All producers are excited to watch their upcoming replacement heifers develop, in anticipation of performance in the milking string as the top genetics of the herd. Management during the first two years of life can have a profound impact on mammary health and ultimately profitability. There is just about nothing more devastating than freshening in a group to find mastitis or even worse, blind quarters.

Heifer mastitis, most often caused by bacterial or intramammary infection (IMI), is a common affliction. However, we know very little about what in stage of production it occurs and how to best diagnosis the root of the problem. Pamela Adkins, D.V.M., at the University of Missouri worked with a team of researchers to capture culture samples from various stages of heifer development to establish standard protocols for sample collection. Their ultimate goal was to help producers better understand how to circumvent this disease cycle for their herds.

Adkins describes these processes and their results on the July edition of the “Dairy Science Digest,” a podcast designed to bring the Journal of Dairy Science straight to the ears of dairy producers.

Timing

More than 30% of heifer mastitis cases occur in the first two weeks of lactation. When a first calf heifer calves in with a high somatic cell count, she is more likely to maintain the high count throughout the first lactation, and is ultimately more likely to be culled.

Infections can develop prior to freshening. “If it occurs within the first 14 days in milk, we typically attribute that to an infection that began during gestation,” explained Adkins. Her team analyzed 304 quarters and found that gestating heifers were 8x as likely to grow pathogens than their nonpregnant counterparts.

“As glands become larger, they also become more vulnerable,” Adkins described. “Hormonal changes and the onset of colostrogenesis are also likely confounding impacts.”

Manage your future

The most common species cultured from this research project were non-aureus Staph. species or NAS. These are bacteria that frequently colonize the teat skin, becoming opportunistic – navigating their way up the streak canal and into the mammary gland. Infections with NAS species are likely not a major problem for heifers, however, some heifers can be found to have IMI with major mastitis pathogens, such as Staphlococcus aureus and Streptococcus dysgalactiae. “These are the infections we would like to be able to figure out the best way to prevent. Unfortunately, there are still several unanswered questions about mastitis progression in the heifer population,” explained Adkins.

Historical best management practices remain important and are worth repeating as they help limit exposure and improve long-term outcomes:

  • Maintain clean heifer environments to reduce exposure to mud.
  • Reduce fly pressure through the environment and feed through larvicides.
  • Reduce nutritional stress of developing heifers by ensuring adequate feed availability.

Pinpointing the cause

If your operation is struggling with mastitis in first-calf heifers, consider working with your local veterinarian to capture samples. This class of animals can be a challenge to assess. Researchers utilized mild sedation to capture clean samples from these “spicy” heifers.

One goal of this investigative project was to determine the ideal way to sample pathogens present in the mammary gland prior to freshening, across a variety of ages. Due to the challenge of gathering samples when there is very little or no fluid available, Adkins’ research team worked to identify the best method of sampling. Fine needle puncture, needle aspirate of the cistern, and teat swap were compared. All sampling methods found pathogens. However, due to the rate of early infection, at this time there’s little advantage to the needle sampling. If a producer prefers to wait until after freshening, a milk sample should suffice.

Typically, freezing milk samples is advantageous to limit “over-growth” of bacteria present in the sample. This is especially important for identifying specific organisms such as Staphylococcus aureus but could limit the recovery of mycoplasma or gram-negative pathogens.

Mammary gland health helps ensure a bright future for your replacements. Taking time to assess your replacement program is on the right path will likely return dividends. Listen in to the “Dairy Science Digest” on any of your favorite podcast platforms to learn how to improve heifer development and limit the tragedy of damaged replacements.

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(c) Hoard's Dairyman Intel 2025

July 28, 2025

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