Where is the dairy stocking rate sweet spot?

Higher milk output doesn’t always translate into additional profits if stocking rates aren’t matched by a farm’s grass-growing capacity, Stuart Childs, Nora O’Donovan, Adrian O’Callaghan and Donal Patton tells us more in this article from Today’s Farm.

In January 2015 at the Irish Grass­land Association Conference, Prof. John Roche asked the audience: “Post quota: will you make money from milk or milk from money?” His data showed that while the average dairy farmer in New Zealand had increased their milk output by 40%, they were making no additional profit. The New Zealand farmers had expanded but lost sight of what was driving profit – the ability of their land to grow grass - the most cost-effective feed source on the planet.

The law of diminishing returns shows that once the point of optimal efficiency is passed, the return from additional units of production will drop and potentially generate a nega­tive return. So, beyond a certain point, overall profit falls.

How does this relate to stocking rate?

If you take stocking rate on either the milking platform or the whole farm to beyond the optimal point, the financial return will begin to decline. This is because the emphasis begins to shift to alternative feeds to complete the feed budget for the increased number of animals.

Michael Egan and his group at Tea­gasc Moorepark have shown greater in­take earlier in lactation than previous­ly observed. Higher overall dry matter intake also, in the order of 19kg DM/head/day of a herd average assuming a 20% replacement rate. Therefore, cows need at least 19-20kg DM per head per day to be fully fed and deliver on their genetic potential.

Average national grass growth

Figure 1 shows the average grass growth figures from PastureBase Ireland for the last five years. From it you can see that while there is a peak growth of 71 kg DM/ha/day in late May, it is short-lived.

Figure 1: Five year average grass growth rate and interactions with various stocking rates

The green line which represents a stocking rate (SR) of 2.5 cows/ha intersects with the average growth curve at a growth of 46kg DM/ha/day in mid-April and stays in surplus until early October.

Depending on the layout of the farm and whether long-term silage is being taken from the block, one could argue that this stocking rate is too low, as there is too much surplus to deal with during the main season.

Surplus of silage

More silage would have to be removed from the platform to maintain grass quality than is needed to meet the feed budget. A surplus of silage is not a bad thing, but repeatedly generating exces­sive surpluses is counterproductive.

The red line (SR = 3 cows/ha) meets the average growth line at 55kg DM/ha/day approximately a fortnight later than the 2.5 stocking rate and stays largely in surplus until the end of Sep­tember. This surplus of growth over demand enables the farm to remove bales to manage grass quality. It also allows reseeding to ensure that sward quality is maintained.

The blue line (SR = 3.5 cows/ha) exceeds demand for approximately a month from early May to early June. There is higher demand than growth for the remainder of the year.

The orange line representing a stock­ing rate on the platform of 4 cows/ha is similar, with the exception that it never grows enough grass to meet demand.

Costs

How does the cost of an excessive stocking rate manifest itself? Firstly, the cost of feeding the cow increases through increased concen­trate feeding to keep the loop closed in the absence of adequate grass growth during the main growing season (see Table 1 below).

Table 1: Growth rate (kg DM/ha) required to sustain different stocking rates with varying levels of fresh weight concentrate input (assuming 20kg total DM intake per day)

Poorer milk production performance can also occur as there is an under­estimation of the intake capacity of the cow. At higher stocking rates, they have to ‘make do’ with less. An increase in silage in the milking diet at the shoulders of the grazing season will also occur.

The stocking rate on the platform creates such a level of demand that the farm has to be almost at full tilt of growth to meet demand and in some cases will never achieve it (Orange line, Figure 1). The result is cows being fed silage as far as mid to late April when growth can surpass requirement.

Building cover

Building cover in August is a key grazing management practice. It ensures there’s a wedge of grass available to be grazed when growth dips below demand again during October and early November.

As we have already outlined, the stocking rate of 2.5 cows/ha effectively builds a cover despite itself, as growth is exceeding demand. With some minor intervention, the stocking rate of three can create a wedge of grass to graze in October and November.

At a high milking platform stocking rate, it is inherently difficult to build cover and is limited by the fact that 2,000-2,200 kg DM/ha is the highest cover that can realistically be grazed well at that time of the year.

On heavier land, these heavy covers can be particularly challenging to graze. The consensus is to not let them to build to greater than 1,800 kg DM/ha. Consequently, at higher stocking rates, we either:

• Start feeding silage early to stretch the grass for as long as possible or
• Run out of grass faster and end up on silage full time sooner.

Therefore, it should be clear that at higher stocking rates:

• Silage is removed from the diet later in the spring;
• Silage needs to be introduced in August if cover is to be built to extend autumn grazing;
• Silage has to be introduced earlier in the autumn to stay out at grass; or cows are fulltime on silage earlier than farms that are stocked to match the growth capacity of the farm.

At higher stocking rates, it is difficult to remove poor quality paddocks during the grazing season as it may result in a deficit the following week.

Reseeding

Figure 1 shows that growth only exceeds demand for a month at a stocking rate of 3.5. Target turnaround time for reseeding is two months, so it is extremely difficult to contemplate reseeding in a high stocking rate scenario.

Without reseeding, swards age and grass growth reduces over time resulting in even lower growth rates than the farm requires.

The argument is often made that there is more money coming in and this is true: turnover will be higher. But what about the costs associated with generating this extra income? These cows are marginal at best in many cases.

This is even before we look at housing capacity, slurry and soiled water storage requirements, milking parlour and bulk tank capacity and labour availability.

Cost of production

It is important to know the cost of production. This has increased in recent years as people know only too well. This cost increase has been very unforgiving where farms are highly reliant on bought in feeds.

Yes, the cost of growing grass has also increased but it is still the cheapest feed source. Matching stocking rate to your average growth rate will maxim­ise output while minimising input cost. This is the key to maximising profit.

In summary, farmers need to know the growth capacity of their farm to set their stocking rate. What is the average level of growth that is required to meet the stocking rate that you have and can your farm consistently deliver this?

The above article first appeared in the September/October edition of Today’s Farm. Access the full publication here.