D. Balnave

Sudies on low metabolisable energy wheats for poultry using conventional and rapid assay procedures and the effects of processing

1. A significant proportion of wheat cultivars grown in New South Wales had low apparent metabolisable energy (AME) values (< 13.0 MJ/kg dry matter) for growing broilers when determined by the conventional total collection technique. 2. The low AME was due to a reduced starch digestibility and was not improved by grinding the wheat finely or by steam pelleting the diet. 3. Higher AME values were obtained when determinations were made with adult cockerels than with growing broilers when the conventional technique was used. 4. AME values determined using a rapid bioassay technique (Farrell, 1978) with growing broilers or adult cockerels were considerably higher than values determined using the conventional procedure with growing broilers. 5. Inter‐laboratory studies showed that the true metabolisable energy (TME) assay gave reproducible values for individual and blended wheat samples, but that these values were higher than AME values determined by the conventional procedure. Similar TME values were found wi...

The influence of environmental temperature, age and sex on the digestibility of amino acids in growing broiler chickens

The ability of the broiler chicken to metabolise energy and to digest and absorb amino acids increased from 30 to 50 d of age. Although sex had no major effect on metabolisable energy or amino acid digestibilities at these ages, the influence of environmental temperature on amino acid digestibilities appeared to be sex-related, there being decreased digestibilities of most amino acids at higher temperatures in female but not male birds.

Effects of dietary mineral supplementation on the performance and mineral retentions of broilers at high ambient temperatures

1. The relationship between broiler performance and two dietary mineral balance equations was investigated at a high constant ambient temperature (30 degrees C) using a range of 11 salt supplements given to male broiler chicks from 21 to 42 d of age. 2. No relationship was found between broiler performance and either of the two balance equations. 3. Re-evaluating these equations using retained, rather than dietary, mineral concentrations did not improve the relationship although changes in mineral retentions associated with the supplements indicated that dietary concentrations were not a good indicator of the impact of the diet on the birds acid-base homoeostasis. 4. Evidence was found that metabolisable anions supplemented in association with mineral cations may have a significant effect on broiler performance.

Comparison between concentrated complete diets and self‐selection for feeding sexually‐maturing pullets at hot and cold temperatures

Abstract 1. Pullets in late growth and early lay were maintained at hot (25° to 35°C) or cold (6° to 16°C) ambient temperatures and either fed complete diets or allowed to self‐select nutrients from separate energy‐ and protein‐rich foods. 2. Manipulating the metabolisable energy (ME) and/or nutrient density (ND) of complete layer diets failed to improve egg output at hot temperatures to that obtained at cold temperatures. 3. At both temperatures self‐selection increased protein, but not ME, intake. This increased egg output and body weight gain at the hot, but not cold, temperatures. At the hot temperatures pullets fed by self‐selection were the only ones to gain weight between sexual maturity and 28 weeks of age. 4. Nutrient intake patterns, related to each pullets physiological age of sexual maturity, identified distinctive changes in protein intake and the selected protein: ME intake ratio of pullets fed by self‐selection. Pullets attempted to maintain a preferred protein:ME intake ratio, irrespectiv...

Phosphorus requirements of laying hens fed on wheat‐based diets

1. Three experiments were carried out to determine the phosphorus (P) requirements of laying hens aged 34 to 58 weeks (experiment 1), 59 to 70 weeks (experiment 2) and 22 to 50 weeks (experiment 3) given diets containing wheat, sorghum and soyabean meals as the main ingredients. Dietary total P (Pt) varied between 3.2 and 7.3 g/kg (experiment 1), 3.2 and 4.6 g/kg (experiment 2) and 3.0 and 6.6 g/kg (experiment 3). Hens were housed at either 18 degrees or 30 degrees C (experiments 1 and 2) and uncontrolled temperature (experiment 3), and in experiment 2 diets were fed without or with a phytase supplement of 500 units/g. 2. Dietary Pt had no significant effect on production measures in any experiment. Increases in dietary Pt adversely influenced egg shell quality although uterine calcium (Ca), ATPase and carbonic anhydrase activities were unaffected. 3. A 3-d-feeding trial in experiment 1 gave maximum Pt retentions of 228 mg/d at 18 degrees C and 204 mg/d at 30 degrees C. These were obtained with diets containing, respectively, 4.6 and 6.0 g Pt/kg. 4. Plasma inorganic P (Pi) increased consistently with increases in dietary Pt at all temperatures but plasma total Ca, and tibia Ca and P, were unaffected. 5. The inclusion of the phytase supplement in diets containing 3.2 and 4.6 g Pt/kg had an adverse effect on egg production at both temperatures in experiment 2. 6. A dietary Pt concentration of 3.2 g/kg, providing a calculated 1.2 g available P (Pav)/kg, with a dietary phytase activity of less than 200 units/kg, satisfied the P requirements of the hens used in these studies. However, the data from experiment 3 suggest that the Pt requirement of some flocks fed on wheat-based diets may be lower than 3.2 g/kg.

Influence of temperature, dietary energy, nutrient concentration and self‐selection feeding on the retention of dietary energy, protein and calcium by sexually‐maturing egg‐laying pullets

1. On a daily temperature cycle of 25 to 35 degrees C and during the onset of lay, gross energy in droppings were increased significantly by 3 to 5%. There were no changes in energy metabolisability. Overall, less energy was excreted and energy metabolisability was improved on higher energy diets. 2. Crude protein and calcium losses decreased and their retention efficiencies increased with the onset of lay. Less protein and calcium were lost at the high temperature with corresponding increases in retention. Less protein and more calcium were lost on the higher energy diet. 3. Crude protein excretion was increased and calcium excretion reduced with self-selection feeding. Energy metabolisability and crude protein retention efficiency were reduced by this feeding practice.

Free‐choice feeding of broilers at high temperatures

Broilers fed complete diets to 21 but not 44 d of age grew faster with a better efficiency of food utilisation than broilers given a free-choice selection of the cereal and protein components. When finisher diets, varying in metabolisable energy (ME) and amino acid:ME ratios, were fed at high ambient temperatures (25 to 35 degrees C) broilers on the free-choice system selected similar amino acid:ME intake ratios, which were lower than the ratios contained in the complete diets. Differences in broiler performance between 22 and 44 d of age reflected variations in ME rather than amino acid intake.

Effect of dietary amino acids and metabolisable energy on the performance of broilers kept at high temperatures

Increasing dietary metabolisable energy (ME) at particular amino acid: ME ratios significantly improved growth and food utilisation of broilers kept at moderate (18 to 26 degrees C) and high (25 to 35 degrees C) ambient temperatures during the finishing period from 22 d of age. The optimum amino acid: ME ratio varied with dietary ME concentration in the hot, but not in the moderate environment. Relatively greater increases in food intake and growth rate occurred in the hot environment when dietary ME was increased and the amino acid: ME ratio was reduced. The minimum rate of food intake did not coincide with the period of maximum temperature. Increasing the dietary protein at particular ME concentrations had little or no effect on the food intake and growth rate of birds kept at high temperatures. Supplementation with dietary fat had no beneficial effect on performance at high temperatures. The rectal temperatures of birds in the hot environment increased with age and, towards the end of the finishing period, when higher energy diets were fed.

Growth and carcass composition of broilers fed sunflower oil and olive oil

Sunflower and olive oils were fed at the same dietary inclusion levels to male broilers as a means of varying the dietary linoleic acid concentration while maintaining similar concentrations of total fat and total unsaturated fatty acids. The type of oil and the dietary supplementation level influenced growth rate, food utilisation and carcass composition. Birds grew faster and utilised food more efficiently when fed the sunflower oil and had higher concentrations of body fat. Increasing the level of supplementation with either oil decreased body fat content. The different responses to the two oils were not related to differences in dietary amino acid balance, ME: protein ratios or rates of food passage through the digestive tract.

Responses in egg shell quality to sodium chloride supplementation of the diet and/or drinking water

1. Supplementing the drinking water of 50-week-old laying hens with sodium chloride (NaCl) concentrations between 0.5 and 2 g/l for 7 weeks significantly increased the incidence of egg shell defects and significantly decreased egg shell quality. Dietary NaCl concentrations between 0 and 2 g/kg had little effect on this response. 2. At similar total NaCl intakes egg shell defects were much greater when the NaCl was obtained from the drinking water rather than from the diet. 3. Hens producing eggs with defective shells as a result of receiving saline drinking water failed to recover the ability to lay eggs with good shells after 8 weeks on normal water. 4. The increased incidence of shell damage was not related to decreased food intake or increased egg weight or production.