Effect of Harvest Stage and Ratio of Forage Sorghum to Corn Silage on Its Nutritional Value and Degradability

 Fodder sorghum is one of the most important forage plants in arid and semi-arid regions of the world. Maize production is low in arid and high salinity regions around the world, and sorghum due to its adaptation to arid and low water conditions, high water use efficiency, C4 photosynthetic system, high clawing power, high production capacity as wet forage, dry and Silos are a good option in these areas. In the past, sorghum was generally grown in areas that were unfavorable for growing corn, but today, with the advent of hybrid fodder sorghums, it produces under ideal conditions corn-like crops, and where moisture is a limiting factor and may have a higher yield than corn. Recently, frequent droughts in Iran have attracted the attention of farmers and livestock breeders to other forages such as sorghum, and due to the limited growing season of this forage, its use as a silo is common. Stage of growth is one of the most important factors influencing nutritional quality of fodder silages. As the fodder matures, the cytoplasmic portion of the cell reduces and the quantity of protein, lipids, soluble carbohydrates and soluble minerals decrease. Due to the drought occurrence on large parts of Iran and the adaptation of sorghum to drought conditions, a very few studies have been done on its chemical composition and nutritional value. Therefore, the aim of the present study was to investigate the effect of plant growth stage and mixing of corn and sorghum on chemical composition and degradability of corn and sorghum silage.

In order to evaluate the effects of harvesting steps and the ratio of forage sorghum blending on nutritional value and its degradability compared to corn silage, this experiment were performed using 45 experimental silos in a factorial experiment based on a completely randomize design with 15 treatments and 3 replications. Experimental groups consist of: sorghum harvest time (first factor) including: 1) before flowering (emergence of flag leaf), 2) about 10-15 percent flowering, and 3) soft seed soils. Sorghum harvested at each of the above time with forage corn with ratios of corn fodder to sorghum (second factor): 100%: 0%, 75%: 25%, 50: 50%, 25%: 75% and % 0: 100% was mixed. Silage samples were analyzed for Dry matter, crude protein, Ash and crude fat according to AOAC (2005) methods. In situ ruminal degradation kinetics parameters of DM, CP and NDF of experiment treatments were estimated using the nylon bag technique. Degradation of dry matter at times zero, 2, 4, 8, 16, 24, 48 and 72 9 hours was determined.

The results of this experiment indicated dry matter, crude protein had an upward trend with growth progression. While, the amount of crude fat, soluble sugar decreased significantly with plant growth. Ash content fluctuated during the growth stages, so that its amount was the lowest in flowering stage and was the highest during the vegetative stage (before flowering). The highest pH was observed in the soft dough stages and the mixing ratio of 25% corn and 75% sorghum, which indicates more proteolysis of silage. The lowest amount of ammonia nitrogen was observed in the soft dough phase treatment with 50% corn and 50% sorghum ratio and the highest amount of lactic acid was observed in the soft dough stage treatment with 100% sorghum, which may be due to increased soluble carbohydrate intake and convert it to lactic acid. Rapidly soluble fraction, degradation rate constant and effective degradability of dry matter, crude protein and cell wall at all passage rates increased significantly with increasing plant growth.

In general, it can be concluded that harvesting corn and sorghum forage in the soft dough stage with a mixing ratio of 25% corn and 75% sorghum improves the pH of silage. Rumen degradability of silage dry matter in the soft dough stage with different levels of corn and sorghum composition can increase feed intake in livestock. Rumen degradability of silage dry matter was also higher in the soft dough stage with different levels of corn and sorghum composition than other stages, and this can reduced feed retention in the rumen and increased feed consumption in livestock. However, more research is needed to investigate the effect of feeding a mixture of corn silage and sorghum in ruminants on voluntary feed intake and production performance.