Document Type : Research Articles
Department of Animal Science, Mohaghegh Ardabili University, Ardabil, Iran
Introduction Moghani sheep, one of the dominant meat breeds among Iranian sheep, is known for its good body size, resistance to changes in weather conditions, and capacity to produce heavy-weight lambs. The Romanov breed is known worldwide for its early sexual maturity, long breeding season, and high productivity. Among high-yielding breeds, the Romanov breed achieves higher twinning and fertility, higher weight of ewes, optimal shelf life of lambs, and heavier final weight of lambs. During past years, increasing productivity of Iranian native sheep breeds, including the Moghani breed, has been implemented through cross-breeding with high-yielding foreign breeds such as the Romanov breed to improve growth and twining rates and reduce size of the fat-tail. Crossbreeding is a way to improve poor production and reproductive characteristics of livestock. Due to the lack of information regarding the fattening performance and carcass characteristics of the Romanov-Moghani crossbreeds, the aim of this study was to investigate the fattening performance carcass characteristics, blood parameters, feed intake and digestibility of Moghani and Romanov-Moghani crossbreed fattening lambs under diets with different energy levels.
Materials and methods This research was conducted using 24 male lambs (10 Moghani lambs and 10 Romanov-Moghani cross-bred lambs) as a factorial design with 4 experimental groups and 6 replications (lambs) in each group. The duration of the experiment was 75 days. The experimental groups in this research include: 1) Moghani lambs fed low energy diet, 2) Moghani lambs fed high energy diet, 3) Romanov-Moghani lambs fed low energy diet, 4) Romanov-Moghani lambs fed high energy diet. A rumen-protected energy powder (Energizer RP-10, IFFCO, Johor, Malaysia) was used to increase the energy level in high-energy diets. Fattening performance was measured by weighing the lambs every two weeks. At the end of the experiment, all the lambs were slaughtered and the carcass characteristics, including hot carcass percentage, cold carcass percentage, tail percentage, and back fat thickness were measured. After 24 hours of storage in 4 ºC, back-fat thickness between the 14th and 13th vertebras was measured with a digital caliper. Blood samples were drawn from the jugular vein of all lambs 3 hours after feed consumption, and the samples were immediately centrifuged at 3500 rpm for 15 minutes then the plasma samples were frozen at -20 ºC till analysis day determining concentrations of blood parameters including glucose, blood urea nitrogen, cholesterol, triglyceride, total protein, albumin, and globulin were determined using commercial kits and spectrophotometer. All the data were analyzed in the form of a completely random design and factorial experiment using the GLM method for statistical analysis.
Results and Discussion The results showed that Moghani lambs had significantly more tail percentage and lower tailless carcass percentage than Romanov-Moghani mixed lambs. Feeding a diet with a higher level of energy by feeding protected rumen fat decreased the percentage of the tail and increased the percentage of the carcass without the tail. Moghani lambs fed with high-energy diet had the highest waist fat thickness compared to all groups. On the other hand, the average daily weight gain was only influenced by the energy level of the diet. Based on the results, Romanov-Moghani crossbred lambs had a higher weight gain than Moghani lambs, and fat supplement feeding improved livestock performance. Due to the fact that no significant difference was observed in the feed consumption of lambs due to fat supplement feeding, therefore, the better fattening performance of lambs in the groups fed with fat supplement can be attributed to the increase in energy intake in these animals as well as the higher efficiency of the metabolic energy conversion of fats compared to carbohydrates (Navidshad and Jafari Sayadi, 2018). Based on the obtained results, Romanov-Moghani mixed lambs had a higher weight gain than pure lambs, and also fat supplement feeding improved the performance of livestock. Based on the obtained results, mixing the tailed Moghani breed with a tailless breed such as Romanov can be considered an efficient solution to reduce the tail percentage of the carcass and improve the yield of the carcass. On the other hand, providing energy in the form of fat may also result in a relative decrease in the percentage of carcass tails. The better fattening performance of lambs in groups fed with fat supplementation can be attributed to the increase in energy intake in these animals as well as the higher efficiency of metabolic energy conversion of fats compared to carbohydrates (Navidshad and Jafari Sayadi, 2018). The lack of effect of fat supplementation on digestibility could be due to the consumption of protected rumen fat that did not affect the activity and fermentation of rumen microorganisms. According to a report, crossbreeding did not have a significant difference in the apparent digestibility of nutrients between Lori Bakhtiari-Romanov mixed lambs and pure Lori Bakhtiari lambs (Mousavinia et al., 2015).
Conclusion: In general, the results of this experiment indicated that crossbreeding the tailed Moghani breed with a tailless breed like Romanov can be an efficient solution to reduce the tail percentage of the carcass and improve the yield of the carcass. On the other hand, providing energy in the form of fat may also lead to a relative decrease in the percentage of carcass tails.