Effect of dietary supplementation with Saccharomyces cerevisiae fermentation product on clinical outcomes in dairy cows during challenge with Streptococcus uberis.

Streptococcus uberis is a common mastitis pathogen that lacks an effective vaccine in the United States and often requires antibiotic therapy. Supplementation of feed with Saccharomyces cerevisiae fermentation products (SCFP) has been associated with decreased SCC in dairy cows. The objective of this randomized clinical trial was to evaluate the effect of oral supplementation with SCFP on clinical and production outcomes in lactating dairy cows in response to intramammary challenge with Streptococcus uberis. Healthy cows (n = 42; parities 1-5; >120 DIM) were enrolled if their pretrial test day SCC was <200,000 cells/mL and they had no history of clinical mastitis in the preceding 60 d. Four cohorts of cows were blocked based on bovine leukemia virus infection status, parity group, milk yield, and DIM then randomly pre-assigned to receive a challenge in one quarter before being assigned to receive a treatment or control diet during a 45-d prechallenge phase, 5- to 7-d challenge phase, and 45-d postchallenge phase. Diets of cows assigned to treatment were top-dressed with 19 g/d SCFP for 45 d, and the control cows received 19 g/d of ground corn. During the prechallenge phase, quarter milk samples were collected weekly and used to determine SCC and IMI. Cows that did not develop IMI during the prechallenge phase (n = 37) were challenged with ∼2,000 cfu of S. uberis 0140J in one rear mammary gland; quarter milk samples were collected daily until antibiotic treatment (d 5 or 7) and data collection continued for another 45 d. Statistical analyses were performed using linear mixed models. Supplementation with SCFP did not affect DMI, milk production, or milk components during the prechallenge, challenge, or postchallenge phases. During the challenge week, there was no effect of SCFP on number of colonies of S. uberis or SCC in milk. The mean time from intramammary challenge with S. uberis until onset of clinical mastitis was 3.88 ± 0.42 d and 4.84 ± 0.44 d for cows in the control group and SCFP treated groups, respectively. The mean days to bacteriological cure were 25.9 ± 3.5 (control cows) and 22.5 ± 3.1 (SCFP treated). As compared with values in control cows, supplementation with SCFP did not affect milk yield, DMI, or SCC of cows that received an intramammary challenge with S. uberis 0140J. Interestingly in a subset of animals that were infected with bovine leukemia virus, but not lymphocytic, before challenge supplementation with SCFP increased DMI 1.3 kg ± 0.6 and increased milk production by 2.3 ± 0.9 kg/ d. This study was performed using a challenge model and a single pathogen type, future studies focusing on naturally occurring mastitis may be of value.