A study using 143 replacement beef heifers was conducted over a 3-year period to determine the effects that progesterone or progesterone and gonadotropin releasing hormone (GnRH) would have on age at puberty in beef heifers. Progesterone treated heifers were 21.8 and 38.9 days younger (P\u3c.05) at puberty than control heifers in the first 2 years of the study, while progesterone plus GnRH treated heifers were 35.4 days (P\u3c.01) and 31.2 days (P\u3c.05) younger than controls. No difference (P\u3e.05) in age at puberty was detected between groups in the third year. While progesterone and progesterone plus GnRH treated heifers had a higher conception rate (P\u3c.01) to Al than controls in the first year of the study, calving records showed they experienced a higher rate of embryonic loss. However, calving rate still remained higher than in the control group. These differences were not observed in the second year and calving data for the final year of the study is currently not available

Larson, C. L.

Long, M. B.

Marshall, D. M.

Miller, H. L.

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South Dakota State UniversityOpen PRAIRIE: Open Public Research Access InstitutionalRepository and Information ExchangeSouth Dakota Beef Report, 1993 Animal Science Reports1993Effects of Administering Progesterone orProgesterone and GnRH on Age at Pubery inCrossbred Beef HeifersC. L. LarsonSouth Dakota State UniversityH. L. MillerSouth Dakota State UniversityD. M. MarshallSouth Dakota State UniversityM. B. LongSouth Dakota State UniversityFollow this and additional works at: http://openprairie.sdstate.edu/sd_beefreport_1993Part of the Animal Sciences CommonsThis Report is brought to you for free and open access by the Animal Science Reports at Open PRAIRIE: Open Public Research Access InstitutionalRepository and Information Exchange. It has been accepted for inclusion in South Dakota Beef Report, 1993 by an authorized administrator of OpenPRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. For more information, please contactmichael.biondo@sdstate.edu.Recommended CitationLarson, C. L.; Miller, H. L.; Marshall, D. M.; and Long, M. B., "Effects of Administering Progesterone or Progesterone and GnRH onAge at Pubery in Crossbred Beef Heifers" (1993). South Dakota Beef Report, 1993. Paper 11.http://openprairie.sdstate.edu/sd_beefreport_1993/11EFFECTS OF ADMINISTERING PROGESTERONE OR PROGESTERONE AND GnRH ON AGE AT PUBERTY IN CROSSBRED BEEF HEIFERS C. L   arson', H. L. ~ i l le? ,  D. M. ~ a r s h a l l ~ ,  and M. B.   on^^ Department of Animal and Range Sciences Summary A study using 143 replacement beef heifers was conducted over a 3-year period to determine the effects that progesterone or progesterone and gonadotropin releasing hormone (GnRH) would have on age at puberty in beef heifers. Progesterone treated heifers were 21.8 and 38.9 days younger (Pc.05) at puberty than control heifers in the first 2 years of the study, while progesterone plus GnRH treated heifers were 35.4 days (P<.01) and 31.2 days (Pc.05) younger than controls. No difference (P>.05) in age at puberty was detected between groups in the third year. While progesterone and progesterone plus GnRH treated heifers had a higher conception rate (P<.01) to Al than controls in the first year of the study, calving records showed they experienced a higher rate of embryonic loss. However, calving rate still remained higher than in the control group. These differences were not observed in the second year and calving data for the final year of the study is currently not available. Key Words: Beef Heifers, Puberty, Progesterone, GnRH, Fertility season. Under typical production conditions, some replacement heifers will not reach puberty until after the onset of the breeding season, and a larger proportion will be in their first estrous cycle at first service. This situation is undesirable since improved conception rates have been realized when heifers are bred on their third or fourth estrus in comparison to the first. Therefore, methods which cause puberty to occur in heifers at an earlier age may be useful and economically advantageous to the producer, since induction of an earlier puberty will in turn cause more heifers to be cycling before the beginning of the breeding season. Several previous studies which have utilized hormone administration to prepuberal heifers to induce puberty at an earlier age have met with varying levels of success. The following study was conducted to determine the effects that administration of progesterone, alone or in combination with gonadotropin releasing hormone (GnRH), would have on age at puberty and the subsequent breeding success in crossbred beef heifers. Materials _and Methods Introduction The study was conducted over a 3-year period on the campus of South Dakota State Replacement beef heifers must calve early University. One hundred forty-three crossbred in the calving season at 2 years of age to beef heifers raised at the Antelope Range achieve maximum lifetime calf productivity. This Livestock Station in northwestern South Dakota implies that yearling heifers must be bred were randomly assigned to one of three successfully in the early portion of the breeding treatments in late winter following weaning. '~raduate Assistant. 2~ssociate Professor 3~ hemist. Table 1 lists the number of days before the breeding season when treatments were applied and the average age and weight of the heifers at time of treatment according to year. Heifers assigned to treatment 1 were designated as controls and did not receive any hormone treatment. Heifers assi ned to treatment 2 were 9 given a Synchromate-B norgestomet implant for 9 days. Heifers assigned to treatment 3 in the first 2 years of the study also received a norgestomet implant for 9 days. U on removal J: of the norgestomet implant, a GnRH implant was given for the following 9 days. In the last year of the study, heifers in treatment 3 were given a 2 mL injection containing 1000 p g  GnRH subcutaneously following the norgestomet implant removal. Table 1. Age and weight of heifers at time of hormone treatment Days before breeding Age, Year season days Wt, Ib Blood samples were collected from all heifers via jugular venipuncture on a weekly basis beginning on the day of progesterone implantation. Upon centrifugation, blood sera was collected and progesterone concentration from each sample was determined with a one-step radioimmunoassay procedure. Samples containing a progesterone concentration exceeding 1 ng/mL were indicative of a functional corpus luteum at the time of collection. When a weekly sampling procedure is used, the exact sequence of high and low progesterone levels will vary from heifer to heifer since the normal luteal phase in the bovine lasts from 10 to 14 days. A heifer was considered to be cycling when her blood serum progesterone levels were over 1 ng/mL for 1 to 2 bleedings, followed by a decrease during the next 1 to 2 bleedings, which was succeeded by a similar fluctuation in progesterone over the next 3 to 4 weeks. Date of puberty was estimated to be 5 days before the first elevated progesterone concentration appeared. All heifers were weighed on a periodical basis and weight at puberty was calculated for each heifer through extrapolation of the two weighings most closely associated with the date of puberty. In early May a 45-day breeding season was begun for each year. A 21-day artificial insemination period was followed by placement of a cleanup bull with the heifers until termination of the breeding season. Blood samples were collected -weekly for four weeks from those heifers detected in estrus to monitor progesterone concentrations. Heifers displaying elevated levels of progesterone for 3 or more consecutive bleedings were considered to be pregnant. Pregnancy rates to the overall breeding season were determined via rectal palpation 60 days after the end of the breeding season. Pregnancy to Al was also determined through examination of the subsequent calving dates in the first two years of the study. Neither palpation or calving data for the 1992 born replacement heifers was available at the time of publication. Conception data derived from the progesterone assays were compared with the calving data in the first 2 years of the study to determine early embryonic loss. Ten heifers had progesterone concentrations over 1 ng/mL on the first bleeding and were removed from the study. One heifer included in the 1993 study group never cycled and was also removed. The remaining 132 heifers cycled at least once during the period in which they were under study and were included in the analysis. Statistical analyses of age and weight at puberty 4~ano f i  Animal Health, Inc., Overland Park, KS. 5 ~ .  J  Kesler, University of Illinois. by treatment were performed using the GLM procedures of SAS. Chi-square analysis was performed for the pregnancy data. Results and Discussion --Age and weight at puberty for each treatment group within year is reported in Table 2. Progesterone treated heifers were 21.8 days and 38.9 days younger (P<.05) at puberty than control heifers in 1991 and 1992, respectively, although there was no difference in age in 1993. Progesterone plus GnRH treated heifers were 35.4 days younger in 1991 (P<.01) and 31.2 days younger in 1992 (P<.05) than control heifers. Age at puberty for these two groups in 1993 was not different. The lack of difference between treatment groups for age at puberty in 1993 may be partially attributed to the small number of heifers used in that year (n = 28). There was no significant weight difference at puberty between progesterone treated and control heifers in 1991 and 1993. Progesterone treated heifers weighed 71.1 Ib less at puberty than nontreated heifers in 1992 (P<.05). Progesterone plus GnRH treated heifers weighed 49.8 Ib less at puberty than control heifers in 1991 (P< .05), but no differences were observed in 1992 and 1993. Since hormone treated heifers weighed less at puberty than controls, this suggests that the hormones used in the treatments accelerated physiological changes associated with puberty rather than causing puberty to occur because of increased body weights. Table 2. Effects of progesterone and progesterone plus GnRH on age arld weight at puberty Treatment Progesterone Control Progesterone plus GnRH 1991 Number of heifers 20 22 23 Age at puberty, daysa 372.1 (6.8)' 350.3 (6.51~ 336.7 (6.41~ Wt at puberty, lba 703.8 (16.5)~ 661.4 (1 5.7) bC 654.0 (1 5.4)' Number of heifers 13 13 13 Age at puberty, days 351.9 (1 0.3)' 313.0 (10.3)~ 320.7 (1 0.3) Wt at puberty, Ib 71 1.5 (20.0)' 640.4 (20.0) 665.2 (20.0)~' Number of heifers 9 9 10 Age at puberty, days 360.7 (12.2) 352.9 (12.2) 352.0 (11.5) Wt at puberty, Ib 701.6 (26.9) 685.1 (26.9) 697.1 (25.5) a~east  squares means followed by standard errors. b lc~eans within a row lacking a common superscript letter differ (P<.05). Table 3 lists the pregnancy rate to Al (according to progesterone concentrations), pregnancy to the overall breeding season, calving rate to Al, and overall calving rate. Pregnancy to Al according to progesterone differed among treatment groups in 1991 at the .O1 level, although calving rate to Al for these heifers differed among treatment groups at the .05 level. No other differences in any year were detected. Although hormone treated heifers in 1991 had higher pregnancy rates to Al than controls, the reduced difference between groups at calving suggests that hormone treated heifers also had a higher rate of embryonic loss. This trend was not apparent in 1992. The results of this study suggest that administration of progesterone or progesterone and GnRH to prepuberal heifers will cause puberty to occur at an earlier age. While heifers given progesterone plus GnRH were younger at puberty than their contemporary controls in 1991 and 1992, no such difference was noted in 1993. This may be explained by the mechanism of GnRH administration. In the first 2 years of the study a GnRH implant was given, whereas the heifers in 1993 received a GnRH injection. It is possible that the injection did not provide as prolonged a release as the implant, although it is difficult to determine if the progesterone plus GnRH treatment was ineffective for this reason. Since heifers treated with progesterone only did not reach puberty at an earlier age in that year either, the small number of heifers used in that year made it difficult to statistically determine any differences between treatments. While administering the hormone treatments immediately before the breeding season may not show a difference in age at puberty between treated heifers and controls, several reports have cited heifers must be of sufficient age and size to be able to respond to the hormone therapy as well. Our results suggest that administration of progesterone or progesterone plus GnRH are both effective in induction of puberty when given to heifers 97 to 120 days before the breeding season. Table 3. Pregnancy and calving rates to Al and overall breeding season No. Pregnancy Pregnancy Calving Calving Yearltreatment heifers to A I ~  to seasona to Ala to seasona 1991 Control Progesterone Progesterone plus GnRH Control Progesterone Progesterone plus GnRH 1993 Control Progesterone Progesterone plus GnRH a~ctua l  values followed by percentage. b 9 c ~ e a n s  within a column within year lacking a common superscript letter differ (P<.01). d s e ~ e a n s  within a column within year lacking a common superscript letter differ (P<.05). f ~ a t a  not available at this time. 

Effects of Administering Progesterone or Progesterone and GnRH on Age at Pubery in Crossbred Beef Heifers

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Effects of Administering Progesterone or Progesterone and GnRH on Age at Pubery in Crossbred Beef Heifers

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