This study aimed to determine the effect of nitrate and/or oils supplementation alone or in combination to diets with different roughage: concentrate ratios on in vitro methane (CH4) production, volatile fatty acid (VFA) and ammonia (NH3) concentrations, pH, and protozoa population. The experimental treatments comprised iso-nitrogenous total mixed rations based on forage with roughage to concentrate ratio of 40R:60C (High concentrate) or 60R:40C (High roughage) supplemented with 2 sources of nitrogen (sodium nitrate (NO3-: 45.94 g/kg DM) or urea (16.45 g/kg DM for control group) and 3 oil sources ((feed-derived oil (FDO: with no oil addition), hazelnut oil (HO: 36.58 g/kg DM) or soybean oil (SO: 36.58 g/kg DM)). For this purpose, 2 x 2 x 3 factorial design in 12 groups were used. The treatments were as follows: 40R:60C + Urea (Control) + FDO, 40R:60C + NO3- + FDO, 40R:60C + Urea (Control) + HO, 40R:60C + Urea (Control) + SO, 40R:60C + NO3- + HO, 40R:60C + NO3- + SO, 60R:40C + Urea (Control) + FDO, 60R:40C + NO3- + FDO, 60R:40C + Urea (Control) + HO, 60R:40C + Urea (Control) + SO, 60R:40C + NO3- + HO, 60R:60C + NO3- + SO. Then, the effect of nitrate, oils (O), roughage:concentrate ratio, and the combined effect of nitrate and oil associated with roughage:concentrate on in vitro methane production, VFA and NH3 concentrations, pH, and protozoa population were evaluated. In this study, while NO3-, O, 40R:60C x NO3-, 40R:60C x O, 40R:60C x NO3- x O, 60R:40C x NO3- 60R:40C x O, 60R:40C x NO3- x O (p<0.01) decreased in vitro CH4, protozoa population, ammonia (NH3) concentration, acetic acid, total VFA, acetic acid: propionic acid ratio and pH, they increased butyric acid and propionic acid concentrations. Furthermore, in vitro CH4 production (12.44 vs 9.09 ml), NH3 (8.23 vs 7.37 mmol/l), propionic acid (19.14 vs 17.93 mmol/l), butyric acid (15.50 vs 14.50 mmol/l), total VFA (86.46 vs 85.66 mmol/l), protozoa population (32.16 vs 26.96 x104 ml.) were high in the 40R:60C treatment (high concentrate). Although, 40R:60C x NO3- x SO, 60R:40C x NO3- x SO, and SO decreased more acetic acid concentration, protozoa population, and thus in vitro CH4 production than other groups.

This study aimed to determine the effects of nitrate, and two oils (O) (soybean and hazelnut oils) alone or in combination, on in vitro methane (CH4) production, volatile fatty acid (VFA) and ammonia (NH3) concentrations, pH, and protozoa population. For that, 2 x 2 x 3 factorial design with 2 two different forage:concentrate (F:C) ratios (40F:60C, and 60F:40C), 2 sources of nitrogen (sodium nitrate (NO−3: 45.94 g/kg DM) or urea (16.45 g/kg DM for control group) and 2 oils (hazelnut oil (HO: 36.58 g/kg DM) or soybean oil (SO: 36.58 g/kg DM)). For every forage: concentrate (F:C) ratio, six (6) treatment groups were formulated: F:C + Urea, F:C + NO−3, F:C + Urea + HO, F:C + Urea + SO, F:C + NO−3 + HO, F:C + NO−3 + SO. For every F:C ratio while NO−3 (p<0.01), oils (p<0.01), and NO−3 + oils (SO, HO) (p<0.01) decreased CH4 content, protozoa population, ammonia (NH3) concentration, acetic acid, total VFA, acetic acid: propionic acid ratio and pH, they increased butyric acid and propionic acid concentrations. Furthermore, CH4 production (12.44 vs 9.09 ml), ammonia (8.23 vs 7.37 mmol/l), propionic acid (19.14 vs 17.93 mmol/l), butyric acid (15.50 vs 14.50 mmol/l), total VFA (86.46 vs 85.66 mmol/l), protozoa population (32.16 vs 26.96 x104 ml.) were high in early lactation period. In both lactation periods, SO, and NO−3 + SO decreased acetic acid concentration, protozoa population, and thus CH4 production.