Effect of milk replacers added with microencapsulated organic acids or essential oils on the performance of weaning calves

The use of antibiotics as feed additives in animal nutrition has been banned in the EU countries and alternative substances are required to control the development of the intestinal microbial communities. Organic acids (OA) have been demonstrated to improve performance in young growing animals, while essential oils extracted from plants (EO) are known to have antimicrobial effects. The aim of present experiment was to compare the effects of two microencapsulated feed additives based on OA and EO on the in vivo performance and health status of weaning calves. The trial was conducted using a total of 36 Friesian male calves, reared from 20 to 52 d of age at the Agricultural Experimental Station "Servadei" of Udine University. The experiment was split in three consecutive randomised blocks of 12 animals, which were divided in three groups and fed with the same milk replacer (diluted at 10.5% in 40°C water) containing no additives (control, C) or added (1% w/w) with commercial microencapsulated supplements based on OA ("ERASE Feed", containing 50% OA) or EO ("RepaXol calves2%", containing 0.8 % EO). Animals were weighted at the beginning (51.3, 50.7 and 50.5 kg, respectively for C, OA and EO; RSD: 5.7 kg), after 20 d and at the end of the trial (at 32 d) and a grab faecal sample was individually collected from the rectum to be analysed for DM content and pH. The faecal samples collected at the start and at the end of the trial were also analysed for the presence of Escherichia coli, Salmonella typhimurium and Clostridium perfrigens. Within each block, a fraction of the third faecal sample was bulked to obtain a mixed sample for each dietary treatment and to be used as inoculum for an in vitro fermentation (gas production technique). 220 mg of air dried milk replacer C were weighted in graduated 100 ml syringes, which were added with 30 ml of diluted faecal material. Three syringes were used for each type of inoculum (C, OA and EO) plus three syringes without substrate as blanks and gas production was recorded at 2, 4, 6, 21 and 24 h from the beginning of the fermentation. One animal of the OA group was excluded from the trial for respiratory disease. The individual DM consumption during the trial was equal to 21.5 kg, without any refusal. The live weight gain was higher and the feed conversion was better (P=0.11 and P=0.07, respectively) for OA and EO groups with respect to the control (369 and 355 vs 287 g/d, respectively and 2.00 and 2.00 vs 2.92 kg/kg respectively). Dietary treatments did not affect the DM content, the pH and the presence of pathogenic microbial strains of the faecal samples, while produced inoculums with different fermentation capacity. In fact, gas volumes recorded at all the incubation times considered, were from 18 to 37 % higher (P<0.01) for calves which received the C milk replacer than those fed the milk added with OA or EO. The trial showed that inoculum from calves fed both the additives studied reduced the in vitro fermentation capacity of substrate in the syringes, as a probable consequence of a lower faecal microbial activity. This positive effect on the intestinal ecological environment could be the reason of the slight improvement in the in vivo performances showed by animals fed the additives.