Introduction: Following the expansion of industrial dairy farms in the country, the technology of silage forage was also introduced and expanded, so that in most dairy cattle breeding units, silage forage is considered one of the main items of livestock diets. Silage forage is based on the principles of fermentation and sometimes adding appropriate supplements and maintaining the maximum nutritional value of the forage in the silo, minimizing waste in order to obtain maximum economic use. Silage is also the most common method for storing high-moisture forage. In this process, lactic acid bacteria ferment the water-soluble carbohydrates in the product into lactic acid, and as a result of the production of these acids, the pH of the ensiled materials decreases and spoilage microorganisms (molds and yeasts) are inhibited. The aim of this study is to determine the changes in the nutritional value of straw enriched with whey, urea, and mineral-vitamin supplements due to ensiling.
Materials & Methods: In the present study, the nutritional value of two types of diets, including diet one based on wheat straw enriched with urea, barley flour and wheat bran, and in diet two, alfalfa was also added to the complete feed. The aforementioned diets were ensiled in double-layer plastic bags and after 60 days, the bags were opened and examined in the laboratory. Also, whey was used as a substitute for water in ensiling the diets. The above diets were studied in the laboratory and on live sheep. For the in vivo test, 5 sheep were used. The two experimental diets were each presented to the experimental animals in 2 different forms. In such a way that finally 4 different diets were produced and fed to the animals. The final diets included 1) the straw portion of diet 1 with a weight ratio equal to whey plus urea, salt, sulfur powder and mineral-vitamin supplement. 2) Total silage of diet 1 ingredients with a weight ratio equal to whey plus urea, salt, sulfur, and mineral vitamin supplement. 3) Straw portion of diet 2 with a weight ratio equal to whey plus urea, salt, sulfur, and mineral-vitamin supplement and alfalfa. 4) Total silage of diet 1 ingredients with a weight ratio equal to whey plus urea, salt, sulfur, and mineral-vitamin supplement and alfalfa. Data analysis related to chemical composition and digestibility was performed in a laboratory method, with a factorial experiment in a completely randomized 2×3 design with three replications. The obtained data were statistically analyzed by SAS statistical software with the GLM procedure and the means were compared with each other using Duncan's multiple range test at the 0.05 level.
Results: Starch content decreased in both diets. Non-protein nitrogen concentration decreased significantly in the first diet. Acid detergent insoluble fiber content in the first diet and acid detergent insoluble lignin content in both diets increased significantly. Ensiling the first diet resulted in a significant decrease in non-protein nitrogen concentration from 2.1% before ensiling to 1.4% after ensiling. While it resulted in an increase in ADF, ADL and pH from 23.80, 3.20 and 5.40% before ensiling to 24.56, 3.23 and 8.40% after ensiling, respectively. Crude ash was not significantly different in both diets. In addition, in the in vitro digestibility of feed parameters in the first diet, the 24-hour gas production parameters, gas production potential, digestibility of fine matter and short chain fatty acids showed a significant decrease (p<0.05) and there was also a significant increase in the efficiency of microbial biomass production (p<0.05). In the second part of the in vivo experiment, in the first fermented diet treatment, the amount of dry matter consumed, dry matter digestibility, organic matter digestibility and urine volume were 1134.83, 61.51, 65.69 and 1181.52, which were significantly increased compared to before the silage period (p<0.05). The results of using the first diet showed that sheep consuming the fermented diet had higher feed consumption compared to the unfermented diet. Also, the consumption of the first diet increased the body weight of the experimental sheep, and there was no significant difference in the weight gain of the animals between the two groups consuming unfermented and fermented diets. Also, in the second diet, the concentration of ammonia nitrogen in the fermented treatment was 33.8 and 17 in the unfermented treatment, which showed a significant increase (p<0.05). Comparing the effect of ensiling in the two diets on the blood parameters of the animals showed that fermentation in these two diets had no effect on the levels of glucose, albumin, aspartate transaminase, alanine transaminase, alkaline phosphatase, blood urea nitrogen, and total protein.
Conclusion: The results obtained in this study showed that ensiling diets with whey can be used as a solution to dispose of this by-product of cheese factories in the country and prevent environmental problems, because it did not have an adverse effect on blood parameters and produced a higher amount of nitrogen for livestock. Also, diets with energy sources showed a more appropriate response in the fermentability process during the ensiling stage, and in contrast, ensiling diets with high protein sources is not recommended.