Effects of enriched mesquite piperidine alkaloid extract in diets with reduced crude protein concentration on the rumen microbial efficiency and performance in lambs

The objective of this study was to evaluate the effects of enriched mesquite piperidine alkaloid (MPA) extract at 31 mg/kg of dry matter (DM) in diets with 16% or 13% of crude protein (CP) compared to a diet with 16% CP without additive (control) and diets with monensin (MON) at 31 mg/kg DM and 16% or 13% CP. The intake, ingestive behaviour, apparent digestibility, body weight gain, microbial protein synthesis and nitrogen balance were evaluated. A total of 30 uncastrated crossbred Santa Inês × Bergamasca lambs were used and allocated in a completely randomized design. No effects of additives on dry matter (DM), organic matter (OM), neutral detergent fibre (NDF), and non-fibre carbohydrate (NFC) intake were observed in diets with 16% and 13% CP compared to the control diet. The total digestible nutrient intake (g/kg BW) for the diet with MPA 13% CP was lower than for the control diet, while the metabolisable energy intake (MJ/kg BW) did not differ between diets. The DM feeding rate (g/min) was reduced for the diet with MON 13% CP compared to the control diet. There was no difference between MON or MPA with CP 16% or 13% and the control diet in the digestibility of DM, OM, NFC, and NDF. MON in the diet with 13% CP reduced the BW gain, which differed from the control diet, while MPA 13% CP did not differ from the control diet. The microbial protein synthesis efficiency was higher for diets with MPA compared to MON 13% CP and the control diet. Dietary nitrogen retention (g/kg metabolic weight) was lower in diets with 13% CP that differed from the diets with 16% CP. The nitrogen retained as a percentage of ingested and digested nitrogen was unchanged with the use of MPA or MON 13% CP due to lower urinary nitrogen excretion. The MPA 13% CP diet does not affect the performance of lambs by increasing the microbial synthesis efficiency in the rumen.