Canola meal

Nutritional Characteristics:

Canola is a widely grown crop in western Canada and production is increasing in other parts of the world. Production has been influenced by the marked increase in the demand for canola oil as well as the ability of this high protein oilseed to grow in northern climates where the short growing season is not suitable for the production of soybeans.

While canola was derived from varieties of rapeseed, its composition has been altered through genetic selection. The level of goitrogens and erucic acid, two of the more detrimental constituents of the original rapeseed cultivars, have been markedly reduced. Erucic acid levels are now negligible while goitrogen levels are down to less than 20 |jg/g and these levels are low enough to be of little or no problem to poultry. Varieties containing such levels of toxins are classified as canola and are often referred to as 'double zero varieties'.

Canola still has enough goitrogen activity to result in measurable increases in thyroid weight, although this does not appear to be a problem affecting the performance of poultry. The tannin levels in canola can also be relatively high, with up to 3% for some cultivars. Again, research has shown that the canola tannins have little influence in the utilization of the protein in diets containing appreciable levels of the meal.

Canola meal also contains significant quantities (1.5%) of sinapine. While this compound poses no problem to most classes of poultry, a significant percent of brown egg layers produce eggs with a fishy and offensive odour when fed canola sinapines. One of the end products of the degradation of sinapine in the intestinal tract is trimethylamine and it is this com pound, which is involved in the production of fishy- flavored eggs. A small proportion of today's brown egg laying birds lack the ability to produce trimethylamine oxidase which effectively breaks down the compound and so the intact trimethylamine is deposited into the egg. Even 1% sinapine in canola can result in off-flavored eggs. It should be pointed out that brown eggs produced by broiler breeders, are not affected by canola sinapines.

While canola meal has been accepted by the feed industry as a high quality feedstuff for poultry, there continues to be isolated reports of increased leg problems with broilers and turkeys, smaller egg size with layers and in some cases, reports of increased liver hemorrhages when diets contain significant amounts of canola meal. There are several reports which suggest that increased leg problems resulting from feeding canola may be due to its having a different mineral balance than does soybean meal. The addition of dietary K, Na and in some cases Cl have, under certain conditions, altered bird performance. Canola is also high in phytic acid and so there is speculation that the high level of this compound may be sequestering zinc and this affects bone development. The smaller egg size reported with canola meal diets seems to be a direct result of lower feed intake. Canola meal levels should therefore be limited in diets for very young laying hens, or at least until feed intake plateaus at acceptable levels.

Within the past few years, there have been reports suggesting that high levels of sulfur in canola meal may be responsible for some of the leg problems and reduced feed intake noted with canola meal diets. Canola meal contains 1.4% sulfur while soybean meal contains around 0.44%.

Up to 75% of the sulfur in soybean meal is contributed by the sulfur amino acids compared to around only 20% for canola meal. High levels of dietary sulfur have been reported to complex intestinal calcium and lead to increased calcium excretion. This could explain the reports suggesting low availability of calcium in canola meal, and so possibly contribute to more leg problems. While lower weight gain has periodically been reported with canola diets, it is usually noted that feed:gain ratios are little affected. This situation suggests that the reduction in gain was not the result of reduced nutrient availability but rather a direct effect on appetite, resulting in reduced feed intake. Recent work demonstrates quite clearly that a soybean meal diet containing the same level of sul fur as that in canola diets results in comparable weight gain and feed intake in young broilers (Table 2.4). In this study, the unsupplemented canola diet contained 0.46% sulfur while the soy diet contained 0.14%. Adding sulfur to the soybean meal diet resulted in a decrease in weight gain. The level of sulfur in the unsupplemented canola diet (0.46%) lies part way between the levels found in the 0.26 and 0.39% sulfur supplemented soybean meal diet. Weight gain for the unsupplemented canola meal diet was 424 g while the average for the two soybean meal diets was 426 g. Higher dietary calcium levels partially overcame the growth depressing effect of high dietary sulfur thus demonstrating the negative effect of sulfur on calcium retention.

Table 2.4 Interaction of sulfur and calcium in canola and soybean meal diets

(%)

Calcium level (%)

Weight gain (g)

-

.46

.37

424

Canola meal

.26

.72

.37

371

-

.46

1.32

560

.26

.72

1.32

481

-

.14

.37

525

.13

.27

.37

519

.26

.40

.37

479

.39

.53

.37

373

Soybean meal

-

.14

1.32

635

.13

.27

1.32

598

.26

.40

1.32

559

.39

.53

1.32

451

Table 2.4 Interaction of sulfur and calcium in canola and soybean meal diets

In view of the reductions in appetite and calcium retention resulting from high dietary sulfur levels, these need to be closely monitored if substantial levels of canola meal are used. High levels of methionine or sulphate salts, along with ingredients with significant amounts of sulfur, such as phosphate supplements, can add considerable sulfur to a diet. Some sources of water can also be high in sulfur. Broilers can tolerate dietary sulfur levels of up to around 0.5% without any effect on performance while laying hens can handle even higher levels. There are reports which suggest that part of the response to increased levels of dietary sulfur is due to its influence in dietary acid-base balance. While Mongin, in his original work, suggested considering Na, K, and Cl in the dietary acid-base balance equation, S, being a strong anion, should also be considered in this equation if > 8% canola meal is used in poultry diets.

Potential Problems:

Canola meal contains less lysine than does soybean meal but slightly more sulfur amino acids per unit of dietary protein. It is also lower in energy than is soybean meal. Levels of up to 8% canola meal can be used in laying diets without any adverse effects on performance although egg size may be reduced by up to 1 g. Energy content is the factor that usually limits inclusion level. Levels of toxic goitrogens should be assayed periodically, together with tannins. Canola meal should not be fed to brown egg layers.

90.0

Methionine

0.69

37.5

Methionine + Cystine

Lysine

2.21

2000

Tryptophan

0.50

Threonine

1.72

0.65

Arginine

2.18

0.45

0.09

Dig Methionine

0.61

0.05

Dig Meth + Cys

1.08

1.45

Dig Lysine

1.76

0.90

Dig Tryptophan

0.38

Dig Threonine

1.30

Dig Arginine

1.92

12.0

kg/m3

lb/ft3

lb/bushel

625

39

50

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