Effects of addition of an essential oil complex to the diet of lactating dairy cows on whole tract digestion of nutrients and productive performance

Essential oils (EO) have been shown to positively impact in vitro ruminal fermentation, but there are few in vivo studies that have examined animal responses. Our objective was to evaluate the efficacy of an EO complex (Agolin Ruminant from AGOLIN SA, Bière, Switzerland), which contained eugenol, geranyl acetate and coriander oil as major components, on the production of lactating dairy cows, measures of efficiency of use of dietary N as well as whole tract digestion of nutrients. Two pens of approximately 310 early lactation multiparous cows were used in a 2 × 2 factorial experiment with treatment reversed 28-day periods. Cows were fed a totally mixed ration (TMR) twice daily for ad libitum intake based on (g/kg TMR DM): wheat silage (137), maize grain (122), alfalfa hay and fresh chop alfalfa (182) and corn silage (66), with numerous other ingredients. The basal TMR was the same for both treatment groups, and differed only in that the EO complex was added to the TMR of the EO assigned pen. Feed premixes, TMR and ingredients were sampled on days 21 and 26 of each experimental period. Cows were milked three times daily with milk yield and components measured at the end of each period. Urine samples were collected at the end of each period from 24 cows/pen that voluntarily urinated, with fecal collections from these same cows 24 h later. The actual refusals corrected EO intake was 0.85 g/cow/d. The TMR contained 547 g/kg DM, 164 g/kg crude protein (CP), 62 g/kg ether extract, 322 g/kg neutral detergent fibre (i.e., aNDFom) and 120 g/kg starch. The DM intake was numerically (i.e., P=0.13) lower with EO feeding (i.e., 26.0 versus 27.4 kg/d) but milk yield was not impacted (mean 49.2 kg/d). However milk fat production (1.63 versus 1.66 kg/d; P=0.02) and milk fat proportion (33.2 versus 33.9 g/kg; P<0.01) were higher for cows fed EO. Cows fed the EO complex diet lost body condition whereas those that were not fed the EO gained body condition (P<0.01). There were no differences in urine parameters or whole tract digestion of organic matter, CP and aNDFom. Feeding this EO complex impacted the production of these high producing dairy cows, primarily by enhancing milk fat synthesis which apparently was the result of an energetic shift away from body condition gain, suggesting that it may have enhanced acetate production and/or the acetate to propionate ratio in the rumen.