Elizabeth Plunkett, Graduate Research Associate, Department of Animal Sciences, The Ohio State University
With the price of heifers continually climbing and reaching historic highs, producers must place even greater emphasis on raising high-quality replacements. Achieving this requires a proactive, preventive approach to heifer management. Although heifers are often viewed as low maintenance compared to lactating cows, they are the future of the herd and warrant significant investment of time and resources. Over the past two decades, research on heifer rearing has advanced significantly, highlighting the economic advantages of optimizing heifer nutrition, housing, and welfare. However, one important area remains underappreciated: heifer mastitis.
What is Mastitis?
Mastitis is inflammation of the mammary gland that typically results from an intramammary infection. Intramammary infections occur due to bacteria entering the mammary gland through the teat canal. In lactating cows, mastitis is a common occurrence due to increased exposure of the mammary gland to potential pathogens during milking. While the mammary gland possesses several physical and immunological defense mechanisms, bacteria have the opportunity to overwhelm these defenses during times when other pressures are present (e.g., parturition). Heifers possess an additional defense, the keratin plug, a wax-like substance that obstructs the teat canal, preventing bacteria from entering the mammary gland. However, the keratin within the teat canal can become overwhelmed with bacteria at any stage of development, and these bacteria can persist for up to a year. The colonization of bacteria within the teat canal can compromise mammary gland development at a crucial time and decrease the future milking potential of infected quarters. Additionally, infected heifers can serve as a reservoir for mastitis-causing bacteria, particularly Staphylococcus aureus, which can create chronic problems in your milking herd.
How do Heifers Contract Mastitis?
Similar to lactating cows, dirty bedding and flies can be a major component of harboring and spreading bacteria in a heifer’s environment. Maintenance of bedding in the milking herd occurs daily, if not more frequently. While heifers may not require this intense regimen, their bedding needs to be thoroughly maintained at least weekly and spot-checked frequently. Clean, dry bedding can be an easy yet extremely impactful way to limit the risk of heifer mastitis by reducing bacterial load in the environment.
Flies are a nuisance not only in our lives, but heifers as well. They serve as the perfect reservoir for bacteria such as Escherichia coli, Klebsiella, and Staphylococcus spp., all known to cause mastitis. Fly populations can amass to over 100,000 flies from just a single pair in as little as 2 weeks, stressing the importance of controlling flies before they have a chance of establishing a notable population. The presence of any unwanted organic matter (e.g., manure in the pens, wet feed in the bunk, wet bedding or bales, etc.) can supply flies with the perfect breeding ground. Additionally, keeping weeds sprayed or mowed around heifer facilities will help limit fly populations and have the added bonus of helping with ventilation. Constructing a pest management plan that includes proper sanitation protocols along with the use of a larvicide, if needed, can be a helpful strategy to mitigate bacterial reservoirs and fly breeding grounds.
Cross suckling in youngstock is a suspected cause of the introduction of bacteria to the teat. Not only can the physical force applied to the teat during this undesirable behavior cause trauma, but if calves are being fed unpasteurized waste milk from infected cows, this can provide the opportunity for bacteria to enter the traumatized teat. While data indicating a direct link between cross-suckling and the incidence of mastitis during first lactation remains inconclusive, this behavior should not be overlooked.
Additionally, times when stressors are high (e.g., pen moves within a farm, weaning, moving to or from contract grower, etc.) provide the perfect opportunity for bacteria to colonize the mammary gland due to weakened host defenses. Therefore, minimizing the number of times animals are introduced to a new pen hierarchy and ensuring weaning is a smooth transition can help keep host defenses prepared to adequately manage unsuspecting bacteria that are looking for an opportunity to strike.
The Physiology Behind Production Losses
The greatest amount of mammary gland development occurs during first gestation. During this time, milk secretory tissue (i.e., parenchymal tissue) increases exponentially while supportive tissue (i.e., stromal tissue) begins to decline as it serves more of a supportive role during milk production, and the increased need for milk secretory capacity creates a competition for space in the mammary gland. Development should not be confused with growth, as development is the specialization of the tissue to complete its specific function, whereas growth is simply an increase in size or number of something. The greatest amount of mammary gland growth occurs from 3 to 12 months. However, the introduction of bacteria during either growth or development can be harmful to future mammary gland productivity.
There are two factors that determine milk production by the mammary gland: the number of secretory cells and their rate of secretion. When bacteria enter the mammary gland and establish themselves, they can damage the growing and developing secretory tissue via the production of noxious agents and through the stimulation of the immune system. Immune cell recruitment into the mammary gland during infection is a natural process; however, when these immune cells complete their effector functions, this causes collateral damage to the surrounding secretory tissue, leading to the development of connective tissue (i.e., scar tissue), which decreases future milking potential. Increased immune cell recruitment to an infected mammary gland can also leave animals in a heightened immune state and lead to nutrients being repartitioned towards fighting an infection when they should be used for maintenance and growth.
When Should You Start to Care?
The simplest answer is, as soon as that heifer calf hits the ground. Every step of growth and development during the heifer’s life is an opportunity to ‘program’ them to be a high-functioning herd mate in the future. But on the downside, for every opportunity that we have to make positive impacts, we also have the opportunity for negative inputs to cause lasting damage that may be irreversible. By making sure we are doing the little things right (e.g., cleaning pens, managing flies, etc.), we can have a big impact on reducing the risk of heifer mastitis and raise high-quality replacements that have the most milk-secreting potential, which is a plus for your future pocketbook.