Effects of replacing soybean products with dried brewer's grains and sunflower meal on growth, digestive utilisation, and blood amino acids and metabolites in lambs.

Soybean products are key ingredients in livestock feeding; however, the EU feed industry is highly reliant on soybean imports, whose production is associated with substantial environmental impacts, thereby compromising the sustainability of livestock production systems. This study evaluated the effects of replacing soybean meal and hulls in a high-cereal concentrate (CON) for fattening lambs with dried brewers' grains and sunflower meal (BGSF concentrate) on lambs' growth, digestive parameters and plasma metabolic profile. In addition, in vitro ruminal fermentation of concentrates was evaluated. Both concentrates were formulated to be isonitrogenous and isoenergetic. Twenty-two male Assaf lambs (15.5 ± 0.34 kg BW) were distributed into two homogeneous groups according to BW, and each group was assigned to one experimental concentrate. Lambs were fed concentrate and barley straw ad libitum until reaching about 25.0 kg BW. No differences between concentrates were observed in average daily gain, hot and cold carcass weight, and organs (liver, spleen, lungs, heart and kidneys) weights, indicating that the BGSF concentrate did not impair animal performance. Similarly, daily feed intake, feed conversion ratio and diet apparent digestibility were unaffected by the concentrate. However, lambs fed the BGSF concentrate showed higher postmortem ruminal pH, lower NH3-N concentrations, and tended to have lower total volatile fatty acid (VFA) concentrations than those fed the CON concentrate. Moreover, the BGSF-fed lambs showed lower molar proportions of butyrate and minor VFAs (sum of isobutyrate, isovalerate and valerate) than those fed the CON concentrate. In contrast, no differences were detected in caecal fermentation parameters, indicating that effects of the concentrate were limited to the rumen. Plasma concentrations of amino acids, metabolites and enzymes were generally similar between treatments, although lambs fed the BGSF concentrate tended to have higher concentrations of methionine and proline and lower concentrations of albumin. In the in vitro fermentation trial, the BGSF concentrate showed lower potential gas production and tended to have lower in vitro CP degradability. These findings indicate that a mixture of dried brewer's grains and sunflower meal can replace soybean meal and hulls in diets for fattening light lambs, thereby reducing the dependence on imported soybean. Moreover, its use could potentially reduce feeding costs and improve farms' sustainability by reducing the environmental impact associated with soybean production and transportation.