Efficacy of the ivomec SR bolus for control of horn flies (Diptera: Muscidae) on cattle in South Texas

The concentration of ivermectin in the serum of Hereford heifers treated with a single Ivomec SR bolus reached a maximum of 8.8 +/- 0.9 ppb at 2 wk post-treatment. The single bolus treatment resulted in <10% mortality of adult horn flies feeding on the blood of the treated animals over the 21-wk trial. Bioassays of the manure from treated cattle showed complete inhibition of development of immature horn flies through week 19 post-treatment. When the trial was repeated using two Ivomec SR boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 post-treatment. During the first 17 wk of treatment, the use of two boluses/heifer resulted in 96.2 and 81.2% mortality of adult male and female horn flies feeding on the blood of treated animals, respectively. From these studies, we conclude that a single Ivomec SR bolus used as an anthelmintic treatment can be expected to provide significant control of immature horn flies developing in the manure, but not of adults feeding on the treated cattle.     

Control of Boophilus annulatus (Acari: Ixodidae) on cattle using injectable microspheres containing ivermectin

The efficacy of an injectable microsphere formulation of ivermectin for control of the cattle tick, Boophilus annulatus (Say), was tested on 2 groups of 6 Hereford heifers held on separate 7-ha, tick-infested, buffel grass pastures. Cattle in one pasture were injected subcutaneously in the neck with a controlled-release microsphere formulation of ivermectin at the rate of 2.4 mg AI/kg body weight; the other group was injected with carrier only. Beginning 4 wk after injection and continuing throughout the remainder of the test (16 wk), no engorged ticks (> or = 5.5 mm) were found on any of the treated cattle, whereas large numbers of engorged ticks were found on the untreated controls. During this period, a few ticks were recovered from untreated sentinel animals placed in the treatment pasture during 7-8 wk after treatment, but none were recovered from animals exposed from 11-12 wk or 14-15 wk. Large numbers of B. annulatus ticks were found on untreated sentinel cattle placed in the control pasture during these same periods. Although the cattle, pastures, and tick habitat were approximately equal, the treated cattle gained an average of 77 kg compared with an average of 42 kg for the control group. This technology offers a possible alternative to the current official program of dipping and vacating pastures for eradication of Boophilus sp. infestations from the quarantine zone in southern Texas. Larger scale testing is needed to determine the potential of the injectable microsphere formulation and to optimize its use in eradication or control strategies.     

Evaluation of a Pour-on Formulation of Fipronil Against Boophilus Annulatus (Acari: Ixodidae) Under Natural South Texas Field Conditions

A long-term field study (60 consecutive weeks) was conducted to determine whether a Boophilus annulatus (Say) population could be eradicated through repeated applications of a 1% pour-on formulation of fipronil on cattle held in an infested pasture. Animals treated repeatedly over time (seven applications) were infested with significantly fewer (p < 0.05) female ticks (5 mm in size) than untreated animals in all except one of the 57 weekly tick counts conducted after the first treatment was applied. As the number of treatments increased over time, there was a progressive decrease in the number of instances in which engorging females were observed on the treated cattle. Tick numbers obtained from sentinel cattle placed in pasture with untreated and treated cattle at various intervals throughout the study indicated that a single fipronil treatment had no observable adverse effect on the field tick population. However, after two treatments had been applied, there were always dramatically fewer ticks obtained from sentinel animals placed with treated cattle than were observed on sentinel animals placed with untreated cattle. Furthermore, tick numbers obtained from sentinel cattle placed with treated cattle over time indicated that the tick population in the pasture declined by stages. While a single treatment had no effect on the tick population, the application of two to four fipronil treatments at various intervals dramatically reduced the tick population, even though substantial numbers of females were still present on the sentinel animals. Ultimately, the application of five to seven fipronil treatments resulted in an extremely low tick population in the pasture, although total eradication of the population was not achieved during the study. The mean weight gain of treated animals was significantly higher (p < 0.05) than untreated animals during the study, indicating that the fipronil treatments had a highly beneficial impact on weight gain production.     

Control of lone star ticks (Acari: Ixodidae) on Spanish goats and white-tailed deer with orally administered ivermectin

Ivermectin administered orally to Spanish goats, Capra hircus (L.), or to white-tailed deer, Odocoileus virginianus (Zimmerman), was highly effective against lone star ticks, Amblyomma americanum (L.). For Spanish goats, daily oral doses of 20 micrograms/kg resulted in greater than or equal to 2 ppb ivermectin in the blood. This level was sufficient to cause greater than 95% reduction of estimated larvae from feeding ticks. A bioassay with horn flies, Haematobia irritans (L.), was developed to estimate oral intake of ivermectin. Probit analysis of dose-mortality data indicated that a 50% reduction in adult horn fly emergence can be expected when the manure from goats treated orally with ivermectin at 10, 20, 35, and 50 micrograms/kg/d was mixed with untreated cow manure at a rate of 0.345, 0.110, 0.100, and 0.092%, respectively. In studies with white-tailed deer, daily oral doses of 35 and 50 micrograms/kg/d provided 100% control of adult and about 90% control of nymphs that were placed on treated fawns. A single oral dose of 50 micrograms/kg gave greater than 90% control of adult and nymphal ticks attached to treated fawns at the time of drug administration and 70% control of ticks placed on treated deer three days thereafter. When ticks were placed on fawns treated with a single dose of ivermectin (50 micrograms/kg) the engorgement period was longer, ticks were lighter in weight, and females laid fewer eggs than ticks detaching from control fawns. A single oral dose of ivermectin at 20 micrograms/kg prevented about 60% of the adult and nymphal ticks attached at the time of drug administration from engorging, but did not affect other ticks placed on the animals after treatment.     

Partial strategic tick control within a herd of European breed cattle in the state of Rio Grande do Sul,southern Brazil

A trial is described, in the state of Rio Grande do Sul, southern Brazil, as one of a series suggested to investigate the effects of strategic but selective acaricide treatments of cattle within herds against Boophilus microplus. They are aimed at considering the repercussions of farmer attempts at immediate reductions in acaricide costs and the potential for creation of ‘refugia’ of untreated ticks. Half (Group 1) of a small experimental herd of European breed heifers were treated strategically against ticks, three times during the late spring–early summer and twice during autumn (southern hemisphere), with an injectable avermectin endectocide, designed to act directly against the first and third generations of parasitic B. microplus per ‘cattle tick year’ at this site, respectively. The consequent levels of infestations on all of the member cattle in their common pasture were monitored. Group 1 showed low to zero tick counts during the 28-day treatment interval periods and up to ca. 14 days after the last of such a series. Treated cattle, however, became re-infested outside of these periods and to levels that would be considered as unacceptable by farmers in the state. The untreated cattle (Group 2) showed infestations at generally higher levels, than their contemporaries, within and outside of the treatment periods. There were thus ample sources of larvae in the pasture, derived principally from falling, untreated engorged female ticks, re-infesting both the treated and untreated cattle. Advantages of maintaining chemically untreated cattle ticks within a herd, compared to their disadvantages as contaminants to classical strategic control procedures, merit re-evaluation, especially in relation to the recent, world-wide resurgence of acaricide resistance in B. microplus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two initial vaccinations with the Bm86-based Gavacplus vaccine against Rhipicephalus (Boophilus) microplus induce similar reproductive suppression to three initial vaccinations under production conditions

Background

The cattle tick, Rhipicephalus (Boophilus) microplus, affects livestock production in many regions of the world. Up to now, the widespread use of chemical acaricides has led to the selection of acaricide-resistant ticks and to environmental contamination. Gavac^plus is a subunit vaccine based on the recombinant Bm86 tick antigen expressed in yeast, capable to control infestations of R. microplus under controlled and production conditions. The vaccine constitutes the core element of broad control programs against this ectoparasite, in which acquired immunity in cattle to Bm86 is combined with a rational use of acaricides. At present, the conventional vaccine scheme consists of three doses that should be administered at weeks 0, 4 and 7, followed by a booster every six months.

Results

In this study we assayed a reduction in the number of the initial doses of Gavac^plus, evaluated the time course and the level of bovine anti-Bm86 antibodies elicited, and analyzed the vaccine effect on ticks engorging on immunized cattle under production conditions. Following three different immunization schemes, the bovines developed a strong and specific immune response characterized by elevated anti-Bm86 IgG titers. A reduction in the weight of engorging female ticks, in the weight of the eggs laid and also in R. microplus viable eggs percentage was obtained by using only two doses of Gavac^plus administered at weeks 0 and 4, followed by a booster six months later. This reduction did not differ from the results obtained on ticks engorging on cattle immunized at weeks 0, 4 and 7. It was also demonstrated that anti-Bm86 antibody titers over 1:640, measured in bovines immunized at weeks 0 and 4, were sufficient to affect weight and reproductive potential of female ticks as compared with ticks engorging on unvaccinated animals. In addition, no statistically significant differences were detected in the average weight of eggs laid by ticks engorged on immunized cattle that showed anti-Bm86 specific titers in the range of 1:640 to 1:81920.

Conclusion

The administration of two initial doses of Gavac^plus containing 100 μg of Bm86 antigen to non-immunized cattle under production conditions is sufficient to affect the weight and the reproductive capacity of R. microplus engorging females. According to these results, cattle herds' manipulation and vaccine costs could be potentially reduced with a positive impact on the implementation of integrated control programs against R. microplus.     

Systemic activity of closantel for control of lone star ticks,Amblyomma americanum (L.), on cattle

Cattle were treated once at 5 mg/kg orally or subcutaneously or daily at 0.1–5 mg/kg orally or 0.1–1 mg/kg subcutaneously with closantel, N-[5-chloro-4-[(4-chlorophenyl) cyanomethyl]-2-methylphenyl]-2-hydroxy-3,5-diiodobenzamide, and numbers and weights of engorged females, weights of egg masses and hatch of eggs of lone star ticks,Amblyomma americanum, were recorded.Effectiveness of treatments on reproduction was determined by comparing total estimated larvae (EL) (EL=wt. egg mass×est. % hatch×20000) or ticks from treated cattle with that of ticks from untreated cattle. With certain treatments, we also determined the effect of manure of treated cattle on survival of larvae of the horn fly,Haematobia irritans, or effect on survival and of fecundity of adult horn flies or stable flies,Stomoxys calcitrans, fed on blood from treated animals.The single oral treatment afforded essentially complete control of total EL only of ticks placed on the animal on the day of treatment, while the single subcutaneous treatment afforded >92% control of total EL of ticks placed on animal on treatment day and for 6 weeks posttreatment. Daily treatments of 0.5 mg/kg or greater orally and 0.1 mg/kg or greater subcutaneously afforded essentially complete control of total EL of ticks throughout the treatment period (3–12 weeks) and for 1–7 weeks after treatment was discontinued. An estimated concentration of >9 g/ml of blood was calculated by probit analysis to be necessary to provide >90% control of total EL of lone star ticks; that same concentration also provided >90% control of hatch of eggs laid by treated females. A higher concentration (40 g/ml) was necessary to prevent engorging of the females. No treatments tested were effective against larvae of the horn fly or adult horn flies or stable flies.     

Moxidectin evaluation against Solenoptes capillatus (Anoplura: Linognathidae), Bovicola bovis (Mallophaga: trichodectidae), and Musca autumnalis (Diptera: Muscidae) on cattle.

Slow release formulations of 375, 750, and 1,125 mg (AI) in 50-g boluses and a subcutaneous injectable formulation (0.2 mg AI/kg body wt) of moxidectin (CL301423) were tested for the control of the little blue cattle louse, Solenoptes capillatus (Enderlein), and the cattle biting louse, Bovicola bovis (L). S. capillatus populations were reduced 4 wk after treatment and complete control was observed 6 wk after treatment in groups treated with boluses, B. bovis were first observed at 3 wk and continued to increase throughout the 14-wk test period. These were experimental boluses and future boluses may perform differently. Subcutaneous injections of moxidectin gave complete control of S. capillatus for a 27-d test period. Feces from animals treated with boluses were tested with face fly larvae, Musca autumnalis De Geer, to demonstrate fecal activity of moxidectin. Larval mortality in these groups ranged from 90 to 30% from 2 d to 10 wk after treatment.     

Control of induced infestations of three African multihost tick species with sustained-release ivermectin

The efficacy of ivermectin, released intraruminally from a 28-day-delivery device was evaluated in two titration studies against induced infestations of adultRhipicephalus appendiculatus, R. evertsi andHyalomma truncatum on cattle. Cattle were given a sufficient number of devices to release ivermectin at approximately 20, 40, 60 or 80 g kg^–1 day^–1 at a steady-state rate 7–28 days after administration. Tick mortality was recorded, engorged female ticks were weighed and individually incubated, and reproductive data were recorded to determine a reproductive index for the species at various dose levels. Mortality of male and female ticks compared to that of controls was directly related to the daily dose of ivermectin, as was the number of ticks not engorging. Ticks fed on ivermectin-treated cattle had a smaller mass when engorged and laid smaller egg-masses, both absolutely and as a proportion of engorged mass.The index of reproduction ofR. appendiculatus was reduced by more than 99.9% at 20 g kg^–1 day^–1, and the reproductive indices ofR. evertsi andH. truncatum were reduced by more than 99.9% at dose rates of 40 g kg^–1 day^–1 and above.Practical implications of the application of sustained-release ivermectin for the control of multihost ticks and tick-borne diseases are discussed.     

Heifers don't care: no evidence of negative impact on animal welfare of growing heifers when using virtual fences compared to physical fences for grazing

Virtual fencing (VF) represents a way to simplify traditional pasture management with its high labour and cost requirements for fencing and to make better use of the ‘beneficial’ agronomic and ecological effects of livestock grazing. In this study, the VF technology (® Nofence, AS, Batnfjordsøra Norway) was used with Fleckvieh heifers to investigate possible welfare impacts on the animals compared to conventionally fenced animals when they were trained to respond correctly to the system. The Nofence® collars (attached to the neck of the heifers) send acoustic signals as a warning when the animals approach the VF line, which was set up by GPS coordinates within the Nofence®-App, followed by an electric pulse when they do not stop or return. The heifers had no experience with VF prior to the study. Two treatments (VF versus physical fencing (PF)) were applied to six groups of four heifers each (three groups per treatment) over three 12-day time replicates. One VF line separated the pasture of the VF group into an accessible or non-accessible area. The control group had a PF line. Both groups were equipped with Nofence® collars (deactivated for the PF group). The trial took place on two adjacent paddocks of 1 000 m² each following a 12-day schedule which was divided into three sections: visual support of the VF line by a physical barrier (first 2 days), only virtual border without visual support, moving the VF line (on day 8). Each time replicate followed the next successively on different paddocks with two new groups of heifers, which were grazed 5 h daily. During the whole experiment, the behaviour of each of the four animals per group was continuously observed; 2 h a.m., 2 h p.m. Exclusion by the VF line was effective in our trial. None of the heifers crossed the virtual boundary, i.e. the time spent in exclusion zone was zero. The heifers received 2.70 ± 2.63 acoustic signals and 0.30 ± 0.36 electric pulses (mean ± SD) per heifer and hour during all time replicates. Main cattle behaviour on pasture was not affected by the fencing system. Live weight gain, herbage consumption and faecal cortisol metabolites also revealed no significant differences. The duration until the heifers restarted grazing after an electric pulse from the Nofence® collar was significantly shorter than after an electric pulse from the physical fence. We can summarise that in our study, cattle well-being on pasture was not negatively affected by VF compared to PF.     

Preliminary studies on the effect of Anaplasma marginale antibodies ingested by Dermacentor andersoni ticks (Acari:Ixodidae) with their blood meal on infections in salivary glands

The effect of Anaplasma marginale antibodies ingested with the tick blood meal was tested on infected male ticks that were allowed to feed on cattle immunized with the erythrocytic stage of A. marginale. The experiments were done in two trials. Trial 1 was done using splenectomized calves (two calves per treated and control groups) while ticks in trial 2 were fed on intact yearling cattle (four cattle per treated and control groups). The cattle were immunized with purified outer membrane proteins of erythrocyte-derived A. marginale using saponin (trial 1) or monophosphoryl lipid-A-trehalose dicorynomycolate adjuvant (trial 2). The corresponding control cattle received adjuvant only. All cattle were challenged using Dermacentor andersoni males infected as adults that were allowed to feed for 7 days. In trial 1, the ticks were allowed to feed a second time on susceptible calves to test whether exposure of ticks to immunized cattle affected their ability to transmit anaplasmosis. Infections in fed ticks were monitored by determining the infection rates in salivary glands with an A. marginale-specific RNA probe and light microscopy. Vaccine-derived antibodies ingested with the tick blood meal did not appear to affect the development of A. marginale in previously infected ticks. The infection rates in the salivary glands were not significantly different among ticks fed on immunized versus adjuvant control cattle. When the vaccine-exposed ticks in trial 1 were allowed to feed a second time on susceptible calves, the resulting clinical symptoms of anaplasmosis were similar to those of the controls. There was no statistically significant effect of tick exposure to the anti-erythrocytic stage antibody on the development of salivary gland infection or transmission of A. marginale by ticks.     

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.     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production in dairy cattle

Abstract. The effect is reported of artificially controlled levels of infestation with adults of Rhipicephalus appendiculatus on the milk yield of twenty commercial Bos taurus dairy cattle on a high plane of nutrition and eighteen crossbed B.taurus × Sanga cattle on a lower plane of nutrition in the highveld of Zimbabwe. The results showed no significant effect on milk yield of infestations averaging twenty engorging ticks per animal per day, despite severe ear damage in some animals. They indicate that milk production of dairy cattle under commercial management is not sensitive to infestation with R.appendiculatus. The results have important implications for management of ticks in Africa, but need to be interpreted within the context of the control of tick-borne diseases.     

Prevalence of ixodid ticks on cattle in Mazandaran province, Iran

A survey was carried out to investigate the prevalence of hard tick species (Acari: Ixodidae) on cattle in Mazandaran province, Iran. A total of 953 ticks were collected from 86 infested cattle during activating seasons of ticks during 2004-2005. Nine species were identified: Boophilus annulatus (51.3%), Rhipicephalus bursa (16.8%), Haemaphysalis punctata (6.3%), Ixodes ricinus (6.8%), Hyalomma marginatum (12.5%), Hyalomma anatolicum excavatum (5.2%), Hyalomma asiaticum (0.6%), Hyalomma detritum (0.2 %), and Dermacentor spp. (0.1%). The results show that Boophilus annulatus, Rhipicephalus bursa, and Hyalomma species are dominant tick species in the surveyed area.     

Active immunization of cattle against partly purified follicular fluid from sheep

Yearling cross-bred heifers were injected with 0.4 or 4 mg total protein in non-ulcerative Freund's adjuvant (Groups A and C, respectively; N = 5 per group), or adjuvant with C. parvum (Groups B and D, respectively; N = 5 per group). Control heifers were not treated (N = 9). No antibodies were detected in heifers in Groups A and C and so these were excluded from the analysis. There was no effect of the treatment on Group B or D heifers after the priming or first booster injection. After a second booster injection one Group D heifer gave a triple ovulation, and two Group D heifers and one Group B heifer gave double ovulations, but for one oestrous cycle only. Group B heifers also showed a significant rise in FSH concentrations after the second booster injection. Group D heifers were given a third booster injection; there was an increase in the mean number of large follicles per heifer, and a decrease in oestrous cycle length, but no increase in ovulation rate. These results indicate that a transient increase in ovulation rate can be induced by actively immunizing cattle against partly purified follicular fluid from sheep.     

Analysis of doramectin in the serum of repeatedly treated pastured cattle used to predict the probability of cattle fever ticks (Acari: Ixodidae) feeding to repletion

Analysis of doramectin concentration in blood serum of pastured cattle injected repeatedly (12 treatments) at two different dosage rates and 28-day intervals throughout the year was used to predict the probability that cattle fever ticks could successfully feed to repletion during the interval between any two consecutive treatments. Treatment at ~270 μg/kg indicated that serum doramectin concentration dropped below the baseline concentration estimated for tick survival (8 ppb) in 7 of the 12 treatments. However, the longest period between any two treatments during which the doramectin concentration remained below the 8 ppb baseline level for successful tick feeding was 15 days, making it virtually impossible for any ticks to reach ovipositional status prior to a subsequent treatment. At a dosage rate of ~540 μg/kg, the concentration dropped below the baseline tick survival level (8 ppb) only once, following the initial treatment, and the duration during which the concentration remained below the baseline level prior to the subsequent treatment was only 6 days. Thus, at the high dosage rate results indicated, with absolute certainty, that no ticks could successfully feed to repletion between any two consecutive treatments. Based on the data obtained in the study it was concluded that analysis of doramectin concentration in serum of treated animals would be a reliable predictor for assessing the probability that ticks could successfully develop to repletion. More importantly, results demonstrated that the trial policy, instituted by the Cattle Fever Tick Eradication Program, of repeatedly treating cattle with doramectin injections at 25–28 day intervals for eliminating cattle fever ticks would produce little or no risk of any viable ticks developing to repletion and re-infesting the field between treatment applications.     

Licking behaviour induces partial anthelmintic efficacy of ivermectin pour-on formulation in untreated cattle

Licking behaviour in cattle has been reported to account for the disposition of topically administered macrocyclic lactones. However, its impact on anthelmintic efficacy remains to be established. Therefore, we evaluated the impact of ivermectin exchange between cattle on the reduction in the faecal egg count (FEC) after pour-on administration in a group of 10 heifers experimentally infected with Ostertagia ostertagi and Cooperia oncophora. Four treated (500 μg/kg, pour-on) and six untreated animals were put together after treatment and plasma and faecal exposure to ivermectin as well as the FECs were evaluated before and over 40 days after treatment. Ivermectin was detected in plasma and faeces of the six untreated heifers, with maximal exposures two- to three-fold lower than the minimal exposures in treated animals. The interindividual variability of exposure was very high in untreated animals, with a ten-fold difference between the upper and lower limits compared with treated heifers, where there was only a two-fold difference. Anthelmintic efficacy, expressed as an average reduction of the FECs over the experimental period, was maximal in the treated group. In untreated heifers, anthelmintic efficacies ranged from zero to maximal efficacy, with intermediary values between 30% and 80%. The use of a classical pharmacodynamic model demonstrated a clear relationship between exposure and efficacy and enabled us to define the critical plasma or faecal ivermectin concentrations delimiting an exposure window associated with partial anthelmintic efficacy. This range of ivermectin plasma concentrations (0.1-1 ng/mL) could be considered as a potential selection window for anthelmintic resistance. Finally, our results show that macrocyclic lactone exchange between cattle after pour-on administration, resulting from natural grooming behaviour, can significantly impact on anthelmintic efficacy. This raises several issues such as the design of comparative clinical trials and the occurrence of partial efficacy which is considered a risk factor for the development of anthelmintic resistance.     

Reproductive and endocrine effects of active immunization against a testosterone conjugate in the heifer

Yearling heifers were actively immunized against 8 mg testosterone-3-carboxymethyloxime-ovalbumin in Non-Ulcerative Freund's Adjuvant, with or without the addition of Corynebacterium parvum (Groups A and B, respectively; N = 4 for each group). After the priming injection, Groups A and B were boosted twice at 4-monthly intervals. Control heifers (N = 9) were not injected. All treated animals except one gave a measurable antibody response, and all responding animals became anoestrous and displayed ovarian cysts after the first booster injection. There were no apparent differences between treatments, and so results for Groups A and B were pooled. At 25 weeks after the second booster 3 of the 7 responding, anoestrous heifers resumed cyclicity; one with two consecutive double ovulations, and one with one double ovulation. The 3rd heifer showed 4 corpora lutea, then became anoestrus again. The 4 remaining acyclic heifers, and the control heifers, were intensively blood sampled; the anoestrous heifers showed significantly higher mean LH and significantly lower mean FSH concentrations and higher LH pulse frequency than did the control animals. These heifers remained anoestrous for 11 months after the second booster, at which point they were injected with GnRH and PGF-2 alpha; only 1 heifer resumed ovarian cyclicity. These results indicate that it is possible to increase ovarian activity in cattle by active immunization against testosterone, but that there is a high incidence of anoestrus.     

The effect of grazing location and oronasal treatment with bull urine on reproductive performance and serum prolactin concentrations of beef heifers

Grazing location and biostimulatory treatments were imposed on 55 Brangus and crossbred heifers in a 2 x 2 x 2 factorial arrangement. Grazing locations (postweaning) were semi-desert rangeland with supplementation or irrigated small grains pasture. Biostimulatory treatment involved either weekly oronasal application of bull urine or no treatment (control). The duration of bull urine treatments was 8 weeks. Grazing location affected heifer weights from February through August (P < 0.01). Rate of weight gain on irrigated pasture exceeded native range (P < 0.01). Cyclicity was similar between the location groups before the treatment period. Post-treatment cyclicity rates of heifers were 25 and 78% for native range and irrigated pasture, respectively (P < .01). Twenty-five percent of cyclic heifers grazing native range went into anestrus during this treatment period, while no loss of cyclicity was observed in the heifers on irrigated pasture (P < 0.10). Heifers maintained on irrigated pasture exhibited more standing estrus following synchronization (P < 0.10), higher pregnancy rates following breeding (P < 0.05), heavier fall weights (P < 0.01), higher body condition scores (P < 0.01), and greater pelvic widths (P < 0.05) than those on native range. Cyclic heifers grazing native range had prolactin levels twice those of irrigated pasture heifers. Serum growth hormone levels were not consistently affected by treatments. Heifers which became pregnant while grazing irrigated pasture had much lower prolactin concentrations in serum collected in January than the noncyclic heifers.