اثرات جايگزيني جو با انواع ذرت فرآوري شده بر عملكرد، تخمير شكمبه اي و سودآوري در بره هاي نر افشار

Effects of replacing barley with different processed corn on performance, carcass quality, rumen parameters and profitability of Afshar feedlot lambs

زمينه مطالعاتي: در پرواربندي گوسفند، جو به عنوان يك غله بومي تنها منبع تامين نشاسته در جيره است؛ اما با توجه به سريع التجزيه بودن نشاسته جو در شكمبه كه موجب كاهش pH و بروز اسيدوز و درنتيجه، افت عملكرد دام مي شود، جايگزيني اين غله با غلات ديگري همانند ذرت كه سرعت تجزيه پايين تري دارد، مفيد به نظر مي رسد. هدف: در اين مطالعه اثر جايگزيني جو با انواع ذرت فرآوري شده بر عملكرد، قابليت هضم خوراك، متابوليت هاي شكمبه، كيفيت لاشه و سودآوري اقتصادي بره هاي نر پرواري مورد بررسي قرار گرفت. روش كار: آزمايش در قالب طرح كاملاً تصادفي با 7 تيمار شامل: جيره شاهد (100 درصد جو)، 2- 50:50 جو و ذرت آسياب شده، 3- 100 درصد ذرت آسياب شده، 4- 50:50 جو و ذرت ورقه شده با بخار، 5- 100درصد ذرت ورقه شده با بخار، 6- 50:50 جو و ذرت پلت شده، 7- 100 درصد ذرت پلت شده انجام شد. به هر تيمار 5 تكرار تعلق گرفت و در كل، 35 راس بره به مدت 84 روز مورد آزمايش قرار گرفتند. نتايج: مقايسات مستقل نشان داد كه در دوره هاي 14، 28، 42 و 56 روزگي تمام تيمارها وزن بالاتري نسبت به تيمار شاهد داشتند (0/05>P). در كل دوره بيشترين ميزان ضريب تبديل غذايي با مقدار 8/62 مربوط به تيمار شاهد و كمترين ميزان آن با مقدار 6/22 مربوط به تيمار50% ذرت آسياب شده بود. تيمار 100 درصد ذرت پلت شده و تيمار شاهد با ميانگين 1/79 و 1/52 به ترتيب، بيشترين و كمترين مقدار مصرف ماده خشك را داشتند (0/05>P). همچنين، تيمارها اثري بر وزن لاشه و قابليت هضم ماده خشك نداشتند، ولي وزن دنبه و نسبت وزن دنبه به لاشه در تيمار 100% ذرت آسياب شده بيشترين مقدار بود (0/05>P). علاوه بر اين، طبق نتايج تحليل اقتصادي، جيره 100 درصد ذرت آسياب شده بيشترين ميزان تاثير نسبي بر سودآوري را داشت. نتيجه گيري نهايي: نتايج اين مطالعه مشخص كرد كه استفاده از ذرت در جيره يا جايگزيني 50 درصد از جو با ذرت، مي تواند عملكرد رشد و سودآوري بره پرواري را بهبود دهد. همچنين، ذرت پلت شده در بين جيره هاي حاوي ذرت، مي تواند افزايش وزن و ماده خشك مصرفي بيشتري ايجاد نمايد.

Introduction: Barley as native cereal is the main source of carbohydrates in fattening sheep in Iran. However, since the starch in barley has higher degradation rate than corn starch, it may cause metabolic disorders such as acidosis and decrease growth performance. Furthermore, the feeding value of a cereal grain is a function of several factors: its nutrient content, different physical and chemical characteristics that influence on digestibility, palatability as it changes feed intake, and associative interactions with the digestive process. In this study, the effect of replacing barley with different processed corn on performance, dry matter digestibility, rumen metabolites and carcass characteristics in Afshari fattening lamb were investigated. On the other hand, change in ration composition has economic and financial effects in addition to the nutritional effect. Decision making about ration composition or changing it ignoring these financial and economic effects, could result in negative consequences. Different ration compositions could simultaneously have different cost and revenue effects and eventually different profitability consequences. So, this study has also tried to investigate all positive and negative economic consequences of replacement barley with different processed corn in fattening lambs. Material and methods: The protocol used in this study was approved by the Animal Ethical Committee at Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran with respect to animal experimentation and care of animals under study. The feeds were formulated according to NRC (1985) recommendations for fattening sheep with equal quantity of energy and protein as 7 treatments including 1) 40% Barley (control) , 2) 20% Grinding Corn, 3) 40% Grinding Corn, 4) 20% Steam Flaking Corn, 5) 40% Steam Flaking Corn, 6) 20% Pelleting Corn and 7) 40% Pelleting Corn (Table 1). Five Afshari ram lambs were allocated to each treatment. The animals kept in a separate pen individually for 84 days (May to July, 2015) in animal research farm of Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. Growth performance data were analyzed as a completely randomized design using the general linear model (GLM) procedure of SAS software (SAS 2003). The significant differences between treatment means were detected by Tukey-Kramer test at p<0.05. Many studies have revealed that the lighter initial weight could result in the higher fattening efficiency. Therefore, in this study initial weight was included in ANOVA analysis as covariate factor. Results and discussion: Animals had a daily body weight gain from 167 to 225 gr/day and mean FCR about 8.46. There was no significant difference between dietary treatments for final body weight, daily weight gain, FCR and gross profit (P<0.05). Also, DMI for the rations include Pelleting Corn was higher (p < 0.05) than the control ration (40% Barley). The independent comparisons showed that all treatments had more weights rather than control treatment in periods 14, 28, 42 and 56-days (p<0.05). In the whole period of fattening highest and the lowest feed conversion ratio were related to control and 50% grinded corn respectively (p<0.05). 100% Pelleted corn and control treatment had the highest and lowest daily feed intake respectively (p<0.05). Although, the treatments had no effects on carcass weight and digestibility, but 100% grinded corn had the highest fat tail weight (p<0.05). Also, The results of economic analysis indicated that the rations control treatment and 100% steam flaking corn respectively have the least and the most cost increase for all periods. Also, the rations control treatment and 100% pelleting corn respectively have the least and the most revenue increase for all periods. Totally, and based on the partial budgeting results the rations 100% steam flaking corn and 100% pelleting corn respectively have the least and the most effects on relative profitability for all periods. Conclusion: Replacing barley with processed corn in feed composition of fattening lambs could have some positive consequences. It could improve body gain, feed conversion ratio and dry matter intake that means improve of growth performance. But, its net effect on the profitability depends on the relative price of barley to corn. In this study, in spite of greater market price of corn than barley and then more feed costs, this replacing could improve profitability. Among the corn based rations, the 40% pelleting corn ration created better growth rate compared to the other processed corn.