181 CHANGES IN THE BODY CONDITION STATUS OF DONOR MARES THROUGHOUT THE BREEDING SEASON AND THEIR RELATIONSHIP WITH REPRODUCTION TRAITS

Abstract

The objective was to investigate the relationship between changes in body condition on reproductive traits of donor mares in an embryo collection program. Fifty-six non-pregnant mares, 3 to 18 years old, were studied from August 2008 through April 2009. Body condition score (BC; 1-9 scale, thin to obese) was estimated monthly. Body weight and tail and rib s.c. fat depths (SF) were measured monthly. SF was determined by ultrasound. Dominant follicle diameter (DF) was measured daily during the follicular phase. Mares were artificially inseminated and embryo transfers were conducted 6 d after ovulation. Analyses were performed with SAS^® (SAS Institute Inc., Cary, NC, USA). Age classes were as follows: age 1, 3 to 6.9 (n = 17); age 2, 7 to 12.9 (n = 25), and age 3, ≥13 years (n = 14). Months in experiment were T1 to T6. BC classes were as follows: B1, <6.5; B2, 6.5 to 6.9; B3, 7.0 to 7.5; and B4, >7.5. Embryo recovery rate was compared by chi square. Effects of month and age on BC, weight, and SF were analyzed by a mixed model. Age, BC, and month fixed effects on DF diameter were analyzed by ANOVA with mare within class as the error term. Means were compared by contrasts. BC was higher (P = 0.02) in older mares (6.78 ± 0.2 and 6.93 ± 0.2 in age 1 and age 2 v. 7.25 ± 0.2 in age 3) and increased (P = 0.009) with time (from 6.79 ± 0.20 to 7.42 ± 0.26 for T1 to T6, respectively). Weight (kg) was not associated with age but increased (P = 0.03) throughout the experiment. Tail fat increased with age (P = 0.04) and decreased with increasing months on experiment (P = 0.02). DF diameter increased daily through the follicular phase (P < 0.0001) and was smaller (P < 0.05) in mares with lower body condition (33.80 ± 0.31 in BC1 v. 34.17 ± 0.31 mm in BC4). DF diameter decreased (P < 0.01) with month on study. Embryo recovery rate was not affected by age or BC but was lower (P = 0.003) in mares that ovulated follicles smaller than 40 mm compared to mares ovulating follicles greater than 40 mm. BC above 6.5 was associated with higher embryo recovery rate, which was, in turn, correlated positively with DF diameter. Thus, our results support the use of BC scoring to predict performance in equine embryo transfer programs. Body condition scoring was not a good indicator of SF under the current experimental conditions because SF decreased during the breeding season. BC scoring may indicate lean tissue gain, which may be a better indicator of reproductive efficiency in mares.

FAPEMIG, CAPES, Haras El Far.