Abstract #T285

# T285
Effects of virginiamycin supplementation on milk yield and its composition in high-producing dairy cows.
P. M. Souza1, J. K. Poncheki1, L. Barbosa2, D. P. D. Lanna3, R. Almeida*1, 1Universidade Federal do Paraná, Curitiba, PR, Brazil, 2Phibro Animal Health, Campinas, SP, Brazil, 3Escola Superior de Agricultura Luiz de Queiroz, Piracicaba, SP, Brazil.

The objective of this study was to evaluate the effects of antimicrobial virginiamycin on milk production and composition in high-producing dairy cows. In a commercial herd in Castro, Paraná State, Southern Brazil, 180 multiparous Holstein cows, bST-treated and milked 3x/day, were blocked by parity, milk yield and DIM. Within each block, cows were randomly allocated to 2 groups; control (CT) and treatment (VM), with VM group being supplemented with 300 mg/cow/day of virginiamycin (V-Max, Phibro Animal Health), and CT group receiving the same amount of corn meal. In the 5-d covariable period, cows had on average 2.9 ± 1.0 lactations, 111 ± 59 DIM, and 51.2 ± 6.4 kg/d milk yield. The experimental period had 6 weeks, and 3 milk collection periods were performed, totaling 45 milk samples for each cow. The corn silage and ryegrass haylage based-diet had on average 17.8% CP, 37.8% NDF, 17.7% ADF, 5.0% fat, and 7.4% ash. Milk composition (fat, protein, casein, lactose and total solids contents), as well as MUN and SCC were determined. Data were analyzed using the MIXED procedure of SAS with a model containing the effects of block, cow within treatment, period (wk 3 and 6), day, and treatment. Milk yield and its composition in the covariable period were included in the model as covariate. Virginiamycin supplemented cows produce more milk (50.34 vs. 49.31 ± 0.34 kg/d; P = 0.03), with higher milk protein (2.98 vs. 2.93 ± 0.01%; P < 0.01) and milk casein (2.32 vs. 2.27 ± 0.01%; P < 0.01) contents than control cows. Virginiamycin treated cows also show higher milk fat (1.704 vs. 1.640 ± 0.020 kg/d; P = 0.02), milk protein (1.471 vs. 1.424 ± 0.012 kg/d; P < 0.01), milk casein (1.143 vs. 1.106 ± 0.009 kg/d; P < 0.01), milk lactose (2.341 vs. 2.288 ± 0.017 kg/d; P = 0.03), and milk total solids (5.897 vs. 5.753 ± 0.051 kg/d; P < 0.05) amounts. No differences (P > 0.05) were found for milk fat, lactose, and total solids contents, as well as MUN and SCC linear score between controls and VM-treated cows. This work demonstrated virginiamycin improves milk production and milk composition, and it could become an important additive for lactating dairy cows.

Key Words: antimicrobial, milk composition