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Nilsson, Maja (2009) Kalvutdragaren - en hjälpande hand? Other thesis, SLU.

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The calf extrator's function has been studied, through measuring traction and how this varies in different situations, in comparison with corresponding manual traction situations. This was done against the background that excessive force at assisted calvings at dystocia can mean life threatening damages on the calf such as grave acidosis, vertebral fractures, femur fractures and rib fractures. The calf extractor has earlier been measured to pull with greater force than the established maximum force of "two strong men". The general instruction is that it should be used "with caution". The hope is to raise a discussion that can lead to better animal welfare for the calves. The experiment was lined up on the basis of the hypothesis that the traction from the calf extractor exceeds the traction of two men, where the calf extractor's force is not influenced of how it is maneuvered. Measurements were done of the traction on one front leg at forced extraction of a dead calf from an artificial cow. The experiment was performed in five parts with mechanical traction and two parts with manual traction. Numbers of pullingperiods and numbers of handle movements per pulling-period were registered. The extractions were applied according to a fictitious contraction scheme. The maximum manual force generated by one respectively two persons, standing and sitting and by the calf extractor, was examined in a laboratory environment. Measurements of the force generated by the calf extractor at varied handle movements were done also. The pulling power in kilograms was registered electronically and computer-logged with one value per second. The load dosage over time was calculated by the area under the curve. The total load on the calf was actually twice as big, since the measured force only represented what was applied on one front leg. The persons who pulled weighed 60-73 kg and were considered "normally strong". The descriptive experiments showed that the hypothesis could to its first part be verified and to its other part be rejected. One person standing on the floor pulls 42 kg and sitting on floor with support for the feet pulls 114 kg. Two persons standing on the floor pull 87 kg. Two persons sitting on the floor with support for their feet pull 184 kg. With the calf extractor one person pulls 300+ kg. A half range pull on the calf extractors handle achieve maximum force slower than a full range pull. Applying additional lubrication was shown to be of great importance in order to decrease the friction and force development. The load increases when the extraction angle is changed from 45° downward to 45° upward, which can arise in a lying cow. The calf extractor can moreover by its placement near the vagina cause a pressure from the outside on the soft tissues that counteracts pulling. The load increases on the calf when using a calf extractor compared with manual extraction. A big difference between mechanical and manual extraction is clearly seen when the passage of delivery is obstructed. When pulling with the calf extractor a 3.35 times greater total load is achieved compared with corresponding manual extraction. This is because of the higher maximum forces achieved and the long duration of remaining tension in the pulling ropes, in between "contractions". Through loosening the brake and pushing the handle of the calf extractor forward between contractions the load would decrease markedly. After difficult deliveries careful survey of the calf is required regarding damages and acidosis. Knowledge of the normal birth is a basic requirement in order to do a correct evaluation. Through awareness, farmers and field veterinarians can make decisions that better protects the animal welfare.

Item Type: Thesis (Other)
Keywords: obstetrik, dystoki, nötkreatur, ko, kalv, kalvning, förlossning, kalvutdragare, utdragning, framdragning, dragkraft
Subject (faculty): Faculty of Veterinary Medicine and Animal Science > Dept. of Clinical Sciences
Divisions: SLU > Faculty of Veterinary Medicine and Animal Science
Depositing User: Maja Nilsson
Date Deposited: 05 Mar 2009
Last Modified: 18 Aug 2015 10:12
URI: http://ex-epsilon.slu.se/id/eprint/3157

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