Evaluation of environmental effects on reproductive characteristics of Mangalarga Marchador mares in a commercial embryo transfer program.

The objective of this study was to evaluate the environmental effects on embryo recovery rate and pregnancy rate of Mangalarga Marchador mares. The reproductive characteristics of donor and recipient mares were evaluated during five years in Brazilian tropical environment. The mares were used throughout the year and seasons were classified as: October to April (breeding season - BS); May (autumn transition out of the breeding season - ATBS); June to August (non-breeding season - nBS); and September (vernal transition into the breeding season - VTBS). Daily temperature rainfall and hours of daylight (photoperiod) were measured during all months and years of evaluation. The embryo recovery rate (ERR) and the pregnancy rate (PR) were observed and frequencies were calculated. The effect of environmental variables, day of flushing, and hormonal treatments (estradiol benzoate and progesterone) were determined for the reproductive measures using the Chi-square and Kruskal-Wallis tests. Significant effects were noted of the year, season and temperature on ERR (P < 0.05), but no significant effects were observed of the environmental parameters (year, season, hormone treatment, rainfall and photoperiod) on PR (P > 0.05). The day of uterine flush affected ERR (P < 0.05) but did not affect PR (P > 0.05). In addition, hormone treatment also supported favorable results of PR in recipient mares during nBS. The conclusion is that mares of this breed can be used in reproduction all year long, with good pregnancy rates, in Brazil's tropical environment. The hormone treatment also supported favorable pregnancy rates in recipient mares during the non-breeding season. It seems that mares can have good pregnancy rates throughout the year in Brazil´s tropical environment.