Effects of oestradiol, zeranol or trenbolone acetate implants on puberty, reproduction and fertility in heifers

Abstract

Summary. The effects of anabolic agents on reproduction in beef heifers were determined by using 300 mg trenbolone acetate (TBA), 36 = 43\m=.\8and 39\m=.\4for age and weight respectively]. Heifers in Group 4 were older (P < 0\m=.\05), but not heavier (P > 0\m=.\05), while those in Groups 2 and 5 were both older (P < 0\m=.\005) and heavier (P < 0\m=.\005) than the controls at puberty. Age and weight at puberty were not different in heifers assigned to Groups 3 and 4, or to Groups 2 and 6. The proportion of heifers showing oestrus before puberty (prepubertal oestrus) were 3/15, 12/15, 6/12, 7/15, 10/13 and 11/11 in Groups 1\p=n-\6 respectively. Heifers in Groups 2 and 5 had higher incidences of prepubertal oestrus than controls, while those in other treatment groups were not different. There was no treatment effect on the incidence of silent ovulations, but the incidence of non\x=req-\ ovulatory oestrus, after puberty, was increased from 4/48 in Group 1 to 26/40 (P < 0\m=.\001),15/56 (P < 0\m=.\05) and 34/57 (P < 0\m=.\001) in Groups 2, 4 and 5, respectively. Heifers in Group 6 had a higher incidence of non-ovulatory oestrus (P < 0\m=.\05), but not of prepubertal oestrus, than did those in Group 2. The uteri of heifers in Groups 2 and 5 were lighter (P < 0\m=.\05) than those of controls, while the uteri and ovaries of Group 6 heifers were lighter (P < 0\m=.\05) than those of Group 2 heifers. Heifers in Group 3 had lighter ovaries than heifers in Group 4 (P < 0\m=.\05). It is concluded that anabolic agents delayed puberty, increased the incidence of non-ovulatory oestrus and retarded reproductive tract development when given to beef heifers from 84 days of age onwards.

Influence of anabolic combinations of an androgen plus an estrogen on biochemical pathways in bovine uterine endometrium and ovary

“…The observed down-regulation of LHR in the ovary of heifers and the following lower responsiveness of this organ towards LH may be responsible for the down-regulation of the VEGF isoforms and their receptor Flt-1. The resulting inhibition of follicular maturation could partly be responsible for known reproductive perturbations like the delayed onset of puberty shown in pre-pubertal animals or the predisposition for non-ovulatory estrus observed in mature cows under the influence of steroidal growth promoters [38]. The changes in gene expression observed in the actual study could also be accounted to mimic the state of regression of the corpus luteum (CL) characterized by a down-regulation of VEGF and an up-regulation of FGF-2 and ANGPT-2 [39].…”

Evaluation of steroidogenic capacity after follicle stimulating hormone stimulation in bovine granulosa cells of Revalor 200® implanted heifers

“…This concept is supported by the demonstrated increase in plasma GH concentrations in response to E 2 [18] or TBA and E 2 [19] implants. High levels of anabolic hormones can also modulate reproduction as demonstrated by TBA induced anestrus in cows [8,20] and delayed puberty and decreased fertility in TBA plus E 2 implanted heifers compared to non-implanted controls [6,21]. …”

“…Additionally, elevated levels of E 2 in culture medium improves growth of oocytes from early antral follicles [27] supporting an important role of E 2 in folliculogenesis. However, elevated exogenous concentration of E 2 can increase the chance of developing cystic follicles and decreases fertility in heifers [6]. …”

“…Consequently, implanting developing heifers has marked impacts on reproductive function. Heifers receiving a TBA and E 2 implant at 84 d of age had delayed puberty and retardation in reproductive tract development [6]. Ewes prenatally treated with testosterone during mid-gestation did not display a delay in onset of puberty but demonstrated absent or disrupted progestogenic cycles, and had larger follicles with prolonged presence [7].…”

Effect of immunization of ewes against prostaglandin F-2 on the life-span of corpora lutea and oestrous behaviour during two breeding seasons

“…The ovaries of all ewes were examined by endoscopy (Boyd & Ducker, 1973) Progesterone. Concentrations were measured by a modification of the extraction radioimmunoassay (RIA) method of Niswender (1973), as described by Moran et al (1990). With an antiserum (Dieleman & Schoenmakers, 1979) dilution of 1:160 000, the sensitivity of the assay was 0-1 ng/ml plasma.…”