Gas Production and In vitro Digestibility of Various Sources of Non-fiber Carbohydrates and Rumen Degradable Protein

Carbohydrates are generally classified as either non-structural or structural carbohydrates. Structural carbohydrates include cellulose, hemicellulose and lignin, and non-fiber carbohydrates (NFC) are present inside the plant cells and are usually more digestible than carbohydrates found in plant cell walls. Dietary non-fiber carbohydrates are the main source of energy for high-producing dairy cows, which provide 30 to 45 percent of the dry matter intake. They are a very diverse group of non-fiber carbohydrates, which include starch, sugars, fructans, and pectin substances. Although the total amount of non-fiber carbohydrates is referred to as a single value, different types of NFC have different effects on digestibility and production properties. The dietary profile of NFC has the potential to alter the supply of metabolizable nutrients to the animal because NFC differ in digestion and fermentation characteristics. Sucrose is rapidly fermented in the rumen compared with corn starch. In vitro fermentation of sucrose, starch, and pectin resulted in different organic acid profiles, digestion characteristics, and maximal microbial protein yields. In addition, these effects may be affected by other feed components, such as the amount of rumen degradable protein. Some researchers have been showed that the impact of starch and sugars on low quality forage utilization may interact with the amount of supplemental rumen degradable protein. This experiment was conducted to investigate the effect of various sources of non-fiber carbohydrates (starch, sucrose, pectin, dextrose) in combination with different levels of rumen degradable protein on gas production and digestibility of fermentation parameters in in vitro condition.

Soybean meal treated with heating at 160°C-60 min and untreated soybean meal were selected as low rumen degradable protein (RDP) and high RDP sources, respectively. Four types of non-fiber carbohydrates (dextrose, sucrose, starch and pectin) supplemented with two levels of rumen degradable protein (RDP) in a 2×4 factorial arrangement by gas production and batch culture. A basal diet including: alfalfa (30%), corn silage (10%), barley grain (25%), wheat barn (9%), salt (0.5%), mineral-vitamin supplement (0.5%), soybean meal (15%) and non- fiber carbohydrate source (10%) was prepared. This study was conducted in two experiments. In the first experiment, the gas production parameters for two levels of high and low rumen degradable protein and four types of non-fiber carbohydrates (starch, sucrose, pectin and glucose) using the gas production technique. In the second experiment, the digestibility of the first experimental treatments were measured in an in vitro batch culture method. In the first experiment, the gas pressure was recorded with the pressure gauge at 0, 2, 4, 6, 8, 12, 24, 36, 48, 72, 96 h after incubation. In the second experiment treatments were incubated in batch culture conditions for 24 hours and the degradability parameters were determined using equations.

the obtained results showed that sucrose had highest gas production potential, organic matter digestibility (OMD), metabolizable energy (ME) and short chain fatty acids (SCFAs) than other NFC type in low RDP level. There was a significant difference in digestibility of organic matter and dry matter between treatments (P<0.05). The highest and lowest ammonia nitrogen concentrations were obtained from treatments with starch in combination with high and low RDP, respectively. Treatments had a significant effect on partitioning factor and production of microbial mass (P<0.05). Among the low-degradability protein-based treatments, pectin treatment had the highest amount of microbial production and among the treatments with high degradability protein content, starch treatment had the highest production of microbial mass and partitioning factor. Overall, the results showed that when the RDP level is low, sucrose has a better performance in terms of fermentation parameters, whereas when using the high RDP, there was no significant difference between different types of carbohydrates. It seems that these interactions should be considered in regulating diets.

The results of this experiment showed that different types of non-fiber carbohydrates and levels of rumen degradable protein had a different responses to fermentation parameters. When using low protein levels, it seems that there is a greater difference between different sources of non-fiber carbohydrates, while at high levels of protein degradation there is no significant difference between the different sources of non-fiber carbohydrates in terms of digestibility. Based on these results, it can be concluded that the non-fiber carbohydrate sources, along with the degradable protein supplement, has the ability to change the characteristics of ruminal fermentation, the source of food and the production.