Growing dairy replacement heifers is no longer the “one-size-fits-all” proposition that it was once assumed to be.
Today, we know that simply using breed-average standards is less than ideal for individual herds and their unique animals. To help dairies evaluate their heifers and raise and breed them to best serve their specific needs, Penn State University has developed a free, customizable, online spreadsheet to track heifer growth.
“If you can use Excel, you can use it,” stated Gail Carpenter, Assistant Professor of Extension and Outreach at Iowa State University and host of The Dairy Podcast Show. “It’s an excellent, easy-to-access tool that can provide great value to dairies.”
Developers Jud Heinrichs and Coleen Jones noted that certain physiological changes like the start of puberty happen not because a heifer reaches a particular weight or age, but because she has matured to a certain proportion of her final, mature body size and composition.
Mature size is a lynchpin in the program. Many herds underestimate the height and weight of their mature cows; it should be assessed specifically rather than relying on breed averages. “If we know the mature size of a heifer and her current size, it is a relatively simple matter to figure out what growth rate we need to achieve to move from the current size to the mature size,” said Heinrichs.
Times in between, such as breeding, can be benchmarked as well, and the spreadsheet generates a customized growth curve for an individual herd based on that herd’s goals for age at first calving. The spreadsheet is based on the following target metrics:
- Body weight of 55% of mature weight at first conception and 85% of mature weight after first calving.
- Height of 55% of mature height at birth and 96% of mature height at first calving.
- 50% of height growth from birth to calving is assumed to occur between birth and 6 months of age, with an additional 25% between 6 and 12 months, and the final 25% between 12 months and calving.
These targets were derived from a comparison of heifer growth data from all breeds to mature heights calculated by assuming mature body weight and using research-validated ratios between withers height and body weight.
Withers and hip height are assumed to change at the same rate throughout the growth phase, so either one can be used to monitor growth, as long as the same standard is used for heifers and mature cows. Mature cow size can be entered as herd average or individually for each animal’s dam.
Heinrichs said the spreadsheet’s greatest benefit is tracking heifer progress and monitoring whether they are hitting growth targets as they develop, rather than waiting to measure heifer performance at first calving. Nutrition, housing, and sales decisions can then be made to steer heifer development and inventories.
The spreadsheet – including metric and Spanish language versions -- can be accessed here.
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