Review/Oorsig Volume 22, Issue 01 - Page 6

Oorsig/Review pH equal to 7,0 is considered neutral – i.e. neither acid nor alkaline. A pH below 7,0 is considered more acid and one above 7,0 indicates a more alkaline environment. Rumen pH = -log [rumen H+]; or [rumen H+] = 10-rumen pH. For example: [H+] of rumen fluid with a pH of 5,0 and 5,5 is 1 x 10-5M and 3,16 x 10-6M, respectively. The above equation illustrates that a relatively small change in rumen pH – for various reasons - constitutes an enormous change in hydrogen ion concentration in the rumen fluid. Rumen pH is one of the critical factors affecting rumen microbial growth. Physical characteristics of feeds as related to their effectiveness in stimulating chewing, rumination and increased rumen motility based on their total cell wall content and particle size within classes of feeds (effective NDF; eNDF) contribute to rumen pH. The eNDF value is defined by bovine nutritionists as the percent of the NDF retained on a 1.18 mm screen. Factors other than particle size that influence the eNDF value are degree of lignification (age of plant – the older, the more unfermentable and indigestible lignin it contains) of the NDF, degree of hydration, and bulk density. Total microbial yield and SC growth rate rapidly declines below a pH of 6.2, which relates to a diet eNDF content of 20%. Microbial yield is reduced by 2.5 percentage units for each percentage drop in diet eNDF below 20 RFW2FRFWBTD`W7B&R67W&FVǒ&VF7FVBF67W&FVǒ&VF7@֖7&&֖6B&GV7FB6VvFvW7F&VVb6w27GW&RFWF'TD`2BW6VB2&FvVVBF'W@FW6RfwW&W26ǒ6W'fRFW7G&FRFRVffV7@bWG&VG2FRFWB'VV֖7&&VBVƖR6GFRfVBFWG2v66VG&FW2FRW2GW&WFV6fR7GW&RF@WW&V6RFR6RFVw&VRbfV7GVF'VV&WGvVVV2FRfW&vR( &( Ч'VVbw&r&fR26ƖvFǒ6BЦ&WBbRbÂvFfV7GVF2FWVFrFRVBBGRb7WVVBVFV`fV7GVF2'VV&RW7VǒFP&W7VBc( "WfVbDԒ( 2vW"DԒW7VǒVFrF7&V6R'VV( "FW'f&WGvVVfVVBFRFWFW&֖W2FPvGVFRbfV7GVF&WGvVVfVV@FP( "&FRbfW&VFFv62FWFW&֖VB'FR7F&6"7Vv"66VG&FbFRFW@( "vFW"FRFWFW2FR'VV6FVB@FV7&V6W2FR6ƗGFW&V`d26VVǗF2&7FW&FBw&rB&VrbBFV"w&wF&FRFV7&V6W0'BRW"W"f"V6VBG&&WGvVVbRBbfW&VFFb6VV6P67W'2BF&FRBbRv2'VVVF'FC'VV֖7&&VFFWFW&֖W2FPVff6V7'v6w&726VvFW&0'&VFvFR'VVF22VffV7@76vR&FRbvW7Fv67G2FRFǒG'GFW"FRDԒg&7GW&R6VB'VV֖7&&VF&RVvFfVǐffV7FVBWWG&FWFW&vVBf&W"FVw&FFࢄDb&&F'&WFW"f"B6Vv2v6266VǒBfW'6Vǒ6'&VFV@vFDԒBV6R76vR&FRv&P&VBF2vVBFvW"FR`7GW&RD( 2VFFVǒVFrFvW"vW"BW&FrFRFVFF֗P&fBW"'VV֖7&&VF2FWFW&֖VB'FP&6R&WGvVV'VVFVw&F&R&FVࢅ$EBf&W"6&&G&FW2d27F&6W2B7Vv'2bFRFWBvW7FVB'FP6rW6W72$E"VWFƗVB$EF&Vv6bd2VG2FvW"FVƗfW'FFRƗfW"v62F&R&VfVBF&Vvf&FbW&VF2V27BgFVvFW"vVf"WRBƖ"6V66VW&R2fVBG'"VƗG7FFpFRFFFWF&Ɩ2gV7F'FPƗfW"F( 6VW( FRVWFƗVB06VFW'&GV7FfRBVG2FW72Vff6V@FW&VF'VW&wWF&Ɨ66