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Estrous response of early postpartum beef heifers to progesterone and estradiol-17β during restricted dietary energy
THERIOGENOLOGY ESTRWS RESPONSE OF EARLY POSTPARTUM BEEF HEIFERS TO PROGESTERONE AND ESTRAOIOL-178 DURING RESTRICTED DIETARY ENERGYa$b G. L. Williamsc, J. G. Butler and 0. E. Ray Department of Animal Sciences The University
of Arizona,
Tucson
85721
Received for Publication: 12/12/79 SUMMARY A study was conducted to determine reproductive response of primiparous beef heifers to an ovulation induction regimen during Thirty-seven Barzona x Hereford restricted dietary energy intake. heifers, maintained under drylot conditions, were utilized. Heifers were restricted in TDN on a pen basis to approximately 50% of N.R.C. recommendations for the first 90 days postpartum, then received 120% All animals received control injections (C) for 8D days thereafter. or 30 mg progesterone on day 15 postpartum followed in 48 hours by 2 mg estradiol-176 (PE). Treated heifers not ovulating at first treatment and/or not cycling, were re-treated at 60 day postpartum, with Intact fertile non-cycling C heifers receiving control injections. bulls were maintained with the heifers from day 1 to 170 days postpartum, with visual observations for signs of estrus and breeding activity conducted twice daily during this period. At first treatment, seven of 18 heifers ovulated, one conceived and four continued to cycle. At second treatment, three of 13 conceived and seven returned to a Although intervals to first synchronized estrus 15 to 21 days later. estrous behavior and estrus favored PE heifers (PC .05), by 90 and 170 days postpartum no advantage in interval to conception or number conceiving was observed. INTRODUCTION Under range conditions suboptimal energy intake during the postpartum period is generally one of the most important factors that limits rebreeding efficiency (1). This is especially true in the primiparous heifer (2,3), whose energy requirements for maintenance, lactation and reproduction are superimposed on those for growth. Alternate management procedures such as early weaning (4,5) or supplementation (6,7) can often be useful from a reproductive standpoint, but may be economically unsound except during extreme drought. Work with exogenous hormone treatments has shown that SYNCRO-MATE-B (G.D. Searle Co.), alone or in combination with 48 hour calf removal or early weaning, may be an effective and practical means of estrus induction in anestrous postpartum cows (8). However, as body condition aArizona
Agricultural
bContribution and Sheep.
Experiment
to W-112,
'Present address: Fargo 58105.
Improving
Department
Reproductive
for technical
Paper No. 3082
Performance
of Animal Science,
We wish to thank Mr. Bud Keister
JULY 1980 VOL. 14 NO. 1
Station Technical
of Cattle
North Dakota
State Univ.,
assistance.
13
THERIOGENOLOGY at treatment decreased, the response to treatment also declined. The endocrinology of another approach to postpartum estrous cycle control has recently been evaluated (9). The objective was to stimulate ovarian activity via prolactin suooression and/or seauential steroid treatment very early in'the postpartum period to-avert 'the establishment of a prolonged lactational anestrum. Prolactin suppression had no apparent effect. However, in adequately fed heifers a single injection of progesterone on day 15 postpartum followed by estradiol-176 (PE) 48 hours later, induced endocrine changes which resulted in issnediate ovulation and establishment of cyclic activity in a majority of treated heifers. The purpose of the following experiment was to test the ability of PE to induce ovulation and estrous activity in drylot heifers during a prolonged dietary energy restriction. MATERIALS AND METHODS Two-year-old Barzona x Hereford heifers, calving for the first time in drylot during September, October and November, were used for this experiment. Prior to calving these animals were fed a maintenance diet of ground alfalfa hay and cottonseed hulls and were grouped in two adjacent pens on the basis of condition score. One aroup consisted of heifers‘ranging in condition from 7 to 9 (avg = 8.7) and the other group ranged from 10 to 12 (avg = 10.2). Condition score both prior to and during the experiment was determined by a single individual using subjective visualappraisal ( 5 = very thin; 15 = very fat). The day after parturition, heifers were assigned at random within condition score grouping to receive sesame oil control injections (C) or an intramuscular injection of 30 mg progesterone in sesame oil on day injection of 2 15 postpartum, followed in 48 hours by anintramuscular mg estradiol-176 (PE). Equal numbers of heifers were then placed into one of two adjacent energy restriction pens, where all animals received aooroximatelv 2.8 ka TBN oer head oer dav until 90 davs oostoartum. The diet consisted of ground alfalfa hay, cottonseed hull; and cottonseed meal and was fed on a pen basis. The diet supplied approximately 50% of the N.R.C. (10) recorenendedallowance of TbN for maintenance-and lactation, calculated on average calving weights. All other nutrients were provided at recomtended levels. At the end of the experimental period on day 91 postpartum, each heifer and her calf were removed from the energy restriction pen and placed into a flushing pen where a roughageconcentrate mixture supplying 120% of N.R.C. energy requirements was provided for the next 80 days. Loose salt and a trace mineral supplement were provided free choice at all times. Calves were allowed access to a'creep feeder containing a mixture of alfalfa and grass hay during the entire experimental period. Weights and condition scores were recorded for each heifer at 30, 60 and 96 days postpartum, in addition to those recorded at calving. An intact bull wearing a chin ball marking device was maintained with each pen of heifers during the entire experimental period (day l-90 postpartum) except at feeding. Placing intact bulls with cows imnediately after calving served two purposes: (1) it allowed for continuous heat detection and (2)
14
JULY
1980 VOL. 14 NO. 1
THERIOGENOLOGY it yielded information on the feasibility of breeding cows as soon after calving as possible. The bulls were rotated between pens, with all cows exposed for an additional 80 days after the 90 day energy restriction period. Visual observations for signs of estrus and breeding activity were conducted twice daily throughout these periods. One week after first treatment the ovaries of all heifers were palpated per rectum to determine ovulation response. Those not responding to first treatment, or which formed a CL but did not continue to cycle, were retreated at 60 days postpartum. Based on information obtained in a previous study (9) response to second treatment was determined by synchronized estrous activity 15 to 21 days followino estradiol iniection. as palpation of ovaries was not conducted. Finai conception rates were determined by palpation approximately 60 days after the bulls were removed. Analyses of variance (11) were conducted on body weight, condition scores and reproductive parameters. Included in the latter are intervals to first signs of estrous behavior (any manifestation of heat), as well as intervals to first estrus (standing heat). Dystocia did not occur in any of the heifers in this experiment. RESULTS AND DISCUSSION Table I shows average weights and condition scores observed in treated and untreated groups during the first 90 days postpartum. These measures did not differ (P>.O5) between groups at calving, 30, 60 or 90 days and indicate that the heifers decreased in weight by an average of 28 kg over this period. Most of this weight loss occurred during the first 30 days oostoartum. Two heifers in the treated oroup and one of the controls failed to lose weight as a probable result of d;minant feeding behavior. Thus, analysis of variance of weights resulted in a non-significant difference (P> .D5) over time. However, when these three animals were removed from consideration,both the 60 and 90 day weights were significantly lower (P< .05) than calving weights for both PE and C heifers. Condition scores at calving averaged (2 SE) 9.3 2.3 for PE and 9.5 2.3 for controls which declined to 8.22 .3 and 8.5 2.3, respectively, after 90 days. At first treatment 14 of 18 heifers exhibited signs of estrous behavior within 48 hours after estradiol-176 (Table II). Eight of the 14 were in standing heat and were bred by the bull. Palpation results indicated that seven ovulations were induced imnediately after treatment, with one heifer conceiving at 18 days postpartum. Of the seven ovulations induced, four occurred in heifers which exhibited standing heat, two which were hyperactive only and one in which no estrous behavior was noted. Between 15 and 21 days after treatment, four of six which had ovulated and were not pregnant had returned to estrus, comoared to one animal in the control group which exhibited estrus 19 days after the last control injection. Thus, two of the heifers which ovulated at treatment and formed a corpus luteum (CL) failed to continue cyclic activity and were not pregnant. The ovulation rate (39.8%) and ability to continue cyclic activity in response to PE on day 15 postpartum was less than previously observed at this station in normally fed heifers (9). This was probably the result et al. (8) and Williams and Ray (12) of the imposed energy restriction. Brundrett -have shown that weight and condition significantly affect the ability of postpartumheifers to respond to exogenous steroids. However, by 60 days postpartum, the effect of energy restriction on the ability of the heifers to respond to treatment appeared to have lessened. At second treatment 10 of 13 (76.7%) exhibited evidence of ovulation, with three conceiving at the treatment
JULY 1980 VOL. 14 NO. 1
15
THERIOGENOLOCY
estrus and seven returning to a synchronized heat 15 to 21 days later. Two PE treated heifers and one control heifer conceived prior to 60 days postpartum, with eight PE and 10 controls conceiving during the next 30 days. The remaining four animals in each group conceived between 90 and 153 days postpartum after being removed from the energy restricted diet and placed on 120% of N.R.C. reconznendations. A sunmmry of overall reproductive performance is shown in table III. Although intervals to first estrous behavior and estrus were significantly different (P c.05) in favor of the treated group, no benefit was gained (P >.05) regarding average interval to conception or number conceiving under the conditions imposed in this experiment. The similarity noted in postpartum intervals to conception between C and PE heifers can be accounted for by: (1) the low ovulatory response of PE heifers to first treatment and (2) the fact that the estrous response noted after treatment at 60 days postpartum occurred coincident with estrous activity and breeding in a substantial proportion of controls. Recent work (13, 14, 15) with postpartum dairy cows using gonadotropinreleasina hormone (GnRH) and with PE in beef cows (9) suggests that the ability of the bovine pituitary.t.0 release normal amounts of luteinizing hormone (LH) is restored within two to three weeks postpartum. Thus, the apparent depression in ovulation response noted in the current study probably cannot be explained by the effect of stage postpartum on LH release. However, inadequate LH release may have occurred because of the nutritional stress. The possible endocrine imbalance resulting from dietary energy restriction which mediates a decline in fertility (6, 16, 17, 18) or response to exogenous stimuli (8, 12) has not been clearly defined. Several studies have been conducted in which patterns of circulating progesterone were monitored during the estrous cycle of cows on dietary energy restriction. The results remain equivocal. During first cycles in which dietary energy was restricted, Donaldson et al (19) and Dunn et al. (20) reported an increase in luteal progesterone --production, whereas Hill -et al. (21) found a decrease. Other experiments (22, 23) have resulted in the conclusion that energy intake has no effect on this parameter. Further, the effects of long-term dietary energy restriction on serum progesterone in subsequent estrous cycles is also unclear, with decreases (19, 22) increases (20), as well as no effect (23) having been reported. A similar disparity exists regarding the effects of energy restriction on circulating LH levels. Gombe and Hansel (22) have reported a decrease in LH, but others (20, 21, 23) observed no change. Low energy diets have been shown to affect fertilization rate in the cow (21), but these conclusions have also been disputed by experiments in the ewe (24) and in the cow(23). It is therefore apparent that a clear explanation of the physiological mechanism(s) by which dietary energy restriction reduces fertility is not available. Investigations to clarify this issue will be necessary if postpartum reproductive efficiency is to be enhanced under less than optimum dietary conditions. The results of the current study further substantiate this point.
16
JULY
1980 VOL. 14 NO. 1
TABLE I.
AVERAGE WEIGHTS AND CONDITION SCORESa FOR HEIFERS FROM CALVING TO 90 DAYS POSTPARTUM PEb
ITEM No. Animals
18
CONTROL 19
Calving 425.5 (2 10.9) 9.5 (2 0.3)
Weight, kg (+ SE) Condition Score (2 SE) 30 Days Postpartum Weight, kg (2 SE) Condition Score ( +SE)
4OA.i .
I",.",; +.
409.5 ( k11.3) 9.0 (? 0.3)
60 Days Postpartum Weight, kg (+ SE) Condition Score (*SE)
392.3 (k 8.4 (?
9.7)
0.3)
90 Days Postpartum Weight, kg ( f SE) Condition Score (+SE) '5 (very thin) to 15 (very fat). b 30 mg progesterone, followed in 48 hours by 2 mg estradiol-176
JULY 1980VOL. 14 NO. 1
17
THERIOGENOLOGY TABLEII.
RESPONSE OF HEIFERS TO PEa AT 15 AND 60 DAYS POSTPARTUM
Treatment
No.
Activity Within 48 Hours After Estradiol Injection NonStanding Standing Return Estrus Estrus Ovulation Conception Estrus
DAY 15 PE
18
8
CONTROL
19
-
PE
13
4
CONTROL
18
-
6
7
1
4c ld
DAY 60 7
N.P.b
3
7=
N.P.
gd
i30 mg progesterone followed in 48 hours by 2 mg estradiol-176. No palpation conducted. @zurrence of estrus 15-21 days after estradiol-176. Occurrence of estrus 1-21 days after second control injection.
TABLE III.
AVERAGE (*SE)
POSTPARTUM INTERVALSa IN PE AND CONTROL HEIFERS TREATMENT
ITEM
PEb
Control
First Estrous Behavior: Average Days Number
23i;c (2 5.5)
75iS4d (2 9.4)
55i;c (2 9.6)
88.8d (2 8.2) 17
85ii (’ 8e5)
88i65(’ 7e1)
First Standing Estrus: Average Days Number Conception: Average Days Number %
78
79
"Means calculated through 120 days postpartum b 30 mg progesterone followed by 2 mg estradiol-176 48 hours later. "dMeans
18
within rows with different superscripts are different (PC .05).
JULY 1980VOL. 14 NO. 1
THERIOGENOLOGY LITERATURE CITED 1.
Neumann, A. L. and Snapp, R. R. Beef Cattle. New York (1969)
2.
Carroll, E. J. and Hoerlein, A. B. Reproductive Performance of Beef Cattle Under Drought Conditions. J. Am. Vet. Med. Assn. 148:1030 (1966)
3.
Mathis, G. W. and Kothman, M. M. Calf Production from Two Age Groups of Hereford Cows. Proc. West. Sec. Amer. Sot. Anim. Sci. 21:345 (1970)
4.
Bellows, R. A., Short, R. E., Urick, J. J. and Pahnish, 0. F. Effects of Early Weaning on Postpartum Reproduction of the Dam and Growth of Calves Born as Multiples or Single. J. Anim. Sci. 39:589 (1974)
5.
Laster, D. B., Glimp, H. A., Cundiff, L. V. and Gregory, K. E. Factors Affecting Dystocia and the Effects of Dystocia on Subsequent Reproduction in Beef Cattle. J. Anim. Sci. 36:695 (1973)
6.
Dunn, T. G., Ingalls, J. E., Zimmerman, D. R. and Wiltbank, J. N. Reproductive Performance of 2-year-old Hereford and Angus Heifers As Influenced by Pre- and Post-calving Energy Intake. J. Anim. Sci. 29:719 (1969)
7.
Ray, 0. E., Roubicek, C. B., Lane, A., Hansen, W. J., Theurer, C. 8. and McGinty, D. D. Supplementation or Early Weaning with Beef Heifers. Proc. West. Sec. Sot. Anim. Sci. 24:246 (1973)
8.
Brundrett, G. N., Sprott, L. R., Songster, B. Burrell, W. C. Walters, D. L. and Wiltbank, 3. N. Beef Cow Reproduction Following Early Weaning and Shang. Proc. West. Sec. Amer. Sot. Anim. Sci. 28:160
9.
Williams, G. L. and Ray, D. E. Hormonal and Reproductive Profiles of Early Postpartum Beef Heifers After Prolactin Suppression or Steroid-Induced Luteal Function. J. Anim. Sci. (In press)
John Wiley and Sons, Inc.,
10.
N. R. C. Nutrient Requirements of Domestic Animals. of Science, Washington, D. C. (1976)
11.
Steel, Robert G. D. and Torrie, J. H. Principles and Procedures of Statistics. McGraw-Hill Book Company, Inc. (1960)
12.
Williams, G. L. and Ray, D. E. Fertility of Range Beef Cows and Heifers After Sequential Injections of Progesterone and Estradiol-176. Theriogenology (In Press)
13.
Britt, 3. H., Kittock, R. J. and Harrison, 0. S. Ovulation, Estrus and Endocrine Response After GnRH in Early Postpartum Cows. J. Anim. Sci. 39:915 (1974)
14.
Kesler, D. J., Garverick, H. A., Youngquist, R. S., Elmore, R. 6. and Bierschwal, C. J. Effect of Days Postpartum and Endogenous Reproductive Hormones on GnRH-Induced LH Release in Dairy Cows. J. Anim. Sci. 46:797 (1977)
JULY 1980 VOL. 14 NO. 1
National Academy
19
THERIOGENOLOGY
15.
Fernandes. L. C., Thatcher, W. W., Wilcox, C. J. and Call, E. P. ;;wFlease in Response to GnRH During the Postpartum Period of Dairy . J. Anim. Sci. 46:443 (1978)
16.
McClure, T. J. Hypoglycemia, An Apparent Cause of Infertility of Lactating Cows. Wt. Vet. J. 124:126 (1968)
17.
Wiltbank, J. N., Rowden, W. W., Ingalls, J. E., Gregory, K. E. and Koch, R. M. Effect of Energy Levels on Reproductive Phenomena of Mature Hereford Cows. J. An'im. Sci. 21:219 (1962)
18.
Wiltbank, J. N., Rowden, W. W., Ingalls, J.,E. and Zinsnerman, 0. R. Influence of Postpartum Energy Levels on Reproductive Performance of Hereford Cows Restricted in Energy Intake Prior to Calving. J. Anim. Sci. 23:1049 (1964)
19.
Donaldson, L. E., Bassett, J. M. and Thorburn, G. 0. Peripheral Plasma Progesterone Concentration of Cows During Puberty, Oestrus Cycles, Pregnancy and Lactation, and the Effect of Under-Nutrition or Exogenous, Oxytocin on Progesterone Concentration. J. Endocrin. 48:599 (1970)
20.
Dunn, T. G., Rone, J., Kaltenbach, C. C.. Van Der Walt, L. A., Riley, M. L. and Akbar, A. M. Hormone Chan es During Underfeeding of Beef Cows. J. Anim. Sci. 39:206 (19743
21.
Hill, J. R., Jr., tamond, 0. R., Henricks, 0. M., Dickey, J. F. and Niswender. 6. 0. The Effects of Under-Nutrition on Ovarian Function and Fertility in Beef Heifers. Biol. Reprod. 2:78 (1970)
22.
Gombe, S. and Hansel, W. Plasma LH and Progesterone Levels in Heifers on Restricted Energy Intakes. J. Anim. Sci. 37:728 (1973)
23.
Sptizer, J. C., Niswender, G. D., Seidel, G. E., Jr., and Wiltbank, J. N. Fertilization and Blood Levels of Progesterone and LH in Beef Heifers on a Restricted Energy Diet. J. Anim. Sci. 46:1071 (1978)
24.
Cunning, I. A., Mole, B. J., Obst, J., De Blockey, M. A., Winfield, C. G. and Goding, J. R. Increase in Plasma Progesterone Caused by Under-Nutrition During Early Pregnancy in the Ewe. J. Reprod. Fert. 24:146 (1971)
20
JULY 1980VOL. 14 NO. 1
of Arizona,
Tucson
85721
Received for Publication: 12/12/79 SUMMARY A study was conducted to determine reproductive response of primiparous beef heifers to an ovulation induction regimen during Thirty-seven Barzona x Hereford restricted dietary energy intake. heifers, maintained under drylot conditions, were utilized. Heifers were restricted in TDN on a pen basis to approximately 50% of N.R.C. recommendations for the first 90 days postpartum, then received 120% All animals received control injections (C) for 8D days thereafter. or 30 mg progesterone on day 15 postpartum followed in 48 hours by 2 mg estradiol-176 (PE). Treated heifers not ovulating at first treatment and/or not cycling, were re-treated at 60 day postpartum, with Intact fertile non-cycling C heifers receiving control injections. bulls were maintained with the heifers from day 1 to 170 days postpartum, with visual observations for signs of estrus and breeding activity conducted twice daily during this period. At first treatment, seven of 18 heifers ovulated, one conceived and four continued to cycle. At second treatment, three of 13 conceived and seven returned to a Although intervals to first synchronized estrus 15 to 21 days later. estrous behavior and estrus favored PE heifers (PC .05), by 90 and 170 days postpartum no advantage in interval to conception or number conceiving was observed. INTRODUCTION Under range conditions suboptimal energy intake during the postpartum period is generally one of the most important factors that limits rebreeding efficiency (1). This is especially true in the primiparous heifer (2,3), whose energy requirements for maintenance, lactation and reproduction are superimposed on those for growth. Alternate management procedures such as early weaning (4,5) or supplementation (6,7) can often be useful from a reproductive standpoint, but may be economically unsound except during extreme drought. Work with exogenous hormone treatments has shown that SYNCRO-MATE-B (G.D. Searle Co.), alone or in combination with 48 hour calf removal or early weaning, may be an effective and practical means of estrus induction in anestrous postpartum cows (8). However, as body condition aArizona
Agricultural
bContribution and Sheep.
Experiment
to W-112,
'Present address: Fargo 58105.
Improving
Department
Reproductive
for technical
Paper No. 3082
Performance
of Animal Science,
We wish to thank Mr. Bud Keister
JULY 1980 VOL. 14 NO. 1
Station Technical
of Cattle
North Dakota
State Univ.,
assistance.
13
THERIOGENOLOGY at treatment decreased, the response to treatment also declined. The endocrinology of another approach to postpartum estrous cycle control has recently been evaluated (9). The objective was to stimulate ovarian activity via prolactin suooression and/or seauential steroid treatment very early in'the postpartum period to-avert 'the establishment of a prolonged lactational anestrum. Prolactin suppression had no apparent effect. However, in adequately fed heifers a single injection of progesterone on day 15 postpartum followed by estradiol-176 (PE) 48 hours later, induced endocrine changes which resulted in issnediate ovulation and establishment of cyclic activity in a majority of treated heifers. The purpose of the following experiment was to test the ability of PE to induce ovulation and estrous activity in drylot heifers during a prolonged dietary energy restriction. MATERIALS AND METHODS Two-year-old Barzona x Hereford heifers, calving for the first time in drylot during September, October and November, were used for this experiment. Prior to calving these animals were fed a maintenance diet of ground alfalfa hay and cottonseed hulls and were grouped in two adjacent pens on the basis of condition score. One aroup consisted of heifers‘ranging in condition from 7 to 9 (avg = 8.7) and the other group ranged from 10 to 12 (avg = 10.2). Condition score both prior to and during the experiment was determined by a single individual using subjective visualappraisal ( 5 = very thin; 15 = very fat). The day after parturition, heifers were assigned at random within condition score grouping to receive sesame oil control injections (C) or an intramuscular injection of 30 mg progesterone in sesame oil on day injection of 2 15 postpartum, followed in 48 hours by anintramuscular mg estradiol-176 (PE). Equal numbers of heifers were then placed into one of two adjacent energy restriction pens, where all animals received aooroximatelv 2.8 ka TBN oer head oer dav until 90 davs oostoartum. The diet consisted of ground alfalfa hay, cottonseed hull; and cottonseed meal and was fed on a pen basis. The diet supplied approximately 50% of the N.R.C. (10) recorenendedallowance of TbN for maintenance-and lactation, calculated on average calving weights. All other nutrients were provided at recomtended levels. At the end of the experimental period on day 91 postpartum, each heifer and her calf were removed from the energy restriction pen and placed into a flushing pen where a roughageconcentrate mixture supplying 120% of N.R.C. energy requirements was provided for the next 80 days. Loose salt and a trace mineral supplement were provided free choice at all times. Calves were allowed access to a'creep feeder containing a mixture of alfalfa and grass hay during the entire experimental period. Weights and condition scores were recorded for each heifer at 30, 60 and 96 days postpartum, in addition to those recorded at calving. An intact bull wearing a chin ball marking device was maintained with each pen of heifers during the entire experimental period (day l-90 postpartum) except at feeding. Placing intact bulls with cows imnediately after calving served two purposes: (1) it allowed for continuous heat detection and (2)
14
JULY
1980 VOL. 14 NO. 1
THERIOGENOLOGY it yielded information on the feasibility of breeding cows as soon after calving as possible. The bulls were rotated between pens, with all cows exposed for an additional 80 days after the 90 day energy restriction period. Visual observations for signs of estrus and breeding activity were conducted twice daily throughout these periods. One week after first treatment the ovaries of all heifers were palpated per rectum to determine ovulation response. Those not responding to first treatment, or which formed a CL but did not continue to cycle, were retreated at 60 days postpartum. Based on information obtained in a previous study (9) response to second treatment was determined by synchronized estrous activity 15 to 21 days followino estradiol iniection. as palpation of ovaries was not conducted. Finai conception rates were determined by palpation approximately 60 days after the bulls were removed. Analyses of variance (11) were conducted on body weight, condition scores and reproductive parameters. Included in the latter are intervals to first signs of estrous behavior (any manifestation of heat), as well as intervals to first estrus (standing heat). Dystocia did not occur in any of the heifers in this experiment. RESULTS AND DISCUSSION Table I shows average weights and condition scores observed in treated and untreated groups during the first 90 days postpartum. These measures did not differ (P>.O5) between groups at calving, 30, 60 or 90 days and indicate that the heifers decreased in weight by an average of 28 kg over this period. Most of this weight loss occurred during the first 30 days oostoartum. Two heifers in the treated oroup and one of the controls failed to lose weight as a probable result of d;minant feeding behavior. Thus, analysis of variance of weights resulted in a non-significant difference (P> .D5) over time. However, when these three animals were removed from consideration,both the 60 and 90 day weights were significantly lower (P< .05) than calving weights for both PE and C heifers. Condition scores at calving averaged (2 SE) 9.3 2.3 for PE and 9.5 2.3 for controls which declined to 8.22 .3 and 8.5 2.3, respectively, after 90 days. At first treatment 14 of 18 heifers exhibited signs of estrous behavior within 48 hours after estradiol-176 (Table II). Eight of the 14 were in standing heat and were bred by the bull. Palpation results indicated that seven ovulations were induced imnediately after treatment, with one heifer conceiving at 18 days postpartum. Of the seven ovulations induced, four occurred in heifers which exhibited standing heat, two which were hyperactive only and one in which no estrous behavior was noted. Between 15 and 21 days after treatment, four of six which had ovulated and were not pregnant had returned to estrus, comoared to one animal in the control group which exhibited estrus 19 days after the last control injection. Thus, two of the heifers which ovulated at treatment and formed a corpus luteum (CL) failed to continue cyclic activity and were not pregnant. The ovulation rate (39.8%) and ability to continue cyclic activity in response to PE on day 15 postpartum was less than previously observed at this station in normally fed heifers (9). This was probably the result et al. (8) and Williams and Ray (12) of the imposed energy restriction. Brundrett -have shown that weight and condition significantly affect the ability of postpartumheifers to respond to exogenous steroids. However, by 60 days postpartum, the effect of energy restriction on the ability of the heifers to respond to treatment appeared to have lessened. At second treatment 10 of 13 (76.7%) exhibited evidence of ovulation, with three conceiving at the treatment
JULY 1980 VOL. 14 NO. 1
15
THERIOGENOLOCY
estrus and seven returning to a synchronized heat 15 to 21 days later. Two PE treated heifers and one control heifer conceived prior to 60 days postpartum, with eight PE and 10 controls conceiving during the next 30 days. The remaining four animals in each group conceived between 90 and 153 days postpartum after being removed from the energy restricted diet and placed on 120% of N.R.C. reconznendations. A sunmmry of overall reproductive performance is shown in table III. Although intervals to first estrous behavior and estrus were significantly different (P c.05) in favor of the treated group, no benefit was gained (P >.05) regarding average interval to conception or number conceiving under the conditions imposed in this experiment. The similarity noted in postpartum intervals to conception between C and PE heifers can be accounted for by: (1) the low ovulatory response of PE heifers to first treatment and (2) the fact that the estrous response noted after treatment at 60 days postpartum occurred coincident with estrous activity and breeding in a substantial proportion of controls. Recent work (13, 14, 15) with postpartum dairy cows using gonadotropinreleasina hormone (GnRH) and with PE in beef cows (9) suggests that the ability of the bovine pituitary.t.0 release normal amounts of luteinizing hormone (LH) is restored within two to three weeks postpartum. Thus, the apparent depression in ovulation response noted in the current study probably cannot be explained by the effect of stage postpartum on LH release. However, inadequate LH release may have occurred because of the nutritional stress. The possible endocrine imbalance resulting from dietary energy restriction which mediates a decline in fertility (6, 16, 17, 18) or response to exogenous stimuli (8, 12) has not been clearly defined. Several studies have been conducted in which patterns of circulating progesterone were monitored during the estrous cycle of cows on dietary energy restriction. The results remain equivocal. During first cycles in which dietary energy was restricted, Donaldson et al (19) and Dunn et al. (20) reported an increase in luteal progesterone --production, whereas Hill -et al. (21) found a decrease. Other experiments (22, 23) have resulted in the conclusion that energy intake has no effect on this parameter. Further, the effects of long-term dietary energy restriction on serum progesterone in subsequent estrous cycles is also unclear, with decreases (19, 22) increases (20), as well as no effect (23) having been reported. A similar disparity exists regarding the effects of energy restriction on circulating LH levels. Gombe and Hansel (22) have reported a decrease in LH, but others (20, 21, 23) observed no change. Low energy diets have been shown to affect fertilization rate in the cow (21), but these conclusions have also been disputed by experiments in the ewe (24) and in the cow(23). It is therefore apparent that a clear explanation of the physiological mechanism(s) by which dietary energy restriction reduces fertility is not available. Investigations to clarify this issue will be necessary if postpartum reproductive efficiency is to be enhanced under less than optimum dietary conditions. The results of the current study further substantiate this point.
16
JULY
1980 VOL. 14 NO. 1
TABLE I.
AVERAGE WEIGHTS AND CONDITION SCORESa FOR HEIFERS FROM CALVING TO 90 DAYS POSTPARTUM PEb
ITEM No. Animals
18
CONTROL 19
Calving 425.5 (2 10.9) 9.5 (2 0.3)
Weight, kg (+ SE) Condition Score (2 SE) 30 Days Postpartum Weight, kg (2 SE) Condition Score ( +SE)
4OA.i .
I",.",; +.
409.5 ( k11.3) 9.0 (? 0.3)
60 Days Postpartum Weight, kg (+ SE) Condition Score (*SE)
392.3 (k 8.4 (?
9.7)
0.3)
90 Days Postpartum Weight, kg ( f SE) Condition Score (+SE) '5 (very thin) to 15 (very fat). b 30 mg progesterone, followed in 48 hours by 2 mg estradiol-176
JULY 1980VOL. 14 NO. 1
17
THERIOGENOLOGY TABLEII.
RESPONSE OF HEIFERS TO PEa AT 15 AND 60 DAYS POSTPARTUM
Treatment
No.
Activity Within 48 Hours After Estradiol Injection NonStanding Standing Return Estrus Estrus Ovulation Conception Estrus
DAY 15 PE
18
8
CONTROL
19
-
PE
13
4
CONTROL
18
-
6
7
1
4c ld
DAY 60 7
N.P.b
3
7=
N.P.
gd
i30 mg progesterone followed in 48 hours by 2 mg estradiol-176. No palpation conducted. @zurrence of estrus 15-21 days after estradiol-176. Occurrence of estrus 1-21 days after second control injection.
TABLE III.
AVERAGE (*SE)
POSTPARTUM INTERVALSa IN PE AND CONTROL HEIFERS TREATMENT
ITEM
PEb
Control
First Estrous Behavior: Average Days Number
23i;c (2 5.5)
75iS4d (2 9.4)
55i;c (2 9.6)
88.8d (2 8.2) 17
85ii (’ 8e5)
88i65(’ 7e1)
First Standing Estrus: Average Days Number Conception: Average Days Number %
78
79
"Means calculated through 120 days postpartum b 30 mg progesterone followed by 2 mg estradiol-176 48 hours later. "dMeans
18
within rows with different superscripts are different (PC .05).
JULY 1980VOL. 14 NO. 1
THERIOGENOLOGY LITERATURE CITED 1.
Neumann, A. L. and Snapp, R. R. Beef Cattle. New York (1969)
2.
Carroll, E. J. and Hoerlein, A. B. Reproductive Performance of Beef Cattle Under Drought Conditions. J. Am. Vet. Med. Assn. 148:1030 (1966)
3.
Mathis, G. W. and Kothman, M. M. Calf Production from Two Age Groups of Hereford Cows. Proc. West. Sec. Amer. Sot. Anim. Sci. 21:345 (1970)
4.
Bellows, R. A., Short, R. E., Urick, J. J. and Pahnish, 0. F. Effects of Early Weaning on Postpartum Reproduction of the Dam and Growth of Calves Born as Multiples or Single. J. Anim. Sci. 39:589 (1974)
5.
Laster, D. B., Glimp, H. A., Cundiff, L. V. and Gregory, K. E. Factors Affecting Dystocia and the Effects of Dystocia on Subsequent Reproduction in Beef Cattle. J. Anim. Sci. 36:695 (1973)
6.
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7.
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8.
Brundrett, G. N., Sprott, L. R., Songster, B. Burrell, W. C. Walters, D. L. and Wiltbank, 3. N. Beef Cow Reproduction Following Early Weaning and Shang. Proc. West. Sec. Amer. Sot. Anim. Sci. 28:160
9.
Williams, G. L. and Ray, D. E. Hormonal and Reproductive Profiles of Early Postpartum Beef Heifers After Prolactin Suppression or Steroid-Induced Luteal Function. J. Anim. Sci. (In press)
John Wiley and Sons, Inc.,
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N. R. C. Nutrient Requirements of Domestic Animals. of Science, Washington, D. C. (1976)
11.
Steel, Robert G. D. and Torrie, J. H. Principles and Procedures of Statistics. McGraw-Hill Book Company, Inc. (1960)
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Williams, G. L. and Ray, D. E. Fertility of Range Beef Cows and Heifers After Sequential Injections of Progesterone and Estradiol-176. Theriogenology (In Press)
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Britt, 3. H., Kittock, R. J. and Harrison, 0. S. Ovulation, Estrus and Endocrine Response After GnRH in Early Postpartum Cows. J. Anim. Sci. 39:915 (1974)
14.
Kesler, D. J., Garverick, H. A., Youngquist, R. S., Elmore, R. 6. and Bierschwal, C. J. Effect of Days Postpartum and Endogenous Reproductive Hormones on GnRH-Induced LH Release in Dairy Cows. J. Anim. Sci. 46:797 (1977)
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National Academy
19
THERIOGENOLOGY
15.
Fernandes. L. C., Thatcher, W. W., Wilcox, C. J. and Call, E. P. ;;wFlease in Response to GnRH During the Postpartum Period of Dairy . J. Anim. Sci. 46:443 (1978)
16.
McClure, T. J. Hypoglycemia, An Apparent Cause of Infertility of Lactating Cows. Wt. Vet. J. 124:126 (1968)
17.
Wiltbank, J. N., Rowden, W. W., Ingalls, J. E., Gregory, K. E. and Koch, R. M. Effect of Energy Levels on Reproductive Phenomena of Mature Hereford Cows. J. An'im. Sci. 21:219 (1962)
18.
Wiltbank, J. N., Rowden, W. W., Ingalls, J.,E. and Zinsnerman, 0. R. Influence of Postpartum Energy Levels on Reproductive Performance of Hereford Cows Restricted in Energy Intake Prior to Calving. J. Anim. Sci. 23:1049 (1964)
19.
Donaldson, L. E., Bassett, J. M. and Thorburn, G. 0. Peripheral Plasma Progesterone Concentration of Cows During Puberty, Oestrus Cycles, Pregnancy and Lactation, and the Effect of Under-Nutrition or Exogenous, Oxytocin on Progesterone Concentration. J. Endocrin. 48:599 (1970)
20.
Dunn, T. G., Rone, J., Kaltenbach, C. C.. Van Der Walt, L. A., Riley, M. L. and Akbar, A. M. Hormone Chan es During Underfeeding of Beef Cows. J. Anim. Sci. 39:206 (19743
21.
Hill, J. R., Jr., tamond, 0. R., Henricks, 0. M., Dickey, J. F. and Niswender. 6. 0. The Effects of Under-Nutrition on Ovarian Function and Fertility in Beef Heifers. Biol. Reprod. 2:78 (1970)
22.
Gombe, S. and Hansel, W. Plasma LH and Progesterone Levels in Heifers on Restricted Energy Intakes. J. Anim. Sci. 37:728 (1973)
23.
Sptizer, J. C., Niswender, G. D., Seidel, G. E., Jr., and Wiltbank, J. N. Fertilization and Blood Levels of Progesterone and LH in Beef Heifers on a Restricted Energy Diet. J. Anim. Sci. 46:1071 (1978)
24.
Cunning, I. A., Mole, B. J., Obst, J., De Blockey, M. A., Winfield, C. G. and Goding, J. R. Increase in Plasma Progesterone Caused by Under-Nutrition During Early Pregnancy in the Ewe. J. Reprod. Fert. 24:146 (1971)
20
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