A Comparison of Two Supplementary Doses of Vitamin A on Performance, Intestine and Immune Organ Development, as well as Gene Expression of Inflammatory Factors in Young Hy-Line Brown Laying Pullets

SIMPLE SUMMARY: In young laying pullets, vitamin A (VA) is a necessary micronutrient that plays an important role in intestinal integrity, cell proliferation and differentiation, and modulation of the immune system. However, the recommended dose for young laying pullets in NRC (1994) is too low to use under practical conditions. Both the feed industry and producers often prefer to supplement diets for chicks with more than 6000 IU/kg VA to improve performance and alleviate negative stresses currently. Therefore, the objective of this study was to compare two supplementary doses (6000 vs. 12,000 IU/kg) of vitamin A on performance, development of intestine and immune organs, as well as gene expression of inflammatory factors in young Hy-Line Brown laying pullets. The results showed that supplementary 12,000 IU/kg of VA improved performance and intestine and immune organ development, and alleviated gene expression of inflammatory factors in young Hy-Line Brown laying pullets. ABSTRACT: The objective of this study was to compare two supplementary doses (6000 vs. 12,000 IU/kg) of vitamin A (VA) on the performance, development of intestine and immune organs, as well as gene expression of inflammatory factors in young Hy-Line Brown laying pullets. A total of 288 one-day-old Hy-Line Brown laying pullets (weighing 42.15 ± 0.23 g) were allotted into two treatments with 12 replicate cages and 12 birds per cage. During the 35-day period, the pullets were fed a basal diet supplemented with different doses of VA (6000 IU/kg VA in control group; 12,000 IU/kg VA in treatment group), respectively. The results showed that supplementary high doses of VA reduced the feed-to-gain ratio from day 21 to 35 (p < 0.05). Moreover, the pullets fed high doses of VA diets had increased length and relative weight of duodenum, jejunum, and ileum (p < 0.05). From observations on morphology, high doses of VA diets increased the villus height and the ratio of villus height to crypt depth in the jejunum and ileum (p < 0.05). High doses of VA diets also increased the relative weight of immune organs (p < 0.05). Furthermore, the gene expressions of inflammatory factors were decreased in the thymus of the pullets fed high doses of VA diets (p < 0.05). In summary, supplementary 12,000 IU/kg doses of VA improved performance and intestine and immune organ development, and alleviated gene expressions of inflammatory factors in young Hy-Line Brown laying pullets.