Relationship of high somatic cell counts in the milk prior to dry off with the incidence of periparturient diseases and milk yield in holstein dairy cows

• Author / Creator

  Egyedy, Ashley

• Intramammary infections of dairy cows are characterized by elevation of milk somatic cell counts (SCC), which are mostly neutrophils. Infections can result in substantial production losses, increased costs for treatments, and veterinary services, besides discarding the antibiotic-treated milk and increased culling rates. The dry period for dairy cows occurs approximately 8 weeks prior to parturition and allows for maximization of milk production in the upcoming lactation. Dairy cows exhibit a state of immunosuppression between and around parturition resulting in high incidence of periparturient diseases. It has been suggested that bacteria and bacterial endotoxins originating from the infected mammary gland might play a significant role in the pathogenesis of periparturient diseases. Previous studies have shown that intramammary challenges with bacterial endotoxins trigger alterations in the blood and milk metabolites. Our lab has previously reported alterations in innate immune reactants and serum metabolite variables in dairy cows starting at -8 and -4 weeks prior to parturition and during diagnosis of several periparturient disease including subclinical mastitis, metritis, lameness, ketosis, milk fever and retained placenta suggesting chronic inflammatory state during the dry period.
  The current study aimed to determine whether high SCC in dairy cows before dry off are related to the incidence of periparturient diseases as well as milk and blood alterations. Somatic cell counts were measured in 140 pregnant Holstein dairy cows one week before dry off, and were classified as either low SCC (200,000 cells/mL). All cows were monitored for the incidence of the major periparturient diseases including mastitis, metritis, lameness, ketosis, and retained placenta for the first 2 weeks after parturition. Results of the study showed that cows with high SCC before dry off had an increase in likeliness to be affected by ketosis. While not statistically significant, high SCC cows did have greater odds of being affected by metritis, lameness, and retained placenta compared to low SCC cows; however other factors could potentialy contribute to disease incidence. Intriguingly the odds ratio analysis indicated that the likeliness of cows to be affected by mastitis were similar for both groups of cows with low or high SCC.
  Another important finding of this study was that cows with high SCC and affected by periparturient diseases produced significantly less milk during the first 60 DIM compared to cows with low SCC or the healthy ones. This was supported by the fact that cows with high SCC and affected by diseases had lower concentrations of lactose and increased concentrations of total milk proteins prior to dry off. Lactose is consumed by bacteria during mammary infection and is the main osmotic metabolite that determines volume of milk and, therefore, milk yield; whereas milk proteins that increase during mammary infections are mostly related to mounting of an immune response to infectious pathogens.
  Data also showed lower concentrations of glucose and cholesterol in the serum prior to dry off in cows with high SCC. Serum glucose is the main precursor of lactose synthesis and it has been shown that decreases during endotoxemia potentially related to mammary gland infection. In addition, cows with high SCC prior to dry off and diagnosed with ketosis exhibited higher concentrations of BHBA and NEFA after parturition where BHBA at +1 week was strongly correlated to SCC prior to dry off. Concentrations of BHBA in the serum were within normal ranges in cows affected by mastitis, metritis, retained placenta, and lameness. Concentrations of NEFA in the serum of cows with high SCC prior to dry off and diagnosed with mastitis, metritis, lameness, and retained placenta were higher in comparison to healthy cows. Concentrations of lactate in the serum of cows diagnosed with metritis were higher in both groups of cows with low and high SCC cows prior to dry off. Interestingly cows with low SCC prior to dry off and diagnosed with metritis exhibited greater concentrations of lactate after parturition.
  
  Overall, results of this study indicate that high SCC prior to dry off can significantly influence the health status, metabolism, and productivity of dairy cows in their upcoming lactation. However, further research is warranted with regards to the reasons for high SCC prior to dry off and their effect on the overall health of dairy cows.

• Subjects / Keywords

  • somatic cell counts
  • mammary gland
  • dairy cows
  • milk yield
  • holstein
  • periparturient disease
  • milk production
  • dairy

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3JW8739D

• License

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