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Optimise lamb growth at grass

Sheep farmers have reported excellent lamb growth rates this season of up to 300g per day. The challenge now is to maintain these rates as pastures undergo the seasonal dip in palatability and digestibility, as the favourable growing season comes to an end. 

David Thornton, Rumenco Technical Manager, believes that lambs are two to three weeks ahead compared to this time last year. “After an exceptional year for grass growth, balancing the drop in quality and quantity through supplementation is going to be a key consideration to avoid losing the early advantages gained this season,” he says.

To monitor the progression of lambs, David recommends weighing and body condition scoring (BCS), ideally at regular intervals. “Clearly this is not always possible, particularly at this busy time of year, but even the use of visual checks to assess lamb performance can be an effective way to monitor growth rates.

“For example, good vigilance to detect any changes in fleece quality and conformation will help determine whether the nutrition is matching the lamb’s requirements.”

David identifies energy and protein as vital components of the diet for ensuring maximum growth rates. But he warns that as the season moves on, notable differences in the quality of grazing can impact intake levels. “As we enter autumn, the declining dry matter (DM) and metabolisable energy (ME) content of grass means lambs require alternative sources of energy and protein, combined with other macro and micro nutrients, to support growth and development.” 

Cobalt and selenium are vital micro nutrients, especially at this time of year, explains David. “They are vital to optimise growth and also contribute to an effective immune response. Cobalt plays a significant role in energy metabolism and therefore deficiencies can lead to declining daily live weight gain (DLWG) and increase an animal’s susceptibility to infection.”

Research by Rumenco has found a lack of both essential micronutrients in soils. “We have carried out mineral profiling on 400 sites across the country over recent years and have consistently seen a lack of cobalt and selenium in grazing, even where sites have been recorded as producing high quality nutritional grazing,” notes David.

“To avoid losses caused by a lack in vital levels of micro-nutrition, and ensure lambs have a robust immune response, it may be necessary to supplement lambs.

“By ensuring lambs are in good health and are receiving an adequate, nutritionally balanced diet, their capacity to deal with parasitic infection and other secondary infections is likely to improve,” he advises.
Small changes in DLWG are not uncommon throughout the year however assessing grazing quality will determine the need and timing to supplement lambs in order to manage and sustain dietary intake levels and maintain growth rates.

“Once grazing quality falls, additional nutrition to bolster diets is likely to benefit lamb development and speed up time to finish,” says David. He points out that whilst lambs are still growing, maintaining a predominantly grass based diet is important to maximise feed utilisation.

He recommends supplementing lambs with block nutrition to provide additional energy, protein and micro-nutrition.  The Rumevite Quality Lamb Block contains 12.5 MJ of metabolisable energy and 18% protein. The block is formulated to include 90 mg per kg of cobalt and 25 mg per kg of selenium ensuring any deficiencies in nutrition is avoided, with the advantage of encouraging total intake and supporting rumen development.
He adds that supplementing grass based diets with creep feed may ensure a measured intake and allow for higher stocking densities, but the bulky content of such feeds tends to reduce overall grazing and can be a costly alternative.

“Lambs supplemented with creep feed tend to rely on concentrates to satisfy their nutritional requirements and are therefore unable to maximise the potential benefits grazing can contribute towards rumen development. Supplementing via a creep system can replace grazing capacity rather than encourage it,” he warns.

Conversely, block nutrition provides supplementation that supports the digestive capacity of the rumen, which remains relatively small as lambs continue to develop, whilst still providing the additional nutrition required.
Trials performed in the east of England on behalf of Rumenco have collated data in support of this. The finishing capacity of 200 cross bred store lambs was monitored to compare the performance of lambs finished on ad lib stubble turnips and grass, with lambs finished on ad lib stubble turnips and grass with free access to Rumevite Quality Lamb Blocks.

Results of the trial have proven that lambs supplemented with Rumevite Quality Lamb Block finished on average 38 days quicker than lambs reared on grass only diets, and achieved an average DLWG of 189g, 95g per day more than finishing on forage only. David comments, “The results of this trial are extremely promising and illustrate how supplementing lambs effectively can have a significant effect on lamb growth rates.”

He also notes that using blocks can also deliver economic benefits in terms of time saving and efficiency of use.“Using block nutrition does not remove the necessity to routinely check stock, but saves the daily hassle that trough feeding can entail.”

The ability to easily move feeding points with blocks can also bring benefits to producers. “Moveable feeding points can help alleviate poaching pressures in wet conditions, and minimise the risk of cross infection which can result from other lamb finishing systems.

“Placing blocks strategically will allow farmers to influence grazing behaviours, with the opportunity to ensure a more uniform sward height across grazed pastures.” For producers who have limited grazing, a degree of rotational grazing can be introduced.

For lambs that have not been introduced to blocks in the early stages of life, David recommends training them to the blocks to maximise usage and intake. A study carried out by The Scottish Agricultural College (SAC) found that placing blocks in highly stocked paddocks of 30 to 40 lambs per acre, for a short period of time was an effective method of training lambs.

“Grouping lambs in small paddocks or dividing pasture using electric fencing for up to a week, and placing blocks within these areas, will encourage usage and allow lambs to develop a taste for the blocks which they will then remember for life.”

David concludes that using blocks is a proven effective and efficient way to ensure performance of finishing lambs, and maintain growth rates. “Three Rumevite Quality Lamb Blocks provides adequate supplementary nutrition for up to 50 lambs a week, ensuring lambs are receiving the nutrition required to support growth rates through to finish.”