Prevalence and reproductive effects of Ureaplasma diversum in beef replacement heifers and the relationship to blood urea nitrogen level

A systematic sample of replacement heifers from 5 herds underwent prebreeding vaginal swab cultures for Ureaplasma diversum. Heifers from three of the herds were subsequently sampled at pregnancy examination. Sampled heifers were given a vaginal lesion score (VLS), reproductive tract score (RTS) and body condition score (BCS), and peripheral blood was collected for serum blood urea nitrogen (BUN) estimation. Culture results revealed an overall prevalence of Ureaplasma diversum of 51% (87/171) at prebreeding and 65% (64/98) at pregnancy examination. Within herd prevalence ranged from 36% to 64% at prebreeding and 54% to 76% at pregnancy examination. Prevalence tended to differ between herds (P=0.08). At the prebreeding examination, heifers with a BCS of 5.5 or less were more likely to be culture positive than heifers with a BCS greater than 5.5 (p<0.05). No relationship was noted between BUN, VLS, RTS, or pregnancy status and prebreeding culture status. There was little variability among the heifers for any of these variables, with vaginal lesion scores generally being mild, RTS scores being high and BCS scores being moderate. At pregnancy examination, heifers that were culture negative tended to be more likely to be pregnant (odds 3.7, p=0.10) than culture positive heifers.     

Artificial insemination at 56 h after intravaginal progesterone device removal improved AI pregnancy rate in beef heifers synchronized with five-day CO-Synch + controlled internal drug release (CIDR) protocol

The objective was to determine whether timed artificial insemination (TAI) 56 h after removal of a Controlled Internal Drug Release (CIDR, 1.38 g of progesterone) insert would improve AI pregnancy rate in beef heifers compared to TAI 72 h after CIDR insert removal in a 5-days CO-Synch + CIDR protocol. Angus cross beef heifers (n = 1098) at nine locations [WA (5 locations; n = 634), ID (2 locations; n = 211), VA (one location; n = 193) and WY (one location; n = 60)] were included in this study. All heifers were given a body condition score (BCS; 1-emaciated; 9-obese), and received a CIDR insert and 100 μg of gonadorelin hydrochloride (GnRH) on Day 0. The CIDR insert was removed and two doses of 25 mg of dinoprost (PGF_2α) were given, first dose at CIDR insert removal and second dose 6 h later, on Day 5. A subset of heifers (n = 629) received an estrus detector aid at CIDR removal. After CIDR removal, heifers were observed thrice daily for estrus and estrus detector aid status until they were inseminated. Within farm, heifers were randomly allocated to two groups and were inseminated either at 56 h (n = 554) or at 72 h (n = 544) after CIDR removal. All heifers were given 100 μg of GnRH at AI. Insemination 56 h after CIDR insert removal improved AI pregnancy rate compared to insemination 72 h (66.2 vs. 55.9%; P < 0.001; 1 - β = 0.94). Locations, BCS categories (≤ 6 vs. > 6) and location by treatment and BCS by treatment interactions did not influence AI pregnancy rate (P > 0.1). The AI pregnancy rates for heifers with BCS ≤ 6 and > 6 were 61.8 and 60.1%, respectively (P > 0.1). The AI pregnancy rates among locations varied from 54.9 to 69.2% (P > 0.1). The AI pregnancy rate for heifers observed in estrus at or before AI was not different compared to heifers not observed in estrus [(65.4% (302/462) vs. 52.7% (88/167); P > 0.05)]. In conclusion, heifers inseminated 56 h after CIDR insert removal in a 5-days CO-Synch + CIDR protocol had, on average, 10.3% higher AI pregnancy rate compared to heifers inseminated 72 h after CIDR insert removal.     

Ovarian luteal activity and reproductive performance of heifers with norgestomet prototype implants

A 122-day trial was conducted with grazing beef heifers (N=120; 14 to 17 months of age) to determine the effects of a silastic Norgestomet prototype implant on heifer weight gain and on the suppression of ovarian luteal activity. The retention rate of the Norgestomet implants and of silastic placebo implants, which were either left untreated, or were topically treated with oxytetracycline, was determined. Medication of the placebo implants with oxytetracycline increased (P < 0.01) implant retention rate at both Day 56 and Day 122. Heifers with Norgestomet implants had higher body weight gains during the last 66 days (P < 0.05), and during the entire 122-day trial (P < 0.07) than heifers with placebo implants. Serum progesterone concentrations on Day 111 or Day 112 indicated a decrease (P < 0.01) in percentage of heifers with ovarian luteal activity on the Norgestomet treatment compared with heifers receiving placebos (23.8% vs 87.7%, respectively). The Norgestomet implant has the potential for suppressing ovarian luteal activity while improving weight gain in beef heifers.     

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.     

Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy

The objectives were (1) to determine the effects of gonadorelin hydrochloride (GnRH) injection at controlled internal drug release (CIDR) insertion on Day 0 and the number of PGF2α doses at CIDR removal on Day 5 in a 5-day CO-Synch + CIDR program on pregnancy rate (PR) to artificial insemination (AI) in heifers; (2) to examine how the effect of systemic concentration of progesterone and size of follicles influenced treatment outcome. Angus cross beef heifers (n = 1018) at eight locations and Holstein dairy heifers (n = 1137) at 15 locations were included in this study. On Day 0, heifers were body condition scored (BCS), and received a CIDR. Within farms, heifers were randomly divided into two groups: at the time of CIDR insertion, the GnRH group received 100 μg of GnRH and No-GnRH group received none. On Day 5, all heifers received 25 mg of PGF2α at the time of CIDR insert removal. The GnRH and No-GnRH groups were further divided into 1PGF and 2PGF groups. The heifers in 2PGF group received a second dose of PGF2α 6 hours after the administration of the first dose. Beef heifers underwent AI at 56 hours and dairy heifers at 72 hours after CIDR removal and received 100 μg of GnRH at the time of AI. Pregnancy was determined approximately at 35 and/or 70 days after AI. Controlling for herd effect (P < 0.06), the treatments had significant effect on AI pregnancy in beef heifers (P = 0.03). The AI-PRs were 50.3%, 50.2%, 59.7%, and 58.3% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PRs were ranged from 50% to 62.4% between herds. Controlling for herd effects (P < 0.01) and for BCS (P < 0.05), the AI pregnancy was not different among the treatment groups in dairy heifers (P > 0.05). The AI-PRs were 51.2%, 51.9%, 53.9%, and 54.5% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PR varied among locations from 48.3% to 75.0%. The AI-PR was 43.5%, 50.4%, and 64.2% for 2.5 or less, 2.75 to 3.5, and greater than 3.5 BCS categories. Numerically higher AI-PRs were observed in beef and dairy heifers that exhibited high progesterone concentrations at the time of CIDR insertion (>1 ng/mL, with a CL). In addition, numerically higher AI-PRs were also observed in heifers receiving CIDR + GnRH with both high and low progesterone concentration (<1 ng/mL) initially compared with heifers receiving a CIDR only with low progesterone. In dairy heifers, there were no differences in the pregnancy loss between 35 and 70 days post-AI among the treatment groups (P > 0.1). In conclusion, GnRH administration at the time of CIDR insertion is advantageous in beef heifers, but not in dairy heifers, to improve AI-PR in the 5-day CIDR + CO-Synch protocol. In addition, in this study, both dairy heifers that received either one or two PGF2α doses at CIDR removal resulted in similar AI-PR in this study regardless of whether they received GnRH at CIDR insertion.     

Estrus synchronization in cattle using estradiol, melengestrol acetate and PGF

In Experiment 1, all cattle were fed MGA (0.5 mg/head/d) for 7 d (designated Days 0 to 6) and given PGF on Day 6. One-half were administered estradiol valerate (EV; 5 mg, im) on Day 0. At Location 1, a higher proportion (P < 0.005) of EV-treated heifers were detected in estrus and bred by AI between Days 7 and 13 than control heifers not receiving EV (27 of 33 versus 15 of 32), but the number of pregnancies (12 vs 10) was not significantly different. Eighty-three of 104 EV-treated and 89 of 106 control cows were inseminated, resulting in 50 and 45 pregnancies, respectively (not significant). At Location 2, cattle were similarly treated and exposed to bulls on Days 7 to 49. Fall pregnancy rate was higher (P < 0.015) for EV-treated than control heifers (44 of 48 vs 33 of 46), but was not significantly different for cows (22 of 26 vs 19 of 23). In Experiment 2, estradiol 17beta (E17beta; 5 mg, im) and progesterone (100 mg, im) were administered on Day 0 (instead of EV). In a third group (designated the PGF group), cattle were bred on Days 0 to 6, and PGF was administered on Day 6 to those not yet bred. For 213 cows, the percentage pregnant to a synchronized estrus was greater in the PGF group (72%) than in either the control group treated with MGA (49%; P = 0.005) or the group receiving MGA and E17beta (54%; P < 0.025). Fall pregnancy rates were 91, 89, and 96% for the 213 cows (not significant) and 89, 93, and 98% for 131 heifers (not significant) in the PGF, MGA and E17beta groups, respectively. In cattle without a functional CL, the average diameter of the largest follicle at Day 6 was 1 to 2 mm smaller in the E17beta + MGA group than in the MGA group (difference significant only in cows at Location 1). Combined for both locations, the synchronized pregnancy rate in heifers without a functional CL on Day 6 was higher (P < 0.05) in the E17beta + MGA group than in the MGA group (11 of 21, 52% versus 4 of 20, 20%). Estrogen treatment caused regression of ovarian follicles with emergence of a new follicular wave. Including estrogen in an estrus synchronization program utilizing MGA and PGF significantly increased fall pregnancy rate in heifers (at 1 location) and the synchronized pregnancy rate of heifers without a functional CL at the time of PGF treatment (combined for both locations).     

The effect of increased dietary intake on superovulatory response to FSH in heifers

We have previously shown that the number of ovarian follicles <4 mm in diameter can be increased by enhanced dietary intake in heifers. This study investigated the effect of the same dietary treatment on superovulatory response. The estrous cycles of 24 mature Hereford x Friesian heifers were synchronized by a standard progesterone plus prostaglandin protocol. The animals were fed with either 100% (group M, n = 12) or 200% (group 2M, n = 12) maintenance requirements for a 3-week period. Starting from day 4 of the synchronized estrous cycle, all the animals were superovulated using a standard 4-day FSH regime followed by an injection of GnRH analogue (GnRHa) to induce ovulation. Rectal ultrasound scanning was carried out to assess ovarian follicular populations at the start of FSH treatment and on the day of GnRHa injection, and to determine the number of corpora lutea 5 days after GnRHa injection. The body weight (BW) and body condition score (BCS) were recorded weekly and plasma samples were collected throughout the experimental period. There were no differences in either BW or BCS between two groups at the start of the experiment. The BW and BCS were maintained during the experiment in the group M, whilst animals in the group 2M showed a non-significant (P > 0.05) increase in BW and BCS. Circulating concentrations of insulin were significantly (P < 0.01) higher in heifers from the group 2M throughout the controlled feeding period. The group 2M had significantly (P < 0.05) more follicles 2-4 mm in diameter at the start of FSH treatment and more (P < 0.01) follicles >9 mm in diameter on the day of GnRHa injection, when compared with the group M. Similarly, 5 days after GnRHa injection there were significantly (P < 0.01) more corpora lutea in the group 2M (18.1+/-2.2) than in the group M (10.6+/-3.0). In addition, plasma progesterone concentrations following GnRHa injection were significantly (P < 0.01) higher in heifers from the group 2M. In conclusion, these results confirm that increased dietary intake can enhance the recruitment of ovarian follicles in heifers. This treatment may provide a valuable approach to improving superovulatory response in cattle.     

Sources of variation of post-partum cyclicity, ovulation and pregnancy rates in primiparous Charolais cows treated with norgestomet implants and PMSG

In this study, sources of variation of postpartum cyclicity, ovulation and pregnancy rates were analyzed for 723 primiparous suckled Charolais cows treated with combined norgestomet implants (Crestar) and 600 IU PMSG (Chronogest) injected at the time of implant removal. The cows were inseminated 48 and 72 h after implant removal. Cyclicity and ovulation rate were estimated by progesterone assay and pregnancy rate by ultrasonography. At time of implant insertion, difficulty of previous calving, body condition score (BCS, from 1 to 5), interval from calving to implant insertion and herd related factors were recorded and their effects analyzed by logistic regression models. Cyclicity, ovulation and pregnancy rates were, respectively, 14.7% (106/723 ), 67.1% (381/568 ) and 42% (303/722 ) and were affected by BCS, calving conditions and interval from calving to implant insertion (P values from < 0.01 to < 0.0001). For ovulation and pregnancy rate, an interaction between BCS and interval from calving to implant insertion was found (P < 0.01). No other main factor or interaction was found to be significant. Cyclicity rate was lower in BCS1 (score < 2.5) cows (9.6%) than in BCS2 (19.8%) or BCS3 (score > 2.5) cows (22.4%), and decreased as difficulty of calving increased (23.2, 13.6 and 10.1%, respectively, for calving conditions 1, 2 and 3 cows). Cyclicity rate increased with interval from calving to implant insertion (8.2, 10.2 and 19.5%, respectively, for interval from calving to implant insertion < 60 d, between 60 and 70 d and > 70 d). Similar trends were found for ovulation rate. Previous difficult calving conditions influenced pregnancy rate negatively (47.9, 43.8 and 32.5% for calving conditions 1, 2 and 3 cows, respectively; P < 0,005).     

Effect of reproductive tract scoring on reproductive efficiency in beef heifers bred by timed insemination and natural service versus only natural service

The objective was to determine the effects of reproductive tract score (RTS) on reproductive performance in beef heifers bred by timed artificial insemination followed by natural service (AI-NS) or by natural service only (NSO). Angus cross beef heifers (n = 2660) in the AI-NS group were artificially inseminated at a fixed time (5- or 7-day CO-Synch + controlled internal drug release protocol) once, then exposed to bulls 2 weeks later (bull-to-heifer ratio = 1:40–1:50) for the reminder of the 85-day breeding season. Angus cross beef heifers (n = 1381) in NSO group were submitted to bulls (bull-to-heifer ratio = 1:20–1:25) for the entire 85-day breeding season. Heifers were reproductive tract scored from 1 (prepubertal) to 5 (cyclic) 4 weeks before, and were body condition scored (BCS) from 1 (emaciated) to 9 (obese) at the beginning of breeding season. Pregnancy diagnosis was performed 70 days after AI for AI-NS group and 2 months after the end of breeding season for both groups. Heifers in both groups were well managed and of similar age (14.9 ± 0.4 [AI-NS] and 14.7 ± 0.8 [NSO] months). Pregnancy rates (PRs) and number of days to become pregnant were calculated using PROC GLIMMIX and PROC LIFETEST procedures of SAS. Adjusting for BCS (P = 0.07), expressed estrus (P < 0.05), year (P < 0.05), and BCS by year interaction (P < 0.05), the AI-PR was greater for heifers in AI-NS group with higher RTS (P < 0.0001; 40.7%, 48.3%, 57.6%, and 64.6% for RTS of 2 or less, 3, 4, and 5, respectively). Controlling for BCS (P < 0.05), year (P < 0.05) and the breeding season pregnancy rates (BS-PRs) were greater for heifers in the AI-NS group with higher RTS (P < 0.01; 81.2%, 86.5%, 90.4%, and 95.2% for RTS of 2 or less, 3, 4, and 5, respectively). Similarly, adjusting for BCS, year (P < 0.05), the BS-PR was greater for heifers in NSO group with higher RTS (P < 0.01; 79.7%, 84.3%, 88.4%, and 90.2% for RTS of 2 or less, 3, 4, and 5, respectively). Heifers with higher RTS in both groups became pregnant earlier in the breeding season compared with heifers with lower RTS (log-rank statistics: P < 0.0001). Heifers in the AI-NS group become pregnant at a faster rate compared with those in the NSO group (P < 0.01). The BS-PR for heifers with RTS 5 was different between AI-NS and NSO groups (P < 0.0001). In conclusion, the RTS influenced both the number of beef heifers that became pregnant during the breeding season and the time at which they become pregnant. Furthermore, irrespective of RTS, heifers bred by NSO required more time to become pregnant than their counterparts in herds that used timed AI. The application of RTS system is reliant on the use of synchronization protocol. The application of RTS for selection may plausibly remove precocious females with lower RTS. On the contrary, application of RTS would help select heifers that will become pregnant earlier in breeding season.     

Effect of prepartum somatotropin injection in late-pregnant Holstein heifers on metabolism, milk production and postpartum resumption of ovulation

The aim of this study was to determine the effect of prepartum somatotropin injection in late-pregnant Holstein heifers on metabolism, milk production and resumption of postpartum ovulation. For this study, 31 late-pregnant Holstein heifers were used. The heifers were assigned randomly into two treatments: (1) 500 mg sc injections of somatotropin (somatotropin treatment, n = 15) at -35 and -21 days, and, if pertinent, at -7 days from expected calving date and (2) no treatment (control group, n = 16). Blood samples were collected weekly from -5 to 7 weeks after calving. Heifers with progesterone concentrations in plasma above 1 ng/ml in two consecutive postpartum samples were considered as having resumed ovarian activity. A higher proportion (P = 0.04) of heifers treated with somatotropin resumed ovarian activity in the first 7 weeks post partum (73.3%; 11/15) compared with the control group (37.5%; 6/16). A higher number (P = 0.02) of heifers in the somatotropin treatment group also ovulated during the first postpartum follicular wave (53.3%; 8/15) compared with the control group (12.5%; 2/16), as indicated by the number of heifers ovulating in the first 3 weeks post partum. Pregnancy rate was not affected by treatments (P > 0.10) and averaged 40.0% (6/15) in somatotropin-treated and 25.0% (4/16) in control heifers when evaluated up to 150 days in milk. Somatotropin treatment increased the average daily milk production by 2.8 kg/cow per day (P < 0.0001) and reduced the somatic cell count (P = 0.009). Plasma IGF-I was higher (P < 0.05) for somatotropin-treated heifers in the prepartum period. Insulin and body condition score were higher (P < 0.05) and non-esterified fatty acids were lower (P < 0.05) for somatotropin-treated cows in the early postpartum period. In conclusion, somatotropin injection during the prepartum period in late-pregnant Holstein heifers was able to increase the proportion of heifers resuming ovarian activity early post partum, inspite of higher milk production.     

Estrus and pregnancy in beef heifers following use of the Syncro-Mate-B treatment (SMB)

Five studies were conducted in yearling heifers which were either puberal or prepuberal utilizing the Syncro-Mate-B (SMB) treatment (G. D. Searle & Co., Chicago, Ill.). In trial 1 the pregnancy rate in Brahman crossbred heifers after 21 days of breeding was 56% and 28% greater (P<.005) in the SMB treated groups than in the nontreated groups. Pregnancy rate in 3 4 Simmental heifers (trial 2) was increased 39% (P<.05) after 21 days of breeding. Hereford and crossbred heifers (trial 3) weighing less than 250 kg failed to respond to SMB treatment whereas heifers weighing greater then 250 kg had increased reproductive performance. Conversely the results obtained in trial 4 using Brahman crossbred heifers was not influenced by weight or SMB treatment. Crossbred Santa Gertrudis heifers (trial 5) weighing greater then 250 kg and treated with SMB had improved reproductive performance compared to the control groups. While in treated heifers weighing less than 250 kg reproductive performance was far from optimum.     

Auto and heterotransplantation of the ovary to the uterus or parotid region in beef cows and prepuberal heifers

Eighteen mature estrous cycling beef cows and 9 prepuberal heifers were stratified by breed, age and weight to determine the effect of ovary-transplantation to a proximal site (right uterine horn) (U) and distal site (parotid region) (P) upon ovarian activity. Active ovaries (AO), ovaries with the corpus luteum (CL), were autotransplanted to the myometrium of the U in 3 cows and to the muscles of the P in 2 cows and their inactive ovaries (IO), ovaries without a CL, remained. Active ovaries of 6 cows were removed and heterotransplanted to 6 prepuberal heifers and their 10 were heterotransplanted to the U or the parotid (3). Six heifers received either a mature AO in the U or in the parotid. Three heifers were ovariectomized and their ovaries were heterotransplanted to 6 cows, 3 per site. Cows and heifers were slaughtered randomly 2 months after surgery and their ovaries were collected for microscopic and histological analysis. The transplants were successfully accomplished in 94% of the cows and in 83% of the heifers. Both of the unsuccessful heterotransplantations were located in the uterus. More estrous activity was found (P<.025) in cows than in heifers with their own ovaries in situ . All prepuberal ovaries in situ showed follicular development when mature AO were transplanted to either the U or parotid. The same trend was found in prepuberal ovaries transplanted to mature cycling cows. Cows with an IO in situ and AO transplanted to either site had more estrous activity than did ovariectomized cows with an IO transplanted to either site. Pregnancy rates in mature cycling cows with an least one ovary in situ were higher (P<.005) in cows with an ovary in the parotid region than cows with an ovary transplanted to the uterus.     

Ovarian responses in Bos indicus heifers treated to synchronise ovulation with intravaginal progesterone releasing devices, oestradiol benzoate, prostaglandin F(2α) and equine chorionic gonadotrophin

The objectives were: (i) improve understanding of the ovarian responses of Bos indicus heifers treated with different ovulation synchronisation protocols, (ii) compare ovarian responses of B. indicus heifers treated with intravaginal progesterone releasing device (IPRD)+oestradiol benzoate (ODB) versus a conventional prostaglandin F(2α) (PGF(2α)) protocol and (iii) investigate whether reducing the amount of progesterone (P(4)) in the IPRD, and treatment with equine chorionic gonadotrophin (eCG) would increase the proportion of heifers with normal ovarian function during the synchronised and return cycles. Two-year-old Brahman (n=30) and Brahman-cross (n=34) heifers were randomly allocated to three IPRD-treatment groups: (i) standard-dose IPRD (Cue-Mate(?) 1.56g P(4); n=17); (ii) half-dose IPRD (Cue-Mate(?) 0.78g P(4); n=15); (iii) half-dose IPRD+300IU eCG at IPRD removal (n=14), and a non-IPRD control group (iv) 2×PGF(2α) (500μg cloprostenol) on Days -16 and -2 (n=18). IPRD-treated heifers received 250μg cloprostenol at IPRD insertion (Day -10) and IPRD removal (Day -2) and 1mg ODB on Days -10 and -1. Ovarian function was evaluated by ultrasonography and plasma P(4) throughout the synchronised and return cycles. The mean diameter of the dominant follicle observed at 54-56h after IPRD removal, was greater for heifers which ovulated than heifers which did not ovulate (P<0.001; 14.5±1.1 vs. 9.3±0.6mm, respectively). The prevalence of IPRD-treated heifers with ovarian dysfunction (persistent CL, failure to re-ovulate, shortened luteal phase) was 39%. This relatively high prevalence of ovarian dysfunction may explain the commonly reported, lower than expected pregnancy rates to FTAI in B. indicus heifers treated to synchronise ovulation.     

Neither plasma progesterone concentrations nor exogenous eCG affects rates of ovulation or pregnancy in fixed-time artificial insemination (FTAI) protocols for puberal Nellore heifers

The objective was to evaluate the effects of plasma progesterone (P4) concentrations and exogenous eCG on ovulation and pregnancy rates of pubertal Nellore heifers in fixed-time artificial insemination (FTAI) protocols. In Experiment 1 (Exp. 1), on Day 0 (7 d after ovulation), heifers (n = 15) were given 2 mg of estradiol benzoate (EB) im and randomly allocated to receive: an intravaginal progesterone-releasing device containing 0.558 g of P4 (group 0.5G, n = 4); an intravaginal device containing 1 g of P4 (group 1G, n = 4); 0.558 g of P4 and PGF_2α (PGF; 150 μg d-cloprostenol, group 0.5G/PGF, n = 4); or 1 g of P4 and PGF (group 1G/PGF, n = 3). On Day 8, PGF was given to all heifers and intravaginal devices removed; 24 h later (Day 9), all heifers were given 1 mg EB im. In Exp. 2, pubertal Nellore heifers (n = 292) were treated as in Exp. 1, with FTAI on Day 10 (30 to 36 h after EB). In Exp. 3, pubertal heifers (n = 459) received the treatments described for groups 0.5G/PGF and 1G/PGF and were also given 300 IU of eCG im (groups 0.5G/PGF/eCG and 1G/PGF/eCG) at device removal (Day 8). In Exp. 1, plasma P4 concentrations were significantly higher in heifers that received 1.0 vs 0.588 g P4, and were significantly lower in heifers that received PGF on Day 0. In Exp. 2 and 3, there were no significant differences among groups in rates of ovulation (65-77%) or pregnancy (Exp. 2: 26-33%; Exp. 3: 39-43%). In Exp. 3, diameter of the dominant ovarian follicle on Day 9 was larger in heifers given 0.558 g vs 1.0 g P4 (10.3 ± 0.2 vs 9.3 ± 0.2 mm; P < 0.01). In conclusion, lesser amounts of P4 in the intravaginal device or PGF on Day 0 decreased plasma P4 from Days 1 to 8 and increased diameter of the dominant follicle on Day 9. However, neither of these nor 300 IU of eCG on Day 8 significantly increased rates of ovulation or pregnancy.     

Norgestomet implants maintain pregnancy in ovariectomized heifers

Fifty-five heifers were synchronized with norgestomet and estradiol valerate and artificially inseminated approximately 48 h after the removal of norgestomet implants. Ten days after Al, 15 of the heifers were ovariectomized and then two 15 mg norgestomet/silicone implants were implanted subcutaneously on the convex surface of the ear. The norgestomet/silicone implants were changed every 55 +/-4 d (mean range) thereafter, and the last set of implants was removed 273 d after Al. At 44 d after Al, 65% (26/40) of the control heifers and 53% (8/1 5) of the ovariectomized heifers with norgestomet implants were pregnant (P > 0.10). Two pregnancies were lost in ovariectomized heifers treated with norgestomet (44 to 96 d after Al) and a third pregnancy failed in a heifer that lost 1 of 2 implants 65 to 96 d after Al. Ninety-six days after Al implants were removed from 2 pregnant ovariectomized heifers with norgestomet implants. These 2 heifers were open at 116 d after Al. All 3 ovariectomized heifers with norgestomet implants pregnant at 273 d after Al calved an average of 41 h after the removal of the last set of norgestomet/silicone implants. Dystocia (P < 0.05), retention of fetal membranes (P < 0.01), and calf mortality (P < 0.01) were higher for the ovariectomized heifers with norgestomet implants than for the control heifers.     

Effects of treatment with LH and FSH between 8 and 12 weeks of age on ovarian follicular development and puberty in heifers

The transient increase in gonadotrophin secretion, seen in heifer calves between 6 and 20 wk of age, may be critical for early ovarian follicular growth and for initiation of sexual maturation. We treated heifers with either 3 mg of bLH (n = 5; sc) or 4 mg sc of bFSH (n = 5; sc), every other day, between 8 and 12 wk of age. During the first 17 d of treatment, bovine gonadotrophins caused a reduction in maximum antral follicle size and in numbers of large antral follicles, compared to control heifers (P < 0.05). In 4 of 5 bLH treated heifers and 3 of 5 bFSH treated heifers, the emergence of a large dominant antral follicle was delayed (P < 0.05). At 34 wk of age, follicular dynamics did not differ among groups. Serum concentrations of estradiol were decreased in bFSH and bLH treated heifers at 35 wk of age and in bFSH treated heifers at 25 wk of age compared with that of the controls. Time of first ovulation was delayed in bFSH treated heifers compared with control heifers (P < 0.05;bFSH 59.0 +/- 1.2; control 51.4 +/- 1.8; bLH 56.2 +/- 2.5 wk of age). In summary, treatment of 8-wk old heifers with gonadotrophins every other day disrupted folliculogenesis over a 17-d period, delayed first ovulation (bFSH), and decreased ovarian estradiol production at 25 (bFSH) and 35 (bLH, bFSH) weeks of age.     

Comparative cryopreservation of avian spermatozoa: effects of freezing and thawing rates on turkey and sandhill crane sperm cryosurvival

In beef cows, reduced energy intake delays first ovulation postpartum and is associated with lesser insulin, IGF-I and leptin concentrations. However, the close relationship among these hormones mask their individual roles in the reinitiation of ovarian activity. A β-adrenergic receptor agonist (βAR) was used to increase body condition score (BCS) and yet reduce body fat and leptin serum concentration to determine the specific role of leptin in the postpartum ovarian activity. Beef cows (n=77) with BCS 3.1 ± 1.4 received 2 kg/day of feed containing 0 or 0.15 mg/kg of zilpaterol (a synthethic βAR), for 33 days. Estrus was induced with a progestin implant applied for 9 d and cows in estrus were bred by artificial insemination (AI). Zilpaterol administration increased (P<0.05) daily weight gain, muscle depth and BCS, with no changes in back fat depth, reducing fat to muscle ratio (P<0.05). At the time of AI, insulin (38%) and IGF-I (26%) concentrations were less in zilpaterol-treated cows (P<0.05), but leptin concentration was unaffected. Ovulation rate and animal with luteal activity after estrus induction were also reduced by 35% (P=0.05) and 56.5% (P=0.007), respectively, in zilpaterol-treated cows. Logistic regression estimates for BCS (P=0.016) and IGF-I concentration (P=0.03) were positively related with the occurrence of luteal activity. In addition, whilst back fat (P=0.009) had a positive effect on luteal activity, leptin concentration did not show a significant relationship. In conclusion, despite an increase in body weight and a positive change in BCS, the reduction in insulin and IGF-I concentrations, associated with βAR treatment, reduced the response to induction of estrus. However only IGF-I, but not leptin or insulin, significantly influenced the odds for the occurrence of luteal activity after estrous induction in cattle with poor BCS.     

Incidence and treatment of abnormal postpartum ovarian function in dairy cows

The objectives of this study were to determine 1) the incidence of abnormal postpartum ovarian function in a large dairy herd in North Central Florida and 2) the effectiveness of gonadotrophin releasing hormone (GnRH) in treating this condition. The study was conducted from April 1988 to June 1989. The internal genitalia of the cows were initially examined per rectum (Day 0) between 19 and 29 (23 +/- 0.25) d after calving and again 14 d later (Day 14) for evidence of uterine involution and ovarian activity. The presence of a palpable corpus luteum (CL) and retrospective determination of plasma progesterone (P4) concentrations > 1 ng/ml were the criteria used to assess ovarian activity. Cows possessing a palpable CL and P4 concentrations > 1 ng/ml on Day 0 were determined to be cycling normally. A total of 1356 cows was used in this study. On Day 0, two groups were formed: Group 1 consisted of normal, cyclic cows, Group 2 of noncyclic cows. On Day 0, alternate cows in Group 2 were treated with GnRH (100ug i.m). On Day 14, the previously nontreated cows in Group 2 were further divided into two groups, forming Group 3, nontreated cows and Group 4, cows treated with GnRH at this time. Group 5 was comprised of cows from Group 2 that did not respond to treatment with GnRH on Day 0; these cows were treated on Day 14 with GnRH (100ug i.m). Group 6 was comprised of nontreated cows from Group 2 that responded spontaneously (presence of a CL) by Day 14. Reproductive parameters evaluated were the percentage of cows pregnant within 180 d after calving and at the end of the study, the number of days open and the number of services per conception. Data were statistically analyzed using Chisquare and survival analysis. The results of this study indicate that the incidence of abnormal postpartum ovarian function in this herd was 30.2% and that the nontreated cows experienced more days open and required more services per conception than the treated cows, those that were cycling normally on the initial examination, and those that responded spontaneously by Day 14.     

Pregnancy rates after fixed-time artificial insemination of Brahman heifers treated to synchronize ovulation with low-dose intravaginal progesterone releasing devices, with or without eCG

The objective was to determine whether eCG in an ovulation synchronization protocol with an intravaginal progesterone (P₄)-releasing device (IPRD) containing a low dose of P₄ improves pregnancy rate (PR) to fixed-time AI (FTAI) in Bos indicus heifers. Day 0, 2 y old Brahman heifers were allocated to either eCG+ (n = 159) or eCG- (n = 157) treatment groups. All heifers were weighed, body condition scored (BCS), and ultrasonographically examined to measure uterine horn diameter and presence of a CL. On Day 0, all heifers received a low-dose IPRD (0.78 g P₄) and 1 mg of estradiol benzoate (EB) im. On Day 8, the IPRD was removed, all heifers received 500 μg cloprostenol im, and those in the eCG+ treatment group received 300 IU of eCG im. On Day 9, all heifers received 1 mg EB im. All heifers were FTAI 52 to 56 h after IPRD removal. Ten days after FTAI, heifers were exposed to bulls. Heifers were diagnosed as pregnant to FTAI, natural mating, or not detectably pregnant (NDP) 65 d after FTAI. Treatment with eCG+ as compared to eCG- did not affect PR to FTAI (28.9 vs 30.6%; P = 0.590), natural mating (51.3 vs 47.7%; P = 0.595), or overall (65.4 vs 63.7%; P = 0.872). Mean live weight gain from Days 0 to 65 d post-FTAI was higher in heifers pregnant to FTAI (72.29 ± 4.26 kg; P = 0.033) and overall (66.83 ± 3.65 kg; P = 0.021), compared to heifers that were NDP (60.03 ± 3.16 kg). Uterine diameter group, 9–11, 12–13, and 14–20 mm (26.2, 31.3, and 33.3%; P = 0.256), presence and absence of CL (29.8 vs 29.4%; P = 0.975), AI technicians 1, 2, and 3 (32.6, 28.8, and 22.4%; P = 0.293) and sires A, B, and C (23.9, 36.0 and 27.0%; P = 0.122) had no effect on PR to FTAI, natural mating, or overall. In conclusion, treatment of primarily cycling Brahman heifers with 300 IU eCG in conjunction with a low P₄-dose (0.78 g) IPRD and EB to synchronize ovulation, did not improve PR after FTAI, natural mating, or overall.     

Use of GnRH agonist implants for long-term suppression of fertility in extensively managed heifers and cows

The ability of gonadotrophin releasing hormone (GnRH) agonist implants to suppress ovarian activity and prevent pregnancies, long-term, was examined in heifers and cows maintained under extensive management. At three cattle stations, heifers (2-year-old) and older cows (3- to 16-year-old) were assigned to a control group that received no treatment, or were treated with high-dose (12 mg, Station A) or low-dose (8 mg, Station B and Station C) GnRH agonist implants. The respective numbers of control and GnRH agonist-treated animals (heifers + cows) at each station were: Station A, 20 and 99; Station B, 19 and 89; Station C, 20 and 76. Animals were maintained with 4% bulls and monitored for pregnancy at 2-monthly intervals for approximately 12 months. Pregnancy rates for control heifers and control cows ranged from 60-90% and 80-100%, respectively, depending on the study site. The respective number of animals (heifers + cows) treated with GnRH agonist that conceived, and days to first conception, were: Station A, 9 (9%) and 336 +/- 3 days; Station B, 8 (10%) and 244 +/- 13 days; Station C, 20 (26%) and 231 +/- 3 days. Treatment with high-dose GnRH agonist prevented pregnancies for longer (approximately 300 days) than treatment with low-dose GnRH agonist (approximately 200 days). In the majority of heifers and cows treated with GnRH agonist, ovarian follicular growth was restricted to early antral follicles (2-4mm). The findings indicate that GnRH agonist implants have considerable potential as a practical technology to suppress ovarian activity and control reproduction in female cattle maintained in extensive rangelands environments. The technology also has broader applications in diverse cattle production systems.