Nutritive value for pigs and poultry of barley cultivars varying in beta-glucan content and starch characteristics : a thesis presented in partial fulfilment of the requirements for the degree of Master in Applied Science (Animal Science) at Massey University, Palmerston North, New Zealand
The nutritive value of a hulled conventional barley (NB) cultivar, four hulless barley cultivars (C0, Cl, C2 and C3) that varied in fibre and β-glucan contents and starch characteristics (waxiness), as well as a wheat (WT) was determined for pigs and broiler chickens. In the pig trial, the apparent digestible energy (ADE) of NB, C0, Cl, C2, C3 and elsewhere WT was determined. In the broiler trial, the apparent metabolizable energy (AME) content and ileal amino acid digestibility of NB, Cl, C2, and C3 were examined without or with exogenous (β-glucanase supplementation. The pig trial utilised 15 growing male pigs (average weight, 32.5 kg). The assay diets contained 99.75% of the test ingredient and were fortified with minerals and vitamins. The total faecal collection method was used. Faeces were collected, weighed and sub-sampled daily for 5 days after a week of acclimatisation period. The apparent digestible energy (ADE) of the four hulless barley cultivars ranged from 15.83 to 16.48 MJ/kg DM. The hulless barley cultivar C2 was significantly different (P<0.05) from hulled NB and wheat WT. However, hulless barley cultivars C0, Cl, and C3 did not differ (P > 0.05) significantly from each other and, even though they were numerically higher than values for NB and WT. In terms of the apparent digestibility coefficient (ADC), hulless barley Cl and C2 had the highest values (0.8795 and 0.8837, respectively), but these were not significantly different (P > 0.05) from hulless barley C0 and WT. The lowest ADE and ADC values were determined for hulled barley (15.59 MJ/kg and 0.8257, respectively). It was observed that the hulless barley with high non-starch polysaccharides (NSP) concentrations had the lowest ADE contents. In the broiler trial, the influence of exogenous β-glucanase (Allzyme BG; Alltech, Inc., Nicholasville, KY) supplementation on the apparent metabolisable energy (AME) and apparent ileal digestibility coefficient (AID) of amino acids in a normal, hulled barley cultivar and three hulless barley cultivars was investigated. The assay diets contained 96.3% barley, and were fortified with minerals and vitamins. Titanium oxide was included as an inert marker for the estimation of ileal amino acid digestibility. The AME of barley was influenced (P < 0.001) by the cultivar type. The AME of the NB was determined to be 12.68 MJ/kg DM. while the values for the three hulless cultivars were 10.87, 12.92 and 10.20 MJ/kg DM, respectively. These data suggest that starch characteristics and β-glucan contents are additional factors that may influence the available energy in barley. Pβ-glucanase supplementation improved (P < 0.001) the AME of all barley cultivars. with improvements ranging from 5.4 to 21.9%. The cultivar type had no influence (P>0.05) on the AID of most amino acids. The average AID of 15 amino acids in the hulled barley and the three hulless cultivars were 0.70, 0.68, 0.72 and 0.73, respectively. Enzyme supplementation improved (P < 0.001) the AID of all individual amino acids in the four barley cultivars, with increases in individual amino acid digestibility ranging from 18.1% for threonine to 11.4% for arginine. The average AID of 15 amino acids in the un-supplemented and supplemented cereal was 0.66 and 0.75, respectively. Overall, it was observed that the barley cultivars, which were high in NSP and β-glucan, had lower energy digestibility for pigs and broiler chickens. Hulless barley C2 that is characterized as having normal starch was found to have the highest available energy for both species.