Lecture 16- Nutrition during lactation Flashcards
How much is the dairy industry worth in Australia?
- Australian dairy industry is worth ~$13 billion
- 9.5 billion L of milk
- Victoria is the biggest producer (61%)
- Export ~ 50% of production (powder & cheese)
- Whey powder & casein • Protein rich
- Used in human and animal feeds
What is the dairy industry like in Australia?
- Aust. Dairy industry remains mainly pasture based • Supplementary grain feeding more common
- Heavily reliant on water • High rainfall zones
- Irrigation
- Seasonal production to utilize maximal pasture quality
- Pasture types based on region
- Need to max quality/quantity efficiently
- Often harvested as hay or silage
- Turning pasture into milk!
What is the physiology of milk production?
• Can produce 20-35 litres per day
• 2 main aims of production
1. Optimum milk production
2. Maximal reproductive potential
• Therefore understanding nutrient partitioning according to stage of lactation is important
• Particularly as a dairy cow can be pregnant and lactating at the same time!
What are the alveoli and ductwork?
• Alveoli is the basic milk producing unit
• Small bulb-shaped structure with hollow center
• Lined with epithelial cells that secrete milk
• Each cubic inch of udder tissue contains 1 million alveoli
• Each alveoli surrounded by network of capillaries and myoepithelial cell
• Contraction of myoepithelial cell stimulates milk ejection
-The mammary gland is comprised of a system of ducts connecting the milk-producing alveoli to the teats
• Groups of alveoli empty into a duct forming a unit called a lobule • Several lobules create a lobe
• Ducts of lobe empty into a galatophore, which empties into the gland cistern
• Ducts provide storage area for milk and a means for transporting it outside
• Lined by two layers of epithelium
• Myoepithelial cells are arranged in longitudinal pattern • Shorten to increase diameter to facilitate flow of milk
What is the milk synthesis controlled by?
• Milk synthesis controlled by two factors
1. Efficiency of nutrient extraction (genetics)
2. Volume of blood flow (genetics and hormones)
- controlled by capillary sphincters
- blood plasma volume increases by 30-40%
(from 3.8 to 4.9% of body weight)
What is the importance of circulation in the udder?
- One gallon of milk requires 500 gallons of blood being passed through udder
- Ratio may increase in low producing cows (1000:1)
- Blood enters the udder through external pudic arteries
- Blood exiting udder from veins at the base of udder blood can travel through two routes
- Via external pudic veins
- Via subcutaneous abdominal veins
What is the metabolic adaptation during milk secretion?
- Increased glucose demand from mammary (for lactose synthesis) increases hepatic glucose production 2-3 fold
- Increased gluconeogenesis
- This causes increased: • liver size
- gluconeogenicenzymaticactivity
- Liverbloodflow
- Propionate & AA absorption from gut • Release of lactate from muscle
- Glycerol from adipose
- AA release from muscle
- Changes prior to parturition prepares adipose for release of fatty acids
- Massive mobilisation of FA at parturition
- Dramatic rise in plasma FFA
- Increased activity of lipiprotein lipase in mammary • Cleaving long chain FA from triglycerides
- A cow in early lactation can lose 20-50kg fat in 6 weeks!
What are the broad impacts of liver lipid accumulation?
- low DMI (Hepatic oxidation of fat)
- Low milk yield (low DMI , low production of glucose • Low gluconeogenisis and blood glucose
- Low ureagenosis (and hence high BUN levels)
- Low liver glycogen reserves
- ketosis
- Suppressed immune status (more later)
- Massive over inflammation status (more later)
- Poor fertility expressed in various ways
- Increased mastitis
- Increased lameness
What are the energy requirements?
- Energy is the most important nutrient to produce milk
* Energy content of pasture declines with pasture maturity
What are the phases of mammary gland?
• 4 phases of mammary gland • 1. Dry period:Development
• 2. Around calving (-4 to +4 days): Differentiation
• 3. Lactation: All cell activity directed towards milk synthesis and no further
mammary growth.
• 4. Involution of the mammary gland: This is the gradual but irreversible regression of the gland (i.e. a reduction in the numbers of active alveoli). This starts after the peak of lactation, but is more pronounced during late lactation
4 phases in detail:
- Phase 1: feed intake does not meet nutrient needs (especially energy)
- Feed more grain •Protein is critical •Consider feeding fats
- Phase 2: intake near max and nutrient requirements are being met
- Phase 3: easiest to manage
- Milk production is declining •Cow is pregnant again •Nutrients easily met & lost condition can be restored
- Phase 4: critical phase – good management can milk yield in subsequent lactation
What are the water requirements?
- High in lactating cattle
- Particularly during warmer months
- 4-5 L per litre of milk produced on top of maintenance requirements
What is the importance of milk lactose?
• Osmoregulator of milk – dictates volume
• Glucose is the major carbon source for both glucose and galactose
that compromises lactose
• Key is lactose synthesis
• 2 enzyme system
• Galactosyl transferase – ubiquitous distribution • α-lactalbumin – only in mammary gland
What is milk protein like?
- 95% of total milk N
- High biological value
- Includes caseins (α,β,γ,κ), β-lactoglobulin, α-lactalbumin, serum albumin & immunoglobulins
- Caseins >80% of total milk protein
- Generally genetic selection has a greater long term impact on milk protein than nutrition
What is the protein synthesis in mammary?
- Induction driven by increased gene expression
- mRNA’s encoding caseins & β-lactoglobulin
- mRNA’s encoding for enzymes in lipid & lactose synthesis
