Variability of Milk Components in 1705 Herds

Biweekly herd milk samples collected for a 1-year period (January 1, 1984 to December 31, 1984) from 1705 herds in eastern South Dakota, western Minnesota and northwestern Iowa were analyzed to evaluate milk components as factors considered in milk pricing programs. The average composition was 3.71% fat, 8.64% solids-not-fat (SNF), 3.28% protein, 12.35% total solids (TS) and 1.8 × 10⁵ CFU/ml (aerobic plate count). Fat was the most variable (8.4% coefficient of variation) milk component, followed by protein, TS and SNF (6.3, 4.1 and 3.4% coefficient of variation, respectively). The concentration of fat, SNF, protein and TS in milk was lowest in July and August and highest during November through March. Correlation coefficients (r) for fat vs. SNF, protein and TS were 0.40, 0.64 and 0.84, respectively, for SNF vs. protein and TS were 0.70 and 0.83, respectively, and for protein vs. TS was 0.79. Grade A milk had lower aerobic plate counts (3.2 × 10⁴ and 3.0×10⁵ CFU/ml), higher % SNF (8.68 and 8.60), and higher % TS (12.39 and 12.31) than manufacturing grade milk. There were no differences in % fat (3.71 and 3.72) and % protein (3.28 and 3.28) between Grade A and manufacturing grade milks. Some cooperatives and milk plants are paying a SNF premium (8.75% base), stating that an 8.75% SNF is equivalent to a 3.2% protein content. This occurred in herds with <3.0% fat; however, for herds producing ≥3 and ≤4% fat, 8.75% SNF was equivalent to 3.31% protein, whereas for herds producing >4% fat, 8.75% SNF was equivalent to 3.46% protein. Solids-not-fat component pricing has the potential to be compared to protein pricing if producer grade, seasonal period and fat content of herd milk are considered.