INTRODUCTION
Since their discovery, antibiotics have been used as therapeutic and growth-promoting agents and this has lead to improvements in the performance of animals (Doyle, 2001). However, the development of bacterial resistance (Ogawara, 1981; Russell, 1991) and the problem of antibiotic residues in animal products have lead to regulatory pressure and public perception of the need to ban antibiotics from animal feeds (Han, 2007). Thus it is necessary to identify alternative to antibiotics to maintain growth performance (Bae et al., 1999). Organic acids, probiotics, prebiotics, and phytogenic substances have been tested as possible alternatives to replace antibiotics (Kamel, 2001; An et al., 2008). The addition of organic acids like citric, fumaric, formic and propionic acid to the diets of pigs is one of the most widely used alternative for antibiotics and has been reported to improve their performance (Kirchgessner et al., 1997; Partanen and Mroz, 1999). Their effects have been related to reduction in the growth of coliform bacteria (Partanen, 2001), known to be involved in digestive disorders.
Wood vinegar is the product obtained by distilling the smoke arising from burning wood and it is a complex mixture of 80-90% water, and 10-20% organic compounds. In addition wood vinegar contains several phenolic compounds such as guaiacol and cresol, and organic acids like acetic, formic and propionic acids. It can be refined by fractional distillation to produce a food-grade product (Sakaguchi et al., 2007). Wood vinegar is being used to remove the odor of landfill site leachate (Huh et al., 1999) and ammonia in animal farms (Park et al., 2003). Wood vinegar has been shown to induce a significant increase in egg production and improvements in the feed efficiency of laying hens (Sakaida et al., 1987; Li and Ryu, 2001) and to enhance intestinal calcium absorption in rats (Kishi et al., 1999). Nonetheless, there are fewer reports on the effect of wood vinegar in pigs and thus further scientific investigations are needed.
Therefore, we conducted this study to determine the optimal inclusion level of wood vinegar (Exp. 1) and to comparatively evaluate the use of wood vinegar as an alternative to antibiotic in the diet of weanling pigs (Exp. 2).
MATERIALS AND METHODS
Experimental design, animals and their diets
In Exp. 1, 224 crossbred weanling pigs (Landracex YorkshirexDuroc; average BW of 6.12 [+ or -] 0.10 kg; 21 [+ or -] 3 d of age) were used to investigate the effect of adding different levels of wood vinegar in the diet on performance and nutrient digestibility. Pigs were randomly allotted to four treatments based on body weight and gender (male: female, 1:1). Each treatment had 4 replications with 14 pigs per replicate. Experimental feeding of mash diets was done for 28 days in two phases: phase I (d 0 to 14) and phase II (d 15 to 28). The ingredient and chemical composition of basal diets for both phases is presented in Table 1. Wood vinegar was added to the basal diets at 0.0, 0.1, 0.2 and 0.3% as dietary treatments. All nutrients met or exceeded NRC (1998) requirements. The diets of 0.0, 0.1, 0.2 and 0.3% wood vinegar treatments had 21.25, 21.18, 21.23 and 21.22% crude protein and 1.66, 1.62, 1.65 and 1.67% lysine in phase I diets, and 19.2, 19.5, 19.3 and 19.2% crude protein and 1.35, 1.35, 1.34 and 1.36% lysine in phase II diets, respectively.
In Exp. 2 comparisons were made among different growth promoters (antibiotic, organic acid and wood vinegar) added to the diets of piglets by studying their growth performance, apparent fecal nutrient and ileal amino acid digestibility and intestinal microflora. Weanling pigs (n = 224; Landrace x Yorkshire x Duroc; average body weight of 6.62 [+ or -] 0.31 kg; 21 [+ or -] 3 d of age) were randomly allotted to four treatments based on body weight and gender (male: female, 1:1). Each treatment had 4 replications with 14 pigs per replicate. The dietary treatments were control (corn-soybean meal basal diet without antibiotics) and basal diets added with 0.2% antibiotic (aparamycin), 0.2% organic acid and 0.2% wood vinegar. The ingredient and chemical composition of experimental diets is presented in Table 2. All nutrients met or exceeded NRC (1998) requirements. The experimental diets in mash form were fed for 28 days in 2 phases: phase I (d 0 to 14) and phase II (d 15 to 28). The analyzed composition of control, antibiotic, organic acid and wood vinegar diets used during phase I showed 20.83, 20.78, 20.82 and 20.80% crude protein and 1.53, 1.50, 1.54 and 1.51% lysine, respectively; and phase II diets had 19.98, 20.00, 19.96 and 19.91 % crude protein and 1.30, 1.31, 1.29 and 1.28% lysine, respectively.
In both experiments, pigs were housed in partially slotted and concrete floor pens of 1.90x2.54 m size with a self feeder and nipple drinker to allow ad libitum access to the feed and water. The experiments underwent proper ethical standards and were approved by the Animal Care and Use Committee of Kangwon National University.
Wood vinegar (Vital Force L[R]) used in the present study was obtained from Kangwon Mogcho Industrial Co. Ltd., Yeongwol-gun, Gangwon-do, Korea. Oak (Quercus acutissima) chips of Yeongwol-gun were burned at 500 to 700[degrees]C then the smoke was cooled by a water cooling system and distilled. The crude vinegar was stored for more than 6 months and then the supernatant was collected, purified and used. The chemical composition of wood vinegar as analyzed by the Korean Forest Research Institute (KFRI, 2002) showed 3.99% acetic acid and 10.89% propionic acid. The organic acid was obtained from Korean Milk Product Inc. (Pyeongtaek, Gyeonggi-do, Korea), and was composed of 21% phosphoric acid, 3.25% propionic acid, 2.8% formic acid, 10% calcium formate and 5% calcium propionate.
Measurements and sampling
In both experiments the individual pigs were weighed at the end of each phase and the feed offered and refusals from each pen were noted to calculate average daily gain (ADG), average daily feed intake (ADFI) and feed efficiency (F/G).
In order to study the apparent fecal nutrient digestibility, all pigs were fed their originally assigned diets mixed with chromic oxide (0.25%) from d 21 to 28 of …
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