Feed additives are non-nutritive feed ingredients that are used in swine to improve production efficiency and performance. In the absence of feed additives in the diet, no deficiency symptoms will result. However, if feed additives are chosen carefully based on the farm needs, they may help increase the profitability of pig production. There are various types of feed additives which have different functions such as increase feed intake, increase weight gain, improve gastrointestinal or reproductive health. The feed additives which this article will focus on are antibiotics, prebiotics and probiotics, copper and zinc, acidifiers, carnitine, chromium, flavours, mold inhibitors, mycotoxins binders, and antioxidants and phytase.
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Antibiotics have been widely used in swine feed for the last decades. This is because early studies show significant improvements in pig growth performance when the antibiotics were fed. Nowadays, people are aware of the antibiotics residue in pork and might affect health of the people. Therefore, with the improvements in production practices and health status of pig herds, in-feed antibiotics are greatly reduced compare to last decades. Antibiotics are included in the feed for promoting growth by inhibiting subclinical pathogenic bacterial infections and bacteria growth reducing microbial metabolism products. Decrease in number of pathogenic bacteria can increase nutrient uptake by the guts thereby improving growth of the pigs. However, the pathogenic microorganisms sometimes develop resistance to certain antibiotics causing the antibiotics to be less effective. Therefore, utilization of antibiotics is safer under a professional veterinarian consultation.
Prebiotics and Probiotics
Prebiotics are non-digestible food substances that can stimulate the growth of favourable species of bacteria in the gut of the pigs. The growth of beneficial bacteria is believed to improve the health of the gastrointestinal tracts, thereby increasing the performance of the host. Prebiotics are primarily derived from non-digestible oligosaccharides which are not digested and absorbed by the pig. Therefore, oligosaccharides such as oligofructose, fructooligosaccharide, and inulin provide substrates for the bacterial growth. Probiotics are live beneficial bacteria supplemented in pigs diet that help improving the microbial balance in gut. A probiotic must be able to survive in feed, able to replicate after passing acidic stomach environment and able to inhibit the growth of harmful bacteria. Probiotics are believed to have the ability to stimulate the immunity of the gastrointestinal tracts thus reduce infectious diseases of the gut.
Copper and Zinc
High dietary levels of copper and zinc are often given to the young pigs as many studies have shown that these two minerals are able to exert positive influences on growth rate. Copper increases growth performance of young pigs when it is supplied at high concentration (100-250 ppm) without the influence of the antibiotics in the diet. However, effect of high levels of dietary copper decreases as the age of the pigs increases or with long period of administration. High levels of dietary copper in feed might lead to copper toxicosis. Jaundice will develop when the skin and mucous membrane of the animals appear yellow due to excess accumulation of copper in the liver. Zinc fed at high dietary levels (2000 to 3000 ppm) reduces incidence of diarrhoea and increases weight gain in newly weaned pigs. If zinc is fed excessively in pigs, they might develop depression, arthritis, gastritis and might even lead to death. In addition, excessive feeding of copper and zinc will also result in more copper and zinc will be excreted out. High levels of copper and zinc being excreted out through faeces will result in accumulation of copper and zinc in the soils and thereby contaminate the soils.
Acidifiers are compounds that have acidic properties which can be in organic or inorganic forms. Organic acids which are commonly used in swine feed include citric, formic, fumaric and propionic acid while phosphoric acid is the most commonly utilized inorganic acid in swine diets. Acidifiers are commonly marketed as growth-promoters and as alternatives for in-feed antibiotics. However, use of acidifiers to replace antibiotic growth promoters is still not justified due to lack of consistent result. Acidifiers improve gut health through reduction of pH and buffering capacity of diets, improve pancreatic secretions which will increase digestibility of nutrient. In addition, acidifiers promote the growth of beneficial bacteria and inhibit growth of pathogenic bacteria. The disadvantages of acidifiers in excess are corrosive and decreased palatability.
Flavours are added to feed to increase the palatability and feed intake. Pigs need to be fed a balanced diet that meets their daily nutritional requirement for maintenance, growth and reproduction. To ensure that pigs receive all the nutrients, flavours are used to increase voluntary feed intake by enhancing the smell and taste. Flavours are often used at stages when feed intake is expected to be lower such as in the post weaning period. Piglets immediately after weaning are subjected to significant stress, so making the feed highly palatable may improve the performance. Most studies show that pigs have preference for sweet taste. Therefore, flavouring agents commonly added to the feed are saccharin and talin. However, pigs show preference for certain flavours when given a choice. When the pigs are not given a choice, flavours do not necessarily improve feed intake. Besides taste, there are many other factors which can affect feed intake. Therefore, evaluate the factors affecting feed intake before adding flavours into swine diet.
Carnitine is a vitamin like, water soluble compound that functions to transport fatty acids across the mitochondria membrane where they are processed to produce energy. Carnitine plays an important role in fatty acids metabolism. Young neonatal mammals do not have the ability to synthesize carnitine from lysine and that has been the driving force for interest in using carnitine in nursery pig diets. Most research that has been conducted with supplemental L-carnitine has been fed at a rate of 50 ppm of complete diet. L-carnitine will improve sow and litter performance by improving fetal growth and development and also increasing milk production. Studies also show that when L-carnitine is added in the diet of gestating sows, piglet birth weights in the subsequent litter will be increased and it also enhanced the development of muscle fibers. L-carnitine enhanced the proliferation and differentiation of myogenic (muscle fibers) precursor cells by affecting the gene expression. This process could give rise to increased fibre numbers at birth due to increased number of embryonic myoblasts, Waylan et al. (2005).
Chromium is a trace mineral that is actively involved in the metabolism of carbohydrates, lipids, protein and nucleic acids in the body. Chromium influences insulin action by increasing the cellular uptake of glucose and intracellular carbohydrate and cellular metabolism therefore improving glucose utilization. Several studies have shown that chromium has the potential in improving sow reproductive performance. Lindemann et al. (2004) reported statistical improvements in live born when sows were supplemented at 600 ppb (10.94) compared to control sows (9.49) and females fed 200 ppb (9.82). Additionally, there may be some additive effects of adding chromium and carnitine to sow diets because carnitine works through fat metabolism and chromium works through glucose metabolism and potentially creating some synergistic effects between the two feed additives.
Mold inhibitors, Mycotoxins Binders, and Antioxidants
Mold inhibitors, mycotoxins binders and antioxidants are added to feed to prolong shelf-life, prevent mold growth or bind mycotoxins present in the feed. Mycotoxins are chemical compounds produced by molds that can negatively affect the pig performance. Nevertheless, not all molds produce mycotoxins. The most significant mycotoxins affecting livestock production are aflatoxin, vomitoxin, zearalenone, fumonisin, and ochratoxin. Ingestion of mycotoxins will cause mycotoxin poisoning which is known as mycotoxicosis. Mycotoxicosis can cause lower resistance to disease, increased sensitivity to stress, and damage to vital organs, such as the liver and kidney.
Mold inhibitors are feed additives used to minimize mold contamination and prevent mold growth, thereby minimizing the risk of mycotoxicosis. Mold inhibitors commonly used are propionic acids and other organic acids. Even though the mold growth has been prevented, there might still have mycotoxins in the feed as mold inhibitors have no effect on mycotoxins already presented in contaminated feed. Therefore, mycotoxins will come to its use when mycotoxins are suspected present in the feed or when preventive measures against molds have failed. The most commonly used and researched mycotoxins binders are clays and zeolites. They are efficient towards aflatoxins but unfortunately they are not effective against other types of mycotoxins. Some studies have shown that the cell-wall fraction ß-glucan of yeasts such as Saccharomyces cereviceae can be effective in binding a wide range of mycotoxins, (Jouany, 2007). An antioxidant is added to the feed to prevent oxidation of fats or vitamins. Ethoxyquin, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and propyl gallate are the common commercial antioxidants. Combination of the antioxidants such as propyl gallate and BHA may provide high level of initial protection and also have longer effect. Antioxidants are highly applicable in areas which have warm climate. Besides, antioxidants are also widely used in diets which have high level of unsaturated fat for example fish meal. Oxidation of unsaturated fatty acids can cause changes in flavours and also cause rancidity of the feed. Adding an antioxidant minimizes fat oxidation, keeps the diet highly palatable, and helps prolong shelf life of the feeds.
Phytase is an enzyme which is added into the feed of the pigs to help in converting phytate into dietary phosphorus. Dietary phosphorus is essential for normal body maintenance and growth in pigs. Phosphorus is available abundantly in the form of phytate in grains such as wheat. With the addition of phytase in the feed the digestibility of phytate phosphorus can be increased. Several factors can influence the efficacy of phytase, including the amount of phytate in the diet, the amount of phytase added to the diet, and the type of phytase. Studies have shown greater responses to phytase in pigs fed diets that contain higher amounts of phytate, (Selle and Ravindran, 2008). Phytase is susceptible to denaturation when subjected to excessive heat for example during pelleting. Phytase does improve availability of calcium and other minerals in the diet, (Kies et al, 2006). Calcium is an essential mineral for milk production. Addition of phytase also results in an overall increase in energy value of the diet. Instead of adding inorganic phosphorus in the feed which has no energy value, more corn is added to the diet to obtain the phosphorus from the corn with the help of phytase, thereby increasing the energy value of the diet.
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Although main nutrient in the feed such as energy and protein are more emphasized than feed additives, many research and studies have been done and show that feed additives can enhance and improve the production of the pigs in different stages. As long as the feed additives are used according to regulations or consultation of a veterinarian, feed additives are usually safe and are able to improve the feed quality.
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