Abstract
This current thesis has as main objectives to assess the effect of the source of dietary carbohydrates on the carcasse fatness in two different swine breeds: the Iberian and the Landrace pigs. In one first experimental phase 48 pigs were used (88.4 kg LW), 24 Iberian and 24 Landrace, which were fed with two experimental diets differing in the main sources of carbohydrates: maize (Diet MZ), highly digestible, or maize-sorghum and acorn (Diet SB), more resistant to the enzymatic digestion and with a higher tendency to be fermented. When animals reached an average body weight of 110 kg, the half of them were slaughtered. The second experimental phase were developed with the rest of pigs, 12 iberian and 12 landrace (108 kg LW). Dietary treatments were maintained, increasing the proportion of acorn in the diet SB in spite of maize. Pigs were slaughtered at an average body weight of 135 kg.Along the experimental period, Iberian pigs showed a higher voluntary feed intake (about 30%: P < 0.01), promoting worse feed:gain ratios. Between experimental diets were not observed differences in productive performances, except for a lower feed intake in pigs fed diet SB in the second experimental phase (P = 0,08), when acorn proportion was increased.
Ileal digestibility of the organic matter was higher in landrace than in iberian pigs (P < 0,05) and in diet MZ than in SB (P < 0.01). Fermentation in hindgut allowed to compensate these differences in part, except for Iberian pigs fed diet SB, which showed the lowest digestibility coefficients in the whole of the digestive tract. The lower ability to ferment the whole of the substrate that reached the hindgut by Iberian pig was mainly associated to the lower transit time of digesta throughout its digestive compartment, calculated based on an indigestible flow marker.
All these differences between breeds and diets affected to the extent and type of fermentation in the hindgut. In particular, differences were observed in the volatile fatty acids concentration and profile. Differences were also observed in purine bases concentration, as a quantitative value of the microflora, and in enzymatic activity of this microflora against different carbohydrate substrates. Landrace pigs showed a higher microflora concentration in caecum (P < 0,05), and lower in colon (P < 0.05) than Iberian pigs. However, microflora in caecum of Iberian pigs showed a higher in vitro activity against all carbohydrate substrates analysed.
In reference to the fatness, Iberian pigs showed a higher lipogenic enzymatic activity than Landrace ones in both, subcutaneous and intramuscular depots. These results were associated with a higher (P < 0.001) backfat thickness and intramuscular fat content. Moreover, the Iberian pig fat had a lower polyunsaturated and higher monounsaturated FA contents. Between diets, there were not differences except for a tendency (P = 0,07) in backfat thickness, higher for diet MZ than for diet SB.
In conclusion, it is evident a genetic contribution in many differences between Iberian and Landrace pigs. However, the type of dietary carbohydrates can promote in each breed different digestive strategies to their digestion. As a result, carbohydrates also could influence in lipid metabolism, although in different way depending on breed.
| Date of Award | 2 Feb 2000 |
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| Original language | Spanish |
| Awarding Institution |
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| Supervisor | Jose Francisco Perez Hernandez (Director) |