Ruminant Nutrition: Minerals and Vitamins - Dairy

The objective of this study was to investigate the effect of dietary cation-anion difference (DCAD = Na + K Cl S in mEq/kg of DM) on lactation performance and blood acid-base balance of early-lactating dairy cows in hot weather. Thirty-six Holstein cows, 43 ± 13 d in milk were allocated into three groups (n=12) according to complete random block design. All diets contained 51% concentrate and 49% forage mix, which were fed ad libitum as a total mixed diet. Cows were fed either a low DCAD diet (L, +130.49 mEq/kg DM), a middle DCAD diet (M, +251.54 mEq/kg DM) or a high DCAD diet (H, +383.87 mEq/kg DM). The DCAD difference was provided through a combination of Potassium Bicarbonate and Magnesium Sulfate. Experimental duration was 7 wk. Cows were milked 3 times/d and milk yields were recorded weekly. Milk samples were collected weekly and analyzed for composition. Blood samples were taken on d 42 from coccygeal vein or artery at 4h postfeeding. The average daily minimum temperature, humidity index and THI were 30.09°C, 59.97°RH and 94.63, respectively. Milk yield and milk fat content were 31.5b, 36.9a and 34.1ab kg/d, and 3.56a, 3.20b and 3.35ab for L, M and H, respectively. With the increasing of DCAD, milk protein (P < 0.05) increased gradually. Blood pH and blood base excess increased predominantly via increased DCAD (P < 0.05). Increasing dietary DCAD tended to increase total carbon dioxide ( P = 0.07), HCO3 concentration (P = 0.07), and glucose (P = 0.06). Increasing DCAD affected blood urea nitrogen (P < 0.002), total protein (P < 0.001) and serum albumin (P < 0.001), and serum creatine kinase (P < 0.05), but blood lactose (P < 0.07) tended to increase linearly as DCAD increased. Overall, diets with the middle level of DCAD (+251.54 mEq/ kg DM) improved lactation performance and blood acid-base status in early lactation cows under heat stress.