Effects of reducing dietary cation-anion difference on lactation performance and milk fatty acid profile of lactating dairy cows

Haley Zynda
Graduate (MS)
Chanhee Lee
Animal Sciences

Reducing manure pH by direct addition of acids reduces NH3 emissions but adds management costs and hazard. Reducing dietary cation-anion difference (DCAD; Na + K - Cl - S) reduces urine pH and, therefore, has potential to lower NH3 emissions from manure. However, while the exact mechanism is unknown, cows fed a low DCAD diet may reduce DMI, milk yield, and milk fat. This study examined the effects of reduced DCAD on DMI, digestibility, production, and manure NH3 emissions (not discussed). In a randomized complete block design, 27 cows were blocked by parity and DIM and randomly assigned to: CON, a typical lactating diet (192 mEq/kg DM); MID, the same as CON with reduced DCAD (101 mEq/kg DM); and LOW, a diet with 1.2 mEq/kg DM. An anionic product (MegAnion) was substituted for urea and soybean meal in CON to decrease DCAD for MID and LOW (isonitrogenous). The experiment lasted 7 wk (1-wk covariate followed by 6-wk data collection). All data were analyzed using the MIXED procedure of SAS (block as random effect; diets, repeated wk, and interaction as fixed effects). Urine pH decreased (8.26, 8.05, 6.38 for CON, MID, and LOW, respectively; quadratic P 0.01). Milk yield and DMI were not different among treatments. Energy corrected milk tended to decrease linearly (P  0.10; 35.1 to 32.7 kg/d) as DCAD decreased. This is due to numerical decreases in milk yield and milk fat content, resulting in a tendency of decreased milk fat yield (1.00 to 0.86 kg/d, P = 0.08) as DCAD decreased. Milk protein yield was not different among treatments. Changes in milk fatty acid profiles were minimal. Trans-10 and trans-11 C18:1 were not affected (average 6.7 and 0.74%, respectively). Although trans-10, cis-12 C18:2 increased linearly (P 0.01) as DCAD decreased, the concentration was low (average 0.03%). However, the concentration of linoleic acid and total PUFA in milk increased (P 0.05) as DCAD decreased. Potential reduction of NH3 emission would need to be compared to the loss in milk fat production efficiency to calculate the value of this low DCAD strategy.