The first of this year’s spring lamb crop is starting to be marketed, but why might your lambs not be achieving expected growth rates? Laura Bowyer speaks to vet Andy Barrett.
Maximising lamb growth rates is key to production efficiency and mineral deficiency can hamper this, says Andy Barrett, of Kingsway Vets, North Yorkshire.
According to Mr Barrett, slower growing lambs can miss peaks in market prices, increase the number sold as stores and reduce fertility in ewe lambs destined for breeding.
He says: “It is common to identify several potential causes of poor growth rates and it is vital to work out which are the important, primary causes.
“Often, mineral deficiencies are ruled out on the basis free access mineral licks are available. However, these often contain unnecessary trace elements, such as iron and salt, to make them palatable and intake of mineral licks or blocks can be variable, meaning truly deficient animals may not eat enough of the required element.
“All of which means they can be uneconomic compared to targeted supplementation.”
Mr Barrett says the main minerals affecting daily liveweight gain in growing lambs are cobalt and selenium. Any deficiency of these will have a detrimental effect on lamb growth and farm profitability.
“Copper deficiencies also regularly affect young lambs, but do not specifically affect lamb growth. Some soil types are deficient in cobalt but the picture is complicated by the presence of other elements which lock cobalt up and by how different plants take up the element and problems seem to be worse in some years than others.
“Cobalt is converted to vitamin B12 in the lamb’s rumen and this is essential for energy production. Deficient animals have poor appetites and they become ill-thriven with poor quality, open fleeces.”
Mr Barrett says if worms are also present, B12 absorption can be reduced further due to diarrhoea which highlights the need for a thorough investigation of ill-thrift problems.
He says: “Initially, cobalt deficiency can be hard to distinguish from many other causes of poor growth rates and considerable sub-clinical losses can occur.”
Mr Barrett recommends blood sampling to diagnose a deficiency.
“Your vet will advise you on the number and type of animals to sample and also how they should be handled prior to sampling. Cobalt drenching gives a quick but short-lived improvement in blood levels but injections and boluses are available as easier, longer term solutions.”
Large parts of the UK are selenium deficient and problems are therefore more common in certain areas.
Mr Barrett says selenium’s main role is as an antioxidant protecting cells from damage, with the main signs of deficiency being ill thrift and poor daily liveweight gains. Growth rates can be reduced by 10 per cent in selenium deficient lambs.
He says: “Selenium deficiency also causes reproductive problems in breeding rams and ewes, and reduce immune function.
“A diagnosis of deficiency in lambs should prompt investigations in older animals.
“Drenches, injections and bolus supplements are all available.
“These signs can be hard to pick up or attribute to a cause, which again highlights the need to involve your vet.”
White muscle disease can be caused by selenium deficiency, resulting in the death of weak newborn lambs. Stiffness and weakness in older animals is also a specific sign which can
be seen, but Mr Barrett says it is much less common now than it used to be.
“Blood sampling lambs is useful in checking their selenium status and it is essential to confirm a deficiency before supplementing as the element is toxic if animals are overdosed,” says Mr Barrett.
“The signs of deficiency can be subtle and similar to other diseases and more common conditions, such as worm infestations, which can make the picture more complicated. With some veterinary help, an accurate diagnosis will allow effective treatment and restore output.”
The feed conversion efficiency of ill-thriven lambs can be as low as half that of healthy animals, according to Mr Barrett, and they are on the farm longer so input costs are higher and they are more susceptible to other diseases, resulting in higher losses.
He says: “Weighing lambs regularly and benchmarking against growth rates obtained in previous years or by similar neighbouring flocks will help reveal any issues. Uneven growth is usually caused by problems before weaning.”
Problems which occur after weaning tend to affect the flock across the board, resulting in more uniform checks to growth.
Some of the causes can be readily apparent and Mr Barrett says an inspection of a group of lambs should reveal the presence of foot rot, scab or respiratory problems and allow appropriate measures to be taken quickly.
But he says this is not always the case. Many causes of ill thrift are complicated and interdependent. For example, lambs malnourished by poor grazing and affected by worms are more susceptible to the effects of mineral deficiency, although the opposite can also be true.
Mr Barrett advises veterinary investigation under these circumstances, and laboratory tests of blood and faecal samples will be essential in most cases.
“If lambs are scouring, faecal samples should be checked before reaching for the drench gun. Several worm species can cause diarrhoea, including nematodirus in some years, but coccidiosis can also cause this, as can cobalt deficiency or a move onto lush pasture. Fluke may also cause problems,” he says.
“Your vet can advise you on the samples to collect for meaningful faecal worm egg counts which will ensure whether there is a real need to worm and, if so, the appropriate anthelmintic is used which will help reduce the spread of resistant worms.”