Lentils are grown primarily in Western Canada for export and for human consumption. Each year, however, part of the production does not meet the grade for export and is used by the feed industry. The latter is attracted by the low price of the product. Lentils belong to the pulse crop family and have a chemical composition quite similar to that of peas, widely used in swine nutrition.

Flaxseed, for its part, possesses properties that make it unique as a feed ingredient, not the least of which is a highly desirable fatty acid profile in the lipid fraction. Possible future uses for flax include the production of omega-3 fatty acid-enriched pork, the development of alternatives to antimicrobial growth promoters and the enrichment of sow diets for essential fatty acids.

Since the use of these unconventional ingredients in swine nutrition is poorly documented, the Prairie Swine Centre carried out a series of experiments in order to determine the composition and nutritional value of lentils in pigs and to study the inclusion of flaxseed in the rations of growing pigs.

Lentils

Two lentil samples were considered for the study: a blend of brown, yellow and red lentils and frozen lentils. The two samples had a quite similar composition, with an average of 27 % of crude protein, 18% of total dietary fibre and more than 40% of starch. On the contrary, the ash and fat contents were very low, accounting for only 3 and 1 % of the dry matter, respectively. The composition is comparable to that of peas, except that the crude protein content is higher than that of peas (22%) and the starch content lower (50% for peas). The amino acid profile is also typical of pulses with a high level in lysine (6.2% of the protein) and a low level in sulphur-containing amino acids (methionine and cysteine: 2%). The lysine level is lower than that of peas (7.3%).

The digestible energy value reached 3,715 kcal DE/kg DM in both cases, which is slightly lower than the value obtained for peas (3,850 kcal/kg DM) but comparable to that of faba beans (3,750 kcal). The digestibility of the protein, measured at the end of the small intestine (ileum) reached 62% on average, which is in agreement with other studies carried out on pulses. For the frozen lentils, no definitive value of protein digestibility could be obtained, for problems encountered during the study but, according to our observations, the value was markedly lower than that obtained for the blend of lentils, which indicates that freezing conditions affect the digestibility of the proteins.

As a conclusion, lentils constitute an appreciable ingredient for the pig, with a nutritional value slightly lower than that of peas, which means that the rate of inclusion in the diet of growing-finishing pigs will probably not exceed 20% of the total.

Flaxseed

Flaxseed is a grain with high levels of oil (35%) and crude protein (25%). The high oil content makes flaxseed a major energy source for the pig (4,650 kcal/kg DM). However, the main interest lies in the oil composition. The oil is mainly composed of linolenic acid, which belongs to the omega-3 group. Pork producers want to know if it is possible to produce omega-3 enriched pork by supplementing the diets with flaxseed. Before any conclusion could be drawn on the quality of the end-product, it was necessary to evaluate the response of pigs to flax in their diet, to confirm the nutrient profile previously developed and to determine if the feeding of relatively high levels of flaxseed causes changes in performance not predicted by the nutrient profile.

Therefore, a growth experiment was carried out with growing pigs fed with diets containing 0, 5, 10, 15 or 20% of flaxseed, at the expense of a control diet composed of barley, wheat and soybean meal. In order to distinguish between the effect of flaxseed and that of the oil level in the diet, four other diets were supplemented with canola oil, in order to match the amounts of oil in the flaxseed diets. The diets contained, respectively 2.2% oil (control diet), 3.5%, 5.0%, 6.7% and 8.5 oil.

There was no adverse impact of flaxseed inclusion on average daily gain, up to 15% inclusion. The highest level of flaxseed inclusion tended to reduce growth rate, something also observed at the highest canola oil inclusion. The highest level of canola oil inclusion significantly reduced daily feed intake; this was probably due to the fact that the canola oil was not completely absorbed from the diet. Intake of the high flax diet was greater than that on the high canola oil diet. There tended to be an increase in feed efficiency at the lower levels of oil inclusion, whether from flaxseed or canola oil; however, only the canola oil diets sustained this improvement at the highest levels of inclusion.

No relationship (r = 0.03) was found between digestible energy intake and average daily gain (Figure 1). This illustrates the fact that the inclusion of up to 15 % flaxseed in the diet does not affect the pig’s performance.

The Bottom Line

It can be concluded that balanced diets containing up to 15 % flaxseed will not adversely affect the average daily gain, feed intake or feed efficiency of growing pigs and that growing pigs tolerate high levels (~ 7 %) of fat in the form of flaxseed better than equivalent levels of canola oil.

January 2006