The dietary vitamin K requirement for poultry suggested by the National Research Council (NRC, 1994) ranges from 0.4 to 1.75 mg per kg (0.2 to 0.80 mg per lb). Young growing turkeys, breeding turkeys and Japanese quail have the highest requirement of 1 to 1.75 mg per kg (0.45 to 0.80 mg per lb). Vitamin K requirements of poultry are met by a combination of dietary intake and limited microbial biosynthesis in the gut. Animals that practice coprophagy, such as the rabbit, can utilize much of the vitamin K that is eliminated in the feces. In rats, the majority of menaquinone (vitamin K3) absorbed resulted from fecal ingestion compared to dietary sources or from direct synthesis and absorption from the intestine (Kindberg et al., 1987). Contrary to most animals, poultry have a limited ability for intestinal synthesis, and so adequate dietary supplies are of greater importance. Chicks were also found to have less hepatic vitamin K epoxide reductase (Will et al., 1992). Activity of this enzyme in chicks was about 10% of that in rats fed the same diets; the inability of chicks to effectively recycle the epoxide of vitamin K (phylloquinone 2,3 epoxide) seems to be a major factor in their high requirement for the vitamin.
Because of microbial synthesis, a precise expression of vitamin K requirements is not feasible. The daily requirement for most animal species falls in the range of 2 to 200 µg vitamin K per kg (0.9 to 91 µg per lb) of body weight. It should be remembered that this requirement can be altered by age, sex, strain, anti-vitamin K factors, disease conditions and any condition influencing lipid absorption. The requirements of poultry for vitamin K are based upon blood clotting responses and there is no information on amounts of vitamin K needed for bone growth. Vitamin K may possibly play a beneficial role in osteoporosis. It is involved in the formation of osteocalcin, a matrix protein associated with bone formation. Dietary supplementation with additional vitamin K during the laying period did not affect osteoporosis (Rennie et al., 1997) or bone mineralization in chicks (Rodrigues et al., 1996). Lavelle et al. (1994) have reported that reduction in skeletal osteocalcin does not impair initial bone development in chicks but there is no information on whether provision of vitamin K above normal amounts may stimulate bone growth over the full rearing period.
