The study investigated the probiotic effects of Saccharomyces cerevisiae on pullets development and hen-day egg performance of the layers. A total of 120 chicks were brooded for 4 weeks, after which 100 pullets were randomly selected and placed in 4 groups (A-D) of 25 birds each. Groups A, B and C had their feed supplemented with S. cerevisiae at graded levels of 0.6, 0.8 and 1.0 g/kg of feed respectively.

Group D diet did not contain S. cerevisiae (control). The diets for all the groups contained 25% PKC and they were isocaloric and isonitrogenous. The pullets were weighed weekly. At 9th, 15th and 40th week of age, 5 birds were randomly selected from each pen and 2 ml. of blood collected into an EDTA bottle for haematology. The blood sample was used to determine packed cell volume (PCV), haemoglobin concentration (HbC), total leukocyte count (TLC) and differential leukocyte count following standard procedures. At 10th and 40th week of age, 3 pullets were randomly selected from each group and placed in four different cages. The quantity of feed consumed and faeces voided were determined, proximately analyzed and used to determine the apparent digestibility of the diets. Eggs were collected three times daily, weighed and their external qualities were assessed. At the 20th week in lay, another set of 5 layers were randomly selected from each group and 5 ml of blood were collected from each bird and allowed to clot. The serum harvested was used to evaluate the serum biochemistry of the layers. At the 22nd week in lay, ten eggs were randomly selected from each group and were used to determine the egg cholesterol content. Five layers from each treatment group were randomly selected at the 70th week in lay, slaughtered and their gastrointestinal tract (GIT) carefully removed. The weight and length of the different sections of the gastrointestinal tract were determined. At the 24th month of age, another set of 5 layers were randomly selected from each group and used to evaluate the carcass quality. Repeat measure and one-way analysis of variance (ANOVA) were used to analyze the results. Variant means were separated using Duncan’s new multiple range test. Significance was accepted at p< 0.05. Group C birds had significantly (p<05) higher mean live weight than the group D birds (control). The PCV of group C birds was significantly higher (p < 0.05) than those of all other groups at weeks 9 and 15 of age. The group C birds also had significantly higher (p<0.05) TLC and lymphocytes counts than the control group (D). Apparent digestibility coefficient of dry matter, organic matter, crude protein and crude fibre were significantly (p<0.05) higher in the probiotic supplemented groups than the control. Group C had an overall significantly (p<0.05) higher hen-day egg performance of followed by groups B and A, while group D had the least hen-day egg performance. Birds in the supplemented groups had significantly higher (p<0.05) serum total proteins and significantly lower serum cholesterol when compared to the control. Eggs from the supplemented groups had significantly (p<0.05) lower cholesterol content when compared to the control. Group C birds had a significantly (p<0.05) longer colon than the control. There was no significant difference (p>0.05) in egg qualities (egg size, egg weight and shell thickness) between the supplemented groups and the control. The economic returns from sale of eggs was significantly higher (p<0.05) in group C birds in the first year of lay, but in the second year of lay, all supplemented groups had significantly higher (p<0.05) monthly revenue from eggs compared to the control. It was concluded that supplementation with probiotic S. cerevisiae significantly (p<0.05) enhanced pullet development, hen-day egg performance and monthly revenue from eggs, and significantly (p<0.05) lowered serum and egg cholesterol levels. The probiotic supplementation was most effective at the level of 1.0 g/kg of feed, and this is recommended.

There have been several definitions for the word probiotics over the years. Lilly and Stillwell (1965) used it to describe substances produced by one protozoan which stimulates another. But Parker (1974) described it as animal feed supplements which had a beneficial effect on the host animal by affecting its gut flora. Fuller (1989) revised the definition and described probiotics as a live microbial feed supplement, which beneficially affects the host animal by improving its intestinal microbial balance. Other workers had also given their own definitions of the term probiotic. Donohue et al (1998) described probiotic bacteria as viable bacteria which when applied in a single or mixed culture, exhibit a beneficial effect on the health of the host. The most recent definition was by Schrezenmeir and De Vrese (2001). They defined probiotics as viable microbial food supplements which beneficially influence the health of the host. This new definition clearly points out the health promoting effect of probiotic agents. Probiotics were more recently defined by a group of experts convened by the Food and Agriculture Organization of the United Nations (FAO, 2005) as "live microorganisms administered in adequate amounts which confer a beneficial health effect on the host”.

The probiotic concept was introduced in the early 20th century by Elie Metschnikoff. Since then, different microorganisms have been used for their supposed ability to prevent and cure diseases leading to the coining of the term probiotics, or “pro-life” (Lilly and Stillwell, 1965) from two Greek wards ‘pro’ which means ‘for’ or in ‘support’ and ‘bios’ which means ‘life’. About 1900, Henry Tissier, a French Pediatrician, observed that children with diarrhea had in their stools a low number of bacteria characterized by a peculiar, Y shaped morphology. Those “bifid” bacteria were, on the contrary, abundant in healthy children (Tissier, 1906). Nobel laureate Elie Metchnikoff in 1907 advocated that the consumption of Lactobacilli helps in controlling endogenous intoxication (autointoxication) caused by wrong types of components in the intestinal flora. He pointed out that the long, healthy lives of Bulgarian peasants were the result of their consumption of fermented milk products which contained probiotics. The works of Metchnikoff and Tissier were the first to make scientific suggestions about the probiotic use of bacteria. The first clinical trials were done in the 1930s on the effect of probiotics on constipation (Koop-Hoolihan, 2001). Majority of the probiotic products in current use contain bacteria from the genera Lactobacillus  or Bifidobacteriumalthough    other    genera,    including     Escherichia,    Enterococcus,    Bacillus     and Saccharomyces have been marketed as probiotics (Oyetayo and Oyetayo, 2005).

In Nigeria, there is a very low animal protein intake as a result of poverty and overpopulation (Obi, 2004). Thus, the great need for a radical approach to livestock production. The present daily protein allowance for Nigerians according to Atsu et al., (2002) is as low as 4.5g of protein per head per day which is abyssimally low compared to the recommended animal protein intake of 14g per head per day by F.A.O.( 1997 ). Poultry production is very important in the agriculture of developing countries (Musangi, 1992). FAO (1997) recommended that the deficit in animal protein supply and consumption in developing countries should be ameliorated by increased poultry, pork and rabbit production. Smith (1990) suggested that the supply of poultry products in poorer countries can be rapidly expanded to meet their animal protein need. This is technically possible because poultry are able to adapt to most areas of the world, have low capital requirement, have rapid generation time and a high rate of productivity. Besides excellent nutritive value, egg possesses several health promoting, immunostimulating and therapeutic properties which makes it a versatile product. At every age and stage of life, eggs have a role to play. During pregnancy; eggs provide high quality proteins, vitamins and minerals, omega-3 fatty oils essential for both maternal and foetal health (Narahari, 2003). Narahari (2003) further stated the importance of nutrients contained in the egg as follows: Egg choline is needed for proper development of a child’s brain. The requirement of a pregnant woman for egg choline is about 450 mg/day, while the requirement for a nursing mother is 550 mg/day. Older people need choline to activate their memory. Egg leutin and zeaxanthin are essential to prevent macular degeneration in adults. There is more to eggs than just a good nutrition. They also contain constituents that help in the treatment of a wide range of human health problems from wounds and rashes to cancer and cardiovascular diseases (Narahari, 2003). Eggs will induce and increase satiety (i.e reduce hunger). This will improve compliance with weight loss diet and enhance the benefits of a weight loss regimen. Despite being the proteinous food with the highest biological value, eggs still cost......

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