Simple Summary Rearing livestock in tropical conditions is a crucial challenge for sustainable production in equatorial countries, where cattle are more exposed to more extreme environmental conditions than those of their origin. Jersey milking cows raised under hot-humid tropical conditions were scored for lameness, and the results were related to postpartum conception. Lameness affected reproductive performance, since more than double the number of inseminations was required to conceive, increasing the days open and decreasing the herd's conception rate. Systematic locomotion scoring represents a fundamental routine procedure to maintain a healthy herd in terms of both foot health and reproductive performance in tropical dairy herds, where environmental conditions greatly worsen common production diseases such as lameness.Abstract Reproductive physiology is one of the first systems which is altered when an animal suffers from an imbalance. This is crucial in tropical dairy farming, where maintaining homeostasis and production is particularly demanding. Lameness is a disorder commonly identified by impaired walking, but its early diagnosis could reduce the negative repercussions on production, welfare, and postpartum conception. To evaluate the effect of lameness on postpartum conception, a prospective observational cohort study with a cross-sectional design was developed. Fifty-two Jersey milking cows raised under hot-humid tropical conditions were scored using a five-point locomotion scoring (LS) system (1-non-lame, 2-slightly lame, 3-moderately lame, 4-lame, and 5-severely lame), considering scores >= 3 to indicate clinical lameness. Inseminations per conception and days open (CCI) were registered. Inseminations were similar in animals scoring 1, 2, 3, and 5, while they increased in cows with a score of 4, which also increased their CCI along with animals that scored 5. Positive correlations were observed between LS and reproductive variables. The herd's conception rate was reduced from 45% to 21.8% in the presence of clinical lameness (score >= 3). Applying the LS system should be essential as part of routine medical examinations used to monitor dairy herds, and it becomes even more crucial under hot-humid tropical environments, where adverse conditions could rapidly aggravate the early stages of lameness and not only increase the costs of hoof care, but also delay fertility in cattle.
