bottom line better because both herd management ex- penses and marketing income can be better controlled. “Cows are pregnant for about 285 days of a 365-day
year,” continues Carpenter. “There is not much time left for reproductive tract recovery and subsequent rebreeding. If cows are to calve every 12 months, the calving season can be no longer than 80 days per year (365 — 285 = 80). Thus, a calving season of 80 days would be followed by an 80-day breeding season.” The popular cliché, “You can’t manage what you
don’t measure,” is appropriate for cow-calf operations where profi ts depend upon effi ciency of the cow’s re- productive system. Unless you measure results of each step of the reproductive process, it’s hard to determine whether a cow is paying her way. It is also important to understand the vernacular
used by animal science consultants and veterinarians in discussing reproduction, so that you can have a thorough understanding of what they recommend.
Table 1. Measures of Reproductive Effi ciency in Cattle1
Reproductive Effi ciency Measure
Conception rate Calculation
Number of females conceiving ÷ number of females exposed to breeding X 100
Management Considerations
♦ Percent conceived ♦ Typically not measured because of the diffi culty in determining if conception has taken place
♦ Cattle may conceive and then suffer early em- bryonic death and may not be distinguishable from cattle that never conceived.
Pregnancy rate Live calving rate
Number of females diagnosed pregnant ÷ number of females eligible for pregnancy X 100
Number of live calves born ÷ (number of females exposed to breeding – number of breeding herd females sold or died + number of pregnant females purchased) X 100
♦ Percent pregnant ♦ Measure of breeding season success
♦ Percent birth calf crop ♦ Measure of collective results of breeding and calving seasons
♦ Cattle must not only conceive, but they must also give birth to live, healthy calves.
♦ Reproductive losses between breeding and calving may be due to reproductive disease.
Weaning rate
(Number of calves weaned + number of calves sold pre-weaning) ÷ (number of females exposed to breeding – number of breeding herd females sold or died + number of pregnant females pur- chased) X 100
Calving interval
(Age in days at fi rst calving – age in days at last calving) ÷ number of calvings
♦ Percent calf crop weaned ♦ Single most descriptive measure of herd re- productive performance
♦ Evaluates conception, pregnancy, calving, and pre-weaning success or failure
♦ Number of days between successive calvings ♦ Measures reproductive success over the last year
♦ Ideally 365 days or less and not average more than 365 days over multiple years to maintain the desired calving season and produce a marketable calf on an annual basis
Reproductive Management of Beef Cattle Herds by Dr. Jane A. Parish, Dr. Jamie E. Larson and Dr. Rhonda C. Vann, Mississippi State University Extension Service. (
http://msucares.com/pubs/publications/p2615.pdf)
1
tscra.org August 2013 The Cattleman 57
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