When lambs are put onto finishing diets we tend to offer the same diet to all breeds and sexes and assume they consume consistent intakes.
But as Dr Ruth Lawson, ruminant nutritionist at W.E. Jameson and Son, explains: “Differences exist between breeds and between individual lambs which may result in inefficiencies if we do not acknowledge this.
“For cattle, we formulate different rations for different breeds and sexes. Black and white bulls are fed differently to Aberdeen-Angus heifers. However, with sheep there is not the difference in rations for different classes of animal.”
Basic good practice is needed whatever the breed and if buying in store lambs, they should be dosed for fluke and worms on arrival and receive clostridial vaccinations. Ammonium chloride should always be included in the ration to prevent urinary calculi (stones) in intensively fed male lambs.
Dr Lawson says: “The transition from autumn grazing to indoor finishing must be handled with care. There is a delicate balance between cereal content and rumen stability. Even when the price of cereals is low, relying too heavily on them to make up most of the ration is not a good idea.
“Starch sources need to be balanced with feeding sources of digestible fibre, such as sugar beet, as this will improve liveweight gain and get lambs onto feed quicker. Rations which contain at least 25 per cent of digestible fibre energy work well. This can be lowered gradually to a minimum of 10 per cent over the first six weeks if more starchy feed is needed.”
Work at ADAS Rosemaund showed growth rates for small breed hill lambs finished indoors improved by 15g/day when switched to rations based on digestible fibre, rather than cereals.
This may be partly due to better intakes with a more palatable ingredient and more settled rumens with some digestible fibre. Hill breeds seems to show more variation in intake than continental breeds and also seem to take longer to go onto feed.
Dr Lawson says: “Yeast is a useful inclusion in lamb finishing diets as it helps rumen stability and feed conversion efficiency and is a must for high cereal diets. Research studies demonstrate yeast supplementation to finishing lambs fed high energy diets improves weight gain and feed-to-gain ratio.
“Lambs can be given access to straw to help stabilise the rumen. Studies from the University of Zaragoza, Spain, showed the absence of cereal straw was a source of stress for lambs, which affected their behavior during fattening. In general, aggressive interactions were higher with lambs without straw.
“Care must be taken feeding hill breeds to make sure they do not get fat, particularly wethers. Rations containing digestible fibre as well as cereal as an energy source will help prevent this, as will ensuring protein level is high enough.
“A barley diet will result in more kidney fat and fattier carcases. Processing has no positive influence on the liveweight gain. Work from Finland found lambs receiving crushed or ground barley or oats had a lower final liveweight than those receiving whole grains. The use of wholegrain was more efficient than that of processed grain.”
Studies from Teagasc show both Texel and Blackface ram lambs had a higher daily gain and were more efficient converters of ration to liveweight gain than castrated wether lambs.
As expected, ram lambs had lower killing out rates. For carcase weights of 20.5kg, the Scottish Blackface lambs were becoming over fat.
Dr Lawson says: “This would suggest that when finishing Scottish Blackface wether lambs on an all-concentrate diet, the target carcase weight should not be more than 18.5-19kg. However, ram lambs can be brought to a heavier carcase weight without becoming over fat.
"Furthermore, animals beginning the feeding period as light lambs [<25kg] have a faster liveweight gain than medium lambs. This might indicate there was some compensatory growth in the lighter lambs, meaning these light lambs could be a better buy than their face value would show.”
There can be a large variation between lambs for intake of concentrates and how quickly they get onto feed. Data collected at W.E. Jameson and Son, by Olivia Ward showed some lambs fed barley had intakes as low as zero during the first two weeks of going onto feed. Intakes also varied considerably throughout the trial.
Dr Lawson says: “Much of the variation in performance is directly related to the intake of concentrate feed by the lamb. Lambs with high intakes of 1.8-2.0kg per day can perform at close to 450-500g per day. While lambs eating less than 1kg per day will perform at about 100g per day. Therefore, in any group of lambs there is going to be a mixture of low- and high-performing lambs.
“Anything we can do to improve palatability and acceptability of rations will help reduce this variation. Managing the transition onto indoor feeding should also be started as soon as possible.
“The optimum crude protein concentrate is between 14.5 and 16 per cent. but will depend on forage and breeds (i.e. rate of liveweight gain).”
Making a healthy diet
To achieve high performance and encourage a healthy gut, the diet should combine high starch sources for rapid gain with high energy fibrous ingredients to help keep the rumen balanced