Heifer Rearing Goals23 July 2013
Targets for rearing heifers have altered in recent years as priority has shifted to weight at time of first calving with age now coming second, write Dave Winston, Virginia State University Extension.
The overall goal of dairy heifer rearing is to economically raise heifers to be of adequate size and body condition and to calve at a reasonable age to produce high quantities of high quality milk during the first lactation. This goal takes many things into account including economics, growth, health, and production.
There was a time when age at first calving may have been overstressed at the expense of body size. Today, growth is emphasized with age being secondary.
It is more desirable to have a well-grown heifer that calves slightly older than one that calves at 24 months but is undersized. An undersized heifer will likely struggle during the first lactation, will not compete well at the feed bunk in the milking herd, and will shift nutrients from production to growth.
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Previously, growth standards were fairly rigid with specific weight goals stated for each breed. However, given that mature body size varies from herd to herd due to genetic selection goals, recommendations for bodyweight at first calving should be expected to vary similarly.
Today’s rule of thumb is to have heifers calve at approximately 82% of their mature bodyweight. In order to evaluate one’s herd status, the dairy farmer needs to know the average weight of mature cows in the herd as well as bodyweights of heifers post-calving. For example, if a herd’s average bodyweight for mature cows is 1,500 lbs., the goal bodyweight at first calving would be 1,230 lbs.
Good management is required in order to reach the overall heifer management goal. It includes a strong nutrition program that encompasses forage testing, ration balancing, pasture management and supplementation, and growth monitoring. Facilities need to be functional, not fancy. Providing animals with clean, dry, and well-ventilated facilities is important for good health and growth.
Herd health for heifers begins before birth by ensuring that dry cows are properly fed, are in good body condition, have been vaccinated, and calve in a desirable environment. Colostrum management should provide at least 2 quarts of high quality colostrum to the calf within the first two hours of birth followed by subsequent feedings at 12-hour intervals for the first 3 days of life.
Providing good nutrition, minimizing stress, and developing a health protocol for heifers with the assistance of the herd’s veterinarian are essentials for raising healthy heifers and achieving growth goals.
Monitoring age at first calving is still important. It is costly to delay calving, especially when feed prices are high. Many factors including growth and reproductive management influence age at first calving. One should be mindful when evaluating age at first calving because there is a 9-month lag between the management functions that resulted in conception and the time of calving.
A timelier parameter to monitor is age at conception. PCDART has a database item (272) for age in days at conception. In order for a herd to reach a goal for age at first calving of 24 months, age at first pregnancy would need to be 15 months. Keeping track of age at first pregnancy for heifers diagnosed pregnant each month would allow the dairy manager to make timelier corrections to the nutrition and reproduction programs as needed. The Heifer Tracker in PCDART makes monitoring this database item fairly simple. Note that age at first breeding would likely need to be 13 months to achieve the age at first pregnancy goal to account for average conception rates.
The ultimate measure of success of the heifer rearing program is how well heifers perform once they are in the milking herd. Peak and summit milk, 305-day mature equivalent milk, and somatic cell counts in the first 40 days of milk can be useful parameters to track on a monthly basis