Source: National Mastitis Council
Just because you’re milking a first-calf heifer, don’t assume she doesn’t have mastitis. In fact, the incidence of mastitis during early lactation is higher in heifers than in older cows, explained Vinicius Machado of Texas Tech University, Lubbock, Texas, during his 2019 NMC Annual Meeting presentation in Savannah, Ga.
Like multiparous cows, heifers are quite susceptible to intramammary infections (IMI) during late gestation. The teat canal opening widens as calving approaches, which increases the risk of pathogens entering the mammary gland and then triggering infection.
A 2011 study found that heifer IMI risk factors at herd, cow and quarter levels are different for distinct pathogen group-specific IMIs. The risk factors caused by major contagious pathogens include high herd somatic cell count (SCC) (>200,000 cell/ml), ineffective fly control, moderate to severe pre-calving udder edema, and comingling with lactating cows before parturition. For IMIs caused by environmental pathogens, risk factors include poor hygiene and lack of pre-calving vitamin and mineral supplementation.
Machado noted NMC’s 10-point program for preventing and controlling heifer mastitis. Click here to review the 10 points. Interventions during late gestation can change risk factors associated with IMIs. While prepartum therapy improves udder health, therapy success varies. Machado discussed a few therapies and their effectiveness.
In heifers, udder edema has been associated with increased IMI risk in early lactation. McDougall et al. (2009) suggests restricting water and salt, and giving anti-oxidant supplements, diuretics and corticosteroids as “treatments” to reduce udder edema. However, Machado noted that further studies must be conducted to research these strategies’ efficacy.
Some research shows that prepartum milking, such as three times daily for two weeks or twice daily for three weeks prepartum, can help reduce udder edema and improve udder health. Additionally, some research shows that prepartum milked heifers experience lower incidence of clinical mastitis, lower milk conductivity readings and lower SCC.
While milking heifers prepartum can improve udder health and productivity, Machado shared some concerns about this practice. Heifers milked prepartum are at greater risk of negative energy balance. Around parturition, they have lower plasma glucose and elevated non-esterified fatty acid (NEFA) and β-hydroxybutyric acid (BHBA), which led to greater incidence of hyperketonemia.
Colostrum is a major concern. Milking heifers (and cows) prepartum lowers colostrum quantity and quality. “Therefore, calves should not receive colostrum from prepartum-milked animals,” said Machado.
A few studies have looked at prepartum teat disinfection to prevent heifer mastitis. In general, this practice did not substantially decrease the number of animals or quarters with mastitis.
However, a New Zealand study found that spraying heifers three times a week during the last three weeks of gestation with an iodinebased teat sanitizer improved udder health of heifers in pasturebased systems. Although teat spraying did not reduce the incidence of clinical mastitis, it reduced the presence of Streptococcus uberis in milk samples collected the first day of lactation and it reduced the incidence of clinical mastitis caused by this pathogen. This suggests that spraying teats with a teat sanitizer during the last three weeks of gestation may contribute to preventing mastitis caused by S. uberis in dairy heifers raised on pasture.
Should heifers receive “dry cow antimicrobials” prior to calving? In general, prepartum infusion of antimicrobials in dairy heifers can improve udder health, lower postpartum IMIs, decrease the incidence of clinical mastitis, lower SCC and improve milk production. However, researchers do not consistently observe these benefits.
The efficacy of prepartum intramammary antibiotic infusion with longacting antibiotic formulations have been tested on heifers. However, non-lactating formulations have a long milk withhold period. To minimize the risk of antibiotic residue in milk in early lactation, administer it at least 45 days before parturition. Or, use a short-acting formulation (lactating cow therapy) 14 days prior to parturition.
From a practical and safety perspective, Machado prefers systemic administration of antibiotics over intramammary therapy. Why? Intramammary infusion of antibiotics can potentially increase new IMI risk if bacteria are “pushed” from the teat canal into the mammary gland. However, study results regarding injectable antimicrobials are mixed. For example, intramuscular injections of 5 g of tylosin for three consecutive days did not improve IMI cure rate.
Moreover, when heifers were systemically treated with penethamate hydriodide two weeks before parturition, they had fewer IMIs in early lactation, but this did not result in fewer cases of clinical mastitis.
Machado reminded NMC members that infusing antibiotics in prepartum heifers may represent extra-label drug use. “Therefore, this intervention should be performed under the herd veterinarian’s supervision and extended milk and meat withholds should be determined, following the Animal Medicinal Drug Use Clarification Act guidelines,” he said.
Internal teat sealants
With internal teat sealants (ITS) gaining rapid adoption as a dry cow mastitis prevention tool, some studies have looked at ITS use in late-gestation heifers. A New Zealand study found that ITS in heifers decreased the prevalence of IMI after calving and lowered the incidence of clinical mastitis.
Machado and Bicalho (2018) evaluated the impact of prepartum ITS on udder health of dairy heifers and combined ITS and intra-mammary infusion of antibiotics. “The incidence of clinical and subclinical mastitis was only reduced for heifers that received the combination of intramammary infusion of amoxicillin and ITS,” said Machado. “When treatments were applied alone, they did not lower the number of mastitis cases.”
In summary, late-gestation interventions can help control and prevent heifer mastitis. “However, before contemplating any of these practices, consider the safety and practicality of these interventions,” said Machado. Also, keep in mind that antibiotic resistance is a public health concern around the world. Only use antimicrobials to control heifer mastitis in herds that have a heifer mastitis problem and where nutrition, stress and hygiene are at optimal levels. Often, these strategies and their effectiveness are herd dependent.
To read Machado’s complete paper, log in to NMC’s Members Only site (http://www.nmconline.org/member-signin) and click on the Proceedings Library tab.