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Questions and Answers
What happens to milk secretion after milking in high-producing cows if milk is not withdrawn?
What is the primary role of oxytocin in the process of milk letdown?
What effect does increasing intramammary pressure have on milk secretion?
What is the primary reason that the last milk evacuated at milking time is higher in fat content?
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Which of the following factors is NOT a stimulus for milk letdown?
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What is the primary precursor for fat synthesis in ruminants?
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What is the primary role of lactose in milk?
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Which hormones are essential for protein production in the mammary gland?
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Which statement best describes milk safety?
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What happens to the volume of milk secreted when lactose concentration increases?
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What is galactopoiesis in the context of milk production?
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What contributes to the salty taste of milk, particularly during mastitis?
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How is milk synthesized in the mammary gland?
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Which component is NOT typically found in blood but is present in milk?
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What initiates the process of lactogenesis in the mammary glands?
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Which vitamin levels in milk depend on dietary intake and body reserves?
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What are the primary constituents of milk that are filtered from the bloodstream?
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What is a common consequence of high-grain, low-forage diets in cows?
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Which of the following describes the aids in milk hygiene?
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Which process is responsible for the secretion of milk from the mammary gland?
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How are the lobes of the mammary gland structured?
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Study Notes
Milk Composition
- Milk is a complex mixture of organic and inorganic compounds, with fat present as an emulsion, lactose and minerals as a true solution, and protein as a colloid.
- Considered a nutrient dense food, providing high-quality protein, all essential amino acids, twelve water-soluble and four fat-soluble vitamins, and lactose as an energy source.
- Calcium absorption is enhanced by the presence of lactose in milk.
Milk Hygiene
- Milk hygiene encompasses all conditions and measures necessary to ensure the safety and suitability of milk at all stages of the food chain.
- Milk safety ensures that milk will not cause harm to the consumer.
- Milk suitability ensures that milk meets the criteria for human consumption according to its intended use.
- The food chain refers to the steps involved in milk production, starting with primary production and ending at the consumer's table.
Milk Production (Biosynthesis)
- Milk is synthesized in the mammary gland.
- The mammary gland consists of lobes, which are the smallest production units, and are spherical in shape.
- Each lobe is composed of alveoli, which are responsible for milk production.
- Multiple lobes form a quarter, and four quarters comprise the udder of a cow.
- Connective tissues and muscles separate the quarters.
- The mammary glands are well supplied with blood vessels and nerves.
Growth and Development of Mammary Glands
- The structural and functional development of the mammary gland (lactogenesis) occurs in multiple cycles.
- These cycles involve development, functional differentiation, and regression.
- Hormonal and growth factor stimulation during gestation facilitates the generation of abundant glandular alveoli.
- Differentiation of epithelial cells within these alveoli leads to the initiation of milk synthesis and secretion at parturition.
Milk Secretion
- Milk secretion (galactopoiesis) involves two primary processes:
- Filtration of certain milk constituents from the bloodstream
- Synthesis of other milk components by cellular metabolism within the alveoli.
Milk Protein
- Milk proteins are derived from both filtration and synthesis.
- Casein, lactalbumin, and lactoglobulin found in milk are not present in blood.
- These proteins are synthesized in the rough endoplasmic reticulum, processed through the Golgi complex, packaged into secretory vesicles, and secreted from the apical surface by exocytosis.
Milk Lactose
- Glucose is a normal blood component, and two active glucose transport systems are present in mammary gland tissues.
- Two glucose molecules enter the secretory cell, where they are combined by lactose synthetase to form lactose.
- The concentration of lactose largely determines the volume of milk secreted.
- Hypoglycemia can occur in high-producing cows in early lactation.
- Lactose can also be derived from short-chain fatty acids (20-30%).
Milk Fat
- More than half of the fat in bovine milk is synthesized within the mammary gland.
- Triacylglycerol is synthesized in the rough endoplasmic reticulum by acyltransferases.
- Triacylglycerol then aggregates forming microlipid droplets, which are released into the cytoplasm, coated with proteins and polar lipids, and fuse to form larger droplets.
- These droplets are transported to the apex of the cell, and a budding process results in their expulsion from the cell.
- The droplets are coated with additional proteins and phospholipids, forming an outer membrane (fat globule membrane).
- In ruminants, acetate is the primary precursor of milk fat.
- Cows fed high-grain/low-forage rations often secrete low-fat milk.
- High temperatures can also lead to reduced milk fat levels.
Milk Minerals
- Minerals in milk are derived from the blood through filtration.
- Milk contains at least 10 times more calcium and phosphorus than blood.
- A decrease in lactose content corresponds to a compensatory increase in the concentrations of sodium and potassium salts.
Milk Vitamins
- Vitamins filter directly from blood into milk.
- B vitamins, synthesized by ruminal microorganisms, are relatively constant in milk.
- Fat-soluble vitamins, particularly vitamins A and D, are dependent upon the quantities present in the ration and body stores.
Milk Water
- Water is filtered from blood into milk, influenced by the concentration of other milk solids.
Milk Discharge (Excretion)
- Milk synthesis occurs continuously between milking intervals.
- Cells become filled with milk and eventually rupture, releasing their contents into the lumen of an alveolus.
Milk Secretion and Letdown
- Milking stimulates milk secretion and release.
- Secretion progresses gradually, leading to an increase in intra-mammary pressure.
- Higher intra-mammary pressure can affect blood flow and impact the release of milk from the alveoli, potentially resulting in lower fat content.
- Milk secretion peaks immediately following milking, declining gradually over time.
- In high-producing cows, milk secretion will stop within 18 to 24 hours without milking.
- The last milk evacuated at milking time is higher in fat.
- Milk letdown is the release of milk from the mammary gland.
- It is an involuntary reflex, stimulated by factors such as suckling, washing the mammary glands, hand milking, and high internal udder pressure.
- Sensory signals are sent from the mammary glands to the brain.
- This triggers the release of oxytocin from the posterior pituitary gland.
- Oxytocin increases intra-mammary pressure and blood flow to the udder.
- Vasopressin is also released from the posterior pituitary.
- Myoepithelial cells surrounding the alveoli contract, squeezing the alveoli and causing milk letdown.
- The teat has a storage capacity of 40 to 50 mL, and each gland cistern can hold 400 to 500 mL.
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Description
Explore the intricate details of milk composition, including its nutrient density and hygiene practices essential for safety in the food chain. Understand how milk's properties like lactose enhance calcium absorption and the production processes behind milk synthesis.
