Dairy feeding options in summer drought conditions outlined
By Dr. Siobhan Kavanagh, Teagasc
Soil moisture and high daily temperatures have begun to strongly impact on daily grass growth nationally, with growth rates on many farms falling below 45kg/day (dry matter).
As a result, average farm covers are beginning to drop below the target of 160-170kg/cow. Given the prospect of sustained dry weather, it is important that prompt actions are taken to manage the situation.
Grazing management decision rules
The main priority now is to reduce daily grass demand to below daily growth rate. This will help to hold grass cover on the farm, protecting current growth and speeding up recovery when rain arrives.
Rotation length must be maintained at 25-27 days approximately. Effectively, this means grazing no more than 4% of the grazing platform daily. Assess the grass available on this area and supplement with forage/concentrate to balance herd demand.
For example, a 140-cow herd is grazing 45ha (3.1LU/ha). The max daily area allowed should be 1.8ha (4% of 45ha). If there’s 1,100kg/ha available, then the paddock has 1,980kg available. Herd demand is 2,520kg/day; therefore 540kg of total supplement is required per day.
In this example, holding total grass allowance to 1,980kg equates to a daily demand of 44kg/day. This will hold grass cover per hectare reasonably well if growth rates are within 5-7kg daily. Larger deficits will rapidly reduce average farm cover.
If there is a larger deficit between growth and demand, it will be necessary to temporarily reduce demand further by reducing grazing stocking rate and feeding extra silage.
Increasing rotation length beyond 30 days may lead to much reduced grass quality in current conditions. Post-grazing residuals of 4-4.5cm must be maintained, otherwise feed is being wasted.
Maintain fertiliser nitrogen (N) at 25kg/ha after grazing. The risk of losses are low with CAN (Calcium Ammonium Nitrate) products. However, if drought conditions persist to >60mm, it is advised to delay N until rain is forecast.
Hints and tips on feeding out forage
Dry field conditions should make the task of feeding out much easier compared to spring. Each farm will have its own preference (based on facilities/machinery/labour), but the main objective remains to reduce total daily grass intake to the level of daily growth or below.
Feeding forage will be necessary for many farms. Once the available daily grass is known, some options for feeding are outlined below.
Separate a proportion of the herd and place on 100% silage plus meal in a convenient paddock. This may be a paddock marked for reseeding later in the year.
A small area of fresh grass can be allocated to this group daily. Some farms have used a double temporary wire feeding rail to good effect. This approach simplifies grazing management of the main group.
Offer silage to all cows in the grazing paddock, placing silage along perimeter fencing. This works best where feed can be allocated with a diet feeder.
Total silage allocation should be calculated to balance available grass on the paddock daily. Forage should be spread along a long linear distance (1m/cow) to reduce competition and bullying.
Hold a proportion of the herd in the yard for silage feeding after milking. These can be turned out with the main group after three-to-four hours feeding. This simplifies feeding out silage; but, in dry conditions, there is a risk of injury due to slippery concrete floors.
It’s also important to ensure full access to clean water.
Whichever actions are chosen, it is vital to act now to ensure that grass supply is stretched out as early as possible. If covers are allowed to drop too quickly, it will result in the entire herd having to be managed on silage for a period and grass recovery will also be delayed.
Plan supplementation until four-to-five days after growth exceeds demand and assess feed plans with this in mind.
Concentrate feeding guidelines
Parlour-fed concentrate will form a major part of the daily feed allowance in drought conditions.
Feed up to 5-6kg of parlour concentrate per day as part of an overall feed plan. This is a relatively safe level, provided adequate forage and water are provided.
A further 2-3kg of high-fibre straights can be fed out of the parlour. Purchase concentrate based on UFL value, targeting a value of >0.94 UFL on a fresh weight basis.
Ration crude protein should be decided based on overall composition of the diet. In normal circumstances, a 14% high-energy ration would be adequate at grass. However, in the current situation, it is likely that lower protein ingredients will form a significant part of the diet.
Also, where grass is under drought stress and lacking N uptake, it is possible that sward protein content could be lower than normal.
Therefore, it is recommended that a 16% ration can be used if grass intake is around 7-10kg/day. If the herd is placed on silage full-time, then a high-energy ration of +18% will be needed in the short term. These targets are for parlour rations fed at 4-6kg.
Be careful not to overfeed magnesium. A rule of thumb is that cows will tolerate up to twice the recommended allowance over a short period (100-120g/day).
Above this level, there may be issues with scouring, as magnesium has a laxative effect. Therefore, if the concentrate is formulated for a 2kg/day feeding rate then the max feeding rate should be limited to 4kg/day.
Decision rules on grazing silage crops
Areas closed for silage and accessible for grazing with <2,200kg/ha covers may be grazed as a ‘standing supplement’. Pre-mowing does not confer any advantage in this situation.
Recent work on zero grazing in Northern Ireland showed a significant drop in milk yield where heavy swards (2,500kg/ha) were cut and fed, relative to cutting or directly grazing lower mass swards (<1,600kg/ha).
The decision to zero graze should be based on pre-grazing yield. Overall, if silage swards have surpassed ideal pre-grazing herbage masses and are nearing cutting stage then it is preferable to leave for silage cutting at this stage.
Options to reduce milking herd demand
Autumn-calving herds can dry off stale cows two-to-three weeks early and feed off the grazing block. Consider offloading problem cows (e.g. high SCC) that are already in line for culling.
Once-a-day (OAD) milking is known to help cows retain body condition at a cost of reduced milk solids output (15-20%).
However, this assumes that cows’ intake is maintained relative to twice daily milking. Where OAD milking is imposed in tandem with reduced feed intake, milk output may be reduced by >30%.
OAD is an option to manage cows in severe situations; but – at this point – the preferred option would be to supplement the required feed instead.
Do not neglect young stock
Total dry matter intake requirements are small relative to the milking herd for young stock; but nonetheless adequate feed dry matter (2.0-2.2% of live weight) must be offered daily