The influence of biostimulation on the occurrence of puberty in beef heifers

Two experiments were conducted to determine the influence of biostimulation on the occurrence of puberty in beef heifers.In Experiment I the objective was to determine if prostaglandin F2α (PGF2α ; 25 mg/head) and/or biostimulation and social interaction of prepuberal heifers with a group of estrous heifers (n=49) could induce first estrus in prepuberal heifers.Angus (A), Hereford (H) and AxH heifers (n=372), approximately 13 months of age,-were stratified within breed by weight to the following treatment groups: I) heifers injected with PGF2α and isolated from estrous heifers (n=91); 2) heifers injected with PGF2α and placed with estrous heifers (n=97); 3) heifers injected with .9%saline and isolated (n=95); and 4) heifers injected with .9%saline and placed with estrous heifers (n=8 9).Isolation groups were placed .5 km away from groups containing estrous females.Heifers were observed for behavioral estrus twice daily fbr 21 days after initiation of treatments.Percentages of heifers exhibiting first estrus within the 21-day observation period were: 26 and 26% for PGF2α and saline-treated groups, respectively (P > .05),and 23 and 28% for biostimulation with estrous heifers and isolation groups, respectively (P > .05).There was no interaction among treatments (P > .05).In Experiment II, the objective was to determine if biostimulation and social interaction with mature bulls would alter the occurrence, age and weight at puberty in beef heifers.Angus (A), Hereford (H), Simmental (S)xA, SxH, Tarentaise (T)xA and TxH heifers (n=109) were stratified within breed by age, weight and origin of heifer and randomly allotted into the following treatments: 1) heifers exposed to the presence of mature bulls (n=54); and 2) heifers isolated from the presence of mature bulls (n=55).Biostimulation group male to female ratio was 1:27.Biostimulation heifers were separated from isolation heifers by .5 km.Heifers were observed for behavioral estrus twice daily for a 152 day observation period.Puberty was defined by three criterion: I) behavioral estrus; 2) presence of a palpable corpus luteum (CL); and 3) rise in serum progesterone above 1 ng/ml.There were no differences (P > .10) between treatments for the proportion of heifers reaching puberty by 11, 12, 13, 14, and 15 months of age.The percentages of heifers reaching puberty were 84.0 and 88.9% for the biostimuIation and isolation groups, respectively (P > .10).Age and weight at puberty were 366.7 days and 291.9 kg and 367.1 days and 293.6 kg for the biostimulation and isolation groups, respectively (P > .10).The results from Experiment I indicate that neither PGF2α nor biostimulation of prepuberal heifers, with a group of estrous heifers, induced first estrus in prepuberal beef heifers.The results from Experiment II indicate that biostimulation from mature bulls did not alter the occurrence of puberty or the age or weight at puberty in prepuberal beef heifers.