Ultrasonographic evaluation of reproductive tract measures and fat thickness traits in pre-pubertal Nellore heifers

Abstract

The aim of this study was to evaluate the relationship between reproductive tract and fat thickness measures obtained by ultrasound in prepubertal Nellore heifers. A total of 128 Nellore heifers born in 2006 and 2007 were submitted to ultrasound evaluations (13, 16, 19 and 22 months of age) of reproductive tract measures and fat thickness traits. These animals were from a selection experiment (NeC: control line, and NeS: selection line) for yearling weight started in 1981. Mean values of ovary area, height of the right uterine horn (HU), maximum follicular diameter (FOL), backfat thickness (BF), rump fat thickness (RF), and body condition score were analyzed. Repeated records were modeled using the PROC MIXED procedure (SAS), fitting a model that included the selection line, year of birth, measurement as fixed effects, and interactions. Body weight differed between the selected (281.48 kg) and control (210.51 kg) lines. Only the least square means of FOL were lower in the NeC line compared to the NeS line (P < 0.05), although the difference in mean HU between the two lines was of only borderline significance (P = 0.06). The rate of growth for the three reproductive traits was similar in the two lines. Simple and residual correlations between the reproductive and subcutaneous fat traits ranged from low to medium. The highest correlations were observed between HU and RF (Pearson correlation = 0.71 and residual correlation = 0.34). The current results are consistent with the literature, indicating that fat thickness traits are not good predictors of prepubertal reproductive traits in heifers. Further studies are necessary to clarify the relationship between reproduction and body fat in Nellore heifers.

Keywords

• espessura de gordura
• Bos indicus
• correlação
• corno uterino
• ultrassom