High Bioavailability Vitamin D3 for Volaille & Swine

Vitamin D3 in the form of cholecalciferol is the standard supplement used in most commercial premixes. While cost-effective, it depends on the liver enzyme 25-hydroxylase to convert it to 25-hydroxycholecalciferol (calcidiol, also known as 25-OH-D3). This conversion is highly variable, influenced by liver health, oxidative stress, and the presence of mycotoxins that damage hepatocyte function. In young animals whose hepatic enzyme systems are immature, the conversion efficiency can be as low as 20–40% of theoretical yields.

Calcidiol (25-OH-D3) — the intermediate metabolite — bypasses this first hydroxylation step entirely. When included directly in the diet, it is approximately 3 to 5 times more potent than cholecalciferol on a mole-for-mole basis because it is immediately available for renal activation to the active hormone calcitriol. VeriVit Hy D3 provides this higher-bioavailability form, ensuring consistent vitamin D3 status regardless of individual animal variation in hepatic conversion capacity.

Research in laying hens has demonstrated that feeding 25-OH-D3 at 50 μg/kg feed produces equivalent or superior bone mineralisation compared to 3,000 IU/kg cholecalciferol, while also improving eggshell thickness by 0.8–1.2% in aged flocks where calcium homeostasis is compromised. In piglets, dietary 25-OH-D3 supplementation at weaning improves calcium apparent absorption and supports faster recovery of gait scores following osteochondrosis-related leg weakness.

The skeletal health consequences of inadequate vitamin D3 availability are among the most economically significant in both poultry and swine production. In poultry, tibial dyschondroplasia (TD) — a condition where the prehypertrophic chondrocyte zone in the growth plate fails to undergo normal ossification — is directly linked to insufficient vitamin D3 status at key developmental stages. The condition causes lameness, reduced mobility, and increased condemnations at processing, with incidence rates of 5–15% reported in commercial broiler flocks not supplemented with vitamin D3 metabolites.

Laying hens face a distinct but equally serious challenge: the daily calcium flux associated with eggshell formation demands sustained vitamin D3 activity to maintain the intestinal calcium transport proteins calbindin and plasma membrane calcium ATPase (PMCA1b). Without adequate vitamin D3, calcium mobilisation from medullary bone cannot keep pace with shell mineralisation requirements, leading to thin, cracked shells and increased proportions of seconds and thirds at packing. In extended laying cycles beyond 72 weeks, this problem intensifies as medullary bone reserves become progressively depleted.

In swine, vitamin D3 deficiency manifests as rickets in the neonatal and grower phases, with clinical signs including enlarged costochondral junctions (beading), bowed long bones, and stiff gait. In sows, inadequate vitamin D3 status during gestation contributes to poor foetal skeletal development and increased pre-weaning mortality due to inadequate colostral calcium. Sows housed indoors without UV light exposure are at particular risk, as they cannot synthesise endogenous vitamin D3 through the skin.

Beyond its classical role in calcium and phosphorus homeostasis, vitamin D3 acts as an immunomodulator through the vitamin D receptor (VDR) expressed in immune cells including macrophages, dendritic cells, and activated T lymphocytes. The active metabolite calcitriol modulates the production of antimicrobial peptides such as cathelicidin (LL-37) and beta-defensins, enhancing the innate immune response to bacterial pathogens including Salmonella enterica and Escherichia coli.

In poultry, this immunomodulatory effect is particularly relevant for broiler breeders and laying hens where vaccine responses need to be robust and durable. Birds with serum 25-OH-D3 concentrations above 30 ng/mL show stronger antibody titres following Newcastle disease and infectious bronchitis vaccination compared to deficient birds. In swine, vitamin D3 sufficiency is associated with improved macrophage phagocytic activity and reduced incidence of post-weaning diarrhoea syndrome, a multifactorial condition where immune dysfunction plays a central role.

The interaction between vitamin D3 and immunity also has implications for intestinal health. In both species, vitamin D3 receptor signalling supports gut barrier integrity by upregulating tight junction proteins such as occludin and claudin-1, reducing the risk of bacterial translocation from the intestinal lumen. This gut-protective effect complements the action of organic acidifiers and probiotic feed additives used in poultry and swine feeding programmes.

Eggshell quality represents one of the most sensitive indicators of vitamin D3 and calcium nutrition in laying hens. The shell is composed of approximately 95% calcium carbonate, deposited as aragonite crystals onto the eggshell membrane during the 18–20 hour shell formation period. This process is under strict hormonal control, with calcitriol (the active vitamin D3 metabolite) acting on the shell gland (uterus) to stimulate the expression of calcium transport proteins and carbonic anhydrase.

In practice, many commercial layer operations observe a progressive decline in eggshell quality after 60 weeks of age, characterised by reduced shell thickness (from ~400 μm to <320 μm), increased breakage rates (from <2% to >5%), and higher proportions of misshapen eggs. The primary driver is reduced efficiency of intestinal calcium absorption, which falls from approximately 60% in young hens to below 40% in aged hens, despite similar dietary calcium levels. Supplemental vitamin D3 — particularly in the calcidiol form — partially compensates for this age-related decline by maintaining higher circulating calcitriol levels and sustaining the upregulation of calcium transporter genes.

Trials with 25-hydroxycholecalciferol (VeriVit Hy D3) in aged layer flocks have reported improvements in shell strength of 8–12%, measured by quasi-static compression testing, alongside reductions in dirty and cracked eggs of 15–20%. These improvements translate directly into fewer seconds at the packing station and higher net revenue per hen housed.

Optimising vitamin D3 nutrition in poultry and swine requires moving beyond simple IU/kg dietary inclusion rates towards a more precise understanding of bioavailability and metabolic demand. The choice of vitamin D3 form is the single most impactful decision: 25-hydroxycholecalciferol (calcidiol) offers superior potency, faster onset of action, and reduced sensitivity to liver health status compared to conventional cholecalciferol.

Integrating VeriVit Hy D3 into premix formulations for poultry and swine ensures that vitamin D3 status is maintained even under conditions of hepatic stress, intestinal disease, or high mineral antagonism. Combined with adequate calcium and phosphorus nutrition, antioxidant support, and attention to overall feed hygiene, bioavailable vitamin D3 supplementation forms the foundation of skeletal health, immune competence, and reproductive performance in modern animal production.