عنوان مقاله [English]
Introduction Carbohydrates (CHO) are the most important source of energy which provides over half of the energy in livestock diets. They are also the major sources of energy for ruminal microorganisms in a dairy cow’s diet. Carbohydrate nutrition influences both the quantity and quality of milk. Carbohydrates are mainly divided to two types of fiber and non-fiber. Determining the quantity of non-fibrous carbohydrates lead in the balance in dairy cows’ diet. The required levels of structural carbohydrates are known and available, but the desired level of non-fibrous carbohydrates is not defined in details. NFC is fermented fast and almost completely in the rumen. They include: starch, sugars, pectins and β-glucans. According to researchers, non-fiber carbohydrates (NFC) can be estimated by subtracting crude protein, NDF, ether extract and Ash from 100 with a correction for crude protein bound to Neutral Detergent Fiber. To reach the highest level of microbial growth, the availability of carbohydrates and protein must be synchronized. It could happen with the best availability level of NFC and rumen degradable protein (RDP).The purpose of this study was to evaluate the levels of non-fibrous carbohydrates in the range of 33 to 42% of the dry matter intake, milk production, milk composition, and body weight in Holstein dairy cow.
Materials and Methods To determine the effect of dietary nonfiber carbohydrate (NFC) level on dry matter intake, milk production and body weight, eight multiparous Holstein cows averaging 107±28 d in milk and 644±68 kg BW in the beginning of trial were used in a replicated 4 × 4 Latin square arrangement (21-d periods). Treatments were 33, 36, 39 and 42% NFC in the DM bases. Experimental diets were formulated to meet the requirements according to National Research Council (2001) for Holstein cows of 620 Kg of BW and production 50 Kg of milk with 3.2% fat per day. Corn and soybean meal were substituted for wheat bran to achieve the requested level of non-fiber carbohydrates. Diets were fed as Mixed Ration (TMR) 37:63 forage to concentrate ratio and were offered three times daily ad libitum (0800, 1600 and 2400 h) for 10% refusals and cows had free access to fresh water. Data were analyzed in a changeover design using the mixed procedure of SAS Institute Inc (2003). The model included fixed effects of treatment and period, random effect of cow and residual error. Least squares means procedure (LSMEANS) was used to detect the difference between dietary treatments.
Results and Discussion The glucose absorption is less when the animal uses the diet with low NFC level and then the glucose intake in hepatic portal vein increase. So, the less portion of glucose is provided to make production (e.g Milk) in animal tissues and as a result, the animal production decreases. With the supply of protein requirements and also the increase of fermentable carbohydrates, due to the synchronizing availability of protein and energy for ruminal microorganisms, their growth will increase which leads the VFA production to increase. The more production of VFA results in more supply of glucose and then energy in ruminants. So it seems that, the growth of NFC will cause to increase the production. Increasing the dietary nonfiber carbohydrate enhanced dry matter intake, body weight, milk production, fat corrected milk production (FCM 3.5%), protein percentage, lactase and solid nonfat (SNF) while, the fat percentage decreased significantly. Although, by increasing NFC the BW increased, the treatments had not any significant effects on that. DMI percentage of body weight was not affected by treatments. The amount of total milk protein was increased by growth in nonfiber carbohydrate. Increasing level of NFC led to significant increase in CP, NFC, DM and OM digestion. The pH of the rumen is the key factor in normal and stable function of it. Because the fermentation and physiologic function of the rumen influences ruminal microbial population. The pH value and the quantity of ammonia N in rumen fluid are substantial parameters to reflect the ruminal fermentation. Ruminal pH and ammonia were decreased by increasing the NFC in which the decrease in treatments for ammonia was significant.
Conclusion Results showed that increasing nonfiber carbohydrate significantly increased milk production and milk protein percentage. It seems that diet of lactating cows in early lactation should contain over 36% NFC on DM bases.