Growth retardation and perosis result from choline deficiency in young poultry. Perosis is the primary clinical sign of a choline deficiency in chicks and turkey poults, whereas Bobwhite quail develop enlarged hocks and bowed legs (NRC, 1994). Ducks given choline-free diets had reduced growth rates and developed severe perosis (Hsu et al., 1988). Perosis is first characterized by pinpoint hemorrhages about the hock joint, followed by an apparent flattening of the tibiometatarsal joint (Scott et al., 1982). Progressively, the Achilles' tendon slips from its condyles, thus rendering the bird relatively immobile. Some studies indicated that in prevention of perosis, choline is required for the phospholipids needed for normal maturation of the cartilage matrix of bone. Although perosis commonly refers to many hock abnormalities, true perosis is described as the classic choline deficiency sign.
Adult chickens probably synthesize sufficient choline to meet requirements for egg production. Minimal dietary choline does not affect hatchability with either chickens or turkeys, but Japanese quail and their developing embryos readily express general signs of deficiency (Latshaw and Jensen, 1972; NRC, 1994). Supplementary choline may be necessary for maintenance of egg size in quail (NRC, 1994). Contrary to some reports, 500 mg per kg (227 mg per lb) of supplemental choline to Leghorn hens increased egg weight while reducing specific gravity (Tapia Romero et al., 1985). Also, the choline growth requirement for quail is apparently higher than for chicks or poults.
Choline requirement of growing chicks decreases with age as it is generally not possible to produce a deficiency at an age over eight weeks. It was observed that methylation of aminoethanol to methylaminoethanol seems to be the rate-limiting step in choline biosynthesis for young birds. High levels of dietary methionine or other methyl donors, therefore, cannot completely spare the chick's requirement of dietary choline, which is in contrast to the situation with growing mammals such as the pig or the rat.
Apparently, choline requirement of laying hens can be influenced by choline level in the diet of the growing pullet (Scott et al., 1982). Hens that received choline-free diets after eight weeks of age were able to synthesize all of the choline required for good egg production. Those that had received choline supplements in the growing diet required supplemental choline in the laying diet for maximum egg production. The deficiency signs noted in these hens were a reduction in egg production and an increase in fat content of the liver. Even with choline deficiency, however, choline content of the egg was not affected by low dietary choline.
Despite lack of evidence that laying chickens require a dietary source of choline for maximum egg production, addition of choline to practical diets markedly reduces the amount of fat in the liver (NRC, 1994). However, a number of reports with chicks and turkey poults did not find fatty livers with deficiency (Ruiz et al., 1983). A choline response in laying chickens is likely to occur only if inadequate daily sulfur amino acids are provided.
Addition of 0.1% of supplemental methionine resulted in no response in laying hens to supplemental choline (Crawford et al., 1969). It appears that benefits from supplemental choline in layer diets occur mainly when supplemental methionine is just adequate to meet methionine requirements. Miles et al. (1983) demonstrated that the addition of 0.11% choline plus 0.1% sulfate could essentially spare all supplemental methionine in broiler diets. However, in turkey poult diets (Harms and Miles, 1984), responses to sulfate and choline addition were not equivalent to the addition of supplemental methionine. Pesti et al. (1980), using young chicks, found that supplementation with methyl donors from either 0.23% choline or 0.23% betaine was equivalent to supplementation with 0.23% methionine in 21-day chick experiments, using basal diets containing 0.31% methionine and 0.43% cystine. Spires et al. (1982) found that supplemental choline could replace up to two-thirds of the supplemental methionine required in broiler diets from 0 to 47 days in diets containing 0.30% methionine and 0.43% cystine in the starter phase, and 0.25% and 0.42% methionine and cystine, respectively, in the finisher phase.
