Thiamin requirements in most species are difficult to establish due to endogenous vitamin synthesis by intestinal microflora. For swine it is doubtful whether the amount of thiamin produced by intestinal synthesis and absorbed is large enough to make a significant contribution to body needs. Hughes (1940) reported that the daily minimum requirement of thiamin for the growing pig (weighing between 60 and 65 lbs at initiation of the experiment) was approximately 1 mg thiamin per 100 lbs body weight. Other early researchers (Van Etten et al., 1940) attempted to determine the thiamin requirement of young swine (approximately 3 weeks of age initially) by using basal diets that were made thiamin-free by either autoclaving or by sodium sulfite-sulfur dioxide treatment of the basal diets and subsequent supplementary feeding of specific amounts of crystalline thiamin hydrochloride. Van Etten et al. (1940) estimated that the requirement for thiamin chloride hydrochloride was between 106 and 120 mg per 100 g of carbohydrate and protein consumed. For today's situations, swine thiamin requirements generally range between 1 and 1.5 mg per kg (0.45 and 0.68 mg per lb) of feed (NRC, 1998). Based on data from an experiment with high health status pigs with a high genetic capacity for lean tissue growth, Stahly and Cook (1996) concluded that 2.2 ppm thiamin was adequate to support growth performance of pigs weighing 22 to 88 lbs. Other researchers (Woodworth et al., 1997) have confirmed these findings with younger pigs. Woodworth et al. (1997) indicated that supplementation of thiamin beyond what is present in typical grain-soybean meal diets is not required for maximum growth of weanling pigs (11 lbs initially). Woodworth et al. (1997) found that average daily gain was identical for pigs fed the control ration to that for those receiving additional thiamin at the rate of 5 g thiamin per ton of diet. Overall growth performance was not improved by the addition of thiamin. Roth-Maier and Kirchgessner (1994) concluded from biochemical analyses only that thiamin maintenance requirements of sows could be met by the addition of 1.2 mg thiamin per day.
Thiamin requirements for swine have been shown to increase in swine as environmental temperature increased from 20° to 35°C (Peng and Heitman, 1974). In addition, diet composition can dramatically influence thiamin requirements. Since thiamin is specifically involved in carbohydrate metabolism, level of dietary carbohydrate relative to other energy-supplying components influences thiamin requirement. The need for thiamin increases as consumption of carbohydrate increases. This was illustrated by Ellis and Madsen (1944); the survival time of thiamin-deficient pigs was increased by increasing fat levels to 28% of the diet at the expense of carbohydrates. When thiamin is deficient, body reserves become depleted more rapidly when animals are being maintained on a feed rich in carbohydrates than when they are receiving a diet rich in fat and protein. The thiamin-sparing effect of fats and protein has long been known.
Thiamin requirements are obviously higher if feeds contain raw materials (i.e., fish) or additives with antithiamin activity. Spoiled and moldy feeds may contain such antagonists or thiaminases. Chicks kept on a feed infected with Fusarium moniliform developed polyneuritis that could be cured with thiamin injections (Fritz et al., 1973). Analysis of moldy feeds showed a thiamin content of less than 0.1 mg per kg (0.05 mg per lb), whereas the same feed not contaminated with Fusarium had a thiamin content of 5.3 mg per kg (2.4 mg per lb). The antagonistic factor could be destroyed by treatment with steam.
Disease conditions also increase thiamin requirements. When dietary thiamin is marginal, typical deficiency signs of thiamin are more likely to develop in infected animals than in normal animals. Endoparasites such as strongyloides and coccidia compete with the host for thiamin in food. It has been shown experimentally that infection with coccidia results in considerable reduction in thiamin blood levels. Thiamin levels found were directly correlated to infection severity (McManus and Judith, 1972). Likewise, conditions such as diarrhea and malabsorption may negatively affect thiamin status and increase the dietary requirement for the vitamin.