Does oral vitamin D3 supplementation help piglet performance post-weaning?

Thursday, October 10, 2013

Pigs raised indoors lack the vitamin D produced by exposure to sunlight. So veterinarians in Minnesota and Kansas set out to test whether supplementation was beneficial in the days
following weaning

by JANICE MURPHY

Historically, vitamin D's claim to fame has been its role in the growth of healthy bones and muscle. However, the focus of an ongoing research effort over the past 20 years has shifted to vitamin D's role in the development and function of the immune system.

Vitamin D enters the body in one of two ways, either through exposure to sunlight or consumption of fortified diets. The primary endogenous source of vitamin D is epidermal production as the result of exposure to UVB sunlight, producing the vitamin D precursor, cholecalciferol. Cholecalciferol is then transported to the liver where it is converted to 25-hydroxy vitamin D (25-OHD), the storage form of vitamin D.

Research has established that the level of 25-OHD is the most useful measure for assessing vitamin D status of an animal. The 25-OHD is converted into its active form by the enzyme 1α-hydroxylase, which was originally thought to be present only in the kidney and bone but is now known to exist in various tissues of the body, including the immune system.

Since the modern swine production unit does not allow pigs direct exposure to sunlight, vitamin D must be supplied in the diet. Research has determined that in most, if not all, weaned piglets the level of 25-OHD is extremely low. One particular study reported reference values for 25-OHD of 25-30 ng/mL. The same study reported values of 8.42-13.75 ng/mL, depending on the season, for nursery pigs raised indoors, compared to 58.54 ng/mL for nursery pigs raised outdoors.

An oral supplement has been developed for administration to piglets early in life. Reports by veterinarians and farm staff from farms where this supplement has been adopted described encouraging improvement in piglet performance.

To examine this phenomenon further, veterinarians in Minnesota and Kansas set out to document the situation on one farm, a privately-owned, 1,500-head sow unit where oral vitamin D3 supplementation was provided to piglets at two days of age. The herd was representative of an overall healthy, well-managed, modern swine facility.

Piglets were weaned twice weekly at approximately 21 days of age to an off-site, continuous-flow nursery managed all-in, all-out by room. Pigs were moved to on-site finishing barns following 26 days in the nursery.

In the study, 387 piglets from 36 gilt litters were assigned to either a group supplemented with vitamin D3 at two days of age or a control group. One piglet from 11 randomly chosen litters was selected the day prior to weaning and blood was collected. The mean serum 25-OHD levels were determined to be 14.4 ng/mL (±2.7 ng/mL). This confirmed the suspicion that vitamin D levels in this herd were below commonly used reference values.

To minimize the potential for confounding by litter, piglets from each litter were evenly assigned to both treatments (control or treatment with vitamin D3). At approximately two days of age, all piglets were processed and allocated to treatment. Farm staff were instructed to allocate pigs visually into the two treatment groups by size; birth weights were not recorded.

They began with the two visually largest piglets; one was given one mL vitamin D3 (40,000 IU/mL)) according to label directions and the other was not supplemented. Staff then processed the next two visually largest pigs, treating and recording as before until all piglets were allocated to treatments. All other procedures, including vaccinations, iron injections and fostering, were performed according to the farm's standard operating procedures, regardless of treatment group.

Piglets were weaned at an average of 21 days of age. On the day prior to weaning, all pigs in the study were individually weighed. One supplemented and one control pig was selected from each litter by a random number generator (72 pigs total) for blood collection for the 25-OHD assay.

In the nursery, study animals were randomly allocated to pens and weights were recorded for every pig at seven and 26 days post-weaning. Blood samples were collected at seven and 26 days post-weaning from the same 72 pigs selected at weaning. The piglets were handled according to the farm's standard operating procedures in the nursery with the trial ending at 26 days post-weaning.

Performance measures and serum 25-OHD results are summarized in Table 1. Pigs supplemented with vitamin D were significantly heavier than controls at weaning and seven days post-weaning; however, this difference evaporated by 26 days post-weaning. There was no significant difference in average daily gain between groups throughout the study.

While birth weights were not recorded, significantly fewer pigs in the supplemented group lost weight during the first seven days post-weaning. Serum 25-OHD levels were significantly higher in supplemented pigs at 26 days post-weaning, even though there was no difference at weaning.

The researchers suggested that, based on the results, it could be speculated that supplemented pigs began consuming pelleted nursery feed more quickly than controls in the initial week post-weaning. Since feed intake was not measured during the study, there is no way to confirm this. However, assuming that this is indeed what took place, it could be argued that pigs receiving the vitamin D supplement might have been easier for farm staff to manage during this critical first week after weaning.

Serum 25-OHD levels were significantly higher in supplemented pigs at 26 days post-weaning even though there was no difference at weaning. The single dose of oral vitamin D3 could have increased serum 25-OHD to a peak level a few days after treatment at two days of age but, in the absence of other sources of vitamin D during nursing, 25-OHD levels may have declined to baseline levels before weaning. The researchers had trouble explaining the significant difference at 26 days post-weaning, considering the fact that the treatment groups were commingled and consuming the same nursery diets.

The herd involved in this study had relatively high health with excellent management. The researchers point out that the effects of supplementation would likely be more pronounced in herds with more disease pressure. No other measures of health status, such as nasal swabs, fecal samples or histopathology samples, were collected during the trial so it was not possible to identify differences in shedding or pathogen load.

This study has only scratched the surface in our overall understanding of the role of vitamin D in growing pigs. It is possible that a one-time dose of 40,000 IU of vitamin D3 is not sufficient in rapidly growing piglets that have a high demand for bone and muscle growth, as well as the demands of a maturing immune system constantly being challenged by pathogens. More research is necessary to fully grasp the pig's response to supplemental vitamin D3. BP

Source: Tousignant SJP, Henry SC, Rovira A, and Morrison RB. 2013. Effect of oral vitamin D3 supplementation on growth and serum 25-hydroxy vitamin D levels of pigs up to 7 weeks of age. J Swine Health Prod. 21(2):94–98.

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.