Effects of stage of lactation and parity on somatic cell counts in milk of Verata goats and algebraic models of their lactation curves

Abstract

Effect of stage of lactation and parity on somatic cell counts in milk was studied in 100 goats of the Verata breed (25 each in the first, second, third and fourth lactation) free of clinical mastitis. Counts from aliquot milk samples collected at 21 d intervals were used to evaluate the parameters of a cell count curve through the lactation with an incomplete gamma function according to Wood (1967): Y( n) = A × n b × e cn, where Y( n) is the average somatic cell counts (SCC) in the 210 d lactation, expressed in millions/ml. Cell counts varied from 0.92 × 10 6/ml in the 1st week and 0.57 × 10 6/ml in the 5th week to 1.81 × 10 6/ml in the 30th week of lactation. Average cell concentration was significantly affected ( P < 0.05) by parity, and did tend to increase from the first (1.27 × 10 6 SCC/ml) to the fourth lactation (2.02 × 10 6 SCC/ml). The curve of somatic cell counts was the inverted image of the lactation curve. That is the reason why the curve was fitted by the incomplete gamma functions of Wood ( R 2 = 0.97). From their equations a minimum cell concentration ( −( b c ) ) was deduced on the following days: first lactation, 28; second lactation, 55; third lactation, 13 and fourth lactation, 25. We observed that the estimation of inflection appearing in conjunction with the first and second months of lactation occurred in the same way as with yield and quality of milk.