A BETTER UNDERSTANDING OF BIRTH WEIGHT TO PERFORMANCE RELATIONSHIP
University studies in Wyoming and data from Montana and Colorado lend credence to the following conclusion
1.
The birth weight itself influences calving ease by 65%.
2. The female has 60-70% influence on birth weight of her calf. 3. The bull has 30-40% influence on birth weight of his progeny. 4. Pelvic measurement and angle, as well as the shape of the calf have 35-40% influence on calving ease. 5. Length of gestation greatly affects birth weight. A fetus can gain over one pound per day in the last days of gestation. 6. Weather and temperature the last 30 days affect the length of gestation. 7. Size and maturity of the cow influence calving ease. If you are not physically recording birth weights, guessing is as accurate as driving with a broken speedometer— what’s thought to be 55 MPH may in fact be 65 of 70 MPH, and what’s thought to be 70-80 lbs may actually be 80-90 lbs. Remember, everything is relative. Increased growth, frame and performance will increase BW. A longer bodied calf will weigh more. If a calf is expected to have genetics for growth, it will display this prior to birth as well as after. As a rule of thumb, it takes a calf weighing 86 lbs at birth to finish at 1200-1250 lbs. A cow should easily give birth to a calf weighing 8% of her own body weight. Thus a 1200 lbs cow should give birth to a 96 lbs calf with ease. Continued selection for low birth weight will ultimately reduce the mature sizes and performance of your cattle.
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