John Roche questions part 1

Published 6 June 14

In the spring DairyCo organised a series of meetings in the north of the country, with Dr John Roche, looking at the management practices needed to maximise milk from grass and avoid the common problems associated with grazing cows.

A large part of the events was an open discussion section. This is part one of a three-part series, with a selection of the questions farmers asked John, and his answers.

Does feed price to milk price ratio drive your decision on how much to feed?

Yes and No! The key driver of profit is cost of production per litre of milk or per kg of fat and protein, depending on the payment system. This metric explains 70-80% of the variation in net margin per ha in the national Milkbench+ dataset. This means, you could confidently predict someone’s net margin/ha if you knew their operating expenses/l milk.

Interestingly, in the national database:

  • There’s only a very small positive relationship between milk price and profit, reflecting greater expenses when milk price is high. To be fair, some of these expenses are deferred costs from low milk price years. However, more often than not, they are a reflection of the farmer becoming less thrifty in “times of plenty”
  • There’s virtually no relationship between feed price and profit, probably because if feed is cheaper, people feed more, and if it is expensive, people feed less or, find cheaper alternatives
  • There’s only a very weak relationship between milk-feed price ratio and net margin/ha: this ratio explain less than 10% of the variation in profit.

Therefore, the feed price to milk price ratio should not be a major determinant of how much to feed. Instead, you need to strategically design your system to require a certain amount of purchased supplement. Although this is set, there must be a degree of flexibility for good (i.e. feed less) and bad (i.e. feed more) years. However, define how much feed you need strategically first.

Post-grazing residual should determine how much to feed. The amount of pasture left behind the cows is directly related to:

  • How hungry the cow is
  • Substitution rate
  • Amount of milk a cow returns for the supplement fed.

Successful grazing systems are a compromise between getting the most of your land and the most out of your cow. To ensure high production/cow and per ha, we need to grow and utilise as much high quality pasture as possible. We, therefore, aim to have the cow eat 90% of what she could eat if left unfettered. This ensures the cow is well fed today and that the quality of the feed during the next rotation is also of the highest quality. In this way, the cow is well fed throughout the year and not just for this grazing rotation.


When a deficit presents itself in the wedge, are you better supplementing with good quality silage or higher levels of concentrate? 

If it is concentrate, to what level does it become prohibitive nutritionally and economically?

Part 1 – Type of feed

You feed the least expensive form of metabolisable energy (ME)from feeds that are at least 10.5 MJ ME.

When cows are grazing fresh pasture, the limiting ‘nutrient’ is metabolisable energy. Therefore, you will get the most milk production from supplement by providing a source of metabolisable energy to cows when they don’t have enough pasture (ie post-grazing residuals are less than 1,500kg DM/ha).

Metabolisable energy is derived from the fermentation and/or digestion of: fibre, protein, sugar, starch, and fat. Research work in Germany 130 years ago showed ruminants had the same level of production gains from cellulose (ie fibre) and starch. Further work, recently highlighted no increase in milksolids production from replacing fibre with starch or sugar, if cows consumed the same amount of ME. However, milk yield (ie volume of white water) did increase when starch was fed compared with fibre.

In summary. The source of the energy is largely unimportant, as long as the feed is of good quality (i.e. greater 10.5 MJ ME). Feeds of poor quality take too long to digest and reduce DM intake. Therefore, if silage ME is cheaper that the ME in concentrate cake, purchasing and feeding silage will result in a greater return from the supplement use than the cake.

Remember though, you must account for all costs and there are greater labour and feeding costs and, generally, more physical wastage of silage than there is of concentrates.

Part 2 – at what point is concentrate too much

There’s no real right or wrong answer to this question.

Cows can be fed very high levels of grain (up to 50% of their diet) in a mixed ration without a problem. Current research in Australia is feeding up to 6-8kg DM of milled barley or wheat during milking (ie two feeds of 3-4kg) and reports no animal health problems. However, in other situations, much smaller levels of concentrate would cause acidosis.

Much of the concentrate cake fed to dairy cattle in the UK contains a significant proportion of fermentable fibre (eg brewers grains, maize gluten, citrus pulp, wheat midds, PKE), all of which are very safe feeds from a rumen health perspective. It is possible to feed a lot more of these feeds safely than high starch grain-based feeds.

The decision to feed concentrate or not, should be based on post-grazing residuals. If post-grazing residuals are below 1,500kg DM/ha, milk production response to supplements will be good. However, keep an eye on total non-fibre concentration of the diet and starch content of the diet. If non-fibre carbohydrate is above 35% and/or starch content exceeds 30% of the diet DM, a rumen upset is more likely. It is also important to keep neutral detergent fibre (NDF) above 30% and NDF from forage (ie longer fibre) at more than 20% of the diet DM.


Supplementary feeding in grass shortage – what effect will feeding hay have rather than silage?

Good hay and good silage would be equally effective nutritionally. However, is your hay good enough?


Does feeding some concentrate, while out at grass, result in more profit?

The key to profitable supplement use lies in the response to the supplement and the cost of the supplement. As the cost is currently low, relative to the price of milk, the determining factor is the marginal milk production response.

This is dictated by how well fed (or hungry) the cow is. A good measure of this, on farm, is the post-grazing residual. Therefore, if residuals are above 1,600kg DM (4cm), milk production responses to supplements will be low and, likely unprofitable. If residuals are below 1,500kg DM (3.5 cm), responses to supplements will be good. Milk to supplement price ratio does not alter this important decision rule.

Concentrates – to feed or not to feed to grazing cows, if so how much and why?

Concentrate supplementation gives grazing farms flexibility to manage feed shortage due to poor grass growth. However, in deciding how much to feed, there isn’t a hard and fast ‘rule’. Every farm needs to do a strategic plan to decide on ‘how they want to farm (eg stocking rate, cow size, business exposure risk). These decisions will dictate how much supplement it will be profitable to feed.

One thing to consider, in this strategic decision making process, is the farm’s exposure to external forces. As farmers we are ‘price takers’. We have no say in the price of milk and very little say in the price of supplementary feeds or fertilisers, for example. If milk price were to decline by 50% or supplement price were to increase by the same amount, what would happen to your farm business? In the last decade, we’ve seen milk price and concentrate price fluctuate by more than 100%. If the business is set up to rely on purchased supplements (ie >20% of the cow’s diet is from purchased feed), the business is at significant risk to upward swings in feed price. This is especially so, if milk price doesn’t follow a similar trajectory at the same time. Effects of such risks are often governed by debt exposure; in situations of low debt-equity ratios, overdraft facilities can be negotiated to provide flexibility. Where debt-equity ratios are high, lending institutions may not be as flexible.

Resilient systems limit the exposure of businesses to external forces. To this end, I believe that a system which imports 5-10% of the feed supply of the cow (300-600kg DM) minimises the risk to the business, while ensuring that peak milk yield/cow and lactation length are optimised to fulfil reasonable milk yield targets. In such a system, the business has limited exposure to external forces and if the feed price doubles (or remains the same with a large drop in milk price), the business should be able to withstand this.


For an autumn calving block, what is the best way to graze dry cows to enable calving down outside (where weather allows)?

Rules for grazing dry and springautumn calvers are similar to milking cows. Residuals lower than 1,500kg DM/ha during summer will limit pasture recovery, especially during dry weather. Grass silage or maize silage can be fed to dry cows to ensure they achieve calving body condition score targets of 3.0 and springers should be limit fed to 9kg DM intake.

Autumn calvers often face milk fever problems. If this is the case, limit fresh pasture to 50% of their intake, supplement with either maize or pasture silage or hay, and ensure cows are supplemented with 20g of magnesium each day (ie 40g Mag Oxide).

Bloat – do you get more or less bloat if you go from paddocks with and without clover, against grazing paddocks full of clover continuously?

Clover increases the risk of bloat, but I am not aware of cows becoming conditioned to bloat-causing factors, such that the risk reduces with time. You must be vigilant. If there is a risk of bloat:

  • Give them their new break in the afternoon (the risk of bloat is greater in the morning)
  • If supplementing, provide the supplement to cows before they go to graze to make them less hungry and less likely to gorge (a risk factor in bloat)
  • Clover after flowering is anecdotally safer than before flowering. However, this very rarely fits with the grazing rotation.

How much magnesium does a cow need in spring?

We aim to supplement cows so they consume an additional 20g magnesium. This is 40g of magnesium oxide/cow per day. If dusting this on pasture in spring, we double the rate to account for losses in wet weather.

How long after turnout is it ok to stop feeding silage for the transition of the rumen?

You do not have to ‘transition the rumen’ from silage to grass. The point at which silage feeding can cease depends on how much pasture you have (ie your pasture cover) and how close you are to ‘balance date’ (ie when pasture growth equals herd demand). If concentrate supplementation is more than 5-6kg/day, it is probably advisable to also feed some silage.

How does the rumen change from a TMR to a grazing diet and how can you make it a smooth transition from one to the other?

The rumen of a grazing cow is substantially larger than that of a cow being fed a total mixed ration. Therefore, the rumen has to grow in size. This can happen very quickly and it isn’t a factor limiting DM intake, per se.

The primary thing which has to change in this transition is the behaviour or the cow (and the farmer). It is important while they are getting used to grazing, they aren’t disturbed by people or tractors that might give them the impression they are about to receive a supplement.

Can you rear youngstock to target on an all grass diet, post weaning?

Yes. Grass and grass clover pastures are excellent feeds for young stock. I would recommend calves continue to receive some hard feeds in addition to pasture until 120-150 days since planned start of calving, though. This ensures the calves have additional feed in bad weather. However, this is an insurance and is not absolutely necessary.

How much DUP is in grass and clover?

DUP stands for Digestible Undegraded Protein and refers to the true protein that has left the rumen (microbial protein and undegraded dietary protein). The amount in grass and clover are probably very similar. Although most of the protein is degradable in the rumen, much of this protein bypasses the rumen because of the rapid passage rate associated with consuming such a low DM feed.

The protein quality in both grass and clover is very high. The microbial protein which results from fermentation is also of very high quality. Therefore, so is all of the protein reaching the small intestine.

However, the amount of DUP will depend on a lot of factors.

When has grass gone too far for grazing – 2800kg DM/ha?

The optimum is probably between 2,800 and 3,300kg DM/ha. However, tHoHohis very much depends on stocking rate and the previous post-grazing residuals.

The previous post-grazing residual dictates how much pasture can be grown without losing quality. When post-grazing residuals are close to 1,500kg DM/ha, pasture will not lose much quality until yields exceed 3,300kg DM/ha.

If stocking rate is low, it is very difficult to get cows to graze to low residuals from high pre-grazing masses.

Grass type – Diploid or Tetraploid?

Recent research from Moorepark, in Ireland, suggests tetraploids offer a 5-10% advantage over diploids. However, this probably depends on the type of tetraploid, and the type of diploid. In Ireland, there is an index similar to the bull list allowing you to choose grass seed on a profitability index rather than deciding on ploidy (the number of sets of chromosomes in the nucleus of the cell) alone.