Search PubMed⌕ Search

Biomedical subjects

G L Williams

Publications and source records attributed to G L Williams.

At least 55 records · Page 3Linked to original sources
PubMed1993

Mammary somatosensory pathways are not required for suckling-mediated inhibition of luteinizing hormone secretion and delay of ovulation in cows.

Four experiments were conducted to evaluate endocrine, lactational, and reproductive features of an experimental animal model employing complete neural disconnection of the udder in beef cows and then to utilize the validated model to study the role of mammary somatosensory pathways in suckling-mediated anovulation. For experiment 1, crossbred beef cows (n = 16) were randomly assigned to suckled/sham-operated control, weaned (calf removed)/sham-operated control, and suckled/mammary-denervated groups between Days 14 and 18 postcalving. Ten additional cows were randomly divided into weaned or suckled unoperated control groups (experiment 2). Complete mammary anesthesia was attained in all denervated cows (experiment 1), but sensory perception was not affected in sham-operated controls. Prolactin release patterns were markedly depressed by denervation; however, oxytocin release, milk production, and calf growth rates were not affected. Although acute sham surgery attenuated weaning-induced increases in LH pulse and ovulation frequency (experiment 1), normal responses to weaning were observed in unoperated controls (experiment 2) as well as in sham-operated cows 1 yr later (experiment 3). Finally, denervated-suckled cows (n = 22) that had been denervated before conception (experiment 4) exhibited LH secretion patterns and mean postpartum intervals to luteal activity similar to those of intact-suckled cows (n = 16). In contrast, the intact-weaned group (n = 16; calves weaned at birth) responded within 2 wk postcalving with an increased frequency of LH pulses, and intervals to onset of luteal activity were shortened compared to those in the other groups. Suckling-mediated anovulation is not dependent upon mammary somatosensory cues.

Animals↗
PubMed1993

Evidence for maternal behavior as a requisite link in suckling-mediated anovulation in cows.

Some component of the suckling process inhibits LH secretion and delays postpartum ovulation in beef cows. To investigate a possible role for maternal behavior in suckling-mediated anovulation, 27 crossbred beef cows were randomly allotted to 1 of 3 groups: 1) alien (dam suckled by alien calf; n = 11); 2) own (dam suckled by own calf; n = 8); and 3) weaned (calf removed for 6 days; n = 8). Beginning 14-17 days after parturition (experimental Day 0), cows were control suckled (10 min every 6 h) in stanchions for 6 days by either their own calf or by an alien calf or were weaned. Mean LH pulse frequencies in the alien and weaned groups were similar but were elevated (p < 0.02) on experimental Days 2 and 4 compared to those in the own group. The incidence of luteal activity by experimental Day 10 was greater (p < 0.01) for the alien (72.2%) and weaned groups (75.0%) than for the own group (12.5%). Frequency of oxytocin release following suckling was greater (p < 0.01) in the own group than in the alien group (Day 2: 100% vs. 36.4%; Day 4: 100% vs. 54.6%), whereas suckling-induced release of prolactin was similar for both groups. Data provide evidence that the mother-offspring bond is an important link in suckling-mediated inhibition of LH secretion and ovulation.

Aggression↗
PubMed1993

Effects of dietary gossypol consumption on metabolic homeostasis and reproductive endocrine function in beef heifers and cows.

Our objectives were to determine the effects of incremental increases in dietary gossypol on metabolic homeostasis and reproductive endocrine function in postpubertal beef heifers and the long-term effects of elevated dietary gossypol on various metabolic and reproductive endocrine characteristics in mature cows. In Exp. 1, heifers (n = 6/group) were fed either 0, .5, 2.5, 5, 10, or 20 g.animal-1 x d-1 of dietary free gossypol for 62 d. Erythrocyte membrane osmotic fragility was increased (P < .0001) in both the 10- and 20-g groups. Slight alterations in plasma concentrations of sorbitol dehydrogenase and K+ were also detected in the latter group. Treatment did not affect ADG, body condition scores, or concentrations of progesterone during the estrous cycle; however, mean concentrations of LH were higher (P < .001) in heifers fed 20 g/d of gossypol than in heifers in all other groups. In Exp. 2, lactating cows (n = 17) exhibiting regular estrous cycles were fed a control (no gossypol, n = 8) or high-gossypol (20 mg.kg BW-1 x d-1 free gossypol, n = 9) diet for 33 wk. Mean BW and body condition scores did not differ during the feeding period. Erythrocyte membrane fragility was greater (P < .05) in the high-gossypol than in the control group. Magnitude of the preovulatory LH surge, luteal phase concentrations of progesterone, follicular fluid concentrations of estradiol and progesterone, in vitro granulosa cell estradiol production, and 60-d pregnancy rates were similar between groups. The amounts of gossypol fed in these experiments are not likely to affect reproductive performance adversely in beef heifers or cows.

Androstenedione↗
PubMed1992

Effects of transcutaneous thermal and electrical stimulation of the teat on pituitary luteinizing hormone, prolactin and oxytocin secretion in ovariectomized, estradiol-treated beef cows following acute weaning.

The objective of the study was to determine if chronic electrical or thermal stimulation of sensory neurons on the surface of the teat is able to activate pathways that suppress the weaning-induced increase in luteinizing hormone (LH) secretion in beef cows. Treatment groups (n = 5 per group) consisted of: 1) control suckled (CS); 2) weaned plus electrical stimulation of the teat (ESTT); 3) weaned plus electrical stimulation of the tail (ESTL); 4) weaned plus thermal stimulation of the teat (TTT); 5) weaned plus thermal stimulation of the tail (TTL) and 6) weaned (WN). Cows were ovariectomized on Day 5 post partum (PP) and were treated with estradiol-17beta to maintain a constant tonic baseline. Beginning on Days 17 to 21 post partum, cows were suckled by their own calf (control), weaned or weaned and electrically or thermally stimulated for 10 minutes every 6 hours for 4 days. Chronic transcutaneous electrical and thermal stimulation of the teat or tail failed to impede the unambiguous rise (P < 0.001) in LH pulse frequency and amplitude following weaning. Positive and negative feedback of estradiol on LH secretion was not affected by treatments. Relatively consistent episodes of oxytocin and prolactin release were observed following control-suckling, but responses to electrical and thermal stimulation were inconsistent. Chronic electrical or thermal stimulation of teat-specific or nonspecific loci did not attenuate heightened secretion of LH after weaning. The results are further evidence against a role for mammary somatosensory neurons in the suckling-mediated inhibition of LH secretion.

Journal Article↗
PubMed1992

Ovarian follicular characteristics, embryo recovery, and embryo viability in heifers fed high-fat diets and treated with follicle-stimulating hormone.

Postpubertal beef heifers (n = 55) were used to examine the effects of high-fat diets, independently of energy intake, on nonesterified fatty acid and lipoprotein metabolic patterns, ovarian follicular dynamics, and embryo recovery/viability after FSH superstimulation. High-lipid (HL) diets (5.4% added fat) increased (P < .01) serum concentrations of cholesterol, but not of nonesterified fatty acids, during the 35-d period before FSH treatment. Development of medium-sized (5 to 9.9 mm) follicles was enhanced (P < .05) during this period in heifers fed the HL diet. The HL diet increased total cholesterol (P < .05) and progesterone (P = .14) concentrations in follicular fluid obtained at ovariectomy (n = 10) 60 h after the onset of FSH treatment, but neither estradiol-17 beta nor androstenedione was affected. Granulosa cells recovered from FSH-induced, estrogen-active follicles in heifers fed the HL diet produced greater quantities of progesterone (P = .06) and less estradiol-17 beta (P < .05) in vitro than did granulosa cells from heifers fed the normal lipid diet. Dietary treatment did not influence FSH-stimulated recruitment of medium and large follicles, number of ovulations, embryo recovery, or embryo viability. Data suggest that increments in dietary fat intake can alter specific aspects of ovarian steroidogenic potential and can increase the population of medium-sized follicles theoretically available for maturation and harvest during the estrous cycle. However, conditions that limited the latter process in the current experiment are not understood and require further investigation.

Animals↗
PubMed1992

Maternal behavior and neuroendocrine regulation of suckling-mediated anovulation in cows.

Although it is clear that the initial endocrine deficit contributing to the length of the postpartum anovulatory period in suckled cows is of pituitary origin, this limitation is only operative for about the first 2 weeks of the puerperium. Thereafter, the pattern of LH secretion required for the final stages of follicular development and ovulation is blocked or attenuated through a more centrally regulated phenomenon. Hence, much of the recently published work in this area has focused on regulatory processes within the hypothalamus. This focus ignores the critical issue of exteroceptive signalling. Recent observations in this laboratory suggest that exteroceptive cues responsible for suckling-mediated anovulation are specifically attributable to the dams' own calf, but are not teat-specific. In fact, suckling does not produce an extended anovulatory state in the absence of a maternal-offspring bond. This review provides an historical perspective of investigations leading to this conclusion, and proposes a conceptual working model that links the special senses, maternal behavior and neuroendocrine centers that drive gonadotropin secretion during the puerperium.

Animals↗
PubMed1991

Mechanical masking of neurosensory pathways at the calf-teat interface: endocrine, reproductive and lactational features of the suckled anestrous cow.

A mammary somatosensory mask was employed in suckled anestrous beef cows to attenuate signals that were hypothesized to play a direct regulatory role in postpartum anestrus. Cows (n = 20) were randomly assigned to one of three treatment groups on Days 15 to 20 postcalving. The three treatments were: 1) masked (n = 7); 2) suckled (negative control, n = 6); and 3) weaned (positive control, n = 7). Four layers of surgical glove latex were used to cover the teats and ventro-lateral prominence of the udder of masked cows with a nonhardening, nontoxic adhesive (Day 0). Masks were designed to prevent direct contact between the skin of the teat/udder and the mouth of the calf and to allow normal suckling and milk removal. Masks were left in place for 7 d, with calves in the weaned group removed to a remote location for 7 d. Calves in the suckled group were allowed ad libitum suckling. Calves in the masked group tended (P < 0.1) to suckle longer than calves in the suckled control group (11.3 +/- 1.3 vs. 7.8 +/- 1.3 min/suckle) posttreatment; however, suckling frequency and calf weight gains did not differ due to treatment. Weaned cows exhibited a four-fold increase (P < 0.01) in the frequency of luteinizing hormone (LH) pulses on Day 2 relative to suckled and masked cows. The percentage of animals ovulating within 12 d after treatment differed (P < 0.05) and was 100, 50 and 0% for weaned, suckled and masked cows, respectively. Presence of the latex mask allowed essentially normal suckling and lactation, but failed to attenuate (and may have potentiated) the negative effects of suckling on secretory patterns of LH, ovulation and estrus.

Journal Article↗
PubMed1991

Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls.

The objective of this study was to examine the role of endogenous inhibin in the regulation of FSH, LH, and testosterone secretion and sperm production in bulls. Bulls were actively immunized against bovine inhibin alpha 1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG) or HAG alone (controls) and emulsified in Freund's complete adjuvant. Primary immunization was at 14 wk of age, followed by booster immunizations in Freund's incomplete adjuvant at 28, 30, and 34 wk of age. Ten days after each booster immunization, scrotal circumferences and body weights were measured, and blood was sampled for determination of bINH antibody titer. Ten days after the third booster, blood was sampled at 1-h intervals for 8 h to quantify serum concentrations of FSH, LH, and testosterone. After this blood sampling period, bulls were castrated and testicular sperm production was determined. Serum diluted 1:4,000 from bINH-immunized bulls bound 36%, 52%, and 53% of radioiodinated bINH after the first, second, and third boosters, respectively. Serum from controls bound less than 1% radioiodinated bINH. After the third booster, serum concentrations of FSH and testosterone were increased (p less than 0.05) and LH concentrations were decreased (p less than 0.001) in bINH-immunized bulls compared with controls. After the third booster, daily sperm production per gram of testicular parenchyma was increased (p less than 0.05) in bINH-immunized bulls compared with controls. Scrotal circumferences and body weights were similar between treatment groups throughout the experiment. We concluded that inhibin has a role in regulation of secretion of gonadotrophins and testosterone and testicular sperm production, but not testicular growth, in bulls.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-Globulins↗
PubMed1991

Diet-induced hyperlipidemia in cattle modifies the intrafollicular cholesterol environment, modulates ovarian follicular dynamics, and hastens the onset of postpartum luteal activity.

Three experiments were conducted with female cattle during the postpartum period and during the estrous cycle to examine the effects of diet-induced hyperlipidemia on lipoprotein-cholesterol and triglyceride (TG) metabolism, ovarian follicular dynamics, and incidence of postpartum luteal activity. Dietary-lipid effects were examined independently of metabolizable energy intake. Feeding a high-lipid (HL) diet (8% total lipid) for the first 3 wk of the puerperium (Experiment 1) increased (p less than 0.0001) the concentration of total cholesterol and high-density lipoprotein-cholesterol (HDL-CH), but not TG, within follicular fluid (FF) of estrogen-active (E-A) and inactive (E-I) follicles. Increases (1.4- to 1.7-fold) were similar in proportion to those observed in peripheral blood serum, but absolute concentrations were about 45% of that in serum. Greater than 95% of the cholesterol in FF was HDL-CH, with a greater (p less than 0.06) proportion of HDL-CH sequestered by E-A compared to E-I follicles. The HL diet increased (p less than 0.06) the number of medium-sized (3.1-9.9 mm) follicles present at ovariectomy 19-21 days postcalving and increased (p less than 0.03) concentrations of FF androstenedione in E-I follicles 5-fold. Granulosa cells from preovulatory follicles (Experiment 2) of heifers fed HL diets secreted 2.1- to 3.5-fold greater (p less than 0.03) quantities of pregnenolone and progesterone in vitro. Finally, feeding HL supplements to postpartum range cattle for 30 days increased (p less than 0.05) the incidence of ovarian luteal activity by 18% (Experiment 3). Shifts in lipid metabolic status modify reproductive potential in cattle, independently of dietary energy intake.

Androstenedione↗
PubMed1990

Suckling as a regulator of postpartum rebreeding in cattle: a review.

An extended and variable period of anovulation and anestrus occurs in suckled beef cows following parturition. This imposes both biological and economic constraints on the efficiency of beef production. A large body of knowledge has linked these phenomena to an attenuation of neuroendocrine signals that subserve gonadal function. During late gestation, high concentrations of placental estrogen inhibit the synthesis of LH, and pituitary stores of LH are depleted at parturition. Maximum pituitary stores of LH, releasable pools of LH and the ability of hypothalamic centers to respond to positive feedback effects of estradiol occur within 3 to 4 wk after calving in suckled cows. However, the requisite pattern of pulsatile LH secretion, which accompanies similar changes in nonsuckled cows within 2 to 3 wk after calving, occurs in only 30 to 50% of suckled animals. The period of acyclicity that continues in the remainder is exacerbated by poor body condition and may persist in some females for periods exceeding 100 d. Utilizing data from the cow, as well as other species, a model for suckling-induced inhibition of pulsatile LH release is proposed. The biological and economic impact of current and future techniques for controlling suckling-induced anestrus also is considered, including a conceptual analysis of nonbiological limitations.

Anestrus↗
PubMed1990

Benzodiazepine receptors and cerebrospinal fluid formation.

There is autoradiographic evidence that peripheral-type benzodiazepine ligands bind with high affinity to the membranes of choroid plexus tissue. In this study, the binding of a 4'-chloro analog of diazepam (Ro 5-4864) to rabbit choroid plexus and cerebral cortex was accomplished utilizing an in vitro radioactive assay method. A kinetic analysis of this binding revealed a relatively high affinity of this ligand (KD) for peripheral binding sites in plexus tissue (KD = 16.1 nM/mg protein). There was a 4.6-fold greater density of binding sites (total receptor density (Bmax) = 2.3 pmol/mg) in choroidal membrane as compared to cortical tissue (Bmax = 0.5 pmol/mg). In 40 rabbits in which a ventricular perfusion system was used, the rate of cerebrospinal fluid (CSF) formation was observed to decrease some 48% in the presence of 10(-4) M Ro 5-4864, although some inhibition of secretory activity was still noted at a CSF concentration of 10(-8) M. The choroid plexus tissue levels of adenosine 3',5'cyclic monophosphate (cAMP) and adenosine triphosphatase (ATPase) were not affected by 10(-4) M Ro 5-4864. The results of this study support the notion that the specific benzodiazepine peripheral binding sites in choroid plexus serve to modulate CSF formation. The mechanism of action is poorly understood but does not involve the transport ATPase system or the second messenger cAMP.

Adenosine Triphosphatases↗
PubMed1989

Patterns of tonic luteinizing hormone release and ovulation frequency in suckled anestrous beef cows following varying intervals of temporary weaning.

Thirty postpartum Brahman crossbred cows were utilized to determine the effects of varying intervals of temporary weaning on tonic LH secretion and ovulation. Cows were assigned randomly on day 17-21 postpartum to one of five groups: 1) Suckled Ad libitum, 2) 48-hr weaned, 3) 72-hr weaned, 4) 96-hr weaned, or 5) 144-hr weaned. The mean maximal rise in LH pulse frequency due to weaning occurred within 2 days and averaged 221 percent of time 0 values. The frequency of LH pulses was greater (P less than .06) in weaned than in suckled controls. This temporal increase was self-limiting, displaying an acute rise followed by a variable rate of decline in all groups. However, pulse frequency remained elevated relative to suckled controls for the longest period of time for weaning durations of 96 and 144 hr (P less than .10). In 48-hr and 72-hr weaned cows, a rapid reversal of the initial increase in LH pulse frequency was observed following calf return. A significant linear regression (y = 1.9 +/- .64x; P less than .03) described the increase in LH pulse frequency that occurred in cows which ovulated following weaning. Nonovulators were sensitive to calf return and responded by exhibiting a linear decline (y = 2.87 - .43x; P less than .04) in LH pulse frequency following this event. The amplitude of LH pulses increased (P less than .02) during the period after calf return in ovulators, but did not change in nonovulators. Percentage ovulating by day 10 increased (P less than .05) with increased weaning duration past 72 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1989

Variability of Doppler flow velocity and cerebral perfusion pressure is reduced in the neonate by sedation and neuromuscular blockade.

Doppler flow velocity (DFV) in the anterior cerebral artery was recorded every 12 h and cerebral perfusion pressure (CPP) continuously in 21 sick, ventilated preterm neonates for 48 h from shortly after birth. Ten received a neuromuscular blocker, seven were sedated with morphine infusions and five received neither of these treatments. Variability of DFV and CPP was assessed by the coefficient of variation (CV) and the autocorrelation function (ACF). Variability of both signals was lowest in the group treated by neuromuscular blockade (DFV CV 3, s.d. = 0.8; CPP CV 9, s.d. = 2.2; CPP ACF 37, s.d. = 19.2), intermediate in the group receiving sedation by morphine infusion (DFV CV 3.4, s.d. = 0.7; CPP CV 11, s.d. = 2.2; CPP ACF 31, s.d. = 21.6) and highest in the group receiving neither treatment (DFV CV 5, s.d. = 1.8; CPP CV 14, s.d. = 2.3; CPP ACF 27, s.d. = 16.7). Variability also increased with decreasing gestational age, suggesting that immature cerebrovascular regulatory mechanisms were present in the least mature neonates.

Birth Weight↗
PubMed1989

Modulation of luteal activity in postpartum beef cows through changes in dietary lipid.

Studies were conducted to evaluate the normal changes in lipid metabolism occurring in the suckled Brahman crossbred female during the postpartum period (Exp. 1) and to examine the function of induced corpora lutea (CL) in postpartum cows fed diets with normal (2.8%) lipid or elevated (8%) lipid content (Exp. 2). Multiparous and primiparous females (n = 20), maintained on pasture without energy or protein supplementation, were used in Exp. 1. A linear increase (P less than .001) in plasma lipid metabolites was observed between the 1st and 8th wk after calving, reaching a plateau of 221 +/- 18.3 and 74 +/- 3.4 mg/dl for total cholesterol and triglycerides, respectively. Seventy percent of all postpartum females exhibited luteal activity within 50 d (x = 34.7 d), and 59% of these animals exhibited short luteal phases (less than 12 d). In Exp. 2, primiparous and multiparous females (n = 32) were assigned to receive a control (n = 16) or high-lipid (HL) diet (n = 16; 30% whole cottonseed) between d 1 and d 38 after calving. The HL diet increased (P less than .001) total cholesterol and triglycerides 1.7- and 1.4-fold, respectively, relative to controls, and increased (P less than .05) the spontaneous occurrence of low-level progesterone elevations. Forty-eight-hour calf removal and gonadotropin-releasing hormone (GnRH; .22 mg/kg BW i.v.) were employed between d 21 and 26 after calving to induce ovulations. Mean concentrations of progesterone in the HL group were markedly higher (P less than .01) than in controls between d 5 and 8 of the induced cycle, and average lifespan of induced CL was approximately twice that of controls (P less than .01).

Animal Feed↗
PubMed1988

Breeding capacity, behavior and fertility of bulls with Brahman genetic influence during synchronized breeding of beef females.

The objective of this experiment was to evaluate the feasibility of using bulls of Brahman-derived breeds for synchronized breeding of females treated with Syncro-Mate-B (SMB). Suckled, postpartum cows (n = 261) and virgin heifers (n = 227) were given the standard SMB treatment. Calves were removed from cows for 48 h beginning at implant removal, and individual bulls were placed in pens with 15 to 20 females (x = 1:15.7 ) for 48 h beginning at implant removal. Bulls (n = 31) were 18 to 36 mo of age and had scored satisfactorily on a breeding soundness evaluation (BSE). The mean +/- SEM percentage of females in estrus, percentage of estrous females serviced and percentage of total females serviced were 77.2 +/- 2.4, 72.9 +/- 2.9 and 55.7 +/- 3%, respectively. Total average services per bull was 23.6 +/- 1.6; however, average number of individuals serviced was only 8.6 +/- 0.42. Mean +/- SEM percentage of females conceiving of those serviced, percentage conceiving of those in estrus and percentage conceiving of total females available were 57.3 +/- 3.7, 40.6 +/- 2.6 and 32.6 +/- 2.5%, respectively. Mean BSE scores of eight Simbrah bulls tested immediately before and 5 d after synchronized breeding did not differ (P > 0.05). These data suggest that the conception rate of Brahman-influenced bulls servicing SMB-synchronized cows is within the normal range. However, the total number of individual females serviced and the total pregnancy rate under the protocol employed was low. This occurred because all estrous females were not inseminated, and some bulls exhibited unpredicted low fertility.

Journal Article↗
PubMed1988

Fontanelle pressure and cerebral perfusion pressure: continuous measurement in neonates.

Fontanelle pressure (FP) and cerebral perfusion pressure (CPP) were measured continuously for the first 5 postnatal days in 21 preterm neonates. A new application device for use with the sensor of an intracranial pressure monitor allows accurate, continuous FP measurement. Accuracy of the technique was established by comparing results using the new device with 14-h continuous intraventricular pressure recordings from four infants before ventricular shunting. Agreement between the two techniques was satisfactory with the mean difference being 0.4 mm Hg. FP rose on each of the first 5 days after birth. CPP also rose over the 5 days but there were periods during suctioning of the endotracheal tube, crying, and vigorous activity when CPP was very low.

Blood Pressure↗
PubMed1988

Timing of preovulatory endocrine events, estrus and ovulation in Brahman x Hereford females synchronized with norgestomet and estradiol valerate.

The purpose of these studies was to investigate the pattern and timing of preovulatory endocrine events, estrus and ovulation in Brahman X Hereford (F1) heifers synchronized with norgestomet and estradiol valerate. In Exp. 1, 66 nulliparous and 191 primiparous Brahman X Hereford (F1) heifers were used to estimate the interval from norgestomet implant removal to onset of estrus. The mean interval from implant removal to onset of estrus was 29.8 +/- .5 h, with 80.9% exhibiting estrus within 48 h. Endocrine and reproductive characteristics were examined in detail during Exp. 2 with 37 primiparous heifers. Continuous observation for estrus, 6-h or 2-h blood sampling and ovarian palpation per rectum were employed. All animals were artificially inseminated 48 h after implant removal. Mean interval from implant removal to onset of estrus and to onset of the luteinizing hormone (LH) surge were closely related (r = .91; P less than .0001). Mean intervals from implant removal to ovulation, onset of estrus to ovulation and onset of LH surge to ovulation were 59.1 +/- 2.5 h, 23.3 +/- 1.4 h and 23.1 +/- 1.6 h, respectively. Approximately 73% of heifers exhibited estrus within 54 h after implant removal (optimal timing); conception rate was 59.3% in this subgroup. Conception rate of heifers that did not exhibit estrus within 54 h after implant removal or exhibited an LH surge later than 12 h after estrus (delayed timing) was 10%. Assessment of plasma estradiol-17 beta concentrations suggested that retarded selection and(or) maturation of the preovulatory follicle following implant removal delayed estrus and lowered conception in up to 28% of females timed-inseminated at 48 h.

Animals↗