Kalvutdragaren - en hjälpande hand?
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.