Application Of Dietary Cation-anion Difference In Dairy Cows

Dietary cation-anion difference (DCAD) has been drawing much attention by dairy nutritionists with the progressive achievement in dairy cow nutrition. It is defined as the difference between the milliequivalents of major cations and major anions in the diet. In the current work, the effects of varying DCAD and Ca supplementatiaon on fluid acid-base balance, blood minerals profiles, health status, and lactational performance were evaluated in multiparous Holstein cows during periparturient (Trials 1 and 2) and peak-lactating periods (Trial 3). Following that, the cation-anion difference (CAD) was investigated for feedstuffs collected from six large-scale dairy farms in Zhejiang province. The DCAD levels in typical diets were also estimated (Trial 4).Trial 1 was conducted to examine the effects of reducing DCAD on fluid acid-base balance, blood minerals concentrations, health status, and subsequent lactational performance. Forty clinically healthy pregnant Holstein dry cows on d 21 prepartum were randomly allocated to four blocks of 10 according to the predicted calving date (21±2 days), age (5-8 years), parity (≥3), and their previous 305-d equivalent milk yield (7584±642 kg/head) using randomized block design; and were fed one of four DCAD diets:+150,+50,-50, and-150 mmol/kg DM. The actually determined DCAD values were+127,+30,-63, and-154 mmol/kg DM, respectively.Feeding of reduced DCAD resulted in continuous decline (P<0.05) in urinary and blood pH values. The blood HCO3- concentrations were unaffected by dietary treatments (P>0.05). The DCAD had significant correlation with urinary pH (P< 0.0001; r2=0.85), significant but low correlation with blood pH (P<0.01; r2=0.28), and non-significant determinant coefficient with HCO3- concentration (P>0.1; r2= 0.09). Urinary pH exhibited significant correlation with blood pH (P<0.0001; r= 0.52). It is indicated that feeding of reduced DCAD may induce mild metabolic acidosis in dairy cow.Cows fed diets of-50 and-150 DCAD produced higher concentration of plasma calcium than those on+50 and+150 DCAD diets (P<0.05), with little difference (P >0.05) among other diets. Diet-150 DCAD induced higher (P<0.05) plasma magnesium level than other three DCAD diets. Plasma phosphorus value was unaffected (P>0.05) by dietary treatments. The nadir of plasma calcium on the day of calving was lower (P<0.05) than the peak level on d 14 prepartum. It is suggested that blood calcium homeostasis can be maintained in dairy cow fed diets with low CAD.No case of milk fever occurred within any treatments. Hypocalcemia case tended to decrease for cows consuming diets of-50 (0%) and-150 DCAD (0%) over those receiving diets of+150 (20%) and+50 (30%). Retained placenta incidence was significantly lower (P<0.05) in cows offered-50 (0%) and-150 DCAD (0%) than those on diets of+150 DCAD (40%). The prevalence of disorders tended to be lower in the group of cows fed-50 or-150 DCAD diets (total disorders:10,7,3 and 2 for the+150,+50,-50 and-150 DCAD diets, respectively). The dry matter intake, milk yield and compositions of fat, protein, and lactose were not-significantly (P>0.05) different among four dietary treatments.It is suggested that feeding negative DCAD in late gestation period can induce mild metabolic acidosis and is beneficial for blood calcium homeostasis and improvement of health status in dairy cows.The work in trial 2 was aimed to evaluate the effect on fluid acid-base balance, serum minerals level, health status, and subsequent lactational performance in periparturient dairy cow fed diets with low CAD. and calcium supplementation. Thirty-six clinically healthy pregnant Holstein dry cows on d 20 prepartum were assigned to three blocks of 12 cows based on their age (4-6 year), parity number (2-4), and previous 305-d equivalent milk yield (7428±770 kg/head) using randomized block design. The cows were randomly allocated to one of three diets with expected CAD levels at+150 (HD),-100 (LD), and-100 mmol/kg DM plus calcium (30g/d, LDCA). The actually assessed DCAD levels were+185,-67, and-67 mmol/kg DM; and Ca intake were 100,100, and 130 g/d for for diet HD, LD, and LDCA, respectively.Feeding of the two LD diets induced lower (P<0.05) urinary and blood pH compared with the HD diet, without significant difference (P>0.05) for blood HCO3-concentration among three diets. However, urinary and blood pH, and blood HCO3-concentrations were not different (P>0.05) for the two LD diets. The DCAD indicated significant correlation with urinary pH (P<0.0001; r2=0.90), significant but low correlation with blood pH (P<0.01; r=0.53), and not-significant correlation with HCO3- concentration (P>0.1; r2=0.02), respectively. A significant correlation was observed (P<0.0001; r=0.77) between urinary and blood pH. Both of the two LD diets resulted in mild metabolic acidosis in dairy cow.Serum calcium level was higher (P<0.05) in cows fed LD diet than in cows on diets HD and LDCA, with little difference between diets HD and LDCA (P>0.05). Cows fed LDCA diet had higher (P<0.05) serum magnesium concentration compared with those on LD diet. Diet LD resulted in higher (P<0.05) serum phosphorus value relative to diet HD. The lowest serum calcium levels were observed on d 0.5 postpartum for all cows. Feeding of diet LD induced higher serum calcium concentration (P<0.05) compared with that of diet HD on d 0.5 and d 2 postpartum, but no effect (P>0.05) was observed for additional supplementation of calcium in diet LDCA relative to diet HD. It is suggested that calcium supplementation to diet low DCAD had little improvement in blood calcium homeostasis for periparturient dairy cow.No milk fever and displaced abomasum occurred within all cows. Hypocalcemia cases were higher (P<0.05) for cows fed diet HD (33%) compared with those on diet LD (0%). Diet LDCA reduced (P<0.05) retained placenta incidence (8%) over diet HD (50%). The similar decreased disorder was observed in the two LD diets, with total 14,4, and 4 for diets HD, LD, and LDCA, respectively. Dietary treatments had little effect (P>0.05) on DMI, milk yield and compositions.It is inferred that calcium supplementation (30 g/d) to-100 DCAD diet could also induced mild metabolic acidosis, but had no further improvement in maintenance of blood calcium homeostasis and health status for periparturient dairy cows.The objective of trial 3 was to assess the effects of varying DCAD levels on blood acid-base balance, serum minerals concentrations, and lactational performance in dairy cows during the peak-lactating period (DIM=20-50). Fifteen clinically healthy Holstein cows were allocated to three blocks of five cows according to their age (4-6 yr), parity (2-4), and previous 305-d milk yield (7571±784 kg/head); and were fed one of three DCAD levels at +250,+400, and +550 mmol/kg DM using a 3×3 quintuplicate Latin square design. The actually measured DCAD values were +242, +389, and +538 mmol/kg DM, respectively. Blood pH and HCO3- concentration, serum minerals, and lactation performance were unaffected (P>0.05) by DCAD alterations.In trial 4, the CAD (Na+K-Cl-S) levels were calculated for the commonly used feedstuffs collected from six representative large-scale dairy farms in Zhejiang province of China, and the DCAD levels were estimated for the typical diet.Corn grain, soybean meal, and wheat bran were the main ingredients in concentrate mixture and their CAD levels were 26,275, and 147 mmol/kg DM, respectively. The CAD levels in concentrate mixture for dry and peak-lactating period were 227 and 323 mmol/kg DM, respectively.Whole corn silage, Chinese wild ryegrass hay, and alfalfa hay were the main roughage ingredients and their CAD values were-50,95, and 429 mmol/kg DM, respectively.The typical DCAD levels in concentrate mixture for dry and peak-lactating periods were 74 and 214 mmol/kg DM, respectively. The DCAD level in dry period was lower than that in peak-lactating period.In summary, feeding of negative DCAD ranged from-100 to-50 to periparturient dairy cows could induce mild metabolic acidosis, increase blood calcium concentration, and improve health status without significant influence on lactating performance. Calcium supplementation (30 g/d) to the negative DCAD did not show further improvement in the above-mentioned parameters. There were no significant effects of positive DCAD on blood pH and HCO3- concentration, serum minerals, and lactation performance. From the average DCAD level in the six investigated dairy farms, it is suggested that anionic salts should be included into the prepartum diet; but there does not seem necessary to DCAD alteration for dairy cows in peak-lactating period.