Sub-clinical Mastitis and Reproduction:Season, Parity and Stage of Lactation Effects onConception Rate and Milk Somatic Cell Count

Abstract

The aim of the present study was to investigate the effect of subclinical mastitis (somatic cell count (SCC)>250000 cells/ml) on
the fertility of Holstein dairy cows in different parities, lactation stages and seasons. Data of 2437 SCC in a dairy farm including
number of insemination, pregnancy detection, date of calving and insemination, SCC after insemination (maximum of 30 days), and
parity were evaluated. The rate of subclinical mastitis in the first, second, third and fourth and more lactation number was 18.8%,
25.7%, 26.5% and 35.4%, respectively and in spring, summer, autumn and winter was 24.5%, 19.7%, 18.5% and 33.6%, respectively.
The likelihood of pregnancy decreased by a factor of 0.73 and 0.91 in cows had subclinical mastitis and for each increase in parity
(from 1 to ≥4), respectively. The likelihood of pregnancy increased in cows inseminated in the mid (1.3) and late (1.7) and in cows
inseminated in the autumn (1.73) and winter (1.38). Conception rate of cows with subclinical mastitis (24.6%) was lower than
cows without subclinical mastitis (30.9%; P=0.003). In addition, the conception rate in the second and third lactation in cows with
subclinical mastitis was significantly lower than in cows without subclinical mastitis. The conception rate of cows with subclinical
mastitis in summer in the second lactation and in winter in the second and third lactation was significantly lower than in cows
without subclinical mastitis. Therefore, subclinical mastitis in mid lactation stage and also in the second and third parities especially
in summer and winter can disturb fertility more than the other conditions. Also, considering these facts during these periods of
times in managing of subclinical mastitis can improve fertility outcome of the herd.