Improving Nitrogen Utilization by Pigs: What's New?

Nutrition Update
Volume 13 No.3, February 2003

There have been numerous reports regarding nitrogen utilization by pigs. Reducing the total crude protein in the diet while maintaining appropriate ratios and amounts of the essential amino acids has received some recent attention. While this practice is not new, it may something that nutritionists may want to place more efforts on when formulating diets in the future. Concerns are being expressed that intensive swine production is producing pig manure that may cause pollution. Dietary manipulation may be one method to alleviate some of the environmental impacts of pig production.

Kerr and Easter (1995) concluded that a 1% reduction in crude protein in pig diets, resulted in an 8% reduction in nitrogen excretion. Since synthetic amino acids are becoming a more attractive option to add to diets. Tuitoek et al (1997) reported it was possible reduce the crude protein levels in diets by 2-3% and still maintain performance, provided the diets were supplemented with synthetic amino acids. More recently, Figueroa et al (2002) reported that the protein content of diets for growing gilts could be reduced by up to 4 percentage units, if adequately supplied with synthetic amino acids, without a reduction in performance. Reducing the dietary nitrogen levels has also been demonstrated to have the additional benefit of reducing urinary nitrogen excretion (Zervas and Zilstra, 2002). This may be an effective strategy to reduce ammonia emission from pig barns.

Despite the opportunities to improve nitrogen utilisation and reduce the ammonia emissions that have been demonstrated in most studies, there does not seem to be a consensus as to how low we can go with crude protein before it is too much. It is possible that differences in experimental methodology, including the type of diets used in the experiments, could explain why there is the variability.

To add to the confusion, a report by Crocker and Robinson (2002) brings genetics into this discussion. Their conclusions were that genetic differences may impact nutrient excretion and that gilts excrete different levels of nutrients than barrows.

What does all this mean? Based on the current evidence, providing the appropriate synthetic amino acids and reducing the crude protein levels by about 2% should not reduce production performance of pigs. Nitrogen excretion will be reduced. Reduced levels of nitrogen in the manure could have a positive effect on the impacts of pig production on the environment. Obviously, there is no one answer for all situations. Improving nitrogen utilization, through a combination of dietary manipulation and an understanding of the genetic differences in utilisation could go a long way toward the goal of environmentally sustainable pig production.

References:

1. Crocker and Robinson. 2002. JAS 80:2809-2816.
2. Figueroa et al. 2002. JAS 80:2911-2919.
3. Kerr and Easter. 1995. JAS73:3000-3008.
4. Tuitoek et al. 1997. JAS 75:1575-1583.
5. Zervas and Zilstra. 2002. JAS 80:3228-3246.

Prepared by: Ian R. Seddon, Ph.D.