الفهرس 
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Abstract
Use of water electrolyte supplementation for three days prior to processing helps alleviate the consequences of a severe thermal challenge on performance in meat chickens.
Abstract:
The effects of supplying water with an ‘in-house’ or commercial electrolyte formulation for 3 d during severe heat stress on performance and meat quality of meat chickens was investigated. At day 35 of age, Cobb-500 meat chickens (N =22, 11 of each sex/treatment) were allocated to 36 floor pens (12 pens/ treatment). The three treatments were, 1: (Control) tap water; 2: ‘In-house’ electrolytes at 416.4 g/100 L water; 3: commercial electrolyte−at 200 g/100 L water. The treatments were applied from 16:00 h on d 39 to 17:00 h on d 42 of age. On d 40-42 the ambient temperature remained at 20-22 ⁰C (17:00-08:00 h), then gradually over 08:00-12:00 h increased to a maximum of 32 ⁰C where it remained until 15:00 h, and then reduced to 20-22 ⁰C at 17:00 h. The severity of heat stress was assessed using the following Thermal-Humidity Index (THI): THI (%) = 0.8Tdb + RH (Tdb-14.3)/100 + 46.3. At 18:30 h on d 42 birds were loaded and transported to the processing plant and held in lairage overnight. Individual body weights, pen feed and water intakes were recorded at the start and end of the supplementations. In the morning, at the processing plant birds were weighed before and after evisceration with carcasses then stored overnight at 2 ⁰C and the following morning breast muscle meat quality traits were determined. Based on the THI values, at peak temperature, birds suffered ‘severe thermal discomfort’. Liveweight was improved in both sexes treated with the ‘in-house’ electrolyte but only males benefited on the commercial electrolyte. The ‘in-house’ electrolyte improved feed efficiency. There were no effects on losses during transport and lairage or breast muscle yield and meat quality. Behavioural observations indicated that birds spent 74-81 percent of their time crouching on the litter. Temperature beneath crouching birds was on average 4.4 ⁰C higher than the ambient temperature and could be adding to the thermal challenge experienced by the birds and warrants further investigation. When supplied during periods of high temperature, electrolyte water supplementation alleviates in part the performance losses.
Chapter 2:
Performance, behaviour, breast yield and AME of meat chickens fed a reduced protein finisher diet while exposed to severe acute or moderate chronic thermal challenges.
Normal performance can be achieved by feeding low crude protein (LCP) finisher diets when supplemented with adequate essential amino acids. The question remains as to the adequacy of LCP diets under high temperature stress. The performance of meat chickens was determined when fed an LCP finisher diet while exposed to an acute (AT) or chronic (CT) thermal challenge or thermo-neutral conditions (TN). Day-old male Ross 308 chicks (N =360) were reared in floor pens until d 28 and then transferred to metabolism cages (5 birds/cage) and housed in environmentally controlled metabolism rooms, maintained at 20 °C until d 38 of age. In room 1, birds were exposed to CT, 28 ℃ for 5 h/d on d 38- 42 (22 cages). Room 2 was maintained at 20 °C on d 38-39 and then increased rapidly to 30-32 °C for 3 h/d (AT) on d 40-42 (22 cages). The birds in the remaining 22 cages of room 2, were removed 1 h before the AT and held in a third room at TN and returned to room 2 when the temperature had returned to 20 °C. For each temperature treatment equal number of cages were fed either a control finisher (20.3 % protein) or LCP diet (17% protein) on d 28-42 of age. Individual bodyweights and pen feed intake were determined on d 28 and d 38 (TN and CT) and d 40 (TN and AT) and all on d 42. Total excreta were collected d 40-42 to determine AME, AMEn and % protein retention. On d 43 breast weight and the % breast muscle yield were determined. Bird behaviours were recorded over d 38-42 of age. The AT resulted in a 32.3 % reduced LWG, had no effect on feed intake but FCR was 22.3 % poorer. The CT had no adverse effects on bird performance. The diet CP had no effects on performance under either challenge. The thermal challenges or diet CP had no effects on breast muscle yields, AME, AMEn or % protein retention. Depending on the thermal condition birds spent 73-90 % of their time crouching. The absence of any adverse effects of the CT suggest it was of moderate severity and birds coped. However, based on the reduced performance, mortality and removals, and high % of birds panting, the AT caused ‘severe’ to ‘life-threating’ conditions. The reduction in CP had no consequence under these thermal conditions.