Relationship between somatic cells and lactation curve characteristics in dairy cows

Carlos Pedraza G.1, Hernán Agüero E.2, Marcela Gómez C.3 Hugo Flores P.1, Alberto Mansilla M.4 y Paola Fajardo R,1

A two-year study was carried out at five dairy farms, to test the effect ofthe increase of somatic cells in milk production. The gamma function recommended by Wood (1967) for the lactation curve was used on records having different levels of sublinic mastitis. In orderto classifythe mastitis, seven levels Were determined from R1= < 100,000 cel.lml through R7= > 5,000,000 cel./ml.
The fitted values for lactation curves, in heifers expressed as determination coefficients from R1 to R6 were follows: 0.91,0.74, 0.74,0.51,0.31 and 0.52, respectively (P< 0.0001). The values in cows were the following: from R1 to R7 0.97, 0.92, 0.94, 0.93, 0.89, 0.90, and 0.71 (P < 0.0001), respectively.
In both gróups of animals, the inicial, maximum and to the 305th day productions tended to decrease with the increase of cellular recount, clearly confirming inferior values for the more elevated ranks of recounts.
The'lactation production per animal s of a first birth were: R1= 6,220 a; R2= 6,032 b; R3= 5,946 b; R4= 5,786 e; R5= 5,633 d; R6= 5,124 e, and R7= 4,385 f (P< 0.01).
The values of cows with two or more births reached as follows: R1= 5,451 a; R2= 5,340 b; R3= 5,050 d; R4= 5,255 c; R5= 4,795 e, and R6= 4,305 f (P < 0.01).
According to this, the extreme losses reach 21 and 29% of the total production of animals of first and second lactations, obtaining statistical significance starting with recounts included between 100,000-200,000 cel./ml and 100,000-500,000 cel./ml, respectively.
It was concluded that gamma functfon is an excellent analytic tool to determine the effects of subclinical mastitis on milk production.

Keywords: lactation curve, subclinical mastitis, somatic cell, milk yield, cows.
1 Centro Regional de Investigación La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.
2 Facultad de Ciencias Veterinarias y Pecuarias, Univ. de Chile, Casilla 2, Correo 15, Santiago, Chile.
3 Actividad privada.
4 Facultad de Ciencias Agrarias y Forestales, Univ. de Chile, Casilla 1004, Santiago, Chile.