Replacing Soybean Meal with Meat Meal in the Diet of Fattening Mehraban Lambs: Effects on Performance, Rumen Fermentation, and Blood Parameters

Abstract:
Background and Objective: Soybean meal is typically rapidly degraded in the rumen; its current price (56%) is higher than that of meat meal, and a major portion of it is imported into Iran. On the other hand, significant amounts of meat meal are produced in the country's livestock and poultry slaughterhouses. This study aimed to investigate the effects of replacing soybean meal with meat meal on growth performance (weight gain, feed conversion ratio, and dry matter intake), rumen fermentation parameters (pH, ammonia nitrogen, and total volatile fatty acids), protozoal population, and blood parameters in Mehraban lambs.

Materials and Methods: In this study, 28 male Mehraban lambs (4 months old, average weight: 36.20 kg) were fattened for 72 days (14 days for adaptation and 58 days for the experimental period) with two different concentrate-to-forage ratios (60% concentrate and 40% forage for the first 25 days, and 70% concentrate and 30% forage for the remaining 33 days). The lambs were randomly assigned to four treatments with seven replicates per treatment in a completely randomized design and housed in individual pens. The experimental diets included: 1) a basal diet (containing 10% soybean meal and no meat meal—control group), and 2) second, third, and fourth treatments: basal diet with 25%, 50%, and 100% replacement of soybean meal with meat meal, respectively. The feed in the first fattening period consisted of 40% forage and 60% concentrate (higher protein, lower energy), while in the second period, it consisted of 30% forage and 70% concentrate (lower protein, higher energy). Lambs had free access to their daily ration, which was distributed at 8:00 AM, 2:00 PM, and 7:00 PM. Growth performance (total weight gain, daily weight gain, dry matter intake, and feed conversion ratio), rumen fermentation parameters (pH, ammonia nitrogen, volatile fatty acids), protozoal population, and blood biochemical parameters (glucose, triglycerides, cholesterol, urea, albumin, and total protein) were evaluated. Methane production was also estimated using equations.

Results: The results showed that replacing soybean meal with meat meal had no significant effect on growth performance but led to a 16% reduction in meat production costs (P < 0.05). In the first month, lambs receiving 5% meat meal (277 g/day) had a higher daily weight gain (32 g more) compared to the control group (244 g/day) (P < 0.05), although higher temperatures (above 25°C) in the second period reduced feed intake. Consequently, the feed conversion ratio in the second period was 5 units higher than in the first period. The rumen pH remained stable throughout the study. Ammonia nitrogen levels decreased significantly with meat meal supplementation (P < 0.05) and were even lower in high-concentrate diets (P < 0.05). Total volatile fatty acids remained constant overall but increased in the first period (P < 0.05), while methane production (P < 0.05) and total gas output (P < 0.05) were lower in meat meal-supplemented groups compared to the control. Replacing soybean meal with meat meal significantly increased the dietary metabolizable energy (P < 0.05). Rumen pH in live animals and gas test results were similar across all four treatments. A comparison of fermentation parameters between the first and second periods showed that rumen stability was achieved in the second period, with no differences among treatments. Except for ammonia nitrogen, all fermentation indices were higher in the second period compared to the first (P < 0.05). The protozoal population was not affected by protein source but increased with higher concentrate levels in meat meal-containing diets (P < 0.05). Throughout the study, only blood cholesterol levels increased with meat meal consumption (P < 0.05).