Abstract

The objective of this study was to investigate the effect of grazing a diverse pasture of plantain, Italian ryegrass, and red clover versus a ryegrass-white clover pasture on the liveweight gain (LWG) and urinary nitrogen (N) excretion of ram lambs over an 82- day experimental period in autumn. Eighty Coopworth ram lambs (8 months old) were allocated to two replicates of two pasture treatments (n = 20), a diverse pasture containing plantain, Italian ryegrass, and red clover (Diverse) and conventional ryegrass-white clover pasture (RGWC). Unfasted live weight (LWT) of lambs was recorded on seven occasions during the autumn experimental period. Apparent dry matter intake (DMI) was estimated as the difference between pre- and post-grazing herbage mass plus daily herbage growth. On two occasions, urine and blood samples were collected from each lamb to determine concentration of urinary N and plasma urea N (PUN). Liveweight gain (P=0.008) and feed conversion efficiency (P=0.022) were greater in Diverse than RGWC treatment (240 vs 160 g/day and 111 vs 86 g LWT per kg DMI, respectively). Urinary N and PUN concentration were similar between treatments; however, when urinary N excretion (g/d) was estimated as a function of PUN, lambs grazing Diverse pasture excreted less (P=0.003) urinary N per 100 g LWG than those grazing RGWC pasture. The proportion of N intake retained in LWG was greater (P=0.008) for lambs grazing Diverse (11.0%) than those grazing RGWC (9.0%). The results indicate that there is a potential to achieve target LWT of lambs in a shorter time and with less N loss to the environment by using a diverse mix containing plantain, Italian ryegrass and red clover in comparison to ryegrass-white clover mix in autumn. Keywords: Growing lambs; liveweight gain; urinary nitrogen; diverse pasture; ryegrass

O, Al-marashdeh, GA Cook, FC Anderson, JPH Meyer, CM Logan, GR Edwards, and TMR Maxwell

New Zealand Journal of Animal Science and Production, Volume 80, Online, 70-75, 2020