THE ROLE OF PROTEASE IN UNLOCKING THE NUTRITIVE VALUE OF SORGHUM GRAIN FOR PIGS

Avril Finn (2011). THE ROLE OF PROTEASE IN UNLOCKING THE NUTRITIVE VALUE OF SORGHUM GRAIN FOR PIGS PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

       
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Author Avril Finn
Thesis Title THE ROLE OF PROTEASE IN UNLOCKING THE NUTRITIVE VALUE OF SORGHUM GRAIN FOR PIGS
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2011-03
Thesis type PhD Thesis
Supervisor Mike Gidley
Ian Godwin
Barbara Williams
Dave Cadogan
Total pages 131
Total colour pages 1
Total black and white pages 130
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary In Australia, and especially Queensland, sorghum is an important animal feed grain due to its drought resistance and heat tolerance. In many instances sorghum is thought to have a lower nutritive value compared to other cereal grains by pig producers due to poor pig performance when fed the grain with respect to rate of gain (ROG), average daily intake (ADI) and feed conversion ratio (FCR). An experiment was conducted on 640 Large White pigs (7.0 to 9.2 kgs) to evaluate the effects of different grain types and cultivars on performance of weaned pigs. The pigs were fed complete diets for 21 days containing 65% of one of 32 test grains (11 sorghum, 9 wheat, 7 barley and 5 triticale) with a calculated DE of 14 MJ/kg and lysine content of 0.90 g/MJ DE. Overall, sorghum was shown to have a significantly (P<0.05) negative effect on pig performance when compared to wheat, barley and triticale. However, it was also shown that some sorghum cultivars could perform just as well as the other grain types. To determine whether pig performance was affected by animal age, a second experiment was conducted on 120 Large White male pigs (16 to 25 kgs) to evaluate the effects of different sorghum cultivars. The pigs were fed complete diets for 21 days containing 82% of one of 10 sorghum grains (one yellow and nine red) with a calculated DE of 14 MJ/kg and lysine content of 1.13 g/MJ DE. Grower pigs fed different varieties of sorghum grains showed statistically significant (P<0.05) differences in ROG, but not ADI or FCR. The performance of the grower pigs compared to the weaner pigs on the same 10 test sorghum grains showed no correlation which leads to the conclusion that the age of a pig can affect its growth performance when fed the same grain. However, in contrast to the modest growth performance of pigs fed sorghum, the total digestible energy (DE) of sorghum is either similar or higher than some grains e.g. wheat. Therefore a third experiment was conducted on 42 Large White male pigs (32 to 37 kgs) to investigate whether DE values in grower pigs from both apparent ileal digested (AID) energy and apparent total tract digested (ATTD) energy measurements vary between different cereal grains. The pigs were fed complete diets containing 95% of each of the 32 grains used earlier with a calculated DE of 13 MJ/kg and lysine content of 0.70 g/MJ DE. There were highly significant (P<0.001) differences in the DE between grain types. The highest DE was from sorghum and wheat, followed by triticale, and the lowest for barley. Grain cultivar had a highly significant effect (P<0.001) on the ATTD energy for the diet on an as received (AR) basis, and the ATTD energy for the grain as an ingredient on an AR and dry matter (DM) basis. However, grain cultivar had no effect on the AID energy for the diet. There was also a significant (P<0.05) effect of the grain variety on the ratio of the diet AID to ATTD with wheat having the highest ratio followed by sorghum, triticale, and barley. One reason for poorer pig performance, when fed sorghum may be due to starch/protein interactions in the endosperm matrix restricting digestion of both starch and (kafirin) protein. Therefore an in vitro experiment was conducted using two sorghum cultivars, the yellow seeded Liberty and a red seed coat hybrid (Red1) to determine the efficacy of specific exogenous enzymes on the digestion of sorghum kafirins. Five exogenous enzymes, xylanase, beta-glucanase, protease, amylase and phytase were used in combination and individually. Enzymes were added to hammer milled whole grain then a protein extraction and sodium dodecyl sulfate polycrylamide gel electrophoresis (SDS-PAGE) analysis was undertaken, which showed that digestion of sorghum α-, β- and γ-kafirins was improved by the addition of protease either on its own or in combination with other enzymes. However, in combination with xylanase, beta-glucanase and amylase it appeared to lose its efficacy. Due to the positive effect of exogenous protease in vitro, an in vivo experiment with 144 Large White male pigs (7 to 9 kgs) was conducted to evaluate the addition of protease enzyme at four different levels (0ppm, 50ppm, 100ppm and 500ppm) to a complete diet containing 65% of either Liberty (yellow), Buster (red) sorghum and a wheat control, with a calculated digestible energy (DE) of 14.57 MJ/kg and an available lysine content of 1.55 g/MJ DE. At 0-21 days, for the highest protease level (500ppm) both sorghums performed better than in the absence of protease, and similarly to the wheat control in terms of FCR. In conclusion, although sorghum and wheat show higher AID and ATTD energy compared to triticale and barley, sorghum typically gives poorer pig performance than wheat, barley and triticale. However, selection of appropriate sorghum cultivars and, particularly, treatment with exogenous protease show promise as means of obtaining pig growth performance and feed conversion efficiency similar to or better than that of other cereals used in Australia.
Keyword sorghum, pig, protease, kafirin, enzymes
Additional Notes Colour: pg 82 A3: 50-51, 60, 124-131

 
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