Physiological responses to selection for greasy fleeceweight in Romney sheep

Abstract Two studies were conducted using rams from the Massey University fleeceweight-selected (FW) and control (C) lines of Romney sheep. In the first study, conducted from April to July, nine ram hoggets from each line (mean liveweight 42.1 kg) were fed 1000 g/day protein-extracted lucerne meal for 6 weeks before being blood-sampled by jugular venipuncture. They were then assigned to one of three groups receiving 0, 30, or 60 g/day formaldehyde- protected casein in addition to the basal diet. Blood sampling was repeated after 4 weeks of casein supplementation. During the pre-casein period, FW rams exhibited lower concentrations of urea (6.1 versus 7.2 mM, SE=0.3, P < 0.05) and thyroxine (3.3 versus 4.3 μg/dl, SE = 0.5, P < 0.10) than Crams. During the period of casein supplementation, intakes of nitrogen (N) in the form oflucerne meal increased with dose of casein (from 24.8 to 26.1 g/day) but were not different between the lines. Casein supplementation also increased plasma urea concentration in a dos...

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