The effect of an oregano oil extract in a lactating dairy cow diet on production responses of Holstein cows
The effect of an oregano oil extract on milk production parameters in Holstein cows Forty Holstein cows, 178 17 (SE) DIM and weighing 624 9 (SE) kg, were used in a lactation trial of 60 days to determine the effect of oregano essential oil on milk production, milk composition and feed intake. The cows were ranked according to milk yield, DIM and lactation number and each consecutive pair formed a block. Treatments were allocated randomly to each of the 20 blocks. An essential oil product (Dosto Concentrate 500) (DOS) was evaluated against a placebo control (CON) treatment. Cows were housed in a semi open free stall barn with sand beds and had free access to fresh water. All cows received a basic diet consisting of lucerne hay (53% NDF and 11% CP) that was offered ad libitum and 28 kg/day of a semi complete lactation feed, offered twice daily at 07:30 and 16:00. The feed refusals were weighed back weekly to determine intake per group. Treatments (DOS and CON) only differed in terms of a maize based supplement. In the case of the DOS treatment, each 300 g maize supplement portion contained 0.5 g of Dosto Concentrate 500. The cows were milked twice daily at 06:00 and 15:30 and the supplements were offered individually to cows in the milking parlour during each milking. Milk yield, milk composition and cow weights were recorded automatically on a daily basis via the Afikim system. Milk samples were also collected during weeks 3 and 8 for composition analysis at the Elsenburg Dairy Laboratory. Data collected over time were subjected to a repeated measurements ANOVA, while mean values were analysed according to a main effects ANOVA with treatment and block as main effects. All data were analysed with the aid of Statistica 64 version 12 and significance was declared at P 0.05. Treatment had no effect on milk yield or milk composition over the entire period. However, in the CON treatment, the lactose content was higher (P 0.05) during the first two weeks and the milk protein content was higher (P 0.05) during weeks four to eight. When data of the top ten milk producing cows per treatment were analysed separately, the fat content and milk fat yield were higher (P 0.05) for the DOS treatment during the first three weeks of the trial and lactose was higher (P 0.05) for the CON treatment in the first week. Mean milk yield of the top ten milk producing cows per treatment did not differ between treatments and was 37.9 kg for the DOS treatment and 37.3 kg for the CON treatment. Mean fat content and fat yield was higher (P 0.05) in the DOS treatment (37.1 g/kg and 1.41 kg/day) than in the CON treatment (33.8 g/kg and 1.26 kg/day) The higher fat content also resulted in a higher (P 0.05) energy corrected milk yield of cows in the DOS treatment than in the CON treatment (38.8 and 36.6 kg/day, respectively) With regards to feed intake, the CON group consumed on average 17.3 kg more roughage per week than the DOS group. It was concluded that oregano essential oil stimulated fat production and increased energy corrected milk yield in high milk producing dairy cows.