About Dairy Wellness

When breeding heifers, how big is big enough?
Posted by Dave Erf

When breeding heifers, the common question “how big is big enough?” could soon be a thing of the past.

Breeding size for heifers is typically based on a one-size-fits-all stature and weight, rather than by age. This is because it is assumed that all heifers should be the same size at the same age. However, the reality is that heifers are genetically predisposed to be different sizes. Waiting for heifers to reach a height benchmark can be a costly practice for dairies, leading to delayed first breeding and delayed entry into the milking herd and delayed milk production.

Genomic testing can more accurately reveal a heifer’s growth potential early in life, allowing producers to accelerate genetic progress with confidence and enhance profitability, all while capitalizing on higher production and profit potential.

Recent herd evaluations from Zoetis show substantial differences in heifer weight and height due to differences in genomic standardized transmitting abilities (STA) for strength and stature.

Zoetis evaluations report:

  • At approximately 12 to 13 months of age, calculated weight varied by approximately 90 pounds due to genetic size differences in genomic STA for strength between -2 and +1.5.1
  • At approximately 12 to 13 months of age, height varied as much as 2 to 2.5 inches in heifers that varied in differences in genomic STA for stature.2  Another way to look at it, is that heifer height ranged from 0.5 to 0.87 inches taller per change of +1 in STA for stature.1,2  

These evaluations demonstrate how genetics play a large part in heifer growth. Genomic information can give you an estimate of whether a heifer is expected to be bigger or smaller than others at that age. Again, why wait for just size to determine breeding age? Consider breeding heifers based on age to avoid losing income because they look smaller, when, genetically, heifers will vary in size and some heifers are supposed to be smaller than others. Of course, animals that are noticeably smaller due to previous health challenges are a different story, which is where good health records can help.

Many farms with genomic testing have yet to utilize data to its fullest potential, and continue to resort to outdated, less accurate methods of gauging breeding age. With the help of genomics, producers can eliminate the guesswork from these decisions. Tune in to the webinar Moving Beyond Phenotype: Genomics vs. Size-based Traits to learn more.

1 Data on file, Zoetis Internal Data, April 2014, n > 1600, Zoetis Inc.

2 Data on file, Zoetis Internal Data, March 2014, n = 160, Zoetis Inc.



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