ABSTRACT:The aim of the study was to evaluate the effect of organic acids and the prebiotic fructans on egg production and eggshell quality when added to the layer diet with different levels of calcium and phosphorus. The experiment was carried out on 168 Bovans Brown hens, allocated to 14 groups of 12 replications. Each hen (replication) was kept in an individual cage 40 cm × 40 cm in size. A 2 × 7 factorial arrangement, with two dietary levels of calcium and phosphorus (normal -3.70% Ca, 0.65% P, and reduced -3.25% Ca, 0.60% P) and with diets supplemented by selected additives (none, 0.75% inulin, 0.75% oligofructose, 0.50% volatile fatty acids (VFA), 0.25% medium chain fatty acid (MCFA), 0.30% VFA + 0.20% MCFA, 0.75% inulin + 0.50% VFA) was used. The experiment was carried out over 34 weeks, from the age of 26 to 70 weeks. There were no statistically confirmed effects of the factors studied in this experiment on egg performance, i.e. laying rate, egg mass, feed intake and feed conversion. Reducing the dietary levels of Ca and P significantly decreased eggshell percent, thickness, density and breaking strength. The additives used had a considerable effect on eggshell quality at 46, 58 and 70 weeks of age, and these positive effects were most pronounced in the case of inulin and MCFA. There was no significant interaction between Ca and P dietary levels and the additives used. It was thus concluded that selected feed additives which lower the pH of the diet and intestinal content can beneficially influence eggshell quality in older high-producing laying hens.

The aim of the 3 × 3 factorial experiment on broilers was to investigate the effect of high dietary levels of potassium (K) and different levels of sodium (Na) on chicken performance, carcass traits, dry matter content in excreta and nitrogen balance. Three hundred and sixty one-day-old Ross 308 chickens were allocated to 9 groups, in 5 replicates of 8 (4♂ and 4♀). Chickens from 1 to 42 days old were kept in cages with wire floors to enable excreta collection, and were provided with water and feed ad libitum. The basal starter (days 1-14) and grower (days15-42) diets contained, as analysed, 1.73 g and 1.89 g·kg -1 chloride (Cl), 10.7 g and 10.8 g K and 0.69 and 0.94 g Na, respectively. Basal diets were supplemented with cations containing, as analysed, 12.2/11.8 g and 12.7/12.5 g·kg -1 K and 1.22/1.25 g and 1.68/1.61 g·kg -1 Na, for the starter/grower periods of feeding, respectively. The molar proportion of Na:K in diets used in the experiment ranged from 0.09 to 0.27 in the starter diet and from 0.13 to 0.25 in the grower/finisher diet; the dietary electrolyte balance (DEB) values varied between 255 to 349 and 264 to 336, respectively.During the starter feeding period, body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) in the chickens were positively affected by increasing the Na supplement. Throughout the feeding period, Na supplementation improved BWG, FI and FCR and production index values and increased carcass yield. The dry matter content of the excreta was negatively affected by the K level in the diet; the 12.7 g K dietary content, in particular, caused a higher moisture content. KORELESKI J. ET AL.The daily intake of nitrogen and nitrogen excretion grew when the dietary Na level was increased from 0.94 to 1.25 or 1.61 g·kg -1 . The proportion of N retained to N intake decreased significantly when the dietary level of Na reached 1.61 g·kg -1 , as compared to the proportion at a level of 0.94 g Na·kg -1 . Interaction between dietary Na and K levels for BWG and other indices of performance, and for nitrogen utilization, confirm a dietary reciprocal relationship for both electrolytes.

In an experiment conducted on caged Bovans Brown hens, the effect of diet supplementation using organic acids and prebiotic fructans on the biomechanical and geometrical indicators of the tibia and femur bones was evaluated. At 25 weeks of age, layers were randomly assigned to 14 experimental groups, each comprising 6 hens kept in individual cages. A 2 × 7 factorial arrangement, with two dietary levels of calcium and phosphorus (normal -37.0 g Ca/kg, 6.5 g P/kg, and reduced -32.5 g Ca/kg, 6.0 g P/kg), and with diets supplemented by selected additives (none; inulin, 7.5 g/kg; oligofructose, 7.5 g/kg; short chain fatty acids (SCFA), 5.0 g/kg; medium chain fatty acid (MCFA), 2.5 g/kg; SCFA, 3.0 g/kg + MCFA, 2.0 g/kg; inulin, 3.0 g/kg + SCFA, 5.0 g/kg) was used. The experiment was conducted for 45 weeks and concluded when the hens were 70 weeks old.At 70 weeks of age, reducing the dietary levels of Ca and P had decreased the bone breaking strength by 8.9% (P ≤ 0.001) and the yielding load by 5.6% (P ≤ 0.05). A similar tendency for bone breaking strength (P ≤ 0.05) and stiffness (P ≤ 0.05) was found in the femur bones. The diet with a lower level of Ca and P negatively affected the geometrical indicators of the bones such as cortex thickness (P ≤ 0.05) and cross section area (P ≤ 0.05), but had no effect on bone weight and length. Hens fed diets supplemented with oligofructose, MCFA, SCFA + MCFA or inulin + SCFA displayed a significantly higher bone breaking strength and yield load in the tibia bone than that of the control group. In the case of femurs, a positive influence of MCFA or simultaneous addition of inulin + SCFA on bone breaking strength was found. The additives had no significant effects on the geometrical indicators of either bone. It was concluded that selected feed additives which lower the pH of the diet and intestinal content can beneficially affect the biomechanical indicators of the bones of high-productive laying hens. Laying hens, bone quality, calcium, organic acids, prebiotic fructansSymptoms of osteoporosis are often observed in modern flocks of high-productive layers, especially in the second part of the laying cycle. Osteoporosis can be defined as a decrease in the fully mineralized structural bone in which Ca is mobilized from the bone in order to contribute to eggshell formation (Whitehead and Fleming 2000). The condition leads to increased bone fragility and susceptibility to fracture. The consequences of this syndrome, also known as 'cage layer fatigue', i.e., poor bone quality, weakness, deformities and breakage, spinal bone collapse and paralysis, can be an important welfare problem, causing acute and chronic pain and distress to the birds (Webster 2004). In the United Kingdom, it was found that, in the end phase of lay, 29% of caged hens had sustained one or more broken bones during their lifetime (Gregory and Wilkins 1989). A study conducted by McCoy et al. (1996) attributed 35% of mortality in commercial caged laying hens to osteoporosis. Bone breakage is also a serious prob...