9.3: ruminant nutrition 2

1. Understand what a ruminant diet consists of. 2. Do a simple energy requirement calculation. 3. Be able to think about and explain how feeding regimes may cause dysfunction to the rumen. 4. Describe and understand the mechanisms by which neonates consume milk and utilise it for energy. 5. Explain how the rumen develops in the neonate as it adapts to hard feedstuffs.

What are the three main factors of ruminant nutrition?

• Voluntary feed intake

• Energy

• Protein

How much voluntary feed intake should ruminants be having every day?

• At least 3% of their body weight

• But probably more than this

• More intake means more milk

What units are used for voluntary feed intake?

DMI - dry matter intake

Define voluntary feed intake.

The amount of feed consumed when the animal has access to food throughout the whole day.

What is NDF?

Nutrient detergent fibre - structural components of the plant, like the cell wall. These are slowly digested.

How is DMI affected by high NDF?

High NDF means a lower DMI - it is more bulky and takes longer to digest, meaning it will stay in the rumen for longer and the animal will not eat as much.

What happens if food is too rapidly digested by the ruminant?

It can cause rumen upset and reduce DMI, as not as much will be absorbed.

What is rumen acidosis?

A metabolic disease that occurs when the ruminant eats too many highly digestible carbohydrates and not enough fibre, leading to the overproduction and accumulation of acids in the rumen.

What is total mixed ration and what are its benefits?

• A mixture of forage and concentrates.

• It minimises fluctuations in rumen pH, as both quick and slow carbohydrates are available at once, easing fermentation.

• It improves the VFI of a cow by up to 30% - chopping up fibre makes it easier to take in.

• You can add tasty supplements to it easily, such as molasses.

• Helps prevent sorting, which helps with competition issues and helps stop rumen acidosis.

• All nutrients are available at once, allowing synchronisation, where microflora can grow on energy and proteins at once.

What is energy measured in when considering ruminant nutrition?

Megajoules

What things are needed for normal breakdown of carbohydrates in the rumen?

• Protein, for the microflora.

• Long fibre, to stimulate the production of enough saliva for buffering and the slow release of VFAs.

What is gross energy?

The total amount of energy the feed contains.

What is digestible energy?

The total energy in the feed (gross energy) not including indigestible food that is passed in the faeces.

What is metabolisable energy?

• The digestible energy of the feed not including losses in methane and urine.

• This is the energy available to the cow to use, and is roughly 80% of dietary energy.

• It is what should be used when stating the energy of a feed.

What is net energy? What is it used for?

• It is the metabolisable energy of the feed not including heat lost as ME is turned into a useable form (e.g. glucose)

• Used for maintenance of body functions, milk production, body tissue growth and foetal growth.

What is MCP and what is it used for in the ruminant?

Microbial crude protein - very good at forming essential amino acids.

What is UDP and why is it important?

Undegraded dietary protein - important for ensuring some protein reaches the small intestine, and isn’t just digested in the rumen and used by the microflora.

What can the effect of a high VFI be on protein digestion in cows?

A high VFI can mean that protein isn’t degraded properly due to an increased gut transit.

What are excessive amino acids used for in ruminants?

Any amino acids not needed for making proteins can be used by the liver to form energy, but this can cause a strain on the liver.

How does the percentage of crude protein in the ruminant diet change throughout stages of lactation?

Early: 17-18%

Mid: 16-17%

Late: 15-16%

How is the crude protein content of concentrates quoted, and how should it be converted?

• Quoted on an as fed basis

• Can be converted to dry matter basis by the equation:

  • CP*DM% = CP% on DM basis

What is FME?

Fermentable metabolisable energy: the proportion of organic matter of feed that is fermented in the rumen.

What is ERDP?

Effective rumen degradable protein - the microbial requirement for nitrogen (the more they have to work, the more nitrogen they need)

What is important to ensure with FME and ERDP?

They need to in balance, with no excess of one or the other. An imbalance will mean that there is either nitrogen loss to environment in urine or fibre isn’t broken down sufficiently.

What are the levels of energy and nitrogen in:

• straw?

• molasses, beet, grain and potatoes?

• oil seeds?

• urea and pulps?

• Straw: low energy, low nitrogen

• Molasses, beet, grain and potatoes: high energy, low nitrogen

• Oil seeds: high energy, high nitrogen

• Urea and pulps: low energy, high nitrogen

List 4 ways that proteins can be lost in the animal.

• Weight gain

• Pregnancy

• Milk production

• Wool and hair growth

What are the pros and cons of using fats in the diet of ruminants?

Pros:

• Very high in energy

• Allow farmers to feed less concentrates to cows, so they eat more roughage

• Cheaper than grain

Cons:

• Can impair microbe digestion, so can decrease food intake and a reduced use of nitrogen, which is then removed as ammonia, and is an expensive waste of protein.

• To prevent this, protected fats e.g. whole oil seeds (not crushed) are given to protect the microbes. It can however be hard to access the innards.

What do you need to check to see whether cows are being fed correctly?

• Visually observe:

  • BCS and bloat

• Milk:

  • Yield, fat and protein %

• Faeces:

  • Diarrhoea?

  • Can sift dung

• Fertility:

  • Check the records

• Look at the feed, and the left-overs

How is energy needed by an animal measured?

IN MJ/kg DM - megajoules per kilogram of dry matter

How do you find the energy of a diet?

You need to multiply the dry matter intake of the diet by the MJ/kg DM:

energy consumed = DM*MJ/kg DM

An ideal diet would provide more energy that is digested as quickly as possible. What problems are faced by this in reality?

• At least 30% NDF is needed to promote rumination and help rumen health - this causes energy to be provided slower.

• A high amount of concentrates risks rumen acidosis - you can crush the grain to more the starch a slower release.

• High energy concentrate diets promote the production of propionate and reduce the production of acetate, which is needed to maintain milk fat levels.

• High protein diets cause excessive deamination, which reduces liver function and fertility.

• Excessive fats in the diet depresses appetite and alters milk fat %.

What is the oesophageal groove?

• A fold of mucosa in calves that directs milk from the pharynx straight to the abomasum.

• Its closure is under voluntary control, but this needs to be taught, showing the importance of consistent feeding practices.

What happens to milk ingested by calves?

• Enters the abomasum.

• The pH, renin and pepsin cause the milk to clot.

• The whey and lactose moves on to the small intestine for digestion.

• The clot is later broken down by pepsin and lipase and the products are absorbed by the small intestine.

What is the benefit of the clot formation in the abomasum of calves?

It allows a slow release of energy for the calf.

What is found in calf milk replacer?

• Crude protein - providing essential amino acids for tissue synthesis

• Crude fat - providing a concentrated energy source and essential fatty acids

  • Calves raised in a cold environment have a higher energy requirement

• Adequate vitamin E - to stop white muscle syndrome

How often should calves be fed milk replacer?

How much should they be fed?

• Little of often so as to not overstress the abomasum

• At least twice a day

• Should be fed at least 15% of their body weight daily, so will increase as calf grows

What is the expected growth rate of calves?

500-1000g/day

What can cause dietary diarrhoea in calves?

• Milk enters the rumen due to a failure of the oesophageal groove, leading to a lack of clotting and digestion.

• Also feeding too much milk at once can cause whole milk to pass into the SI, where lots of bacteria can replicate, causing malabsorption and therefore diarrhoea.

How does the rumen develop in neonates as it adapts to hard feedstuffs?

• Initially, the rumen has very little papillae and no bacteria.

• The calf is provided with ad lib concentrates and water to allow bacterial growth.

• Anaerobic bacteria allow the production of VFAs, esp. propionate, essential for papillae formation.

• The provision of forage promotes growth of the muscular part of the rumen, and also prevent formation of keratin on papillae, which would prevent VFA absorption.