Abstract
Dairy cows commonly undergo negative Ca balance accompanied by hypocalcemia after parturition. A negative dietary cation-anion difference (DCAD) strategy has been used prepartum to improve periparturient Ca homeostasis. Our objective was to determine the influence of a negative DCAD diet with different amounts of dietary Ca on the blood acid-base balance, blood gases, and metabolic adaptation to lactation. Multiparous Holstein cows (n = 81) were blocked into 1 of 3 dietary treatments from 252 d of gestation until parturition: (1) positive DCAD diet and low Ca (CON; containing +6.0 mEq/100 g DM, 0.4% DM Ca); (2) negative DCAD diet and low Ca (ND; -24.0 mEq/100 g DM, 0.4% DM Ca); or (3) negative DCAD diet plus high Ca supplementation (NDCA; -24.1 mEq/100 g DM, 2.0% DM Ca). There were 28, 27, and 26 cows for CON, ND, and NDCA, respectively. Whole blood was sampled at 0, 24, 48, and 96 h after calving for immediate determination of blood acid-base status and blood gases. Serum samples collected at -21, -14, -7, -4, -2, -1, at calving, 1, 2, 4, 7, 14, 21, and 28 d relative to parturition were analyzed for metabolic components. Results indicated that cows fed ND or NDCA had lower blood pH at calving but greater pH at 24 h after calving compared with CON. Blood bicarbonate, base excess, and total CO2 (tCO2) concentrations of cows in ND and NDCA groups were less than those of cows in CON at calving but became greater from 24 to 96 h postpartum. The NDCA cows had lower blood bicarbonate, base excess, and tCO2 at 48 h and greater partial pressure of oxygen after calving compared with ND. Cows fed ND or NDCA diets had lower serum glucose concentrations than CON cows before calving but no differences were observed postpartum. Serum concentrations of total protein and albumin were greater prepartum for cows in ND and NDCA groups than for those in CON. Postpartum serum urea N and albumin concentrations tended to be higher for ND and NDCA cows. Cows fed ND or NDCA diets had elevated serum total cholesterol concentration prepartum. During the postpartum period, triglycerides and NEFA of cows fed ND or NDCA diets tended to be lower than those of CON. Cows fed the NDCA diet had greater postpartum total cholesterol in serum and lower NEFA concentration at calving than ND. In conclusion, feeding a prepartum negative DCAD diet altered blood acid-base balance and induced metabolic acidosis at calving, and improved protein and lipid metabolism. Supplementation of high Ca in the negative DCAD diet prepartum was more favorable to metabolic adaptation to lactation in dairy cows than the negative DCAD diet with low Ca.
Highlights
The transition period, a critical physiological stage for dairy cows, invokes acute alterations of energy and protein metabolism and mineral metabolism, being linked closely with health, immune status, and productive performance after parturition (Drackley et al, 2005)
We observed an interaction between treatments and DIM (P < 0.01), in which blood pH of cows fed negative DCAD (ND) or negative DCAD plus Ca supplementation (NDCA) was higher than control diet (CON) (P < 0.05) at 24 h postpartum but similar thereafter (Figure 1)
The pressure of CO2 (pCO2) at 48 h after calving differed among treatments (P < 0.05) with cows fed CON showing the lowest pCO2 and cows in ND group were greater than NDCA
Summary
The transition period, a critical physiological stage for dairy cows, invokes acute alterations of energy and protein metabolism and mineral metabolism, being linked closely with health, immune status, and productive performance after parturition (Drackley et al, 2005). Owing to dramatically increased demand of Ca for initiation of lactation, postcalving dairy cows often have hypocalcemia. More common is subclinical hypocalcemia (SCH, total Ca ≤2.125 mmol/L; Leno et al, 2017), which still affects around 50% of cows in second lactation or greater (Goff, 2014). Research has demonstrated that cows with SCH have decreased feed intake, leading to worsening of negative energy balance (NEB) and. Maintenance of Ca homeostasis around parturition has attracted widespread interest in the dairy industry due to its considerable negative effect on transition cows
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