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By Edgar O. Oviedo-Rondón and Michael J. Wineland , North Carolina State University, Raleigh, NC, USA
The incidence of splayed legs in chicks and poults at hatch is very low, normally no more than 0.35 to 0.50%, but it can increase on some occasions. Birds with this condition have one or both legs splayed laterally from the coxofemoral joint and are unable to stand. Sometimes, the problem is only observed on the farms and constitutes another cause of culling during the first three weeks of age.This condition has been associated with high humidity during incubation, but the results of our research indicate that higher temperature conditions during the last phase of embryo development may have a bigger impact. Splayed legs are also observed when newly hatched chicks are placed on slippery floors. Higher temperatures during incubation may have the bigger impact on splayed leg incidence because they affect bone, tendon and muscle development, and thyroid metabolism. Embryos can be heat stressed in commercial hatcheries due to incubator and hatcher design that prevents adequate air flow around the eggs in some locations. Occasionally reduced ventilation during incubation and extended length of hatching time (12 to 24 hours) may cause the heat stress that triggers higher incidence of splayed legs.
Muscle development
Poults and chickens exposed to elevated incubation temperatures may have lower muscular strength to stand up at hatch because they have lower glycogen reserves in the muscles and their myofibers are also thinner. Elevated incubation temperatures accelerate embryo growth to rates that demand higher oxygen consumption than can passively diffuse through the pores of the eggshell. Consequently, the embryo shifts energy metabolism from utilising lipids of the yolk, which requires oxygen, to using limited amounts of glycogen the embryo stored in muscles. Glycogen catabolism does not require oxygen, but produces lactic acid. When acidity increases important contractile and metabolic functions of muscles are hindered. In the case that acidity is not regulated, the accumulation of lactic acid may be a factor in muscular fatigue. Sometimes, this effect can be severe and cause late embryo mortality, but frequently the overheated poults or chickens that hatch will be lethargic, may appear exhausted, slow to search for feed and water, and potentially become the starve outs at the farm increasing the first week mortality.
Poults and chickens exposed to elevated incubation temperatures may have lower muscular strength to stand up at hatch because they have lower glycogen reserves in the muscles and their myofibers are also thinner. Elevated incubation temperatures accelerate embryo growth to rates that demand higher oxygen consumption than can passively diffuse through the pores of the eggshell. Consequently, the embryo shifts energy metabolism from utilising lipids of the yolk, which requires oxygen, to using limited amounts of glycogen the embryo stored in muscles. Glycogen catabolism does not require oxygen, but produces lactic acid. When acidity increases important contractile and metabolic functions of muscles are hindered. In the case that acidity is not regulated, the accumulation of lactic acid may be a factor in muscular fatigue. Sometimes, this effect can be severe and cause late embryo mortality, but frequently the overheated poults or chickens that hatch will be lethargic, may appear exhausted, slow to search for feed and water, and potentially become the starve outs at the farm increasing the first week mortality.
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Source: World Poultry, Vol. 27, No. 5
