A STUDY OF THE EPIDEMIOLOGY OF ANAPLASMA MARGINALE INFECTIONS OF CATTLE IN SOUTHERN QUEENSLAND: CLINICAL DISEASE AND THE PREVALENCE OF COMPLEMENT FIXING ANTIBODIES

SUMMARY A total of 386 clinical outbreaks of anaplasmosis were confirmed in Queensland south of the 22nd parallel over the period 1967 to 1976. Seventy-eight per cent of these outbreaks occurred during autumn and winter and only 6.8% involved cattle less than 1 year of age compared with 54.8% for cattle more than 3 years old. Dairy breeds were involved in 48.1% of 258 outbreaks compared with 51.9% for beef breeds. Bos taurus beef breeds were involved in 90.7% of 118 outbreaks compared with 9.3% for Bos indicus crossbreds. Approximately 3 times as much clinical disease per head of population was confirmed in tick (Boophilus microplus) infested southern Queensland south of the 25th parallel (south zone) than in areas between the 25th and 22nd parallel (north zone). A survey was conducted during 1975 in which 3,810 cattle from 241 herds were sampled on the basis of the distribution of the cattle population. The prevalence of CF reactors in tick-infested areas was 42.1% of 3,026 samples compared with 0.4% of 784 samples from tick-free areas. The prevalence in the north zone was 52.3% compared to 30.2% for the south zone and it also varied with the type of animal sampled. The prevalence in Bos taurus cattle was significantly greater than in Bos indicus types and it increased with age of the animal. No significant difference in susceptibility to infection attributable to sex could be demonstrated. Animals exposed to heavy to medium tick infestations had significantly more CF reactors than those exposed to light infestation. Higher stocking densities were associated with higher prevalence levels. Thus anaplasmosis is predominantly a disease of autumn and winter and of cattle greater than 1 year of age. Both clinical and subclinical infection occur only in tick-infested areas and B. microplus is considered to be the main, if not the only vector. Both clinical and inapparent infection are more frequent in Bos taurus than in Bos indicus types.     

Modulation of cutaneous inflammation induced by ticks in contrasting phenotypes of infestation in bovines

Tick saliva contains molecules that are inoculated at the site of attachment on their hosts in order to modulate local immune responses and facilitate a successful blood meal. Bovines express heritable, contrasting phenotypes of infestations with the cattle tick, Rhipicephalus (Boophilus) microplus: breeds of Bos taurus indicus are significantly more resistant than those of Bos taurus taurus. Tick saliva may contain molecules that interfere with adhesion of leukocytes to endothelium and resistant hosts may mount an inflammatory profile that is more efficient to hamper the tick's blood meal. We show in vitro that adhesion of peripheral blood mononuclear cells to monolayers of cytokine-activated bovine umbilical endothelial cells was significantly inhibited by tick saliva. The inflammatory response to bites of adults of R. microplus mounted by genetically resistant and susceptible bovine hosts managed in the same pasture was investigated in vivo. The inflammatory infiltrates and levels of message coding for adhesion molecules were measured in biopsies of tick-bitten and control skin taken when animals of both breeds were exposed to low and high tick infestations. Histological studies reveal that cutaneous reactions of resistant hosts to bites of adult ticks contained significantly more basophils and eosinophils compared with reactions of the susceptible breed. Expression of the adhesion molecules – intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin – was higher in adult-infested skin of susceptible hosts undergoing low infestations compared to resistant hosts; when host was exposed to high infestations expression of these adhesion molecules was down-regulated in both phenotypes of infestations. Expression of leukocyte adhesion glycoprotein-1 (LFA-1) was higher in skin from susceptible hosts undergoing low or high infestations compared to resistant hosts. Conversely, higher levels of E-selectin, which promotes adhesion of memory T cells, were expressed in skin of resistant animals. This finding may explain the resistant host's ability to mount more rapid and efficient secondary responses that limit hematophagy and infestations. The expression profiles observed for adhesion molecules indicate that there are differences in the kinetics of the inflammatory reactions mounted by resistant and susceptible hosts and the balance between tick and host is affected by the number of tick bites a host receives. We show that the contrasting phenotypes of infestations seen in bovines infested with R. microplus are correlated with differences in the cellular and molecular composition of inflammatory infiltrates elicited by bites with adult ticks.     

THE EFFECT OF CATTLE TICK (BOOPHILUS MICROPLUS) ON PREGNANT AND LACTATING BRAHMAN-CROSS AND BRITISH-BREED COWS IN NORTHERN AUSTRALIA

Natural infestations of cattle tick (Boaphilus microplus) on breeding Hereford, Shorthorn and Brahman-cross cows were observed in a dry tropical environment. Herefords were dipped three times and Shorthorns four times during a 12 month period, while the Brahman-cross cattle were dipped twice during a 3-year period. No differences in tick infestations could be shown between pregnant and non-pregnant or lactating and non-lactating cows even though they were under severe nutritional stress. No consistent negative correlations were shown between body- weight changes and tick counts. This was probably due to the effect of dipping in the Herefords and Shorthorns. There was a trend towards significant negative correlations in July and August over each of three years for undipped Brahman-cross cows. Some form of tick control on breeding Brahman-cross cows, aimed at reducing tick burdens during July to September may be beneficial in the environment under study.     

Recombinant mid gut antigen (Bm95) as a vaccine against Indian Rhiphicephalus haemaphysaloides in Bos indicus cattle

In the present study, we report for the first time the efficacy of recombinant Bm95 mid gut antigen isolated from an Argentinean strain of Rhipicephalus microplus strain A in controlling the tick infestations in India. The synthetic gene for Bm95 optimized for expression in yeast was obtained and used to generate yeast transformants expressing Bm95 which was purified to apparent homogeneity. Liquid chromatography-mass spectrometry analysis of the purified protein confirmed its identity as Bm95. Vaccine was prepared by blending various concentrations of purified Bm95 with aluminium hydroxide as an adjuvant. Immunogenicity studies of the vaccine in rabbits and cattle indicated that the vaccine was highly immunogenic. The efficacy studies of the vaccine was done in cattle. Naïve Bos indicus cattle were vaccinated with the recombinant vaccine and were challenged with the larval, nymphal and adult forms of Rhiphicephalus haemaphysaloides. The vaccine protected the animals from larval, nymph and adult tick challenges with an efficacy of 98.7%, 84.6% and 78.9% respectively. The results obtained from the above studies clearly demonstrated the advantage and possibilities of the use of Bm95 in controlling R. haemaphysaloides infestations in the field.     

Immunoprotective Efficacy of a Purified 39 kDa Nymphal Antigen of Hyalomma anatolicum anatolicum

Soluble nymphal antigens (HNAg) were purified by immunoaffinity chromatography using CNBr-activated Sepharose 4B coupled with immunoglobulin ligands from animals immunized with HNAg and 69–71% protected against challenge infestations, and 8% recovery of the purified protein (Aff-HNAg) was obtained. Following immunization of crossbred calves (Bos indicus×Bos taurus) with 1600 g of Aff-HNAg in three divided doses, significant rejections of larvae (p<0.001, 84.2%), nymphs (p<0.05, 61.4%) and adults (p<0.05, 58.7%) were recorded. No significant changes were recorded in the engorgement weights of the larvae and nymphs, but there was a significant (p<0.05) reduction in the weight of the engorged adults. Immunization conferred a significant decrease in the numbers of resultant nymphs (p<0.001) and adults (p<0.001) that had fed on the immunized animals. SDS-PAGE analysis identified a 39 kDa protein, previously isolated from larvae of Hyalomma anatolicum anatolicum, as the antigen responsible for the induction of resistance against all the stages of the tick.     

Studies on the Epidemiology of Tropical Theileriosis (Theileria annulata Infection) in Cattle in Central Anatolia,Turkey

An epidemiological survey for Theileria annulata infection was conducted in 12 selected villages around Ankara in Central Anatolia, Turkey, during the period April 1990 to January 1993. During the survey, 198 cattle of 30 local breeds, 84 Holstein-Friesian×local breeds and 84 Holstein-Friesian breed were examined for antibodies to T. annulata and the presence of the vector ticks. Four species of Hyalomma ticks were identified: Hyalomma anatolicum anatolicum, Hyalomma anatolicum excavtum, Hyalomma detritum and Hyalomma marginatum marginatum. Salivary gland staining indicated that infected adult ticks of all four species were present and, therefore, were implicated in the transmission of tropical theileriosis in the field. Generally, the Hyalomma infestation rate was low, with the heaviest infestations occurring on the older animals. Young adults and calves had very low infestation rates. Most ticks seen on cattle were adults, very few nymphs were found. The blood smear and serological examination of the 198 cattle conducted in March, before the start of the first disease season, showed that the prevalence of piroplasmosis was 11.1% (22 out of 198) and the seroprevalence of T. annulata was 10.6% (21 out of 198). Forty-three animals were then excluded from the study because they were seropositive and/or harboured piroplasms. Ninety-two seronegative animals showed piroplasmosis (92 out of 155) and 34 seronegative animals became seropositive for T. annulata (34 out of 155) during the three disease seasons. One animal became clinically ill with tropical theileriosis and required treatment. The incidence of cattle showing piroplasmosis and disease in the total study sample was 50.7% and 0.5% per disease season, respectively. The seroconversion rate of new infection with T. annulata in the total study was 14.3% per animal season. The number of cattle showing piroplasmosis was much greater than the number of seropositive cattle, which may indicate the presence of another species of Theileria. The two different management systems encountered in the study were considered to have influenced the tick infestation levels.     

Plasma Antimullerian Hormone as a Predictor of Ovarian Antral Follicular Population in Bos indicus (Nelore) and Bos taurus (Holstein) Heifers

In Bos taurus cattle, antimullerian hormone (AMH) has been demonstrated to have a high degree of correlation with ovarian antral follicle count and the number of healthy follicles and oocytes. To document the correlation between the plasma concentration of AMH and follicular number in Bos indicus and Bos taurus heifers, Nelore (Bos indicus, n = 16) and Holstein heifers (Bos taurus, n = 16) had their ovarian follicular waves synchronized. After synchronization, ovarian antral follicular population (AFP) was evaluated three times at 60‐day (d) intervals (T‐120 d, 120 days before plasma AMH determination; T‐60 d, 60 days before; and T0, at the time of plasma AMH determination). The plasma AMH concentration was positively correlated with the number of ovarian follicles on the day of the follicular wave emergence in Bos indicus (Nelore) and Bos taurus (Holstein) heifers at each evaluation time (p < 0.05). The AFP was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.05). Similarly, the AMH concentration was higher in Bos indicus (Nelore) than in Bos taurus (Holstein) heifers (p < 0.0001). When heifers were classified as to present high or low AFP according to the mean of the AFP within each genetic group, high‐AFP heifers presented a greater (p < 0.0001) AMH concentration than low‐AFP heifers, regardless of the genetic group. In conclusion, the AFP is positively correlated with plasma AMH concentration in both Bos indicus (Nelore) and Bos taurus (Holstein) heifers. Furthermore, Bos indicus (Nelore) heifers presented both greater plasma AMH concentrations and AFP than Bos taurus (Holstein) heifers.     

Relationship between the resistance of crossbred cattle to ticks, Boophilus microplus (Canestrini, 1887) and Hyalomma anatolicum anatolicum (Koch, 1844)

Studies were undertaken to determine the effect of repeated pure infestations with Boophilus microplus on susceptibility to subsequent pure infestations with Hyalomma anatolicum anatolicum, and the effects of pure infestations with both species of tick on susceptibility to a series of mixed infestations. Crossbred (Bos indicus X Bos taurus) calves were infested with Boophilus microplus (17 times), H. a. anatolicum (four times), followed by five mixed infestations of B. microplus and H. a. anatolicum. The decline in B. microplus engorgement from a mean yield of 274.4 +/- 60.3 ticks per host after the first exposure, to a mean yield of 9 +/- 4.6 per animal after the seventeenth exposure, was observed in animals exposed to only B. microplus. This might be due to acquired resistance. However, these animals were found to be as susceptible to H. a. anatolicum as animals which had never been exposed to ticks of either species. A decline in the yield of H. a. anatolicum from a mean yield of 92.1 +/- 10.7 after the first exposure to 54.7 +/- 11.3 after the fourth exposure, indicated that the cattle could also acquire resistance to repeated pure infestations with this species. After repeated pure infestations with both tick species, cattle reacted to five mixed infestations showing a high degree of resistance to B. microplus and low resistance to H. a. anatolicum (mean yield for B. microplus was only 10 +/- 8.1 ticks per host after the first mixed exposure and declined to 1.3 +/- 1.7 after the fifth, whereas the mean yield for H. a. anatolicum was 71.4 +/- 11.3 ticks per host following the first exposure and declined to 37.3 +/- 7.8 after the fifth). Host responses elicited to one species do not provide cross-resistance to the second species used in this study.     

Seasonal Activity of Ticks on Small Ruminants in Tamil Nadu State,India

The seasonal activity of ticks on sheep and goat populations was examined from December 2000 to November 2001 in the state of Tamil Nadu, India. This longitudinal study spread over four seasons and seven agroclimatic zones took into consideration the spectrum of species involved, the levels of infestations, the seasonal epidemiology of ticks and the associated management practices. The most common species of tick spread throughout the state was Haemaphysalis bispinosa followed by Rhipicephalus haemaphysaloides, Hyalomma marginatum isaaci and Hyalomma anatolicum anatolicum with mixed infestations being the rule. Although the infestations were found throughout the year, they were greater during the rainy season and rainfall seemed to be the most important climatic factor affecting seasonal variation. In general, most of the small-ruminant populations carried moderate tick burdens with mixed infestations and this varied with the management practices.     

Cyhalothrin—a novel acaricidal and insecticidal synthetic pyrethroid for the control of the cattle tick (Boophilus microplus) and the buffalo fly (Haematobia irritans exigua)

SUMMARY Cyhalothrin, a novel synthetic pyrethroid, was evaluated for control of the major resistant strains of the cattle tick (Boophilus microplus) and for control of the buffalo fly (Haematobia irritans exigua) on cattle. In regulated treatment trials with 0.007% cyhalothrin, greater than 99% control of the Biarra, Mackay, Mt Alford, DDT resistant and Ulam cattle tick strains was obtained. Protective-period trials were conducted in which animals which had been sprayed with 0.007% cyhalothrin then received a continuing heavy challenge of the organophosphate-resistant Biarra tick strain. The first semi-engorged adult ticks appeared no earlier than 27 days after treatment, which corresponds to a minimum protective period against reinfestation of 7 days. Protective-periods ranging from 7 to 15 days were obtained in trials that were conducted.     

Immunoprotective potential of a Rhipicephalus (Boophilus) microplus metalloprotease

Ticks have serious impacts on animal and human health, causing significant economic losses in cattle breeding. Besides damage due to the hematophagous behavior, they transmit several pathogens. Low cost and environmental safety have made vaccines a promising alternative control method against tick infestation. Metalloproteases (MPs) have been shown to be essential for diverse biological functions in hematophagous organisms, inhibiting blood clotting, degrading extracellular matrix proteins, and inhibiting host tissue repair via anti-angiogenic activity. In this study, we analyzed the immunoprotective potential of a recombinant MP against Rhipicephalus (Boophilus) microplus infestation. First, a cDNA encoding R. microplus amino acids sequence with highly conserved regions of the metzincin (reprolysin) group of MP was identified (BrRm-MP4). After expression and purification, recombinant BrRm-MP4 was used as a vaccinal antigen against R. microplus infestation in cattle (Bos taurus taurus). All vaccinated bovines developed immune response to the antigen, resulting in increased antibody level throughout the immunization protocol. Immunization with rBrRm-MP4 reduced tick feeding success, decreasing the number of engorged females and their reproduction potential, representing a 60% overall protection. These results show that rBrRm-MP4 provides protection against tick infestation, placing it is a potential candidate for an anti-tick vaccine.     

Differential expression of insulin‐like growth factor family members in immature cumulus–oocyte complexes from dairy cows with different genotypes

It has been evident the improvement of in vitro embryo production (IVEP) in dairy cows. Nevertheless, it is known that differences in the number and quality of oocytes between taurine and zebu females impact the efficiency and economic viability of IVEP. As the insulin‐like growth factor (IGF) system is related to follicular and oocyte development, we aimed to quantify mRNA abundance of IGF system members and pregnancy‐associated plasma protein‐A (PAPPA) in the cumulus–oocyte complexes (COCs) of Gir, 1/2 Holstein × 1/2 Gir and Holstein cows. Four pools of 30 immature COCs from Gir, 1/2 Holstein × 1/2 Gir and Holstein cows were obtained by ovum pickup (OPU), and the oocytes and cumulus cells (CC) were mechanically separated and stored at ?80°C. Total RNA was extracted from pools of 30 oocytes and their respective CC. Expression of target genes was assessed by real‐time RT‐PCR. In oocytes, the abundance of IGFR1 mRNA was higher (p < .05) in Gir cows compared with the other breeds. In contrast, in CC, mRNA encoding IGF2 (p < .05), IGFR2 (p < .05) and IGFBP4 (p < .01) was higher in Holstein donors compared with Gir and 1/2 Holstein × 1/2 Gir cows. Additionally, the abundance of PAPPA mRNA was higher in oocytes (p < .001) and CC (p < .01) in Gir and 1/2 Holstein × 1/2 Gir cows compared with the Holstein donors. In conclusion, the higher abundance of PAPPA mRNA in the oocytes and CC from Gir and cross‐breed donors combined with the low expression of IGFBP4 in the CC suggests an enhancement of the bioavailability of IGF‐free when compared with Holstein COCs.     

The Effects of Salivary Gland Extracts from <Emphasis Type="Italic">Boophilus microplus</Emphasis> Ticks on Mitogen-stimulated Bovine Lymphocytes

The effect of salivary gland extract (SGE) from the tick Boophilus microplus was examined in mitogen-stimulated lymphocytes in vitro. SGE was added to lymphocytes of seven cattle together with the mitogens concanavalin A (ConA), phytohaemagglutinin (PHA) and pokeweed mitogen (PWM). Semi-purified B cells from another seven cattle were stimulated with the mitogen lipopolysaccharide (LPS). PHA and ConA stimulated proliferation of lymphocytes to the same extent, but the inhibition due to SGE of Boophilus microplus on the proliferative response stimulated by PHA (39.0% ± 9.3%) was less than the inhibition of proliferative response stimulated by ConA (75.4% ± 6.9%). In contrast, SGE of B. microplus stimulated the proliferation of B cells in the presence of LPS in a dose-dependent manner. Enhanced stimulation of B cells by SGE at >4 μg in culture was greater than twice that observed when B cells were stimulated by LPS alone. SGE does not have a direct suppressive effect on bovine B cell proliferation; however, in vivo the effectiveness of B cell responses might be influenced by other immune factors, such as cytokine profiles.     

Does Rhipicephalus microplus tick infestation increase the risk for myiasis caused by Cochliomyia hominivorax in cattle?

The larval phase of Cochliomyia hominivorax (screwworm) is an obligate parasite of vertebrate animals, particularly mammals, and widespread in South America, where it remains one of the most important parasitic diseases of domestic animals. The skin of cattle highly infested by ticks, with cutaneous lesions, exudation of tissue fluid and blood scent seems to produce the ideal environment for fly attraction. However, an association between these parasites was never investigated. The aim of this work was to verify if there is an association between Rhipicephalus microplus tick load and the occurrence of C. hominivorax myiasis in cattle, and to quantify the risk. Sixty bovine (Bos taurus taurus, Angus breed) under field conditions were observed for 24 weeks, during which weekly tick counts and examination for the presence of myiasis were performed. There was a significant association between a high tick burden (24-week mean above 50 ticks per animal) and myiasis occurrence (P = 0.0102). The calculated relative risk (RR) for C. hominivorax myiasis occurrence in cattle with high tick burden was 3.85 (CI95% = 1.23–12.13); indicating that cattle highly parasitized by R. microplus have about four times more risk of myiasis than those with a low parasite load. As far as we aware, this is the first statistically based evidence of the relationship between R. microplus parasitic load and occurrence of myiasis by C. hominivorax. This result could be useful for the design of integrated control strategies for these parasites and to provide more information for the understanding of cattle tick parasitism in cattle production.     

Attempted immunisation of crossbred calves (Bos taurus × Bos indicus) by repeated natural attachment of ticksHyalomma anatolicum anatolicum Koch (1844)

Summary Crossbred calves (Bos taurus × Bos indicus) were repeatedly infested with the ixodid tick,Hyalomma anatolicum anatolicum. The parameters of engorgement, pre-oviposition period, oviposition period, engorged weight, egg batch weight, and per cent hatch of eggs all showed statistically significant differences between first to tenth infestation. Only the time to engorgement did not change. It is concluded that repeated infestations of this tick stimulate acquired resistance.

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Resumen Terrneros cruzadosBos taurus × Bos indicus se infestaron de manera natural. Con la grrapata ixodes,Hyalomma anatolicum anatolicum. Los parámetros medidos de ingurgitación, período de pre-oviposición, período de oviposición, peso de ingurgitación, peso del bache de huevos puestos y el porcentaje de eclosión de los mismos, presentaron diferencias estadísticamente significativas entre la primera y décima infestación. Lo único que no cambió fue el tiempo de ingurgitación. Se sugiere que la infestación repetida de esta garrapata, estimula la resistencia adquirida.

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Résumé Des veaux issue de croisementsBos taurus × Bos indicus ont été soumis à une infestation répétée parHyalomma anatolicum anatolicum. Les paramètres suivants: gorgement, périodes de préet d'oviposition, poids en fin de gorgement, poids du lot de ponte et pourcentage d'oeufs éclos, ont tous montré des différences significatives entre la première et la dixième infestation; seule la durée de gorgement n'a pas varié. Les auteurs concluement que les infestations répétées par cette tique stimulent la résistance acquise des veaux.

     

Hard ticks on one-humped camel (Camelus dromedarius) and their seasonal population dynamics in southeast, Iran

The primary objective of this study was to determine the diversity and intensity of ticks found on camels (Camelus dromedarius) and their seasonal population dynamics in Kerman, southeast of Iran. For this purpose, a total of 426 tick specimens were collected from 217 infested camels in southeast of Iran during activating seasons of ticks (April 2009 to March 2010). The species collected from camel were Hyalomma dromedarii (84.7%), Hyalomma marginatum (8.7%), Hyalomma anatolicum excavatum (5.4%), and Hyalomma anatolicum anatolicum (1.2%). The highest seasonal activities occurred in summer. The ratio of male ticks was more than female ticks. H. dromedarii was the predominant tick species and accounted for 84.7% of the ticks.     

Dairy Production and Reproduction by Crosses of Holstein,Jersey or Brown Swiss Sires with Holstein-Friesian/Gir Dams

The performance was compared of cows sired by Holstein, Jersey or Brown Swiss bulls out of Holstein-Friesian×Gir dams of 1/2 to 3/4 Holstein-Friesian content. The animals were kept in a single herd under the same management. The data were analysed by least-squares techniques under a model that included the fixed effects of breed of sire, Bos taurus fraction of the dam, parity, year and season of calving, and a random cow effect. Based on 480 observations, the milk yields per lactation for the Holstein, Jersey and Brown Swiss sired groups were 2821±163, 2320±61 and 2418±119 kg, respectively. The corresponding means for fat yield per lactation were 96.9±6.6, 86.8±2.5 and 92.8±4.8 kg; for protein yield per lactation were 85.3±5.1, 71.3±1.9 and 76.3±3.7 kg; for lactation length, 339±18, 283±7 and 313±14 days for fat percentage, 3.37±0.10, 3.73±0.04 and 3.77±0.07%; and for protein percentage, 3.02±0.05, 3.10±0.02 and 3.16±0.04%. The respective calving intervals were 487±24, 408±11 and 461±245 days. The yields of milk and protein per day of calving interval were similar in the Jersey and Holstein sired groups, while the former had higher yields of fat, implying that production economics might favour the smaller Jersey crosses in production systems in which the males were not reared. Crossing with Brown Swiss did not improve performance over the Holstein sired crosses.     

Studies on seasonal dynamics of ticks of ogaden cattle and individual variation in resistance to ticks in eastern Ethiopia

In this study the dominant tick species identified were Amblyomma cohaerens 52.2%, Rhipicephaluspravus 19.3% and A. variegatum 14.6%. A. cohaerens occurred throughout the sampling period and showed a peak during March. Their number declined significantly (P < 0.01) from August to December. R. pravus occurred from July to December only and peaking in September (P < 0.01). A. variegatum occurred in low numbers throughout the study period with a marked seasonal variation (P < 0.01) and abundant numbers of ticks were observed from May to July. The other tick species identified were Boophilus decoloratus, R. bergeoni and R. evertsi evertsi. Individual variation in tick infestation level was observed among the animals (P < 0.05). Since all the animals were of the same breed, age group and were managed similarly the selection of animals with low infestation level can be a component of tick control strategy.     

Diversity of Ectoparasites in Sheep Flocks in Sa~o Paulo,Brazil

The occurrence of ectoparasites in sheep flocks is frequently reported but seldom quantified. Sheep production used to be a predominantly family activity in the state of Sa~o Paulo (Brazil), but it began to become a commercial activity in the past decade. Thus, information about the ectoparasites existing in sheep flocks has become necessary. The present data were obtained by means of questionnaires sent to all sheep breeders belonging to the `Associaça~o Paulista de Criadores de Ovinos' (ASPACO; Sa~o Paulo State Association of Sheep Breeders). Response reliability was tested by means of random visits paid to 10.6% of the respondents. Most of the properties (89.5%) reported the presence of one or more ectoparasites. Screw-worm (Cochliomyia hominivorax) was the most frequent ectoparasite (72.5%), followed by bot fly larvae (Dermatobia hominis, 45.0%), ticks (Amblyomma cajennense) and Boophilus microplus, 31.3%) and finally lice (Damalinia ovis, 13.8%). Combined infestations also occurred, the most common one being screw-worm with bot fly larvae (36.0%) followed by bot fly larvae with ticks (13.9%), screw-worm with ticks (9.3%), bot fly larvae with lice (6.9%), and ticks with lice (5.0%). The most common triple combination was screw-worm, bot fly larvae and ticks (12.8%). Breeds raised for meat or wool were attacked by bot fly larvae and ticks more often than other breeds. Lice were only absent from animals of indigenous breeds. The relationships among these ectoparasites are discussed in terms of sheep breeds, flock size, seasonality and the ectoparasitic combinations on the host.     

Seasonal variations in sexual behavior, testosterone, testicular size and semen characteristics, as affected by social dominance, of tropical hair rams (Ovis aries)

The purpose of this study was to examine the effect of day length on seminal characteristics, testicular size, sexual behavior and testosterone concentration (T4) in dominant and subordinate Pelibuey rams. Six groups of three animals were evaluated every 2 weeks over a 12 month period. Dominant (D), medium (M) and subordinate (S) animals in each group were identified through a food competition test every 15 days. All rams ejaculated and produced semen throughout the year. A linear hierarchy was clearly established and maintained during the year. S rams had lower levels (P < 0.05) of semen volume, sperm concentration and testicular volume than D rams, regardless of season. Scrotal circumference was not influenced (P > 0.05) by their social position. D rams were more affected by the photoperiod, decreasing (P < 0.05) reaction times, increasing (P < 0.05) T₄ and producing more (P < 0.05) sperm per ejaculation than S rams during short days (14.65 ± 1.22 vs 26.92 ± 1.65 s; 8.68 ± 0.44 vs 7.37 ± 0.40 ng/mL and 3.37 ± 0.17 vs 2.04 ± 0.16 sperm/10⁹, respectively). Semen volume and sperm concentration were significantly (P < 0.05) greater during short days in all rams, regardless of their social status, with the exception of sperm concentration in D rams where no variation was found. M rams displayed variable values in the range between the D and S rams. It was concluded that the magnitude of the seasonal effects was not sufficient to prevent the rams being used for breeding throughout the year and that seasonal variation within the variables affected the social ranks differently.