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.
Highlights
Animal production in the tropics is severely limited by nutritional constraints, with animals losing up to 30 % of their total body weight during the dry season (Almeida et al, 2006)
It was decided not to replace the complete rumen degradable N (RDN) fraction of the sunflower meal (SFM) with urea (100 % non-protein N (NPN) treatment) as the quantity of urea necessary to replace the total RDN fraction of the SFM would have been more than 16 g urea wether−1 d−1, which, at approximately 1.6 % of the dry matter (DM) intake, would have been well above the 1 % DM recommendations for wethers (Edjtehadi et al, 1978)
Results from various studies suggested that DM intake, microbial nitrogen (N) synthesis (MNS) and effective degradability (ED) in sheep (Kanjanapruthipong and Leng, 1998) and neutral detergent fiber (NDF) intake, MNS and ED in cattle (Detmann et al, 2009) consuming low quality tropical grasses are influenced by the rumen ammonia nitrogen (RAN) concentrations, with ED being maximised at 8 mg NH3-N dL−1 as was discussed earlier
Summary
Animal production in the tropics is severely limited by nutritional constraints, with animals losing up to 30 % of their total body weight during the dry season (Almeida et al, 2006). Low quality tropical roughages contain less than 6 % crude protein (CP) (Detmann et al, 2009; Leng, 1990), which is insufficient to meet the ruminants’ maintenance requirements (NRC, 2007). Nutritional deficiencies during these periods can be overcome by nitrogen (N) and/or protein supplementation (Ferrell et al, 1999; Köster et al, 1996). Recent studies suggest that microbial needs to optimise forage utilisation and microbial N synthesis (MNS) differ between ruminants consuming either low quality tropical or temperate grasses (Detmann et al, 2009; Kanjanapruthipong and Leng, 1998). The aim of the study was to investigate whether the form of RDN supplemented either as a true protein or as an NPN source will influence forage intake, digestibility and MNS in sheep fed a basal diet of low quality tropical roughages
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