There are few things I hate more than hearing that one of our cows at Miner has mastitis…except for maybe that one of our cows has mastitis again. The mastitis can negatively affect the health and welfare of the cow, farm profitability, and public perception of the modern dairy farm. In addition, it complicates the execution of research studies especially when the mastitis is severe or recurrent.
The clinical symptoms and systemic severity of mastitis in cows differ among the causative organisms. Common classifications or groupings of mastitis causing organisms include gram-positive (e.g. Streptococcus species), gram-negative (Escherichia coli, Klebsiella, Citrobacter, Enterobacter, Pseudomonas), and other organisms (Arcanobacterium pyogenes, Mycoplasma, Corynebacterium bovis, yeast). The identification or grouping of the organisms can be helpful in making treatment and management decisions since the pathogenicity of the organisms can result in different short-term and long-term consequences.
Over the last several years, Cornell University researchers have studied the effect of mastitis caused by different organisms on milk loss, reproduction, culling, and mortality on seven New York dairy farms. Multiparous cows had more mastitis (30% vs. 17%) and a higher lactational incidence risk of a second (11% vs. 4%) and third (4% vs. 1%) case of mastitis than primiparous cows. Interestingly, only about a third or less of the recurrent cases of mastitis were caused by the same pathogen as was isolated in the first case. Cows, especially multiparous cows, with gram-negative mastitis were more likely to die or be sold than cows with gram-positive or other mastitis. The probability for death was greatest in the first month of lactation.
Milk loss in multiparous cows due to gram-negative mastitis (669 lb) was greater than the loss from gram-positive mastitis (282 lb) and other mastitis (202 lb) in the 50 days following the mastitis. The response was similar in primiparous cows with milk loss of 502 lb, 293 lb, and 246 lb for gram-negative, gram-positive, and other mastitis, respectively. The severity of a recurrent case of mastitis was not reduced by previous cases of mastitis.
Mastitis occurring within the interval of 14 days before until 35 days after AI was associated with a reduction in the probability of conception. Mastitis caused by gram-negative bacteria had a more detrimental effect on the probability of conception than did mastitis caused by gram-positive bacteria or other organisms. There was an 80% reduction in conception with gram-negative mastitis occurring within a week after AI. The reduction was 47 and 49% with gram-positive and other mastitis, respectively.
The type of mastitis and the reoccurrence of mastitis are important factors in herd management. Gram-negative mastitis seems more unfavorable for the cow and the farm (and our research studies) because of the severe systemic effects and negative effects on milk yield, reproduction, and survival. Farms are encouraged to implement management practices for the prevention and treatment of gram-negative mastitis.
Editor's note: This article first appeared in the October 2011 issue of the Miner Institute's Farm Report.