Influence of vitamin D3 and lactic acid on performance, egg quality, and hatchability in broiler breeder hens

Vitamin D3 is one of the important vitamins in calcium metabolism, which is significantly involved in the absorption of calcium from the intestine. The main role of 1, 25-hydroxyvitamin D3 in vertebrates is to regulate calcium homeostasis, as 1, 25-hydroxyvitamin D3 has a direct effect on the gut, kidney, and bones by inhibiting the production of parathyroid hormone in the parathyroid glands. The synthesis of 1, 25-dihydroxycholecalciferol is tightly controlled, and the main stimulus for its synthesis is the reduction in plasma calcium. This is a feedback stimulus for the release of parathyroid hormone from the parathyroid gland. This hormone in turn stimulates the 1-hydroxylase enzyme complex in the kidney and causes the conversion of 25-hydroxycholecalciferol through the synthesis of calcium-binding protein in the duodenum, thereby increasing dietary calcium absorption and ultimately plasma calcium. Another powerful factor in calcium absorption is organic acids. By lowering the pH of the digestive tract, organic acids (lactic acid) prevent the formation of an insoluble complex of phytic acid with minerals, making phytate more sensitive to the action of endogenous phytase and preventing it from interfering with the absorption of minerals. Therefore, the purpose of this research was to study the effect of vitamin D3 and lactic acid on performance, egg quality, and hatchability in broiler breeders. A total of 240 broiler breeder hens and 24 roosters of Ross 308 strain were used in a completely randomized design with a 2×2 factorial arrangement including two levels of vitamin D (3500 and 5500 IU) and two levels of organic acid (zero and 500 mg/kg) in four treatments, six replications, and 10 hens and one rooster per replication. During the experiment, the percentage of hatchability, the number, and weight of eggs produced by each pen were recorded and using the common formulas of egg mass (as the percentage of laying multiplied by the average egg weight), the percentage of egg production as chicken-day and the feed conversion factor (as grams of feed consumed per gram of egg), the amount of feed used to produce each number of eggs and each piece of chicken, as well as the number of chickens produced per chicken was also calculated. Egg characteristics (egg weight and shape index) and egg shell quality (egg specific weight, eggshell weight compared to total egg weight and eggshell thickness), albumen and yolk pH, yolk index, Haugh unit, yolk color, percentage albumen and yolk percentage of four eggs from each replicate were measured every 28 days. The specific weight of the eggs was determined using the flotation method. The egg shape index was determined by measuring the width and length of the egg with a caliper to calculate the ratio of width to length. To determine eggshell parameters, eggs were identified and broken individually. Eggshells were washed under running water and dried at 35 °C for 72 hours. Then the eggshells were weighed and their relative weight was calculated. A digital micrometer (Series 500, Mitoyota, Tokyo, Japan) was used to measure the shell thickness. Results showed that the main effect of vitamin D3 at higher concentrations was affecting egg weight and reducing egg weight (P<0.05). The main effect of vitamin D3 at higher concentrations caused an increase in albumen pH, shell percentage, shell thickness, and specific gravity of the egg, and a decrease in yolk pH (P<0.05). Probably, with the increase in vitamin D3, the concentration of 1,25-cholecalciferol and the amount of calcium absorption increase, and since most of the shell is related to calcium carbonate, this leads to an increase in the thickness of the eggshell. The main effect of lactic acid showed a significant effect on performance parameters, and the addition of lactic acid improved performance (P<0.05). Lactic acid also significantly increased hatchability and shell thickness and reduced the number of broken eggs (P<0.05). It appears that organic acids increase the solubility of wheat phytates during germination. Therefore, acidification of the diet provides a better environment for phytase to reduce the amount of phytate present in digestion and flowing into the small intestine, thereby largely preventing the formation of insoluble mineral-phytate complexes and increasing the quality of the eggshell. Also, the main effect of lactic acid showed no significant influence on the internal quality of the eggs. The low levels of vitamin D3 and the addition of lactic acid improved shell thickness and reduced the percentage of shell breakage (P<0.05). In general, according to the results of the present experiment, the use of lactic acid at the rate of 500 mg/kg along with 3500 IU of vitamin D3 can increase the percentage of production, shell thickness, reduce the number of broken eggs, improve the feed conversion ratio, increase chicken production and reduce feed consumption per egg and chicken at the end of the production period of broiler breeder hens.