INFLUENCE OF BREWERS DRIED GRAINS ON THE RUMINAL VOLATILE FATTY ACIDS (VFA)PRODUCTION AND MILK CONSTITUENTS IN ZEBU COWS

Résumé

Four lactating White Fulani (Zebu) cows fitted with permanent rumen cannular were fed four. diets: (A) Acha hay (Digitaria exilis Stapf, (B) 50% acha hay plus 50% brewers dried grains (BDG), (C) 75% BDG plus 25% hay and (D) 100% BDG in a 4 x 4 latin square design. Analysis of rumen total Volatile Fatty acids (VFAS), individual VFAs, ammonia-N and pH as well as some milk constituents were carried out simultaneously. Mean ruminal pH and total VFA (MM/100ml) were 7.1,6.2; 6.5, 8.0; 5.8,  14.9 and 5.8, 13.1 for A, B, C, and D respectively. The corresponding acetate to propionate (A/P) ratios were 4.97, 4.40, 3.20 and 3.40. The molar percent values of butyrate yielded by A and B were similar and less (P<0.05) than the value for C or D. Ruminal ammonia-N (mg/100ml) ranged from 5.7 for A to 6.8 for D. Total VFA, NH3-N and pH of the rumen fluid were affected by time of feeding (P<0.05). The correlations between ruminal pH and acetate (r = 0.98), pH and total VFA (r = -0.90), and acetate and propionate (r = -0.75) were significanct(P <0.05). Cows on treatment A (acha hay) yielded higher percent milk fat (P<0.05) and lower percent milk protein than those on B, C, or D. Treatment effects on milk pH and percentages of lactose, solids-not-fat (SNF) and ash were not significant. The observed depression in milk fat of cows on treatments B, C and D in comparison with cows on treatment A wasrelated to a decrease in rumen acetate and an increase in propionate. It was observed that the fermentation of BDG yielded acetate within limits required for efficient milk production.