New University of Minnesota research shows anionic dry cow diets increases milk production
Feeding negative dietary cation-anion difference (DCAD) diets to dairy cows during the dry period is used to reduce the risk of hypocalcemia (low blood calcium (Ca)) or milk fever after calving. Reducing diet DCAD induces a metabolic acidosis in which Ca is resorbed from bone into the blood stream to compensate for Ca secreted in colostrum and milk. Previous studies have shown that feeding DCAD lowering feed additives (such as Biochlor®) prior to calving results in higher blood calcium (Ca) at calving. Increasing amounts of available Ca helps reduce the incidence of low blood calcium or hypocalcemia (blood Ca < 8.0 mg/dL). Cows with hypocalcemia often experience depressed immune response, reduced skeletal muscle function (down cows) and reduced smooth muscle function predisposing cows to displacement of the abomasum, metritis and mastitis due to failure of teat end closure after milking.
Dry cow forages high in potassium can increase DCAD, which has detrimental effects on Ca resorption from bone and increases the risk for milk fever. Moderate energy high-fiber (MEHF) diets based on wheat straw and corn silage are inherently low in potassium and therefore typically have a lower DCAD than diets containing ingredients such as grass hay and alfalfa hay. Some producers have been asking "If I feed a low potassium dry cow diet, do I need to add a DCAD lowering product?" Additionally some producers are reducing the number of dry cow pen moves by feeding one dry cow diet; however, a one group dry cow diet complicates feeding due to unknown effects of extended exposure to negative DCAD diets.
Effects of feeding negative DCAD diets more than 21 days have not yet been thoroughly explored. Perhaps combining a shortened dry period (42 days) and a negative DCAD diet during the whole dry period will allow producers to manage a single group dry cow system and also reduce the risk of hypocalcemia.
We designed a trial to address these questions. Objectives were to: 1) determine if decreasing DCAD is beneficial for cows fed MEHF diets, and 2) determine if the number of days (21 vs. 42) that low DCAD MEHF diets are fed prepartum impacts postpartum performance and blood calcium at calving.
Sixty Holstein and Holstein-cross multiparous dairy cows housed in a tie-stall barn were randomly assigned to one of three treatments 42 days prior to expected calving. Treatment assignments were balanced by body weight, body condition, parity, breed and previous lactation 305ME. Dietary treatments included: 1) Control (CON, DCAD= +55.8 mEq/lb DM), 2) 21 days including Bio-Chlor® in the diet (21-day negative DCAD (21-ND), DCAD= +55.8/-71.7 mEq/lb DM), and 3) 42 days including Bio-Chlor® in the ration (42-ND, DCAD= -71.7 mEq/lb DM), with all diets composed of 38.7% corn silage, 22.9% chopped wheat straw, 17.4% protein mix, 12.1% chopped alfalfa hay, 6.0% liquid molasses supplement, and 2.9% ground corn on a dry matter basis. Two protein mixes: 1) Control (97.5% soybean meal), and 2) Bio-Chlor® (52.8% Bio-Chlor®, 45.8% soybean meal) were used for the positive and negative DCAD diets, respectively. Control cows received the positive DCAD diet for the entire dry period. The 21-ND received the positive DCAD diet for the first 21 days, and then switched to the negative DCAD diet 21 days from expected calving. The 42-ND cows received the negative DCAD ration for the whole dry period. After calving, all cows received the same lactation diet through day 56. Urine pH for 21-day and 42-day treatment groups was lower compared with control cows, demonstrating effectiveness of DCAD adjustments with Bio-Chlor®.
Figure 1. Milk production during the first eight weeks of lactation for cows fed prepartum diets varying in cation-anion difference; 1) Control (CON), 2) 21 days Bio-Chlor (21-ND), 3) 42 days Bio-Chlor (42-ND).
Prepartum DMI did not differ among treatments and averaged 29.8, 31.6 and 28.2 lb/day for control, 21-ND and 42-ND, respectively. Postpartum DMI averaged 39.4, 42.7, and 43.2 lb/day during the first month of lactation for Control, 21-day and 42-day treatment groups, respectively. Treatment effects on milk yield (Figure 1) showed that 21-day and 42-day treatment groups tended to produce more milk than Control during week 1 and significantly more milk during weeks 2 and 3.
We collected blood samples from cows before and after calving to determine if the treatments affected blood calcium. The 21-day and 42-day treatments tended to have higher blood calcium at 12 hours after calving and had higher blood calcium 72 hours after calving compared to Control. Higher postpartum blood Ca observed in anionic supplemented diets could explain the increase in postpartum performance compared to Control.
Does the milk response pay for the negative DCAD program? We did a simple economic analysis by looking at postpartum feed costs and milk value only. Using fixed value of milk ($18/cwt) and feed costs ($0.14/lb of DM), we calculate an income over feed cost of $8.91, $10.14 and $9.73/cow/day for Control, 21-day and 42-day treatments, respectively.
- Performance by cows fed low potassium dry cow diets (MEHF) can be increased by reducing the DCAD, and this improvement in milk yield alone pays for the negative DCAD program.
- Anionic supplementation to dry cows may result in better calcium homeostasis and postpartum performance if extended to a 42-day feeding regimen.
For further details on this feeding trial, contact Dr. Noah Litherland at firstname.lastname@example.org.