Effects of feeding moderate-energy high-forage diets with reduced DCAD for twenty-one or forty-two days prepartum on mineral homeostasis and postpartum performance

Abstract

In spite of decades of research, feeding strategies that prevent milk fever and hypocalcemia in the transition cow are not completely understood. Extended negative dietary cation-anion difference (DCAD) feeding in the prepartum diet would allow producers to utilize a one group dry cow pen; reducing social stress on cows while providing protection against hypocalcemia. High-fiber prepartum diets including wheat straw are inherently low in potassium and have been shown to reduce risk of hypocalcemia. Few studies examine effects of inclusion of DCAD lowering feed additives in low-potassium dry cow diets. The combined effects of extended low DCAD in a low-potassium diet remaining unexplored. To test objectives, Holstein and Holstein-cross dairy cows (n = 49) blocked by breed, parity, body weight, body condition score and previous milk production were randomly assigned to one of three treatments 42 d prior to expected calving to evaluate effects of feeding negative DCAD for 21 or 42 d during the dry period on postpartum production and mineral homeostasis. Treatments included: 1) CON, DCAD = +12 mEq/100 g DM, 2) 21-ND, DCAD = +12/-16 mEq/100 g DM, 3) 42-ND, DCAD = -16 mEq/100 g DM. Prepartum diets were similar in nutrient composition, averaging 17.0% CP, 42.0% NDF and 1.5 Mcal/kg DM. Control and anionic diets were achieved using two isonitrogenous protein mixes: 1) 97.5% soybean meal and 2) 52.8% Bio-Chlor® (Church and Dwight, Franklin Lakes, NJ), 45.8% soybean meal. CON was fed high DCAD prepartum for 42 d. 21-ND received high DCAD for the first 21 d of the dry period, and the anionic diet from d 22 until calving. 42-ND received anionic diet for the entire dry period. Supplementing anions induced a metabolic acidosis reducing urine pH for 21-ND and 42-ND compared to CON. Prepartum DMI was not affected by prepartum anionic supplementation. Postpartum DMI tended to be higher for anionic diets than the control diet (20.1 vs. 18.1 kg/d). Prepartum anionic supplementation significantly affected milk production, with CON, 21-ND and 42-ND averaging 39.1, 45.7 and 43.8 kg/d, respectively. Also, overall postpartum total blood calcium increased with extended feeding of the anionic diet. Blood magnesium through calving was highest for 42-ND. Diets had no effect on postpartum energy-related metabolites or liver composition, however overall means for liver total lipid, liver triglyceride and blood ketone concentrations were highest for CON. These data suggest low DCAD in high fiber diets for 21 or 42 d during the dry period can have positive effects on postpartum mineral homeostasis and production.