Effect of clinical mastitis and other diseases on reproductive performance of Holstein cows.

The objective of this study was to evaluate the effect of clinical mastitis and (or) other diseases on reproductive performance in lactating Holstein cows. Cows (n=967) from a commercial dairy farm were divided into four groups retrospectively: cows with clinical mastitis and other diseases (MD, n=54), clinical mastitis only (M, n=154), other diseases only (D, n=187), and cows with no record of clinical mastitis or other diseases (H, n=572). Days in milk at first service (DIMFS), services per conception (S/C), days not pregnant (DNP), the rate at which animals became pregnant over time and the proportion of cows that remained non-pregnant during 224 days of lactation were evaluated. Groups MD and M had greater (P<0.05) DNP compared with H (155+/-15 and 140+/-5 vs. 88+/-2, respectively). Moreover, MD and M had greater (P<0.05) S/C compared with H (3.0+/-0.4 and 2.1+/-0.1 vs. 1.6+/-0.1, respectively). The rate at which animals became pregnant over time was less (P<0.05) for MD and M and tended (P=0.1) to be less for D when compared with H. In addition, proportion of cows that remained non-pregnant by 224 days of lactation was greater (P<0.05) in MD, M, and D compared with H. Cows with mastitis were also divided into three groups according to the day of occurrence of the first case of clinical mastitis: (1) clinical mastitis occurred before 56 days postpartum (MP1); (2) clinical mastitis occurred between 56 and 105 days after parturition (MP2); and (3) clinical mastitis occurred after 105 days postpartum (MP3) Regardless of the time of occurrence, DNP was greater (P<0.05) for cows with mastitis compared with H. Time of mastitis occurrence affected S/C in that cows in MP2 and MP3 had a greater S/C compared with H cows (P<0.05). Reproductive efficiency was decreased by the presence of clinical mastitis alone because a greater proportion of cows with mastitis remained non-pregnant over time. Moreover, a greater proportion of cows with mastitis or diseases remained non-pregnant by 224 postpartum. Furthermore, the negative effects on reproduction were exacerbated when cows experienced both clinical mastitis and other diseases.