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Chest Circumference
In certain beef cattle management systems, where live weight cannot be recorded directly, chest circumference of animals may be recorded as indicator trait for growth rate in beef performance recording. Chest girth can be recorded using a measuring tape; alternatively, it is possible to record chest girth using dedicated devices that can predict chest girth from the processing of digital images of the animal. Such devices must be composed by a digital - optical part that is in charge to take digital images of the animal and by a software that must interpret digital images and, using dedicated software, produce animal's chest girth estimate. The device precision in chest girth estimation must be periodically verified by field calibrations where the average difference between tape and predicted chest girth should not exceed 2,5% of tape chest girth. Live weight, a direct beef performance trait, can be estimated from chest circumference using a transformation formula that includes both:
a. The age of the animal, and
b. Its chest circumference.
The age of the animal is calculated as the difference in days between date of recording and animal’s birth date. Transformation formulas may be specific to breed and sex.
It is suggested that use be made of transformation formulas derived from sufficiently large datasets where both chest circumference and live weight were recorded on the same animal, and collected on animals at different ages. Where transformation formula derived from a multiple regression approach are used then the relative R2 should be at least 0.90.
Where chest circumference data is used to estimate live weight, it is recommended:
a. That the recorded trait of chest circumference is specified, and that the appropriate units (centimetres, inches, meters, etc.) are specified.
b. That the actual chest circumference is recorded.
c. That chest circumference is stored in the central database and used to estimate live weight using appropriate and approved conversion formulae.
d. That estimated live weight derived from chest circumference together with original chest circumference be recorded together on the database.
e. That a code be recorded on the database with the animal record to indicate the procedure used to estimate growth from the chest measurement.
