Non Technical Summary
Achieving maximal growth, development, and productivity in the dairy cow's udder depends on the unrestricted delivery of nutrients from the blood. While it is well appreciated that blood vessels deliver the nutrients to the milk synthesizing tissues in the cow's udder and remove metabolic waste products, it is unknown how and when blood vessels grow and develop within the cow's udder during key developmental time points and lactation. The overarching hypothesis being tested here is that the milk synthesizing tissues of the cow's udder directs blood vessel growth and function. The first research objective is to identify the mechanisms that drive blood vessel growth during first pregnancy, which is when the udder's secretory tissue is rapidly grow and develop in preparation for lactation. The second objective is to determine if blood vessel growth continues into early lactation and identify the mechanisms that regulate blood vessel function and substrate exchange. We expect that blood vessel growth will continue into early lactation, as milk production increases, and that blood vessel growth and function will be significantly associated and influenced by the productivity of the cow's udder. The significance of this research is that we will determine when and how blood vessels grow and increase their functionality to allow the milk secreting tissue to reach it's maximal potential. Allowing the udder to be fully developed and unhindered increase milk production efficiency which improves dairy production sustainability and producer profitability.

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
305	3410	1020	100%

Knowledge Area
305 - Animal Physiological Processes;

Subject Of Investigation
3410 - Dairy cattle, live animal;

Field Of Science
1020 - Physiology;

Goals / Objectives
The long-term goal is to develop and apply management practices that maximize mammary gland capillary growth and function to improve mammary development and lactational performance. The central objective of this work is to determine when and how the bovine mammary microvasculature accommodates mammogenesis and lactogenesis during pregnancy, and elucidate how the capillary network satisfies the demands of increasingly metabolically active secretory cells during early lactation.Aim 1. Define the local mechanisms that drive microvasculature growth, organization, and competency during alveoli formation and lactogenesis in non-lactating mammary glands developing for the first time.Aim 2. Identify the local factors that regulate capillary number, function, and substrate exchange during early lactation.

Project Methods
Pregnant heifers and early lactation primiparous cows will be used in 2 separate experiments. For, the pregnant heifer study, 3 distinct gestation ages will be examined (4, 6, and 8 months gravid). Blood samples will be obtained from each heifer for 3 weeks' time to determine net mammary gland substrate uptake and then be euthanized for whole udder collection and tissue collection for later histological analysis. For the early lactation cow study, 1 udder half of each cow will be milked 1x/day while the other udder half will be milked 4x/day. Blood samples will be collected throughout the milking period to determine metabolite uptake by the mammary gland. Cows will be randomly selected for euthanasia at 4, 16, and 60 days in milk and udders will be removed for analysis and tissue collection. Tissues collected in each experiment will be used to assess total mammary gland growth and measure assess blood vessel formation and organization within different regions of the mammary gland. Collected blood vessels will also be examined to assess relative abundance of vasodilators.