General guidelines on liquid feeding for pigs

By the UK's Meat and Livestock Commission - This article looks at the potential advantages of liquid feeding for pigs, and looks at the reasons to liquid feed, controlled fermentation, restricted or ad lib, ingredients, considerations, hygiene and equipment maintenance.
calendar icon 14 August 2003
clock icon 11 minute read

Why liquid feed ?

Meat and Livestock Commission

Liquid feeding is not new. Traditionally many pigs were fed on meal mixed in a bucket with whey or water. Increasing farm size and the need for automation saw a move to dry feeding but recent developments in computer-driven systems have led to a revival of liquid feeding.

Piglets are fed on liquid milk by their mothers until weaning and it is logical to continue to feed them on a liquid diet provided that it can be delivered by a reliable and hygienic system. Growing and finishing pigs as well as lactating sows have been shown to perform better on liquid feed provided that the diet is formulated correctly and proper hygiene control is maintained.

Liquid feed can provide the pig with its essential daily energy and nutrients at a lower cost because it enables the use of industrial co-products from the human food industry that can be cheaper than conventional feed ingredients. In addition digestibility is often improved by using liquid feed.

The digestibility of feeds can be improved by the use of enzymes, which work more efficiently in liquid than in dry diets. Controlled fermentation of liquid feeds can exclude undesirable bacteria which present a risk to pig health and to the safety of pig meat for human consumption.

A few considerations over liquid feeding

Many existing units were designed for dry feeding and the capital cost of conversion to liquid feeding can be high. For new units, the cost of installing liquid feeding is no higher than for dry feed systems at comparable levels of automation and control over feed delivery.

Liquid ingredients and finished feeds ferment and this can cause problems if not controlled. Young piglets are particularly sensitive to unpalatable feed, whether wet or dry and this can adversely affect feed intake and growth performance. The level of hygiene required to achieve good results from liquid-fed weaners must be high, but results can justify the higher degree of control.

Effluent output can be higher when liquid feed is used because of the extra volume of water consumed by the pigs. However, the quantity of waste nitrogen and phosphorus excreted by liquid-fed pigs is not increased compared with dry feeding, and furthermore can be reduced by phase-feeding and the application of feed enzymes to improve digestibility.

Anyone setting up a liquid feeding system will be classified as an “on-farm mixer of animal feed stuffs”, and accordingly will need to be registered with the local Trading Standards office under Statutory Instrument No. 1872, “Feeding Stuffs (Establishments and Intermediaries) Regulations 1999”. Under this legislation,Trading Standards are required to inspect the premises and examine mixing facilities, equipment, processes and quality control.

The inspection may also involve submitting a sample of feeding materials for analysis. Any premises carrying out on-farm mixing is required to comply with quality standards, one of which is to have a written quality control plan. Trading Standards should provide guidance on any such requirements.

The potential for controlled fermentation of liquid feeds

Over many centuries, fermentation has been safely used to produce a range of human food and drinks such as wine, beer and dairy products. Liquid feed will start to ferment immediately after dry and wet ingredients are mixed. This is caused by naturally occurring bacteria and yeasts present in feed ingredients and the environment.

They will convert starch and sugars in the feed into organic acids such as lactic acid, acetic acid and into alcohol. If malfermentation ensues, feed soon becomes unpalatable to pigs, for example with the production of excessive amounts of the vinegar acids such as acetic acid. However, some fermentations can enhance both the palatability and the digestibility of feed and recent MLC and Defra funded research has set out to find a means of establishing and maintaining these beneficial fermentations and ensuring their safe use on farms.

One important benefit of fermentation is the establishment of a low pH in the feed as this can increase digestibility and also improve bio-security. A pH of 4 or less in a lactic acid-based fermentation will, within 12 hours, inactivate or kill Salmonella and Coliform bacteria that may be naturally present in the feed.

A low pH can also be achieved by using acidic ingredients such as whey or by adding organic acids to each batch of feed.

Early liquid feed systems were designed for restricted-feeding of growing and finishing pigs in long troughs but now short trough systems have been developed, which are based on ad libitum feeding using sensor technology. There are different merits associated with each of these two systems and a number of factors will influence which system is appropriate for a given situation. These include existing building design, genotype, staff experience and management.

Restricted or ad lib feeding ?

Restricted feeding systems need to provide each pig within the pen with a feeding space at the trough. The length of trough required per pig should be calculated for the maximum weight of pig to be housed (see Table 1).

Table 1: Recommended trough space allowance for restricted liquid feeding.)
Average liveweight (kg) Trough length (mm/pig)
10 130 mm
10-20 160 mm
20-30 185 mm
30-50 215 mm
50-85 260 mm
85-110 275 mm
110-120 290 mm

Many restricted feeding systems rely on a feed curve to increase steadily feed allowance per pig per day. This should be calibrated in terms of energy and lysine supply per pig per day rather than weight of dry matter to allow for variations in raw materials.

Ad lib systems can run successfully with up to 8 pigs per feeding space but it is important to recognise that younger pigs prefer to feed together, and inadequate provision of trough space can lead to stress, vices and variable growth rates. Providing more than one trough per pen can reduce the effect of dominant pigs that may seek to restrict access to troughs. Ad lib systems rely on electronic probes that can malfunction if mounted close to metal pen divisions without proper insulation. All troughs should be observed at least twice daily to ensure that they are functioning correctly.

Ad lib systems are increasing in popularity and have been recommended to improve meat tenderness. However, with certain genotypes they may result in downgrading as a result of excessive fat deposition in the finishing stage, as pigs tend to find liquid feed more palatable and will consume more energy per day than on dry feed (see Table 2 for feed intakes).

Table 2: Average consumption of liquid feed (by volume) by pigs of different weights assuming 24-25% dietary dry matter, offered on an ad lib basis.
Liquid feed intake
(litres per pig per day)
10-20 2-4
20-40 4-8
40-60 5-10
60-100 9-14
Lactating sows 30-50

Feed ingredients used in liquid feeding

It is possible to use conventional dry rations mixed with water for liquid feeding, but one of the main benefits of using a liquid system is the ability to use a bigger range of raw materials. There is a range of liquid co-products from the human food industry of which the best known is whey. Others in common use are liquid potato, chocolate, yogurt and brewery co-products. Some products are brand marketed such as Greenwich Gold and Abrocarb, which are derivatives from the cereal processing industry.

Another range of materials which can be used in liquid feed systems are unripe cereals such as Corn Cob mix, crimped cereals and legumes and “humid maize” which is in common use in some other countries. All of these crops are harvested at 30-40% moisture content and are then processed by milling or crimping and ensiling.

A few key considerations

Diet construction and pig health and performance

  • Make sure that all ingredients meet regulatory requirements for pig feeding.
  • Take advice from experienced pig nutritionists before purchasing new ingredients, particularly liquid co-products as there may be nutritional and storage issues to consider (deliveries can often be in the region of 28 tonnes).
  • Use experienced pig nutritionists to formulate rations for liquid feed containing co-products and advise them of any changes in ingredients that may affect the formulation of premixes and rations.
  • Take samples for all feed ingredients delivered; some co-products can show high variability in dry matter content and nutritional value. Samples should be analysed for dry matter content and if necessary for nutritional composition. These values should be used to adjust feed formulations and control the dry matter content of the final diet. Dry matter content is important to intake and growth performance and can affect pig health if too low.
  • Samples should be placed in strong plastic bottles with secure tops to limit the risk of spillage. Sample bottles should be clearly labelled (date, ingredient type, address with postcode). Never use glass containers as these may explode under pressure from fermenting liquid feeds and may crack if frozen. Similarly, do not overfill your plastic sample pots.
  • Ensure that pigs have access to potable water in addition to liquid feed and bear in mind that rations containing co-products may vary in salt content.
  • Ensure that water is of potable quality and if possible above 20 degrees centigrade when added to liquid feed. Borehole water should be analysed before use.


  • Liquid co-products are often fermenting when delivered and can develop foam if not monitored. Pumps will not operate properly in a foaming liquid and pigs may not get the correct quantity of feed.
  • To limit the possibility of malfermentation, feed should be mixed in small quantities and fed to pigs within one hour of being mixed and troughs licked clean within 30 minutes. This is easier to manage with restricted feeding systems where feed can be mixed immediately prior to feeding.
  • With ad libitum systems, a volume of feed is retained in the tanks to meet the little and often feeding pattern of pigs throughout the day, and it is important that the risk of malfermentation is reduced by acidification through controlled fermentation or by the addition of acidified products.
  • If a controlled fermentation is used, do not feed a newly mixed ration until fermentation has been well established.
  • Risk of malfermentation can be reduced by developing a monitoring and quality control system with the advice of an experienced liquid feed nutritionist.

Hygiene and equipment maintenance

  • All surfaces in feed storage and processing areas should be cleaned regularly for operator safety and hygiene maintenance.
  • Ensure that any food splashing is cleaned up regularly and tank surfaces are washed to prevent growth of moulds and the attraction of rodents, wild birds or insects. Liquid feed mixing areas should have drainage points to allow them to be regularly pressure washed.
  • Dry ingredients should be stored away from wet mixing areas to prevent damp and development of moulds.
  • Pests and rodents should be controlled in feed storage and processing areas, and within pig buildings, as they can cause considerable damage to equipment and contaminate feeds.
  • Keep liquid feed tanks covered to prevent aerial contamination. Wet feed can quickly start fermenting after mixing. Ensure that troughs are cleaned up regularly as stale wet feed will quickly become unpalatable. In ad libitum systems this can be achieved by switching off delivery valves for appropriate periods of time (eg for 1–2 hours at the end of peak feeding activity).
  • Troughs should be thoroughly washed between batches of pigs. Storage tanks should be washed regularly.
  • Inspect all equipment regularly and look out for signs of wear and tear. Replace parts immediately if they are likely to cause systems failure.
  • Ensure that feed valves and computer systems are operating properly at all times. Valve rubbers deteriorate and a regular programme of maintenance should be part of the farm routine. Ensure that you have stock of any spare parts which require regular replacement or are at a high risk of frequent failure. Strategic installation of hand valves next to automatic valves in new installations will make servicing quick and easy.

Thinking of investing in a liquid feeding system ?

Reliable modern computer controlled liquid feeding systems offer many benefits and conveniences to pig production. However, to avoid potential pitfalls, producers new to liquid feeding should take independent advice before investing capital in a new system. Some helpful tips are given below:

  • Explore all potential suppliers with a proven track record in the manufacture, supply and installation of liquid feeding systems.
  • Take independent advice: commercial nutritionists with an established customer base using liquid feeds are a good source of information.
  • If possible, visit other units with liquid feeding installations and find out as much information as possible on the advantages and disadvantages found and experiences of other producers.
  • Ensure that the supplier can provide technical backup support, especially in the event of systems failure.
  • Consider the lifetime performance of the system. Make sure that replacement parts will be readily available.
  • Consider the likely range of products you may use as the viscosity of materials will impact on choice of pumps, (eg positive displacement or centrifugal).
  • Consider the level of complexity and staff training for systems operation.
Source: MLC - July 2003
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