Continuous loading of the skeleton by the body's weight is an important factor in establishing and maintaining bone morphology, architecture and strength. However, in fast-growing chickens the appendicular skeleton growth is suboptimal making these chickens predisposed to skeletal mineralization disorders and fractures. This study compared the macroand microstructure as well as the mechanical properties of the tibiotarsus of a novel dualpurpose, Lohmann Dual (LD) and a highly developed broiler, Ross (Ross 308) chicken line. Eighty one-day-old male chicks of each line were grown until their body weight (BW) reached 2000g. Starting at the day of hatching, six birds of each line were sampled weekly. The weight, length and width of the tibiotarsus were measured and its mechanical properties (rigidity, M-Max and the M-fracture) were evaluated using the three-point bending test. Additionally, the mineral density of both, trabecular and cortical bone, the bone volume fraction, the trabecular number, thickness and separation plus cortical thickness of both chicken lines were analyzed using microcomputed tomography. The growth of the tibiotarsus in both chicken lines followed a similar pattern. At the same age, the lighter LD chickens had shorter, thinner and lighter tibiotarsi than those of Ross chickens. However, the LD chickens had a similar cortical thickness, bone volume fraction and similar mineral density of both trabecular and cortical bone to that of Ross chickens. Furthermore, the tibiotarsus of LD chickens was longer, heavier and wider than those of Ross chickens of the same BW. In addition the rigidity of the LD tibiotarsus was greater than that of Ross chickens. This suggests that the tibiotarsus of LD chickens had more bending resistance than those of Ross chickens of the same BW. Consequently, fattening LD chickens to the marketable weight should not affect their leg skeleton stability.

The use of dual-purpose chickens is a strategy to avoid killing one-day-old male chicks of egg laying lines. Lohmann Dual (LD) is a novel dual-purpose chicken line created by the crossbreeding of layer and broiler lines. However, many of the cardiovascular diseases of broilers are likely to be associated with intensive genetic selection for growth and feed conversion efficiency. This study aimed to compare the macroscopic and microscopic structure of the heart and the aorta of the LD chicken line with that of the broiler chicken line, Ross 308 (Ross) under typical husbandry conditions for meat production. Eighty, one-day-old male chicks of each line were housed for 5 weeks (Ross) and 9 weeks (LD). Six birds of each line were sampled weekly. Heart mass, thickness of ventricular walls, cardiomyocyte size and blood capillary density as well as aortic diameter and thickness, number of elastic lamellae and elastic fiber percentage in the aortic wall were determined. The growth patterns of the heart were the same in the two lines. Although LD chickens had a lower absolute heart mass than that of Ross chickens, the relative heart mass in both lines was similar. The cardiomyocytes of LD chickens were larger than those of Ross’s of the same body weight (BW), nevertheless both lines had similar thicknesses of their ventricular walls. The blood capillary density was greater in the LD heart than in that of the Ross heart. The aorta of LD chickens had proportionally; a greater aortic lumen radius, larger numbers of elastic lamellae and more elastic fibers than in Ross chickens. Our results suggest that the heart and aorta of the LD chickens have not been disadvantaged by their intensive genetic selection; furthermore, LD chickens have a better myocardial capillary supply and better aortic mechanical properties than those of Ross chickens.

Rearing dual-purpose chickens is a practicable approach to avoid culling one-day-old male layer chicks. The present study examined the impact of a conventional fattening diet on the liver of a novel dual-purpose chicken line (Lohmann Dual, LD) in comparison to a broiler (Ross 308) chicken line. Age-related changes of structure and lipid content of the liver were assessed. One hundred twenty and newly hatched chicks (LD = 66, Ross = 54) were kept under the same husbandry conditions and fed a commercial diet for 5 weeks for Ross and 9 weeks for LD. Six birds of each line were examined weekly. Their body weight (BW) and liver mass were recorded. Microscopic structure and ultrastructure of the liver were investigated and the liver lipid content was measured using a pre-validated method. During the study period, liver mass increased with age, while normalized liver mass decreased. Furthermore, liver mass of Ross birds was greater than that of LD birds of the same BW. Overall, no significant differences were observed in the hepatic structure or ultrastructure between the two chicken lines. The hepatic lymphatic aggregations were without fibrous capsules and their number and area increased throughout the first week, then the values began to fluctuate with age in both chicken lines. The changes in the liver lipid content of the two chicken lines were within the normal physiological range over the term of the study. The liver lipid content correlated negatively with age and body weight in both lines. It was the highest on the first day then decreased until day 7 and thereafter did not change in both chicken lines. However, given the same body weight, the Ross chickens had a 9% greater liver lipid content than LD chickens. It is concluded that there is no apparent adverse effect of a high-energy diet on the liver of LD chickens.

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