Investigating milk cell population changes in response to heat stress and characterizing functionality of epithelial cells in milk of lactating dairy cows
| dc.contributor.author | Cappellina, Anna Lofhjelm | en |
| dc.contributor.committeechair | Corl, Benjamin A. | en |
| dc.contributor.committeemember | Daniels, Kristy Marie | en |
| dc.contributor.committeemember | Rhoads, Michelle | en |
| dc.contributor.department | Animal and Poultry Sciences | en |
| dc.date.accessioned | 2025-05-21T08:02:09Z | |
| dc.date.available | 2025-05-21T08:02:09Z | |
| dc.date.issued | 2025-05-20 | |
| dc.description.abstract | Understanding the number of mammary epithelial cells a cow maintains is essential to maximize milk synthesis in lactating dairy cows. This thesis aimed to investigate milk cell population changes in lactating dairy cows in response to heat stress (HS) using a pair-feeding model (PFTN). Additionally, this thesis explored the potential role of mammary epithelial cells in milk of lactating dairy cows as phagocytic cells capable of efferocytosing apoptotic mammary epithelial cells. The first study evaluated cell shedding into milk in response to nine days of HS or PFTN. There was a decline in dry matter intake (DMI) and milk yield (MY) in response to HS and pair-feeding. Milk yield decreased over 9 days for both treatments and PFTN cows had a greater MY on d 2,7, and 8 compared to HS cows. The concentration of MEC shed into milk did not change after nine days of HS or PFTN and there were no differences between groups. There was a lower concentration of immune cells in milk from HS cows and a higher concentration of BTN+CD45-CD14+ cells than PFTN cows. The second study examined the potential role of mammary epithelial cells as phagocytes in consuming apoptotic mammary epithelial cells during lactation. Mammary epithelial cells act as non-professional phagocytes during the dry period to aid in maintaining tissue homeostasis. The role of mammary epithelial cells as phagocytes during lactation in dairy cows hasn't received investigation. In this study, mammary epithelial cells in milk consumed cultured apoptotic mammary epithelial cells under in vitro conditions. Factors that influence mammary epithelial cell shedding into milk play an important role in milk production. By investigating factors that affect cell shedding into milk we can better understand the dynamics of the mammary gland and potentially improve milk production and lactation persistency in cows. | en |
| dc.description.abstractgeneral | Milk production is dependent on cells in the mammary gland whose function is to synthesize milk. This thesis aims to investigate how milk cell populations change in response to heat stress which reduces milk yield and to understand unique functions of the secretory cells. Epithelial cells play a critical role in milk production and their presence in milk provides insights into mammary gland physiology and factors that influence cell maintenance and milk production. Understanding factors that can alter milk production are essential to improve profitability for the dairy industry. In recent decades, global temperatures have increased, and the dairy industry is confronted with heat stress. Losses due to reduced milk production during HS are significant and HS impacts dairy cattle health and well-being. Cows experiencing HS decrease the amount of feed they are consuming, which only explains 50% of the milk production losses. The other 50% could partially be explained by changes in cell number or secretory capacity in the mammary gland. The objective of the first study was to investigate milk cell population changes in response to HS, which causes a reduction in both DMI and MY and changes the milk composition by decreasing fat and protein content in milk. In this study, mammary epithelial cell losses were constant despite decreased milk production. There were changes in some cell populations with PFTN cows having a greater concentration of immune cells in milk than HS cows on day 9. Results of this investigation point to reduced nutrient availability and potentially decreased synthetic capacity of MEC as possible explanations for decreased MY instead of changes in cell number. Phagocytic cells have the ability to consume dying cells to help maintain tissue homeostasis. There is a high level of turnover in the mammary gland due to cells that are developing into mature cells, cells that are dying at the end of their productive life or due to stressors, and cells that are dividing. The cells that are dying need to be cleared from the mammary gland. Professional phagocytes such as macrophage, a type of white blood cell as well as other immune cells are known to consume dying cells in the mammary gland. Additionally, non-professional phagocytes, such as mammary epithelial cells have been observed to consume dying mammary epithelial cells in the involuting mammary gland but not the lactating mammary gland. In this study, under in vitro conditions, mammary epithelial cells from the lactating mammary gland consumed apoptotic mammary epithelial cells. These results help us better understand the many mechanisms employed by the mammary gland to maintain function during lactation. Overall, this work contributes to understanding the complexities of milk production and factors that may impact lactation physiology through cell population changes. In summary, to improve the amount of time a cow maintains lactation, functional mammary epithelial cells must be maintained. | en |
| dc.description.degree | Master of Science | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:43324 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/133536 | |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | mammary gland | en |
| dc.subject | milk cell populations | en |
| dc.subject | heat stress | en |
| dc.subject | efferocytosis | en |
| dc.title | Investigating milk cell population changes in response to heat stress and characterizing functionality of epithelial cells in milk of lactating dairy cows | en |
| dc.type | Thesis | en |
| thesis.degree.discipline | Animal and Poultry Sciences | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | masters | en |
| thesis.degree.name | Master of Science | en |
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