Predictive efficiency of infrared thermography for pregnancy in 14-month-old heifers under FTAI

Abstract

This study aimed to evaluate the association between physiological variables and surface heat emission, as assessed by infrared thermography, and pregnancy rate in Nelore heifers subjected to fixed-time artificial insemination (FTAI) at 14 months of age. The study was conducted at Fazenda Água Fria, Xinguara, Pará, Brazil.  A total of 50 purebred Nelore heifers (mean body weight: 347.46 ± 38.33 kg; mean age: 14.02 ± 0.25 months) were included in the study. Heifers received a progesterone device and 2 mg estradiol benzoate (i.m.) on Day 0; on Day 8, the device was removed and 0.15 mg PGF2α, 300 IU eCG, and 1 mg estradiol cypionate (i.m.) were administered. FTAI was performed 48–56 h later. At the time of insemination, rectal temperature (RT), vaginal temperature (VT), and surface heat emission (infrared thermography) from the face, eye, and muzzle regions were recorded. Pregnancy diagnosis was performed 28 days post-FTAI. Data were analyzed using PROC LOGISTIC (SAS 9.2). Logistic regression analysis identified physiological and thermographic variables significantly associated with pregnancy outcomes. BW had a positive effect on pregnancy probability (P = 0.0039), with each 1 kg increase resulting in a 1.2% increase in the chance of conception. VT showed a negative association (P=0.0045), where each 1°C increase decreased the pregnancy probability by 94.5%. Regarding thermographic measurements, each 1°C increase in facial temperature was associated with a 17.4% reduction in pregnancy chance (P=0.0073), while a 1°C increase in muzzle temperature reduced the likelihood of conception by 5.7% (P=0.0011). These findings indicate that heifers with higher body weight, lower vaginal temperature, and lower surface heat emission in specific head regions at the time of FTAI have a greater chance of pregnancy. Infrared thermography, combined with physiological assessments, appears to be a promising tool for early reproductive screening in beef heifers.