MACROMINERAL ELEMENT INTERRELATIONSHIPS AND LACTATIONAL PERFORMANCE -EMPIRICAL-MODELS FROM A LARGE DATA SET

The objectives were to model empirical interrelationships among dietar y macromineral elements and cation-anion difference influencing DMI, m ilk yield, 4% FCM yield, and milk composition of dairy cows. The datab ase consisted of 1022 cow-period means collected from 326 midlactation cows in experiments with incomplete block designs. Dietary concentrat ions of elements ranged from below to above current recommendations, a nd cation-anion difference (Na + K - Cl) was from +5.8 to +61.2 meq/10 0 g of dietary DM. interrelationships were detected for dietary concen trations of Na by K for DMI, 4% FCM yield, and milk fat percentage; Na by Ca for DMI, milk yield, and 4% FCM yield; K by Cl for DMI, 4% FCM yield, and milk protein percentage; K by Ca for 4% FCM yield, milk pro tein, and fat percentages; Na and P for DMI and milk protein percentag e; and K by P for 4% FCM yield and milk fat percentage. Maximal DMI an d milk yield were observed with .58% Na, .40% Mg, and +38 meq/100 g of dietary DM. Agreement was close for DMI and milk yield responses to d ietary cation-anion difference from our database and independent data sets. The models developed are empirical, do not necessarily establish cause and effect, and should be evaluated prudently; however, they pr ovide useful information to design future research.