Liquid feed in a broad sense can include any form of Liquid feed material and products in room temperature, such as molasses, Liquid oil, Liquid methionineanalog, Liquid milk Replacer and full price Liquid feed used in pig farming. Typical liquid feed usually refers to the mixture of water and feed or the mixture of food industry liquid by-products and conventional feed raw materials, dry matter content of 20% ~ 30%. Liquid feed (LF) or non-fermented Liquid feed (NFLF) if the water and feed are mixed in a 1.5-4:1 ratio immediately, or the fermented time is short.
Plus, if the mixture ferments long enough to get to a steady state, it's called Fermented Liquid feed (FLF), which usually includes both natural and inoculated feed Liquid feed used in pig production system is usually fermented liquid feed.
1、History of liquid feed development
In 1814, Henderson first advocated the use of liquid feed. The commercial-scale liquid feed production started in the United States in 1951, which is a rapidly developing field (Williams, 2003). The current annual output is about 2 million tons (AFIA, 2002, 2008). The LiquidFeedCommittee of the American Feed Industry Association holds an annual Industry meeting. But it wasn't until 1976 that Smith first showed that by soaking the feed in water for a certain amount of time before feeding, the naturally occurring lactobacillus and yeast in the grain would multiply and produce lactic acid, acetic acid and ethanol, which would then reduce the pH of the feed, possibly the precursor to fermented liquid feed. By the 1960s and 1970s, suspension technology was in use, allowing greater flexibility in liquid feed production. In recent years, foreign liquid feed after a few years of low after the rise again, gradually by nutritionists and aquaculture enterprises attention. However, the processing and utilization of liquid feed in China is still a new technology, and its research and production have just started. People's understanding of its effectiveness and importance is not deep enough.
2、Application characteristics of liquid feed
Liquid feed can use the by-products of the human food industry to reduce the feed cost. Many liquid by-products of food production are used in pig feed worldwide. In Europe, the recycling of liquid by-products from the food industry as nutrient-rich ingredients for pigs is particularly prevalent, such as starch-rich and sugar-rich byproducts: liquid wheat starch, potato steam skin and cheese whey. At least 30% of pigs in the European Union are fed liquid feed, mostly from dairy by-products, according to the survey. Liquid feed can also reduce dust loss during feed disposal and feeding and reduce dust in the air, thus improving the piggery environment and the health of pigs.
Pigs have a good palatability in obtaining both water and feed from liquid feed, so there is no need for separate training in gathering and drinking water. Feeding liquid feed can increase the feed intake and feed digestibility of piglets after weaning. However, care should be taken to assess the actual intake of food per day, otherwise pigs may overeat certain nutrients, such as protein. Excess protein inhibits feed utilization and eventually leads to restricted dry matter intake or diarrhea.
Feeding liquid feed, especially fermented liquid feed, had a positive effect on the intestinal health of pigs and reduced the number of salmonella bacteria. In addition, fermented liquid feed can be used as a cost-effective strategy to replace antibiotic growth promoters. The liquid feed can change the intestinal microbial fermentation of tryptophan to the production of indoles by using fecodine, reduce the deposition of indoles in the backfat of fattening pigs, and thus reduce the odor of boar taint.
But liquid feed also has its limitation in the process of application. Some researchers have noticed that liquid feed waste is relatively high, which may be related to the design of feed tank. In addition, although there is no direct evidence, tests have shown that liquid pig feeding is sometimes associated with the development of gastrointestinal bleeding syndrome, flatulence, and stomach ulcers. Fermentation also causes the loss of essential nutrients in the feed, such as vitamins and amino acids. Bioamines, for example, convert lysine into corpse amines, resulting in an irreversible loss of amino acid nutrients in pigs, which is why some researchers advocate partial grain fermentation rather than full feed fermentation.
3、Application of liquid feed on weaned piglets
Liquid feed can improve intestinal health of piglets. Deprez et al. (1987) reported that liquid feed could improve intestinal health and physiological function of piglets. Hurst(2001) found that the height and absorptive area of intestinal villi were significantly higher than those of weaned piglets fed with liquid feed. Kiyoshi et al. (2010) fed 4-week-old weaned piglets with fermented liquid feed significantly increased the structural diversity of ileum and cecum flora of piglets. Li Yongming et al. (2010) found that fermented liquid grain feed could promote the diversity of intestinal microflora and the balance of intestinal microecosystem in 14-day-old super early weaned piglets. According to the analysis by Li And others (2010), the content of E. coli in piglets' feces was reduced by 84.9%, the content of Lactobacillus was increased by 145.9%, and the ratio of Lactobacillus to E. coli was increased by 10.3 times, thus enabling piglets to have stronger resistance to deal with the microecological disturbance of digestive tract caused by various factors.
Liquid feed can improve palatability of feed and growth performance of piglets. Li Fang (2010) reported that the daily feed intake of weaned piglets was increased by 41.7%(P<0.01), the daily weight gain was increased by 107.5%(P<0.01), and the feed conversion rate was increased by 36.9%. Liu Yan (2016) reported that when weaned piglets were fed liquid feed, the feed intake increased by 10.45% ~ 20.05%, and the weight gain rate increased by 7.75% ~ 13.61%. Li Yongming et al. (2010) also found that feeding fermented grain liquid feed could significantly increase the daily feed intake and daily weight gain of super early weaned piglets. Chen Xixin et al. (2011) showed that lactobacillus inoculation could improve diarrhea of weaned piglets and increase apparent digestibility of nutrients, and lactobacillus maize inoculation had the most significant effect.
Russell et al. (L996) found that weaned piglets fed with a water feed ratio of 2.5∶ L had a higher feed intake and growth rate than those fed with the same formula. Murphy et al. (2002) reported that the weight of l4-day-old weaned piglets fed with liquid feed increased by 2L % and the average daily weight gain increased by 44% compared with the dry diet piglets fed with the same nutritional level. Piglets fed liquid diet for the first 3 days after weaning gained weight almost 4 times faster than piglets fed dry diet (248 g/d Vs 64 g/d). However, the difference in average daily weight gain between liquid and dry feed piglets decreased rapidly as the day age of the piglets increased. Therefore, the effect of liquid feed on piglets at the early weaning stage is more obvious.
4、Application of liquid feed to growing and fattening pigs
In the fattening stage of pigs, the important advantage of liquid feed is that cheap liquid raw materials, such as liquid amino acids, enzymes and food industrial by-products (beer by-products, potato processing by-products) can be used in the feed formula in large quantities, which not only reduces environmental pollution, but also reduces feed cost. As far as feeding effect is concerned, the digestive tract and immune system of growth and finishing pigs are well developed, so the application effect of liquid feed on growth and finishing pigs is generally worse than that of piglets. However, liquid feed also has an impact on the microbial community and growth performance of growth and finishing pigs. Studies have shown that the number of days required to reach the same weight (110 kg) during liquid feeding decreased by 3%(150.6d Vs 154.7d) and the homogeneity of marketed pigs increased. Canibe(2003) reported that the feeding of liquid feed improved the growth performance of growing pigs (995 g/d Vs 961 g/d), reduced the pH in pigs' stomachs (4.0 Vs 4.4 ~ 4.6), and increased the lactic acid level in pigs (113 mmoL/kg Vs 50 ~ 60 mmoL/kg). Chen Xixin et al. (2010) found that lactic acid bacteria fermentation liquid feed could improve the level of lactic acid bacteria in manure of finishing pigs, reduce the level of Escherichia coli and Salmonella, and improve the growth performance.
5、Application of liquid feed to sows
Liquid feed can promote satiety in pregnant sows; It can improve dry matter feed intake and production performance of Suckling sows. Fermented liquid feed can also improve the health of piglets by improving the intestinal health of sows. Jensen(1998) and Demeckova et al. (2002) found that the amount of E. coli in intestines and feces of sows fed with fermented liquid feed was significantly reduced, which was helpful to reduce the amount of E. coli in the living environment of piglets and enhance the physique of Suckling piglets. Demeckova et al. (2002) also found that fermented liquid feed could improve the mitogenic activity of small intestinal mucosal epithelial cells (IEC-6) and blood lymphocytes of sows, and could increase the content of growth-promoting and immune-active substances in sows. The authors also found that the number of lactic acid bacteria in the feces of piglets fed with fermented liquid feed was significantly increased and the number of E. coli was significantly decreased.
6、Development trend of liquid feed
In general, liquid feed was more effective than growing pigs and sows. The feeding effect of piglets in the first 2 weeks after weaning was significantly better than that in the second 2 weeks. However, the research on liquid feed is still at the exploratory stage, and its application is mainly limited to weaning piglets. There are still a series of problems to be studied, such as: how to develop a more scientific and reasonable liquid feed formula? How to match with modern large-scale farming methods in terms of processing, transportation and feeding? How to develop reliable and efficient liquid feed processing equipment and feeding equipment? How to rationally apply the liquid by-products of food industry in each physiological stage of pig? How to add various additives (organic acids, enzyme preparations, probiotics, etc.) in liquid feed scientifically and how to replace the feasibility of antibiotics? And so on.
It is a scientific attitude to stick to problem orientation, find and solve problems. It is believed that with the continuous deepening and systematization of liquid feed research, the continuous development of processing machinery and equipment, the continuous improvement of supporting feeding technology, and the reduction of use cost, liquid feed will be gradually accepted by breeding enterprises, and will play an increasingly important role in pig production, and liquid feed will have a broad application prospect.
