Interpretive Summary: Effect of reduced feed intake in broiler breeder hens on their stress levels and the growth and immunology of their offspring.
By: Dr. Caitlin Vonderohe
Events that occur during early embryonic development can have dramatic effects later in life. Some investigators have found that restrictions of uterine space, or maternal nutrition can impact progeny growth, health and metabolism. More recently, investigators have examined the effect of maternal stress on the immune system of the progeny. However there has been significant limitations in this research in broiler chickens. Breeder hens exposed to different stressors and under-nutrition, due to the common practice of feed restriction. It is important to determine how these practice may affect the offspring of these chickens. Bowling et al. recently published a paper in Translational Animal Science exploring the effect of feed restriction of hens on the growth and immunity of their offspring. The authors hypothesized that the offspring of hens experiencing the greatest degree of feed restriction, and therefore stress, would have reduced growth and immunity.
Thirty-six broiler hens were maintained at a low, medium or heavy body weight, in separate groups, by feed restriction of a commercial diet. Hen behavior was monitored throughout the project. Eggs were collected over a three week period from each group and incubated until hatched. Egg yolk and serum samples were measured for immunoglobulins. When the chicks were hatched, they were weighed and placed into pens with chicks from hens in the same treatment group. All chicks were reared with similar management practices and identical diets and were weighed weekly. Blood samples were collected from chicks to measure white blood cell ratios, cortisone, and response to Infectious Bronchitis vaccination. Sixty-nine of these meat birds were euthanized at 42 days of age, and tissue samples from different organs were taken. The remaining birds were challenged with an injectable endotoxin and E. coli challenge, and weighed immediately before and after the challenge, to measure the bird’s response to immune challenge.
Hens maintained at the low body weight foraged less, and pecked at objects in the cages more, than hens in the medium and heavy bodyweight groups. A greater proportion of male chicks were hatched from the heavy body weight hens than the low body weight hens. There were no differences in yolk immunoglobulins in eggs produced by chickens in each body weight group. Female chicks from hens fed to a heavy body condition score had greater levels of plasma corticosterone than female chicks from hens fed to a low body weight on day 23. However males from hens that were most feed restricted had higher corticosterone than males from hens fed to a heavy body weight, but the opposite was found on day 42. Male chicks from low body weight hens had lower body weights than male chicks from heavy bodyweight hens. Interestingly, progeny from heavy bodyweight hens had higher antibodies, and therefore a greater response to vaccination than chicks from low bodyweight hens. Of the birds challenged with LPS, the female progeny of heavy hens were significantly affected by LPS, by having a reduced body weight after the challenge, but males were not affected the same way.
The authors strongly believe that the behaviors exhibited by feed restricted chickens, coupled with a changed white blood cell ratio indicates that feed restricted chickens are under chronic stress. However, the chickens fed to a medium body weight had the lowest corticosterone levels and stress behaviors, indicating that these animals were the least stressed. Hen bodyweight significantly affected both the bodyweight and immunity of the offspring, and these effects were often sex-dependent. The reduction in growth in low body weight hens can be attributed to elevated corticosterone, which has been previously associated with reduced offspring growth, particularly in male chicks. Hen bodyweight was also a significant indicator of response to vaccination, which has a significant impact on the health and productivity of offspring.
Overall it is important to understand how nutrition management of hens may affect the health and growth of their offspring. Bowling et al. clearly demonstrated that stressed hens produce offspring, particularly male offspring, that do not grow nor respond to immune challenges as efficiently as birds from non-stressed hens. Therefore it is highly important to diligently manage the welfare of breeder hens so their offspring are productive and healthy.
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