Abstract #T256

# T256
Milk and components response of dairy cows when supplemented with a rumen protected B vitamins blend during heat stress.
Tanya F. Gressley*1, Ian C. Shivas2, Hélène Leclerc3, 1University of Delaware, Newark, DE, 2Renaissance Nutrition Inc, Roaring Springs, PA, 3Jefo Nutrition Inc, St. Hyacinthe, QC, Canada.

A trial was conducted at the University of Delaware dairy center to compare milk and component responses to supplemental rumen protected B vitamins (BV; Lactation VB, Jefo, 3 g/cow/d) supplying vitamins B5, B6, B7, B9 and B12 in replacement for non-protected vitamin B7 alone (B; 20 mg/cow/d). B was provided for > 30 d (Period 1) before milk testing, switched to BV for the following DHIA test (Period 2), then cows were switched back to B for period 3. Intake was not measured. Milk results were analyzed using individual cows (65) in a paired t-test, adjusted to a common 150 DIM using the following equations: Adjusted milk = milk + milk × (DIM − 150) × 0.0029; Fat % = fat percent − 0.00269 × (DIM − 150); Protein % = protein % − 0.00167 × (DIM − 150). Days adjusted milk and component yields were greater for Period 2 with the use of BV than for Period 1 (P < 0.05; Table 1).There was substantial heat during both periods. High temperatures on test days were 28 and 31°C for Periods 1 and 2, respectively. The highest temperature on the Period 3 test day was 22°C, and results were used to assess production without heat stress. The temperature humidity index was 79, 83, and 70 for Periods 1, 2 and 3, respectively. Comparison of adjusted milk and component yield responses for the 2 B periods indicated that milk losses were substantial when cows were under heat stress conditions (Period 1 Vs Period 3, Table 1). These results showed that BV increased milk and component yields over B during periods of heat stress. When compared with the period without heat stress, BV appeared to alleviate a portion of the loss in production that occurs during heat stress. Table 1.
ItemHeat stressNo heat stressP value
Period 1Period 2Period 3
Control (B)Test (BV)Control (B)1 vs. 21 vs. 3
Milk, kg/d33.737.539.40.0010.001
ECM, kg/d34.137.941.80.0010.001
Fat, kg/d1.231.331.500.0040.001
Protein, kg/d0.931.091.230.0010.001
Fat, %3.833.603.880.0130.628
Protein, %2.792.913.130.0010.001

Key Words: rumen-protected B vitamins, heat stress, milk production