3.0 Effect of Canola Oil on Animal Pathology
In terms of animal pathology there appears to be little difference whether canola or high-erucic acid rapeseed (HEAR) oil is fed. Corner (1983 {1915}) concluded that degenerative lesions seen in the hearts of swine fed various rapeseed oils bear no relationship to the diet fed and the feeding of HEAR oils to swine produces lipidosis only slightly more severe than when control oils are fed. This is in agreement with Kramer and Sauer (1983 {1923}) who summarized that pigs fed diets without added oil or varying levels of control, LEAR or HEAR oils do not develop specific diet induced heart lesions. Heart lesions that were present were generally much less severe than those found in rats. Chuang et al. 1995 {1623}) found rapeseed oil may inhibit the incorporation of arachidonic acid into lung lipids and thereby reduce the production of prostanoids which modulate physiological and pathophysiological reactions like vascular resistance, thrombosis, wound healing, inflammation and allergy.
For young piglets high levels of rapeseed oil addition
are not generally recommended. The inclusion of 100g kg-1
rapeseed oil (0.40g kg-1 erucic acid) in the diet of
newly weaned pigs resulted in ultrastructural modification to
the liver. These included a loss of microvilli in the bile canaliculi,
dilation of the lumen, closely aligned mitochondrial cristea,
elevated peroxisomes and an unusual increase in the size and number
of membrane bound spaces in zone 3 of the liver acini. The loss
of microvilli may affect the flow of bile and disturb lipid metabolism
(Cullen et al. 1996 {1617}).
4.0 Meat Quality and Carcass Composition of Pigs Fed Canola Oil
Increasing dietary rapeseed oil (0-160g kg-1) did not alter total intramuscular fat but did influence fatty acid composition (Jorgenson et al. 1996 {1615}). The neonate pig is capable of desaturation-elongation of the 18:2-n-6 and 18:3 n-3 fatty acids of canola oil to produce C20 and C22 PUFA. By using a milk replacer containing canola oil both the level and type of fat deposited in the carcass can be controlled (Farnworth et al. 1994 {1649}). Significant increases in the n-3 (omega 3) polyunsaturates can be attained in accord with contemporary diet recommendations by the addition of 20g kg-1 canola oil and 10g kg-1 fish oil to the diet of pigs, with no appreciable differences in carcass characteristics (including color) and no difference in acceptability of chops or sausages (Leskanich et al. 1997 {1604}). At higher levels of canola oil inclusion, an increase in the linoleic and linolenic content of adipose tissue corresponds negatively with firmness (r=-0.83) (Soumi et al. 1993 {1714}; Jaskiewicz and Matyka 1995 {1618}.)
Inclusion of 200g kg-1 canola oil in
the diet of growing pigs decreased saturated fatty acids in adipose
(from 40 to 15%) and muscle tissue (42 to 23%). These changes
occurred without any effect on backfat thickness, longissimus
muscle area or marbling scores. Although the fat was substantially
more oily and soft, sensory panel evaluations indicated no differences
in juiciness, flavor, tenderness or connective tissue content.
Intermediate changes were noted with the addition of 100g kg-1
canola oil (St. John et al. 1987 {1873}; Myer et al.
1992 {1752}). Contrary to the above findings, two studies (Shackleford
et al. 1990b {1812} and Shackleford et al. 1990a
{1806}) found sensory panelists rated canola oil fed bacon and
hams lowest for both visual quality and palatability. Canola
oil treatments had the most reported off flavors as compared to
the beef tallow control (65% versus 5% in bacon and 25% as compared
to only 2.5% in the ham) due to linolenic acid oxidative products.
As well, canola oil treatments (100g kg-1 of diet)
decreased pork belly slicing yields (because the tissue was not
firm enough to withstand pressing and slicing). Miller et
al. (1990 {1808}) attributed higher off flavours in chops
to 2-pentanol and 2,4 heptadienal derivatives of linolenic acid.
Oxidative rancidity of fresh pork sausage was higher for canola
oil than safflower, sunflower or beef tallow (100g kg-1
addition level); however, it still was below half the unacceptable
limit. Color evaluation indicated that initially the canola oil
treatment had the lightest color, but after 10 weeks there was
no distinguishible color differences between any of the oil treatments
(Miller et al. 1993 {1707}). No significant effect on
muscle cholesterol content was noted with diets containing 100-200g
kg-1 canola oil (Bohac and Rhee 1988 {1855}). The
best overall perspective was provided by Myer et al. (1992
{1767}), where canola oil (50 and 100g kg-1) in grower-finisher
diets improved performance (ADG and FC) when the ME:lysine ratio
was kept constant. Marbling appeared be lower in canola fed diets
however, analysis of the loins proved that marbling was present
but not visible. As expected a reduction in total saturated fatty
acid level in the back fat was obtained (23% less for 5% canola
oil), and carcass firmness was still acceptable to the packer
at the 50g kg -1 oil inclusion level.