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Nitrogen partitioning differs between sheep offered a conventional diploid, a high sugar diploid or a tetraploid perennial ryegrass cultivar at two feed allowances

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posted on 2023-05-03, 15:42 authored by Arjan JonkerArjan Jonker, Long Cheng, Grant Edwards, German MolanoGerman Molano, Prue TaylorPrue Taylor, Edgar Sandoval, Gerald CosgroveGerald Cosgrove
Grazing sheep on ryegrass based pasture with elevated water soluble carbohydrate (WSC) concentration might improve N use efficiency and reduce N excretion into the environment. Diploid ryegrasses with elevated WSC have been bred and released as a high-sugar cultivars (HSG), and tetraploid ryegrass (TRG) generally has elevated WSC compared to conventional diploid ryegrass (CRG). The objective of the current study was to determine N partitioning in sheep fed HSG, TRG, and CRG offered at two feed allowances. Three N partitioning trial periods (Sep 2013, March 2014 and Nov 2014) were conducted with 30 Romney wethers (different sheep in each period) over 5 d of excreta collection measurements per period. For each period, three perennial ryegrass types (HSG, CRG and TRG) were each offered at two allowances (0.7 and 1.0 kg DM/d) (6 treatments × 5 sheep). As a proportion of N intake, urinary-N excretion was greater (P =  0.016) for sheep fed TRG compared with sheep fed CRG, and intermediate for sheep fed HSG. There was an interaction between cultivars and feed allowance levels for N retained as a proportion of N intake (P =  0.04) with retained-N being similar among cultivars at the high feed allowance, while sheep fed CRG had a greater retained-N as proportion of N intake than sheep fed TRG at low feed allowance, with HSG fed sheep intermediate. The ratio of urinary-N:faecal-N was lower (P <  0.001) for sheep fed CRG and HSG compared with sheep fed TRG. The ratio of digestible N to organic matter (OM) was greater (P =  0.003) for sheep fed TRG than sheep fed HSG, with sheep fed CRG intermediate. Forage WSC concentration and WSC:Crude protein and WSC:Neutral Detergent Fibre ratios correlated negatively (r −0.46 to −0.56) with urinary-N as proportion of N intake. Offering a higher forage allowance was, however, a more effective strategy to decrease N excretion and increase retained N, both as a proportion of N intake. In conclusion, urinary-N as proportion of N intake was lower for sheep fed CRG than for sheep fed TRG, with sheep fed HSG intermediate, and it was lower at a the higher feed allowance.


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Journal title

Animal Feed Science and Technology




Jonker, A., Cheng, L., Edwards, G. R., Molano, G., Taylor, P. S., Sandoval, E., & Cosgrove, G. P. (2018). Nitrogen partitioning differs between sheep offered a conventional diploid, a high sugar diploid or a tetraploid perennial ryegrass cultivar at two feed allowances. Animal Feed Science and Technology, 245, 32–40. doi:10.1016/j.anifeedsci.2018.09.004

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