Providing high levels of nonstructural carbohydrate (NSC) in ruminant diets tends to change fermentation lowering rumen pH and reduce milk fat content. Balancing readily available N and energy-yielding carbohydrate may enhance microbial growth rate, alter fermentation and fibre digestion in the rumen, which subsequently may have an impact on nutrient supply to host animal. Therefore, the objective of this study was to measure the effects of dietary nonstructural carbohydrate and protein level on intake, ruminal fermentation and performance of dairy cows using cassava as main energy source.

Forty-two crossbred cows (60.9% Holstein Friesian, 26.8% Danish Red, 10.2% Red Sindi) at a mean of 71.0 ± 28.5 days in milk (DIM) with a pre-treatment milk yield of 13.2 ± 2.2 kg/d and a BW 373.1 ± 33.4 kg. Cows were tethered in stalls and randomly allocated to receive one of six total mixed ration (TMR) on ad-lib basis. Isocaloric diets (ME 11.2 MJ/kg) were formulated to contain Ruzi grass silage and a concentrate mix (20:80 ratio) containing NSC (30, 35, 40%) in combination with 2 levels of crude protein (15.7, 18.4%).