Rural Industries Research & Development Corporation

|| Home || Search || Contact || Publications Eshop || Privacy Statement ||

Executive Summary

Cereal grains undergo post-harvest changes during storage.  The change is characterised by increased apparent metabolisable energy (AME) value of cereal grains in broiler chickens, sometimes up to 3 MJ in the case of wheat.The grains responding positively to storage usually have low, highly variable metabolisable energy value at the time of harvest.This is known as the "new season grain phenomenon" in the poultry industry.

The current project was conducted to examined the new season grain phenomenon as follows:  (a) repeated (4 times each year) measurement of the AME of wheat, barley, triticale, oats, sorghum and maize over two harvest seasons; (b) investigation of the possible mechanism of action including endogenous enzyme activities in the grain and effect of storage temperature, and (c) establishment and demonstration of practical strategies that may be used to minimise its impact in the feed and poultry industries.

In a preliminary study on 6 wheat samples obtained during the 1995/1996 season, four months of conventional storage increased the AME values up to 29%.  The wheats had an average AME value below 12.5MJ/kg DM at the time of harvest.  Two of the wheats did not undergo any change during storage, even when the samples were stored for up to 10 months.

The results from the 1996/1997 harvest season showed that the post-harvest changes in AME of cereal grains differed widely, with wheats responding most positively (up to 3MJ increase) to storage.  Barleys and oats also responded positively (>1MJ), but the magnitude of increase in AME was smaller compared to that in wheats.  The AME of triticale did not change due to storage.  For these samples, the time of maximum responses in AME varied between 3 to 12 months for wheat, 6 months for barley, and 3 months for oats.

For the 1997/1998 harvest season, a total of 17 samples consisting of 4 each of wheat, oats and triticale; 3 barley samples; and one each of maize and sorghum was collected and assayed.  The highest responses in AME were obtained for wheat after 6 months of storage.  No marked responses to storage were observed for the 3 barleys, 4 oats, 4 triticales and 1 maize sample assayed during this season.  The AME of the sorghum fluctuated between assays, but the initial and the final values were similar, indicating no real increase in the AME due to storage.

Endogenous xylanase and b-glucanase levels in the grains were determined to examine their relationships with post harvest changes.  In the current study, no apparent correlation between the two parameters was found.  It was noted that the levels of both enzymes were relatively high for oats.

Extract viscosity determined using water extraction correlated well with the AME value of wheat stored for a period of time.  However, the method could not be applied across different grain types.  For barley and oat samples, the acid extract viscosity method of Greenburg and Witmore (1974) closely correlated with the AME values.

The effect of storage temperature on the change in AME of new season grains was also examined.  Storage at low temperature (4oC) appeared to delay the onset of post-harvest increases in AME.  The differential responses of male and female birds, however, made it difficult to draw a conclusion.  Female birds generally gave 0.3-0.5MJ higher AME values and, at times, responded highly positively in AME to storage.

Supplementation of new season grains with appropriate NSP-degrading enzymes increased the AME values of 7 wheat samples (2 samples from 1995/1996 harvest; 5 samples from 1998/1999 harvest) to a potentially attainable value regardless of the initial values with concomitant reduction in variation.

A large between-bird variation in AME is a characteristic of some new season grains and low-ME wheats. The current project investigated: (a) the mechanism of action, and (b) whether feed enzymes could eliminate this variation.  Xylanase supplementation increased (P<0.01) the AME of a wheat from a control value of 12.5 (SD=1.13) to 13.1 (SD=0.52) MJ/kg DM and decreased ileal viscosity from 58.6 to 9.5 mPa.s.  The excreta from the control birds had a viscosity of 14.8 mPa.s, whereas that from birds fed the enzyme-supplemented diet had a viscosity of 4 mPa.s.  The significantly lower (P<0.01) viscosity values for excreta compared with ileal digesta in the control fed birds suggest that the gut microflora of the chicken do produce some NSP-degrading enzymes. Indeed, the caecal xylanase activity was significantly correlated (r= 0.72; P<0.001) with AME, a clear indication that the between-bird variation was related the activity of the gut microflora of individual chickens.

It may be concluded that the post-harvest changes in the nutritive value of cereal grains for poultry occur widely, but not for all grains or samples within the same grain type.  Wheat is highly responsive to storage, also most variable in response.  Storing grains conventionally for 3-4 months will be beneficial, but there appears to be little or no benefit of storing sorghum, maize and the modern varieties of triticale.  Implementation of extract viscosity techniques and strategic use of feed enzymes are recommended.
 

Site map Contact us Feedback Links Disclaimer Privacy Statement

Last updated: 18 October 2000
Copyright RIRDC
http://www.rirdc.gov.au/reports/AFT/00-143sum.html