Relation of Milk Production Loss to Milk Somatic Cell Count

Abstract

Milk production loss was studied in relation to increased somatic cell count (SCC). Available data were weekly test-day milk yields and SCC (in 1,000 cells/ml), and mastitis incidences. In total, 18,131 records from 274 cows were used. Production loss was determined for test-day kg milk, kg protein, and kg energy-corrected milk. Least-squares analysis of variance was used to estimate the direct effect of Log₁₀(SCC) on production. The recorded measures of production were first corrected for fixed effects, with adjustment factors estimated from a healthy data-set.

The average daily milk yield was 19.7 kg/day in first lactation and 22.0 in later lactations. The geometric mean of SCC was 63.1 in first lactation and 107.2 in later lactations. The incidence of clinical mastitis treated by a veterinarian was 19.8% of the lactations-at-risk. Linear relationships were found between the production parameters and Log₁₀(SCC). Quadratic and cubic effects were evaluated, but were found to contribute little to the overall fit of the models. The individual milk yield loss was 1.29 kg/day for each unit increase in Log₁₀(SCC) for cows in first lactation. Milk yield decreased by 2.04 kg/day per unit Log₁₀(SCC) for older cows. Corresponding values for protein yield were 0.042 and 0.067 kg/day for first and later lactations, respectively.

Sammanfattning

Sambandet mellan avkastning och cellhalt studerades på ett material omfattande 18.131 veckovisa observationer från 274 kor på en försöksstation. Avkastningsförluster skattades med minsta-kvadrat metodik för kg mjölk, kg protein och kg energikorrigerad mjölk. I syfte art undvika skattningsfel korrigerades avkastningsuppgifterna, före analys, till en nivå som kunde förväntas för uppgifter som inte påverkats av mastit.

I första laktationen var den genomsnittliga avkastningen 19,7 kg/dag, det geometriska medelvärdet för cellhalt 63,1 1000-tal celler/ml och incidensen klinisk mastit 14,5 fall per 100 risk-laktationer. Motsvarande siffror för äldre kor var 22,0 kg/dag, 107,2 1000-tal celler/ml respektive 22,7 fall per 100 risk-laktationer.

Resultaten visade på ett linjärt samband mellan avkastning och log₁₀(cellhalt). Kvadratiska och kubiska termer undersöktes, men de bidrog mycket lite till modellens forklaringsgrad. Den uppskattade förlusten per enhets ökning i log₁₀(cellhalt) var 1,29 kg mjölk/dag i första laktation och 2,04 kg/dag i senare laktationer. Motsvarande siffror för protein-avkastningen var 0,042 kg/dag respektive 0,067 kg/dag.