| Probiotics have been used as effective, natural feed additives in the dairy industry to improve animal health and performance. Yeast product supplementation can be beneficial in the diet of lactating dairy cows by increasing feed efficiency, alleviating disease, and improving production performance under heat stress. Objectives of this study were to evaluate supplementing a concentrated brewer's yeast in the ration of a lactating dairy cow by assessing milk yield and composition, blood metabolites, rumen fermentation, and feed intake and efficiency. We hypothesized that diets containing a concentrated brewer's yeast supplement would increase milk and component yields, benefit rumen fermentation, and improve feed efficiency and nutrient utilization. Thirty-six Holstein cows (24 multiparous and 12 primiparous; DIM = 71.17 +/- 16.42) were used in an 8-wk randomized complete block design experiment. Cows were blocked by milk yield, DIM, and parity. Treatments include: 1) control with no yeast (CON), 2) a concentrated brewer's yeast product ( Y1), and 3) a commercial yeast product (Y2). Cows were fed a common TMR, except for yeast supplements (14.2 g/hd/d), once daily using the Calan Broadbent feeder system to determine daily individual dry matter intake (DMI). All milk weights were recorded daily and each week milk samples, body condition scores (BCS), and body weights were collected. Blood, rumen fluid, and fecal samples were taken during wk 7 and 8. Data were analyzed using MIXED procedures with repeated measures and means were compared using Tukey's test. Dry matter intake was similar among treatments, but there was a treatment by week interaction (P < 0.01) with cows fed Y1 having greater DMI during wk 2, 3, 4 of the study. Milk production and components, including fatty acid composition were similar (P > 0.05) among treatments. Feed efficiencies, calculated as energy-corrected milk/DMI, were similar among treatments, but there was also a treatment by week interaction (P < 0.01). A treatment effect for plasma urea nitrogen ( PUN) was detected (P < 0.01) and a treatment by group interaction for glucose was determined (P < 0.01). No statistical significance on treatment effects were determined for ruminal parameters and total-tract digestibilities. Yeast products maintained performance, rather than improving production as hypothesized. |
