Lactational and digestive responses of reducing dietary protein level and supplementing rumen-protected methionine in early-lactation dairy ewes

Abstract

We used 48 multiparous Lacaune dairy ewes (37 ± 2 DIM) to assess the effects of CP and digestible methionine levels on the performance, digestibility, metabolic efficiency and oxidative status of high-yielding dairy ewes in early lactation. Ewes were allocated into 8 balanced groups (6 ewes/pen) and milked twice daily and fed high-energy rations. The experiment lasted 51 d following a 2 × 2 factorial design, with ewes blocked into 2 CP levels (low protein [LP-15%CP], 14.8%; and high protein [HP-17%CP], 16.6%; on a DM basis), and 2 Met levels (control, 0 g/d Met [CON]; or 5 g/d Met [MET]), implemented in a crossover design with two 20-d periods separated by an 11-d washout period in between. Met supplementation was fed individually at morning milking. Individual DM intake was assessed using a pen-external marker approach (polyethylene glycol, 10 g/d per ewe). Milk yield was recorded daily, and milk composition, blood metabolites (6 h after Met administration), BW, BCS, and wool growth were measured for each period. No effects on DM intake, milk yield, milk protein, milk casein contents, or digestibility and efficiency were attributable to CP or Met dietary treatments. However, HP-17%CP diets increased milk urea content by 18%, whereas decreased milk fat content by 4% and total milk solids content by 2%, compared with LP-15%CP. Plasmatic urea decreased by 45% and plasma glucose increased by 6% in LP-15%CP compared with HP-17%CP, with no effects on other metabolites. Although positive energy balances were observed, protein balance values were unlikely negative, suggesting the need to revise the stated INRA requirements for dairy ewes. Plasma Met concentration was unaffected by dietary CP level, although it markedly increased (by 77%) with Met supplementation. Wool growth remained unchanged across dietary treatments. Under our conditions, neither dietary CP levels nor digestible Met supplementation improved lactational performance, oxidative status, or wool growth of dairy ewes.