Effects of two different prepartum diets on some metabolic traits and productive response in multiparous Holstein cows in early lactation

Twenty-six multiparous Italian Holstein cows were used to compare two feeding strategies for the prepartum period. Cows were allocated to two dietary treatments on the basis of their parity (3.1 +/- 1.1) and mature equivalent production (11473 +/- 1449 kg). From 20 +/- 7 d precalving to the calving day, one group of 13 cows (parity = 3.1 +/- 1.0; mature equivalent production = 11473 1606 kg) was fed a Control diet made by mixing a 50:50 as fed combination of the far off dry ration and the lactation diet fed postpartum. The remaining cows (parity = 3.1 1.1; mature equivalent production = 11473 1338 kg) were fed a prepartum diet (Anionic) obtained by supplementing the far off dry ration with energy and protein sources plus calcium chloride. This diet had a lower dietary cation-anion difference than the Control diet (7.35 vs 26.66 meq/100 g DM; P<0.05) and it induced a significant decrease in the cows' urine pH (7.58 vs 7.95; P<0.01). Cows fed the Anionic diet had the lowest DM intake during the prepartum (12.0 vs 13.4 kg/d; P<0.01), but at parturition they showed a limited drop in plasma Ca reducing the incidence of subclinical hypocalcaemia in comparison with the Control group (8 vs 62%; P<0.01). No differences due to the prepartum diet were observed for the plasma levels of several indicators of hepatic function (aspartate-amino transferase, Y-glutamil transferase, creatin-kinase and bilirubine). After calving, all the cows were co-mingled and fed the same lactation ration and those that had received the Anionic diet during the prepartum showed a significant increase in milk yield with no changes in milk quality. Average production at the peak of lactation was 43.8 kg/d for Control cows while it raised up to 47.8 kg/d (P<0.05) for the animals fed the Anionic diet during the prepartum. This positive result was obtained with a lower loss in cows' body condition score measured at 30 and 60 days in milk and without any effect on the uterine involution process. The use of the Anionic diet has proven to be an effective alternative to the common practice of feeding close-up diets made by a partial replacement of the far off dry ration with the diet fed to the lactating cows. This strategy should be particularly recommended for dairy herds in which there is a great incidence of metabolic and health problems related to clinical or subclinical hypocalcaemia in the early postpartum.