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Age and cereal effects on the performance, gut parameters and nutrient utilisation in the newly hatched broiler chick : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science at Massey University
This study was intended to provide a platform for enhanced nutritional management of modern broilers through better understanding of changes in nutritional utilisation in the newly hatched chick. Differences in performance, nutrient utilisation and the development of the gastrointestinal tract in the young broiler chicken fed diets based on different cereals were examined. Diets based on wheat, sorghum and maize and formulated to contain iso-energy and iso-lysine levels were fed to broiler chicks between days 1 and 14 post hatch. Birds fed the maize based diet grew faster (P < 0.05) than those fed the sorghum based diet. Weight gains of birds fed the wheat based diet did not differ (P > 0.05) from those fed either maize or sorghum based diets. There were numerical differences in feed:gain with the sorghum based diet having the highest feed per gain, but the differences were not significant (P > 0.05). The relative weights of digestive organs and digestive tract showed no significant cereal treatment differences (P > 0.05). The treatments had no effect (P > 0.05) on the relative length of the digestive tract or gut histology measurements. The wheat based diet contained a commercial xylanase which may have ameliorated the digesta viscosity of this diet and reduced the NSP effect on gut structure and morphology. Furthermore, gut morphology samples showed a high degree of variation, suggesting that a large sample size would be necessary for significant differences to be determined. Two experiments were conducted to investigate cereal and age effects on nutrient utilisation in the young broiler chicken. Experiment 1 determined the nitrogen-corrected apparent metabolis able eneigy (AMEn) of diets based on wheat, sorghum and maize during 14 days post-hatch. Changes in the total tract digestibility of starch and fat were also measured. The second experiment was conducted to confirm the results of Experiment 1 using wheat and maize based diets and was of 21 days duration. In both experiments, changes to AMEn with age were similar for all diets, declining from day 3 to days 5-9 and increasing again. In experiment 1, cereal effects were significant (P < 0.05) with maize and sorghum based diets having higher AMEn values than the wheat based diet, In experiment 2, cereal effects were significant (P < 0.05) with the maize based diet having a higher AMEn than the wheat based diet. In experiment 1, total tract starch digestibility determined for days 5, 7 and 14 showed no cereal differences (P > 0.05). Age effects were significant (P < 0.05) with starch digestibility declining from day 5 to day 7, and then increasing again. Total tract fat digestibility on day 7 was significantly lower for the wheat and sorghum based diets than for the maize based diet, but no cereal differences (P > 0.05) were observed on days 5 or 14. Age effect was highly significant with fat digestibility declining from day 5 to day 7 and increasing again. These results showed that nutrient utilisation is compromised during the first week of life of the broiler chick. Samples of diets and excreta from Experiment 1 were analysed for minerals to determine changes in the apparent total tract mineral retention of the broiler chick during the first two weeks post-hatch. The diet and excreta samples were analysed for calcium, phosphorus, potassium, sodium, magnesium, iron, manganese, zinc and copper, and their retention was determined. The retention coefficients of individual minerals differed widely and the retentions of major minerals were much greater than those of minor minerals. The cereal effects were significant (P < 0.05) for several minerals, with a general tendency for the sorghum diet to have greater retention than maize or wheat diets. Age effects were significant (P < 0.05) for all minerals. In general mineral retention coefficients were higher at day 3, declined to day 7 and remained unchanged to day 14. Decline in mineral retention with age was similar in all three diets. The studies reported in this thesis investigated the performance and nutrient utilisation of broiler chicks fed diets based on wheat, sorghum or maize. A significant reduction in nutrient utilisation over the period 5-9 days of age was observed suggesting that nutrient digestion and absorption is compromised during the first week of life of the broiler chick. Further work is required to identify the specific causes of the decline in digestibility during the early stages of chick development.