Influence of lactation measure of somatic cell content on milk yield

The objective was to estimate the amount of change in 305-day milk yield and effect on herd yield associated with an increase in lactation average somatic cell count. Data file contained 17264 records from German Holstein cows, the average 305-day milk yield was 9517 kg. Lactation mean somatic cell scores were taken as the average of linear somatic cell score (log2) of individual tests during the lactation. Only cows with 290-305 days in milk and mean lactation somatic cell scores from 0.5 up to 6.0 were used. A multiple lactation animal model was used including regression functions (third degree) of milk yield on somatic cell scores. The regression functions always differed significantly from zero (p ≤ 0.01). Elevated somatic cell score levels in individual milk were found significantly associated with a loss in milk yield. Yield loss by increase in lactational geometric mean from 50,000 to 100,000 cells/ml milk was 106 kg milk (1.2%) in first and 369 kg milk (3.6%) in third or later lactations. The increase of lactational geometric mean from 50,000 to 800,000 cells/ml milk was associated with a decrease in milk yield of 543 kg milk (6.3%) and 980 kg milk (9.6%) in first and third or later lactation. The judgement of total losses on herd basis included milk losses per cow, the distribution of cows in different classes of lactational somatic cell scores and the distribution of cows in lactations. Respective 31 % of total losses per herd in milk yield were found in classes with geometric means of 51,000 to 100,000 and 101,000 to 200,000 cells/ml milk. The proportional loss of cows with geometric mean of 400,000 to 800,000 cells/ml milk was only 14 % because of the low frequency of cows in this realm. Subclinical mastitis should be taken seriously, because it causes high milk losses and can develop to clinical cases.

Vollversion deutsch