Poultry production has been recognized as a short-term solution to meeting the protein needs of the people (Obi and Sonaiya, 1995). However, poultry production is hampered to a large extent by production losses due to diseases and high cost of medication (Appiah, 1993). Prevalent diseases include bacterial (e.g. Chronic respiratory disease), viral (e.g. Newcastle disease and Gumboro) and protozoan (e.g. Coccidiosis) which affect birds at various stages of life (Koney, 1993). Farmers rely heavily on vaccines, antibiotics and coccidiostats to maintain the health and productivity of these birds (Aning, 2006). The addition of sub-therapeutic doses of antibiotics to the diets of farm animals, according to Buchanan et al., (2008) was approved in the 1950‘s due mainly to the increase in demand for animal produce which called for the reduction in floor space of individual animals so as to allow the existing structures to accommodate more animals and the resulting problem of compromised sanitation and environmental conditions like improper ventilation (Doyle, 2001). Cook (2004) explained that the addition of sub-therapeutic doses of antibiotics to the diets of farm animals was accepted worldwide since these small doses of antibiotics did not only reduce the chances of disease outbreaks but also promoted the growth of farm animals leading to the reduction of time required for farm animals to reach market weight.
The use of antibiotics however can result in the development of resistant strains of microorganisms with associated increase in cost of control (Dibner and Richards, 2005). Attempts to minimize the use of veterinary drugs include adherence to hygienic standards and use of probiotics as feed additive (Simon, 2005).
Feed additives are substances of non-nutritive nature (e.g. chemicals, microbiological products including probiotics or microorganisms, hormones and drugs) used in minute amounts for the improvement of farm animal performance (Kamra and Pathak, 1996). Feedadditives may be added to the ration to increase weight gain, aid in controlling infections, or help in controlling parasites (Gillespie, 1983).
Probiotics are viable microbial and microbial fermentation products which exert their beneficial effects by decreasing the undesirable micro-flora population in the gastro-intestinal tract (Chiang and Hseih, 1995) and build-up resistance against diseases by stimulating the immune system (Cheeke, 1991). Probiotics have also been an approach that has been reported to have the potential to reduce enteric disease in poultry and subsequent contamination of poultry product (Chapman, 1989; Patterson and Burkholder, 2003). Guilot (2000) observed that there has been a renewed interest in the incorporation of probiotics as a result of reduction in the use of antibiotics as feed additive in animals. Many probiotics are isolated from gastro intestinal tract of healthy animals and hence natural which makes them devoid of unhealthy side effects to the animal and subsequently to the consumer (WU et al., 2008). Bonsu et al. (2012) found that the inclusion of a probiotic product, RE-3, in the diets of layers and layerss resulted in considerable reduction of body fat and serum cholesterol content (up to 16%) in layerss, a 15% decrease in cholesterol level of eggs, improved egg weight and reduced mortality in both layerss and layers. Dei et al., (2010) also indicated that the addition of RE-3 to the diets of grower birds significantly reduced mortality compared to birds on a control diet containing no probiotic. Probiotic (RE-3) has also been found to have a positive influence on average daily gain in pigs (Okai et al., 2010).
Probiotic-based products are continually being developed and studied. Some of these are RE-3 Plus, which is a fermentation product of RE-3, and P3, which is a Paenebacillus polymyxa-based probiotic product (BEST, Canada). The study therefore sought to assess the effects of these probiotic products (RE-3, RE-3 PLUS and P3) on egg production performance, mortality, fertility and hatchability of eggs.
Probiotics have been introduced as an alternative to antibiotics. The use of antibiotics as routine feed additives has been banned in some countries because of public concern over possible antibiotic residual effects and the development of drug-resistant bacteria. The commercial use of probiotics in poultry industry is relatively new. Probiotic represents a single or mixed culture of live microorganisms which when applied to animals, affects the host beneficially by improving the properties of indigenous micro flora (Hong et al., 2005).
Probiotics come under the category of as Generally Recognized as Safe (GRAS) ingredients classified by Food and Drug Administration (FDA). They have no side and residual effects. Probiotics regulates the microbial environment in the gut, reduce digestive upsets and prevent pathogenic gut bacteria, thereby improve live weight gain, improve feed conversion ratio, reduce mortality, increase feed conversion ratio in layers and increase egg production. Probiotics commercially available contains strains of genera lactobacillus (mainly), Bifidobacterium, Streptococcus, Bacillus, Bacteroides, Pediococcus, Leuconostoc, Propionibacterium,Saccharomyces cerevisiae and Aspergillus oryzae(Chaucheyras et al., 1995). In vitro and in vivo studies have demonstrated that lactic acidproducing bacteria are able to inhibit the growth of poultry pathogen like Salmonella and E. coli by lowering the pH of the gut (Kung, 2001; Lee et al., 2003; Frizzo et al., 2010).
The development of favorable micro flora in the gut of poultry can be enhanced by using probiotic especially during period of stress (Krehbiel et al., 2003). Consumption of contaminated feed, bad weather, poor-management,transportation, poor housing conditions, changes in feed, presence of aflatoxins in feed, prolonged antibiotic therapy and disease stress). Proposed production benefits of probiotics include enhanced survival of chicks, reduction or prevention of gastrointestinal disorders, increased growth rate, improved feed efficiency, enhanced immune responseand ammonia gas emission in layers house etc. The application of probiotics like Lactobacillus, yeast etc. is receiving much attention. The addition of these substances to the feed or their introduction to animal body exploits the potential of utilization of feed and improves the efficiency of utilization of feed (Nocek et al., 2002; Rose, 1987). Keeping all these facts in mind present study was undertaken to know the effect of probiotic on the performance of layers in terms of their growth, feed efficiency and meat quality etc.
In poultry, yeast probiotics have been found more effective than other probiotics to improve performance of birds (Reisinger et al., 2012; Yasar and Desen, 2014). Furthermore, a new report testing several probiotics of Lactobacillus spp. showed no favorable effects on layers performance (Olnood et al., 2015). Nevertheless, the supplementation of the diets with yeast probiotics at 0.15 to 0.3% have been shown to improve the performance of birds to a level achieved by the use of dietary antibiotic levels (Onifade et al., 1999). It has been recently shown that this kind of effect is due to the bacteriocin-producing effects of yeast probiotics when used single or together with lactic acid bacteria species in the diet of layers chickens (Chen et al., 2016).
1.1 AIM AND OBJECTIVES
The objectives of this review are to describe the effect of direct fed on digestive morphology and criteria for selection of probiotics and to summarize their application in the poultry industry.
1.2 Specific objectives
- Determination of weight, digestive organs (liver, gizzard).
- Histological assessment of the ileum
- Determination of the length of proventriculus and intestine.