PHYSIOLOGY AND MANAGEMENT Effects of Gonadotropin-Releasing Hormone and Human Chorionic Gonadotropin on Pregnancy Rate in Dairy Cattle G. S. LEWIS,' D. W. CALDWEll, and C. E. REXROAD, JR. Reproduction Laboratory US Department of Agriculture Agricultural Research Service Beltsville, MD 20705
H. H. DOWLEN and J. R. OWEN Dairy Experiment Station US Department of Agriculture Agricultural Research Service and Agricultural Experiment Station The University of Tennessee Lewisburg 37091 ABSTRACT
chorionic gonadotropin on d 15 increased them. This study does not support the general use of gonadotropin-releasing honnone at AI or human chorionic gonadotropin 15 d after AI as methods for enhancing pregnancy rates of dairy cattle. (Key words: pregnancy rate, gonadotropin-releasing hormone, human chorionic gonadotropin)
This study was to detennine if gonadotropin-releasing hormone, human chorionic gonadotropin. or their interaction would affect pregnancy rate or milk progesterone profiles in dairy cattle. Cows and heifers eligible for first, second, and third services were assigned to four treatments: 1) saline Lm. within 5 min after AI (d 0) and saline 15 d after Al (n =222 AI); 2) gonadotropin-releasing hormone (100 JLg) i.m. within 5 min after AI and saline on d 15 (n 223); 3) saline after AI and human chorionic gonadotropin (3500 IU) Lm. on d 15 (n 196); 4) gonadotropin-releasing honnone at AI and human chorionic gonadotropin on d 15 (n = 195). Progesterone was quantified in milk samples collected twice weekly for 5 wk from all cows. Neither gonadotropin-releasing hormone, human chorionic gonadotropin, gonadotropin-releasing hormone x human chorionic gonadotropin interaction, age, nor service number affected pregnancy rate, which averaged 46.2%. Pregnancy and human chorionic gonadotropin affected milk progesterone profiles. Pregnancy maintained progesterone concentrations and human
INTRODUCTION
Various hormonal treatments have been used in attempts to improve pregnancy rates in cattle. Recent interest has focused on gonadotrop!n-releasing honnone (GnRH) or GnRH agomsts and human chorionic gonadotropin (heG), but results of experiments to test the effects of these honnones on pregnancy rates are inconsistent. When cows and heifers were treated with GnRH at first or later AI and at times ranging from 6 h before to 6 d after AI, the differences in pregnancy rates in treated and control cattle ranged from -10 to +25 percentage points (I, 3, 6, 10, 13, 15, 17, 18, 19,20, 23, 25, 28). Over all studies, first service pregnancy rates in GnRH-treated cattle generally were about 5 percentage points greater than those in control cattle, but .wi~in studies, this difference usually was not slgmficant. Human chorionic gonado?"~pi~ has. been given in single or multiple inJectIons, In doses ranging from 200 to 10,000 IV and at times ranging from 0 h to 35 dafter AI or mating (4, 8, 9, 16, 26, 27, 28). Differences in pregnancy rates between hCG- treated
=
=
Received July 21,1988. Accepted July 13, 1989. IRepnnt . requests. Present address: Department of Animal Science, Virginia Polytechnic Institute and Slate University, Blacksburg 24061.
1990 J Dairy Sci 73:66-72
66
PREGNANCY RATES AFrER HORMONAL TREATMENTS
and control cattle ranged from -18 to +13 percentage points. Differences in experimental designs and physiological conditions of cattle among studies with GnRH and hCG were great, and those differences may explain some of the variation in effects of GnRH and hCG on pregnancy rates. Two factors that may account for variation among studies with GnRH or hCG were numbers of cattle per treatment group, which ranged from 20 to about 700, and whether the studies were blind, Le., whether participants knew what they were injecting or to which treatment groups cattle were assigned. Blind studies prevent participants from unintentionally biasing results for or against a treatment. Six of the studies reviewed were truly blind. Even though there are numerous studies on the effects of either GnRH or hCG on pregnancy rates, studies to determine if GnRH and hCG interact to affect pregnancy rate have not been reported. Therefore, the purpose of our study was to determine if GnRH at AI, hCG 15 d after AI, or the interaction of GnRH and hCGwould affect 1) pregnancy rate and 2) changes in milk progesterone profiles in dairy cattle. MATERIALS AND METHODS
Cows and heifers eligible for first, second, and third services in USDA herds at Beltsville, MD (Holsteins) and Lewisburg, TN (Jerseys) were used. When cows at least 45 d postpartum and heifers with no recent histories of reproductive disorders were seen in standing estrus, they were assigned to the study. Treatment groups were: 1) saline (.9% NaCI solution) within 5 min after AI (d 0) and saline 15 d after AI; 2) GnRH (100 J.l.g; Cystorelin®, CEVA Laboratories, Overland Park, KS) within 5 min after AI and saline on d 15; 3) saline after AI and hCG (3500 IV; LyphoMed, Inc., Melrose Park, IL) on d 15; 4) GnRH at AI and hCG on d 15. Hormones and saline were injected Lm. Cattle were inseminated about 12 h after they were first seen in estrus. Approximately 60 d after AI, uteri were palpated per rectum for pregnancy. Herd managers were responsible for twice daily estrous detection, AI, injections, and keeping appropriate records. On each Tuesday and Friday for 5 wk after AI, composite milk samples were collected from all cows. Samples were stored at -20'C until progesterone was quantified.
67
Precautions were taken to prevent herd managers from knowing the treatments to which cattle were assigned. Treatments were randomized in blocks; each treatment was replicated once per block. Randomized treatments were coded with consecutive numbers (1 to 960), and only the first author had a key to the codes. Separate lists of coded randomized treatments were used for each herd. Hormones were diluted to equal volumes and desired concentrations with sterile saline. Injectables were packaged in glass serum vials, arranged according to randomized treatments, assigned serial numbers, stored at -20'C until used, and injected as 3.5 ml of clear liquid. Except for different serial numbers, all vials and their labels were identical. When a cow or heifer was allocated to the study, she was assigned the next available consecutive number and treated with the contents of the appropriate vial at AI and on d 15. A radioimmunoassay was developed and used to quantify progesterone in unextracted milk samples. Sheep antiprogesterone serum (G. D. Niswender #337) was used in the assay. The antiserum crossreacted 100% with progesterone and 11a-hydroxyprogesterone, 4% with corticosterone, 1.5% with pregnenolone, and
H. H. DOWLEN and J. R. OWEN Dairy Experiment Station US Department of Agriculture Agricultural Research Service and Agricultural Experiment Station The University of Tennessee Lewisburg 37091 ABSTRACT
chorionic gonadotropin on d 15 increased them. This study does not support the general use of gonadotropin-releasing honnone at AI or human chorionic gonadotropin 15 d after AI as methods for enhancing pregnancy rates of dairy cattle. (Key words: pregnancy rate, gonadotropin-releasing hormone, human chorionic gonadotropin)
This study was to detennine if gonadotropin-releasing hormone, human chorionic gonadotropin. or their interaction would affect pregnancy rate or milk progesterone profiles in dairy cattle. Cows and heifers eligible for first, second, and third services were assigned to four treatments: 1) saline Lm. within 5 min after AI (d 0) and saline 15 d after Al (n =222 AI); 2) gonadotropin-releasing hormone (100 JLg) i.m. within 5 min after AI and saline on d 15 (n 223); 3) saline after AI and human chorionic gonadotropin (3500 IU) Lm. on d 15 (n 196); 4) gonadotropin-releasing honnone at AI and human chorionic gonadotropin on d 15 (n = 195). Progesterone was quantified in milk samples collected twice weekly for 5 wk from all cows. Neither gonadotropin-releasing hormone, human chorionic gonadotropin, gonadotropin-releasing hormone x human chorionic gonadotropin interaction, age, nor service number affected pregnancy rate, which averaged 46.2%. Pregnancy and human chorionic gonadotropin affected milk progesterone profiles. Pregnancy maintained progesterone concentrations and human
INTRODUCTION
Various hormonal treatments have been used in attempts to improve pregnancy rates in cattle. Recent interest has focused on gonadotrop!n-releasing honnone (GnRH) or GnRH agomsts and human chorionic gonadotropin (heG), but results of experiments to test the effects of these honnones on pregnancy rates are inconsistent. When cows and heifers were treated with GnRH at first or later AI and at times ranging from 6 h before to 6 d after AI, the differences in pregnancy rates in treated and control cattle ranged from -10 to +25 percentage points (I, 3, 6, 10, 13, 15, 17, 18, 19,20, 23, 25, 28). Over all studies, first service pregnancy rates in GnRH-treated cattle generally were about 5 percentage points greater than those in control cattle, but .wi~in studies, this difference usually was not slgmficant. Human chorionic gonado?"~pi~ has. been given in single or multiple inJectIons, In doses ranging from 200 to 10,000 IV and at times ranging from 0 h to 35 dafter AI or mating (4, 8, 9, 16, 26, 27, 28). Differences in pregnancy rates between hCG- treated
=
=
Received July 21,1988. Accepted July 13, 1989. IRepnnt . requests. Present address: Department of Animal Science, Virginia Polytechnic Institute and Slate University, Blacksburg 24061.
1990 J Dairy Sci 73:66-72
66
PREGNANCY RATES AFrER HORMONAL TREATMENTS
and control cattle ranged from -18 to +13 percentage points. Differences in experimental designs and physiological conditions of cattle among studies with GnRH and hCG were great, and those differences may explain some of the variation in effects of GnRH and hCG on pregnancy rates. Two factors that may account for variation among studies with GnRH or hCG were numbers of cattle per treatment group, which ranged from 20 to about 700, and whether the studies were blind, Le., whether participants knew what they were injecting or to which treatment groups cattle were assigned. Blind studies prevent participants from unintentionally biasing results for or against a treatment. Six of the studies reviewed were truly blind. Even though there are numerous studies on the effects of either GnRH or hCG on pregnancy rates, studies to determine if GnRH and hCG interact to affect pregnancy rate have not been reported. Therefore, the purpose of our study was to determine if GnRH at AI, hCG 15 d after AI, or the interaction of GnRH and hCGwould affect 1) pregnancy rate and 2) changes in milk progesterone profiles in dairy cattle. MATERIALS AND METHODS
Cows and heifers eligible for first, second, and third services in USDA herds at Beltsville, MD (Holsteins) and Lewisburg, TN (Jerseys) were used. When cows at least 45 d postpartum and heifers with no recent histories of reproductive disorders were seen in standing estrus, they were assigned to the study. Treatment groups were: 1) saline (.9% NaCI solution) within 5 min after AI (d 0) and saline 15 d after AI; 2) GnRH (100 J.l.g; Cystorelin®, CEVA Laboratories, Overland Park, KS) within 5 min after AI and saline on d 15; 3) saline after AI and hCG (3500 IV; LyphoMed, Inc., Melrose Park, IL) on d 15; 4) GnRH at AI and hCG on d 15. Hormones and saline were injected Lm. Cattle were inseminated about 12 h after they were first seen in estrus. Approximately 60 d after AI, uteri were palpated per rectum for pregnancy. Herd managers were responsible for twice daily estrous detection, AI, injections, and keeping appropriate records. On each Tuesday and Friday for 5 wk after AI, composite milk samples were collected from all cows. Samples were stored at -20'C until progesterone was quantified.
67
Precautions were taken to prevent herd managers from knowing the treatments to which cattle were assigned. Treatments were randomized in blocks; each treatment was replicated once per block. Randomized treatments were coded with consecutive numbers (1 to 960), and only the first author had a key to the codes. Separate lists of coded randomized treatments were used for each herd. Hormones were diluted to equal volumes and desired concentrations with sterile saline. Injectables were packaged in glass serum vials, arranged according to randomized treatments, assigned serial numbers, stored at -20'C until used, and injected as 3.5 ml of clear liquid. Except for different serial numbers, all vials and their labels were identical. When a cow or heifer was allocated to the study, she was assigned the next available consecutive number and treated with the contents of the appropriate vial at AI and on d 15. A radioimmunoassay was developed and used to quantify progesterone in unextracted milk samples. Sheep antiprogesterone serum (G. D. Niswender #337) was used in the assay. The antiserum crossreacted 100% with progesterone and 11a-hydroxyprogesterone, 4% with corticosterone, 1.5% with pregnenolone, and
