The Role of Egg Production in the Etiology of Keel Bone Damage in Laying Hens

Abstract

Keel bone fractures and deviations belong to the most severe animal welfare problems in laying hens and are influenced by several factors such as husbandry system and genetic background. It is likely that egg production also influences keel bone health due to the high demand of calcium for the eggshell, which is, in part, taken from the skeleton. The high estrogen plasma concentration, which is linked to the high laying performance, may also affect the keel bone as sexual steroids have been shown to influence bone health. The aim of this study was to investigate the relationship between egg production, genetically determined high laying performance, estradiol-17ß concentration, and keel bone characteristics. Two hundred hens of two layer lines differing in laying performance (WLA: high performing; G11: low performing) were divided into four treatment groups: Group S received an implant containing a GnRH agonist that suppressed egg production, group E received an implant containing the sexual steroid estradiol-17ß, group SE received both implants, and group C were kept as control hens. Between the 12th and the 62nd weeks of age, the keel bone of all hens was radiographed and estradiol-17ß plasma concentration was assessed at regular intervals. Non-egg laying hens showed a lower risk of keel bone fracture and a higher radiographic density compared to egg laying hens. Exogenous estradiol-17ß was associated with a moderately higher risk of fracture within egg laying but with a lower risk of fracture and a higher radiographic density within non-egg laying hens. The high performing layer line WLA showed a significantly higher fracture risk but also a higher radiographic density compared to the low performing layer line G11. In contrast, neither the risk nor the severity of deviations were unambiguously influenced by egg production or layer line. We assume that within a layer line, there is a strong association between egg production and keel bone fractures, and, possibly, bone mineral density, but not between egg production and deviations. Moreover, our results confirm that genetic background influences fracture prevalence and indicate that the selection for high laying performance may negatively influence keel bone health.

Keywords: deviation; egg production; fracture; hen; keel bone; laying performance; radiographic density.

Figure 1

Radiograph of a deviated keel bone. The keel bone surface area is circumscribed with blue color; the area of deviation is circumscribed with red color. The blue-red line marks the straight line between both extremes of the deviated outline. The aluminum step-wedge can be seen at the bottom of the figure.

Figure 2

Antennae location. Schematic, not to scale representation of the pen, demonstrating the location of both antennae in relation to the elements of the housing equipment.

Figure 3

Body weight. Each boxplot represents the median, first and third quartile, and minimum and maximum of the body weight of a specific treatment group and layer line within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each sampling period. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 12th−13th week of age, 2 = 19th−20th week of age, 3 = 26th−27th week of age, 4 = 32nd−33rd week of age, 5 = 39th−40th week of age, 6 = 49th−50th week of age, 7 = 60th−61st week of age.

Figure 4

Survival analysis of keel bone fractures. Note that only hens that lived until the end of the study and of which all seven radiographs could be evaluated for fractures were included in the analysis. (A) Proportion of hens without keel bone fractures of the four different treatment groups for all seven sampling periods. (B) Proportion of hens without keel bone fractures of the two different layer lines for all seven sampling periods. These data include all treatment groups. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying)l; SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 13th week of age, 2 = 20th week of age, 3 = 27th week of age, 4 = 33rd week of age, 5 = 40th week of age, 6 = 50th week of age, 7 = 61st week of age.

Figure 5

Survival analysis of keel bone deviations. Note that only hens that lived until the end of the study were included in the analysis. (A) Proportion of hens without keel bone deviations of layer line G11 for the four different treatment groups and all seven sampling periods. (B) Proportion of hens without keel bone deviations of layer line WLA for the four different treatment groups and all seven sampling periods. For comparison, the intercept (control hens of layer line G11) is also included in the graph (black, bold line). C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 13th week of age, 2 = 20th week of age, 3 = 27th week of age, 4 = 33rd week of age, 5 = 40th week of age, 6 = 50th week of age, 7 = 61st week of age.

Figure 6

Severity of keel bone deviations. Each boxplot represents the median, first and third quartile, and minimum and maximum of the proportion of the deviated keel bone area (POD) of a specific treatment group and layer line within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each treatment group. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 13th week of age, 2 = 20th week of age, 3 = 27th week of age, 4 = 33rd week of age, 5 = 40th week of age, 6 = 50th week of age, 7 = 61st week of age.

Figure 7

Radiographic density of the keel bone. Each boxplot represents the median, first and third quartile, and minimum and maximum of the radiographic density of a specific treatment group and layer line within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each sampling period. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 13th week of age, 2 = 20th week of age, 3 = 27th week of age, 4 = 33rd week of age, 5 = 40th week of age, 6 = 50th week of age, 7 = 61st week of age.

Figure 8

Estradiol-17ß plasma concentration. Each boxplot represents the median, first and third quartile, and minimum and maximum of the estradiol-17ß plasma concentration of a specific treatment group and layer line within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each sampling period. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA = high performing layer line; Sampling period 1 = 12th−13th week of age, 2 = 19th−20th week of age, 3 = 26th−27th week of age, 4 = 32nd−33rd week of age, 5 = 39th−40th week of age, 6 = 49th−50th week of age, 7 = 60th−61st week of age.

Figure 9

Locomotor activity. Each boxplot represents the median, first and third quartile, and minimum and maximum of the locomotor activity of (A) a specific treatment group within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each sampling period. (B) a specific layer line within a certain sampling period. The black lines represent the model estimates. Numbers of hens that were included in the analysis are given under each sampling period. C, control hens (egg laying); E, hens treated with estradiol-17ß (egg laying); S, hens treated with deslorelin acetate (non-egg laying); SE, hens treated with deslorelin acetate and estradiol-17ß (non-egg laying); G11, low performing layer line; WLA, high performing layer line; Sampling period 1 = 14th−15th week of age, 2 = 21st−22nd week of age, 3 = 28th−29th week of age, 4 = 34th−35th week of age, 5 = 41st−42nd week of age, 6 = 51st−52nd week of age, 7 = 61st−62nd week of age.