Manure is a mixture of excreta (urine and faecal matter). It is composed of undigested dietary components, endogenous components and products from indigenous microorganisms and the biomass of those microorganisms. Some odorous volatile components (OVC), short-chain volatile fatty acids (VFA), and other volatile carbon-nitrogen and sulphur-containing compounds from microbial fermentation in the GI tract can be emitted immediately. Others are emitted at various times after excretion. Around 200 or more odour-causing compounds have been identified. The sensitivity of the individual compounds by olfactometry threshold detection varies widely (Aarnink, 1997; Sutton et al., 1999). Tables of threshold values are given in these papers. Similarly, Aarnink (1997) showed in model calculations that a 9% reduction of N in ammonium in slurry could be reached with each 1% reduction in dietary crude protein content, and this was confirmed by Sutton et al. (1999). They reduced crude protein from 13 to 10% or from 18 to 10% and added synthetic amino acids. The reduction in ammonia emission with each 1% reduction in CP is less than indicated above, if housing systems are such that high emission floors are used. The quality of manure will become important for the future. Some developments already show this. It is well known that by allowing proper microbial fermentation in the large intestine, more microbial biomass will be present in the excreta (Canh et al. 1998; Fig. 24.3). This results in apparently lower amounts of digestible N. However, ileal digestible N may be the same. The other consequence is that there is less N in the urine. This only occurs if fermentation continues in the large intestine of pigs (Houdijk, 1998).
As a consequence the C/N ratio in the manure is much higher. This is considered beneficial for soil life. Moreover loss of ammonia from the excreta is less.
Until now most emphasis has been on reducing total N in manure. It can be expected that by combining both a reduced excretion and a shift from urinary excretion to faecal excretion, reducing N in feed will result in an increase in fermentation. Jongbloed and Henkens (1996) reported that nitrogen excretion was reduced by 12% from growing pigs. The data were collected in The Netherlands from 1973 to 1995.
The successful implementation of most of the strategies that follow for reducing nutrient excretion is dependent on: (i) the accuracy of the estimates of the available nutrient requirements of the class of pig in question, (ii) the accuracy of the compositional information, w co
Control ■ Coconut A Soybean ♦ Sugarbeet
100 200 300 400 500
NSP intake (g day-1)
Fig. 24.3. Ammonia emission from slurry by pigs with different intakes of non-starch polysaccharides (NSP). (Canh et at., 1998.)
and (iii) the bioavailability of nutrients in the feed ingredients to be used.
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