Prepartum level of dietary cation-anion difference fed to nulliparous cows: Lactation and reproductive responses

Objectives were to determine the effects of 3 levels of dietary cation-anion difference (DCAD) fed prepartum to nulliparous cows on productive and reproductive performance. We enrolled 132 pregnant nulliparous Holstein cows at 250 (248-253) d of gestation in a randomized block design. Cows were blocked by genomic merit of energy-corrected milk yield and assigned randomly to diets varying in DCAD, +200 (P200; n = 43), -50 (N50; n = 45), or -150 (N150; n = 44) mEq/kg of dry matter (DM). Dietary treatments were fed during the last 22 d of gestation and, after calving, postpartum cows received the same lactation diet. Productive performance was evaluated for the first 14 wk of lactation, and reproduction was assessed until 305 d postpartum. Intake of DM prepartum decreased linearly (results presented in sequence as least squares means ± standard error of the mean, P200 vs. N50 vs. N150) with a reduction in DCAD (9.0 vs. 8.9 vs. 8.4 ± 0.1 kg/d), which resulted in linear decreases in net energy balance (0.34 vs. 0.20 vs. -0.36 ± 0.20 Mcal/d), body weight change (1.1 vs. 0.8 vs. 0.3 ± 0.1 kg/d), and mean body weight (652 vs. 649 vs. 643 ± 2 kg) prepartum. Treatment did not affect yield of colostrum (6.3 vs. 5.8 vs. 5.1 ± 0.6 kg) or the contents or yields of fat, protein, lactose, IgG, Ca, or Mg in colostrum. Intake of DM (19.4 vs. 19.2 vs. 19.0 ± 0.2 kg/d), yields of milk (36.6 vs. 36.7 vs. 35.8 ± 0.6 kg/d) or energy-corrected milk (36.7 vs. 36.3 vs. 35.9 ± 0.5 kg/d), feed efficiency (1.93 vs. 1.92 vs. 1.93 ± 0.03 kg of energy-corrected milk per kilogram of DM intake), and content and yield of milk components did not differ among treatments during the first 14 wk of lactation. Prepartum DCAD did not affect the cumulative milk yield by 305 d of lactation (9,653 vs. 10,005 vs. 9,918 ± 196 kg). Of the 132 cows, 40 P200, 45 N50, and 43 N150 received at least 1 artificial insemination (AI), and treatment did not affect pregnancy per AI at first (32.5 vs. 35.6 vs. 37.2%) or all AI (30.6 vs. 33.9 vs. 40.2%), although reducing the DCAD increased the proportion of cows pregnant by 305 d postpartum (76.7 vs. 88.9 vs. 93.2%) without altering the rate of pregnancy. Collectively, manipulating the DCAD of prepartum diets, from +200 to -150 mEq/kg of DM, fed to late gestation nulliparous cows did not affect subsequent lactation productive performance, but may have provided some benefit to reproduction, which warrants further confirmation.