Heifers at grass

Published 22 May 15

Grazing heifers and the opportunity cost of land

A recent AHDB Dairy-funded study by Dr Alana Bolton, at the Royal Veterinary College, demonstrated that the cost of rearing a replacement heifer can be reduced by increasing the time they spend at pasture. However, according to Piers Badnell, AHDB Dairy Technical Extension Officer, grazing benefits in more than one way.

For example, land used for grazing heifers that is set stocked is relatively easy to manage but it is an inefficient use of pasture. With suitable grazing land often costing in the region of £25,000/ha to buy, or over £500/ha to rent, Piers suggests that rotationally grazing the heifers improves the overall farm efficiency.

A move from set stocking to rotational grazing means you can either carry about 25% more stock on the same area, or reduce the land needed for the same amount of heifers by 25%. Set stocking does require a higher level of management, and there is an extra cost in terms of fencing and water allocation. However, there will be a return from the increased time committed.

So why does rotational stocking improve land use efficiency? The ryegrass plant has only three live leaves. The first leaf is the smallest (15% of plant yield), the second is larger (40% of plant yield) and the third is biggest (45% of plant yield). In an appropriately set-stocked environment, animals select the youngest leaves and the plant never gets the chance to grow the third leaf before being eaten. When this happens, regrowth is also retarded and annual yield is reduced. Moving to rotational grazing allows the grass plant to grow to the three-leaf stage before the cows get a change to eat it. Full information about how the grass plant grows can be found in Factsheet 15 of Grass+.

Fencing and water allocation.

Changing from set stocking to a rotational grazing system requires some spend on fencing and water-trough layout. However, the set-up can be as complicated or simple as you want it to be, explains Piers. For example, a fixed fence can be installed down the centre of the field, splitting it into two equal portions. This will form the permanent barrier along which the trough can be moved (see Figure 1). A temporary fence can then be used to facilitate daily allocations of pasture. Using two fences and a movable water trough allows for back fencing and complete protection of the regrowth. It is important to use a water trough that can be moved by hand/quad bike, with a pipe attachment that is long enough and flexible enough so you can empty it out and move it to its new location. 

Rotational grazing plan 

Figure 1. Example of a rotational pasture layout

Pasture allocation

The area allocated should match pasture cover and stock demand, the latter will vary depending on animal size (Table 1). So, for example, if the pasture cover is 2,700kg DM per ha and there are 50 x 200kg heifers to be allocated in a field 100m wide:

2,700kg DM opening cover – 1,500kg DM closing cover = 1,200kg DM available pasture

1,200kg ÷ 10,000 m2 = 0.12kg DM pasture available per m2

50 heifers x 4.2kg (Table 1) = 210kg DM required

210kg pasture required ÷ 0.12kg per m2 supplied = 1750m2 required

1750m2 ÷ 100m (paddock width) = 17.5m allocation for one day

Table 1 highlights that only calves weighing 100kg or less require concentrate supplementation on the high-quality pasture, as they are not capable of meeting their energy requirements from pasture alone. Pastured replacement heifers at other weights are capable of meeting their requirements from pasture alone which, when compared to housed animals, allows for significant savings in concentrate usage. Table 1 is useful as it gives the intake potential and energy requirement for heifers at various weights. However, it is important that you regularly check the growth of your animals either by weighing or measuring the height at withers, see Tables 10.1, 10.2, 10.4 and 10.5 from Feeding+ Chapter 10  for more information.

Table 1 Heifer growth rates, DMI and energy requirements:

Heifer weight

Dry matter intake Kg/DM (DMI) *

Energy requirements MJ ME *

Grass DMI x 12ME (excellent grass)

Grass DMI x 11ME (average grass)

Grass DMI x 10ME (poor grass)

100

2.5

31.8

30

28

25

200

4.2

44.4

50

46

42

300

5.7

67.8

68

62

57

450

9

84.9

108

99

90

* National Research Council, 2001. Nutrient Requirements of Dairy Cattle. 7th rev. ed. Washington, D.C. National Academy Press.

In summary, there are clear benefits to moving from a set stocking to rotational pasture management system. Each farmer should examine their own system and weigh up the costs and benefits of moving to rotational grazing but the increased efficiency of land use in a land limited environment will allow for more resources to be allocated to the milking herd and an improvement in overall farm efficiency.