Abstract
The purpose of this study was to evaluate the effect of clinical mastitis between calving and next conception on reproductive performance in Chinese Holstein cows. Six hundred and three multiparous Holstein cows from a commercial dairy farm were divided into three groups respectively: cows with first clinical mastitis before first artificial insemination (AI) (MG1; n = 113), cows with first clinical mastitis between first AI and pregnancy diagnosis (MG2; n = 36) and cows without any clinical disease (CG; n = 454). Clinical cases of mastitis were identified at every milking by the trained milkers or the herd manager based on abnormal milk or signs of inflammation of the mammary gland. Number of days from calving to first AI and days from calving to conception, number of AI per conception, and the conception rate at first AI were evaluated in each group. The number of days to first AI was significantly greater for cows in MG1 than MG2 and CG (P < 0.01). The number of days to conception was similar for cows in MG1 and MG2 (P > 0.05), but they were all greater than cows in CG (P < 0.01). The number of services per conception was significantly greater for cows in MG1 and MG2 than CG (P < 0.01), and cows in MG1 had fewer number of services per conception as compared to MG2 (P < 0.05). Conception rate at first service was similar for cows in MG1 and MG2 (P > 0.05), however, conception rate for those groups were both lower than for CG (P < 0.01). In conclusion, clinical mastitis during early lactation markedly and negatively influenced reproductive performance of dairy cows. Therefore, reduction of clinical mastitis in early lactation should also improve reproductive performance of dairy cows. Further study is needed to better understand the mechanisms of how clinical mastitis affects reproductive performance in dairy cows which could lead to better strategies to avoid such negative effects. Key words: Mastitis, dairy cows, reproductive performance.  
Highlights
Mastitis, an inflammatory reaction of the mammary gland is the most dreaded disease of dairy farmers because of reduced milk production, increased treatment costs, labour, milk discarding following treatment, death and premature culling (Yang et al, 2011)
Six hundred and three multiparous Holstein cows from a commercial dairy farm were divided into three groups respectively: cows with first clinical mastitis before first artificial insemination (AI) (MG1; n = 113), cows with first clinical mastitis between first AI and pregnancy diagnosis (MG2; n = 36) and cows without any clinical disease (CG; n = 454)
Clinical cases of mastitis were identified at every milking by the trained milkers or the herd manager based on abnormal milk or signs of inflammation of the mammary gland
Summary
An inflammatory reaction of the mammary gland is the most dreaded disease of dairy farmers because of reduced milk production, increased treatment costs, labour, milk discarding following treatment, death and premature culling (Yang et al, 2011). Mastitis has been recently reported to have a detrimental effect on reproductive performance in lactating dairy cows (Barker et al, 1998; Hertl et al, 2010; Nava-Trujillo et al, 2010; Santos et al, 2004; Schrick et al, 2001). Yang et al 2575 number of days to first artificial insemination (AI), artificial inseminations per conception and the number of days to conception Both Gram negative and positive pathogens may act through similar mechanisms to increase inflammatory mediators, leading to reproductive failure during early lactation. Schrick et al (2001) reported that subclinical mastitis reduced reproductive performance of lactating cows which is similar to clinical mastitis. Peake et al (2011) found that cows with neither subclinical nor clinical mastitis in the first two months of lactation had a negative effect on fertility parameters
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