Influence of subclinical mastitis during early lactation on reproductive parameters

Our objective was to determine the effects of mastitis during early lactati on on the reproductive performance of jersey cows. From 1986 to 1997, quart er foremilk samples were collected every 4 to 8 wk during lactation, at dry ing off, near calving, and when clinical mastitis was diagnosed and were ev aluated microbiologically to identify causative bacteria. Services per conc eption, days open, and days to first service were obtained from DHIA record s on 752 cows. Cows were separated by mastitis type (clinical, n = 186; sub clinical, n = 240; control, uninfected or infected after confirmed pregnanc y, n = 326). Cows were reclassified based on the time of clinical or subcli nical mastitis as follows: period 1, before first service (n = 374); period 2, between first service and pregnancy (n = 52); and period 3, after confi rmed pregnancy or uninfected (control; n = 326). Milk production did not di ffer for any group separations. Reproductive performance did not differ bet ween gramnegative or gram-positive mastitis pathogens. Cows with clinical o r subclinical mastitis before first service had increased days to first ser vice (77.3 +/- 2.7 and 74.8 +/- 2.7 d), days open (110.0 +/- 6.9 and 107.7 +/- 6.9 d), and services per conception (2.1 +/- 0.2 and 2.1 +/- 0.2) compa red with controls (67.8 +/- 2.2 d, 85.4 +/- 5.8 d, 1.6 +/- 0.2; P < 0.05). Days to first service were not increased in cows with clinical or subclinic al mastitis during period 2 (70.6 +/- 3.3 and 61.2 +/- 7.8 d). However, day s open (143.6 +/- 8.5 d) and services per conception (3.0 +/- 0.2) were inc reased (P < 0.05) in cows with clinical mastitis during period 2, but not i n cows with subclinical mastitis (90.9 +/- 20.2 d and 2.1 +/- 0.5). Cows in itially diagnosed subclinical that became clinical during period 2 exhibite d increased days to first service (93.9 +/- 10.1 d), days open (196.0 +/- 2 6.2 d), and services per conception (4.3 +/- 0.7) compared with control ani mals (P < 0.05). In conclusion, subclinical mastitis reduced reproductive p erformance of lactating cows similar to clinical mastitis. Subclinical mast itis followed by clinical mastitis resulted in the most severe loss in repr oductive performance.