R.J. van Barneveld2
1 SARDI, Pig and Poultry Production Institute, Adelaide University, Roseworthy SA, Australia.
2 Barneveld Nutrition, South MacLean, QLD. Australia.
In situ degradation of non-starch polysaccharide components by endogenous enzyme activity in whole grains is thought to improve the apparent metabolisable energy (AME) value of some wheats in the early post-harvest period.
This study examined changes in AME and subsequent growth performance of broiler chickens fed barley, sorghum, triticale and wheat that were subjected to controlled germination for 20 or 48 hours to activate endogenous enzymes in the grains.
Germination of barley for 48 hours improved AME by about 1 MJ/kg, but there was improvement by germination for 20 hours. Germination for 20 and 48 hours did not alter AME values for wheat, triticale and sorghum.
Introduction
Optimising the supply of available energy to broiler chickens is fundamental to improving production efficiency. It is already common practice to use exogenous enzymes in broiler diets as a means of increasing apparent metabolisable energy (AME) and to reduce variation in AME between samples. This is accomplished primarily by reducing the viscosity of digesta and disrupting cell walls to expose substrates such as starch to digestive enzymes (Hughes and Choct, 1999). Similarly, storage of grains between 3-6 months is also known to increase AME, possibly through in situ degradation of non-starch polysaccharide components by endogenous enzyme activity (Choct and Hughes, 1997).
To this end, controlled germination of cereal grains prior to incorporation into poultry diets may represent a further means of exploiting endogenous enzymes to increase AME and reduce variation within and between grain types. Germination of cereal grains is a complex process and is triggered when ripe grain imbibes adequate moisture at an appropriate temperature to promote growth of the seed embryo. Growth of the embryonic axis is accompanied by the production of hydrolytic enzymes, which solubilise nutrients stored in the endosperm and can promote hydrolysis (Evers et al., 1999).
The aim of this experiment was to measure the influence of controlled germination of different types of cereal grain on subsequent AME values and resulting growth performance of broiler chickens. No special attention was directed towards variety of particular cereals, as the main intention was to compare responses across the main types of cereal used in poultry diets in Australia.
Materials and methods
Small samples (1 kg) of all grains were control sprouted at 20oC for 0, 16, 18, 20, 22, 24, 26, 28, 40 and 48 hours. The relative α-amylase activity was determined by dye-labelling of substrate (Barnes and Blakeney, 1974). Larger quantities (20 kg) of 20 h and 48 h sprouted grain were produced for the feeding trial. Following germination, grains were dried at 40oC until average moisture content was 11% then tested again to determine the relative α amylase level to confirm that the 20 h and 48 h samples of each grain had medium and high enzyme activity, respectively.
The AME values of grains were determined in a conventional energy balance experiment involving measurements of feed intake and excreta output as described by Mollah et al. (1983) with minor modifications, and subsequent measurement of gross energy values of feed and excreta by bomb calorimetry.
Day-old feather-sexed broiler chickens were raised in floor pens on a commercial broiler diet to 20 days of age then transferred in single-sex pairs to metabolism cages in controlled temperature rooms to allow chickens to adapt to the cages. At 22 days of age, one bird was removed from each cage. Air temperature was maintained at 26°C at the start of the 7-day experiment and lowered daily until it was 23oC at the end.
Experimental diets contained (per kg) 800 g grain, 155 g casein, 20 g dicalcium phosphate, 11 g limestone, 7 g DL-methionine, 5 g mineral and vitamin premix, 3 g salt, and 2 g choline chloride (60%). Dietary treatments were replicated six times (three cages of males and three cages of females). Cold-pressed diets were fed for seven days. The first three days enabled the chickens to adapt to the feeds. During the following four days, all excreta were collected and dried at 85oC. Moisture content of excreta voided over a 24 hours period was measured. Feed intake was measured during the adaptation and collection phases of the study. Birds were weighed at the start and end of the 7-day period.
Dry matter (DM) contents of samples of pelleted and milled feeds were measured. Gross energy values of dried excreta and milled feeds were measured with a Parr isoperibol bomb calorimeter. AME of the grain was calculated by subtracting from the total energy intake the energy contribution of casein, which was assumed to be 20.1 MJ/kg dry matter (Annison et al., 1994).
Results and discussion
The effects of type of cereal grain, germination time and sex of chicken are summarised in Table 1. The 2-way interaction between germination time and sex of chicken, and the 3-way interaction between type of grain, germination time and sex of chicken were not significant (P>0.05) for any measurement. The moisture content of excreta from birds given barley (702 g/kg) was significantly higher (P<0.05) than that from chickens given wheat (658 g/kg) and sorghum (634 g/kg). Other differences in moisture content were not significant (P>0.05). The effects of the significant (P<0.05) 2-way interaction between cereal grain and germination time on AME and dry matter digestibility (DMD) are summarised in Table 2.
Controlled germination for 20 hours did not improve AME or DMD (Table 2) for any of the cereal grains, nor was growth performance affected (Table 1). The significant decline in AME and DMD of wheat germinated for 20 hours is difficult to explain except to point out that two birds (one male and one female) voided large amounts of excreta with normal moisture and gross energy contents relative to other birds in the same treatment group. Hughes (2003) concluded that alteration of the balance between the host and its resident microflora (by feeding different grains, for example) can result in outcomes that are difficult to predict, particularly if the diet is not supplemented with feed enzymes or antibiotics.
Controlled germination of grains for 48 hours significantly improved AME and DMD for barley only (Table 2).
The 1 MJ/kg increase in AME by germination of barley is the same as the increase in ileal digestible energy reported by Svihus et al. (1997) who soaked barley for 24 hours at ambient temperature then germinated it for 48 hours. Svihus et al. (1997) also observed significant improvements in weight gain (21%) and feed conversion (16%) with this treatment of barley. They attributed the improvements to decreases in the soluble and total β-glucan contents, and to a reduction in acid extract viscosity of the grain.
There were large differences in feed intake, growth rate and feed conversion between male and female chickens given barley (Table 3). Differences between males and females given other cereal grains were not significant for any measurement except for a significant improvement in feed conversion of the triticale diet by males compared with females (Table 3). It is possible that differences between males and females were associated with proliferation of hindgut microflora (Hughes, 2003) following the influx of relatively large quantities of undigested β-glucan from barley.
Conclusions
With the exception of barley, controlled germination of cereal grains had no beneficial effects on energy metabolism or performance of broiler chickens. The increase in AME value was of the same order (approximately 1 MJ/kg DM) as that previously reported with use of feed enzyme products.
Acknowledgments
Financial support was provided through the GRDC Premium Grains for Livestock program. We gratefully acknowledge the efforts of Ms Annette Tredrea, Wheat Research Centre, Narrabri, for preparing the experimentally germinated grains, and the SARDI poultry research staff at the Pig and Poultry Production Institute.
References
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From Proceedings of the "16th Australian Poultry Science Symposium", New South Wales, Australia.
