Grass Utilisation

To successfully utilise grass with a modern dairy herd grass must be grazed to a sufficiently low sward height to maintain sward quality at the next grazing, but must not be grazed so low as to limit grass intakes which result in reduced herd performance.

High quality grazed grass has been shown through research trials to have the potential to support up to 27 litres of milk production. This is only possible under ideal grazing conditions during May as shown in figure A. Actual production from grass will depend on: the stage of lactation of the cows, the quality of the grass, and the weather conditions while grazing. The grass intakes required to support the full productive potential of grass are also shown in figure A. Achieving this level of production from grass in practice assumes that all cows in the herd are yielding at least 27 litres. This is rarely the case in practice on many N. Ireland dairy farms as a result of the spread of calving patterns.

Figure A. Potential milk production from grass and grass dry matter intakes required

Date of calving has an important bearing on milk from forage and especially on milk from grass. Figure A. above shows the potential milk production from grass over the grazing season. Assuming that good quality silage has the potential to support up to 15 litres of milk production when supplemented with concentrates and fed to freshly calved cows, figure B shows how a 7000 litre cow calving in October wastes a lot of the potential milk production from forage over the calendar year.

Figure B. Potential milk from forage with the 7000 litre October calving cow

A 7000 litre cow calving in January (Figure C), utilises more of the potential production from grass calving closer to the start of spring grass growth. Lower yielding cows, calving later in the spring, ie March, will more closely match the cows lactation curve to the potential milk production from grass.

Figure C. Potential milk from forage with the January calving cow

The predominant grazing system on N. Ireland dairy farms are 24 hour paddocks with fresh grass made available at each grazing. Within a paddock system, grass needs to be managed to ensure that pre-grazing grass covers are sufficient to meet the needs of the herd. With an autumn/winter calving herd, the number of grazings per paddock and the number of paddocks in the rotation need to be adjusted according to grass growth and as the cow numbers grazing are reduced through the late summer period as shown in table A.

Table A. Daily paddock area/paddock numbers for the autumn/winter calving Herd at Greenmount Campus as milking cow numbers decrease, assuming a pre-grazing cover of 3500 KG DM/ha and a post grazing cover of 1600 KG DM/ha

An extensive system of laneways is essential for grassland management

Given the limited flexibility of the 24 hour paddock system, grass should be topped as necessary during the season and or paddocks removed for big bale silage during periods of rapid grass growth. Under slow growing conditions, additional paddocks, previously used for silage, need to be grazed to slow down the grazing rotation.

With block autumn calving herds, more grazings per paddock and consequently fewer paddocks will be required in the August to October period. By contrast, a block spring calving herd will require more paddocks brought into the grazing rotation as grass growth slows down during the late summer and autumn.

The potential to produce milk from grass has been illustrated in figure A above. However it must be recognised that with rapidly increasing genetic potential for milk production within the N. Ireland dairy herd, there may well be cows within a herd which require concentrate feeding at grass to avoid excessive loss of body condition score. If the system being operated on a farm excludes the possibility of feeding concentrates to cows, detailed consideration should be given to the genetic potential of cows being bred on such farms.

At Greenmount Campus the management policy is to feed cows according to milk yield through a computerised feeding system. Milk yields above which concentrate supplementation was introduced to the High Forage Herd are detailed in Table B.

Table B. Milk yields above which concentrates are introduced to the High Forage Herd

Response to concentrates during poor weather conditions

During poor weather with high rainfall and low grass dry matter contents, grass intakes can be reduced by 10 to 20 percent. In this situation the feeding of concentrates to cows yielding up to five litres less than the levels in the above table during the April to June period can be economically justified at current milk prices.

Extended grazing in practice with the High Forage Herd at Greenmount Campus

During periods when ground conditions are poor applying the principles listed below can dramatically improve grass utilisation and minimise sward damage. These principles can apply to the main summer grazing period as well as early and late season grazing.

Target turnout to housing dates for the Greenmount Campus High Forage Herd are from early March to late November.

Each day added to the grazing season has the potential to increase margins by £1 per cow per day.