Effect of gamma irradiation on barley grain varieties on changes of chemical compounds and rumen starch and crude protein degradability

Barley is mainly used as a feed grain for livestock in Iran. Historically, barley has been traded at a significantly lower price than corn in the world market (FAOSTAT 2015). The endosperm of the barley kernel is surrounded by the pericarp, which is overlain by a fibrous hull, which is extremely resistant to microbial degradation in the rumen (Wang et al 2003). Some of the feed processing technique treats that remove or cracked the hull makes the starch more accessible to microbes, and increases the rate and extent of starch ruminal degradation. In these cases, processing is essential to maximize the utilization of barley grain by cattle, but extensive grain processing increases ruminal starch degradation, which often decreases feed intake in ruminants. On the other hand, in some cases, the feeding of barley-based high concentrate diets has been linked to an increased incidence of digestive disorders, resulting reduced feed intake, cattle going off-feed, laminitis, bloat, acidosis, rumenitis, and liver abscesses (Yang et al 2000). It is assumed that the rapid rate of fermentation of starch in barley grain contributes to these nutritional and health problems. Differences in chemical composition exist between barley cultivars. Individual barley varieties differ in terms of the composition of the protein matrix in the starchy endosperm of the grain and this characteristic might be expected to influence degradability in the rumen (Gholizadeh et al 2017). Optimum alteration of the site of starch digestion requires processing methods or conditions that increase starch flow to the duodenum without reducing its total tract digestibility. Additional glucose absorption at the duodenum may reduce the needs for gluconeogenesis and increase productivity of ruminants (Nocek and Tamminga 1991). According to Parrott et al (1969), they have reported improved nutritional efficiency due to grain processing in ruminants. Radiation is a physical process approach that has the potential to replace other methods of processing without affecting the protein structure without radioactive activity, and this process is likely to cause cross-linking and clumping of proteins (Mani and Chandra 2003). Shawrang and Sadeghi (2006, 2007 and 2008) argued that the protective mechanism of proteins from rumen degradation in highly processed feeds has been very wrapped, and chemical reactions such as the millard reaction that occurs during thermal processing may be responsible for the reduction of rumen degradability. These reactions have the effect of converting the protein into resistant compounds to rumen degradation. The ionizer rays affect the structure of the protein and cause it to tear apart. It has been argued that irradiation may form cross-linking and protein binding (Gaber 2005, Ebrahimi et al 2011). Previous studies have confirmed that differences in rate of degradation can occur between barley cultivars. Although, these differences may indicate that certain cultivars of barley are more desirable as feed grains than the others. There are a limited data available for Iranian barley grains and their response to processing to make solid recommendations in this regard. In order to improve the nutritional value of fast fermentation cereal grains in the rumen, gamma irradiation can be used as a suitable treatment method in this regard. It is also important to choose the best radiation duration and dosage in the irradiation method. The aim of this study was to determine the effects of gamma irradiation on ruminal dry matter, starch and crude protein degradability of different varieties of barley grain. Additionally, protein profile in metabolizable protein system was calculated. Barley varieties Makoei, Bahman Abi, and Sahand were irradiated with the use of the gamma ray of 60 cobalt and 50, 100, and 150 KGy doses at the center of radiation in Yazd. Kinetics and parameters of protein and starch degradability of nylon bag samples were evaluated using three male Holstein calves equipped with ruminal fistula at 0, 2, 4, 6, 8, 12, 24, and 48 hours based on a completely randomized block design. Incubations were repeated two times to ensure day to day variations. All barley samples were grounded to pass a 2 mm screen. Approximately 5 g (air dry) of samples were weighed in triplicate into 10 cm × 20 cm nylon bags (porosity = 50 μm). Dry matter was determined by oven-drying at 55 °C for 48 h. The crude protein and starch content were determined, accordingly. The protein profile based on the metabolic protein system was determined based on the relevant equations. The amounts of crude protein and starch in the samples before and after incubation were measured using the Kjeldahl system and acid digestion and anthrone, respectively. Parameters of degradability and effective degradability at different rumen crossing velocities were determined by nonlinear equations of McDonald and Erskoff and McDonald using (PROC NLIN) statistical software SAS 9/4. The AFRC equations were used to estimate the amounts of fast rumen protein, slow rumen protein, rumen effective protein, total rumen protein, and rumen nonmodifiable protein. Analysis of variance showed that gamma irradiation at different levels reduced starch and protein degradability in rumen among different cultivars (P<0.05). Among different studied cultivars, the Sahand varietie was affected more than other cultivars. Different responses of barley grain varieties to different levels of processing can be related to the content of nutrients in the fiber shell, the distribution of starch in different grain segments and the difference in the structure of starch granules. The results of this study showed that the cultivation of different barley grain varieties with gamma rays reduced the fast degradability (P<0.05). Based on the results, the differences in the response of different barleys to gamma rays showed that the best response was affect the nutritional parameters in order to improve rumen fermentation, protein degradation, starch and increase starch values can be irradiated at 50 kGy. Gamma irradiation can be used as one of the commonly treatments to reduce the degradability of dry matter, starch and rumen protein, and increase starch and digestible escape protein and fermentation, it improves the rumen's ecosystem and reduced the risk of acidosis.