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Delay in Calving Heifers Costly in many Ways
Dairy Pipeline: May 1999
Tom L. Bailey
Dairy Production Medicine
Virginia-Maryland Regional College of Veterinary Medicine
Virginia Tech
(540) 231-3936
baileyt@vt.edu
Calving heifers at an older age has many disadvantages other than increasing nonproductive life and delaying potential milk income. When heifers calve at ages greater than 24 to 25 months, larger inventories or numbers of heifers must be maintained in the heifer herd. Increasing the age at calving also increases the generation interval, delaying the introduction of genetically superior replacements in the herd. If the annual replacement rate is 33 percent in a 100 head herd, a minimum of 33 calving heifers are needed per year. In a real situation, assuming a 15 percent attrition factor for death loss, infertility and selection within the heifer pool, approximately 38 to 40 heifers are needed to calve each year for culling purposes. When calving is delayed to an age greater than 24 or 25 months, heifers are accumulating in the replacement pool. For every one month increase in the age at calving over 24 months, the replacement inventory numbers are increasing at a rate of 4.2 percent. This figure takes into account the inventory of heifers from birth through calving. Therefore, if a herd is calving 28-month old heifers with an average culling rate of 33 percent, we have now increased the number of replacement heifers on the farm from 76 to 89. This equates to 13 additional heifers or an increase of 16.8 percent in the total number of heifers consuming feed, labor, fuel, facilities and management on a yearly basis.