Nutrient digestibility, nitrogen metabolism and hepatic function of sheep fed diets containing solvent or expeller castorseed meal treated with calcium hydroxide

Abstract Nineteen sheep averaging 56 kg of initial body weight were used in a completely randomized design to investigate the effects of feeding Ca(OH) 2 -treated (40 g/kg, on fresh matter basis) or untreated castorseed meal (CSM) sources on intake, total tract digestibility, hepatic function, and microbial protein synthesis and efficiency. Animals were maintained in metabolic crates for 21 days with 16 days for diet adaptation and 5 days for data and samples collection. Sheep were fed once daily experimental diets containing one of the following 5 protein supplements (150 g/kg of the diet DM): (1) soybean meal (SBM); (2) solvent CSM (SCM); (3) SCM treated with Ca(OH) 2 (TSCM), expeller CSM (ECM); or ECM treated with Ca(OH) 2 (TECM). Treating SCM and ECM with Ca(OH) 2 reduced the ricin concentration in 63% leading to an average decrease from 2.46 to 1.06 g/kg of BW in the ricin daily intake ( P P  > 0.05). There was no effect of diets on intake of nutrients ( P  > 0.05) with the exception of non-fibrous carbohydrates (NFC) intake, which was greater ( P  = 0.029) in sheep fed SBM vs. CSM diets and that of ether extract, which was lower ( P  = 0.049) in sheep fed solvent CSM diets vs. expeller CSM diets. However, treating SCM and ECM with Ca(OH) 2 tended to increase intakes of DM, CP and NFC. Apparent total tract digestibility of nutrients was not affected by diet ( P  > 0.05) with the exception of ether extract digestibility, which was lower in sheep fed SBM vs. CSM diets ( P  = 0.001) but greater ( P  = 0.023) in sheep fed solvent CSM diets vs. expeller CSM diets. Treating SCM and ECM with Ca(OH) 2 increased or tended (0.05 >  P  > 0.10) to increase the apparent total tract digestibility of nutrients with the exception NFC. Microbial protein synthesis ( P  = 0.013) and microbial efficiency expressed either as g of microbial CP per g of CP intake ( P  = 0.043) or as g of microbial CP per g of rumen-degradable CP intake ( P  = 0.030) were all increased by treating SCM and ECM with Ca(OH) 2 . Despite the increase ( P  = 0.022) in the urinary excretion of urea-N (g/day) by treating SCM and ECM with Ca(OH) 2 , the greater microbial efficiency reduced ( P  = 0.021) fecal-N losses expressed as proportion of N intake numerically increasing retained-N by 21.3%. Treating SCM and ECM with 40 g of Ca(OH) 2 /kg did not completely denaturate ricin but increased microbial protein synthesis and the efficiency of N and energy by ruminal microbes with no detrimental effect on the hepatic function of sheep.