| Summary: | The small ruminant (goats and sheep) industry in Malaysia can be described
as slow growing as compared to the demand for the products. On the other
hand, ruminant products are known to contain high amount of saturated fatty
acids (SFA) which are often implicated as a source of modern-day diseases.
To date, limited comparative studies have been carried out to characterize
differences between goats and sheep, hence the two species are often
assumed to be similar and thus raised and managed similarly. To meet the
local demand, there is a need to improve the productivity of the small
ruminant industry, by optimizing the growth protential of each animal species;
and at the same time, to produce healthier meat and meat products. It is
hypothesized that the feeding of high concentrate diet supplemented with
linseed oil as a source of polyunsaturated fatty acids (PUFA), could improve
the growth rate of the animals and at the same time, fortifying the meat and
products with health beneficial PUFA. The primary objectives of this thesis
were to co-compare rumen fermentation characteristics, growth performance,
meat quality attributes and fatty acids profile in tissues of goat and sheep fed
high concentrate fattening diet, with and without supplementation of PUFA;
and to infer the differences in fatty acids profile due to the dietary treatments
and animal species (goats vs sheep) through the expression of adipogenesis
related genes. Three experiments were conducted to achieve the above
objectives. In the first experiment, in vitro rumen fermentation characteristics
in goats and sheep with or without PUFA added to the substrate were
evaluated. Results showed superior fermentation characteristics in goats with
higher in vitro gas production rate (P<0.001), accompanied by higher volatile
fatty acids (VFA) production and in vitro organic matter digestibility (P<0.05).
The higher population of total bacteria and two major cellulolytic bacteria
(Ruminococcus albus and Butyrivibrio fibrisolvens) in goat compared to
sheep also indicates higher digestive capability in goats. The addition of 4%
linseed oil to the substrate did not show any negative effect on fermentation
characteristics nor the VFA production, suggesting that the level oil was
appropriate. Experiment 2 consisted of a 100-day feeding trial to determine the growth
performance, digestibility and meat quality attributes of goats and sheep fed
fattening diet with or without oil supplementation, in a 2 species x 2 diets
factorial experiment with 6 animals (replicates) per treatment. Results of the
study showed that irrespective of diet, sheep had better body weight gain
(BWG) and feed efficiency (FE) compared to goats. Overall, supplementation
of linseed oil at 29 g/day improved BWG by about 65 g/day (45%
improvement over the control) and FE by 15% (5.01 vs 5.93). There was no
species difference (except for crude protein) and no effect of dietary
treatments on apparent digestibility. Goat meat had better quality attributes
(P<0.001), including lower lipid oxidation and higher water holding capacity
than sheep. Linseed oil supplementation did not affect meat lipid oxidation,
indicating that the level of supplementation was appropriate.
The fatty acids profile in various tissue, in vivo rumen fermentation and
expression of adipogenesis related genes from the above feeding trial are
reported in Chapter 5 with the objective of determining whether differences
exist in fatty acids profile in goats and sheep fed similar diets and to elucidate
the possible mechanisms for any differences exist. Results of the study
showed that there were significant differences in the fatty acids profile in the
longissimus dorsi (LD) muscle, subcutaneous (SC) fat and liver tissue
between species and between dietary treatments. Although no species
differences were observed in the total SFA, MUFA and PUFA content in the
LD muscle, several individual fatty acids were significantly different between
species, including higher n-3 PUFA in LD muscle of goats. Sheep had higher
total SFA content but lower UFA in the SC fat and liver tissue. Linseed oil
supplementation increased the linolenic acid content by 4.5 to 6.1 folds in the
tissues samples analyzed suggesting oil supplementation provides a viable
approach to enrich meat and ruminant products with essential PUFA.
The result of the in vivo rumen fermentation characteristics explained for the
differences in the fatty acids profile between species. The higher production
of total VFA and acetic acid (primary precursor in fatty acid synthesis) in
sheep suggest higher lipogenesis activity, and explained for the higher SFA
content. The higher population of B. fibrisolvens in sheep than goats, which
on the other hand had higher population of total methanogens and
methanobacteriales, explained for the higher biohydrogenation intermediate
in sheep.
Relative expressions of adipogenesis related genes were used to elucidate
the differences in the fatty acids profile between species and dietary
treatment. The study found that, irrespective of diet, sheep had higher
expression of fatty acid synthase gene (FASN) gene and also higher Acetyl-
CoA carboxylase gene (ACACA) with oil supplementation. The higher
expression of the above genes led to higher production of SFA content
(especially palmitic acid) in the SC fat and liver tissue in sheep. Stearoyl-CoA
desaturase (SCD) gene, which responsibles for the unsaturation of SFA, was lower in sheep than goats and was further downregulated with the addition of
oil, which explains for the lower mono-unsaturated fatty acids (MUFA)
content in sheep and in the oil supplemented group. On the other hand,
peroxisome proliferator-activated receptor alpha (PPARα), which serves as
the transcriptional factor for many lipogenic genes, is negatively correlated
with ACACA and FASN genes. Therefore the downregulation of PPARα gene
was accompanied by upregulation of ACACA and FASN genes in sheep and
the opposite in goats, accounting for the different SFA production between
species.
Result of this thesis suggests that high concentrate feeding supplemented
with PUFA (linseed oil at 4% level) is an applicable approach to improve the
growth performance of small ruminants, and to produce healthier meat with
beneficial fatty acids profile, without detrimental effect on rumen fermentation
or meat quality attributes. Species differences in fatty acids profile were partly
influenced by the various lipogenic genes expression and therefore, dietary
manipulation of adipogenesis related genes expression (nutrigenomics) can
be a useful tool especially in reducing the SFA content, in order to produce
healthier ruminant meat and meat products.
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