Effect of application of an external teat sealant and/or oral treatment with a monensin capsule pre-calving on the prevalence and incidence of subclinical and clinical mastitis in dairy heifers.
OBJECTIVE
To assess the effect of applying an external teat sealant or a slow-release intraruminal monensin capsule pre-calving on the prevalence and incidence of subclinical or clinical mastitis in dairy heifers post-calving.


METHODS
The studies were undertaken in 13 herds. In two herds application of an external teat sealant was compared with a negative control; in nine herds treatment with monensin was compared with controls, and in two herds treatments were applied in a 2 x 2 factorial design. Heifers were randomly assigned within herd to be treated with a slow-release intraruminal device containing 32 g monensin (n=383), or left as untreated controls (n=389), approximately 30 days before the start of the spring calving period; or to be treated with a latex external teat sealant (n=206) when calving was impending, or be left as untreated controls (n=205). Milk samples were collected from each gland between 0 and 5 days after calving and from any gland diagnosed with clinical mastitis. The effect of the treatments on the prevalence of intramammary infection (IMI), i.e. subclinical mastitis, and clinical mastitis were initially analysed at the univariate level, with associated variables (p<0.2) being used in construction of multivariable models.


RESULTS
The prevalence of IMI was 18.4% at the gland level, and coagulase-negative staphylococci followed by Streptococcus uberis were the most common isolates. Treatment with an external teat sealant reduced the prevalence, compared with controls, of any IMI (12.1 (SE 1.7)% vs 16.5 (SE 2.1)%, respectively; p=0.05) or IMI caused by a major pathogen (3.8 (SE 0.8)% vs 6.0 (SE 1.1)%, respectively; p=0.05). Monensin treatment did not affect the prevalence of any IMI (p=0.68) or IMI due to a major pathogen (p=0.11). The cumulative incidence of clinical mastitis was 14.2%. Neither monensin treatment (p=0.47) nor application of an external teat sealant (p=0.71) altered the risk of clinical mastitis. There was no interaction between the monensin and external teat sealant in the two herds where the treatments were applied in a 2 x 2 factorial design.


CONCLUSIONS
Application of an external teat sealant resulted in a lower prevalence of any IMI and of an IMI caused by a major pathogen. Despite monensin reducing the mobilisation of body tissue and the risk of subclinical ketosis, it had no effect on the prevalence or incidence of IMI or clinical mastitis.


CONCLUSIONS
Application of an external teat sealant is an option for reducing the prevalence of IMI in pasture fed dairy heifers.
McDougall
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Animal Health Centre, PO Box 21, Morrinsville, New Zealand. smcdougall@anhealthc.co.nz
Parker
K I
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Weir
A M
AM
Compton
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CW
D000284:Administration, Oral; D000287:Administration, Topical; D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial / Q000662:veterinary; D003612:Dairying; D005260:Female; D015994:Incidence; D007476:Ionophores / Q000008:administration & dosage*; D007774:Lactation; D007840:Latex / Q000008:administration & dosage*; D008321:Mammary Glands, Animal; D008414:Mastitis, Bovine / Q000097:blood / Q000453:epidemiology / Q000209:etiology / Q000382:microbiology / Q000473:pathology / Q000517:prevention & control*; D008985:Monensin / Q000008:administration & dosage*; D009520:New Zealand / Q000453:epidemiology; D011247:Pregnancy; D015995:Prevalence; D012720:Severity of Illness Index; D013291:Streptococcus / Q000302:isolation & purification; D016896:Treatment Outcome
D007476:Ionophores; D007840:Latex; D008985:Monensin