High feed ingredient prices dominated the talk at a number of meetings on pig nutrition held in Ireland toward the end of last year. Several of the international speakers insisted that, with the price climate dictating a focus on obtaining the most out of the cereals used in livestock diets, more attention should be paid to the repercussions of the variability inherent in common grains.

"The livestock industries are slowly acknowledging that great variability exists in the energy content of common feed ingredients," suggested Dr John Patience from Canada when addressing a series of pig conferences organised by Irish farm development agency Teagasc. "All of the feed ingredients commonly used by the pork industry vary much more in energy content than most of us expected."

Varying energy values

Dr Patience heads the Prairie Swine Center research establishment in Saskatchewan, Canada. He used an example from work at the centre to illustrate the problem of ingredients varying with regard to energy. The experiments had found a marked contrast between the digestibility energy intended from formulation and the actual DE values measured in the pig.

"Clearly, we tend to overestimate the energy in weaning pig diets," he commented. "But even for growing and finishing pigs, we do not achieve the level of precision in diet formulation that we would like. Errors of this magnitude will definitely have an impact on pig performance."

Fundamentally, he continued, the goal in evaluation is to identify samples that have an inferior nutrient content so the ingredient can be either segregated or discarded. Within reason, lower-quality ingredients can still be fed effectively to pigs provided that they can be identified, characterised, priced appropriately and handled easily within the feed milling complex.

"The challenge rests in finding a solution to this problem. It is certain that bushel weight, the ubiquitous trading standard in the grains industry, must be discarded. Other than for extreme highs and lows, it has proven to be a poor indicator of the actual value to the pig."

A range of energy availability values has been reported for common grains in feeds, as illustrated by Table 1. Practical issues of variability could be addressed, for example, by analysing a specific sample of the grain in order to determine its nutrient composition. But this approach tends to be too slow and cumbersome for application in feedmills that constantly receive consignments of purchased cereals. It is better suited to farms growing their own grain. Another possibility is to handle the variation statistically. The greater the number of sources of grains and proteins in a diet, the less the impact will be of any error in estimating the composition of an individual ingredient. So the outcome of a wrong estimate should be less serious in a mixture comprising, say, two to three grains and proteins than in a simple diet containing only one form of grain and one protein. Errors affecting each ingredient are likely to average out, so the nutrient levels achieved are close to those targeted.

As Dr Patience pointed out, however, there is also the modern choice of using near-infrared spectroscopy. Considerable progress has been made in the use of NIR to sample ingredients rapidly, he remarked. It offers a much faster answer than from traditional laboratory analysis. At the same time, formulators must remember that it is accurate only if the prediction equations are updated on a constant basis.

Formulation on grain characteristics as determined by NIR will become a more regular occurrence, agreed pig nutrition specialists when they met recently in Northern Ireland. Expensive grains must be used to maximum effect and the near-infrared technique meets the need for a reliable way to evaluate them.

Dr Elizabeth McCann of Northern Ireland's ARINI agricultural research institute commented that the accurate prediction of the nutritive value of cereals had become more important than ever in view of the price rises. She called NIR particularly promising for this purpose, reports a note in an Irish advisory bulletin.

Grains do differ in terms of their nutrient digestibility, Dr McCann observed. Such differences can be seen, for example, when comparing one variety of wheat with another. However, her studies have cautioned against assuming that these will necessarily be reflected in animal performance. Feeding different varieties of wheat to pigs demonstrated little connection between variety and results.

Researchers in Australia have developed NIR calibrations to allow dietary formulation to be matched more closely to the characteristics of the grain, revealed Dr Roger Campbell from Australia's coordinated research centre on pigmeat (Pork CRC) to the latest European pig symposium held in Ireland by Alltech.

Understand variability

A current project at the centre involves assessing 40 types of grain for their feeding value, Dr Campbell reported. It has already supported the case for taking care to specify grains closely before formulating with them.

Clues to the variability within grains had existed previously. Among them, Australian trials showed quite a contrast between measurements of available energy for different farm animals when comparing three categories of sorghum (Table 2). In a 1999 comparison at a large Australian pig producing enterprise, wheat cultivars that were apparently similar for DE nonetheless differed in their effect on the amount of the diet eaten by the pigs (Table 3). But now the 40-grain CRC project has already yielded further evidence. The feed intake and efficiency of weaned pigs differed according to the grain type in the diet (Figures 1 and 2). In this work, two types of barley gave daily intakes of 398 grams and 480 grams with feed:gain ratios of 1.41 and 1.22. Comparing types of triticale in feeds for these young pigs, Type 1 was associated with an intake of 396 g/day and 1.35 feed:gain whereas Type 2 produced 478 g/day and 1.09.

"We have seen effects from sorghum and triticale for the feed conversion ratio of the pigs and we know we can find this difference also in wheats and barleys," said Dr Campbell. "The next step is to identify why they differ in this way so that we can work out how to intervene and make them more consistent, such as by the addition of enzymes. Until then, the important thing to remember is that grains are not just grains there are potentially important differences between varieties and batches that need to be recognised in feed formulation."