چكيده لاتين :
Introduction: Milk and other dairy products, important in human diet, are valuable sources of protein, vitamins, and minerals. Milk fat contains substances known to have various bioactivities (e.g., antioxidant, anti-cancer, …). Fat milk due to extensive bio hydrogenation of unsaturated fatty acids in the rumen and the synthesis of short and medium saturated fatty acids in the mammary glands have a high concentration of saturated fatty acids (Shingfield et al., 2010). Goat, providing a variety of products in particular milk, is grown as one of the domestic ruminants in different parts of the world. Goats are highly adaptable to unfavorable environmental conditions and resistant to many diseases making the maintenance and cultivation of these small size animals possible in rural areas (Cheng, 1991). Cereals are one of the most important nutrients in livestock feed, which greatly affects the economic aspects of production (McAllister et al., 1990). The lactating animals during and after the transition period undergo significant changes in the metabolism of glucose, fatty acids, and minerals. In order to meet the metabolic needs of livestock, different nutritional strategies have been used in this period (Overton and Waldron, 2004). Feeding non forage carbohydrates and fat in the diet or reducing the percentage of milk fat at the start of lactation through some specific fatty acids to reduce energy demand in early lactation have commonly been used by breeders (Bauman and Griinari, 2003). Use of fat in the diet is a management tool in controlling metabolic events around childbirth (Doepel et al., 2002). This experiment was conducted to investigate the effect of using rapeseed as a source of fatty acid in corn- and barley-based diets on the functional and metabolic responses of the Mahabadian goat breeder in early lactation period. Materials and methods: The treatments consisted of barley- and corn-based diets, barley + 5% rapeseed (w/w) diet and corn + 5% rapeseed (w/w) diet. Feeds were provided to livestock in the form of TMR. This experiment was carried out on 16 female Mahabadian goat breeders in the early stage of lactation in a completely randomized design, 2 × 2 factorial arrangement, with two source factors of cereals and rapeseed. The mean of treatments was compared with Tukey test at 5% confidence level. This study was conducted in a one-month trial period after birth and 14 days of adolescence. During the experimental period, the amount of feed intake and weight gain were recorded. Feeds were sampled weekly to determine dry matter intake, nutrient organic matter, dry matter, crude protein, insoluble fiber in neutral detergent and insoluble fiber in acidic detergent. Blood samples were obtained from veins of the goats on the last day of experiment, 4 hours after morning meal, to measure selected blood parameters. The blood samples were immediately transferred to the laboratory, centrifuged (6000 rpm for 7 minutes), and then the serum was isolated and stored at -20°C. Triglyceride, cholesterol, urea nitrogen, total protein and glucose levels of the serum were measured using Pars Azmon kit and ELISA reader (DANA-3200 model, made by Garni Company in Germany country). Rumen fluid samples were obtained in the final day of experiment (4 hours after feeding) to measure the protozoa count, ammonia nitrogen, volatile fatty acids as well as pH. The pH of the rumen fluid was measured immediately using a pH meter (Schott Titrator Titroline easy model, Germany). Rumen fluid samples were smoothed using 4-layer sackcloth.
Results and discussion Addition of rapeseed to feed did not significantly affect dry mater intake. The apparent digestibility of DM, OM, CP, and EE were not significantly affected by the diet but the amount of NDF, ADF was lower compared to the control group. The fatty acids significantly increased total cholesterol and total protein but no significant changes were observed in albumin, urea, triglyceride, and glucose concentrations. Milk composition was not significantly affected by treatments, but milk production was significantly higher in corn + rapeseed and barley + rapeseed treatments. Effects of diet were insignificant on pH of rumen fluid but the number of protozoa decreased. The amount of iso-voleric and voleric acid increased from ruminal fluid VFA, but there was no significant change in the amount of propionic acid and butyric acid.
Conclusions: According to the results, it can be concluded that the use of rapeseed as a source of fatty acid in a grain-based diet improves the performance of lactating goats. Addition of 5% (w/w) rapeseed in corn- and barley-based diets can reduce dry matter consumption while increasing milk production. Therefore, the use of 5% is recommended in grain-based rations at the lactation stage in Mahabadian goats.
