Electronic boluses with biotelemetry capabilities enable wireless monitoring of animals’ physiological data (e.g., temperature, pH). The aim of this study was to design and experimentally validate a novel multiband (434, 868, and 1400)-MHz conformal patch antenna for in-body biotelemetry applications for cows. The optimal frequency band was studied prior to the design of the antenna, based on the dielectric measurements of the antenna environment (i.e., rumen). The antenna was integrated in a 13.5- -cm bolus and simulated in a -mm spherical phantom with electromagnetic properties of cows’ rumen fluid. The proposed antenna presented a high performance with a realized gain of (−38.5, −41.2, and −45.7) dBi and a radiation efficiency of (0.012%, 0.0045%, and 0.001%) at 434, 868, and 1400 MHz, respectively. Following the numerical analysis and optimization, a prototype was manufactured to experimentally evaluate the antenna performance. Good agreement was obtained between the measurements and simulations both for reflection coefficients and radiation performance. The measured gain was −36.3, −40.4, and −43.6 dBi, at 434, 868, and 1400 MHz, respectively. The proposed multiband antenna will enable the development of a new generation of boluses for animal biotelemetry applications to enhance the performance of the animal monitoring systems.