WITH THE quality of conserved forages poorer than usual this winter – and the weather – this means greater dependence on supplementary feed for pregnant ewes if they are to lamb down with the ease and supply colostrum that present-day reduced shepherding demands.

So what is important when it comes to scrutinising compound feed formulations and deciding on which one to opt for?

Because of their importance to lamb vigour at birth and the acquisition of immunity to disease, vitamin E and selenium are often highlighted in compound feed industry adverts for ewe feeds. So, too, is iodine.

But here a word of warning. Too high a level of iodine in the ewe’s diet, particularly those grazing close to the sea where forage iodine levels may be above average, can impair the new born lamb’s ability to absorb colostrum’s immunoglobulins and vitamin E that are essential for combating infection.

Through its role in maintaining blood calcium levels, vitamin D is important in reducing the risk of hypocalcaemia, but again supplementary levels in compound feeds are normally more than adequate.

Hypocalcaemia is more likely to arise from too high a level of calcium in the diet coupled with an associated sudden fall in dietary supply as a result of an abrupt change in feeding strategy and/or a metabolic upset, such as acidosis.

For energy, the indicator of quality is metabolisable energy(ME) concentration, with expected values for compound concentrate feeds being 12 to 12.5 MJ/kg dry matter.

A key requirement of a compound concentrate feed is its ability to act as a supplement to forage rather than a substitute for forage. Avoidance of cooked and finely milled ingredients and by-products from the biscuit and confectionary industry is, therefore, recommended as it leads to a more stable rumen fermentation and better digestion of plant fibre than highly-processed and rapidly fermenting ingredients.

These conditions are favourable for good rumination, good levels of forage consumption and optimal yields of rumen microbial protein for digestion in the small intestine.

Despite all the advances that have been made in understanding protein metabolism and protein needs of the ewe in late pregnancy and early lactation, the absence of any useful information on the nature of the protein (rumen degradable verses undegradable) in compound sheep feeds is a major concern.

A crude protein percentage tells us nothing about the ability of a compound feed to supply the useful protein that is essential for the rapid growth of the unborn lamb and the production of colostrum.

Neither does digestible crude protein. In fact, protein sources such as rapeseed and sunflower have high values for crude protein digestibility but much of this so-called digestible protein is too rapidly and extensively degraded to ammonia in the rumen for the ammonia to be synthesised into high-quality microbial protein.

As a result, too much of it ends up being excreted as urea via the kidney. Not only does its excretion put an extra burden on the ewe but, as a fertiliser, it makes the current high price of nitrogen fertiliser look remarkably cheap.

Therefore, as far as the protein quality of sheep feeds is concerned, one has to rely on the ingredient list for guidance.

With the gold standard for protein supplements, fish meal, banned, then in terms of providing the essential extra high quality rumen undegradable protein that can make the difference between success and failure, soyabean ranks half as good as fish meal; rapeseed is less than half as good as soyabean and sunflower less than a third as good as soyabean.

So look at the ingredients when making your choice; the cheapest now may be the most costly in the long run!