NUTRITION ▶▶▶
Water-to-feed ratios in growing-finishers
Interest in giving pigs wet feed has increased in recent decades, especially in Europe. There are still many unanswered questions about how to do this most efficiently. For instance: how much does the water-to-feed ratio matter in terms of the digestibility of energy and nutrients?
BY TREENA HEIN, CORRESPONDENT A
study of water-to-feed ratios in growing-finishing pigs was recently published by Professor Josep Gasa and colleagues at the Autonomous Universi- ty of Barcelona (UAB) in Spain, including Dr Ra-
mon Muns, who graduated from UAB and now leads the Mo- nogastric Research Group at the Agri-Food and Biosciences Institute (AFBI) in Northern Ireland, UK.
Why is liquid feed popular? Before looking at the results of this particular study, it is good to quickly recap the topic of liquid feed and why it has become a popular method for feeding pigs in many countries in Europe. In Prof Gasa’s view, one reason for this is the availability of liq- uid food industry co-products (e.g. from dairy processors), which makes liquid feeding cheaper than other alternatives. However, he adds, “Co-products vary significantly in composi- tion, and diet formulations need to be reviewed frequently. Also, in hotter months in warmer regions, for example Mediter- ranean countries, it is crucial to pay attention to the cleanliness and disinfection of liquid feeding systems.” Liquid feeding involves blending dry feed (a mixture of raw materials “as fed”) with water or a liquid co-product in a central tank before the mixture is pumped to the feeding pens through pipes. It contains about 700–800g of water per kilo- gramme, and the capacity of the pump and pipes that the feed travels through from the central tank to the feeding pens de- termines how much dry matter can be added to the mixture, that is, it must be thin enough to be pumped properly.
Study results In their research, Prof Gasa, Dr Muns and their colleagues found that the optimal water-to-feed ratio for improving organic matter and gross energy digestibility varies accord- ing to the age of the animal. “In particular, the water-to-feed ratios that improve digestibility coefficients were lower for young growing pigs and higher for older finishing pigs,” the team states. “The data suggest that optimum efficiency is
34 ▶ PIG PROGRESS | Volume 37, No. 1, 2021
reached with a less water-diluted diet for young animals, when compared to older pigs.” Younger pigs have a smaller gut, and the larger volume of a liquid diet can therefore make it difficult for them to con- sume the amount of dry matter (and therefore absorb enough nutrients) that will result in optimal growth. Prof Gasa notes that older pigs may produce more enzymes, boosting nutrient absorption. Their stomachs are also more developed, not just larger, making them inherently more able to absorb more nutrients/energy from liquid feed com- pared to younger pigs with less-developed guts. He con- cludes that with current technology (a feed kitchen, mixing tanks, pumps and pipes), “it is not clear that using liquid feeding across all stages would be beneficial. For the finish- ing and gestation stages it’s usually good, but at the nursery and lactation stages it might result in suboptimal intake.” When he was asked whether the speed of mixing and dis- tributing liquid feed to the pigs could make a difference in pig performance at any age, Prof Gasa said he doesn’t think so. “I don’t believe that shortening mixing or distribution time (we would be talking about a difference of ten or may- be 30 minutes) would affect digestibility and intake,” he says.
Wet/dry systems At AFBI, Dr Muns has recently been involved in some trials with a newish type of wet/dry feeding system, but wet/dry is also used to refer to feeders that have a water nipple in the trough. “In our system at AFBI, which happens to be made by Spotmix, water and the compound feed are kept separate up to the point of delivery to the feeding trough where they mix to some extent,” he explains. “This somewhat homogenises a meal diet, but it doesn’t work as well with pellets. I would say it’s closer to liquid feeding because you can have different dilution ratios that are similar to liquid systems. In their preliminary analysis, Dr Muns and his colleagues have found that feed conversion ratios with
PHOTO: DR RAMON MUNS
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