259
4 Discussion
4.1 Fatty Acid Composition in M. Longissimus Dorsi (LD)
The higher proportion of palmitic (C16:0) and oleic (C18:1) acid observed in LD
muscle from concentrate-supplemented goats may be due to the higher intake of the
concentrate diet (Table 1). In agreement with our findings, Aurousseau et al. (2004)
and Pordomingo et al. (2012) observed a rapid increase in the proportion of C16:0 in
the longissimus muscle when the lambs and cattle were shifted from grazing to
concentrate feeding. Saturated fatty acids such as palmitic, myristic (C14:0) and
lauric (C12:0) raise LDL-cholesterol concentrations in blood, a risk factor for cardiovascular diseases (Lee et al. 2008). However, the health benefits associated with
higher proportion of rumenic acid (a CLA), oleic acid as well as DFA recorded in
LD from concentrate-supplemented goats partially compensate for the disadvantages associated with increased levels of C16:0. Conjugated linoleic acids (CLA)
have been shown to have a number of health-promoting benefits including anticarcinogenesis, improved immune system and lipid metabolism and prevention of
diabetes and cardiovascular diseases (Schiavon et al. 2011; Carvalho et al. 2015;
Bravo-Lamas et al. 2016).
The higher proportion of CLA observed in LD from goats on higher levels of
concentrate supplementation (T66 and T100) in the present study agrees with that
of Warren et al. (2008) and Horcada et al. (2012) and could be due to increase in
fatness (Juarez et al. 2008). However, Juarez et al. (2008) reported an increase in
CLA content as a result of switching from a concentrate-based diet to pasture. We
have no plausible explanation for this discrepancy. In the rumen, linoleic (C18:2
n-6) and linolenic (C18:3 n-3) acids are hydrogenated to stearic (C18:0) acid
(French et al. 2000; Warren et al. 2008; Bessa et al. 2008). However, increased levels of linoleic acid in ruminant diet tend to block complete hydrogenation of unsaturated fatty acid leading to accumulation of intermediate products such as vaccenic
acid (C18:1 trans 11) and CLA in the rumen (Bas and Morand-Fehr 2000; Marinova
et al. 2001; Daniel et al. 2004; Pordomingo et al. 2012). Part of these intermediates
escape the rumen and are incorporated into body tissues and ruminant products. In
addition, compared to forage diets, concentrate-based diets have a higher quantity
of available carbohydrate, which shortens the retention time of feed in the rumen,
consequently reducing the extent of biohydrogenation of polyenoic acids (Diaz
et al. 2002; Demirel et al. 2006). Ruminant products are the major natural source of
CLA. Juarez et al. (2008) reported a positive relationship between cis 9-trans11
CLA isomer content in meat and total fat content. Overall, the comparable proportions of CLA, linolelaidic, oleic, total MUFA as well as n-6/n-3 PUFA ratio in LD
from T66 and T100 goats suggest that there is no gain in the deposition of such fatty
acids beyond concentrate supplementation at 66% of ad libitum intake.
The decrease in n-3 in LD from goats on high levels of supplementation could be
attributed to an increase in fatness. Increased fatness is associated with an increased
proportion of SFA and MUFA in neutral lipids and a decline in the proportion of n-3
PUFA caused by dilution from SFA (Warren et al. 2008; Lee et al. 2008). In addition,
Effects of Concentrate Supplementation on the Fatty Acid Composition of Fat Depots…
4 Discussion
4.1 Fatty Acid Composition in M. Longissimus Dorsi (LD)
The higher proportion of palmitic (C16:0) and oleic (C18:1) acid observed in LD
muscle from concentrate-supplemented goats may be due to the higher intake of the
concentrate diet (Table 1). In agreement with our findings, Aurousseau et al. (2004)
and Pordomingo et al. (2012) observed a rapid increase in the proportion of C16:0 in
the longissimus muscle when the lambs and cattle were shifted from grazing to
concentrate feeding. Saturated fatty acids such as palmitic, myristic (C14:0) and
lauric (C12:0) raise LDL-cholesterol concentrations in blood, a risk factor for cardiovascular diseases (Lee et al. 2008). However, the health benefits associated with
higher proportion of rumenic acid (a CLA), oleic acid as well as DFA recorded in
LD from concentrate-supplemented goats partially compensate for the disadvantages associated with increased levels of C16:0. Conjugated linoleic acids (CLA)
have been shown to have a number of health-promoting benefits including anticarcinogenesis, improved immune system and lipid metabolism and prevention of
diabetes and cardiovascular diseases (Schiavon et al. 2011; Carvalho et al. 2015;
Bravo-Lamas et al. 2016).
The higher proportion of CLA observed in LD from goats on higher levels of
concentrate supplementation (T66 and T100) in the present study agrees with that
of Warren et al. (2008) and Horcada et al. (2012) and could be due to increase in
fatness (Juarez et al. 2008). However, Juarez et al. (2008) reported an increase in
CLA content as a result of switching from a concentrate-based diet to pasture. We
have no plausible explanation for this discrepancy. In the rumen, linoleic (C18:2
n-6) and linolenic (C18:3 n-3) acids are hydrogenated to stearic (C18:0) acid
(French et al. 2000; Warren et al. 2008; Bessa et al. 2008). However, increased levels of linoleic acid in ruminant diet tend to block complete hydrogenation of unsaturated fatty acid leading to accumulation of intermediate products such as vaccenic
acid (C18:1 trans 11) and CLA in the rumen (Bas and Morand-Fehr 2000; Marinova
et al. 2001; Daniel et al. 2004; Pordomingo et al. 2012). Part of these intermediates
escape the rumen and are incorporated into body tissues and ruminant products. In
addition, compared to forage diets, concentrate-based diets have a higher quantity
of available carbohydrate, which shortens the retention time of feed in the rumen,
consequently reducing the extent of biohydrogenation of polyenoic acids (Diaz
et al. 2002; Demirel et al. 2006). Ruminant products are the major natural source of
CLA. Juarez et al. (2008) reported a positive relationship between cis 9-trans11
CLA isomer content in meat and total fat content. Overall, the comparable proportions of CLA, linolelaidic, oleic, total MUFA as well as n-6/n-3 PUFA ratio in LD
from T66 and T100 goats suggest that there is no gain in the deposition of such fatty
acids beyond concentrate supplementation at 66% of ad libitum intake.
The decrease in n-3 in LD from goats on high levels of supplementation could be
attributed to an increase in fatness. Increased fatness is associated with an increased
proportion of SFA and MUFA in neutral lipids and a decline in the proportion of n-3
PUFA caused by dilution from SFA (Warren et al. 2008; Lee et al. 2008). In addition,
Effects of Concentrate Supplementation on the Fatty Acid Composition of Fat Depots…