Between 40% and 45% of the lamb kill occurs from November to April each year. A large proportion of these are finished with the aid of concentrates. While grass is the cheapest feed for lambs, as the season progresses from late summer into autumn, lamb performance can be quite variable.

Performance at grass

Throughout August and up to mid-September, well-managed grass is capable of delivering lamb growth rates of 1kg to 1.2kg/week (150g – 170g/day).

From mid-September to early November, this performance declines, with growth rates exceeding 120g/day unlikely in late October or early November.

From then on, performance can be very variable. Quality of grass deteriorates, quantity declines often times coupled with difficult grazing conditions, leading to very poor performance from grass alone. The available grass may be required by ewes and therefore offering it to lambs may not be a wise choice. The information presented in Table 1 summarises expected lamb performance from well managed autumn grass.

Variable

The question then arises as to what is the best option for fattening store lambs in the autumn?

Lambs greater than 37kg liveweight

For lambs that are approaching the target slaughter weight, with not more than 5kg to 6kg extra liveweight needed, but grass quality is deteriorating or getting scarce, there may simply be a shortage of energy to maintain the desired growth rate.

Performance can be maintained by offering an extra supply of energy at grass. A straight cereal such as standard dried whole or rolled barley should be sufficient. Approximately 0.5kg/head/day should be enough but more may be needed if grass is very scarce.

This meal should be introduced gradually and built up over a period of five to seven days to avoid digestive upsets. These lambs should grow at 150 to 170g/day and be ready for slaughter in less than 40 days.

Lighter lambs of less than 37kg liveweight

For lambs of less than 37kg liveweight, various factors need to be considered. The majority of farmers have access to grass silage and concentrates.

However, silage quality is very variable. Silage should not be used to fatten store lambs without first having the silage analysed and then should only be considered if the silage is of top quality, greater than 75% DMD.

The average DMD of silage analysed for Teagasc clients in 2013 was less than 69% DMD. It was substantially below this in 2012. This emphasises further the need for silage analysis.

The majority of farmers should not use silage as the main portion of the diet to fatten lambs. Even when top-quality silage is available, it is generally still more attractive to fatten lambs on an all or high-concentrate diet.

The information outlined in Table 2 compares expected lamb performance on three finishing diets. In all cases, silage is good quality with a DMD of 75%.

Concentrates fed ad-lib or at rates of 0.8kg or 0.5kg fed with ad-lib silage are compared. When concentrates are offered ad-lib, it is common practice to offer a small level of silage, such as 0.1kg silage dry matter to help prevent digestive upsets.

As can be seen from the data presented in Table 2, the benefits of finishing lambs on all or high concentrate diet as opposed to silage and concentrates are described below:

  • Higher liveweight and carcase gain;
  • Higher kill-out proportion, therefore higher carcase weight for a given liveweight;
  • Lambs reach slaughter weight much quicker
  • Extra batches of lambs can be put through the system in a given time frame;
  • Reduces fixed costs per lamb going through the system;
  • Lamb performance is predictable on an all-concentrate diet;
  • Higher margin over feed;
  • Do the budget

    A decision to fatten lambs or not must be based on good economics. You need to do the figures for your own situation.

    Factors you need to consider include:

  • Price of store lamb;
  • Price of a good quality ration;
  • Availability of a suitable well-ventilated shed to house the lambs;
  • Price of straw or availability of slats;
  • Medicines required and their cost (worms and fluke, dipping or pour-ons, vaccinations and foot treatments);
  • Expected price per kg carcase when you go to sell the fat lambs;
  • Anticipated mortality.
  • Selecting and preparing for store lamb fattening

    Finishing period

    The length of time taken to finish store lambs is affected by many factors:

    These include:

  • Liveweight at start of fattening period;
  • Target weight at slaughter;
  • Whether the lambs have gone through a store period leading to some form of setback;
  • Growth rate during the finishing period which is determined by a number of factors including diet offered and the health of the lambs.
  • The heavier the lambs are at start of finishing period, the less time it will take and the less it will cost to take them to their target slaughter weight.

    This will have a bearing on the diet option chosen to finish the lambs. Lambs that have gone through a store period and suffered some setback will also take some extra time to recover and reach desirable growth rates. These will benefit from receiving additional protein in their diet to help them recover as quickly as possible.

    Lambs that are light due to having suffered some setback will therefore be worth less money than lambs that are light but young and healthy.

    Health

    Lambs that have had health issues in the past such as severe worm or fluke burden or other problems may thrive poorly and should be avoided. For home-produced lambs that have had health problems, it is worth considering slaughtering at light weights as it could prove very costly to take to normal target slaughter weight.

    Quarantine Dose

    All bought-in sheep should be quarantined for as long as possible, ideally at least three to four weeks to ensure they are healthy and to avoid spreading any diseases to the sheep already on the farm.

    They should be treated as potential carriers of worms that are resistant to anthelmintics. Therefore, they should be given a quarantine dose comprising of either an abamectin and derquantel combination product (5-S1 Startect) or with a moxidectin (3-ML) injection and a 4-AD monepantel drench (Zolvix).

    The lambs should also be treated for liver fluke with a product effective against immature fluke. The animals should be held in the yard or housed for 24 to 48 hours to allow time for any worms that survive the dose to be passed out of the sheep in their faeces.

    Other Treatments

    Vaccination: Store lambs should be vaccinated against clostridial diseases, with a normal course involving two injections 4-6 weeks apart.

    Lameness: Regular foot-bathing in either 10% Zinc sulphate or 10% copper sulphate is essential to prevent lameness becoming a problem.

    Blowfly Attack: In mild weather in September or October, blowflies can still cause a threat and a treatment may be justified.

    Scab: Either dip lambs or use an injectable product suitable for scab treatment. This may be covered by the wormer used at time of quarantine dosing.

    Withdrawal dates: Observe withdrawal dates with medicines used. Particular care will be needed with lambs that will have a short finishing period.

    Preparing grass

    When lambs are being finished on grass, careful planning is essential in advance. Performance is maximised when grass is green to the butt and is approximately 6cm to 7cm in height.

    This involves ensuring the fields/paddocks required are grazed out well in early autumn approximately a month before being required. (A longer rest period is required as we move into late autumn or early winter).

    Pasture would have benefitted from an application of fertilizer Nitrogen, (plus Phosphorous and Potassium if soil levels are low). However, any Nitrogen required should be applied by mid-September and preferably several weeks before that.

    Ensure fences are stock-proof to enable management of a rotational grazing system. Where fields are large, erect some temporary electric fencing. A rotational system, allowing lambs graze out paddocks in three to four days, and then moving on to fresh pasture, helps maximise growth potential.

    Housing

    A number of factors should be considered when housing lambs for fattening. It is essential to provide adequate lying and feed space as described in Tables 3 and 4.

    Ventilation is probably the most important factor to get right, as failure to do so can lead to major disease outbreak and high mortality. The house should be airy with free air movement. However, ensure there are no draughts at sheep level.

    Water

    An ad-lib supply of clean fresh water is critical, whether lambs are housed or fattened outdoors. Growing sheep require up to three litres of water per day.

    Make sure all lambs can access the trough. Particular care is needed with small lambs as they may not be able to reach a high trough. Concrete blocks placed in front of the trough for small lambs to use as a step may help.