Evaluation of digestive models of lactating cow diets containing citrus dry pulp using gas production method

Introduction: Iran is one of the sixth-largest citrus producing countries in the world, producing a large number of citrus varieties annually. The remaining citrus pulp comes from juices or composting plants that are widely produced in Mediterranean countries. Thousands of residual citrus processing plants are left untreated annually, while being one of the valuable resources in animal nutrition. Citrus pulp contains the skin and inner pieces of fruit collected from the citrus family (such as oranges, lemons, and grapefruits). Citrus wastes contain high energy for ruminants, so that the metabolizable energy of the dry pomace and its wet pomace is equal to 10.30 and 2.4 Mcal / kg, and can be used as a high-energy feed in ruminant nutrition (Nazim, 2001). Due to the high fermentation capacity of fiber feedstuffs, many citrus pulp wastes are suitable for use in ruminant rations (Grasser et al., 1995). Therefore, citrus pulp has long been considered as an energy-rich feed to meet the growth and lactation needs of ruminant animals (Solomon et al., 2000). According to the results reported by (Lashkari and Taghizadeh, 2015) it is possible to replace some of the cereal sources used in the livestock feed with citrus pulp, which significantly reduces the cost of regulated diets. Citrus pulp also has an antioxidant role that enhances the animal's immunity and enriches milk with phenolic compounds as anticancer compounds in lactating cows. In mixed diets, replacing starch feeds with light digestive cell wall feeds such as citrus pulp prevents the negative effects on forage digestibility produced by starch feeds. (Barius Urdanta et al 2003) The pectin consumed in citrus pulp has the ability to form gels and increase digestive capacity (Veragen et al. 2001). Non-fiber carbohydrates are made up of varying amounts of starch, simple sugars, beta-glucans, galactans and pectins. In vitro, gas production increases with the addition of non-fiber carbohydrates, and agrees with the notion that gas production increases with increasing fermentable precursor content (Blummell and Ørskov, 1993). The use of dried citrus pulp beet as a source of non-forage fiber in a lactating dairy cow in a diet is effective in improvement of performance and increasing of milk fat. The energy content of diet increased when dried citrus pulp used in ruminant nutrition. Dried citrus pulp dough is suitable for feeding Holstein cows and improves livestock performance, especially Holstein infants. As well as antioxidant compounds of citrus pulp, it strengthens the phenolic compounds of milk. Our results some positive effects of citrus pulp on diet degradability and in vitro fermentation parameters and indicate that maize in dairy sheep diets can be totally replaced by dried citrus pulp without negatively affecting ruminal fermentation. The use of citrus pulp would reduce the amount of human-edible ingredients used in the diet of dairy sheep. Its accumulation can cause environmental problems, and it causes high disposal costs for citrus processing factories (Jairo García et al. 2020).
Purpose: This experiment was conducted to determine the nutritional value of the ration of lactating cows containing citrus pulp and determine the fermentation parameters and degradation of dry matter and crude protein in citrus pulp. The amount and rate of gas production were determined by Manek and Steingass. Method (1988). According to Sunvold et al. (1995), about 450 g / kg of the cell wall contains citrus pulp pectin, which is fermented in the rumen at high rates. Dried Citrus pulp has high pectin, which is used in rumen microflora and improves fiber digestion (Barius-Urdanta et al. 2003). By using pectin-rich foods such as citrus pulp, they reduce the cost of feed, prevent gastrointestinal disorders in ruminants and help improve digestibility of cellulose compounds (Brodrick et al. 2002). To overcome the difficulties of using cereal grains in ruminants, it is best to use different energy sources such as dried citrus pulp and sugar beet or their mixture ) (Kalle and Adsule. 1995). According to Bumpidis and Robinson (2006) citrus pulp content contains 24.10 grams of soluble sugars per kg of dry matter. Estimated dietary variables of lactating cows including metabolizable energy (ME), lactation energy net (NEL), digestible organic matter (DOM), short chain fatty acids (SCFA) are possible using gas production method.
Materials and methods: Evaluation of the diet of lactating cows was performed using gas production method. The experimental treatments included dietary control of the diet without the use of dry citrus fruits, diets with 50%, 75% and 100% replacement of dietary maize with mixed dry bark. For this purpose, gas production was recorded at 2, 4, 6, 8, 12, 16, 24, 28, 48 and 72 hours. Three different digestive models were used to evaluate the dry matter and protein content of citrus pulp. Ørskov model were used without regard to the delay phase (1979), the model of france et al. (1993) and the model of france et al. (1999). To select the best evaluation model, the minimum variance and maximum explanatory factor were used.
Results and discussion: The results showed that there is no significant difference between treatments at different incubation times. By considering of MSE and R2 in fitted models, the best digestible models for the gas production of diet containing of citrus pulps were selected. For control diet, diet containing of citrus Pulps (50 and 75%), and diet containing of 100% citrus pulps models of Ørskov without delayed phase, France model and Ørskov without delayed phase were fitted, respectively. The production of soluble and insoluble part gas (a + b) in citrus pulp 0, 50, 75 and 100% is 225.79, 235.55, 245.83, 239.35 ml / g dry matter respectively. The rate of gas production (c) in the above treatments was 0.079, 0.049, 0.054 and 0.063 ml / h, respectively.
Conclusions: According to the results of gas production experiments, citrus pulp is a suitable source of energy for ruminants. The results also showed that citrus pulp could be used as a non-forage fiber with greater biodegradability and gas production in ruminant rations. According to the suitability of the model and the biological behavior of the digestive kinetics of the Ørskov model without delay phase (1979) y = A (1 – e-ct), the best model is determined.