Rumen fermentation characteristics and digestibility of cattle diets containing different whey:maize ratios

Three experimental diets were formulated to contain the same amount of fescue hay (560 g kg−1 dry matter (DM) Festuca arundinacea) and differing condensed rennet whey:maize meal ratios (0:100, 50:50 and 100:0 on a DM basis, diets M, MW and W, respectively). The diets were fed during two experimental periods to six rumen fistulated, non lactating Simmental cows (average level of intake: 77 g DM kg−1 LW0.75, four cows per treatment). sed alone caused a lower rumen pH at 1.5 and 3.0 h after the morning meal (P < 0.01) in comparison with the other two diets, while after 4.5 h rumen acidity values were similar between diets. feeding, the inclusion of whey led to regular increases (P < 0.05) in the concentrations of propionic acid at 1.5 h (12.4 mmol, 18.3 mmol and 23.8 mmol l−1, respectively for M, MW and W diets), while at 3.0 h the W diet remained significantly higher than the other two (22.1 mmol vs. 14–14.2 mmol l−1, P < 0.01). This was also the case for butyric acid where higher (P < 0.01, 1.5 h) levels were observed for diets containing whey (11.6 and 13.3 mmol vs. 7.9 mmol l−1). The dry and organic matter in the W and MW diets were 3 percentage points (P < 0.05) more digestible than the M diet. The soluble cell content fraction digestibility regularly and significantly increased (P < 0.05) as whey substituted maize (from 749 to 814 g kg−1). clusion of whey caused an increase in rumen liquid turnover rate (from 7.1 to 13.4–12.3% h−1, P = 0.058) and enhanced levels of urinary volume which almost doubled in diets containing whey (from 78 to 132–138 mg kg−1 LW0.75, P < 0.05). y allantoin output did not differ between dietary treatments while higher urinary outputs of uric acid were found for cows fed diets containing whey (2.39–2.58 g vs. 1.36 g day−1, P < 0.05).