The objective of this study was to assess the effect of high somatic cell counts (SCC) in early lactation on the probability of cows to conceive at first artificial insemination (FAI). A total of 6642 lactations started from 2003 to 2015 from 5 dairy herds having SCC records 21 d before and 21 d after the first artificial insemination (FAI) were included in the study. Lactations were classified as: healthy (HEA) when both SCC were <150,000 cells/mL (<150K); as cured (CUR) when they had SCC >150K before and <150K after their FAI; as new cases (NEW) when they had SCC <150K before and >150K after their FAI; and as chronic (CHR) cases when they had SCC >150K before and after FAI. Logistic regression models were run to test the effect of SCC (healthy, cured, new, chronic) on the odds of conception at FAI (model 1); and to assess the effect of severity of chronic cases, classified according to their SCC after FAI as light (≥150K and <400K), mild (≥400K and <1000K) or severe (≥1000K) on the odds of conception (model 2). Both models also accounted for the effect of year (2003–2015), herd (1–5), parity (1 vs. 2 vs. 3+) and accumulated milk yield up to 150 DIM. In model 1, the odd of conception at FAI was 14.6% lower in chronic cases compared with healthy cows (P < 0.05, Table 1). In model 2, the odd of conception at FAI was 33% lower in severe chronic cases compared with healthy cows (P < 0.05, Table 1). In both models, the remaining groups had numerically lower non-significant odds of conception (Table 1). In conclusion, cows having high SCC (>150,000 cells/mL) around FAI have reduced fertility, and this effect depends on the severity of the case. Table 1. Logistic regression model assessing the odds of conception at first artificial insemination (FAI) in grazing dairy cows (n=6642)

	N	CR (%)1	Odds ratio	95%CI
Model 1
Healthy	3,067	41.8	1
Cured	1,038	41.3	0.98	0.84–1.14
New case	1,134	39.7	0.92	0.79–1.10
Chronic case	1,403	38.0	0.85	0.74–0.99*
Model 2
Healthy	3,067	40.3	1
Lightly chronic	728	38.9	0.94	0.78–1.13
Mildly chronic	376	35.7	0.82	0.64–1.05
Severely chronic	298	31.1	0.67	0.50–0.89*

¹Conception rate at first AI (least squared mean). *P < 0.05.