Doctoral Degrees (Animal Sciences)

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Browsing Doctoral Degrees (Animal Sciences) by Subject "Animals -- Growth"

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    The potential of quercetin to improve growth performance and meat quality in rabbits
    (Stellenbosch : Stellenbosch University, 2019-04) North, Megan Kim; Hoffman, Louwrens C.; Zotte, Dalle A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    ENGLISH ABSTRACT: Flavonoids are naturally-occurring bioactive compounds that may improve livestock production and product quality. Unfortunately, while their antioxidant, antimicrobial and other activities have been demonstrated, there has been limited research on their practical use as a livestock dietary supplement. This study investigated the effects of quercetin dihydrate (0 or 2 g/kg feed) on the growth performance and meat quality of growing New Zealand White rabbits. Sixty-six rabbits (31 males, 35 females) were fed control (Ctrl, 34 rabbits) or quercetin-supplemented (Qrc, 32 rabbits) feeds from weaning (5 weeks) until slaughter. The growth, feed intake and feed conversion ratio (FCR) were measured, and serum hormone levels were determined at 11 weeks old. Sixteen males and 16 females were slaughtered at 12 weeks old; carcass and meat quality traits were measured and the fatty acid composition of the caecotrophes, dissectible fat, loin meat and hindleg meat were determined using GC-FID. Fifteen males and 19 females were slaughtered at 13 weeks old; caecal contents were collected from 12 rabbits for the 16STM metagenome sequencing of the microbiome, and the loins were minced and stored for 1, 3 or 5 days at 3.2 C under oxygen-permeable wrapping to test the shelf-life. Quercetin-supplementation did not improve live performance, with Qrc rabbits only tending (P ≤ 0.10) to have higher overall FCRs, smaller sex-differences in growth and FCR, and higher free triiodothyronine levels. Quercetin-supplemented rabbits also only had higher proportions of some Firmicutes families and Anaerofustis and lower proportions of Roseburia, Oscillibacter and Ruminococcus albus in the caecal microbiome. This limited effect may have been due to the aglycone being absorbed prior to the caecum. Strong correlations between the composition of the microbiome and live performance traits were found, supporting further research on this topic. Quercetin-supplemented rabbits had higher hindleg meat:bone ratios due to lighter bones, which could increase meat yields but could also cause bone-breakage problems. This was contrary to previous findings that flavonoids decrease bone demineralisation, but may have been due to its effects on the connective tissue, which could have also caused the higher skin weight found. The largest effect of supplementation was on the loin fatty acid (FA) composition, increasing C18:3n-6, C20:3n-6, C20:3n-3 and C20:4n-6, and decreasing C20:2n-6, among others, thereby decreasing the n-6:n-3 ratio and improving the nutritional quality of the meat. This suggested an interaction between quercetin and endogenous lipid metabolism, which may have been influenced by the FA composition of the diet. The caecotrophes, dissectible fat and hindleg FAs were unchanged by quercetin. Quercetin-supplemented rabbits’ meat samples had lower day one concentrations of hexanal (an oxidation indicator), but no difference in oxidation (TBARS and FRAP) or microbial status during the shelf-life study. Dietary quercetin therefore did not improve the shelf-life of rabbit meat. Further research on the effects of quercetin on lipid metabolism should be done, particularly testing different inclusion levels and dietary FA compositions. The effects on bone-integrity, whole-carcass meat:bone ratio and pelt/skin quality should also be looked into. While some sex differences were found in these studies, they did not meaningfully affect production or product quality.