*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Kamuela, Hawaii. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected].

CANOLA is the registered name for a cultivar of rapeseed containing less than 2% erucic acid in the oil and less than 30 micromol/g of glucosinolates in the air-dried, oil-free meal.

Canola meal is a protein source that is commonly used as an alternative to replace some of the soybean meal in poultry diets.

Although the concentration of glucosinolates has already been reduced to low levels in canola meal, there is experimental evidence that the current level of glucosinolates in canola meal has not yet totally eliminated the liver toxicity problem associated with glucosinolates.

Canola meal also contains a higher fiber content and lower protein content than soybean meal, which probably accounts for the lower metabolizable energy and digestible amino acid content in conventional canola meal versus soybean meal.

Chen et al. of the University of Illinois reported a series of experiments that were designed to determine the true metabolizable energy, corrected to zero nitrogen balance (TMEn), and amino acid digestibility of experimental canola meal samples.

The test meals were produced from new varieties of canola that were developed to contain less fiber and more protein and amino acids. A total of 14 sources of test canola meal, six sources of conventional canola meal and four sources of soybean meal were used in this study.

The 20 canola meal samples and four soybean meal samples were individually assigned to five experiments (a total of 24 treatments in five experiments) consisting of precision-fed rooster assays that were conducted to determine the TMEn and standardized amino acid digestibility coefficients for the 24 canola meal and soybean meal ingredient samples.

In general, TMEn was determined using conventional roosters, and amino acid digestibility was determined using cecectomized roosters. In a few experiments, both TMEn and amino acid digestibility were determined in cecectomized roosters because of bird availability and to expedite the research.

Rather than presenting the individual results for the 24 treatments in the five experiments, I have chosen to consolidate the results in a "meta-analysis." The Table shows the arithmetic average of the 14 test canola meal samples, the six conventional canola meal samples and the four soybean meal samples for each of the items measured. All of the values (with the exception of dry matter) are expressed on a 100% dry matter basis.

I believe this Table captures the essence of the research results. For readers interested in more detail, the original paper is referenced.

The nutrient values for the 24 ingredient samples are shown in the top fourth of the Table. As mentioned, the 14 test canola meals were specifically developed to contain less fiber and more protein and amino acids.

Although there was some variation in crude fiber content, the neutral detergent fiber (NDF) and acid detergent fiber (ADF) were consistently lower in the test canola meals than in the conventional canola meals. However, NDF and ADF in the test canola meals were not nearly as low as in the soybean meals. The crude protein content in the test samples was much higher than in the conventional canola meal samples and was nearly equivalent to the crude protein content of the soybean meals.

The average results for glucosinolates indicated that the levels in conventional canola meals were lower than in the test canola meals. However, these results were skewed by two extremely low values in two conventional canola meal samples: 5.54 and 2.30 micromol/g. These extremely low values suggest that there is an opportunity to genetically select for lower levels of glucosinolates.

Congruent with the lower values for NDF and ADF, the TMEn values for the test canola meal samples were consistently higher (an average of 6% higher) than the TMEn values for the conventional canola meal samples. The measured energy content of the test canola meal samples was higher but still was not equivalent to the energy content of the soybean meal.

The second portion of the Table shows the average amino acid analysis for those amino acids most likely to be deficient in a poultry diet. All of the individual analysis values for the test canola meal were higher than the corresponding individual amino acids for the conventional canola meal, with the exception of a single sample analysis for tryptophan in one test canola meal. On average, the amino acids in the test canola meal samples were 17% higher than the average analysis for the amino acids in the conventional canola meal.

It is interesting that the levels of the sulfur amino acids methionine and cysteine were higher than the corresponding amino acids in soybean meal. This observation would suggest that, in feed formulation, canola meal and, in particular, the test canola meal would be a good complement to soybean meal, which generally is deficient in the sulfur amino acids.

The third portion of the Table shows the standard ileal digestibility (SID) coefficients for the amino acids. The coefficients for the test canola meal were also consistently higher than those for the conventional canola meal (about 4% higher, on average).

The researchers suggested that the digestibility coefficients were higher for the test samples primarily because the test canola meal had lower levels of fiber (NDF and ADF), and fiber tends to reduce amino acid digestibility. Again, the values for the test canola meals were higher but not equivalent to the values for soybean meal.

Multiplying the digestibility coefficient by the total amino acid content resulted in the SID amino acid content shown at the bottom of the Table. The combination of higher total amino acid levels and higher digestibility coefficients resulted in an average of 22% higher levels of digestible amino acid content when comparing the test canola meals with the conventional canola meal samples.

To summarize, the researchers said, "The results of the current study indicated that there were increased (crude protein) and amino acid concentrations and reduced fiber content, as measured by NDF and ADF, for all test canola meal compared with conventional canola meal. In addition, most test canola meal had significantly higher TMEn values than the conventional canola meal samples within experiments, but all were lower than that of soybean meal (P < 0.05).

"For amino acid digestibility, the test canola meal had higher digestibility values than conventional canola meal in experiment 1, 2 and 4 (P < 0.05) and higher concentrations of digestible amino acids in all five experiments because the total amino acid levels were increased," the researchers continued. "These results indicate that genetically selected canola meals contain increased digestible amino acid levels and increased TMEn in poultry and, therefore, are of greater nutritional value compared to conventional canola meal."

The Bottom Line

The experimental canola meal samples tested in this research are not currently available commercially. However, the results provide a glimpse of the potential improvement in nutritional value and economic value of canola meal in the future. The industry can always use new and better feed ingredients in formulations.

Reference

Chen, X., C. Parr, P. Utterback and C.M. Parsons. Nutritional evaluation of canola meals produced from new varieties of canola seeds for poultry. 2015. Poult. Sci. 94:984-991.

Volume:87 Issue:21