Abstract
Simple SummaryThere is a renewed interest on the potential inclusion of urea in ruminant diets, reducing the contribution of vegetable protein supplements. This study was designed to evaluate the effect of replacing soybean meal with different proportions of urea in protein-rich diets for heavy fattening lambs (from 29 to 50 kg of live body weight). Our results suggest that 39% of soybean meal of such diets can be replaced with urea reducing the feeding costs without any adverse effects on feed efficiency, rumen fermentation, or carcass and meat quality. Nevertheless, urea supplementation even at levels of 1% of dry matter may trigger mild metabolic acidosis that can affect animal health in the long term.Thirty-six Assaf male lambs (29.4 ± 3.10 kg body weight (BW)) were used to study the feasibility of including urea (at 0, 0.6 or 0.95% of dry matter for Control, Urea1, and Urea2 diets, respectively) in substitution of soybean meal in fattening diets. Animals were individually penned and feed intake was recorded daily. Blood samples were taken at days 35 and 63 of the experimental period to determine the acid-base status and the biochemical profile. At the end of the experiment (nine weeks), lambs were slaughtered, ruminal contents were collected and carcass and meat quality were evaluated. There were not differences (p > 0.05) among treatments in dry matter intake, animal performance, ruminal fermentation pattern, and carcass and meat parameters. Serum albumin concentration was higher and concentration of HCO3 and total CO2 in blood were lower in Urea2 compared to Urea1 and Control lambs. These results, together with the tendency to lower (p = 0.065) blood pH in this group might suggest a moderate metabolic acidosis. Partial replacement of soybean meal with urea did not impair growth rate in heavy fattening Assaf lambs (from 29 to 50 kg body weight), reduced feeding costs and had no adverse effects on feed efficiency, rumen fermentation and carcass and meat quality.
Highlights
Global demand of vegetable protein feeds for livestock is growing as a result of the increased demand for animal-based protein
Animals were randomly allocated to three experimental groups (12 animals per treatment group, equilibrated by body weight (BW) and age) and fed the following diets: Control, Urea1 (6 g of urea/kg dry matter (DM)), and Urea2 (9.5 g of urea/kg Dry matter (DM))
In the in vitro assay, volatile fatty acids (VFA) production was reduced in the Urea1 group compared with Control and Urea2 groups, with no differences in the other parameters evaluated
Summary
Global demand of vegetable protein feeds for livestock is growing as a result of the increased demand for animal-based protein. It is expected that livestock production by 2020 will become the most important agricultural sector in terms of added value, if the challenges related to environmental impact and competition for resources are adequately addressed [1,2,3,4]. In this context, the European Union is increasingly aware of the deficit in vegetable protein for animal feeding and alerts about the importance to reduce the massive dependency on imports of protein crops because of the environmental impact in producing regions and the volatility of the protein prices in international markets [5]. Current situation of the growing global demand of vegetable protein for livestock feeding has renewed interest in extending the use of urea as much as possible in ruminant feeding, and a research effort is being made to establish the optimal level of this non-protein nitrogen source for each specific nutritional situation [6,7,8]
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