Influence of growth rate and exposure to bulls on age at puberty in beef heifers

Abstract

Two experiments were conducted to test the following hypotheses: 1) exposure of beef heifers to sterile bulls increases the proportion of heifers attaining puberty by 14 mo of age and 2) rate of growth interacts with bull exposure to influence age at puberty in beef heifers. In Exp. I, heifers were assigned to one of two treatments: 1) heifers were exposed to bulls (BE approximately 7 0 d period of exposure) or 2) heifers were isolated from bulls (NE) and served as controls. In Exp. 11, heifers were assigned to either BE or NE treatments (175-d period of exposure to bulls) and were fed to gain at a moderate (MG, .6 kdd) or high (HG .8 kdd) growth rate. Blood samples were collected twice weekly to determine concentrations of progesterone indicative of onset of corpus luteum function and puberty. In Exp. I a greater (P e .05) propodon of heifers receiving the BE treatment than of heifers receiving the NE treatment initiated corpus luteum function by 14 mo of age. In Exp. 11, there was a bull exposure x growth rate interaction (P e .05). The effect of bull exposure was greater within the HG groups than within the MG groups. However, heifers fed to attain a moderate or high growth rate and exposed to bulls attained puberty at younger ages than heifers not exposed to bulls and fed to attain a moderate or high growth rate. Mean ages at puberty were 375, 422,428, and 449 (pooled SEM = 8.6) d for heifers in the BE-HG, BE-MG, NE-HG, and NE-MG groups, respectively. Therefore, we accept our working hypothesis that exposure of heifers to bulls increased the proportion of heifers attaining puberty by the initiation of breeding at 14 mo of age. Furthermore, growth rate interacts with the stimulatory influence(s) of bulls to influence age at puberty in beef heifers.

Optimising reproductive performance of beef cows and replacement heifers

“…In contrast, bull exposure reduced age at puberty in both years of a 2-year study (Pennel et al,. 1986) and in 3 of 4 years of a multiple year study (Roberson et al, 1991). In the latter study there was some evidence of an interaction between nutritional status and bio-stimulatory challenge with heifers on the higher plane of nutrition responding more strongly to the presence of a bull than heifers on the more moderate plane of nutrition.…”

The onset of puberty in female mice as reflected in urinary steroids and uterine/ovarian mass: interactions of exposure to males, phyto-oestrogen content of diet, and ano-genital distance

“…Exposure to adult males can induce early onset of sexual maturation in juvenile females of several mammals including mice (Vandenbergh 1967), rats (Vandenbergh 1976), lemmings (Hasler & Banks 1975), deer mice (Teague & Bradley 1978), voles (Spears & Clarke 1986), opossums (Harder & Jackson 2003) and cattle (Roberson et al 1991), a phenomenon often called the Vandenbergh effect. Within 24 h of male presence, juvenile females begin to show changes in uterine growth followed by surges in serum luteinizing hormone and follicle-stimulating hormone by the third day (Bronson & Stetson 1973).…”

Exposure of prepubertal beef bulls to cycling females does not enhance sexual development

“…That prepubertal beef heifers exposed to mature bulls or to bull excretory products attain puberty at a younger age than heifers not exposed to bulls or their excretory products is well documented [1,15] and part of the basis for our hypothesis that bulls exposed to cycling females also would have decreased age at puberty. The females used in the present study were managed such that a group of at least three females were displaying estrus each week.…”

“…Although prepubertal beef heifers exposed to mature bulls can achieve puberty at an earlier age than unexposed heifers [1], it is not evident that this phenomenon occurs in developing bulls. Our observed lack of influence of cycling females on developing males is in agreement with previous work in pigs [16].…”

“…Researchers have established that beef females can achieve puberty at earlier ages and reduced duration of postpartum anestrus when exposed to mature bulls [1][2][3] and puberty is hastened in prepubertal gilts when exposed to boars [4].…”