Abstract:
12n PREDICTING CRUDE PROTEIN SUPPLY TO THE INTESTINES OF GRAZING SHEEP J.L. CORBETT* and F.S. PICKERING* Nx6.25) Crude protein leaving the stomach of ruminants (CPLS=non-ammonia comprises: (i) the fraction of crude protein intake (CPI) undegraded in (ii) `microbial protein in amounts related to dietary energy the rumen; and which can be expressed as digestible organic matter intake (DOMT); (iii) CP of endogenous origin. These and related variables, except (iii), were measured,in 23 experiments with sheep grazing phalaris, lucerne or 'native pastures, using techniques described by Corbett (1981). Measured CPLS (g/d) are compared below with those predicted with Eons (l), derived _a. from studies on dried forages, and (2) derived from a wide range of feeds. : (1) CPLS = 0.36 CPI -+ 0.16 DOMI + 6 (2) CPLS = 0.41 CPI + 0.124 DOMI (Hogan and Weston 1981) (Verite et al 1979). These imply, respectively, that 0.64 and 0.59 of CPI is degraded, ' and that microbial CP'production is 160 and 124 g/kg DOMI; the intercept in (1) indicates 6 g/d endogenous CP. Predictions with [0.33CPI+O.l8DOMI] (Hogan and Weston 1981) were similar to those with (1). Reqression analyses showed that when measured CPLS was greatest, abou.t 170 g/d, both equations overestimated by about 25%, and (2) underestimated to a similar extent at CPLS = 70 g/d. The overestimations may have stemed from overallowance for CPI, the underestimation from too low predictions of and microbial CP,. .dur mean values were 0.87 for the degradability of herbaqe ' CP, whence the appropriate expression would be 0.13 CPI, and 174.~3. microbial CP/kg DOMI (thus 0.174 DOMI). The model 'for predicting CPLS appears promising, but appropriate coefficients have to be determined for various types of pastures and for season of year. For example, microbial * CP was 144 cs/kq DOMI in autumn but areater (207 q/kg DOMI; P<O105), on the same pastures in summer. .CORBETT, J.L. (1981). In 'Forage Evaluation: Concepts and Techniques', (CSIRO: Melbourne.) P* 383, editors J.L. Wheeler and R.D. I'4ochrie. HOGAN, J.P. and WESTON, R.H. (1981). Ibid., p. 75. VERITk, R., JOURNET, M. and JARRIGE, R. (1979). Livest.Prod.Sci-. - 34% C;-: * CSIRO, Division of Animal Production, Armidale, NSW' 2350. '