Abstract #T252

# T252
Supplementation to late lactation dairy cows during summer with dead yeast culture.
J. D. L. Dias1, R. B. Silva1,2, L. E. C. Graças1, K. Ferreira1, L. C. Resende1, R. C. Araujo3, R. A. N. Pereira2,4, M. N. Pereira*1,2, 1University of Lavras, Lavras, Brazil, 2Better Nature Research Center, Ijaci, Brazil, 3Grasp Industria e Comercio, Curitiba, Brazil, 4Minas Gerais State Ag Research Enterprise (Epamig), Lavras, Brazil.

The supplementation of dairy cows with yeast probiotics may increase diet digestibility, plasma niacin concentration, heat dissipation, and lactation performance. We evaluated the response of Holsteins in late lactation (234 ± 91 DIM) to dead yeast culture (YC. Fifteen g/d, Factor SC, Grasp. Saccharomyces cerevisiae) during Brazilian summer (THI >68 for 92.2% of time). Thirty-two cows were individually fed a standard TMR for 14 d and treatments Control (CTL) or YC for 35 d, in a covariate adjusted randomized block design. Response was evaluated in wk 5 or as repeated measures over time. Cows were milked 3x/d and treatments were orally dosed to each cow after each milking. Plasma niacin was 1.50 and 1.66 µg/mL on CTL and YC, respectively (P = 0.02). The YC reduced rectal temperature, respiratory rate, and body surface temperature (P ≤ 0.05) and tended to increase the sweating rate (P = 0.13) evaluated twice per week at 0730, 1500, and 2200 h. The proportion of cows with rectal temperature ≥39.2°C on CTL and YC was, respectively: 8 and 0% at 0730 h, 52 and 25% at 1500 h, and 35 and 26% at 2200 h (P ≤ 0.05. GENMOD of SAS). Plasma glucose in wk 3 and 5 were increased by YC (P = 0.01). The total-tract apparent digestibility of nutrients, plasma urea-N concentration, ruminal VFA profile, urinary allantoin excretion, ingestion and chewing behavior, and the proportion of daily intake in the morning, afternoon, and night were not affected by treatment (P ≥ 0.16). Cows on CTL rejected feed particles >19 mm in the morning (P = 0.02), in the afternoon were less selective against long feed particles (P = 0.05) and in favor of particles <8 mm (P = 0.03), and did not sort against short particles at night (P = 0.05). Milk yield was 30.5 kg/d for CTL and 30.2 for YC (P = 0.58). The YC reduced DMI (19.4 vs. 20.3 kg/d. P = 0.04) and increased the milk to DMI ratio (1.64 vs. 1.50. P = 0.05). Milk solids yield and concentration, linear SCC score, and MUN did not differ (P ≥ 0.21). The YC increased plasma niacin concentration, heat dissipation, and feed efficiency of late lactation dairy cows.

Key Words: heat stress, niacin, yeast