Pre-hatch stress linked to leg problems

Overheating, insufficient oxygen during incubation could cause early abnormalities in commercial turkeys.

Leg problems in commercial turkeys — a leading cause of culling and late mortality — could be due to elevated temperatures and insufficient oxygen or ventilation during incubation.

“Bone weight, length, thickness and strength are affected by incubation conditions,” Dr. Edgar O. Oviedo-Rondón of North Carolina State University, Raleigh, said at the Midwest Poultry Federation Convention.

An estimated 2% to 6% of all turkey flocks display some observable signs of leg abnormalities and many more are affected with locomotion problems, the veterinarian said.

“At present, the incidence of leg problems in turkeys may exceed 15% in some flocks and up to 5% of flock mortality may be due to leg abnormalities, especially during the last weeks of life. This costs the US turkey industry over $150 million per year,” he added.

Leg problems, Oviedo-Rondón acknowledged, can be due to many factors, ranging from nutrition to infectious disease. But when they are observed at hatch or during the first week of life, etiologies related to maternal effects and embryonic development should be considered.

Ossification (bone formation) begins during embryonic development. Other investigators have conducted studies indicating that ossification in turkeys can actually start at 12 days of embryonic development and that it speeds up after 20 days of incubation, just a week prior to hatch, he said.

STUDY RESULTS

Oviedo-Rondón and colleagues have conducted several studies designed to evaluate the effects of incubation conditions on leg health in turkeys and broilers.

In one study focusing on long-bone development in Nicholas turkeys, standard incubation conditions were used up until 24 days, then eggs with viable embryos were randomly divided and placed in cabinets with temperatures ranging from 36° C to 39° C (96.8° F to 102.2° F); 36° C is considered a cool incubation temperature, while 39° C is considered hot. Some embryos in the study received oxygen concentrations ranging from 17% to 23%. Other embryos received both varying temperatures and oxygen concentrations.

Hotter temperatures caused a reduction of tibia weights and increased shank weight compared to cooler temperatures. The length of the femur, tibia and shanks were reduced in the 39° C group and relative asymmetry of leg weights was increased at 38° C and 39° C.

Poults from the 23% oxygen group had bigger shanks and heavier tibias than those in the 17% oxygen group; low oxygen reduced tibia and shanks as a proportion of the whole body, Oviedo-Rondón and colleagues found in their study, published in Poultry Science in 2008.

OTHER CAUSES OF LEG PROBLEMS

Poor bone development isn’t the only cause of leg problems, however. Improper development of tendons, joints and ligaments may be a contributing factor, the investigator said at the meeting.

Tendon development and strength, for instance, are crucial for adequate locomotion in all avian species but especially turkeys. Tendon problems can affect bone development, walking and mobility as well as future bone development. Studies by Oviedo-Rondón and colleagues with broiler chickens have demonstrated that improper incubation temperatures can affect collagen fibers and, hence, tendon development.

Oviedo-Rondón also addressed the role of genetics. Leg problems among turkeys incubated under the same conditions may be explained by different turkey strains, but “our latest research results [indicate] that incubation temperature may have a stronger effect on leg health than the genetic background,” he said, noting that similar results have been observed in broiler chickens.

The reason that commercial turkeys become exposed to elevated temperatures during incubation vary and include hatchery machine design, failure to ventilate during incubation and, sometimes, extending the length of hatching time. These situations increase the chance that some poults in a flock may be overheated, adversely affecting development, he said.

“In all our experiments, we have observed that pre-hatch stress impairs embryonic development and increases fluctuating or relative asymmetry in turkeys; higher asymmetry of bone traits has also been linked to locomotion problems and worsening of gait scores,” Oviedo-Rondón said.

He concluded that proper incubation temperatures are critical for proper bone development and to reduce relative asymmetry between bilateral traits in the bones. In addition, the effects of adequate incubation have been observed on the incidence of leg problems and gait scores at 6 weeks of age in turkeys.