January 24, 2009

Cattle farm husbandry – feeding principles

Cattle, farming, husbandry, feeding, nutrition, maintenance & production, dry matter, energy, protein, fats, water, digestibility, feed conversion efficiency, negative nutritional balance, feeding milking & beef cows.

By Dr Clive Dalton

A well fed Angus cow

Feed stock well

If you keep feeding your stock well and they are healthy and producing well, you’ll probably not need any of this blog.

Cattle eat and drink a lot compared to other species on the farm. For example a newly-calved dairy cow will eat up to 17kg of dry matter each day which is about 85kg of wet grass, so if you haven’t got that amount of feed on the farm, then you’ll have to make some important decisions to keep her milking which is the concept of “feed budgeting” or balancing feed demand with feed supply.

Don’t forget water. A milking cow will drink about 70 litres of water each day and more if it’s hot. So there are plenty of issues to consider as feeding is a major part of profit. Here are some basic principles – some of them a bit academic but they are important.

Troughs should be clean enough for you to drink out of!

Dry Matter (DM) – what is it?

This is feed with all the water removed, and using DM is an easy concept as you can measure it yourself. Here’s how to do it:
  • Put a weighed sample of feed into an oven at about 100°C for about an hour, or microwave on defrost for 5 minutes or until it stops losing weight.
  • Then calculate the (Dry weight/Wet weight) x (100/1). This is DM%.
  • It’s useful when you want to compare feeds and especially when you are buying them.
  • For example if you are offered surplus kiwi fruit at 30cents/kg in the orchard, and the DM is only 10%, is this a good buy or not? It’s maybe better to buy meal at 80cents/kg which has 86% DM. You could be buying very expensive water- even if you get free delivery.

The concept of maintenance and production
  • A cattle beast uses part of its feed for “maintenance” which is to keep its basic functions working like a stationary car, parked with the handbrake on and the engine ticking over.
  • So a beast needs nutrients like protein, carbohydrates, minerals and trace elements to maintain its basic body function such as body temperature, digestion, blood flow, organ function and minimal movement.
  • Then there are the feed nutrients needed for “production” which is over and above maintenance. This is needed when the animal starts to grow, become pregnant, lactates or walks long distances each day to find feed, water or to be milked. It’s the car now moving with your foot down on the accelerator.
  • How much an animal needs for maintenance is based mainly on its live weight.
  • Now this is not a specialist book on dairy cows, but the milking cow is a good subject to understand the principles so bear with her for a while (see below).
  • To maintain a dairy cow in the late months of pregnancy when she is dry, she’ll need about 1.2% to 1.3% of her live weight in DM. After calving this needs to be increased to 1.5% – 1.6% of live weight.
  • So it’s very important to appreciate this concept as if you provide bare maintenance feed for any stock that should be fed for production - a familiar problem on farms in spring. You’ll end up with skinny stock and an animal welfare problem.

Feeding a milking cow
Look at the table below to see how much DM a cow needs based on its liveweight at different stages. See the key points from the table.
  • It sets it all out showing the months before and after calving when the cow is dry then milking, and what an average Friesian, Jersey and a Crossbred will need in terms of DM/head/day.
  • Note that after calving the cow has lost the weight of the calf and fluids it was carrying

Key points from the table
  • See how the cow’s weight dictates her feed needs.
  • Note that after calving the cow has lost the weight of the calf and fluids (conceptus).
  • The DM values in the table are the minimum worked out for a cow, standing indoors in a stall at an experimental station.
  • So when the cow is outside in a cold wind and has to walk long distances to find feed, then these maintenance values will be far too low, and the cow will use its own body reserves to meet the deficiency and lose weight and condition.
  • When a cow starts to lactate, then her DM needs rocket up and she will be limited by her appetite, especially on pasture which is a bulky feed.
  • Some very large cows can eat up to 4% of their live weight in DM, but that’s the limit on a pasture diet which is our New Zealand system where no high-energy feeds such as grain are fed because it kills the profit.
  • A cow that satisfies her appetite long before her nutritional needs are met ends up in negative nutritional balance which can have serious implications.

Negative nutritional balance
  • This is a fancy term to describe the state of a cow after calving. It simply means that she is pouring out more energy in milk than she is taking in by feed, so she makes up for the deficiency by using up her body reserves of fat, and if things worsen, her muscles.
  • She’s in “negative nutritional balance: for about 6-8 weeks after calving, but big heavy-milking modern Holstein Friesians can be in negative balance for much longer – up to 20 weeks, losing body condition much faster. They have been selected for a high metabolic rate so keeping body condition on them is a major challenge.
  • Is this anything to worry about? Yes it is, because six weeks after calving when the cow is pouring out energy in her milk, she’s expected to start cycling and become pregnant again after only one mating or insemination. She often fails to do this, requiring money to be spent on hormone stimulation and veterinarian visits.

Feeding a beef cow
Feeding a beef cow is a much simpler challenge. The table below shows general figures for beef cows for different periods before and after calving down the side, and for three different average weights along the top.

Key points from the table:
  • After weaning and before the next calving - increase DM by 15% for lean cows and reduce it by 15% for fat ones.
  • 3 months before calving - Add 0.9kg DM/day to the cow’s needs for pasture eaten by the calf.
  • 5 months after calving – Add 2.7kg of DM/day to the cow’s needs for pasture eaten by the calf.
  • If you want to put condition back on a cow, a mature cows needs about 6.5kg of DM for every 1Kg of live weight above what it needs for maintenance.

Feeding young growing cattle
  • With young stock it’s very important that they are always fed above maintenance as their future performance is dictated by how well they are reared.
  • The effects of poor rearing last right through the animal’s life.
  • The table below shows the feeding levels for animals of different starting weights down the side, and for different growth rates along the top.

Key points from the table
  • These are general values and they’ve been around a long time. So be generous when you use them and increase rather than decrease the values.
  • Over winter or when feed is short, stock should grow at a minimum of 0.25kg/head/day.
  • In the spring flush of pasture, aim for growth close to 1kg/head/day.

Target weights
  • The table below for dairy stock and the table for beef stock show some currently accepted target weights for stock of different ages.
  • Note that target weights are not “average” weights.
  • A “target” weight is the weight every animal in the group should have reached by the defined age.
  • Again realise they are general values used as a guide.

  • When a cattle beast eats feed, only some of the nutrients are digested and end up in the bloodstream to be used for maintenance and production.
  • What’s left passes out in the faeces so the “digested” nutrients are the most important bits.
  • Here’s the full definition of digestibility written as an equation.

Digestibility % = [(Feed Eaten – Feed excreted) / [Feed eaten] x [100 / 1]

  • So it’s important to know the digestibility of the DM, the protein, and the energy (see later) in the feed, as these are what cost money.
  • It’s not surprising that feeds vary greatly in their digestibility (Table 9), as it’s controlled a lot by the maturity of the plants which make up the feed.
  • As crops mature, fibre content increases (which is harder to digest) and protein decreases (which is easy to digest).

Key points from the table
  • Milk is a highly nutritious feed. Nature got it right!
  • Young grass is a good feed but it declines in value with maturity.
  • Note the importance of always feeding good quality hay and good silage.
  • Straw has very little feeding value but it’s useful if you want to make the animal feel full.
  • Root crops have good feeding values but are very high in water which restricts how much the animal can eat. They are very bulky feeds.

Feed conversion efficiency (FCE)
  • This is also called Feed Conversion Ratio (FCR) and is used to measure how much live-weight gain (LWG) you get for the feed eaten.
  • It’s the basis of profit and is expressed as kg DM/kg LWG.
  • The general principle is that the faster an animal grows, the better the FCE. See Table 10 for a 300 kg steer.
  • Again realise these are general figures and measuring FCE with pasture-fed stock is difficult and nothing near as precise as when cattle are fed grain in a feedlot.

Important nutrients in a diet

  • These are needed for growth and muscle so are important for young stock such as young calves that need 13-14% protein of their total DM intake.
  • Lactating animals need about the same with finishing animals slightly less at 10-11%. Mature stock on a maintenance diet only need 8.5% protein.
  • Once animals get on to good green pasture – a protein deficiency is not very likely. Indeed in the spring flush there is too much protein and it is wasted, just passing through the animal.
  • Clovers have three times the amount of protein found in grasses.
  • It’s a good idea to have some carbohydrate rich feed like maize silage or good hay to help balance up the excess protein in the diet. Even feeding some barley straw is a good idea.

  • Carbohydrates in feed provide energy and meeting the animal’s energy needs will be your main concern.
  • Good short green pasture is rich in energy as well as protein, but the problem is to provide this all year round.
  • Silage made from a crop when it was short and green and hence highly digestible is an ideal source of energy and protein, especially when pasture is in short supply as in winter and droughts.
  • Cereal grains are the highest source of energy but it’s an awful waste and costly in New Zealand to feed grain to ruminants that were designed to digest fibrous plants.

  • Fats are similar to carbohydrates but supply more energy and you’ll see they are included in diets for calves or high producing dairy cows.
  • Fat is nature’s way of storing large amounts of energy in concentrated form in the body. People trying to slim and use it up know all about this.

Vitamins, minerals and trace elements
  • There’s a wide range of these each with a specific function, and it’s easy to be concerned about possible deficiencies in your stock. Copper, selenium and cobalt are the main ones.
  • The key is to provide a balanced diet containing high-quality green pasture and you need not worry too much about deficiencies.
  • Seek veterinary advice if your stock are not performing well to check if it’s a vitamin or mineral deficiency.
  • Water is not a nutrient but don’t forget about it. It’s essential to life and good health.
  • It must be good quality (potable) so it’s important to have it tested if you suspect it may have problems – and there are plenty of them.
  • Examples are bacteria (coliforms and faecal coliforms) algae, and toxic minerals like manganese and iron, as well as chemicals like nitrates that can cause disease. These are not good for humans and they are not good for animals either.
  • There is also the problem of dead birds and vermin in water supplies which risk both animal and human health from salmonella and the like.

More about ways to compare feeds
You regularly need to compare feeds on the basis of nutrient content, especially when looking at value for money if they have to buy them, or what you should charge when selling feed.

Pasture Equivalent Dry Matter (PEDM)

  • This very old and crude concept is used to compare the DM in feeds using a “standard” which is taken as “good leafy pasture of 70% digestibility” – like spring pasture.
  • This is given a value of 1.0 so you compare the DM in any other feed and express it as a “Pasture Equivalents”.
  • Clearly, it can only be a very crude measure to express overall feeding value, and it has been used for many years in farm management. Table 11 shows some values used.
  • The way it works in a feed budget is that you measure or estimate all the feed on the farm and convert it into PEDM units.
  • Then you see what the animals need in terms of DM and calculate if you have enough, too much or too little. See later.

Energy Values
  • Thinking about energy levels in feed is a big leap forward, but is a bit more complicated.
  • Energy is what animals are most often short of for most of the year, and it’s what you’ll have to buy when things get difficult.
  • So here you go a step further than measuring just the DM%; you find out from a laboratory feed analysis how much energy there is in the DM – expressed as “Energy Units”, and this will cost you money as you cannot do it yourself in the kitchen.
  • When broken down the term Energy Unit is a bit of a mouthful. It’s the “Megajoules of Metabolisable Energy per Kg of Dry Matter” in the feed.
  • It’s abbreviated to “MJ/ME/Kg DM” and then to “ME units” which avoids the need to pronounce “metabolisable” (met-a-bol-iz-able) which is a bonus!
  • So farmers now can get ME values done on their hay or silage before they start feeding out, and certainly on any feed before they buy it.

What is ME?
  • If you take a feed and explode and burn it in a special chamber in the laboratory, you can measure the total heat (energy) produced from it measured in joules. This is called Gross Energy.
  • But the animal doesn’t use all that, as energy is lost in faeces and urine and methane belched from the rumen.
  • So what’s left after those three parts have been removed is the energy that can be “metabolised” for maintenance and production – called Net Energy.
  • A part of Metabolisable Energy is used to provide heat to keep the system going, so when you see the letters ME – it’s the energy in the feed that the beast can put to full use to earn income.
  • This is a big advance from just thinking about DM – you now can find out how much energy is in each Kg of the DM of different feeds as shown in the table below. But be warned about the limitations of these general figures and get a proper analysis done on a representative sample of feed from a registered laboratory (see the Yellow pages in the telephone directory) or through your veterinarian.

Energy for mature beef cattle
The table below shows the ME requirements for mature beef cattle of different live weights down the side, at different stages of pregnancy along the top.

The cow live weights are minus the weight of calf and fluids (conceptus). Average figures used for conceptus are 20kg at 190 days, 36kg at 240 days and 55kg at 265 days.

Energy for growing cattle
The table below shows how much energy growing cattle need. It is presented for different starting live weights down the side, and the different daily weight gains required along the top.

Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.

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