whole diet fermentation to minimise loss of free amino acids from the diet during fermentation. This review examines the microbiome of liquid feed and explores how optimisation strategies impact both feed microbial quality and the gut microbiota and growth of liquid-fed pigs. It also covers cleaning and disinfection of liquid feeding systems and how this might impact liquid feed microbial quality.There is evidence that spontaneous fermentation frequently occurs in liquid pig feed that is intended to be delivered as fresh liquid feed, often with a resultant deterioration in the microbial and nutritional quality of the feed, which can negatively affect pig health and growth. Strategies including controlled fermentation with microbial inoculants, pre-fermentation or soaking of the cereal fraction of the diet, enzyme supplementation and dietary acidification have been employed to inhibit pathogens and prevent deterioration of feed nutritional quality, with promising results obtained in many cases. This review evaluates the impact of these strategies on the microbial quality of liquid feed and discusses how they can be further improved. It also investigates if/how these strategies impact the pig gut microbiota and growth performance of liquid-fed pigs. Finally, we review liquid feed system sanitisation practices, which are highly variable from farm to farm and discuss the impact of these practices and whether they are beneficial or detrimental to liquid feed microbial quality. Overall, we provide a comprehensive review of the current state of knowledge on liquid feed for pigs, focusing on factors affecting microbial quality and strategies for its optimisation, as well as its impact on the pig gut microbiome.
Highlights
Introduction to Liquid FeedIn this review, liquid feed refers to a mixture of dry feed components combined with either water and/or liquid food industry co-products, in a mixing tank to a pre-defined water:feed ratio, prior to feed-out
In addition to the improved dry matter (DM) intake and growth rates observed with liquid feeding [20,35,40], there are a number of practical benefits over dry feeding which include the ability to optimise microbial and nutritional quality via addition of feed additives such as starter cultures for controlled fermentation, enzyme preparations to improve nutrient digestibility, and direct acidification of feed using organic acids [16,41]
The SEGES Danish Pig Research Centre reported that it took several days following cleaning and/or disinfection of liquid feeding systems for lactic acid bacteria (LAB) fermentation to become re-established in the feed, allowing for the proliferation of coliforms in the days following cleaning, likely contributing to diarrhoea in the herds they studied [82]
Summary
Liquid feeding is common in many parts of the world, most notably in western Europe [3]. Approximate figures from Best [5] indicate that >60% of Danish and Swedish finishers, as well as the majority of sows, are liquid-fed. Liquid feeding has been adopted more readily in Europe due to the widespread availability of inexpensive nutrient-rich co-products from the food, beverage and biofuel industries, which aid in reducing feed costs by up to 17% compared to dry feed [3,9,10].
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