Amino acids in swine diets are under review internationally. Although revised estimates of requirements or allowances are also being proposed for the nursery pig and for the later stages of the finishing period, the most important revisions may be those relating to the nutrition of the gestating sow.
The obvious situation facing formulators everywhere is that the modern sow produces more piglets and more milk than her counterparts of only a few years ago. Inevitably, it has meant a significant change in her requirements for amino acids. However, the methods for estimating how much of the essential amino acids are required have still to be refined.
Hot topics
Digestibility and availability remain hot topics in this respect. That was underlined when representatives of pork production from North America and Europe met earlier this year for the latest annual Banff Pork Seminar in Canada. The delegates were told that a clearer idea of the difference between sows and growing pigs in terms of amino acid digestibility could make a big impact on diet costs.
It seems today that the standardized measurement of ileal digestibility for lysine and other amino acids in common feed ingredients such as corn and soybean meal would show a significantly greater value for the sow than for the growing pig. If confirmed, the ingredient inclusion levels for sows could be adjusted to achieve a lower cost without impacting performance.
Most of all, this is suggested to relate to the sow in gestation. For several years now there has been evidence that most amino acid digestibilities in gestating sows can be assumed to be approximately mid-way between those of growing pigs and of sows in lactation. More recently, however, the U.S. research reports have referred to trial results showing limit-fed gestating sows having higher standardized digestibility coefficients than for growing pigs or for lactating sows fed ad lib.
At the same time, the point was made that comparison is made difficult not only by differences in feed intake but also by the concentration of amino acids in the diet. What is more, the higher digestibility attributed to gestating sows may be less true for certain amino acids such as tryptophan than for lysine.
Estimated needs
The newer estimates of the amino acid requirements of sows appear more clear-cut. In particular, European sources have joined together in suggesting that these requirements increase in the final part of gestation.
An early test of this concept in Denmark had cast some doubt on its value, when half the gestating sows in the trial herd were given a diet that was complied with current national standards for amino acids in gestation while the other half was switched in the final month on to a lactation-type amino acid profile. In this instance, the extra feeding produced no additional litter weight at farrowing, nor was there any less variability for size between the individual pigs.
But Danish advisers insist from practical experience that sows receiving more protein or amino acids in their feed in the last four weeks before farrowing go on to give birth to heavier piglets.
Strong support for this view can be seen in recently revised recommendations in Germany. Since its revision completed in 2006, the German animal feeding authority Gesellschaft für Ernährungsphysiologie or GfE has advocated feeding to promote the growth of fetuses by adding to the amino acid levels for sows from Day 85 of gestation.
In a similar direction, Canadian studies at the University of Alberta were reported to the Banff seminar to have demonstrated a doubling of the sow's requirement for threonine in the final third of gestation, in order to achieve maximum synthesis of protein for the litter.
Recommendations
Of course, in a North American context, such remarks will always be judged alongside the published recommendations of the National Research Council. Alberta's indications on the late-stage gestation needs for threonine are considerably above those cited by NRC in 1998. Other work at the same center has reported that whereas NRC-98 said non-pregnant sows needed 36 mg/kg0.75 of lysine per day for maintenance, the daily lysine requirement in a high-productivity population of Hypor sows was determined to be about 30% greater at 49 mg/kg0.75.
There is also a seasonal factor to be taken into account. In Alberta's results, the heat production of the sows was shown to be at its lowest when their dietary lysine was at least adequate, at 46.8 mg/kg0.75. The risk of heat stress on sows in the summer months often is addressed by an adjustment of the nutrient density of their diet as compensation for any downturn in daily feed intake. While feeding less crude protein to the sow in hot times certainly works, however, the percentage reduction achievable in practice is limited by the necessity of maintaining the balance of amino acids available through the feed.
A common way of judging the essential amino acids (apart from lysine) required by the lactating sow depends on determining how much she secretes in her milk. But this is appropriate only for those amino acids actually involved in milk production. Therefore, it says little about the requirement for maintenance or growth.
Kansas State University researchers have drawn attention to the further difficulty of a lack of published studies into the requirement of the lactating sow for sulfur amino acids. Their own investigations have yielded clues that the ratio of total sulfur amino acids to lysine should be well above 50%, not the 48% calculated from NRC-98 recommendations.
Optimal lactation diet formulations are also now said to be increasingly related to the sow's parity. The case is made for special feeding of first-parity females so that their daily lysine intake is maintained despite a typically smaller appetite for feed. It also appears that for these same animals, achieving top reproduction results imposes an even higher lysine requirement than for most milk production.
Feeding by parity imposes obvious strains on storage and equipment inventory as well as on management control.
Nevertheless, herd owners with enough sows and an appropriate production site organization to handle separate feeds should benefit from the split approach. It should certainly be less expensive than the alternative of giving a higher-nutrient diet to all sows in the herd.
Multiple-phase feeding
In fact, the case is being made for multiple-phase feeding of modern high-performing sows in both gestation and lactation.
This could supply the extra nutrients considered useful in late gestation, rather than the usual approach of providing the same feed type in a set amount each day throughout pregnancy. It would recognize the parity differences in lactation.
There should be the additional advantage of a saving in total feed usage, particularly if late-gestation increases succeed in cutting the loss of backfat cover during lactation so that less compensatory feeding is needed to restore condition after the next weaning.
Special first-parity formulations for both gestation and lactation also can take account of new research, such as that published last year in the Journal of Animal Science, arguing for an increased supplementation of arginine in diets given in the first parity as a boost to pre-weaning piglet growth rates. The weight gained while in the suckling period was significantly better for piglets from supplemented sows.
