Use of in vitro gas production technique for evaluation of corn meal nutritional value and fermentative predictions with comparison to some cereal sources

Corn meal is a by-product of corn grain which is a relatively new feedstuff in ruminant nutrition. This feed stuff is a by-product of corn after oil extraction. There is lack of information regarding the chemical analysis as well as its nutrient degradation in rumen. Moreover, the nutritional characteristics did not compare with other grains yet. Therefore, identification of its nutritional value is necessary for ration formulation. The aim of the present study was to evaluate and compare the nutritional value of corn meal with different corn varieties based on gas test technique as well as identification of microbial mass and short chain fatty acids (SCFA) concentration predicted based on this technique. The microbial protein production prediction was estimated as well to evaluate and compare the potential to produce microbial protein in corn meal and other grain sources. Material and Different grain sources which had been used extensively in local dairy farms had been used to compare their potential for gas production with corn meal as new feedstuff. The treatments were as follows 1) corn meal, 2) ground barley grain, 3) ground corn grain (contain semivitreous starch), 4) ground corn grain (contain floury starch), 5) ground corn grain (contain vitreous starch), 6) ground dent corn grain, 7) pure corn starch. Different grain sources were categorized based on starch form content. All the samples were ground to pass 1 mm sieve. The rumen liquor was collected from three non-lactating, non-pregnant dairy cows fed a similar basal diet. The gas production technique was conducted in three periods for and each sample has three subsamples in each period (totally nine repeat for each experimental feedstuff). Gas production was measured on 2, 4, 8, 12, 24, 36, 48, and 72 h after incubation. The measurement was done based on gas produced for fast and slow degradable fractions of feedstuffs and total volume was measured based on total gas produced through 72 h after incubation. In addition to gas production measurement, other fermentation parameters such as partitioning factor (PF), organic matter digestibility (OMD), microbial biomass production (MBP), metabolisable energy (ME), SCFA were estimated as well. In addition, the cumulative gas produced based on ml gas produced per mg of dry matter for different experimental feedstuffs was calculated. Results showed that corn meal has the lowest gas production volume from rapidly degradable pool, and floury starch contained corn had the highest rate of gas production volume. Slowly degradable pool of corn meal, also, has the highest (greatest) gas production volume. Despite these differences among treatments regarding the gas production in different sampled times, however, the total amount of gas produced in the different treatments was not significant. The results show that the proportional ratio of gas production was different based on different incubation times, but total produced gas was similar among treatments. The results show that cumulative gas produced (ml/mg DM) was differed between treatment with the lowest value for corn meal (124.48 ml/mg DM). The prediction results based on gas test method showed that digestibility of dry matter and organic matter from corn meal was lower in comparison with all varieties of grain corn. This may have related to chemical composition of this feedstuff in comparison to other treatments. Partitioning factor was statistically constant among treatments. Microbial biomass production as well as its efficiency was similar among treatments. This shows that corn meal was as same as other grain sources in affecting the microbial fermentation in vitro. Furthermore, metabolizable energy and predicted volatile fatty acids concentration of corn meal had the lowest value among treatments (10.30 Mj/Kg DM). The lower concentration for volatile fatty acid (1.10 mmol) predicted for corn meal clear that this by-product could not supply as adequate energy as supplied by other treatments for animal on farm scale. The lower ME content as well as the lowest SCFA predicted in corn meal treatment may be related to greater fiber content in comparison with other treatments. The greater cell wall content has potential to reduce energy content and total volatile acid production in rumen. Although the predicted SCFA concentration of other grain sources were greater than that of corn meal, all the predicted values were similar among grain sources. This was mostly because similar chemical analysis among these grains. The results of the present study showed corn meal had lower energy content compared to corn grain varieties as well as barley grain. However total gas volume production and microbial biomass produced for this feedstuff was similar to other experimental feedstuffs. Future studies need to evaluate the performance of the animal fed with corn meal when compared with other conventional grains.