Multi-strain yeast: nutritional solutions to reduce antimicrobial treatments in male veal calves and improve animal welfare

INTRODUCTION Among the effects of feed additives, the immunomodulatory properties represent a perspective of considerable interest for the bovine species. [1,2,3]. To this aim, multi-strain yeasts, composed of a combination of different Saccharomyces cerevisiae strains, are commonly used to improve animal health and performance [4, 5]. The use of multi-strain yeasts in animal nutrition can have several benefits. Firstly, they can improve the digestibility and utilization of nutrients in the feed [6], leading to better growth and feed conversion rates [7]. They can also help maintain a healthy balance of microorganisms in the animal’s gut, which is important for overall gut health and immune function [8]. Therefore, the present study aimed to investigate the effects of the dietary supplementation of a multi-strains yeast (Saccharomyces cerevisiae and Cyberlindnera jadinii fractions) on health parameters (including number of antimicrobial treatments) and growth traits of Italian Holstein male dairy calves. MATERIALS AND METHODS The experimental trial was conducted from February to end July 2019 in a commercial dairy farm located in northern Italy (after the authorization of the Ethics Committee of University of Bologna, N° 1039). A total of 158 Italian Holstein male veal calves were enrolled and divided in two groups: a control group (CTR) 57 animals (without yeast supplementation) and a treated one (TRT) 101 animals (yeast supplementation), both balanced for initial live weight (53.83±2.96). Each calf was enrolled in the trial from 17±3 day of age (T0) until 190 days of age (TF), when animals were slaughtered. Both groups were fed with a mixture of milk replacer (chemical composition %: crude protein 19, ether extract 17, ash 8) from 400 to 2600 g/h/d in 4-16L/h/d, and grain mix with chopped straw (chemical composition %: crude protein 13.5, ether extract 3.2, crude fibre 8.2, ash 4.1, dry matter 88) from 100 to 3500 g/h/d. The TRT group received 5g/h/d of the product through the milk replacer during the first 30 days, then 3 g/h/d until day 90. From day 90 to 190 (slaughter) the diet was the same for both groups. For all animals, individual carcass weights, mortality and morbidity (veterinary treatments) were collected. Blood parameters (Hg, RDW, MCV; d30, 73, 115 and 150) and electrophoresis for blood protein characterization (d47 and 118) were analysed in 23 randomly selected animals (12 CTR and 11 TRT). On sampled animals, body weights were measured (d0, 47, 82). RESULTS AND DISCUSSION Calves’ health was improved, but no difference was observed on mortality. Morbidity was reduced from 56% in CTR to 38% in TRT (P<.05), with a lowered number of chronic animals (≥2 treatments per animal) by 50% (P<.05, table 1). Numerically, the reduction of veterinary treatments in TRT (-26%) was mainly due to a lower prevalence of enteric diseases. ADG in TRT was 263 g/day and 321 g/day, significantly higher (P<.01) than CRT from day 0 to 47 and from day 47 to 82. Our results are consistent with those reported by Davies et al. [9]. No differences were observed on carcass weights at slaughter and carcass classification. Content of total proteins was higher in TRT (P<.01), with higher percentage of γ-globulins (P<.01) and α1-globulins (P<.01). These results indicate a better activation of the immune system in TRT veal calves. No differences were observed on RDW and MCV. No differences in Hg average concentration, but lower variability in TRT. Similar results were observed by other authors [8,10] who reported an improvement of animals' resistance to pathogens (especially during periods of high stress, such as weaning) leading to a lower incidence of digestive disorders [8]. CONCLUSION Our results demonstrate that the addition of a multi-strains yeast supplement in the milk replacer during the first 90d of the lifecycle improved the health status of veal calves. These results are in line with the reduction in the use of antimicrobial treatments in farms.