Dairy Unit

Dairy Breeds Established for many years Major breeds of dairy in north america

Dairy Breeds Ayrshire –Excellent grazing ability

Dairy Breeds Brown Swiss –One of oldest dairy breeds

Dairy Breeds Guernsey –Originated in the Isle of Guernsey –Rank second in total number cattle registered in US

Dairy Breeds Holstein-Friesian –90 % of all cows in US –Produces the most milk

Dairy Breeds Jersey –High butterfat –Smallest of all the breeds

Dairy Breeds Milking Shorthorn –Dual purpose breed used for meat and milk

Chapter 15: Lactation of mammals Chapter overview: –the anatomy and physiology of lactation, including: comparative anatomy of mammary system of various mammals growth and development of the mammary system physiology of milk production and release

Lactation: Lactation may be defined as milk production A part of the definition of a mammalian species is the ability to produce milk Mammary glands produce the milk Mamma - a Latin word which means breast Milk production is an endocrine and exocrine function

Mammary System: Comparative Anatomy Bovine - four glands in the inguinal area; each teat serves one gland Ovine and caprine - two glands in the inguinal area; each teat serves one gland Equine - four glands formed into two units in the inguinal area; each teat serves two glands

Mammary System: Comparative Anatomy Porcine - multiple glands from pectoral to inguinal area, arranged in two rows; each teat serves two glands Canine and feline - multiple glands from pectoral to inguinal area, arranged in two rows: each teat has up to 10 streak canals

Structures of the Mammary Gland: Alveolar cell- basic cell producing milk in the mammary gland Alveolus - microscopic unit made up of alveolar cells with an open lumen for collection of secreted milk Myoepithelial cell- muscle-like cell surrounding the alveolus; contracts to express milk from the alveolar lumen

Structures of the Mammary Gland: Collecting duct - tubules formed into a network from fine ducts leaving each alveolus to ever enlarging branches that terminate in the udder cistern Udder cistern - small collecting area for milk above the teat Teat cistern - open collecting area in the teat

Structures of the Mammary Gland: Teat - the terminal structure of the mammary system from which milk will be nursed or drawn by machine Streak canal - exit from the teat surrounded by a sphincter muscle to maintain closure until nursing or milking Udder - term applied to the entire system

Manufacture of Milk: Milk is manufactured in the mammary gland by a combination of screening components from blood and by construction of components from precursors –Blood brings components via pudic arteries –Blood carries away byproducts via the pudic and subcutaneous abdominal veins –Lymph system carries away escaped plasma

Mammary Development: Present at birth in mammals: –Teats –Streak canals –Teat and gland cisterns –Rudimentary collecting ducts

Mammary Development: Impact of puberty and cycling –Extension of duct development Impact of pregnancy –Development of alveolar system –Generally visual evidence of growth –At parturition the mammary system of most farm mammals is fully developed for the subsequent lactation period; swine continue development until peak lactation

The “Dry Period”: The “dry period” is a period of nonlactation between subsequent lactations A dry period is necessary for optimum lifetime production Between lactations the mammary gland proceeds through a revitalization process of involution, alveolar regeneration, and return to lactation at the next parturition

Hormonal Impact on Lactation: Prolactin - initiates lactogenesis (lactation); source: anterior pituitary Somatotropin - influences growth rate of the glands and level of milk secretion; source: anterior pituitary Thyroid hormones - influences milk production by regulating rate of metabolic processes; source: thyroid gland

Hormonal Impact on Lactation: Parathyroid hormone - regulates blood calcium and phosphorus; related to “milk fever”; source: parathyroid glands Adrenal hormones - small amounts necessary for normal milk production; large amounts during stress are counter- productive; source: adrenal glands

Hormonal Impact on Lactation: Oxytocin - causes contraction of myoepithelial cells for milk letdown; source: posterior pituitary Placental lactogens - hormones with prolactin and growth hormone-like activities; source: placenta Insulin - moves glucose across membranes for milk synthesis; source: pancreas

Milk Synthesis: Water, vitamins and minerals - screened from arterial blood Lactose - manufactured in the alveolar cell Protein - 90 percent is manufactured in the alveolar cells; some passage from blood; critical exception: immunoglobulins in colostrum are transported from dam’s blood Fat - 75 percent is manufactured in alveolar cell

Milk “Letdown”: Milk letdown is the evacuation of milk from the alveolar lumen to the duct system –Nerves receive stimuli at the teat end or nipple –Stimuli is received in the posterior pituitary –Oxytocin is released from pituitary into blood –Blood circulation brings oxytocin to mammary tissue –Targets are the myoepithelial cells that contract

Normal Cessation of Production: As a lactation cycle proceeds, alveolar cells are lost normally Eventually an animal ceases milk production due to degree of loss of secretory cells “Drying off” and involution can be enhanced by cessation of milking or nursing and reduction of caloric intake

Factors Impacting Milk Production: Inheritance - genetic selection for increased production is effective Stage of lactation - cows “peak” about 45 days into lactation, then decline until dry Frequency of milking - more milk is harvested with more frequent milking

Factors Impacting Milk Production: Pregnancy - late pregnancy fetal demands reduce production, but pregnancy is required for normal initiation of lactation Age - production increases as animals reach maturity, but decreases as older animals begin to physically decline Estrus - production is generally reduced during estrus

Factors Impacting Milk Production: Dry period - lack of a dry period will reduce production in subsequent lactation Body condition - over or under conditioned animals may have reduced production Environment - high temperature and humidity reduce milk production; extreme cold stress reduces milk production

Factors Impacting Milk Production: Feed - well balanced diets are critical to maximum production and proportion of some components in milk Proper preparation at milking time and lack of stress - critical to milk letdown and complete removal of milk

The Dairy Industry in the Twenty- First Century Started with most every family having a cow As America grew small herds started Into 21 st century now less herds but more cows per herd In cow hers was large In ,000 cow hers were common Now 28,000 cow herds are seen Changes will depend on the amount of technology used