Effect of protein source and quality on feedlot growth performance and rumen fermentation characteristics of Dohne Merino lambs

Abstract

The importance of protein quality in the formulation of ruminant rations has been regarded as inconsequential in the past. Moreover, the use of agro-industrial by-products as feed ingredients have become attractive alternatives in the animal feed industry, whereby several of these products characteristically have alternative protein qualities. Dried brewer’s grains (DBG) is a by-product originating from the beer manufacturing industry, frequently incorporated in the diets of feedlot lambs, however, has caused obstacles in some feed mills in South Africa. The oilseed by-products: canola-, soybean- and cottonseed meal, have all been proposed as suitable protein sources which can be included lamb feedlot diets. In this study, DBG, canola meal, soybean meal and cottonseed meal were incorporated as protein sources into concentrate-rich feedlot lamb diets. All experimental diets were formulated to contain 14% crude protein (CP) and 10.2 MJ ME/kgDM. The four experimental treatments differed in terms of the inclusion of the primary protein source which was either DBG, canola meal, soybean meal or cottonseed meal. Two experiments were conducted. The first experiment, comprising a feedlot growth experiment, utilized a randomised complete block design (RCB) as the experimental design. It was conducted using 200 Dӧhne-Merino lambs in order to investigate the effect of protein quality on the growth performance, feed intake and carcass parameters. The average total weight gained over the duration of the feedlot growth trial, as well as the average daily gain (ADG) of the canola meal treatment, was lower (P<0.05) than the other three treatments. Higher (P<0.05) feed intakes were realised on the cottonseed meal diet as opposed to the other three treatments. Additionally, lower (P<0.05) feed intakes were realised on the DBG diet when compared to the other three treatments. The feed iv conversion ratio (FCR) of the DBG diet was better (P<0.05) than the canola-, soybean- and cottonseed meal treatments, respectively. Conversely, the FCR realised for the canola meal diet was poorer (P<0.05) than the other three treatments. The lower (P<0.05) final live weights of the lambs from the DBG treatment, in comparison to those from the canola meal and cottonseed meal treatments, translated into lower (P<0.05) hot and cold carcass mass. Carcass classification remained unaffected (P>0.05) by treatment. Nevertheless, dissimilarities (P<0.10) were detected in the dressing percentages of the canola meal treatment and cottonseed meal treatment, whereby the dressing percentages of the former were higher. The second experiment entailed four mature cannulated wethers being subjected to a 4×4 Latin square design in order to investigate the effect of protein quality on the intake, apparent total tract digestibility, degradability and some rumen fermentation parameters of the sheep. Feed intake was greater (P<0.05) for the DBG diet as opposed to the soybean meal diet. Thus, the feed intake results of the two separate experiments differed from one another. The apparent DM digestibility of the DBG diet was lower (P<0.10) than the soybean meal diet. A higher (P<0.05) apparent CP digestibility was realised on the soybean meal diet, as opposed to the DBG and canola meal diets. The apparent total tract starch and NDF digestibility remained unaffected (P>0.05) by treatment for the current study. A lower dry matter (DM) degradability estimate (P<0.05) was realised for DBG, when compared to the other three treatments. No differences (P>0.05) were detected in the CP degradability estimates between the four respective protein concentrates, however could have been predisposed to experimental error. Average ruminal pH was higher (P<0.05) for the cottonseed meal diet, as opposed to the other three treatments and average ruminal ammonia nitrogen concentration did not differ (P>0.05) between treatments. The results advocate that protein quality has the potential to influence growth parameters, digestibility and rumen fermentation in sheep. Further research needs to be conducted on the inclusion levels of the respective protein concentrates and the breakpoint in the feeding period, where protein quality can be regarded as not important anymore.