Mould and Salmonella Remain Key Enemies of Feed Quality
Mould and Salmonella are two key enemies of feed quality and both impact animal production and the consumer's perception on food safety. Implementation of feed hygiene programmes holds promise to help the industry defeat these two key enemies.
Most Asian countries use imported corn as the major source of energy for animal feed. Managing raw materials under adverse climatic conditions is crucial for retaining acceptable feed quality. Proper storage at high ambient temperature and high relative humidity is critical. Quality feed will only come from quality raw materials. Furthermore, feed is not consumed immediately after manufacture and considerable storage time of final feed is often required, e.g. 6-7 weeks in China. Mould and mycotoxin prevention and treatment are major challenges.
Mould growth poses a serious quality threat for crop growers, grain handling authorities, feed manufacturers and farmers. Cereal grains and by-products constitute important sources of energy and protein for pig and poultry diets. There is a significant risk of mycotoxin contamination when cereal grains and animal feed are colonised by mould. It is often decided that the amount of moisture in grain is insufficient to allow moulds to grow. However, it is often forgotten that moisture is not evenly distributed within a grain mass. Multiple samples need to be taken and the highest moisture level should be used when considering mould risk. It is well known, but often ignored, that moisture will move within a silo of grain in accordance with temperature gradients with condensation occurring on the inside surface of the silo. This dramatically increases the risk of mould growth and mycotoxin production and also creates grain lumping and flow problems. Broken kernels increase the susceptibility to mould growth.
The design and implementation of a sound mould inhibition strategy for grain and finished feed is vital for successful feed milling in countries with similar climatic conditions to Taiwan where corn is imported and stored in a very humid environment. Table 1 presents a broad guideline for applying a mould inhibitor to corn upon receipt in Taiwan. Note that the exact dosage of a mould inhibitor will be a function of initial moisture level, initial level of mould contamination, relative humidity in the grain storage environment, duration of storage and the physical quality of the grain including whether it's ground or whole. Preventing mould growth will prevent mycotoxin contamination.
Table 1. Guideline for mould inhibitor application at corn upon receipt
*Abnormal means undesirable ratio of fine materials, dust and black damaged kernels
** Consult Kemin for specific recommendations due to variable conditions
Salmonella control in feed and raw material
Control of the spread of Salmonella and Salmonellosis infection is a major concern for animal industries. Although the infection may be derived from a variety of sources, it is believed that a major problem is the contamination from feed and raw materials. Davis & Wray (1997) conducted a survey across UK feed mills and revealed the status of contamination from feed manufacturing sites (detection rate) as:
Many strategies have been taken to reduce Salmonella shedding in feed and animals, which included heat treatment or irradiation of feeds, feeding of competitive exclusion organism to animals, feeding of particular carbohydrates to animals and the application of organic acid products to feed. The use of organic acids has some advantages which include: no heating of feed required, commercial products are readily available, residual long-term effects, safe for humans and animals and unlikely to create bacterial resistance problems. As shown in table 2, a liquid Salmonella inhibitor is able to eliminate Salmonella from naturally contaminated poultry feed. No Salmonella were detected in poultry feed treated with Sal CURB after 24 hours.
Table 2. Control of natural Salmonella infection in poultry feed
*As organisms per 100 grams
Salmonella control in raw materials also requires good silo hygiene. Using dry Salmonella inhibitory products applied with a portable powder fogger can reduce the enterobacteriacceae counts in silos (Table 3).
Table 3. Control of total Enterobacteriacceae's in silo with Sal CURB dry*
*1 kg/10 tonnes capacity
Feed moisture content and pelleted feed
Pelleted feeds are fed to broilers due to ease of handling and improved gains in bird performance. Fairchild and Greer (1999) have demonstrated that increasing the moisture content of mash feed at the mixer subsequently decreased pellet mill energy usage and increased pellet durability. Free moisture as steam is added to feed during the pelleting process and despite cooling after pelleting, the added free moisture may increase the feed's water activity (aw) which can increase the risk of mould growth. Pelleted feed can also attract and absorb moisture during storage, which would present another challenge to feed quality. Hence, awareness of managing the risk of mould growth in pelleted feed is important. A trial was recently conducted in Taiwan to demonstrate how a liquid mould inhibitor can successfully assist in the prevention of mould growth in pelleted feed and hence ensure sound feed quality. Control feed was compared with the same feed treated with 0.5kg of mould inhibitor per tonne of feed. Feed samples were incubated in the laboratory and carbon dioxide was measured in the air space as a measure of microbial growth. The number of days taken to reach 8% carbon dioxide was greater with feed treated with the mould inhibitor indicating a more microbiologically stable feed (Figure 1). Hence, appropriate application of a mould inhibitor is an important part of the overall management of pelleted feed quality.
Figure 1. Carbon dioxide production from pelleted feed with and without Myco CURBÃ’ treatment
Mycotoxins and economic impact in pig production
Mycotoxins can produce a wide range of harmful effects in animals. Pigs fed with grains or grain by-products contaminated with mould or mycotoxins may exhibit chronic signs such as poor feed conversion, reduced productivity and decreased resistance to infection. Interference with reproductive capacity may have greater economic impact than that due to death. Safe levels of mycotoxins for pigs are not clear and can be complicated due to the combined effects of more than one toxin. However, the total cost associated with aflatoxin in corn and peanuts in Thailand, Indonesia and the Philippines was estimated to be USD 290 million per annum with corn accounting for 66% of the cost (Lubulwa & Davis, 1994). Recently, a total of 233 feed samples were collected from 8 feed mills and four regions in Taiwan for fumonisin determination. This survey showed that the fumonisin (FB1, FB2) contamination rate in swine feed and corn was 42% and 10-17% respectively (Table 4, Cheng et al., 2002).
Table 4. Prevalence and concentration of fumonisins (FB1, FB2) in corn-based feed & corn in Taiwan
a Percentage of positive samples detected by thin layer chromatography
b Means of fumonisin concentration detected by affinity chromatography from positive samples only
c,d Means in the same column with different superscripts differ significantly (P<0.05)
Toxin control and decontamination
The first line of defense should always be mould prevention and reduction with the use of a mould inhibitor on corn and finished feeds. However there are possibilities for preventing mycotoxicoses. Inclusion of sorbent materials in complete feed to reduce the adverse effects of mycotoxins is practised in the field. Figure 2 shows some results from a trial conduced by university researchers in India which confirmed that the use of a hydrated sodium calcium aluminosilicate (HSCAS) based sorbent material can effectively reduce the harmful effects from aflatoxin contamination. This study confirmed earlier work (Kubena et al., 1993). This HSCAS based toxin binder can be effectively applied to pig feeds when toxin problems are suspected.
Figure 2. Effects of Toxi BindÃ” Dry (2.5 kg/tonne) in broiler chickens
In modern feed formulation and production, feed quality is not only manufacturer's concern in order to produce 'clean' feed required for healthy animal production, but is also needed to satisfy the consumer's perception of food safety. Appropriate and proper application of mould inhibitors and Salmonella preventative and corrective actions as part of a total programme can provide the industry with tools to defeat the mould and Salmonella enemy and satisfy the ever increasing demands of the consumer.