This article was written by Teagasc.
Research carried out in Teagasc Athenry has highlighted the potential to reduce the amount of concentrates fed to ewes in late pregnancy when high feed value silage is available. Damian Costello, Sheep Specialist has information and advice
Grass silage is the forage of choice offered to the majority of ewe flocks during the winter housing period. Focusing on producing high-quality silage for sheep has many advantages. Dry matter digestibility (DMD) is the key factor influencing silage feed value.
High-DMD silage has a high metabolisable energy (ME) concentration along with high intake characteristics. Ewes eating high DMD silage will have a high ME intake which results in high animal performance.
In studies conducted at Teagasc Athenry, feeding high DMD silage to housed ewes was found to have a positive impact on ewe body condition at lambing and lamb birth weight.
Each 5% rise in silage digestibility improved ewe bodyweight immediately after lambing by 6.5kg and lamb birth weight increased by 0.25kg which in turn resulted in lambs being on average almost 1kg heavier at weaning time (Keady & Hanrahan 2011, 2012).
Potential to reduce concentrate feeding in late pregnancy
A laboratory analysis is the only way to establish the feed value of your silage and is essential in determining the appropriate level of concentrate supplementation.
Research carried out in Teagasc Athenry has highlighted the potential to reduce the amount of concentrates fed to ewes in late pregnancy when high feed value silage is available.
Table 1 summarises the total pre-lambing concentrate supplementation required by twin bearing lowland ewes when fed along with both precision chopped clamp silage and unchopped silage bales of varying DMD values.
The total concentrates required for single bearing ewes is 5kg less than twin requirements listed, with 8kg to be added to figures in Table 1 for ewes carrying triplets.
Feeding ad-lib high feed value silage along with lower levels of concentrate supplementation clearly offers financial benefits whilst still hitting key performance targets in relation to ewe body condition, colostrum production and optimum lamb birth weights.
Short chop length silage increases ewe intake which further lowers concentrate requirements relative to the similar DMD unchopped silage. Although chopped silage is preferred for sheep, the bigger savings on concentrates can be attributed to the high digestibility silages.
An added advantage to chopped silage is that it is more suitable for feeding to ewes that are on slatted floors.
Table 1: Effect of silage feed value on concentrate requirements of twin bearing ewes in late pregnancy (kg/ewe)
|Big bale/single chop||12||24||34||40|
Key determinants of silage digestibility (DMD)
The majority of factors determining silage digestibility are within the control of the producer with the primary one being harvest date/stage of growth at which silage is harvested.
Other factors include length of wilting, crop lodging, graze out pre closing, mowing height and quality of preservation. The aim should be to make 75% DMD silage, the remainder of this article looks at some of the practical steps needed to achieve this
Conserving high feed value silage for sheep – practical tips
- Aim to harvest leafy material before grass heads out and before the base of sward begins to decay – regularly inspect the crop, watch the weather and take the best available opportunity to mow around the planned harvest date;
- Where grazing days ahead allows, skip a grazing on heavy covers and take out surplus grass as high-quality silage bales;
- Maintain soil pH and P & K indices at target levels based on soil analysis. When closing, apply up to 100 to 120kg/ha N in the form of protected urea taking note that some N previously applied for grazing will still be available to plant;
- Remove dead butt by grazing out properly to 3.5 to 4cm prior to closing for silage. Roll ground where necessary to reduce the risk of soil contamination. If clods of soil end up in silage (pit or bale) there is a risk that sheep fed on this silage can ingest the bacteria that causes listeriosis;
- Aim for a rapid wilt of 24 to 36 hours after mowing as wilting negatively impacts digestibility. Target 25% dry matter at ensiling for pit silage and 30% dry matter for bales. Spreading heavier crops over the ground straight after mowing helps achieve this but is generally not necessary for light crops;
- Ensure silage pit is covered and fully sealed as soon as possible after filling. With bales extra layers of plastic wrap combined with careful handling and storage will help ensure air is totally excluded from the bale.
- Do not delay the harvest date for a long period due to weather waiting for suitable wilting conditions. Research has shown that for each week harvest is delayed digestibility goes down by 3% units per week (Keady et al, 2000);
- Do not delay harvesting of these paddocks so as to get them back into the grazing rotation as quickly as possible;
- Do not overdo it with chemical N as this can cause lodging of the crop pre-harvest which will negatively impact digestibility. Also don’t forget to replace P & K after silage crop with slurry and/or chemical fertilizer. A crop of grass silage will remove approx. 4kg P and 25kg K per ton of grass DM;
- Do not mow too bare to avoid dead material and the risk of soil contamination. Where soil contamination may be an issue due to poor ground conditions at harvest do not feed to ewes next winter. In the case of bales clearly identify those intended for sheep and store so they will be accessible;
- Do not risk soil contamination by ensuring that mowers and tedding machines are set at the correct height to avoid rooting up the soil.
- Don’t go for a prolonged wilt especially on lighter crops – surplus bales should be baled and wrapped relatively soon after cutting particularly if good drying conditions prevail;
- Do not allow birds or other vermin damage your silage clamp or bales and don’t forget to repair any bales damaged in transit to avoid moulds and wastage.