Changes in and correlations between some serum constituents and milk components from early to late lactation in a dairy herd with subclinical production disorders.

Changes in some serum constituents and milk components and correlations between them, were used for defining the reason(s) of suboptimal milk composition in a dairy herd with a history of low protein tests during summers. Four groups of 8 adult Holsteins, 20-70, 70-110, 110-150 and 150-210 days in milk (DIM),under heat stress, with similar feeding and management practices were sampled for blood and milk four times on a 10 day interval. Milk volume, percentages of milk fat and protein and levels of serum glucose, total protein, albumin and BUN were determined. Milk volume decreased as DIM increased (P 0.05). Milk fat showed normal changes, but milk protein was similarly low in all groups (P 0.05), showing probable shortages in energy and/or protein intake. Serum parameters showed no significant differences among groups (P 0.05). Weak positive correlations were found between serum total protein and milk components after 150 DIM (maximum correlation with milk fat, r = 0.61). It is concluded that shortage in intake of energy and/or protein, which may result in lowered milk protein, may not be differentiated by measuring serum glucose. total protein, albumin and BUN and milk components. More detailed experiments on serum and milk are necessary for defining the problem properly.