Pedometer readings for estrous detection and as predictor for time of ovulation in dairy cattle

The objective of this study was to study the relationship between increase in number of steps measured by pedometers, behavioral estrous parameters and time of ovulation, in order to investigate whether the number of steps can be used as a tool for estrous detection and as a predictor for time of ovulation. In total, 63 ovulations were observed in 43 Holstein-Friesian cows. Different behavioral signs of estrus were observed at 3h intervals. Cows were equipped with pedometers, which stored number of steps in 2h time periods and pedometer estrus alerts were defined using different algorithms and thresholds. The percentage of behavioral estruses also detected by pedometers measurements, ranged between 51 and 87% for all estrous periods. When only estrous periods where taken into account in which more than one animal was in estrus, detection percentages increased up to 95%. Number of steps taken during the estrous period was higher when more animals were in behavioral estrus at the same time, and number of steps taken during the estrous period was also higher for primiparous cows compared to multiparous cows. Ovulation occurred 29.3+/-3.9h after onset of increased number of steps (ranging between 39 and 22 h) and 19.4+/-4.4h after the end of increased number of steps (ranging between 35 and 12h). The intervals were not influenced by the number of animals that were in estrus at the same time or by parity. In conclusion, pedometers can detect estrus accurately and appear to be a promising tool for prediction of ovulation and hence could be a tool for improving fertilization rates.     

Effects of intrauterine infection on the function of the corpora lutea formed after first postpartum ovulations in dairy cows

This study was carried out to determine the relationship between postpartum intrauterine infections, endocrine patterns and the function of corpora lutea formed following the first postpartum ovulations in dairy cows. Blood samples were collected daily starting from the day of parturition until 30 d after parturition or until the second postpartum estrus, whichever occurred first. Sera were assayed for progesterone (P(4)), prostaglandin F(2alpha) metabolite (PGFM), and luteinizing hormone (LH) concentrations. Palpations per rectum and real-time ultrasound scanning of the reproductive tracts were carried out in all cows once every 4 d for 1 mo, starting from Day 4 after parturition. In addition, endometrial swabs were collected aseptically from each cow once every 4 d during the first month postpartum. The swabs were cultured for aerobic and anaerobic bacteria. Twelve cows (60%) exhibited short estrous cycles (SC; 6 to 14 d long) following first postpartum ovulations. The mean preovulatory LH surges and LH patterns during the first postpartum cycles were similar in both groups, leading us to believe that lack of luteotrophic stimulation was not a factor in the occurrence of SC. Bacterial isolations were frequent in SC cows. The occurrence of moderate to heavy bacterial growth patterns and the repeated isolations of the similar organisms during postpartum suggests the persistence of uterine infections in SC cows. Increases in PGFM concentrations prior to luteolysis in SC cows were associated with moderate to heavy infection. Thus, postpartum uterine infections do not appear to affect ovulations, but prostaglandin (PGF(2alpha)) released in response to uterine infection may contribute to early demise of the corpus luteum formed after the first postpartum ovulation.     

Chronic stress, hormone profiles and estrus intensity in dairy cattle

The objectives of the present study were to determine if lameness, a model for a natural chronic stressor, affects hormone concentrations in milk prior to estrus and/or the subsequent expression of estrus in the postpartum period. Dairy cows>20 days postpartum were scored for lameness and observed for estrus intensity using a weighted scoring system (>100 points=estrus=Day 0). Increasing lameness score was not associated with daily profiles of milk progesterone (throughout Days -18 to 0), estradiol (Days -6 to 2) or cortisol (Days -18 to 2) around estrus, maximum estradiol values or estradiol concentrations on Day 0. However, post hoc pair wise comparisons revealed that prior to estrus, severely lame cows had lower maximum progesterone concentrations compared to nonlame cows (1.3+/-0.1, 1.2+/-0.2, 0.7+/-0.1 ng/ml milk; P=0.042). Furthermore, severely lame cows expressed behavioral estrus with lower intensity (284+/-128 points, n=9) compared to moderately lame (662+/-310 points, n=9) or nonlame animals (583+/-275 points, n=18; P=0.05 and P=0.02, respectively). Resting concentrations of cortisol (Days 20-80 postpartum) did not vary between days postpartum or lameness score. The incidence of behavioral estrus was not affected by increasing lameness score, as 54.2%, 56.2% and 50.0% periods with low progesterone were associated with spontaneous estrus expression, respectively. Concluding, in this biological model of chronic stress, lameness did not affect the incidence of behavioral estrus but did reduce estrus intensity once ovarian cyclicity had resumed after calving. This reduced intensity of estrus was associated with lower maximum progesterone values prior to estrus but not abnormal daily cortisol or estradiol values in milk.     

Effects of work and diet on progesterone secretion, short luteal phases and ovulations without estrus in postpartum F1 crossbred dairy cows

The effects of work and diet supplementation on progesterone secretion and on incidence of short luteal phases and ovulations without estrus was investigated in 40 postpartum F(1) crossbred dairy cows. These cows were allocated to 1 of 4 treatment groups: Group SPNW, supplement-nonworking; Group SPW, supplement-working; Group NSNW, nonsupplement-nonworking; and Group NSW, nonsupplement-working. After calving, working cows pulled sledges with a load of 300 to 450 Newtons(N); 4 hours per day 4 days per week, for a total of 100 days over a 1-year period. All cows were fed natural grass hay ad libitum while the supplemented cows were fed 3 kg of concentrate per head per day. The proportion of cows which showed behavioral estrus by 1 year post partum was 100, 100, 60 and 20% for Group SPNW, SPW, NSNW and NSW cows, respectively. Based on plasma progesterone concentrations, ovulation started 62 days earlier than onset of behavioral estrus. A total of 73 ovulations occurred by 1 year post partum. Forty-nine (67.1%) and 26 (32.9%) ovulations occurred in the supplemented and nonsupplemented cows while 33 (45.2%) and 40 (54.8%) ovulations occurred in the working and nonworking cows, respectively. Of the total ovulations, 26 (35.6%) were not associated with behavioral signs of estrus and occurred in 13 (32.5%) cows. The incidence of ovulation without estrus was higher (P<0.05) in working (42.4%) than in nonworking (30%) cows and in nonsupplemented (41.7%) than in supplemented (32.7%) cows. Short luteal phases occurred in 32.5% of the cows before the establishment of normal estrous cycles. In working cows, diet supplementation off-set the negative effect of work on the onset of estrus and conception. However, a relatively higher number of cows in Group SPW had ovulations without estrus before a normal estrous cycle was established. The incidence of short luteal phases or ovulations without estrus did not influence the pregnancy rate in subsequent normal estrus periods. In conclusion, in the supplemented cows, work did not influence the proportion of cows showing estrus and conceiving, but it significantly delayed the postpartum anestrus interval. In the nonsupplemented cows, reproductive activity was impaired in both working and nonworking cows, but was pronounced in working cows. However, once pregnancy was established there was no effect of work on the maintenance of pregnancy. Our study shows that with appropriate feeding regimens lactating crossbred cows could be used for draught purposes without any detrimental effects on fertility, but calving intervals would be extended. Finally, the physiological mechanisms involved in anestrus and ovulations without estrus and the significance of such phenomena in affecting postpartum reproductive performance and fertility in working cows require further investigation.     

Factors affecting walking activity at estrus during postpartum period and subsequent fertility in dairy cows

The postpartum period is critical for efficient reproduction, and certain features of the normal estrus cycle during this period have been associated with subsequent reproductive performance. The objectives of the present investigation were to evaluate the effects of environmental, production, and reproductive factors on walking activity at estrus as determined using pedometers during the first 50 days in milk (DIM) (study 1). In a second study, we tried to establish whether pedometer measurements recorded during this period could be used to predict subsequent fertility by considering the number of cows becoming pregnant before 90 DIM. We analyzed data derived from 995 parturitions in a single herd. Detection of estrus was performed using a pedometer system. Variables were screened for associations with walking activity by analysis of variance (ANOVA) through generalized linear model procedures (PROC GLM). Increased milk production and parity, and a mean relative humidity (RH) higher than 95% were associated with lower pedometer measurements. A higher number of animals simultaneously in estrus rendered higher pedometer readings. No significant effects of the year, season, DIM, number of previous estruses, and climatic data other than high mean RH were observed. Relationships between pedometer measurements and other variables recorded during the first 50 days postpartum, and subsequent fertility were assessed by applying logistic regression models. We detected no significant effects of year, milk production, season, and mean activity increase at estrus on high fertility. The likelihood of pregnancy before 90 DIM decreased for each additional lactation and for cows in anestrus between days 0 and 50 postpartum. However, pedometer readings during the first 50 days postpartum were unable to accurately predict subsequent fertility.     

Comparison of three devices for the automated detection of estrus in dairy cows

Considerable technological advances have been made in the automated detection of estrus in dairy cattle, but few studies have evaluated their relative performance on the same animals or assessed cow-related factors that affect their performance. Our objective was to assess the performance and reliability of three devices commercially available in France for cow estrus detection. The devices were a pedometer (PM; Afitag) and two activity meters (AM1; Heatime-RuminAct, and AM2; HeatPhone). Two algorithms were tested for AM2. We fitted 63 lactating Holstein cows with the three detectors from calving to 90 days after calving. The onset and pattern of cyclicity were monitored from 7 to 90 days postpartum measuring progesterone concentration in milk twice weekly. A total of 211 ovulations were identified. Cyclicity was classified as normal in 60% of cows (38/63). Calculated over the operating period of all the devices (179 periods of estrus), the sensitivities and positive predictive values were, respectively, 71% and 71% for PM, 62% and 84% for AM1, 61% and 67% for the first algorithm of AM2, and 62% and 87% for the second algorithm of AM2. Both activity meters had a lower sensitivity but a higher positive predictive value than the PM (P < 0.05). For all devices, the performance in estrus detection was much poorer at the first postpartum ovulation than at subsequent ovulations (P < 0.05). Lactation rank and milk production affected some devices (P < 0.05). These devices could be used to reinforce visual observations, especially after 50 days postpartum, the minimum recommended delay to insemination. However, their full benefit remains to be verified in different farming systems and taking into account the specific objectives of the dairy farmer.     

Effects of presynchronization during the preservice period on subsequent ovarian activity in lactating dairy cows

Among the strategies aimed at overcoming difficulties in estrus detection in dairy herds, presynchronization with two PGF2alpha treatments 14 days apart before a timed AI protocol has been related to a significant increase in pregnancy rates. The aim of the present study was to evaluate the effects of presynchronization during the preservice period on subsequent ovarian activity in clinically normal lactating dairy cows. A second objective was to evaluate the incidence of reproductive disorders on Day 50 postpartum. Depending on the chronological order of parturition, cows were alternately assigned to a control (n=102) or treatment (n=101) group. Animals in the treatment group were administered two cloprostenol treatments 14 days apart, beginning on Day 22 postpartum. The reproductive tract of each animal was examined ultrasonographically on Days 43 and 50 postpartum to monitor ovarian structures and uterine contents. Blood samples were collected on Day 50 for progesterone determination. Cows were inspected for signs of estrus between Days 50 and 71 postpartum and were then inseminated. Follicular persistence rates were similar in the presynchronized (14.9%) and control (13.7%) groups. Cows in the presynchronized group showed a lower metritis-pyometra rate (0% < 3.9%; P=0.045); a lower ovarian cyst rate (3% < 10.8%; P=0.03); a higher luteal activity rate (progesterone concentrations>/=1ng/ml) on Day 50 postpartum (76.2% > 52.9%; P=0.0005); a higher estrus detection rate (73.3% > 47.1%; P<0.0001); a higher ovulation rate (72% > 44%; P<0.0001) and a higher pregnancy rate (29.7% > 15.7%; P=0.02) than controls. Our results indicate that presynchronization during the preservice period reduces the incidence of ovarian cysts and metritis-pyometra determined on Day 50, and improves ovarian activity from Days 50 to 71 postpartum along with pregnancy rates in clinically normal lactating dairy cows.     

Factors affecting postpartum ovarian activity in crossbred primiparous tropical heifers

The relationship between postpartum ovarian activity and a total of 9 variables was studied in a dry tropical environment. Primiparous cows (n=61) that had shown no peripartum abnormalities, and were not suckled but milked twice daily, were used in the study. Independent variables included crossbreeding, sex of the calf, season, body condition, weight of cow at calving, age of dam at calving, uterine involution, calf weight and accumulated milk yield. Diet was a controlled variable. Dependent variables were first estrus postpartum and/or first milk progesterone elevation prior to first estrus. A bull fitted with a chin ball marker was used to detect first estrus postpartum, while ovarian structures were palpated per rectum once a week. Progesterone was measured by RIA in milk samples collected twice weekly. First postpartum estrus was detected at 56 +/- 32 days postpartum, a first milk progesterone elevation was observed in 50.8% of cows at 42 +/- 27 days. Cows calving in the dry season had longer intervals and those who calved males had shorter postpartum intervals. Accumulated milk yield affected both intervals significatly (p < 0.01). Weight, age and uterine involution were asociated with first milk progesterone elevation, while crossbreeding, weight at calving and weight postpartum change were associated with the dependent variables.     

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.     

Postpartum reproductive management of dairy cows in a large Florida dairy herd

Dairy cows (n = 199) were assigned randomly at Day 14 post partum to a control group or a programmed reproductive treatment group (PRT). Cows in the PRT group received 8 ug of GnRH on Days 14 and 50 post partum and 25 mg of PGF2alpha injected on Days 21, 34 and 57 post partum. Cows in the PRT group had a greater frequency of progesterone (P4) concentrations > 1 ng/ml (50% vs 30%; P < 0.01). Frequency of cows having P4 > 1 ng/ml at both Days 21 and 34 post partum was greater in the PRT group than in the control group (39% vs 20%; P < 0.01). Accumulation of days with a palpable cystic ovary was lower in the PRT than the control group (11.4% vs 6.5%; P < 0.05). The frequency of anestrous cows through Day 57 post partum was not different between the 2 groups. Cows that were anestrous had a lower body condition score throughout the postpartum period than the cyclic cows (2.7 vs <3.0; P < 0.01). Conception rate to first service, conception rate to all services, services per conception and days open were not different between the groups. Intensity of estrus detection was low for the study based on a low estrus detection rate (42%) and a low palpation pregnancy rate index (below 68%) throughout the study period. Accuracy of estrus detection was low based on the distribution of normal interestrus intervals for the study (19 to 23 d; 13.5%). It is concluded that programmed reproductive treatments during the postpartum period are functionally effective relative to altered ovarian activity; however, potential advantages to such a system are not evident without good estrus detection practices in a large commercial herd.     

Superovulatory responses in dairy cows following ovulation of the dominant follicle of the first wave

In the present study we investigated the effect of hCG administration on Day 7 (Day 0 = day of standing estrus) to ovulate the dominant follicle of the first wave and the associated increase in progesterone concentration on subsequent superovulatory response in dairy cows. Twenty cyclic lactating cows were allocated at random to 2 groups: control (n = 10) and hCG-treated (n = 10). The ovaries of each cow were scanned using an ultrasound scanner on Day 7, to confirm the presence of the dominant follicle and thereafter every other day until embryo recovery. All cows received a total dose of 400 mg Folltropin-V in decreasing amounts for 5 days (Days 9 to 13) and 35 mg PGF(2alpha) on Day 12. In addition, the treated cows received 1000 IU hCG on Day 7. All cows were inseminated twice during estrus, and the embryos were collected 7 days later by a nonsurgical procedure. Blood smaples were taken at different times of the treatment period for progesterone determination. All cows possessed a dominant follicle at Day 7, and all but one of the hCG-treated cows ovulated the dominant follicle and formed an accessory corpus luteum. Plasma progesterone concentrations were significantly higher (P<0.01) in hCG-treated cows than control cows on the first day of Folltropin treatment and on the day of PGF(2alpha) injection. The mean number of follicles at estrus, the number of ovulations, the total number of embryos and the number of transferable embryos were not different (P>0.05) between control and hCG-treated cows.     

Absorbable deslorelin implants (Ovuplant) prolong postpartum anestrus in early ovulating dairy cows

Two experiments were conducted to investigate the use of a bioabsorbable implant of the GnRH agonist deslorelin to temporarily delay the resumption of postpartum ovulatory cycles in Holstein cows. In Experiment 1, recently calved cows were paired and received either a single implant (Ovuplant); Peptech Animal Health, Sydney, NSW, Australia) within 48 h of parturition (OVP; n=17), or remained as untreated controls (CON; n=17). Blood samples were collected for plasma progesterone assay three times weekly for 6 weeks to profile the pattern of resumption of ovulatory cycles. In Experiment 2, there were 15 CON and 15 OVP cows initially treated as for Experiment 1 as well as 15 OVP+SYNCH cows. Each cow in the CON and OVP+SYNCH groups received a progesterone vaginal insert (CIDR); Genetics Australia, Bacchus Marsh, Vic., Australia) for 7 days at 23 days postpartum (23 dpp) to synchronise estrus in cycling animals or to induce an ovulation with estrus in anestrus animals. Blood samples were collected weekly until removal of the CIDR insert, and then twice weekly until 56 dpp to monitor plasma P4 for retrospective determination of ovulation. Milk yield was monitored by twice daily electronic volume measurements and milk composition with once weekly milk composition analysis.In Experiment 1, CON cows began ovulating from 9 dpp; 15 of 17 had ovulated by the end of blood sampling at 42 dpp. None of the OVP cows ovulated until at least 24 dpp, and only 6 of 17 had ovulated by 42 dpp. The average day of first ovulation was extended from 22.4+/-2.7 dpp to 39.3+/-2.7 dpp (P<0.05). In Experiment 2, ovulation had occurred in 8 of 15 CON cows at the time of CIDR insertion (23 dpp), 0 of 15 OVP cows and 1 of 15 OVP+SYNCH cows. By 40 dpp (or 10 days following removal of the CIDR insert) every CON cow (15/15) had ovulated, but only 2 of 15 OVP+SYNCH cows and 1 of 15 OVP cows. None of these effects of treatment was associated with any changes in milk yield or composition in either experiment.In conclusion, inserting a bioabsorbable implant of deslorelin within 48 postpartum extended the interval to first ovulation to at least 24 dpp in 46 of 47 cows. Recovery periods were highly variable. This variability was not reduced by using a form of intravaginal progesterone supplementation that did produce a synchronised estrus with ovulation in anestrus animals that had not been treated with deslorelin.     

Evidence for a role of intrauterine infections in the pathogenesis of cystic ovaries in postpartum dairy cows

Patterns of uterine microbial recovery and serum concentrations of prostaglandin F(2alpha) metabolite (PGFM), cortisol, luteinizing hormone (LH) and progesterone (P4) were determined in normal postpartum dairy cows (n = 12) and in postpartum cows that developed cystic ovaries (n = 12). Palpation per rectum, ultrasound examinations of the reproductive tract and endometrial swab harvest were carried out once every 4 d during the first month postpartum. Daily blood samples were collected during the first 30 d postpartum and every other day until Day 60 postpartum for hormone assay. Bacterial growth densities of cultures of uterine swabs were high in cows that developed cystic ovaries. Cysts were detected between Day 8 and 16 postpartum and persisted for a period of 18.6 +/- 9.9 d (range 8 to 41 d), followed by spontaneous regression and ovulations. Serum PGFM and cortisol were elevated for several days prior to detection of cystic ovaries but not prior to first postpartum ovulations. Serum LH concentrations in cystic cows were at basal concentrations prior to discovery of cysts. The results suggest that postpartum intrauterine infections may provoke increased secretion of prostaglandin F(2alpha) and cortisol associated with the formation of cystic ovaries in dairy cows.     

Progesterone profiles in postpartum Holstein dairy cows as an aid in the study of retained fetal membranes, pyometra and anestrus

This study was carried out to investigate the utility of enzymeimmunoassay (EIA) - derived progesterone profiles in the investigation of postpartum reproductive abnormalities and the effect of their use on reproductive performance in Holstein cows. Whole milk samples, collected twice weekly from parturition until confirmation of pregnancy or removal from the herd, were assayed for progesterone (P4) concentration using a commercially available microtitre plate EIA. The sensitivity, specificity, precision and accuracy were satisfactory to distinguish cyclic changes of P4 reflecting ovarian activity. The P4 profiles indicated that retained fetal membranes and anestrus were associated with increased mean intervals to first ovulation and first estrus (P < 0.05). The first luteal phase of cows with pyometra was prolonged compared with that of normal herdmates (P < 0.05). Anestrus cows had an increased number of ovulations before first service and before pregnancy (3.9 and 5.9) in comparison with normal herdmates (2.1 and 3.5; P < 0.05). Calving to pregnancy interval was increased above normal (74.8) for pyometra (125.0) and anestrus (152.7) (P < 0.05). Pregnancy rate for anestrus cows (82%) was lower than for normal cows (100%) and more anestrous cows were culled (27%) than normal cows (5%) (P < 0.5). The P4 profiles indicated that the major problem in the herd studied, anestrus (32% incidence rate), was most likely due to the failure to observe estrus rather than acyclicity.     

Reproductive performance of postpartum dairy cows under a highly intervenient breeding program involving timed insemination and combinations of GnRH, prostaglandin F2alpha and human chorionic gonadotropin

Lactating Holstein cows (n=288) were grouped as pairs at parturition and randomly assigned to two treatments (control, C vs intervenient treatment, T). The reproductive management of the Group C cows (n=130) consisted of the intramuscular administration of 500 microg PGF2alpha analogue (PG) on Days 28 and 63 postpartum and breeding on the basis of estrus signs with the a.m.-p.m. rule after Day 63. Cows that were not bred by 77 d postpartum received another injection of PG and were bred at estrus or 84 h after PG treatment. Pregnancy diagnoses were perfomed by palpation of the uterus per rectum 42 to 48 d after AI. Cows in the T group (n=139) received intramuscular injections of 100 microg GnRH 14 d and PG 28 d after calving. On Day 56 postpartum, cows were given a second dose of GnRH followed by PG on Day 63 postpartum and a third GnRH injection 48 h after PG (OvSynch). Cows were inseminated at a fixed time (22+/-1 h) after GnRH. Five days after the fixed-time insemination cows were given 1500 IU hCG i.m.. Group C and T cows that returned to service or were diagnosed as non-pregnant continued to receive PG at intervals of 14 d with breeding at estrus or 84 h after the second PGF2alpha dose. A sustained increase in milk progesterone concentration was observed in 59.0% of T cows after GnRH administration on Day 14. A similar rise in milk progesterone concentrations was observed in 53.8% of C cows. The PG on Day 28 induced luteolysis more in Group T cows (53.2%) than in Group C cows (36.9%). The PG on Day 63 reduced milk progesterone concentrations to basal levels in 50.7% of T and 49.2% of Group C animals. The first service pregnancy rates (T, 40.3% vs C, 36.2%) and the overall pregnancy rates (all services, T, 83.5% vs C, 86.9%) were not different between the two groups. The two treatments did not differ in the interval from first service to pregnancy, calving to pregnancy or in calving interval, number of services per pregnancy or culling rates.     

Plasma progesterone profiles and fertility status of anestrus Zebu cattle treated with norgestomet-estradiol-eCG regimen

Zebu cattle are notorious for poor fertility characterized by late maturity and long intercalving intervals attributed to a variety of factors, including genetic, nutritional and climatic. The aim of the present investigation, therefore, was to induce fertile estrus in acyclic pubertal heifers and postpartum anestrous Zebu cows by hormonal intervention. Pubertal Hariana and Sahiwal anestrous heifers (n=51) and postpartum cows (n=55) were either assigned a placebo (controls, N=6 for each breed and parity) or treated with 10-d norgestomet (3 mg) subcutaneous ear implants, with an initial injection of 3 mg, im norgestomet + 5 mg estradiol valerate, followed by 500 IU eCG at implant withdrawal (NOR-treated groups). Jugular venous plasma samples were obtained from a total of 28 animals (controls : 4 heifers and 4 cows; NOR-treated : 12 heifers and 8 cows) on Days 0 (implant insertion), 3, 7, 9 and Day 10 (implant withdrawal), every 12 h on Days 11 and 12, and then once daily on Days 17, 24 and 31. All the samples were assayed for progesterone. Almost all (97%) heifers and 81% cows were induced to estrus, the majority (92% heifers and 79% cows) within 120 h of implant removal. Synchrony of the induced estrus was better in cows, but interval to estrus and estrus duration were significantly longer in heifers (P<0.05). Post-treatment fertility, based on Day 28 nonretum rate, first service, and overall conception rates, was better in heifers (78.9, 60.5 and 73.7%, respectively) than cows (77.1, 48.6 and 62.9%, respectively), but the differences were significant only for the overall pregnancy rate (71.8% for heifers and 51.2% for cows; P<0.05). Low pre-treatment plasma progesterone values (<0.5ng/mL) were consistent with ovarian inactivity, confirming the true anestrus status of experimental animals. Controls failed to exhibit estrus and maintained low progesterone concentrations throughout the study. In treated animals, high progesterone values from Day 17 onwards suggested ovulatory estrus. These early luteal phase progesterone concentrations in nonpregnant (P=0.06) and nonpregnant, nonretum (P<0.05) animals were low in comparison with those of pregnant animals. Good fertility resulting from breeding according to estrus, inspite of variable intervals to estrus and estrus duration, advocates its advantage over fixed-time insemination in norgestomet-treated anestrous Zebu cattle.     

Effect of days postpartum and exogenous GnRH on reproductive hormone and ovarian changes in postpartum suckled beef cows

Two experiments were conducted to determine the effect of days postpartum and exogenous gonadotropin releasing hormone (GnRH) on reproductive hormone and ovarian changes in postpartum suckled beef cows. In experiment 1, eight suckled cows were bled at .5 hour intervals for 4 hours on days 7, 14, 21 and 28 postpartum. Although mean concentrations of plasma luteinizing hormone (LH) were positively correlated with days postpartum, mean concentrations did not differ. The mean maximum change and the variance of plasma LH were low on days 7, 14, 21 and 28 postpartum. Although the number of cows with an ovarian follicle and follicular size increased with days postpartum, mean concentrations of estradiol-17beta did not change. The interval from parturition to the first detected ovarian follicle and the first postpartum estrus was 17.5 +/- 2.6 days and 36.0 +/- 2.2 days, respectively. An elevation in plasma progesterone was detected about one week prior to the first postpartum estrus in 6 of the eight cows in the absence of corpora lutea. In experiment 2, gonadotropin releasing hormone (GnRH) induced ovulation in 4 of the 8 cows treated on day 27, 28 or 29 postpartum whereas none of the 8 saline treated cows ovulated to treatment. The interval from parturition to first estrus and conception were similar for both groups (P >.10).     

Milk progesterone profiles in crossbred Brown Swiss x Nellore cattle following natural service

Ovarian activity and estrous behaviour were monitored through milk progesterone determinations and twice daily visual observations in 70 crossbred Brown Swiss x Nellore cows following natural service. Whole milk samples were collected on the day of estrus (Day 1), Day 11, and every 5 d thereafter until the next estrus or pregnancy confirmation. Seventy percent of the cows behaved as expected, i.e. they showed a 19-to 25-d interval between estrus and the next ovulation, or they became pregnant. Estrous cycles of regular length (18 to 24 d) were found in 54% of the cases. Prolonged luteal phases (interval from estrus to next ovulation > 28 d) were found in 15.7% of cows. Short estrous cycles (interestrous interval < 18 d) were found in 7.1% of the cases. Periods of acyclicity (basal progesterone levels for periods >/= 15 d) were found in 5.8% of the cases, and one cow exhibited estrus while pregnant and had a high progesterone concentration. Cows with a prolonged luteal phase and those with a short estrous cycle had an interval between ovulations of 35.0 +/- 6.7 d (x +/- SD) and 9.6 +/- 3.1 d, respectively. Signs of estrus were not detected in 33.3% of the ovulations confirmed by progesterone determinations. Low conception rates, failures in estrus detection and a high frequency of abnormal postbreeding luteal phases were found.     

The use of heat detection aids in estrus synchronization programs

The use of tailhead paste and chin-ball markers for estrus detection in beef cows following estrus synchronization was evaluated. The estrous cycles of 85 cows were synchronized with a prostaglandin analogue in a two-injection program. At the time of the second injection, each cow's tailhead was painted with an estrus detection paste and the cows were placed in pastures with four intact bulls with chin-ball markers. Blood samples for plasma progesterone assays were obtained at the time of each injection and daily for five days following the second injection. Based on progesterone values, tailhead paste was incorrect 27% of the time in indicating estrus and chin-ball markers were incorrect 24% of the time. Detecting particular cows in estrus in groups of synchronized cows is difficult even with estrus detection aids.     

Effects of Calf Removal at Parturition on Postpartum Ovarian Activity in Zebu (Bos indicus) Cows in the Humid Tropics

To assess endocrine and morphological responses of ovaries to total weaning at parturition, 6 Zebu (Bos indicus) cows 5 years or older were investigated. Following parturition, blood samples were collected daily during the first month and twice weekly thereafter until day 60 to determine concentrations of progesterone (P4) and prostaglandin F2α metabolite. It took between 25 to 32 days to complete uterine involution.The prostaglandin metabolite remained elevated for a mean period of 14.2 days (range, 4-21) postpartum. Five of the animals resumed cyclicity with a short estrous cycle starting between days 7 to 34 and lasting between 7 and 14 days. No estrous behavior was recorded prior to the short estrous cycles, but subsequent normal-length estrous cycles were all preceded by signs of estrus. In the 1 animal that resumed cyclicity with an estrous cycle of normal length on day 37 (length 20 days), the cycle was preceded by estrous behavior. Progesterone concentrations reached a mean maximum of 4.8 nmol liter−1 during the short estrous cycles, and prostaglandin metabolite concentrations peaked while P4 concentrations were decreasing. P4 concentrations reached a mean maximum of 12.2 nmol liter−1 during the estrous cycles of normal length. The interval from parturition to the first estrous cycle of normal length varied between 16 and 48 days, and the length of the cycle was 18 to 22 days. Starting 2 days postpartum, ovaries from 5 of the cows were scanned by ultrasonography every second day until day 30 postpartum. Medium-sized follicles were detected between days 4 to 7 postpartum in 4 of the scanned cows that later had short estrous cycles. The time between parturition and the appearance of the first dominant follicle was 7.6 days (range 6-10 days). The interval between parturition and the appearance of the first ovulatory-sized follicle was 10.2 days (range 8-13 days). In 3 of the scanned cows this ovulatory-sized follicle ovulated. We conclude that cyclic ovarian activity in Zebu cows can start early in the postpartum period in the absence of offspring, and that short luteal phases, not preceded by estrous behavior, may play an important role in establishing normal postpartum ovarian activity.