Browsing by Author "Enger, Kellie M."

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    Cellular proliferation and apoptosis in Staphylococcus aureus-infected heifer mammary glands experiencing rapid mammary gland growth
    Baker, Pari H.; Enger, Kellie M.; Jacobi, Sheila K.; Akers, R. Michael; Enger, Benjamin D. (Elsevier, 2023-04)
    Intramammary infections in nonlactating mammary glands are common and can occur during periods of rap-id mammary epithelial cell (MEC) accumulation, which may ultimately reduce total MEC numbers. Reduced MEC numbers, resulting from impaired MEC prolifera-tion and increased cellular apoptosis, are expected to reduce future milk yields. The objective of this study was to measure the degree of cellular proliferation and apoptosis in the epithelial and stromal compart-ment of uninfected and Staphylococcus aureus-infected mammary glands hormonally induced to grow rapidly. Nonpregnant heifers (n = 8) between 11 and 14 mo of age were administered supraphysiological injections of estradiol and progesterone for 14 d. One mammary gland of each heifer was randomly selected and infused with Staph. aureus (CHALL) while another mammary gland was designated as an uninfected control on d 8 of injections. Mammary tissues were collected on the last day of hormonal injections from center and edge parenchymal regions and subject to proliferation assessment via Ki-67 staining and apoptotic assess-ment via terminal deoxynucleotidyl transferase dUTP nick-end labeling. Differences in cellular proliferation between CHALL and uninfected control quarters were not apparent, but proliferation of MEC was marginally greater in edge parenchyma than in center parenchyma. Coincidently, CHALL quarters experienced a greater percentage of apoptotic MEC and lower percentage of stromal cells undergoing apoptosis than uninfected control quarters. This study also provides the first in-sight into the mechanisms that allow the mammary fat pad to be replaced by expanding mammary epithelium as edge parenchyma contained a greater percentage of apoptotic stromal cells than center parenchyma. When taken together, these data suggest that Staph. aureus intramammary infection impairs mammary epithelial growth through reductions in MEC number and by preventing its expansion into the mammary fat pad. These factors during periods of rapid mammary growth are expected to impair first lactation milk yield.
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    The Impact of Parlor Equipment and Milking Procedures on Milk Quality in the Southeast US
    Enger, Kellie M. (Virginia Tech, 2017-12-05)
    Milk quality has continued to improve over the last several decades in the US, but still remains to be a problem for dairy producers in the southeast (SE) US. The purpose of these analyses was to evaluate associations between parlor equipment function, milking procedures, and bulk tank somatic cell count (BTSCC) and bulk tank standard plate count (BTSPC) on SE US dairy farms. Data from dairies in Virginia (n = 96), Kentucky (n = 96), Tennessee (n = 84), and Mississippi (n = 7) were collected at a single visit for each farm. Monthly BTSCC and BTSPC data were retrieved from state regulatory offices for (n = 263) farms, and averaged over the 12 months prior to each farm visit and used as the dependent variables in each analysis in a backwards elimination regression model. Increased herd size was associated with lower BTSCS, but higher BTSPC. Utilization of an internal teat sealant was associated with lower BTSCS. Farms that housed cows exclusively on pasture had greater BTSCS than farms that keep lactating cows in confinement with no pasture access. Utilization of a freestall for lactating cow housing was associated with lower BTSCS. The likelihood of future dairy operation in 10 years as reported by the farm owner or manager influenced BTSPC. Beginning water temperature of the detergent wash cycle was found to influence BTSCS. These findings suggest that the most influential variables explaining milk quality are herd demographic information and farmer perceptions as well as a few management variables such as the use of an internal teat sealant and beginning water temperature of the detergent wash cycle. These findings suggest that farmer perceptions and attitudes may be influencing milk quality more than previously thought. Further research is needed to evaluate social factors that could be influencing milk quality. Milking equipment function has improved substantially over the last several decades and was not found to significantly influence milk quality among the evaluated SE US dairies in these analyses. Milking procedures such as pre- and post-milking teat disinfection are widely accepted by most dairies in the US. Minimal differences were found between milking procedures such as teat disinfectant active ingredient or using paper towels versus cloth towels suggesting that these factors may not be the most influential factors influencing milk quality.
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    Staphylococcus aureus intramammary challenge in non-lactating mammary glands stimulated to rapidly grow and develop with estradiol and progesterone
    Enger, Benjamin D.; Crutchfield, Carly E.; Yohe, Taylor T.; Enger, Kellie M.; Nickerson, Stephen C.; Parsons, Catherine L. M.; Akers, Robert Michael (2018-06-05)
    Intramammary infections (IMI) are prevalent in non-lactating dairy cattle and their occurrence during periods of significant mammary growth and development (i.e. pregnant heifers and dry cows) is believed to interfere with growth, development, and subsequent milk production. However, direct study of IMI impacts on non-lactating but developing mammary glands is lacking. The objectives of this study were to (1) define how IMI affected total and differential mammary secretion somatic cell counts in mammary glands stimulated to rapidly grow using estradiol and progesterone, and (2) characterize changes in mammary morphology in response to IMI. Mammary growth was stimulated in 19 non-pregnant, non-lactating cows and 2 quarters of each cow were subsequently infused with either saline (n = 19) or Staphylococcus aureus (n = 19). Mammary secretions were taken daily until mammary tissues were collected at either 5 or 10 days post-challenge. Staph. aureus quarter secretions yielded greater concentrations of somatic cells than saline quarters and contained a greater proportion of neutrophils. Staph. aureus mammary tissues exhibited higher degrees of immune cell infiltration in luminal and intralobular stroma compartments than saline quarters. Infected tissues also contained reduced areas of epithelium and tended to have greater amounts of intralobular stroma. Results indicate that IMI in non-lactating glands that were stimulated to grow, produced immune cell infiltration into mammary tissues and secretions, which was associated with changes in mammary tissue structure. The observed reduction of mammary epithelium indicates that IMI impair mammary development in rapidly growing mammary glands, which may reduce future reduced milk yields.