By Coleen Jones and Jud Heinrichs, Penn State
A new growth spreadsheet that generates a customized growth curve for an individual herd based on that herd’s goal for age at first calving and the mature size of animals in the herd. Using this tool, you will be able to tell at every step of the way whether heifers are on track to calve at the right size and age, eliminating the delay that comes with not measuring heifer performance until first calving.
Monitoring height and weight of calves and heifers is essential to tracking the progress of each animal throughout the heifer-rearing period. Although we can readily spot fat and thin heifers, it is difficult to look at a heifer and determine if her height and weight are appropriate for her age. With just a few objective measurements, tracking heifer performance becomes much easier.
Traditionally, heifer growth has been compared to breed standards to determine ‘normal’ progress. However, this type of comparison is not useful if the group of heifers you want to monitor happen to be genetically programmed to be larger or smaller than breed average or if there is considerable variation in the genetics within a group of heifers. Crossbred heifers can be a bit of a challenge to benchmark as well, because they fall between the standards for the breeds of their sires and dams. We also know that certain physiological changes (such as the start of puberty) happen not because a heifer reaches a particular weight, but because she has matured to a certain proportion of her final mature size and body composition.
For these reasons, recommendations for heifer growth benchmarks based on the mature size of the animal were adopted in the 2001 Nutrient Requirements of Dairy Cattle. 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, or to benchmark times in between, such as breeding. We have developed a new growth tracking spreadsheet that automates these calculations and can generate a customized growth curve for an individual herd based on that herd’s goal for age at first calving and the mature size of animals in the herd.
The new Customized Dairy Heifer Growth Chart from Penn State asks you to enter the average body weight and height of third lactation cows in your herd, average birth weight of calves, average services per conception for heifers, and the goal for age at first calving. From this information a customized growth chart is generated, allowing you to track heifer performance against the growth required to meet your goals. The customized growth goals are presented in table form, as well as in graphs for height and weight (using inches and pounds) and a graph of the percent of mature size. Users can plot growth data from heifers on these graphs to compare individual heifer performance to the goals. Using this tool, you will be able to tell at every step of the way whether heifers are on track to calve at the right size and age, eliminating the delay that comes with not measuring heifer performance until first calving. A version of the spreadsheet using metric units is also available.
The spreadsheet assumes a target body weight of 55% of mature weight at first conception and 85% of mature weight after first calving, as cited in the 2001 Dairy NRC. Height targets are assumed to be 55% of mature height at birth, 85% of mature height at conception and 96% of mature height at first 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 the relationship between withers height and body weight determined by Heinrichs et al., 1992 (Journal of Dairy Science 75:3576-3581). Withers and hip height are assumed to change at the same rate throughout the growing period, meaning either one can be used to monitor growth as long as the same measurement is used for heifers and mature cows. Mature size of cows can be entered as a herd average or individually for each heifer's dam.
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