Archive: Feast or famine?

Published 7 November 14

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Autumn grass for heifers – Feast or Famine?

Autumn grass for heifers – is it feast or famine, asks DairyCo technical extension officer Piers Badnell.

The answer depends on your management and what you present to your heifers. Well-managed grazing throughout the season does deliver quality grazing in the autumn. Recent analysis from Forage for Knowledge sampling farmers shows 11.5 – 12 ME, for leafy grass, from around the country. This shows the quality is there but what about the quantity?

Autumn grass dry matter can range from 18 – 19% in dry conditions and to 14 – 15% on wet days. A seven-month, 200kg heifer, which requires an average of 50MJ/day of energy for maintenance, needs 4.54kg dry matter per day to achieve this and her target live weight gain (LWG). 

We can measure and calculate the amount of dry matter available to heifers by using the allocation area, and by plate metering this to calculate entry covers and residuals. Remember, calculations are not real life, so it is crucial to monitor what you do, how much heifers are eating and the quality of the grass.

As long as the quality is there, and we are sure of how much they are eating, we can be confident of good heifer growth on autumn grass.

So this is the feast option but, travelling around the country, I see over many hedges the famine option. I notice how many heifers and dry cows are grazing set stocked areas, generally this cover is low, sub 2,000kg DM/ha, the quality may be good but the quantity isn’t.

The key to graze heifers successfully in the autumn is the combination of quality and quantity. If the above heifer only gets 3.5kg DM at 11.5 ME, this then only supplies 40 MJ of the required 50 MJ/day. In this scenario, she is not going to achieve optimum LWG.

This potential problem can also be seen with dry cows. If they do not get the intakes they require they will lose weight. If this weight loss is significant, it can affect both peak yields and fertility in the next lactation.

The table below, from Grass+ section 14, gives the reason for this problem. A cow/heifer can only bite 60 times per minute. When this is on a low cover on a set stocked scenario, the dry matter per bite will be lower than optimal. Combine this with wet weather and she is not going to get enough intake to supply the energy total she requires to grow at optimum level.

 

Figure 1 The components of sward intake

Fig 14.1

 

The answer is rotational grazing. Allocate an area with a good cover and let heifers graze to a good residual of 1,500kg DM/ha. Supply an area for three days and then, when they hit the residual, provide the next area. This does depend on having a good cover in the first place, I suggest 3,000kg DM/ha, but this autumn I have seen plenty of swards with this cover.

Give the heifers no more than three days allocation, as more enables them to choose what they eat. For the first two of the three, the heifers are completely satisfied with big mouthfuls, on the third day they are clearing and finishing up. The DMI will drop a little on this last day, but the next two coming days are full appetite again. Dry matter intake is optimised and thus growth maintained.

Heifers can meet the required DMI for growth on rotational grazing and there are other benefits as well. With silage costing two to three times more than grazing, and with housing costs anywhere between £0.50 and £1.70 a day for cows, and £0.50 a day for heifers, there are savings to be made. 

In higher yielding herds, where cows may have been housed earlier, grazing heifers gives the option of saving money, but, equally importantly, they also help to manage the closing up of swards to enable early turnout on quality grazing. Growth rates have been so good this autumn that, unless fields are closed up at 1,500kg DM/ha in succession over the October to end of November period, the threat is taking too much cover over winter and suffering loss of quality in the spring.

An additional benefit of grazing heifers in the autumn is that they are trained to graze. It is not easy to put a monetary value on this, but it is very valuable. This can be seen in the two photos below which were taken in the very wet summer of 2012.

Photo 1 shows a reasonably high-yielding herd taking cover and not grazing, compromising dry matter intake and thus yield potential, fertility and body condition.

Photo 1 Older cows in wet weather

Wet weather cows

 

 

However, in that same herd, the heifers, which had not seen a shed the previous winter as they were deferred grazed and then went onto outwintering crops, were still grazing hard (Photo 2). They were maximising the potential of grazing in terms of yield, fertility and body condition.

 Photo 2 Grazing heifers in wet conditions

Grazing heifers

Monitor animal growth and performance, and supplement if necessary.

Take the feast option, grow heifers well and cheaply on grass, and set up grazing for spring 2015. On top of that, this will train heifers to graze hard once they are in the herd.

For more information, see Grass+ section 14 and Feeding+ Chapter 10.