Bovine Nutrition and Metabolic Disease 2 - Energy and Protein Flashcards
- What is the next rate limiting step?
- Energy requirement per cow per day?
- Energy - measured in joules or megajoules (J or MJ).
1MJ = ~1 four bar KitKat (250 kcal). - 70MJ.
Energy sources - carbohydrates.
Simple carbohydrates (e.g. simple sugars / starch).
- rapid fermentation.
– produce lactic acid (2C).
– produce CO2 and methane.
– +/- lowers pH and causes acidosis.
- fermentable metabolisable energy (FME).
– available for use by rumen flora.
- e.g. wheat.
Feeding the rumen.
Rumenal microbes require energy to make protein and nucleic acid.
- unable to use fats and fermentation acids.
- fermentable metabolisable energy (FME):
– ME, less energy in fats and fermentation acids.
– largely simple CHO
– FME:ERDP ratio.
(ERDP = effective rumen degradable protein).
Energy sources - carbohydrates.
Complex CHO (cellulose, hemicellulose).
- slow fermentation.
– VFAs are absorbed into the bloodstream.
– acetic acid (2C).
– propionic acid (3C) goes to oxaloacetate (glucogenic).
– butyric acid (4C).
– CO2 and methane.
Energy sources - fats.
Predominantly digested in abomasum / SI.
V high energy density.
- ~35MJ/kg DM (c.f. wheat 13.5MJ).
Used as “glue” in pelleted feeds.
Limitations:
- coat fibre affecting digestion.
- most reduce milk butterfat.
- restrict to <6% of total diet.
Protected fats do not degrade in the rumen:
- calcium salts (e.g. Megalac).
- oil seeds e.g. whole rapeseed.
- protein coated.
- insoluble fats.
C16 protected fats (e.g. energiser).
Energy sources - protein.
Amino acids can be deaminated in liver to produce glucose.
Explain ME system.
Start with gross energy.
Some of gross energy lost in faeces.
GE minus faecal energy = digestible energy.
Some DE lost to methane, some to urine.
DE minus methane and urine energy = metabolisable energy (ME).
ME used for:
- lactation.
- maintenance (incl. exercise).
- pregnancy.
- growth.
*energy lost as heat in all these processes (significant due to size).
- ME requirements for maintenance and factors affecting?
- ME requirements for lactation and factors affecting?
1.1MJ/10kg/day.
Depends on cow size and diet quality.
2. 5MJ/litre of milk produced.
Depends on total yield and diet quality.
Variable with amount of fat in the milk.
- ME requirements in pregnancy.
- What is conversion efficiency dependent on?
- 25wks = 5MJ/d.
30wks = 10MJ/d.
35wks = 20MJ/d.
40wks = 45MJ/d. - Use of energy.
Quality of feed.
Animal production level.
- Calculating quality of the diet.
- Calculating animal production level (APL).
- APL and conversion efficiency relationship?
- q = ME/GE.
The higher the q the higher the conversion efficiency.
Fibrous feeds are harder to digest so more energy is used to make the energy available. - APL =
total energy requirement / energy for maintenance. - Increased APL means increased DMI means reduced gut transit time means reduced conversion efficiency.
Weight change and energy.
In lactation, 1kg body mass lost = ~20MJ energy, which produces ~4L of milk. ~35MJ energy required to gain back 1kg body mass.
In dry period, 1kg body mass lost = ~25MJ energy. ~60MJ energy required to gain back 1kg body mass.
Lactation is the most efficient time for the cow to lose and gain body mass.
Want to dry cows off in the same body condition that want want them to calve as body mass gain/loss less efficient in dry period.
- Calculating protein content in diet.
- Nitrogen in rumen.
- Nitrogen x 6.25 = protein content.
Protein content may be digestible or indigestible. - Both protein nitrogen and non-protein nitrogen e.g. urea etc.
Rumen microbes can utilise both.
Explain metabolizable protein system.
Dietary intake of protein.
- some degraded in rumen (RDP), some not (UDP).
- UDP to SI to be digested or out into faeces unchanged.
Proportions degraded in rumen depend on time spent in the rumen, which depends on DMI.
- RDP degrades into peptides and then to AAs, which can be built back up into microbial protein.
- microbes will use FME along with AAs and non-protein nitrogen to produce microbial protein which will ultimately pass out of the rumen into SI and be digested.
- Rumen outflow rate and protein metabolism.
- Protein sources and degradability.
- Slow outflow means increased digestion which means increased RDP.
Increased VFI and APL means faster outflow and more UDP. - Fish meal = 60% RDP.
Soya bean = 90% RDP.
- Protein digestion at the abomasum and intestine.
- Where are VFAs produced and absorbed?
- Like monogastrics.
All digested down to AAs and absorbed in SI. - The rumen - absorbed across the rumen wall.
