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The effect of rBST on follicle populations of nelore heifers during the dry season in Brazil
Theriogenology
342
THE EFFECT OF rBST ON FOLLICLE POPULATIONS OF NELGRE HEIFERS DURING THE DRY SEASON IN BRAZIL J. A. Carter’, H:N. Paranagua Jr.‘, H. F. N. Paranagu@and R. A. Godke’ Department of Animal Science’, LSU Agricultural Center, Baton Rou e, Louisiana 70803 USA and Fszenda Miridar?, Parnagt& Piaui, Braxis Historically, cattle in the northeast region of Brazil have a low reproductive rate during the winter months (dry season). The dry season normally begins in April-May following the last rain, and may extend through September-October, during which very few or no rains occur, and is characterized by warm temperatures during the day (25-35°C) and cool temperaturesat night (lo-20°C). Consequently,grassesbecome dry and have reduced nutritional content. Recently, the administration of recombinant bovine somatotropin (rBST) has been found to afIkct the ovarian follicle populations in both dairy and beef cattle, with follicle size category a&c&d depending on nutritional status. In this experiment, rBST was administered to cycling and noncycling Nelore heifers to determine its effect on ovarian follicle populations. This study was conducted during the dry season at the Miridan ranch, in Pamagua, Piaui, in northeastern Brazil. The heifers used in this study were maintained on berm&a-grass/native pastures prior to and during the experiment. Nelore heifers (n=24) of similar age (18-24 months), weight (280-330 kg) and body condition (BCS 4-6) were allotted to 1 of 4 groups: (A) rBST-Cycling, (B) No rBSTCycling, (C) rBST-Noncycling and (D) No rBST-Noncycling. Heifers were determined to be cycling if a CL could be detected during the course of the experiment by ultrasonography. Heifers were synchronized using a progestin implant (Syncro-Mate B (SMB), Rhone Merieux, Athens, GA) for 7 days, with 25 mg of PGFza (Lutalyse, Upjohn, Kalamazoo, MI) administered on day 6 following implant insertion. A 500 mg sustained-release form of rBST (Posilac, Monsanto, St. Louis, MO) was administered (s.c.) at SMB implantation, then at IO-day inter-
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Ultrasound Examination
F@ure 1. Number of small ovarian follicles (2-5 mm) in cycling and noncycling Nelore heifers treated with rBST (n=l 1) or saline (no rBST) (n=lO). vals. Controls similarly received an equivalent dose of saline. Ultrasound examinations were performed every 3 days for a period of 27 days beginning on day 1 (1” rBST injection). No differences were detected in the number of large (>lO mm) or medium (6-10 mm) follicles (GLM, SAS). However, there was a significant increase (PcO.05) in the number of small follicles (2-5 mm) per female receiving rBST compared with those not receiving rBST (*SE) (26.5f1.6 vs. 20.2zkl.O).Interestingly, all groups showed a rise in numbers of small follicles by the 2”dand 3ti ultrasound examination. Control heifers then leveled off, while heifers receiving rBST tended to have more follicles throughout the experiment (Figure 1). Cycling heifers also had significantly more small follicles than non-cycling heifers (25.2k1.3 vs. 21.2+1.5). There was no interaction between treatment and cyclicity. These results further support previous findings of increased number of small follicles in cattle following administration of rBST.
342
THE EFFECT OF rBST ON FOLLICLE POPULATIONS OF NELGRE HEIFERS DURING THE DRY SEASON IN BRAZIL J. A. Carter’, H:N. Paranagua Jr.‘, H. F. N. Paranagu@and R. A. Godke’ Department of Animal Science’, LSU Agricultural Center, Baton Rou e, Louisiana 70803 USA and Fszenda Miridar?, Parnagt& Piaui, Braxis Historically, cattle in the northeast region of Brazil have a low reproductive rate during the winter months (dry season). The dry season normally begins in April-May following the last rain, and may extend through September-October, during which very few or no rains occur, and is characterized by warm temperatures during the day (25-35°C) and cool temperaturesat night (lo-20°C). Consequently,grassesbecome dry and have reduced nutritional content. Recently, the administration of recombinant bovine somatotropin (rBST) has been found to afIkct the ovarian follicle populations in both dairy and beef cattle, with follicle size category a&c&d depending on nutritional status. In this experiment, rBST was administered to cycling and noncycling Nelore heifers to determine its effect on ovarian follicle populations. This study was conducted during the dry season at the Miridan ranch, in Pamagua, Piaui, in northeastern Brazil. The heifers used in this study were maintained on berm&a-grass/native pastures prior to and during the experiment. Nelore heifers (n=24) of similar age (18-24 months), weight (280-330 kg) and body condition (BCS 4-6) were allotted to 1 of 4 groups: (A) rBST-Cycling, (B) No rBSTCycling, (C) rBST-Noncycling and (D) No rBST-Noncycling. Heifers were determined to be cycling if a CL could be detected during the course of the experiment by ultrasonography. Heifers were synchronized using a progestin implant (Syncro-Mate B (SMB), Rhone Merieux, Athens, GA) for 7 days, with 25 mg of PGFza (Lutalyse, Upjohn, Kalamazoo, MI) administered on day 6 following implant insertion. A 500 mg sustained-release form of rBST (Posilac, Monsanto, St. Louis, MO) was administered (s.c.) at SMB implantation, then at IO-day inter-
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2
3
4
5
6
7
6
9
Ultrasound Examination
F@ure 1. Number of small ovarian follicles (2-5 mm) in cycling and noncycling Nelore heifers treated with rBST (n=l 1) or saline (no rBST) (n=lO). vals. Controls similarly received an equivalent dose of saline. Ultrasound examinations were performed every 3 days for a period of 27 days beginning on day 1 (1” rBST injection). No differences were detected in the number of large (>lO mm) or medium (6-10 mm) follicles (GLM, SAS). However, there was a significant increase (PcO.05) in the number of small follicles (2-5 mm) per female receiving rBST compared with those not receiving rBST (*SE) (26.5f1.6 vs. 20.2zkl.O).Interestingly, all groups showed a rise in numbers of small follicles by the 2”dand 3ti ultrasound examination. Control heifers then leveled off, while heifers receiving rBST tended to have more follicles throughout the experiment (Figure 1). Cycling heifers also had significantly more small follicles than non-cycling heifers (25.2k1.3 vs. 21.2+1.5). There was no interaction between treatment and cyclicity. These results further support previous findings of increased number of small follicles in cattle following administration of rBST.