Investigating Chemical Composition and Effects of Different Dietary Levels of Whole Carrot Tops on Ruminal Digestion and Fermentation Kinetics in vitro

Introduction Animal husbandry is one of the most important agriculture sectors, and with increasing population; demand for animal products has been increased. Currently, due to shortage of water and feed resources as well as increased compete for production of food between human and animals, cost of animal feeds has been enhanced considerably. The global price of feed ingredients such as corn, wheat, fish meal and soybean meal has increased by 160, 118, 186 and 108%, respectively in the previous years. Thus, in this situation, using agro-industrial by-products in the ruminant diets could reduce feed production costs and also improve profitability. Whole carrot tops (WCT) are one of such agricultural byproducts. It remains after harvesting the main product (carrot) and could be used as silage for animal nutrition. Crude protein (CP), crude fiber, ash, nitrogen free extract, Ca and P contents of WCT has been reported 144, 25.1, 151, 189, 493, 24.3 and 7.7 g/kg DM respectively. In another study, WCT contained 11−12% CP, 17% crude fiber and up to 18% ash due to residual dirt. Leaves in WCT have more nitrogen and ash but lower fiber content compared to stems. Due to phenolic content of WCT, using it in ruminant nutrition may be improves rumen protein metabolism via binding dietary CP content. WCT replacing 50% of berseem hay in the diet of Rahmani sheep increased nutrient digestibility. Adding WCT up to 20−30% at the expense of Trifolium alexandrium hay in growing rabbit rations improved growth performance and feed conversion efficiency. However, higher levels (67 to 100%), replacing clover hay in the diet, depressed the performance of growing rabbits. There are a few reports about investigating the nutrition value of WCT as a new by-product in animal nutrition. Therefore, this study was conducted to evaluate chemical composition, in vitro gas production (IVGP), fermentation parameters and nutrient digestibility of WCT compared to alfalfa and wheat straw (WS) using IVGP technique. Effects of different dietary levels of WCT at the expense of forage potion up to 20 % of dry matter (DM) were also investigated using IVGP technique.  Material and Methods This study was conducted in animal house and laboratories of Lorestan University. Two Lori sheep (about two years old) with permanent rumen fistula were used as rumen liquor donor in present work. A two-week diet adaptation period was followed by collection of the rumen contents from each sheep before the morning feeding. Four complete carrot plants were collected during October 2017 from commercial carrot field in Share-Kord city (Iran). At the first part, chemical composition, IVGP and fermentation parameters of WCT were determined compared to alfalfa and WS (totally three treatments). After that, different levels of WCT including 0, 5, 10, 15 and 20 % of DM (five treatments) were replaced with forage (alfalfa hay and WS) portion of diet and incubated in vitro using IVGP technique. Dry matter, CP, ash, neutral detergent fiber, acid detergent fiber and lignin were measured.Results and Discussion Results showed that CP content of WCT was significantly higher than WS, but it was comparable with alfalfa. At 16 h of incubation, highest and lowest volume of GP was observed by WCT and WS, respectively (P<0.05). However, highest and lowest GP at other incubation times, potential (b) and rate (c) of GP, DM, organic matter (OM), estimated metabolizable energy (ME), ammonia-N concentration and short chain fatty acid (SCFA) production were noted by incubation of alfalfa and WS respectively (P<0.05). Highest microbial protein synthesis (MPS) was observed by incubation of WCT and lowest amount was for WS (P<0.05). By inclusion of WCT up to 20 % of diet, except for MPS which was increased significantly (P<0.05), other IVGP and fermentation parameters were unchanged among dietary treatments (P>0.05).Conclusion In conclusion, results from the present study indicate that WCT has potential nutritional value to be used in ruminant diets at up to 20% DM without the risk of digestive disturbances. Its nutritive value was also higher that wheat straw while it had a comparable CP content to alfalfa. However, further in vivo studies are needed to validate the benefits of introducing such a by-product in ruminant nutrition. Further studies such as determining potential anti-nutritional factors, as well as the mineral profiles of WCT, will be of great help for optimizing their incorporation in animal nutrition.