Males' sexual preference toward heavier heifers is only observed in competitive situations with lighter heifers

Abstract

The objectives of the present study were to determine if the sexual behavior of androgenized steers (AS) toward heavier or lighter heifers was different in competitive and non-competitive sexual tests. Hereford × Aberdeen Angus heifers (12–24 mo-old, 256.7 ± 4.4 kg) were assigned according to body weight to one of the following groups: 1) High weight heifers (HWH, n = 8), heifers with body weights between 260 and 290 kg (mean = 273.0 ± 2.8 kg), and 2) Low weight heifers (LWH, n = 8), heifers with body weights between 220 and 250 kg (mean = 241.0 ± 2.2 kg). In Trial 1, the behavior of each AS with heifers in competitive situations was determined in tests with one AS, one HWH and one LWH simultaneously, while in Trial 2 AS' behavior with one HWH and one LWH in non-competitive environments was recorded. Variables evaluated in both trials were: time to first approach (s), total time < 1 body length between AS and the female/s (s), time the AS tracked each female, and time each female tracked the AS (s), and number of times that they were < 1 body length, number of times that AS followed females and females followed AS, number of vocalizations, number of nods and number of sniffing. In Trial 1, HWH were more number of times at < 1 body lengths from the AS than LWH (P < 0.05), and tended to be more at < 1 body length from AS (P = 0.1). Both the total time of tracking and number of times that females followed the AS, tended to be greater in HWH than LWH (P = 0.1), and HWH tended to receive more sniffing from the males than LWH (P = 0.1). In Trial 2, no differences were observed in none of the variables evaluated between HWH and LWH. We concluded that AS' preferences for heavier heifers were only observed when they were in competitive environments with lighter heifers. Therefore, factors associated with females' competition and not the body weight of the heifers itself, may be determinants of the greater stimulus received from the males.