Evaluating the inclusion of alfalfa hay in diets fed to pregnant and non-lactating Holstein cows during the prepartum period

The study objectives were to determine the dry matter intake, urine pH, Ca concentration in blood, Ca output in urine, and incidence of hypocalcemia from pregnant, non-lactating dairy cows during the prepartum period consuming diets containing either grass hay (GH) or alfalfa hay (AH) with the inclusion of either calcium chloride (CL) or polyhalite mineral (PO). Eighty Holstein cows in their 2nd parity or greater were fed an experimental diet according to a 2 2 factorial arrangement of treatments during the prepartum period (21 d before calving). All diets had a dietary cation-anion difference (DCAD) below -190 mEq/kg/DM. Grass hay contained 7.5% CP, 74.9% NDF, 0.36% Ca, 0.02% Na, 1.88% K, 0.38% Cl, and 0.15% S. Alfalfa hay contained 19.6% CP, 45.6% NDF, 1.52% Ca, 0.16% Na, 2.5% K, 0.77% Cl, and 0.32% S. Cows consuming grass hay tended to consume more dry matter than cows consuming alfalfa hay (11.6 vs 10.8 kg/d), but dry matter intake (DMI) was not affected by the acidogenic products. Urine pH decreased below 6.5 for all diets and was greatest for cows consuming the GHPO diet. The concentration of calcium in plasma decreased significantly (P < 0.01) around calving but neither the hay type (P=0.86) nor the acidogenic product (P =0.81) affected it. Urinary calcium output was less for cows consuming the GHPO diet. Cows consuming diets containing alfalfa hay had a greater incidence of normocalcemia (37 and 40% for AHCL and AHPO, respectively) than cows consuming diets containing grass hay (20 and 25% for GHCL and GHPO, respectively). In conclusion, alfalfa hay can be included in prepartum diets without necessarily increasing the incidence of hypocalcemia, and the cation-anion difference of alfalfa hay is a determinant of whether it can be included in the prepartum diet.