Effects of diets containing gossypol on ovarian histology, function and fertility in prepubertal beef heifers

Forty-five crossbred beef heifers (weight = 268.3 +/- 5.7 kg) were used to determine the effects of dietary gossypol on ovarian morphology, erythrocyte fragility and fertility. Heifers were randomly assigned to 1 of 3 isonitrogenous dietary treatments. The diet consisted of rice mill feed and milo supplemented with soybean meal (n = 13; control), cottonseed meal (n = 16; low supplementation) which supplied 6.1 g free gossypol animal(-1) day(-1), or whole cottonseed (n = 16; high supplementation) which supplied 13.7 g free gossypol animal(-1) day(-1). The heifers were group-fed each diet for 64 days and were maintained on similar but separate fescue pastures overseeded with wheat. After 64 days, 4 heifers from each diet were confined and fed their respective diets. On Day 10 following estrus, each animal was unilaterally ovariectomized, and the ovary containing the corpus luteum was removed. The remaining ovary was removed 6 to 12 hours after detection of estrus in the next cycle. Erythrocyte fragility increased (P < 0.02) in heifers receiving gossypol compared with that of the controls. Cyclicity in the heifers was 81.3, 68.8 and 38.4% for high, low and control diets, respectively, at the end of the 64-day treatment period. First service conception rate, as determined by palpation per rectum, was similar among treatments (58.3, 33.3, 33.3% for high, low and control groups, respectively). Weight gain increased (P < 0.03) in control heifers compared with that of heifers receiving gossypol. Gross ovarian morphology and histology were similar for all heifers. Although gossypol produced mild toxicosis in heifers, no adverse reproductive effects could be detected from gossypol intake.     

Mechanisms linking under-nutrition and ovarian function in beef heifers

Prolonged reduction in energy intake in beef heifers has been reported to suppress ovulation but the mechanisms involved are poorly understood. The objective of this study was to examine whether changes in the pattern of LH secretion following each of three different tests predicted the functional state of the hypothalamo-pituitary-ovarian (H-P-O) axis. Test 1 examined the ratio of LH secretion during the 1h before and 2h after naloxone (NAL) administration. The other two tests assessed the LH surge following an exogenous oestradiol positive feedback signal (Test 2) or exogenous progesterone priming (Test 3). In phases 1 and 3, each of 8 weeks duration, the heifers were fed 100% of their maintenance energy requirements. In phase 2, of 9 weeks duration, they were fed 50% of their maintenance energy requirements. Oestrus was induced in all heifers by PG administration at the start of the experiment.Heifers were administered a naloxone challenge of 50, 100, 200 or 400mg naloxone hydrochloride i.v. (one dose per heifer) during the mid-luteal period of phase 1 and all four naloxone treated heifers received 400mg naloxone hydrochloride at the end of phases 2 and 3. Doses of 10, 20 or 40 mg oestradiol benzoate (EB) i.m. were each administered to two of the remaining heifers during the mid-luteal period of phase 1. One heifer on each dose of oestradiol benzoate in phase 1 had the same dose administered at the end of phases 2 and 3. The progesterone challenge was administered to three heifers by insertion of a PRID for 12 days starting in the middle of phase 2.In Test 1, the ratio of LH secretion before and after naloxone administration in phase 1 was 1:1 (50mg), 1:4 (100mg), 1:4 (200mg) and 1:9 (400mg) (50mg versus 100mg and 100mg versus 200mg doses, P<0.05); 50mg versus 400mg doses, P<0.001). In phase 2, this ratio was 1:1 and there was no response to 400mg dose of naloxone in any of the four heifers. In phase 3, the ratio depended on the ovarian activity in the heifer and ranged from 1:1 to 1:4 (P<0.05). In Test 3, a positive oestradiol feedback signal was detected in cyclic heifers in phases 1-3 but not in the acyclic heifer in phase 2. Heifers challenge with exogenous progesterone did not have oestradiol or LH values above threshold levels.We conclude that all three tests successfully predicted the functional state of the hypothalamo-pituitary-ovarian axis. In nutritionally undernourished beef heifers onset of ovarian acyclicity is either preceded or accompanied by the loss of a positive feedback signal (Test 2) and progesterone priming ability (Test 3), and that a plasma LH ratio of > or =1:2 following naloxone challenge (Test 1) is a sign of recovery of the functional state of the hypothalamo-pituitary-ovarian axis.     

Beta-carotene does not influence fertility in beef heifers

Eighty-four 18-month-old crossbred beef heifers, 3 to 4 months pregnant, were assigned by stratified randomization to either a high or low (control) beta-carotene (B-car) diet to determine the effect of long-term supplementation of B-car on reproductive performance. The heifers were followed through pregnancy, calving and subsequent breeding. The basal diet consisted of barley, canola meal and barley straw. Heifers supplemented by B-car received 625 mg B-car per day in the concentrate. Vitamin A and D complex injections were given monthly to all heifers. Heifers were bred by artificial insemination after Day 60 postpartum. Throughout the study heifers fed the B-car supplement had higher levels of B-car in plasma (> 300 ug/dl) (P < 0.01) than the heifers fed the control diet (< 50 ug/dl). Vitamin A status was satisfactory in all heifers throughout the study. Birth weight of calves, weight gain, and incidence of mortality were not influenced by B-car. For the control and B-car treatments, days postpartum to first normal luteal phase were 67.5 and 62.6 days; days postpartum to first detected estrus were 70.1 and 65.3, and services per conception were 1.24 and 1.29, respectively. Long-term supplementation of B-car increased prepartum plasma progesterone but had no effect on postpartum fertility.     

Growth and ovarian function of weanling and yearling beef heifers grazing endophyte-infected tall fescue pastures

Growth and ovarian function of crossbred beef heifers grazing low and high endophyte-infected tall fescue pastures were studied for 2 successive years. In April of each year, 20 weanling and 20 yearling heifers were included in the study. All heifers were weighed at 28-d intervals for 112 d. Blood samples were collected from each heifer on Day 0 and +7 of each of five 28-d periods and analyzed for progesterone concentration. Heifers with progesterone concentrations >/= 1.5 ng/ml on either or both Day 0 and +7 were classified as having normal cyclic ovaries. High endophyte-infected fescue pastures adversely altered the ovarian activity (P < 0.05) of weanling heifers in both years. In each trial, average weight gains were lower (P < 0.05) in yearling and weanling heifers grazing the high endophyte-infected pastures than in heifers grazing low endophyte-infected pastures. In 1992, heifers were synchronized with PGF(2alpha) administered on Days 101 and 112. Blood samples were collected on 0, 4, 8 and 12 d after the second PGF(2alpha) injection for progesterone analysis. Heifers grazing high and low endophyte-infected pastures were pastured separately with 4 bulls each and were given heatmount detectors. At 96 h, less estrus activity was observed (P < 0.10; power=0.63) in weanling heifers grazing the high vs. low endophyte pastures although pregnancy rates were similar for all groups. Progesterone concentrations suggested that weanling heifers on the high endophyte pastures had a higher incidence of luteal dysfunction after PGF(2alpha) synchronization. In summary, high endophyte-infected pastures decreased growth in both weanling and yearling heifers, ovarian activity and luteal function were adversely altered in weanling heifers with subsequent decreased estrus response to estrus synchronization.     

Incidence of delayed ovulation in Holstein heifers and its effects on fertility and early luteal function

In the first of 3 experiments 134 first-service and 108 repeat-breeder Holstein heifers were palpated at 12-hour intervals starting 24 hours after insemination to compare the incidence of delayed ovulation in the 2 groups. Delayed ovulation was defined as failure to ovulate within the first 24 hours after insemination. Ovulation occurred within 24 hours post insemination in 92.1% of the animals and was delayed in 7.9% of the cases, with no differences between first-service and repeat-breeder heifers, indicating that the subfertility of the repeat-breeder animals was not due to delayed ovulation. The duration of the delay was at most 12 hours since all the animals had ovulated by 36 hours post insemination. Conception rate of the 19 animals with delayed ovulation (42.1%) was not different (P>0.05) from that of the 223 heifers that ovulated on time (44.8%). In a second experiment, no differences were detected between 15 heifers with delayed ovulation and 15 animals that ovulated on time with respect to their progesterone concentrations during the first 8 days post insemination, indicating that delayed ovulation is not associated with delayed luteinization or subnormal early luteal function. In the third experiment, the conception rate of 126 repeat-breeder heifers that were treated with hCG at the time of insemination was 26.7%; the conception rate of 101 repeat-breeder heifers that were inseminated twice, at 12 and 24 hours after the onset of estrus, was 34.6%; and the conception rate of 105 repeat-breeder heifers which were not treated with hCG and which were inseminated only once was 30.5% (P>0.05) It is concluded that delayed ovulation is not an important cause of infertility and does not constitute an important component of the repeat-breeding syndrome in Holstein heifers.     

The effect of exogenous acth and pen-confinement on estrous cycle length, plasma steroid levels and ovarian function of beef heifers

Each of 24 pasture-reared crossbred beef heifers were herded from a large pasture on day 14 of the estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field ACTH (FA), Pen Control (PC) and Pen ACTH (PA). Field groups were maintained in a small field, and pen groups were confined in a pen in a pole barn. ACTH groups received 200 IU of ACTH IM daily for days 17 through 21 of the cycle and control groups received only the gelatin carrier IM on the same cycle days. Average cycle lengths for FA and PA heifers were 25 and 24.3 days with an average period from plasma progesterone decline below 1 ng/ml to estrus of 5.5 days. During the ACTH injection period, follicular growth was suppressed and the proestrus plasma estrogen rise was delayed. Average cycle lengths for FC and PC heifers were 20.8 and 22.8 days respectively. All control group heifers exhibited estrus within 2 days of the plasma progesterone decline below 1 ng/ml. In addition, pen confinement heifers showed a trend for extended luteal function and consequent extended estrous cycle length.     

Effects of monensin and forage:concentrate ratio on feed intake, endocrine, and ovarian function in beef heifers

Several reports have suggested that a treatment before in vitro maturation might improve oocyte competence and increase its developmental potential. Therefore, the objectives of the present study were to establish the kinetics of IVM in Zebu oocytes, to assess the effect of 6-dimethylaminopurine (6-DMAP), a phosphorylation inhibitor, on meiotic resumption, and to verify the developmental potential of the blocked oocytes after removal of the inhibitory conditions. To establish the kinetics of in vitro maturation 1422 oocytes were obtained from Nellore cows ovaries and matured in presence and absence of gonadotropins. Samples of oocytes were taken from culture at 0, 6, 9, 12, 15, 18, 21 and 24h, and the oocytes were fixed, stained and evaluated for nuclear morphology. Germinal vesicle break down (GVBD) occurred between 6 and 12h of culture in both groups. By 21h the majority of the oocytes had reached metaphase II in presence (71%) and absence (62%) of gonadotropins. In order to examine the inhibitory effect of 6-DMAP, 585 oocytes were cultured for 12, 18 and 24h in the presence or absence of 2mM of 6-DMAP. At each time point the oocytes were evaluated for nuclear morphology. To test the reversibility of meiotic inhibition 366 oocytes were incubated for 0, 12, 18 and 24h in the presence of 6-DMAP and then were transferred to the maturation medium and cultured for further 24h. A total of 429 oocytes were used to evaluate the developmental potential after meiotic inhibition. The oocytes were cultured in the presence of 6-DMAP for 0, 12, 18 and 24h, and then were matured, fertilized and cultured in vitro. Culture of bovine oocytes in the presence of 6-DMAP up to 24h completely blocked GVBD with more than 90% of the oocytes at GV stage. The inhibitory effect of 6-DMAP was fully reversible since maturation rates were similar (P>0.05) among all treatment groups. The evaluation of embryo development after various periods of meiotic blockage showed that inhibition, regardless the time period, had no effect (P>0.05) on penetration and cleavage rates. However, the proportion of embryos at blastocyst stage was reduced after inhibition for 12 (20.2%), 18 (20.1%) and 24h (19.0%) compared with the control group (35.6%). 6-DMAP has a reversible effect on maintenance of meiotic arrest, but reduced further embryo development.     

Effect of passive immunization against testosterone on reproductive hormone secretion and ovarian function in dairy cows and pubertal beef heifers

Multiparous dairy cows were divided in 3 groups from Day 5 up to Day 56 post partum: high energy level (Group H, n=10), low energy level (Group L, n=10) and low energy level plus anti-testosterone bovine immunoglobulins (Group LI, n= 10). Undernutrition decreased body weight, body condition score, milk yield and energy balance in Groups L and LI compared to Group H (P<0.05), but had no effect on secretory pattern of LH. Passive immunization against testosterone increased LH secretion in Group LI (P<0.05). Follicular score and the presence of follicles >/= 10mm on the ovary were not affected by underfeeding but were higher in Group LI than in Group L after immunization (P<0.01). The duration of the first luteal phase was shorter in Group H than in Groups L and LI and maximum progesterone levels reached were higher in Group LI than in Group H (P<0.01). Reproductive performance was not depressed by underfeeding and immunization. In the pubertal beef heifers maintained in anestrus by undernutrition had very low LH secretion. After passive immunization against testosterone, the increase of LH pulses number became almost significant (P=0.07). Following injection of exogenous LH, the number of follicles >/= 9mm was higher in immunized (Group I, n=8) than in control heifers (Group C, n=7). Group I developed a dominant follicle sooner and of greater size than Group C. Passive immunization against testosterone increased LH secretion and follicular development.     

Effects of pulsatile infusion of luteinizing hormone-releasing hormone on luteinizing hormone secretion and ovarian function in hypophysial stalk-transected beef heifers

Hypothalamic regulation of luteinizing hormone (LH) secretion and ovarian function were investigated in beef heifers by infusing LH-releasing hormone (LHRH) in a pulsatile manner (1 microgram/ml; 1 ml during 1 min every h) into the external jugular vein of 10 hypophysial stalk-transected (HST) animals. The heifers were HST approximately 30 mo earlier. All heifers had increased ovarian size during the LHRH infusion. The maximum ovarian size (16 +/- 2.7 cm3) was greater (P less than 0.01) than the initial ovarian size (8 +/- 1.4 cm3). Ovarian follicular growth occurred in 4 of 10 HST heifers in response to pulsatile LHRH infusion. In 2 heifers, an ovarian follicle developed to preovulatory size, but ovulation occurred in only 1 animal after the frequency of LHRH was increased (1 microgram every 20 min during 8 h). In blood samples obtained at 20-min intervals every 5th day, LH concentrations in peripheral serum remained consistently low (0.9 ng/ml) and nonepisodic in the 10 HST heifers during infusion of vehicle on the day before beginning LHRH. In 7 of 10 HST animals, episodic LH secretion occurred in response to pulsatile infusion of LHRH. In 3 of these long-term HST heifers, however, serum LH remained at basal levels and the isolated pituitary seemingly was unresponsive to pulsatile infusion of LHRH as indicated by sequential patterns of gonadotropin secretion obtained at 5-day intervals. These results indicate that pulsatile infusion of LHRH induces LH release in HST beef heifers.     

Ovarian function in crossbred beef heifers treated with dexamethasone

Each of 32 crossbred beef heifers was brought from pasture on day 16 of its estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field Dexamethasone (FD), Pen Control (PC), and Pen Dexamethasone (PD). Field groups were kept in a 0.8-ha field and pen groups were kept in 4.6-x 9.8-m pens in a pole barn during the trial. Dexamethasone (DEX) groups received 20 mg of DEX on cycle day 16 and 30 mg daily on days 17 through 20. Control heifers received an equal volume of physiological saline solution on corresponding cycle days. Average treatment cycle lengths (±SD) for control heifers in FC and PC groups were 21.1 ± 2.8 and 21.6 ± 1.8 days, respectively, and were not significantly different. Average time from progesterone decline (<1 ng/ml) to estrus was two days for each of the control groups. Four DEX-injected heifers had not shown estrus by day 44 of the treatment cycle. Progesterone had declined for two of these heifers by cycle day 18 and remained below 1 ng/ml past cycle day 48. The other two showed a decline in plasma progesterone by cycle days 18 and 32, respectively, and a progesterone rise by day 42 without having been detected in estrus. The remaining 12 DEX heifers had an average cycle length of 29.4 days. Four extended cycles resulted from extended CL function, five from an extended period from progesterone decline to estrus and three from a combination of these factors. These observations suggest that the administration of pharmacological doses of glucocorticoid during the late diestrus or early proestrus may result in altered ovarian function.     

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.     

Animal and temporal effects on ovarian follicular dynamics in Brahman heifers

The aims of the current study were to determine if the pattern of ovarian follicular growth and development in Bos indicus heifers is different to that reported in Bos taurus breeds, and to examine the factors that determine which dominant follicle will ovulate. In addition, the extent to which variation in follicular dynamics is attributable to variation between animals and over time was evaluated. The ovaries of 17 Brahman heifers were examined daily by transrectal ultrasonography using a 7.5 MHz transducer for a total of 117 interovulatory intervals over a period of 10 months. Size and position of individual follicles ⪖5 mm in diameter, and size of corpora lutea (CL) were recorded. Circulating progesterone concentrations were determined from plasma samples obtained twice weekly. Although size of dominant follicles and CL within the ovaries of Bos indicus heifers were smaller than reported for Bos taurus breeds, the overall patterns of dominant follicle growth were similar. There were significant correlations between number of dominant follicles occurring prior to ovulation and time of appearance of the second dominant follicle, duration of detection of CL and size of the ovulatory follicle in the preceding oestrous cycle (P < 0.05). There were significant animal effects on a number of ovarian characteristics including number of dominant follicles per oestrous cycle (P < 0.001), with one heifer having four dominant follicles in more than a third of oestrous cycles observed. In addition, changes in daylength over the 10 month period were related to changes in duration of the interovulatory interval, persistence and maximum diameter of CL and size of ovulatory follicles. Liveweight change over the same period was related to changes in maximum diameter of the first dominant follicle.     

Effect of transportation stress on ovarian function in superovulated Hereford heifers

A study was conducted to determine the effect of transportation stress on ovarian function in superovulated heifers. Thirty cyclic Hereford heifers of similar age and weight and in good body condition were randomly assigned to control and stress-treated groups. All animals received two daily injections of 5 mg follicle stimulating hormone (FSH) for 4 d beginning on Day 10 to 12 of the estrous cycle. A blood sample was collected at each FSH injection. On the fourth day of injections, heifers were given 25 mg prostaglandin F(2)alpha (PGF(2)alpha) in the morning and a second injection of 15 mg PGF(2)alpha in the afternoon. During superovulation, the stressed heifers were transported to a different location every 12 h whereas control animals remained at the pretrial site. Following 4 d of intermittent transporting and FSH treatment, stress-treated heifers were recombined with control animals. Ovaries were examined 8 d following the onset of standing estrus to determine length, width, thickness, and number of corpora lutea (CL). Peripheral plasma levels of cortisol were higher in the stressed group (P< 0.1). Least squares means for numbers of CL were 20.4 +/- 2.1 and 15.4 +/- 1.7 for control and treated heifers, respectively (P< 0.1). There were no treatment differences (P> 0.1) between length, width, or thickness of ovaries when the number of CL was held constant. These data suggest that stress of the type, intensity, and duration imposed in this study increased plasma levels of cortisol and reduced ovulation rate as determined by CL formation in superovulated heifers.     

The economic effects of an estrus synchronization protocol using prostaglandin in beef heifers

We estimated the effect of estrus synchronization on reproduction, production and economic outcomes in 272 beef heifers randomly allocated to a synchronized Test group or an unsynchronized Control group. The Test group received AI upon estrus detection for 6 days followed by PGF2 treatment of heifers that had not shown estrus by day 6 (PGF/6). In both groups AI was continued for 50 days, followed by a 42-day bull breeding period. Heifers were followed through their second breeding season and until they had weaned their first calves. Synchronization resulted in a reduction in median days to first insemination (8 vs. 11 in the Test and Control groups, respectively, P < 0.01) and median days to calving of calves born to AI (14 vs. 20, P = 0.04). There was no significant difference in pregnancy rate to the AI period (60.0% vs. 51.8%, P = 0.18), final pregnancy rate (82.2% vs. 83.2%, P = 0.87) or pregnancy rate to the subsequent breeding season (96.0% vs. 95.0%, P = 1.00). Although mean calf weaning mass was not significantly different (207.0 kg vs. 201.4 kg, P = 0.32), the total mass of calves weaned in this study was 14,843 kg vs. 13,060 kg and the benefit: cost ratio for synchronization was 2.8. It was therefore concluded that a PGF/6 protocol may affect the total mass of calves weaned by changing days to calving, weaning rate, the ratio of male: female calves born and/or the birth mass of calves.     

The economic effects of an estrus synchronization protocol using prostaglandin in beef heifers

We estimated the effect of estrus synchronization on reproduction, production and economic outcomes in 272 beef heifers randomly allocated to a synchronized Test group or an unsynchronized Control group. The Test group received AI upon estrus detection for 6 days followed by PGF2 treatment of heifers that had not shown estrus by day 6 (PGF/6). In both groups AI was continued for 50 days, followed by a 42-day bull breeding period. Heifers were followed through their second breeding season and until they had weaned their first calves. Synchronization resulted in a reduction in median days to first insemination (8 vs. 11 in the Test and Control groups, respectively, P < 0.01) and median days to calving of calves born to AI (14 vs. 20, P = 0.04). There was no significant difference in pregnancy rate to the AI period (60.0% vs. 51.8%, P = 0.18), final pregnancy rate (82.2% vs. 83.2%, P = 0.87) or pregnancy rate to the subsequent breeding season (96.0% vs. 95.0%, P = 1.00). Although mean calf weaning mass was not significantly different (207.0 kg vs. 201.4 kg, P = 0.32), the total mass of calves weaned in this study was 14,843 kg vs. 13,060 kg and the benefit: cost ratio for synchronization was 2.8. It was therefore concluded that a PGF/6 protocol may affect the total mass of calves weaned by changing days to calving, weaning rate, the ratio of male: female calves born and/or the birth mass of calves.     

Effects of estradiol cypionate (ECP) on ovarian follicular dynamics,synchrony of ovulation,and fertility in CIDR-based,fixed-time AI programs in beef heifers

Estradiol cypionate (ECP) was used in beef heifers receiving a controlled internal drug release (CIDR; insertion = Day 0) device for fixed-time AI (FTAI) in four experiments. In Experiment 1, heifers (n = 24) received 1mg ECP or 1mg ECP plus 50mg commercial progesterone (CP) preparation i.m. on Day 0. Eight or 9 days later, CIDR were removed, PGF was administered and heifers were allocated to receive 0.5mg ECP i.m. concurrently (ECP0) or 24h later (ECP24). There was no effect of treatment (P = 0.6) on mean (+/-S.E.M.) day of follicular wave emergence (3.9+/-0.4 days). Interval from CIDR removal to ovulation was affected (P<0.05) only by duration of CIDR treatment (88.3+/-3.8h versus 76.4+/-4.1h; 8 days versus 9 days, respectively). In Experiment 2, 58 heifers received 100mg progesterone and either 5mg estradiol-17beta or 1mg ECP i.m. (E-17beta and ECP groups, respectively) on Day 0. Seven (E-17beta group) or 9 days (ECP group) later, CIDR were removed, PGF was administered and heifers received ECP (as in Experiment 1) or 1mg EB 24h after CIDR removal, with FTAI 58-60h after CIDR removal. Follicular wave emergence was later (P<0.02) and more variable (P<0.002) in heifers given ECP than in those given E-17beta (4.1+/-0.4 days versus 3.3+/-0.1 days), but pregnancy rate was unaffected (overall, 69%; P = 0.2). In Experiment 3, 30 heifers received a CIDR device and 5mg E-17beta, with or without 100mg progesterone (P) i.m. on Day 0. On Day 7, CIDR were removed and heifers received ECP as described in Experiment 1 or no estradiol (Control). Intervals from CIDR removal to ovulation were shorter (P<0.05) in ECP0 (81.6+/-5.0h) and ECP24 (86.4+/-3.5h) groups than in the Control group (98.4+/-5.6h). In Experiment 4, heifers (n = 300) received a CIDR device, E-17beta, P, and PGF (as in Experiment 3) and after CIDR removal were allocated to three groups (as in Experiment 2), with FTAI 54-56h (ECP0) or 56-58h (ECP24 and EB24) after CIDR removal. Pregnancy rate did not differ among groups (overall, 63.6%, P = 0.96). In summary, although 1mg ECP (with or without progesterone) was less efficacious than 5mg E-17beta plus 100mg progesterone for synchronizing follicular wave emergence, 0.5mg ECP (at CIDR removal or 24h later) induced a synchronous ovulation with an acceptable pregnancy rate to fixed-time AI.     

Genetic relationship between cyclic ovarian activity in heifers and cows and beef traits in males

Records were collected in an experimental herd over an 11-year period from purebred Charolais heifers (n = 351), cows (n = 615) and young entire bulls (n = 383). The objective of the study was to estimate the genetic relationship between the components of female ovarian activity (age at puberty and postpartum anoestrus length), their growth rate and body condition score and beef traits measured on related bulls. Two methods were used to estimate age at puberty and postpartum anoestrus length: the detection of oestrous behaviour and a test of cyclicity based on plasmatic progesterone assay. This study shows the existence of significant heritability estimates for the different cyclicity traits (h² between 0.11 and 0.38). Most of the genetic correlation coefficients between ovarian activity and growth rate of females and males are negative and favourable (r_g between -0.43 and 0.06). Cyclicity is also favourably related with body condition score in young or adult females (r_g between -0.65 and -0.22). The genetic relationship between female ovarian activity and proportion of adipose tissue in the male carcass is, however, close to zero. These results show that an antagonism between male beef traits measured in this study and female ovarian activity is unlikely to be a cause for concern in the short term.