Effects of boron supplementation alone or in combination
with different vitamin D3 levels on laying performance,
eggshell quality, and mineral content and fatty acid composition
of egg yolk in laying hens

This study aimed to evaluate the effects of dietary boric acid with vitamin D3 on laying performance, eggshell quality, and mineral content and fatty acid composition of egg yolk in hens. In the experiment, 160 late-phase laying hens were equally divided into four groups, 40 birds each (10 replicates of 4 hens each). The study included a control group and three treatment groups. In the control group, there was no additive, while the experimental groups contained: 1) vitamin D3 3000 IU/kg + 120 ppm boric acid, HDB; 2) vitamin D3 300 IU/kg + 120 ppm boric acid, LDB; and 3) 120 ppm boric acid, B; respectively. After 12 weeks of feeding, the egg mass was significantly reduced in HDB group in comparison to the control and feed efficiency was increased in HDB group in comparison to the control and B groups (P < 0.05). No significant differences were observed in eggshell quality among groups (P > 0.05). Egg yolk cholesterol content was decreased in LDB group in comparison to B group (P < 0.05). The concentration of C18:3 fatty acid was the highest (P < 0.05) in B group. In comparison to the control group, the C16:0 fatty acid concentration was lower in B group (P < 0.05). So, the combination of boric acid (120 ppm) and a high dose of vitamin D3 (3000 IU/kg) is not recommended in laying hen feeding as it negatively influences laying performance parameters. On the other hand, although the supplementation of 120 ppm boric acid without additional vitamin D3 increases egg yolk omega-3 fatty acid content, the cholesterol-reducing effect (but without fatty acid profile change) may be obtained only when boric acid is added simultaneously with a low level of vitamin D3 (300 IU/kg), which can be used to produce functional food. 4 Corresponding author: e-mail: ozgeabacioglu@gmail.com 2 Boron and vitamin D3 in laying hen nutrition account for 73.4% of the world’s boron reserves (Kılıç et al., 2018; Sokmen and Buyukakinci, 2018). Boron taken in the diet affects mineral metabolism (Ca, P, Mg), energy metabolism (triglycerides, glucose) and protein metabolism (amino acids) (Białek et al., 2019). Much of the interest in boron in animal nutrition is due to the fact that this mineral may stimulate the growth of chicks deficient in vitamin D3. Such results might suggest that boron affects vitamin D3 metabolism or exerts a synergistic effect with vitamin D3 to increase the performance parameters (Hunt and Nielsen, 1981). We hypothesized that using boron in combination with different levels of vitamin D3 could have a positive effect on the quality of eggshell regarding mineral content and the egg yolk fatty acid profile. The present study aimed to investigate the effects of supplementing boron as boric acid in laying hens on laying performance, external quality of egg and fatty acid profile of egg yolk, which may be important from the point of view of human nutrition. The idea of using boron minerals together with vitamin D3 in laying hen nutrition and the possibility of the synergistic effect between the examined components prove the originality of this study. Material and methods The study was approved by the Animal Experiments Local Ethics Committee of the University of Ankara (Ethical Approve Number: 200515). Animal management and experimental diets In the study, 160 Hyline-White 98, 59-weekold layers were randomly allocated into four experimental groups according to dietary treatments. The trial was conducted in the experimental poultry house of Ankara University, Faculty of Veterinary Medicine (Turkey). In each treatment group, there were 10 replicates, each with four layers. The house was provided with programmable lighting and ventilation during the whole 12-week experimental period. Laying hens were housed in cages (50 × 59 × 60 cm) in an environmentally controlled room with a temperature between 20–22 °C according to good management practice. Hens were exposed to a 17-hour constant light schedule until the end of the experiment. Feed and water were provided ad libitum throughout the experiment, and the diets were in a mash form. The experimental diets based on maize-soyabean were formulated to be isocaloric and iso-nitrogenous and to provide adequate levels of all nutrients as recommended for laying hens by the National Research Council (NRC, 1994). The experimental treatments used were: CON – no additives; HDB – vitamin D3 at a dose of 3000 IU/kg + 120 ppm boric acid; LDB – vitamin D3 at a dose of 300 IU/kg + 120 ppm boric acid; and B – 120 ppm boric acid. Boric acid used in this study contained 17.5% boron. Although the inclusion of at least 2 ppm boron in poultry feed was recommended by NRC (1984), no matter which poultry category or type of production, such suggestions are not present in the requirements for poultry in NRC (1994). Thus, the only suitable suggestions for boron doses are taken from the experimental diets used in the previous studies (Sizmaz and Yildiz, 2016). Basal diet composition and nutritional values (analysed according to the reference methods (AOAC Interntional, 2000)) are shown in Table 1. Sampling and handling On the last day of each 3-week interval (after 3, 6, 9 and 12 weeks), two eggs from each replicate (20 eggs from each treatment) were randomly selected and analysed for external egg quality (eggshell strength, eggshell thickness and egg shape index). At the end of the experiment, in total 40 eggs (one egg from each replicate; 10 eggs per treatment) Table 1. Basal diet composition and nutritional level