Annual Cow College explores structure and development of a dairy cow's udder
CLINTONVILLE - The 57th annual UW-Extension College opened Jan. 8 at the Fox Valley Technical College Regional Center.
The three-session program was initiated by former Waupaca County Agricultural Agent Joe Walker, who passed away on Dec. 31 at age 93. Program sessions are designed to provide new and valuable information to Wisconsin dairy producers, students and other agriculture industry professionals.
Forty people, including students from Fox Valley Technical College and New London High School, heard Dr. Laura Hernandez from the Dairy Science Department at UW-Madison about her research on the mammary system of dairy cows.
Hernandez began by reviewing the exterior physiology of a cow’s mammary system, noting that the right and left halves of the udder are separated by a longitudinal groove. “Front and rear quarters seldom show any marked line of demarcation, however, rear quarters are usually larger because there’s 25-50% more secretory tissue in the rear quarters,” she explained.
According to Hernandez, the weight of the udder ranges between 25 and 60 pounds, excluding milk. “Udder size is one of the more common factors limiting the capacity for milk secretion,” she noted. “The udder increases about one-third in size during the period between milkings. After the first two months of lactation, mammary weight decreases at a rate of about .6 pounds per month.”
Proper teat formation and size are critical to milking ease, according to Hernandez. “They shouldn’t be too short or too long,” she emphasized. “They should be well placed squarely beneath the gland and have a sufficiently large opening. Cows with funnel-shaped teats tend to produce 12% more milk than those with cylindrical teats,” she related.
Interior gland physiology
Supportive interior structures between the udder and abdominal wall include skin that provides minor udder stabilization, fine areolar connective tissue that attaches skin to the udder surface and coarse tissue that provides a loose bond between the upper surface of the front quarters and abdominal wall.
Lateral suspensory ligaments, located above the udder, serve as a framework for the gland. “The deep lateral suspensory ligament continues to the lower border of the gland where it fuses with the medial suspensory ligament that attaches to the medial flat surfaces of the two glands and divides the udder in half,” Hernandez explained.
The arterial system provides blood flow to the udder. Arteries divide ending in the arterioles surrounding the alveoli or papillary arteries of the teats,” said Hernandez. “The larger papillary arteries, together with the venous plexus, form the corpus cavernous of the teat.”
Cows have many more veins than arteries, and blood leaves the udder by two main routes: The external pudendal vein, which is 2 to 3 times larger in diameter than the corresponding artery, and the subcutaneous abdominal veins that emerge from the anterior basal border of the udder as a continuation of the anterior/cranial mammary vein.
“In pregnant or lactating animals all veins are greatly enlarged due to mammary development,” Hernandez noted.
Summing up, she stated that each teat contains a streak canal, Furstenberg’s rosette, teat cistern, and a cricoid fold that separates the dorsal portion of the teat cistern from the gland cistern. “A group of alveoli and their associated ducts constitute a lobule, and a number of lobules form a lobe, with each mammary gland containing a number of lobes.”
She also noted that teat canal patency and length increase as the number of lactations increase. “Cows with more patent streak canals are more susceptible to udder infection.”
Normal, uninfected cows have two cell layers lining the teat cistern. “Accessory glands are often found in the wall of gland and teat cisterns, and they are probably milk secreting glands,” Hernandez said.
Hernandez stressed the importance of maintaining proper calcium levels in a cow’s diet for both good health and good milk production.
“All animals need a lot of calcium for proper bone growth and development,” she said, “and Calcium is the cows’ most highly concentrated mineral. They need a lot of calcium during pregnancy but even more during lactation.
“During lactation, on average, a cow will secrete about 80 grams of calcium per day into her milk. Cows will lose up to 13% of their bone mass during their first 30 days in milk,” she said.
“Calcium is needed to contract muscles and to help protect the immune system. Lack of calcium can make the cow more susceptible to a variety of illnesses,” Hernandez said.
Prevention is better than treatment in keep calcium levels up. She noted that zeolite clay has had some success in increasing calcium levels when used for two weeks pre partum.
“We’re really trying to understand the different parts of the equation of how much addition calcium is needed to keep in balance and prevent too great a calcium loss,” she said.
Following her presentation, Hernandez and graduate student Meghan Connelly conducted an interactive lab session where they dissected udders to help illustrate the various components of the mammary system.