
%0 Journal Article
%A Coombe, JB 
%T Wool growth in sheep fed diets based on wheat straw and protein supplements
%J Australian Journal of Agricultural Research
%D 1992/04/01
%V 43
%N 2
%P 285-299
%K sheep;wool growth;straw;proteins
%R https://doi.org/10.1071/AR9920285
%U https://www.publish.csiro.au/paper/AR9920285 
%X Wool growth of sheep fed wheat straw and various nitrogen (N) supplements was studied in two experiments lasting 16-20 weeks. In experiment 1, penned Crossbred wethers were fed wheat straw supplemented with urea (36 g kg-1 straw) and starch, or equivalent (N basis) amounts of formaldehyde-treated (F) casein (FCAS), rapeseed meal (RSM) or F-treated RSM or sunflower meal (FRSM and FSFM), all at the same total DM intake of c. 1240 g day-1. They produced from 7.9 to 13.9 g clean dry wool (CDW) day-1, and gained from 40 to 100 g day-1 for the urea and FCAS diets respectively. Mean digestibilities of organic matter (OM) and cell wall constituents were 0.53 and 0.42, with few differences between diets, while N digestibility of the FRSM diet (0.76) was significantly (P < 0.05) lower than all others (mean 0.89). During 1-6 h post-feeding, mean rumen pH and volatile fatty acid levels (6.43 and 55.2 mM respectively) were similar for all diets, whereas rumen ammonia levels were significantly (P < 0.01) higher with the urea and RSM supplements compared with the F-treated supplements. In experiment 2, penned Merino wethers fed 770 g DM day-1 of the urea-supplemented diet produced 5.0 g CDW day-1 and lost 50 g live weight day-1. In other sheep, fed at the same DM intake on wheat straw plus increasing levels (c. 70-350 g sheep-1 day-1) of an FRSM supplement, wool growth was quadratically related to supplement-N intake, with a maximum of 10.1 g CDW day-1 at a N intake of 15.6 g day-1. Digestibility of OM and N balance were significantly (P < 0.05) reduced at FRSM levels < 127 g sheep-1 day-1, while mean rumen ammonia levels during 6 h post-feeding remained < 70 mg N L-1 at FRSM levels < 183 g sheep-1 day-1. It was concluded that protein supplements resistant to ruminal degradation will substantially increase wool production in sheep fed straw diets at approximately maintenance levels. 
