The thiamin content of most common feeds should be three to four times greater than requirements for most species (Brent, 1985). For swine consuming typical diets (e.g., corn-soybean meal), thiamin is one of the vitamins least likely to be deficient. Although thiamin levels supplied by feedstuffs in the diet are generally considered adequate for swine, thiamin deficiency and inadequacy have been observed in swine under commercial production conditions.
Utilization of available thiamin in feedstuffs may be limited and may also be impaired by thiamin antagonists; therefore, it is common practice to add supplemental thiamin to swine diets to replace thiamin lost during processing and storage.
Drying and processing can lower the concentration of available thiamin in feedstuffs because thiamin is heat labile. For example, it has been reported that use of high-moisture barley treated with sulfur dioxide resulted in destruction of 61% of dietary thiamin for pigs (Gibson et al., 1987). Treatment of feed ingredients with sulfur dioxide inactivates thiamin. This process was used to produce deficient diets in early studies to determine the pig’s thiamin requirement (NRC, 1998).
Based on thiamin status indicators, reduced pig weight gains were attributed to thiamin deficiency. Thiamin supplementation should be greatly modified if diets contain antithiamin substances, such as thiaminases from raw fish and moldy feeds. As an example in free-range farming, pigs may occasionally suffer from bracken fern poisoning, as the roots contain anti-thiamin substances. The animals can be saved by timely thiamin injections. Anti-thiamin substances present in some feedstuffs and weeds, such as oxythiamin, should likewise be considered. Other thiamin antagonists, such as free bisulfite, may be present in feeds and reduce free thiamin activity.
Stability of thiamin (hydrochloride and mononitrate forms) in feed premixes can be a problem. More than 50% of the thiamin was destroyed in premixes after one month at room temperature (Verbeeck, 1975). Thiamin in premixes without minerals showed no losses when the premixes were at room temperature for six months. When the minerals were supplied as sulfates, the losses of thiamin were also greatly lowered.
As recent genetic and technologic advances have allowed the production of pigs with accelerated rates of lean tissue growth, the nutrient fortification optimal for growth must be considered so that adequate energy is available. Thiamin is vital as the coenzyme involved in the energy-producing TCA cycle. Therefore, it would be logical to consider whether or not thiamin concentration would affect rate and efficiency of gain in pigs with high lean growth potential and high health status. However, Stahly and Cook (1996) did not find any significant improvement in pig performance when higher dietary concentrations (200% and 720% of NRC [1988] recommendations) were supplied to growing pigs (22 lbs initially through 88 lbs body weight). Stahly and Cook (1996) indicated that the lack of response to thiamin may likely be related to the pig’s apparent unique ability to store thiamin for as long as two months on a thiamin-deficient diet. Thus, Stahly and Cook (1996) suggested that although there may have been an increased demand for thiamin, body stores were sufficient to meet the need. These authors concluded that 2.2 ppm, the dietary thiamin value of a corn-soy-based diet, would be adequate for optimal growth performance in high lean growth pigs.
