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Animal Nutrition 324 > lactation > Flashcards

lactation Flashcards

1
Q

What is the major constituent of milk?

A

Water

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2
Q

What are the two phases that make up milk?

A
  • water phase (solids non fat ) SNF
  • fat phase
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3
Q

What is dissolved in the water phase of milk?

A

Organic elements

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4
Q

What makes up these organic elements in milk?

SWEL

A
  1. Soluble nitrogen elements (UCAA)
    - urea
    - creatine
    - amino acids
    - albumin (protein)
  2. Lactose - energy source
  3. Enzymes
  4. Water-soluble vitamins B and C
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5
Q

What makes up the fat phase of milk?

A
  1. Triglycerol ( 98% - major fat found in milk)
  2. Fat associated substances (2%)
    - Phospholipids
    - Pigments
    - Cholesterol
    - Fat-soluble vitamins
    - Traces of protein and heavy metals
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6
Q

Discuss fat variability in the milk of different species

A

The fat content and composition in milk can vary significantly between different animal species.

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7
Q

Is milk interchangeable to feed young ones between species?

A
  • Milk from different species is not interchangeable for feeding young animals.
    -Each species has milk tailored to meet the specific nutritional needs of its offspring.
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8
Q

What is the overall composition of milk ? (MVPFL)

A
  • Minerals
  • Vitamins
  • Protein
  • Lactose
  • Fat
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9
Q

Explain protein composition in milk

A
  • made of the following
  1. Nitrogen
    - 95% of N in milk comes from protein
    - the remainder of N is in the form of urea and ammonia that is filtered from the blood into milk (an alternative way to excrete urine)
  2. Urea

3.Casein
- the primary protein in milk

  1. Amino acids
    - Absorbed from the blood by the mammary gland for protein synthesis.
    - AA in the blood is NOT EQUAL to AA in glands because some AA is synthesized directly in the mammary glands.
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10
Q

Explain lactose composition in milk

A
  • it is the main carbohydrate in milk
  • provides energy
  • glucose + galactose
  • cannot be produced in the mammary glands but is derived from blood glucose (
  • Lactose concentration is stable and influences milk yield through regulating osmotic balance of milk, drawing water into the udder, which forms part of the milk
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11
Q

We cannot change lactose [ ] as lactose is a precursor for milk yield, why

A

Any alteration in lactose synthesis could disrupt the osmotic balance, leading to reduced water influx into the udder, and consequently, lower milk production.

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12
Q

Explain fat composition in milk

A
  • Consists mainly of triacylglycerols with both saturated and unsaturated fatty acids.
  • Sources of Fatty Acids:
    1. Chylomicrons and very low density lipoproteins (VLDLs) from blood: Transport fat to the mammary glands.
    2. Acetate from blood: Derived from rumen fibre fermentation, involved in triacylglycerol production which make up the fat component of milk
  • Half of the fatty acids come from blood lipids; the rest are synthesized in the mammary glands.
  • the balance between fat synthesis in the mammary gland and the mobilization of body fat reserves is crucial for milk yield and is regulated by hormones and nutrient availability
  • Fat synthesis in the mammary gland produces the fat component of milk.
  • Fat reserves from body tissues can be mobilized when dietary intake is insufficient
    -Hormones like insulin, growth hormone, and glucagon regulate fat storage and mobilization.
  • Propionate (a VFA), glucose, and certain amino acids are glucogenic substances important for gluconeogenesis (glucose production from propionate).
  • Increased glucogenic substances from diet changes can lead to higher glucose production and fat deposition in body tissues.
  • An increase in fat deposition in body can reduce the availability of fat precursors (like fatty acids , acetate) for the mammary gland. (fat deposition requires acetate and fatty acids , the same fatty acids and acetate are also needed by the mammary gland for milk fat synthesis)
  • Acetate is a primary precursor for de novo synthesis of milk fat in the mammary gland.
  • If acetate levels are low in the rumen due to a high proportion of propionate, the mammary gland receives fewer fat precursors for milk fat synthesis, decreasing milk fat synthesis.
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13
Q

Explain the mineral component of milk

A
  • not synthesised in mammary glands
  • consists of
    1. Calcium
    2. Phosphorous
    3. Sodium
    4. Magnesium
    5. Chlorine
  • Mammary glands selectively absorb trace elements from the blood.
    -Concentrations of minerals in milk cannot be manipulated by feeding higher levels in the diet.
  • The transfer of minerals between blood and milk is abnormal during colostrum production, resulting in much higher iron content in colostrum compared to regular milk.
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14
Q

Explain vitamins in milk composition

A
  • Vitamins are not synthesized in the mammary glands but absorbed from the blood.
  • High concentration of vitamins A and B
  • Vitamins C and D are present in very small amounts
  • Vitamins E and K only occur as traces
  • High-producing animals might need B vitamin supplementation. Under ideal ruminal conditions, rumen microbes can produce B vitamins, so typically, ruminants do not need external B vitamin supplements.
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15
Q

What does the NUTRIENT requirements of a dairy cow depend on

A
  • milk yield
  • milk composition
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16
Q

Factors Affecting Milk Yield?

A
  1. Breed
    - Breed is the most significant factor influencing milk yield
    - Different breeds are genetically predisposed to produce varying amounts of milk
    - e.g Holstein produces more milk than Jersey
  2. Age
    - Older cows typically produce more milk compared to younger ones
  3. Stage of lactation
    - Milk production typically increases during the initial weeks of lactation.
    - The peak production often occurs around 4 to 6 weeks into lactation, though this can vary among individual animals.
    -After reaching the peak, milk yield generally starts to decline at a rate of about 2 to 2.5% per week.
    - This decline continues throughout the rest of the lactation period until the cow is dried off.
17
Q

Why do older cows produce more milk than younger cows?

A
  • the first lactation period is often less efficient because young cows are still growing and their bodies are not fully adapted to high milk production.
  • Cows generally reach their mature body weight by the time they have their third calf.
  • At this stage, they are fully grown and can allocate more energy to milk production rather than growth.
  • Younger animals divert some of their energy towards growth and live weight gain. This means less energy is available for milk production compared to older cows that have already reached their full size.
18
Q

Factors affecting milk composition?

A

1.Milking technique
- Incomplete milking : Occurs when the milking cluster is removed before the cow has been fully milked. The leftover milk in the udder will have a higher fat percentage because the fat content increases towards the end of milking.
- Unequal milking intervals : Happens when the intervals between milking sessions are not consistent (e.g., milking at 08:00 AM and then at 22:00 PM). Inconsistent intervals can stress the cow and reduce milk yield and fat content. REMEMBER - High-yielding cows are more sensitive to changes and inconsistencies in milking schedules.

2.Dieases
- e.g Mastisis
- an inflammation of the mammary gland, significantly lowers the overall solid-not-fat (SNF) and total solids content in milk.

  1. Breed
    - Different breeds have different milk compositions which can influence the energy requirements for cows.

4.Age
- As cows age, milk quality (composition) decreases, but milk production increases.
- in the first 4 lactations , fat content remains constant
- After 4 lactations , fat content gradually decreases
- the higher the milk yield , the lower the composition

5.Stage of lactation
- Early stage : high milk yield with lower composition (more diluted)
- Later stage : low milk yield with higher composition ( Iess diluted )

19
Q

What key components are considered when estimating the ENERGY requirements for lactation ?

A

1.Gross energy value of milk (EV)

  1. Efficiency of utilisation of feed energy for milk production
  2. Energy requirements for maintenance and milk production
  3. Liveweight change in lactation
  4. Responses to increments of dietary energy
20
Q

Explain how the gross energy value of milk determines the energy requirements of a lactating cow

A
  • Refers to the total amount of energy contained in the milk produced by the cow.
  • EV calculated using fat , protein , lactose
  • EV is used to determine the NE requirement for lacTation
  • EV (MJ/kg) x milk yield (kg) = NE requirement
  • NE is the actual amount of energy that the cow needs to produce milk .
21
Q

Explain how the efficiency of utilization of feed energy for milk production determines the energy requirements of a lactating cow

A
  • k is the efficiency with which ME is converted milk energy
  • k ranges from 0.6 to 0.65 (0.62 average)
  • the differences in k are due to variations in energy concentrations of different diets
  • efficiency (k) is linked to the protein level in the diet
    -INADEQUATE PROTEIN : body tissues are catabolised to make up for the protein deficiency , which is an energy intensive process , thus reducing the efficiency of utilization of energy .
    -EXCESS PROTEIN : Excess protein will be used as an energy source but it is an inefficient source of energy compared to fat or carbohydrates , reducing the overall efficiency of ME utilization

-k is linked to VFA in the rumen
- A balance between acetate and propionate is needed for optimal energy utilization.
- ACETATE: is the primary precursor for milk fat production
- PROPIONATE :precusor for gluconeogenesis (glucose production from propionate ) which is cruical for lactose synthesis in milk
- ACETATE < 0.5 : Insufficient acetate for optimal milk fat synthesis, leading to lower milk fat content.
- ACETATE >0.65 : Excess acetate leads to propionate shortage, causing the cow to use amino acids for gluconeogenesis, which is inefficient as it requires a lot of energy and may lead to protein synthesis deficiencies as the AA are not being used to make protein

22
Q

What is kl (efficiency of lactation) linked to

A
  1. Metabolisability of diet, qm
  2. Protein level in diet
  3. VFA in rumen
23
Q

Explain how liveweight change in lactation determines the energy requirements of a lactating cow

A
  • During lactation, a cow’s body weight and condition undergo constant changes due to varying energy demands and nutritional intake
  • during the WEIGHT GAIN PHASE : cow converts feed energy into body weight gain. It typically occurs when the cow is recovering body condition lost during early lactation.
  • during WEIGHT LOSE PHASE : cow uses its body reserves to maintain milk production when dietary energy intake is insufficient.Body fat and other reserves are mobilized to provide the necessary energy for sustaining milk yield.
  • High BCS: Indicates higher body fat content, thus a higher energy value (reserves) per unit of live weight change.
  • Low BCS: Indicates lower body fat content, leading to a lower energy (reserves) value per unit of live weight change.
  • kg is higher in lactating cows than non-lactating cow
24
Q

How does BCS influence energy requirements of a lactating cow

A
  • BCS reflects the energy reserves in a cow’s body
  • during EARLY LACTATION (higher BCS) , there is a high energy demand due to onset of milk production . The energy value of tissue is high because of high fat reserves high in energy .The protein-to-fat ratio decreases because the body is using fat for energy rather than protein
  • during LATER LACTATION (lower BCS) ,the cow depletes its energy reserves . Energy demands for milk production decrease compared to early lactation.The energy value of tissue decreases because the body has fewer fat reserves and relies more on protein for energy. The P/F ratio increases because the remaining body reserves contain a higher proportion of protein relative to fat.
25
Q

kg is higher in lactating cows than non-lactating cow . WHY

A
  • The efficiency is higher because lactating cows are using energy from feed to support both milk production and tissue deposition (growth)
  • The efficiency is lower because there is no additional energy demand for milk production, and the energy is primarily used for maintenance and less efficiently for tissue deposition.
26
Q

Explain how energy requirements for maintenance and milk production determine energy requirements for lactation

A
  • The ENVIRONMENT of the cow determines its energy requirements for maintenances
  • Cows kept indoors may have different energy requirements compared to those kept outdoors due to differences in temperature regulation and activity levels.
  • Grazing animals typically walk longer distances, which increases their energy expenditure compared to housed animals. This increased activity level contributes to higher maintenance costs
  • the GENETIC factors determine energy requirements of a cow
  • Modern dairy cows with higher genetic merit for milk production have greater lean body mass, which increases their basal metabolic rate and maintenance requirements.
  • Higher milk production levels result in increased physiological strain, leading to higher maintenance costs to sustain these functions.
  • DIET composition determines the energy requirements for maintenance
  • Diets with higher fibre content require more energy for maintenance due to increased work of rumination and digestion
  • Increased fermentation associated with higher fibre content also contributes to increased maintenance requirements, particularly for maintaining the intestinal tract.
27
Q

Explain how responses to increments of dietary energy determine the energy requirements of a lactating cow

A
  • The cows respond by
    1. INCREASED MILK YEILD
    2. INCREASE IN ENERGY REQUIREMENT PER KG OF MILK AS YEILD INCREASES
    3. LIVEWEIGHT CHANGE
  • As energy intake increases, milk yield does not increase at the same rate
  • The extra energy consumed by the cow is partitioned between milk production and body gain.
  • The response is negatively curvilinear for milk yield and positively curvilinear for liveweight gain.
28
Q

What phase is better for Body Condition Restoration in dairy cows?

A
  • Better to restore body condition during late lactation phase than during the dry
    phase (after lactation) because metabolizable energy is used with higher
    efficiency in lactating animal compared to non-lactating animals.
  • also ensures cows enter the dry period with adequate fat reserves.
29
Q

The response to increase in energy intake is negatively curvilinear for milk yield and positively curvilinear for liveweight gain.Explain

A

NEGATIVE CURVILINEAR FOR MILK YEILD
- initially, as energy intake increases, there is a significant increase in milk yield.
- However, as energy intake continues to increase, the rate of increase in milk yield slows down.
- Eventually, there may even be a point where further increases in energy intake result in diminishing returns or plateau, where additional energy does not lead to a proportional increase in milk yield.

POSITIVE CURVILINEAR FOR LIVEWEIGHT GAIN
- Initially, as energy intake increases, liveweight gain also increases at rapid rate.
- However, as energy intake continues to increase, the rate of increase in liveweight gain begins to slow down.
- Eventually, there may be a point where further increases in energy intake result in diminishing returns in terms of liveweight gain

30
Q

In the ruminant animal, dietary protein performs two functions:

A
  1. Satisfy N requirements of rumen microbes
    * RDP/ERDP
  2. Supply readily absorbable true protein to satisfy AA nitrogen requirements at tissue level
    * MP
31
Q

Explain the effective rumen degradable protein ERDP requirements in dairy cows

A
  • ERDP refers to the protein required by rumen microbes to support their growth and activity.
  • it’s calculated relative to the dietary intake of fermentable metabolizable energy (FME).
  • ERDP (g/day) = FME (MJ/day) x y
  • Rumen microbes utilize ERDP to synthesize microbial protein, which contributes to satisfying the demand for metabolizable protein (MP).
  • However, at high levels of production, the demand for MP may exceed the capacity of microbial protein synthesis.
  • When the production demand for MP exceeds the microbial protein supply, the deficiency is compensated for by truly digested undegradable protein (DUP).
32
Q

Explain the metabolisable protein requirements in dairy cows

A
  • defined as the quantity of truly absorbable true protein required to satisfy the demand for amino acid nitrogen at tissue level.
  • net protein demand
  • Net protein demand at tissue level made up of:
    1. Maintenance component
    2. Dermal component (loss of hair and scruff)
    3. Milk component
    4. Live weight change
33
Q

Explain Mineral requirements for diary cows?

A
  • forages and concentrates are the sources of minerals
  • Forages
    → Calcium – 0.3
    → Phosphorous –0.64
  • Concentrates
    → Calcium –0.6
    → Phosphorous –0.7
  • recommended Ca:P ratio is 1:1 to 2Ca:1P
  • During early lactation, calcium levels in the cow’s body decrease significantly due to the high demand for calcium for milk production.
  • Salt supplementation primarily for provides sodium (Na)
  • recommendations:
    28 grams per cow per day.
34
Q

Explain vitamin requirements in dairy cows

A
  • If the levels of vitamins in the diet are sufficient to meet the needs for maintenance, normal growth, and reproduction, it is likely that they will also be sufficient for lactation.
  • vitamin content of the milk is crucial for the health and development of the young animals. Therefore, ensuring adequate vitamin levels in the diet is essential, as milk serves as the primary source of nutrition for the offspring
  • Green forage, such as pasture, is particularly high in vitamin A. This vitamin plays a crucial role in various physiological functions and contributes to the color of milk
  • Vitamin E acts as a natural antioxidant, helping to prevent conditions like mastitis. helps maintain udder health
  • In high-producing dairy cows, especially those with diets primarily composed of concentrates and limited forage intake, rumen function may not be optimal. - This can lead to lower production of B vitamins by rumen microbes.
    -Therefore, supplementation of B vitamins may be necessary to ensure adequate levels for the cow’s metabolic functions.
35
Q

Effects of limitation of food intake on milk production

A

-DMI is directly linked to milk yield and composition
- low DMI = low milk yield = high milk composition
- limited energy intake affects the solid-not-fat content of milk , increasing it
- however , lactose concentrations remains constant despite changes in intake
- limited energy intake decreases protein content : HOW?
- When cows are on low-energy diets, their bodies resort to gluconeogenesis, a process where amino acids are converted into glucose for energy.
- his increased gluconeogenesis occurs due to a reduced supply of propionate, a key component derived from carbohydrates in the diet
- As a consequence, there’s a decrease in amino acid availability to the mammary gland, which is crucial for milk protein synthesis.
- Additionally, low dietary energy limits microbial protein synthesis in the rumen, further reducing the amino acid supply to the mammary gland.

Animal Nutrition 324 (8 decks)

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