Discussion
In lamb fattening, one of the main ways to improve farmer´s profit, is to reduce feeding cots or improve feed efficiency of feedstuffs. Therefore, this objective can be achieved by improving weight gains and feed conversion (De Sousa et al. 2012). One strategy could be by replacing expensive feedstuffs with alternative resources. In this sense, in this study, soybean meal was replaced by sesame meal, which is normally less expensive than soybean meal in central Mexico.
According to the present study, lamb productive parameters were not affected after replacing soybean meal with sesame meal. This agrees with Mahmoud and Bendary (2014), who fed sesame meal on fattening lamb at an inclusion of 12.5% DM with 12.5% DM Nigella sativa meal to replace ingredients rich in protein such as soybean meal and cottonseed, and inclusion of sesame meal led to increase profitability.
Similarly, with fattening Awassi lambs, Obeidat et al. (2009), replaced soybean meal (16% of the total diet) either partially (8% soybean meal + 8% sesame meal) or totally (0% soybean meal + 16% sesame meal) with sesame meal and reported lower dry matter intake and daily weight gains compared to soybean meal fed animals. However, in the present study, no differences were detected in dry matter intake. It is noteworthy mentioning that in Obeidat et al. (2009) study, feed conversion and the cost per kg of lamb was improved in those animals feed only on sesame meal. This coincides with the fact that sesame meal could be a more profitable feeding strategy compared to the use of soybean meal.
Gebreslassie and Melaku (2009), found a positive effect when replacing wheat bran with sesame meal in lambs fed on a stubble diet. Treatments in that study consisted of supplementing 300 g/day of a supplement only based 100% sesame meal, 100% wheat bran, 65% wheat bran + 35% sesame meal or 35% wheat bran + 65% sesame meal. Daily weight gains and feed conversion were higher in animals receiving the highest content of sesame meal. It is important to mention that this sesame diet had the highest protein content than that of wheat bran. This study also, support our findings showing that sesame meal can be used to replace soybean meal in lamb diets.
In another study, Hassam et al. (2013) replaced wheat bran and peanut meal with sesame meal, at 15% or 20% inclusion, where at 15% inclusion level, daily weight gains (0.143 kg) were lowest, followed by inclusion at 20% (0.166 kg) being highest in the diet without sesame meal (0.179 kg). For feed conversion, the highest value was for 15% sesame meal (9.02) followed by 20% sesame meal (7.65) and the lowest for the diet without sesame meal (6.87). These results differ from those of our study probably due to the difference in the quality of inclusion of sesame meal in the diets, which in our study was 50 and 100% compared to 15 and 20% in the study mentioned above.
In this study, the highest gross profit margin was obtained from animals fed with 100% sesame meal. This is because the sesame meal price is considerably lower than that of soybean meal (sesame meal is 0.16 USD while soybean meal is 0.41 USD). This cal-culation was based on the existing prices during the study. Our results coincide with studies using Awassi lambs (Obeidat et al. 2009; Abo Omar 2002). In Obeidat et al. (2009) study, lambs had lower DWG and higher FC when fed with 100% soybean meal, which is a clear indicator that the differential in the price of sesame meal is significant. On the contrary, Abo Omar (2002) reported that inclusion of sesame meal did improve the DWG and FC with regard to diets without sesame meal. In this study, there was no significant difference in productive parameters, however, production costs were lower with sesame meal inclusion.
In this study, except for carcass length, carcass quality characteristics were similar between treatments. Fitwi and Tadesse (20013) found an improvement in the performance of Koraro sheep carcasses with diets based on teff stubble and with different inclusion levels of sesame meal instead of wheat bran. In that study, carcass yield was similar between different inclusion levels of sesame meal, and this could be explained because diets were isoproteic and isoenergetic. Similarly, Gorbani et al. (2018) used Zel lambs and reported no effects on carcass characteristics when replacing soybean meal with sesame mea at different levels of inclusion (0%, 25%, 50%, 75% and 100%) and diets were also isoproteic and isoenergetic.
For lamb production, the search for protein-feed alternatives that are less expensive compared to the conventional use of soybean meal is important. Especially when the use of alternative sources such as sesame meal do not have detrimental effects on productive traits and carcass characteristics. This suggests that the diets with sesame meal will have a lower price without reducing productivity and carcass quality, resulting in a lower production cost and a higher profit margin.