Effects of yeast extracts, with and without oxygenised™ water, on the performance and gut histology of broiler chickens

Strict restrictions in the EU on the use of antibiotic growth promoters in poultry diets were introduced in June, 1999. This was due to the concern over the possibility of resistant bacteria being passed from animals to humans, resulting in infections that are more difficult to treat. For European animal production to remain competitive with the rest of the world, where such products are likely to remain in use, there is a clear need for safe alternatives. One such alternative is the addition of yeast and yeast products to poultry diets. The inclusion of yeast in the diet has been shown to improve bird performance and decrease mortality (Miles and Bootwalla, 1991; Madrigal et al., 1993; Bradley et al., 1994). Oxygenised water has been reported to improve performance under field conditions but no scientific studies have been reported. The aim of this experiment is to investigate the effect of yeast products, with or without oxygenised water, on the performance and gut histology of broilers. Birds were fed a diet based on commercial formulation containing (g/kg) wheat 650, soya 194, full fat soya 40, fish meal, 40, vegetable fat blend 25, minerals etc. 51. The diet was split into 4 batches; to three of the batches a different yeast product was added (Y2, Y6 and Y8) at a rate of 100 g/tonne and the 4th batch was the control (C). Y2 and Y6 were yeast extracts and Y8 was a dried yeast. Half of the birds in each batch were given oxygenised water, giving a 4 2 factorial design. All of the diets contained enzyme and coccidiostat. Sixty four Cobb broiler chicks were used in two consecutive time replicates. At hatch, 100 birds were placed in a tiered brooder and given ad libitum access to a commercial starter diet, half being given oxygenised water (O) and the other half normal tap water. At 7 d, the birds offered oxygenised water were weighed and 32 were blocked in units of 4 and randomised to one of the 4 diets. The same was done for the birds given tap water. Birds were placed in individual wire metabolism cages and arranged by weight block throughout the room. The birds were fed ad libitum from 7–35 d, with the oxygenised water being replaced daily. The birds and feed consumed were weighed weekly to allow the calculation of weekly dry matter intake (DMI), live weight gain (LWG) and gain: feed of each bird. A 7 d excreta collection was carried out for AME determination between 14 and 21 d. At 35 d the birds were killed by lethal injection. The intestine was removed and sections of tissue taken from three positions (duodenum, jejunum and ileum). The viscosity of jejunal digesta supernatant was also determined. The results were statistically analysed using analysis of variance (ANOVA). For the first 7 d of the experiment, DMI and LWG were affected (P < 0.05) by the addition of yeast, with Y2 having a positive effect (Table). The effect on gain : feed was almost significant (P1⁄4 0.055). Over the duration of the experiment total DMI, LWG and gain : feed were not significantly affected by the yeast treatments but were numerically higher (DMI 5; 4%; LWG 8; 3%) for yeasts Y2 and Y8 than for the control. The oxygenised water had a negative effect (P < 0.05) on DMI and LWG during the first 7 d, but this effect was lost over the complete period. There was a water*diet interaction for metabolisability (ME/GE) of the diets but differences were small. As expected villus height decreased along the intestine in all birds (Table). Neither histological