1. A total of 72 H&N Brown Nick laying hens, 76 weeks of age (moulted at 60 weeks of age), were randomly assigned into a 3 × 3 factorial arrangement with three limestone particle sizes and three dietary Ca concentrations (30, 36 and 42 g/kg Ca); with 8 replicates per treatments, and one hen (individual) per experimental unit. 2. Particle sizes of the limestone were: distributions smaller than 2 mm (Fine), between 2 to 5 mm (Medium), and larger than 5 mm (Large). The fine, medium and large limestone particles were all obtained from the same source, and sieve sizes used had screen sizes 2 mm and 5 mm. 3. The different concentrations of dietary Ca, particle size or interactions had no significant effect on egg production, egg weight, egg mass, feed intake or feed conversion ratio. 4. The concentrations of dietary Ca and particle sizes had no significant effect on egg breaking strength, eggshell as % by weight of whole egg or eggshell thickness. The interactions between Ca concentrations and particle sizes had a significant effect on eggshell breaking strength, but not on other parameters. 5. Different dietary particle sizes had no significant effect on the Ca, P and Mg mineral contents of eggshell. While the different concentrations of Ca in diets had a significant effect on the P content of eggshell, they had no significant effect on Ca and Mg contents. 6. Different dietary concentrations of Ca had a significant effect on shear stress, and Ca and Mg contents of tibiae, but not other parameters. Also, dietary particle sizes had a significant effect on shear stress and Ca contents of tibiae. The interaction between Ca concentrations and particle sizes had a significant effect on tibia shear force and Ca content. 7. According to the results of this study, moulted brown laying hens should be fed 36 g/kg Ca and a medium limestone particle size (2–5 mm) in the diet to maintain performance, eggshell and bone quality.

This study was conducted to evaluate the efficiency of dietary zinc forms and dosages on egg production performance, egg quality, and bone characteristics in laying hens. Forty-two-week-old, 144 Lohmann LSL-Lite laying hens were allocated to 12 experimental groups in a 4 (forms) × 3 (dosages) factorial arrangement. Four zinc forms including zinc-sulphate and zinc-oxide as inorganic forms, zinc-glycine as organic form and nano zinc-oxide powder as nano form at different dosages (50, 75 and 100 mg per kg diet) were tested. Compared to the inorganic (zinc-sulphate) form, the zinc-glycine supplementation significantly depressed the egg weight, egg mass and feed conversion ratio. The eggshell thickness was significantly decreased by supplementation with nano zinc-oxide. The shear force of tibia was significantly decreased by zinc-glycine or nano zinc-oxide supplemented in the diet when compared to inorganic forms of zinc. On the other hand, the dietary 50 mg/kg dosage of zinc was sufficient for optimum performance and the dietary 75 mg/kg dosage of zinc significantly improved shear force of tibia in laying hens. Tibia zinc content increased with the dietary 100 mg/kg dosage of zinc. The interactions between zinc forms and dosages had a significant effect on egg weight, feed intake, feed conversion ratio, eggshell thickness, shear force and shear stress of bone, and tibia calcium concentration. The highest egg weight and the lowest eggshell thickness were observed for the group fed with nano Zn-oxide at 100 mg/kg in the diet. These results showed that nano zinc form supplementation negatively affects the eggshell thickness and bone mechanical properties. The zinc in nano form may not be suggested for feeding laying hens, but other forms of zinc could be used safely in layer diets.

The bone is a mineral reserve for metabolic requirements and eggshell formation as well as providing support to the bodies of birds. Bone weakness in laying hens has caused many problems such as bone deformation, osteoporosis, cage layer fatigue and fractures. These problems result in economic losses and are detrimental to animal welfare. Breaking strength is a good indicator of the health and strength of bone and an increase in breaking strength in laying hens would be important to decrease economic losses and improve the welfare of animals. One of the main factors affecting bone breaking strength is nutrition, as it is closely related to dietary calcium, phosphorus, vitamin D and particle size of the calcium source, particularly when the dietary calcium is insufficient. It has been accepted that the composition of the diet, trace elements, especially boron, vitamins, and feed additives play important roles in maintaining bone health and improving the breaking strength of bone in laying hens. This article reviews the results of studies in laying hens wherein the effect of nutrition on the breaking strength of bone were examined.

Manganese (Mn) is an element required in nutrition, functioning largely in the enzyme systems involved in lipid and carbohydrate metabolism. It plays an important role in growth, bone development, perosis prevention, optimal eggshell quality and performance maintenance of poultry. The current NRC ( 1994 NRC (1994) Nutrient Requirement of Poultry, Washington, DC, National Academy Press. [Google Scholar] ) guidelines recommend 20 and 60 mg/kg of Mn for laying hens and broilers, respectively. In practical poultry feeds, however, the dietary requirement of Mn is considered higher than these values. Traditionally, Mn is added to the diet in the sulphate form, which is typically used as the standard in nutritional studies. However, in recent times, other, more natural forms have been made available to the feed industry, e.g. organic chelates. From this current review of published data, it appears that inorganic Mn supplementation up to 200 mg/kg is ineffective on the performance of both laying hens and broilers but at lower levels it improves eggshell quality. The dietary Mn requirement of laying hens and broilers appears to be 90 mg/kg, and the availability of Mn-sulphate is higher than that of other inorganic Mn sources but lower than its organic sources. More studies should be undertaken to determine the optimum Mn requirement in its various forms for laying hens and broilers.

The aim of this study was to investigate the effect of seven different levels (0, 25, 50, 100, 200, 400, and 600 mg/kg) of a phytogenic feed additive containing a mixture of essential oils from thyme, black cumin, fennel, anise and rosemary on performance, eggshell quality, bone biomechanical properties and bone mineralization in laying hens. This study consisted of a total of 112, 21-week-old Super Nick laying hens, which were randomly distributed into seven experimental groups. During the 12-week experimental period, each experimental group of four replicates of four birds each was fed with seven treatment diets. Egg weight and egg mass were positively linearly affected by essential oil mixture supplementation. Also, eggshell thickness was increased quadratically by essential oil mixture supplementation. The biomechanical properties and tibia mineral content were adversely affected by essential oil mixture supplementation at the level of 600 and 400 mg/ kg, respectively. These results demonstrated that dietary supplementation with a low or medium concentration of essential oils improved bone parameters, while at high levels were adversely affected in laying hens.

Using additives can reduce the negative effects of aging on factors affecting profitability, such as the availability of nutrients, production, and egg quality. Maca is an herbaceous plant rich in protein, crude oil, essential acids, and pharmacological compounds. Maca has positive effects on different health parameters. In this study, the effect of adding Maca powder to the diets of young and old laying quails at the end of the 10-week trial was investigated. In total, 150 laying Japanese quails (Coturnix japonica) (209.1 ± 10.0 g) were randomly distributed to a 2 × 3 factorial arrangement with two ages (10 weeks and 30 weeks) and three Maca powder levels (0, 1, or 2 g/kg), with five subgroups per treatment. According to the study, eggshell quality, total cholesterol, triglyceride, progesterone, and testosterone concentrations of serum were lower in old quail than in young quail, while egg weight, feed intake, and follicle-stimulating hormone increased significantly as quail aged. (p < 0.05). Furthermore, aging negatively affected the histomorphology of the ileum and cortical bone thickness (p < 0.05). Additional findings show that adding 1 g/kg Maca powder to the diet of quail significantly improved eggshell, ileum, and bone traits that deteriorate with age, without affecting performance, and adding 2 g/kg Maca powder to the diet significantly reduced serum total cholesterol levels (p < 0.05). Incorporating Maca powder into the diet of aged birds could reduce the negative effects of aging.