While variety is often referred to as the spice of life, it is not always a good thing. The benefits of variety and choice are clearly demonstrated across the pages of the 2011 directory, and the various entries cater to each and every individual need.

But there are times when variety can lead to confusion, and a lack of clarity can lead to the wrong choices. There are times when choices need to be limited and standards measured.

The need for new measures and standardization were amongst the areas discussed at the 1st International Phytase Symposium, held in Washington DC, toward the end of last year.

Demand and definition  

This need for greater measurement and understanding continues to increase. Hardly a day goes by without reports of the rising prices of key feed ingredients, and this understandably adds to the pressure on feed manufacturers to maximize the efficiency of nutrient utilization.

Much of this cost pressure has been on two nutrients in particular: energy and phosphorous. One solution to this problem is to use phytase at considerably higher rates, as this would not only increase phosphorous release from phytate, but also spare energy.

One of the strongest messages to come out of the symposium, which was jointly hosted by AB Vista, Massey University, the University of Maryland and the University of Sydney, was that the extensive use of phytase enzymes in pig and poultry diets has raised the need for more accurate determination of phosphorous and calcium requirements.

Alongside this, another key issue is the ongoing differences in terminology and methodology and how this could hold back progress. For example, AB Vista’s technical manager, Dr Peter Wilcox, noted that pig and poultry requirements in the US were predominantly stated as “available” phosphorous, while in Europe, the dominant terminology was “digestible” phosphorous. Taking into account the huge number of factors affecting phosphorous digestibility, he continued, such as feedstuff variation, genetics, age, weight and calcium-to-phosphorous ratio, making comparisons between different studies becomes difficult.


Hard to choose  

Further difficulties with measurement were also highlighted. There are many phytase products on the market. But which one to choose?

Dr Jan Dirk van der Kils, of Schorthorst Feed Research, noted that without a reasonable standard to measure phytase, it is very hard for nutritionists to make the right decision.

He continued that an in vitro testing methodology for phytase must be accurate, cheap and quick. However, he also highlighted the fact that assays can only really measure degradability, not actual digestibility, due to the large number of interations and variability that exist within a bird, such as the differing response to phytase addition at differing dietary levels. Measurement, therefore, needs to be related to in vivo data.

According to Dr Ralf Greiner of the Max-Rubner Institute, the development of a reliable in vitro assay for phytase efficacy is further complicated by the fact that neither the phytate substrate nor the first degradation product can be measured by spectroscopy. Current assays tend to measure the release of phosphate, which is an inherently less accurate method than measuring the disappearance of phytate itself, he noted.

AB research director, Dr Mike Rutherford, suggested that the variation in phytase activity with pH might not only help to explain differences in bird performance, but also lead to the development of a more effective assay for screening phytases for use in poultry diets. There was good evidence, he stated, that the majority of phytase activity takes place in the stomach and gizzard, with measurements carried out at perhaps pH2.5-3.0 likely to be more relevant to in vivo activity.

So while the use of phytase has increased significantly over the last decade, and is expected to increase further, more work needs to be done to make the most of this important ingredient. However, in the 2011 Buyer’s Guide, a lot of work has been done already so enjoy the results.