Abstract:
The aim of the present study was to determine whether sunflower meal (SFM), a
highly rumen degradable protein (RDP) source, can be substituted with non-protein nitrogen
(NPN, urea) without impacting negatively on intake, digestibility, rumen fermentation and microbial
nitrogen (N) synthesis (MNS) in wethers consuming low quality Eragrostis curvula hay. Five
wethers were fed ad libitum, low quality hay and supplemented twice-daily in equal proportions,
via the rumen cannulae, one of five iso-nitrogenous and iso-energetic supplements in a 5 × 5
Latin square design experiment. The supplements differed in the ratios of rumen degradable N
(RDN) supplied by either SFM and/or urea and is presented as percentage of RDN supplied by
urea: T0 (100 % SFM, 0 % urea); T15 (85 % SFM, 15 % urea); T30 (70 % SFM, 30 % urea); T45
(55 % SFM, 45 % urea) and T60 (40 % SFM, 60 % urea). Forage intake and total tract dry matter
(DM) digestibility did not differ; however, higher forage neutral detergent fiber (NDF) digestibilities
were observed in the sheep supplemented with the higher urea-treatments (T45 and T60) compared
to T15. Neither rumen pH nor total rumen volatile fatty acid (VFA) concentraions differed.
The mean rumen ammonia nitrogen (RAN) concentration of the sheep supplemented with T60
was higher than T30 (9.35 mg dL−1 vs. 7.41 mg dL−1); however, no differences were observed in
MNS or efficiency of MNS among treatments. Results suggest that up to 60 % of RDN supplied
by SFM can be substituted with urea, without affecting intake, digestibility or MNS in wethers fed
a low quality tropical hay.
