Association between hoof lesions and reproductive performance of lactating dairy cows

Introduction
Lameness is an important disease in dairy cattle. Hoof lesions (HL) are responsible for over 90% of lameness (Phillips, 2002) and can be categorized into noninfectious lesions such as sole hemorrhage (SH), sole ulcer, white line disease, or infectious lesions, digital dermatitis and foot. Relationship between lameness and reproductive performance is conflicting. Possible reasons for these conflicting findings could include different lameness causes in herds and the timing of lameness/HL relative to reproductive events. Objectives were to evaluate ovarian cyclicity and pregnancy in lactating dairy cows with or without HL. 

Materials and Methods
This study was conducted in a dairy herd with a total of 10,000 Jersey cows in MN. Cows were enrolled at 20 ± 3 DIM postpartum (d20) using convenience sampling and examined for HL. At 120 ± 3 DIM (d120), cows were reexamined for HL. Ovarian cyclicity was determined by ultrasonography at 27 and 41 ± 3 DIM postpartum. Pregnancy was diagnosed by transrectal ultrasonography on d 34 and re- examined on d 62 after AI. According to preexisting HL status at d20, cows were divided into healthy (without HL, n = 1,197) or lesion (with HL, n = 429). According to HL type at d20, cows were grouped as healthy, SH (n = 280), noninfectious (n = 113), and infectious (n = 36). According to HL development, cows without HL at d20 and d120 were defined as healthy (n = 308), cows with HL at d20 and without HL at d120 were defined as cured (n = 72), cows without HL at d20 but with HL at d120 were defined as new (n = 597) and cows with HL at d20 and d120 were defined as chronic (n = 226). Data analyses were conducted using Stata® 14.1 (StataCorp, TX). Differences were compared and estimates with P ≤ 0.05 considered significant. Hoof lesion status and parity were forced into the final models. 

Results
Hoof lesions were found in 26.9% and 68.4% of cows at d20 and d120, respectively. Cows with HL at d20 had reduced odds of being cyclic (38.3 vs 51.9%) and longer time to first service (58 vs 51d) compared with healthy herdmates. Also, cows with infectious HL at d20 had reduced odds of first service P/AI (16.7 vs 38.3%) compared with healthy herdmates. Cows with SH at d20 were more likely to lose their pregnancies following the first service postpartum compared with healthy counterparts (10.5 vs. 5.2%). Cows with SH at d20 had smaller hazard of pregnancy (67.9 vs 75.5%) and more days open (88 vs. 77) compared with healthy cows. Sole hemorrhage accounted for 93% of new hoof lesions that developed between 20 and 120 DIM. No evidence for a difference in pregnancy hazard was observed between cows that remained healthy and cows that developed new HL. 

Conclusions
Results from our study showed that HL at d20, but not new HL, were associated with decreased odds of cyclicity, smaller hazard of first service postpartum, longer time to first service postpartum and reduced pregnancy hazard in cows. The impact of early HL diagnosis and management to reduce chronic HL in lactating dairy cows warrants further investigation.