Utilisation of spent brewer’s yeast as a protein feed supplement for growing pigs.
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A study consisting of a diagnostic survey and a feeding trial was conducted to establish the potential of utilising spent brewer’s yeast (SBY) as a protein source in diets of growing pigs. A pre-tested questionnaire was administered to a population of 30 farmers to characterise production, recovery and utilisation of SBY. A feeding trial was then conducted for 120 days involving 64 pigs (Large White x Landrace) with an initial mean weight of 9.3±0.5 kg. Pigs were randomly assigned to four dietary treatments to determine growth performance, digestibility of nutrients, slaughter characteristics and cost of feeding when dried SBY was used as a replacement for fish meal (Rastrinoabola argentia) at levels of 6, 8 and 10 percent in diet. The control diet contained pure maize bran and 0% SBY (1:0), other diets contained dried SBY recovered by sun drying the pasty mixtures of maize bran and liquid SBY in ratios 1:1, 1:1.5, 1:2, (w/v) on tarpaulins. A 14- day digestion trial involving 16 pigs was conducted to determine the digestibility of nutrients. Thirty two (32) pigs were slaughtered to determine the carcass yield and carcass characteristics. The financial benefit of replacing fish meal with SBY was determined using Gross Margin Analysis. The study revealed that 7.5% of the total fresh SBY production is fed to pigs, 4.8% dried by breweries and 87.7% is wasted. The majority of respondents (84%) use plastic tanks during transportation and storage of fresh SBY. Of these, 56% use hired vehicles to transport fresh SBY. The respondents (76.7%) were intensive farmers (10-59 pigs) within 10 km radius from breweries. Most of them (90%) were feeding pigs on water diluted SBY and 10% on boiled SBY. Majority (81.5%) were using specific dilution ratios (from 1:1 to 1:2) while 18.5% were not specific. They reported to ever noted incidences of drowsiness (40%), aggressiveness (36.7%) and diarrhea (23.3%) among pigs fed on fresh SBY. The unused SBY was being disposed in soak away pits (70%), open pits or buried (26.6%) and in water bodies (3.4%). The replacement of fish meal with 6% dried SBY in pig diet significantly (P<0.05) increased growth, chest width (21.94 cm) and intra-muscular fat (11.9%). Using more than 6% dried-SBY in diet significantly reduced nutrient digestibility (P<0.05). Dried SBY inclusion at 10% of diet significantly (P<0.05) reduced chest width (20.04cm), carcass length (80.40cm), weight of the 6th rib (154.01cm) and increased percentage weight of the liver (2.16%) and spleen (025%). A 6% dried SBY diet significantly (P<0.05) reduced the feed cost per kg gain (1902.23 Ushs) and with the highest gross margin (67282.18Ushs). Substituting fishmeal with dry SBY at 10% saves the farmer 500Ushs per kilogram but with lowest GI (14527.00 UShs). In conclusion, mixing maize bran with liquid SBY and subjecting the mixture to sun drying is an appropriate option for prolonged use of SBY and reduction in cost of pig feeding at farm level. For optimum economic and growth performance, replacement of fish with SBY in diets of growing pigs should not exceed 6%. Inclusion of SBY in diets of pigs produces leaner carcasses with low intra-muscular fat content.