ABSTRACT
Effect of clinical mastitis on milk production

Carlos Pedraza G.1
 
Study developed at the Research Station La Platina of INIA, Chile. Ten years accumulated productionand sanitary records were used.
Main objectives were:
- using a mathematical model, evaluate losts on milk production as a consecuence of a clinicalmastitis;
-observe the effects of mastitis on lactation in cows and heifers and on their later productive life;
-evaluate the effects of the periods in which mastitis appears in the lactation curve.
Productions from healthy and sick animals were compared, after and adjustment of the Wood'sgamma function, y(n) = anbe-cn, where y(n) is the milk production on the (n) lactancy day and a, b and care the estimated paramethers for each curve, through a multiple lineal regretion; establishing a totalproduction, day and maximum production and decline index of the lactation curve.
The research was accomplished with a total of 216 and 88 lactations, equivalent to an equal number ofcows and heifers, half of which belong to healthy animals.Milk production (litres) obtained on the 300 days on healthy and sick cows were: 5,256a and 4,522b (P≤ 0.01), respectively. Considering the season on which mastitis appeared (summer, fall, winter, spring)production was: 5,005 and 4,861 N.S., 5,284a and 4,368b; 5,412a and 4,611b, and 5,075a and 4,079b(P ≤ 0.01), respectively. Heifers lowered their production in a 16,1% compared to the healthy 4,639aand 3,890b (P ≤ 0.01) respectively.
lt was determinad that mastitis which appeared during the first 100 days of production, affected in ahigher degree the milk curve than when it occurred later. The effects of mastitis lasted to the nextlactation, affecting the production level (P ≤ 0.05) in a 2.2% for cows and 3.5% for heifers.
Key words: clinical mastitis, milk, production, milk curve.
1Estación Experimental La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.