Rumen fermentation and production effects of Origanum vulgare L. leaves in lactating dairy cows.

A lactating cow trial was conducted to study the effects of dietary addition of oregano leaf material (Origanum vulgare L.; OV; 0, control vs. 500 g/d) on ruminal fermentation, methane production, total tract digestibility, manure gas emissions, N metabolism, organoleptic characteristics of milk, and dairy cow performance. Eight primiparous and multiparous Holstein cows (6 of which were ruminally cannulated) were used in a crossover design trial with two 21-d periods. Cows were fed once daily. The OV material was top-dressed and mixed with a portion of the total mixed ration. Cows averaged 80 ± 12.5 d in milk at the beginning of the trial. Rumen pH, concentration of total and individual volatile fatty acids, microbial protein outflow, and microbial profiles were not affected by treatment. Ruminal ammonia-N concentration was increased by OV compared with the control (5.3 vs. 4.3mM). Rumen methane production, which was measured only within 8h after feeding, was decreased by OV. Intake of dry matter (average of 26.6 ± 0.83 kg/d) and apparent total tract digestibly of nutrients did not differ between treatments. Average milk yield, milk protein, lactose, and milk urea nitrogen concentrations were unaffected by treatment. Milk fat content was increased and 3.5% fat-corrected milk yield tended to be increased by OV, compared with the control (3.29 vs. 3.12% and 42.4 vs. 41.0 kg/d, respectively). Fat-corrected (3.5%) milk feed efficiency and milk net energy for lactation (NE(L)) efficiency (milk NE(L) ÷ NE(L) intake) were increased by OV compared with the control (1.64 vs. 1.54 kg/kg and 68.0 vs. 64.4%, respectively). Milk sensory parameters were not affected by treatment. Urinary and fecal N losses, and manure ammonia and methane emissions were unaffected by treatment. Under the current experimental conditions, supplementation of dairy cow diets with 500 g/d of OV increased milk fat concentration, feed and milk NE(L) efficiencies, and tended to increase 3.5% fat-corrected milk yield. The sizable decrease in rumen methane production with the OV supplementation occurred within 8h after feeding and has to be interpreted with caution due to the large within- and between-animal variability in methane emission estimates. The OV was introduced into the rumen as a pulse dose at the time of feeding, thus most likely having larger effect on methane production during the period when methane data were collected. It is unlikely that methane production will be affected to the same extent throughout the entire feeding cycle.