Supplemental degradable protein sources for beef cattle consuming low quality roughage

[摘要] English: A study was conducted to determine the best natural source of rumen degradable protein (RDP) not provided by urea to maximize the digestible organic matter intake (DOMI) of a SA natural winter pasture hay (3.51% crude protein (CP) and 74, 23% neutral detergent fibre (NDF). The crude protein degradability of natural winter pasture hay (Cymbopogon- Themeda), cotton oilcake, soybean oilcake and sunflower oilcake was determined by means of the in- sacco- technique. These crude protein degradability values were used to formulate three RDP supplements according to current recommendations (4.01g RDP/kg W 0.75) using the three oilcakes respectively. Urea provided 50% of the supplemental RDP. The other feed ingredients were salt, begasse, molasses, feed grade sulphur and trace minerals. Seven steers (217 SD ± 9.91 kg) per treatment randomly divided were used. The experimental period consist of 14 -day's adaptation, 21- days' intake and 7 days collection period (conventional digestibility study). A significant (P< 0.0001) higher apparent digestibility of NDF occurred when the sunflower oilcake supplement was fed to the steers. The apparent digestibility of dry matter (DM), organic matter (OM), CP and gross energy (GE) was however not influenced significantly (P> 0.05) when different oilcakes supplements were fed. Likewise DOMI/kg W 0.75 , rumen volatile fatty acid concentration and rumen pH did not differ significantly (P> 0.05). The ammonia nitrogen (NH3N) concentration of the rumen fluid of steers that consumed the sunflower oilcake supplements were significantly (P< 0.04) lower than that of cotton oilcake. In a second study the optimum ratio of supplemented urea to the most available oilcake (cotton seed) was investigated. Urea replaced: 0%, 25%, 50%, 75% and 100% of the natural supplemental RDP. The same procedure as described in the first study was used. Steers with an average mass of 200 ± 19.96 kg were used. The replacement of natural supplemental RDP with urea did not significantly (P>0.05) influenced the apparent digestibility of DM, CP, NDF and GE. Accordingly DOMI/kg W 0.75did not differ significantly (P>0.05). The highest (P< 0.05) acetate and propionate concentration in rumen fluid of steers was recorded when urea replaced 75% of the natural RDP in the supplement. The highest (P= 0.008) value for isovalerate concentration in rumen fluid was found when 25% of the supplemental degradable protein was from urea. Increasing levels of urea had no affect on either the rumen NH3N concentration (P=0.3508) or pH (P= 0.0810). According to the results of both studies it seems that urea can supply all the supplemental RDP to steers on low quality roughage. From the results it was concluded that further research is needed on the RDP-requirements of ruminants consuming different types of low quality roughages.

[发布机构] University of the Free State