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Breeding objectives and animal protection considerations are often in opposition to one another. For moral and legal reasons, matters of animal protection should of course always be given precedence and seen as a top priority. In the area of turkey farming and breeding in particular, considerable advances have been made in recent decades to meet consumer requirements and demand for more turkey products at the lowest possible price.
Focus on the breeding side has been on faster and improved liveweight gain with minimal possible feeding effort and simultaneous development of economically interesting meat areas such as the breast musculature. The repeated occurrence primarily of diseases specific to poultry and turkey farming (e.g. "leg weakness", cardiovascular diseases) and promotion thereof due to breeding modifications, has been insufficiently considered or gone unexamined for a long time. Only in recent years have we seen a change of attitude in light of the heightened importance of animal protection and welfare.
This paper seeks to contribute to this topic by comparing a wild turkey strain still largely unaffected by breeding manipulation, with the modern high performance strain BUT-BIG6, using computer tomography recordings to describe more accurately the changes brought about by breeding techniques and the possible influence on disease complexes relevant to animal protection. To this end, 5 male specimens were examined using computer tomography at 7 life stages within the first 20 weeks of life (weeks 2, 6, 10, 12, 14, 16 and 20). Besides the organs' geometrical dimensions, blood flow through different organ systems was calculated using contrast media.
In accordance with expectations, the BUT-BIG6 animals (16.0kg ± 0.71kg) were significantly heavier than the wild turkeys at the end of the examination period (5.1kg ± 0.12kg). Furthermore, a significantly accelerated weight gain on the part of the farm animals compared to the wild strain was discernible during the last 6 weeks of the examination period. Similarly significant differences were recorded for breast muscle volume BMV.
Here too the results for the BUT-BIG6 animals (5649cm³ ± 1177cm³) were, at the end of the examination, significantly above those of the wild turkeys (2229cm³ ± 574cm³).
As with the liveweight LG, the farm animals exhibited, from the 14th week (LW), accelerated growth of their breast muscle volume. As no other organ system nor long bones display similar growth tendencies from the 14th week, the massive liveweight gain of the BUT-BIG6 animals at the end of their farm period is due mainly to the growth of breast muscle volume. This volume growth is characterised by an increase in breast muscle thickness BMD (wild turkey BMD20LW 33mm ± 3mm, BUT-BIG6 BMD20LW 65mm ± 7mm).
An expected adjustment of sustentative (heart) and supportive structures (femur, tibiotarsus, sternum) to these increased demands does appear to occur, but is insufficient. Thus, despite the increase of absolute heart volume (HV) in the BUT-BIG6 animals (HV20LW 133cm³ ± 13cm³) compared to the wild turkeys (HV20LW 82cm³ ± 8cm³), the LG/HV and BMV/HV ratios between both groups, above all in the 16th week, is highly significantly worse for the farm than for the wild animals. It is noteworthy that during the farming period frequent animal losses occur through cardiovascular diseases. Parameters for the objective assessment of heart size such as the ratio of heart width HB/thorax width THB (wild turkeys Ø61% ± 4%, BUTBIG6 Ø58% ± 6%) and hearth width HB/sternum length SL (wild turkeys Ø28% ± 3%, BUTBIG6 Ø28% ± 2%) yield no differences between the groups that suggest an adequate heart adjustment in the BUT-BIG6 animals.
This thesis of insufficient adjustment to the increased bodily demands is also reinforced by consideration of lung capacity. While it is true that total lung volume GLV in the BUT-BIG6 animals increases (GLV20LW 458cm³ ± 68cm³) compared to the wild turkeys (GLV20LW 268cm³ ± 22cm³), here too, primarily in the last third of the examination period, the ratios LG/GLV, HV/GLV and BMV/GLV are at times highly significantly worse for the farm animals. Though in the BUT-BIG6 turkeys the leg skeleton's supporting bones femur and tibiotarsus (femur20LW 143mm ± 8mm, tibiotarsus20LW 227mm ± 10mm) do grow longer than in the wild turkeys in absolute terms (femur20LW 129mm ± 2mm, tibiotarsus20LW 207mm ± 3mm), the growth rate WR of the wild turkeys for both long bones in the last third of the examination period is above that of the farm animals.
But because the largest liveweight gain and increase of breast muscle volume occurs simultaneously with the forwards extension of the body's centre of gravity, the adjustment in the farm animals to these increased demands is judged insufficient. This fact is decisive in the frequent occurrence of leg skeleton diseases in the final third of the farming period that are summarised under the term "leg weakness".
In the 20th week, the BUT-BIG6 animals' sternum, the supporting but also rigidly limiting bone of the breast musculature, grows only 1.3 times longer than the absolute length (251.6mm ± 42.3mm) of the wild turkeys' (191.4mm ± 9.6mm). With the simultaneous increase of the breast muscle volume BMV of around 2.5 times, this leads to the already mentioned massive gain in breast muscle thickness BMD. In this way, the pressure on the breast musculature increases and, likely in connection with other factors such as animal handling, causes the increase in the instances of pectoral myopathy due to insufficient blood flow. It was, in particular, observation of blood flow using contrast media and the subsequent measurement of thickness and change that revealed large differences between the animal groups in the course of the examination period. Apart from the measurement of the liver, the native density of the other examined organs (breast musculature, heart, spleen, kidney) did not reveal any group differences. Directly after intravenous application of the contrast medium, however, measured organ density in the wild turkeys increased more than in the BUTBIG6 animals. This permits conclusions on a more effective and quicker distribution of the contrast medium with the blood flow.
The heart thus seems capable of superior performance as a pump in the wild animals. After the contrast medium is distributed, the wild turkeys and BUT-BIG6 animals display similar values in the scan series HE3 for the breast musculature.
This is due to their similar capillary thickness, which nevertheless has to sustain considerably more musculature and larger fibre diameter in the farm animals. Because of these longer diffusion distances, only an insufficient supply of oxygen and nutrients to the musculature is possible, especially under increased stress.
From the 12th week, the blood flow in the liver in scan series HE3 is clearly stronger in the BUT-BIG6 animals, which is indicative of to increased anabolic processes.
For the measurements in the spleen, no group differences could be determined in scan series HE3, consequently a similar blood flow is to be assumed. In contrast to this, blood flow through the kidneys appears significantly stronger in the wild turkeys, which is reflected in large density differences (wild turkeys HE3 132.3HU ± 62.2HU, BUT-BIG6 99.0HU ± 13.3HU). While it is striking that there is a large difference in density values for all the wild turkeys' observed organs between scan series HE2 and HE3, this can be explained by the more effective and quicker distribution of the contrast medium through the heart. These results, in connection with individual parameters such as liveweight LG, breast muscle volume BMV, heart volume HV and liver-spleen volume LMV, as well as the ratios arising therefrom, do however permit the conclusion that the anatomical and physiological adjustments in the modern farm turkeys BUT-BIG6 to the desired, bred-in changes, above all in the the 2nd farm period, are insufficient. This causes diseases of both the cardiovascular and skeletal systems, and thus unnecessary suffering and pain to the farm animals. These results should therefore be included in the establishment of new breeding objectives and criteria on moral and animal protection grounds, so as to fulfil humanity's responsibilities for the well being of the animals it uses.