Estimated biotin requirements for various poultry species vary from 0.1 to 0.3 mg per kg (0.05 to 0.14 mg per lb) of ration (NRC, 1994). Biotin requirements are difficult to establish because of variation in feed content and bioavailability of biotin. Likewise it is difficult to obtain a quantitative requirement for biotin, as the vitamin is synthesized by many different microorganisms and certain fungi. These microorganisms are found in the lower part of the intestinal tract, a region in which absorption of nutrients is generally reduced. However, it is believed that intestinal microflora make a significant contribution to the body pool of available biotin. In general, combined urinary and fecal excretion of biotin exceeds the dietary intake. What is not known for the various species is the extent of microbial synthesis or the biotin availability to the host.
It is concluded that microorganisms contribute to meet animal and human biotin requirements, as the use of some sulfa drugs, such as sulfathalidine, can induce deficiency under some circumstances. Microorganisms that provide significant quantities of biotin to most species apparently supply a variable, undependable amount of biotin for poultry (Frigg, 1987). Biotin deficiency was less severe in cecetomized than in normal chickens, indicating that cecal microorganisms do not supply chickens with significant amounts of biotin but instead compete with the host animal for dietary biotin, thus increasing the requirement (Sunde et al., 1950).
Rate and extent of biotin synthesis may depend on the level of other dietary components. It has been shown that in poultry polyunsaturated fats, ascorbic acid and other B vitamins may influence the demand for biotin. Addition of polyunsaturated fatty acids (PUFA) to fat-free, biotin-deficient diets increased severity of dermal lesions (Roland and Edwards, 1971). Biotin is rapidly destroyed as feeds become rancid. Pure biotin was inactivated to an extent of 96% in 12 hours when linoleic acid of a high peroxide number was added to the diet (Pavcek and Shull, 1942). In the presence of alpha-tocopherol, this destruction amounted to only 40% after 48 hours.
Biotin requirements can be influenced by a number of factors, one of which is the genetic selection for performance (growth and feed efficiency). Whitehead (1988) suggested that the biotin requirement for broilers in 1976 was 170 µg per kg (77 µg per lb) of diet, whereas Whitehead (1998) estimated the requirement to be 180 µg per kg (82 µg per lb) of feed for the fastest growing strains of broilers. Li et al. (1994) reported biotin deficiency lesions (foot pads) in broilers and suggested that 300 µg per kg (136.4 µg per lb) was the requirement for birds on a wheat-based diet. Recently, Whitehead (2000) reported a biotin requirement of 200-300 µg per kg feed, depending on whether linear or curvilinear statistical analysis was performed on the data.
In work with turkey breeders, both Atkinson et al. (1976) and Robel (1991) observed improvements in hatchability of fertile eggs when the diets of hens were fortified with 550 µg per kg (250 µg per lb) or 520 µg per kg (236.4 µg per lb) of d-biotin, respectively. In either experiment, the majority of hatchability improvement was noted after hens were in lay for more than eight weeks. Also, Chen et al. (1994) reported that higher levels of supplemental biotin were beneficial in supporting later reproductive performance in one of two experiments. Furthermore, Atkinson et al. (1976) noted heavier 10-week body weights when the diet of poults was supplemented with 250 µg per kg (113.6 µg per lb) of d-biotin regardless of the biotin status of hens.
