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action of ∆-9 desaturase (Aldai et al. 2007), a substantial amount of oleic acid
(C18:1 n-9) found in animal tissues is derived from the concentrate diet (Daniel
et al. 2004). As seen in the present study (Table 1), concentrate diet contained considerable amount of oleic acid. On the other hand, the higher proportions of transMUFA observed in MM from concentrate-supplemented goats could be attributed
to ruminal biohydrogenation of unsaturated fatty acids (UFA). The higher content
of UFA, especially linoleic acid (C18:2), in the concentrate diet than in grass hay is
a probable source of variation. Similar to the findings from the present study, Warren
et al. (2008) found that meat from concentrate-fed animals has higher proportions
of linoleic acid, CLA and vaccenic acid (C18:1 trans 11). However, Aurousseau
et al. (2004) reported that the proportion of vaccenic acid was higher in grazing than
in concentrate-fed lambs, findings that do not correspond with those of the present
study. We have no plausible explanation for this discrepancy. Trans fatty acids have
been linked to increased levels of plasma low-density lipoprotein (LDL) cholesterol, which has negative health effects (Mensink et al. 2003; Bas et al. 2007). The
main trans isomer in meat (vaccenic acid), however, is not a significant risk factor
for cardiovascular diseases compared to trans fatty acids formed by chemical hardening of vegetable oil (Nuernberg et al. 2005).
The observed increase in margaric acid (C17:0) with higher levels of concentrate
supplementation may indicate changes to the rumen environment triggered by
intake of a concentrate diet favouring amylolytic bacterial species and propionate
production (Turner et al. 2012). Oliveira et al. (2015) observed a twofold increase in
margaric acid in meat from goats with access to castor de-oiled cake compared with
the control group. This indicates that margaric fatty acid content in goat meat can be
influenced by diet alterations and is synthesised by rumen microorganisms.
In the present study, the ratio of n-6/n-3 in MM from goats on beyond 66% level
of concentrate supplementation was beyond 4, indicating that the 66% of ad libitum
feed is the maximum level of concentrate supplementation for goats in order produce meat with salubrious fatty acids (Horcada et al. 2012).
4.3 Fatty Acid Composition in Omental Fat (OF)
The observed limited effect of concentrate supplementation on the proportion of various fatty acids in OF depot disagrees with the conclusion of Barber et al. (2000) and
Aldai et al. (2007) that the fatty acid profile of internal fat depots is affected by the
preferential deposition of absorbed dietary fat into these depots. We have no plausible
explanation for this discrepancy. Irrespective of the level of supplementation, n-6/n-3
PUFA ratio was above 4, indicating potential health risks associated with the consumption of internal fat depots such as omental fat. The increase in the proportion of
rumenic acid with concentrate supplementation may stem from an increased supply of
substrates for biohydrogenation, mainly linoleic acid. However, the comparable proportion of rumenic acid in T66 and T100 may indicate that the highest level of concentrate supplementation required for maximisation of rumenic acid deposition in OF
Effects of Concentrate Supplementation on the Fatty Acid Composition of Fat Depots…
action of ∆-9 desaturase (Aldai et al. 2007), a substantial amount of oleic acid
(C18:1 n-9) found in animal tissues is derived from the concentrate diet (Daniel
et al. 2004). As seen in the present study (Table 1), concentrate diet contained considerable amount of oleic acid. On the other hand, the higher proportions of transMUFA observed in MM from concentrate-supplemented goats could be attributed
to ruminal biohydrogenation of unsaturated fatty acids (UFA). The higher content
of UFA, especially linoleic acid (C18:2), in the concentrate diet than in grass hay is
a probable source of variation. Similar to the findings from the present study, Warren
et al. (2008) found that meat from concentrate-fed animals has higher proportions
of linoleic acid, CLA and vaccenic acid (C18:1 trans 11). However, Aurousseau
et al. (2004) reported that the proportion of vaccenic acid was higher in grazing than
in concentrate-fed lambs, findings that do not correspond with those of the present
study. We have no plausible explanation for this discrepancy. Trans fatty acids have
been linked to increased levels of plasma low-density lipoprotein (LDL) cholesterol, which has negative health effects (Mensink et al. 2003; Bas et al. 2007). The
main trans isomer in meat (vaccenic acid), however, is not a significant risk factor
for cardiovascular diseases compared to trans fatty acids formed by chemical hardening of vegetable oil (Nuernberg et al. 2005).
The observed increase in margaric acid (C17:0) with higher levels of concentrate
supplementation may indicate changes to the rumen environment triggered by
intake of a concentrate diet favouring amylolytic bacterial species and propionate
production (Turner et al. 2012). Oliveira et al. (2015) observed a twofold increase in
margaric acid in meat from goats with access to castor de-oiled cake compared with
the control group. This indicates that margaric fatty acid content in goat meat can be
influenced by diet alterations and is synthesised by rumen microorganisms.
In the present study, the ratio of n-6/n-3 in MM from goats on beyond 66% level
of concentrate supplementation was beyond 4, indicating that the 66% of ad libitum
feed is the maximum level of concentrate supplementation for goats in order produce meat with salubrious fatty acids (Horcada et al. 2012).
4.3 Fatty Acid Composition in Omental Fat (OF)
The observed limited effect of concentrate supplementation on the proportion of various fatty acids in OF depot disagrees with the conclusion of Barber et al. (2000) and
Aldai et al. (2007) that the fatty acid profile of internal fat depots is affected by the
preferential deposition of absorbed dietary fat into these depots. We have no plausible
explanation for this discrepancy. Irrespective of the level of supplementation, n-6/n-3
PUFA ratio was above 4, indicating potential health risks associated with the consumption of internal fat depots such as omental fat. The increase in the proportion of
rumenic acid with concentrate supplementation may stem from an increased supply of
substrates for biohydrogenation, mainly linoleic acid. However, the comparable proportion of rumenic acid in T66 and T100 may indicate that the highest level of concentrate supplementation required for maximisation of rumenic acid deposition in OF
Effects of Concentrate Supplementation on the Fatty Acid Composition of Fat Depots…