Abstract
The study's goal was to evaluate the impact of concentrate diets containing fermented cassava pulp with yeast waste (CSYW) with various roughage to concentrate ratios (R:C) on ruminal fermentation, nutritional digestibility, milk production, and milk composition in lactating cows. Four mid-lactation Thai crossbred dairy cows were randomly assigned a 2 × 2 factorial arrangement in a 4 × 4 Latin square design, weighing 440 ± 60.0 kg (75% Holstein Friesian and 25% Thai native breed), and having 90 days-in-milk (DIM). The different dietary treatments consisted of the following: factor A: soybean meal (SBM) and replacing SBM with CSYW at 100% dry matter (DM) in the concentrate diet, whereas factor B consisted of varying the R:C ratio from 60:40 to 50:50. An interaction effect between protein source and R:C ratio on intake was not observed (P > 0.05). The CSYW-diet did not affect the intake of concentrate and rice straw. However, when the R:C ratio was changed to 50:50, there was a significant increase in the apparent digestibility of neutral detergent fiber and acid detergent fiber (P < 0.05). There was no evidence of an interaction effect between CSYW and the R:C ratio on the parameters of the rumen, the microorganisms in the rumen, or blood urea-nitrogen. The concentration of ammonia-nitrogen in the rumen, however, significantly increased (P < 0.05) when animals were given a concentrated diet containing CSYW. Total VFA, C2:C3 ratios, acetic acid (C2), propionic acid (C3), butyric acid (C4), and methane levels were unaffected by the replacement of SBM with CSYW in concentrate diets or the R:C ratio given to lactating cows (P > 0.05). There was no evidence of an interaction between CSYW and the R:C ratio across any and all milk-related parameters (P > 0.05). The R:C ratio had no effect on milk production or composition (P > 0.05). With the exception of milk protein (P < 0.05), milk yield and milk composition were not affected by replacing SBM with CSYW in concentrate diets (P > 0.05). The concentration of protein in milk produced by animals fed a CSYW-diet increased from 3.05 to 3.25%. On the basis of this research, it is recommended that CSYW be used as a protein source in a concentrate diet in place of SBM with a R:C ratio of 60:40 or 50:50.