Semen evaluation techniques and their relationship with fertility

This review summarizes those methods - established and emerging of semen assessment whose outcom e intents revealing its potential fertility and, as a carry over concept, that of the sire whose semen we examined. The review does not, however, focus on the wide display of current techn iques designed to explore specific or multiple sets of sperm attributes essential for fertilization but on two basic con cerns present: the heterogeneity of the sperm suspension and the multitude of attributes required for each spermatozoon to be fertile; concepts that shadow our diagnostic capabilities. The review points out advancements in the exploration of the genome, the transcriptome, and the proteome of both spermatozoa and the seminal plasma which unveil how spermatozoa modulate their own survival an d signal to the environment when displaying degenerative changes. Specific seminal plasma components, both among individuals and portions of the ejaculate, not only relate to survival but also signal differential immune tolerance by the female with a previ ously unattended linkage to fertility. Lastly it foresees how Cytomics, combining novel designed motility analyzers, flow cytometers and enhanced digital imaging shall dominate the landscape of andrological laboratories and enable quick determinations on huge sperm numbers for markers highly relevant to sperm function and hence, for fertility.

Sperm biotechnologies in domestic species: state of the art

Modern livestock breeding is basically dependent on the proper use of semen for artificial insemination of femeles and of other reproductive biotechnologies such as the production of embryos in vitro for embryo transfer (IVP). Both these techniques have made possible not only the wide dissemmation of genetic material onto breeding populations but also anhanced the selection of best sires, owing to the development of better diagnostic techniques for sperm function and of preservation of seminal material over time. Although use ofliquid semen cooled to room temperature, to intermediate temperatures (+16-20ºC) or chilled (+5ºC) dominates in different species cryopreservation is preferred in bovine A1 and it is advancing in other species by the design of new containers, freezing methods and the use of better insemination strategies. Techniques to separate the aliquot of most robust spermatozoa from an ejaculate have shown a renascent particularly for sires with low sperm quality, and technological advances in separating spermatozoa for c hromosomal sex make the technique suitable for commercial use, following applicat ion of novel findings in sperm and seminal plasma (SP) diagnostics and function. Alongside, knowledge of the epigenome and signalling c apabilities of the semen (sperm and SP) call s for further studies regarding transgene production via ICSI for IVP or AI.

Sperm biotechnologies in domestic species: state of the art

Modern livestock breeding is basically dependent on the proper use of semen for artificial insemination (AU) of femeles and of other reproductive biotechnologies such as the production of embryos in vitro for embryo transfer (IVP). Both these techniques have made possible not only the wide dissemmation of genetic material onto breeding populations but also anhanced the selection of best sires, owing to the development of better diagnostic techniques for sperm function and of preservation of seminal material over time. Although use ofliquid semen cooled to room temperature, to intermediate temperatures (+16-20ºC) or chilled (+5ºC) dominates in different species cryopreservation is preferred in bovine A1 and it is advancing in other species by the design of new containers, freezing methods and the use of better insemination strategies. Techniques to separate the aliquot of most robust spermatozoa from an ejaculate have shown a renascent particularly for sires with low sperm quality, and technological advances in separating spermatozoa for c hromosomal sex make the technique suitable for commercial use, following applicat ion of novel findings in sperm and seminal plasma (SP) diagnostics and function. Alongside, knowledge of the epigenome and signalling c apabilities of the semen (sperm and SP) call s for further studies regarding transgene production via ICSI for IVP or AI.(AU)

Semen evaluation techniques and their relationship with fertility

This review summarizes those methods - established and emerging of semen assessment whose outcom e intents revealing its potential fertility and, as a carry over concept, that of the sire whose semen we examined. The review does not, however, focus on the wide display of current techn iques designed to explore specific or multiple sets of sperm attributes essential for fertilization but on two basic con cerns present: the heterogeneity of the sperm suspension and the multitude of attributes required for each spermatozoon to be fertile; concepts that shadow our diagnostic capabilities. The review points out advancements in the exploration of the genome, the transcriptome, and the proteome of both spermatozoa and the seminal plasma which unveil how spermatozoa modulate their own survival an d signal to the environment when displaying degenerative changes. Specific seminal plasma components, both among individuals and portions of the ejaculate, not only relate to survival but also signal differential immune tolerance by the female with a previ ously unattended linkage to fertility. Lastly it foresees how Cytomics, combining novel designed motility analyzers, flow cytometers and enhanced digital imaging shall dominate the landscape of andrological laboratories and enable quick determinations on huge sperm numbers for markers highly relevant to sperm function and hence, for fertility.(AU)

Routine assessment of motility of ejaculated stallion spermatozoa using a novel computer-assisted motility analyzer (Qualisperm™)

Visual motility analysis is the basis for routine quality evaluation of stallion semen, although its prognostic value for fertilizing ability is considered low. The present study evaluated the ability of a novel computer-assisted motility analyzer (QualiSperm™) to determine the motility and velocity of ejaculated, extended stallion spermatozoa (collected from 10 stallions, 3 ejaculates/stallion) and following two different colloidal centrifugation methods (one- or two- layer), compared to visual evaluation by two independet operators. The Qualisperm™ instrument was able to retrieve and analyze ~10 times more spermatozoa per sample compared to routine visual estimation on the same time frame (~1,100 vs ~100 spermatozoa).The proportion of motile spermatozoa increased after the colloid-separation, compared to the extended ejaculates (P < 0.05) in some stallions. However, owing to the large variation seen among ejaculates and stallions, both for extended ejaculate (P < 0.05) as well as for the colloid centrifugations (P < 0.01), the differences were lost when the entire population was examined statistically. Interestingly, significant differences were seen for individual stallions between the measurements ofQualisperm™ and observers, as well as between observers (P < 0.05). Apart from the significantly higher number of spermatozoa analyzed at one time, the Qualisperm™ system provided a parameter that could simply not be estimated by visual assessment; mean sperm velocity (in µm/sec). Sperm velocity, upon which every computer assisted instrumentation base their evaluations, varied among stallions (and ejaculates within stallions, P < 0.05), with a tendency to increase after colloid-separation, thus suggesting the Qualisperm™ system might be able to differentiate sperm sub-populations. Due to its higher accuracy (in terms of sperm numbers examined) and speed, the Qualisperm™ system appears to be a suitable instrument for routine evaluation of equine semen.

Routine assessment of motility of ejaculated stallion spermatozoa using a novel computer-assisted motility analyzer (Qualisperm™)

Visual motility analysis is the basis for routine quality evaluation of stallion semen, although its prognostic value for fertilizing ability is considered low. The present study evaluated the ability of a novel computer-assisted motility analyzer (QualiSperm™) to determine the motility and velocity of ejaculated, extended stallion spermatozoa (collected from 10 stallions, 3 ejaculates/stallion) and following two different colloidal centrifugation methods (one- or two- layer), compared to visual evaluation by two independet operators. The Qualisperm™ instrument was able to retrieve and analyze ~10 times more spermatozoa per sample compared to routine visual estimation on the same time frame (~1,100 vs ~100 spermatozoa).The proportion of motile spermatozoa increased after the colloid-separation, compared to the extended ejaculates (P < 0.05) in some stallions. However, owing to the large variation seen among ejaculates and stallions, both for extended ejaculate (P < 0.05) as well as for the colloid centrifugations (P < 0.01), the differences were lost when the entire population was examined statistically. Interestingly, significant differences were seen for individual stallions between the measurements ofQualisperm™ and observers, as well as between observers (P < 0.05). Apart from the significantly higher number of spermatozoa analyzed at one time, the Qualisperm™ system provided a parameter that could simply not be estimated by visual assessment; mean sperm velocity (in µm/sec). Sperm velocity, upon which every computer assisted instrumentation base their evaluations, varied among stallions (and ejaculates within stallions, P < 0.05), with a tendency to increase after colloid-separation, thus suggesting the Qualisperm™ system might be able to differentiate sperm sub-populations. Due to its higher accuracy (in terms of sperm numbers examined) and speed, the Qualisperm™ system appears to be a suitable instrument for routine evaluation of equine semen.(AU)

Prolongation of stallion sperm survival by centrifugation through coated silica colloids: a preliminary study

Difficulties to be overcome in the widespread use of artificial insemination (AI) in mares are low sperm survival and poor sperm quality, which are encountered frequently among breeding stallions. Therefore, a method is needed to prolong the useable life of stallion spermatozoa destined for AI. In a preliminary study using 8 ejaculates from one stallion, density gradient centrifugation or centrifugation through a single layer of silica colloid appeared to prolong sperm motility compared to uncentrifuged spermatozoa, thereby potentially extending the useable life of treated stallion spermatozoa for AI. Furthermore, there was an improvement in sperm morphology, with the number of morphologically normal spermatozoa increasing from 42 to 60.5% and with the removal of approximately 60% spermatozoa with head or tail defects from the original population. No difference between the two centrifugation methods, in terms of yield or duration of spontaneous motility, could be detected in this study. Either of these methods of colloidal centrifugation could be a useful aid to preparing stallion spermatozoa for artificial breeding techniques, including AI.

Prolongation of stallion sperm survival by centrifugation through coated silica colloids: a preliminary study

Difficulties to be overcome in the widespread use of artificial insemination (AI) in mares are low sperm survival and poor sperm quality, which are encountered frequently among breeding stallions. Therefore, a method is needed to prolong the useable life of stallion spermatozoa destined for AI. In a preliminary study using 8 ejaculates from one stallion, density gradient centrifugation or centrifugation through a single layer of silica colloid appeared to prolong sperm motility compared to uncentrifuged spermatozoa, thereby potentially extending the useable life of treated stallion spermatozoa for AI. Furthermore, there was an improvement in sperm morphology, with the number of morphologically normal spermatozoa increasing from 42 to 60.5% and with the removal of approximately 60% spermatozoa with head or tail defects from the original population. No difference between the two centrifugation methods, in terms of yield or duration of spontaneous motility, could be detected in this study. Either of these methods of colloidal centrifugation could be a useful aid to preparing stallion spermatozoa for artificial breeding techniques, including AI.(AU)

Computer-assisted analysis of sperm motion in goats and its relationship with sperm migration in cervical mucus.

In vitro sperm migration in cervical mucus relates to sperm concentration at the utero-tubal junction and to in vivo fertilization performance in goats. The present study aimed to characterize, using Computer-Assisted Sperm Analysis (CASA), motility patterns depicted by buck sperm and their relation to the migration efficiency in homologous (goat) and heterologous (heifer) cervical mucus in vitro. Semen was collected from 23 sexually mature bucks from three breeds by artificial vagina and sperm were assessed for motility parameters with a Hobson Sperm analyzer following extension in Sperm Analysis Medium (SAM). To study the relationship between kinematics parameters and the ability of sperm to migrate in cervical mucus, in a first experiment, motility performance of buck sperm suspended in SAM was compared against seminal plasma. In a second experiment, kinematics parameters of sperm were characterized. In a third experiment, bucks with sperm that differed in specific motion parameters were compared for the ability of their sperm to migrate through goat and bovine cervical mucus collected at estrus. In a fourth experiment, ejaculates that were compared in their migration ability and were assessed simultaneously for their motility parameters. Overall, sperm suspended in SAM medium had better velocity and similar linearity and lateral head displacement than those suspended in seminal plasma; furthermore, caprine sperm swam relatively fast (relative to bovine and ovine sperm), following a very linear trajectory. Under the conditions used, velocity parameters, linearity and lateral head displacement seemed to be related to sperm migration efficiency in homologous mucus but not in bovine cervical mucus.

Fertility of ram semen frozen in Bioexcell and used for cervical artificial insemination.

The current use of ingredients of animal origin, such as egg yolk, in semen extenders presents a risk of microbial contamination, and has led to the search for alternatives. Such an extender is commercially available for bull semen (Bioexcell), IMV, L'Aigle, France), and it has previously been tested in vitro for freezing ram semen, with satisfactory results. The aim of the present study was to compare the fertility results of ewes in Uruguay, after cervical insemination with ram semen that was frozen in Bioexcell versus semen frozen in a conventional milk-egg yolk extender (control). Semen from five Corriedale rams was frozen, using a split sample design, in either milk-egg yolk or Bioexcell extender, using a two-step extension method. The sperm parameters assessed after thawing were subjective motility, membrane integrity (SYBR-14/PI), and capacitation status (CTC). Thawed semen was inseminated intracervically once during spontaneous estrus in 970 Corriedale ewes that grazed in natural pastures, under extensive management conditions. Fertility was recorded as nonreturn rates at 21 days (NRR-21) and 36 days (NRR-36) after artificial insemination (AI), as well as pregnancy rate (PR-US, diagnosed ultrasonographically 50 days after AI of the last ewe). Subjective motility was slightly higher in Bioexcell than in the milk extender (47 vs. 46.5%; NS), as was membrane integrity (38 vs. 37.7%; NS) and the percentage of uncapacitated spermatozoa (28.5 vs. 26.3%; NS). There were no statistically significant differences in fertility rates found between Bioexcell and the control extender: NRR-21 (35.9 vs. 33.2%), NRR-36 (34.8 vs. 32.6%), and PR-US (28.4 vs. 27.2%). In conclusion, Bioexcell appears to be an alternative to the conventional milk-egg yolk extender for freezing ram semen, and provides similar fertility results after cervical AI under extensive management conditions. Thus, Bioexcell, containing no additives of animal origin, can offer a safer alternative when frozen semen is used for introducing new genetic material into a flock or a country.

Seasonal variations in testicular consistency, scrotal circumference and spermiogramme parameters of extensively reared Brahman (Bos indicus) bulls in the tropics.

Twenty-five mature Brahman (Bos indicus) extensively reared breeding bulls were clinically examined and electroejaculated at monthly intervals for 13 months to study if testicular consistency (TC), scrotal circumference (SC), sperm motility and morphology show seasonal variation under tropical conditions. Changes in SC were positively related to body condition (BC) (beta = 0.7 cm, P < 0.001) and age (P < 0.01). These changes were, however, not associated with deviations in TC, sperm motility or morphology (P > 0.05). Sperm motility was higher in samples collected during the breeding season than in samples collected at other times (62 versus 52%, LSM, P < 0.01). The frequency of bent tails with cytoplasmic droplet entrapped fluctuated between monthly ejaculates, (LSM range 3-21%, P < 0.05). However, there was no relationship between these fluctuations and environmental temperature, rainfall or changes in BC, TC or SC of the bulls (P > 0.05). Other sperm abnormalities did not change significantly during the study period. The absence of a relationship between any of the climatic variables studied and SC, TC and sperm motility or morphology, respectively, indicates that temperature is not a main factor influencing reproductive performance in Brahman bulls in the tropics. On the contrary, the changes found in BC followed by variations in SC suggest that nutrition may be a major factor affecting seasonal variations in male reproductive parameters, especially testicular size, in these sires.

Salivary gland myoephitheliomas: cytological, histological, immunohistochemical and electromicroscopical studies of four cases

Se presentan los resultados multidisciplinarios de cuatro casos de mioepiteliomas de glándula salival diagnosticados por biopsia por aspiración con aguja fina y resecados posteriormente. Histológicamente dos casos fueron benignos y dos malignos. Los extendidos celulares de las variedades benignas contenían una población uniforme de células discretamente alargados con citoplasma bipolar y membranas celulares conspicuas. El núcleo fue pequeño y oval con cromatina homogénea. Las células se disponían en grupos y nidos sobre un fondo proteináceo. Se observaron células aisladas adyacentes que presentaban citoplasma eosinófilo, granular y claro con núcleo central, redondo e hipercromático. En uno de los extendidos se observó numerosos capilares con células endoteliales prominentes y fondo con matrix condroide. Dos casos presentaron cambios citológicamente malignos con un fondo necrohemorrágico, pleomorfismo, nucléolo prominente, hipercromatismo y mitosis atípicas ocasionales. Las reacciones de inmunohistoquímica demostraron positividad para proteína S-100 y vimentina y focalmente para citoqueratina. Los hallazgos de la microscopia electrónica correspondieron a células mioepiteliales.

Influence of pre- and post-pubertal grazing regimes on adult testicular morphology in extensively reared corriedale rams.

The aim of the present study was to determine whether pre- and post-pubertal young rams on different grazing regimes, resulting in differences in live weight (LW), would show corresponding differences in testicular growth or testicular morphometry that could influence the reproductive traits of these rams upon reaching adulthood. Forty-one spring-born Corriedale rams were reared on either native pasture (low feeding level, Group L, n=22) or improved pasture (higher feeding level, Group H, n=19) from 1 to 7 months of age. Thereafter, half the animals in the native-pasture group were placed on improved pasture and vice versa, thus creating an additional four differential-grazing treatment groups (Groups LL, n=11; LH, n=11; HL, n=10; and HH, n=9). Animals were managed in this way until 18 months of age. Half the animals from each group were then castrated and their testes were subjected to morphometric analysis. The remaining animals (Groups LL, n=6; LH, n=6; HL, n=5; and HH, n=4) were managed together until 30 months of age (from 18 to 27 months on native pastures and from 27 to 30 months of age on improved pastures, at a stocking rate of two to three rams per hectare), whereupon they were also castrated for testicular morphometry. LW and scrotal circumference (SC) were recorded every 60 days. The stereological analysis of testicular parenchyma included counts of elongated spermatids and Sertoli cells. Differences (P<0.001) in LW were observed between feeding levels, even at 30 months of age. Differences (P<0.001) in SC existing at the end of the differential treatment (18 months of age) disappeared (n.s.) soon after. Most differences (P<0.05) in testicular morphometry existing at the end of the differential treatments were no longer significant 1 year later. It is concluded that changes in grazing management during pre- and post-pubertal periods can induce short-lived differences in testicular post-natal growth in Corriedale rams but do not influence testicular morphology or function later in life.

Transvaginal collection and ultrastructure of llama (Lama glama) oocytes.

Ultrasound-guided transvaginal follicle aspiration has been described as a noninvasive and repeatable procedure for oocyte collection in several species, but its use has not been described for any of the members of the family, Camelidae. A study was designed to determine the feasibility of an ultrasound-guided transvaginal approach for oocyte collection in llamas. Fifteen non-pregnant, adult female llamas (10 non-stimulated and 5 superstimulated) were examined by transrectal ultrasonography with a 7.5-MHz linear-array transducer to determine the number and diameter of follicles available for aspiration. After caudal epidural anesthesia was induced, the 7.5-MHz linear-array transducer was fastened to a long rigid handle and inserted intravaginally. The free hand was placed into the rectum to manipulate the ovaries, one at a time, in position against the vaginal wall over the face of the transducer. A 20-gauge, 55-cm-long, single-lumen needle was advanced through the vaginal fornix and into follicles > or = 3 mm in diameter. Follicular contents were aspirated using a regulated vacuum pump (flow rate = 33 mL/min; approximately 150 mm Hg) into a tube containing 3 mL of phosphate buffered saline and 0.2% BSA. Fluid was filtered (75 microm mesh), and oocytes were located and morphologically evaluated using a stereomicroscope. Overall, 134 follicles were aspirated, and 76 oocytes were collected (collection rate = 57%). Thirty-two oocytes (42%) were surrounded by multiple layers of compacted granulosa cells and had homogenous dark ooplasm; 13 oocytes (17%) were surrounded by the corona radiata layer only and had heavily granulated ooplasm; 9 oocytes (12%) were denuded and had homogenous dark ooplasm; and 22 oocytes (29%) were denuded and displayed signs of ooplasm degeneration. The ultrastructure of llama oocytes was similar to that of cattle except for conspicuous accumulation of large lipid droplets in the cytoplasm. Twenty-four hours after follicle aspiration, the ovaries were examined by transrectal ultrasonography and intrafollicular hematomas were detected in 3 llamas (9 of 48 follicles aspirated). Results demonstrate the potential utility of a transvaginal ultrasound-guided technique for oocyte collection and in vitro embryo production in llamas. Oocytes of llamas bear an ultrustructural resemblance to those of cattle, but are distinguished by a predominance of cytoplasmic lipid.

Hepatic carcinoma with spleen metastasis in a California sea lion from the Gulf of California.

A primary hepatic carcinoma with a neuroendocrine pattern was detected in an adult female California sea lion (Zalophus californianus) found dead on Granito Island in the Gulf of California (Mexico) in January 1996. At necropsy, several light yellow nodules of different sizes were observed on the entire surface of the liver and spleen. Microscopic examination of these nodules using routine haematoxylin-eosin stain, revealed cubic, polyhedral and pleomorphic cells with three to four bizarre mitotic figures per field (40X). An immunohistochemistry test revealed a positive reaction of indirect immunoperoxide to cytokeratin (CK2). This is the first known case of a primary hepatic carcinoma in free-ranging California sea lions from Mexican waters.

Influence of grazing management on the seasonal change in testicular morphology in Corriedale rams.

The present study was conducted: (a) to determine the degree of seasonal variation in testis stereology in Corriedale rams between autumn and winter; (b) to test the hypothesis that testis stereology of Corriedale rams grazing native pastures during autumn and winter would differ from those of Corriedale rams grazing sown pastures and supplemented with grain during the same period; and (c) to determine whether Sertoli cell numbers differ in adult rams between the breeding season (autumn) and the following non-breeding season (winter). Twenty experimental animals were studied. Six rams (autumn control group, C-A) that had been grazing on native pasture (stocking rate = 2-3 animals ha(-1)) were castrated at the beginning of the experiment (March, early autumn). Seven rams (winter control group, C-W) continued to graze on native pasture at the same stocking rate until the end of the experiment (August, late winter). Another seven rams (treated group, T) grazed on improved pasture (stocking rate = 1-2 animals ha(-1)) and were supplemented with 1 kg grain ram(-1) day(-1) until the end of the experiment. Live weight, scrotal circumference, serum testosterone concentration and selected testicular stereological parameters were measured. The treatment did not impede the winter reduction in testicular activity and reduced its magnitude slightly (group T) compared with controls (group C-W). Sertoli cell numbers were higher in autumn (group C-A) than in winter, both on native (group C-W) and sown pastures (group T). Diminishing Sertoli cell numbers between autumn and the following winter suggest the occurrence of that Sertoli cell death during this period. The results indicate that, although the reproductive activity of Corriedale rams is moderately seasonal, a restricted change in grazing and grain supplementation can only modify it to a limited extent.

[Atypical biological behavior of alveolar rhabdomyosarcoma in five patients]. / Comportamiento biológico atípico del rabdomiosarcoma alveolar en cinco pacientes.

Five cases of alveolar rhabdomyosarcoma with atypical clinical features are reported. Three patients showed lymphadenopathy as the first clinical manifestation, mimicking a lymphoma or a non identified primary tumor with lymph node metastases. One patient presented systemic neoplastic disease and two had the primary tumor in atypical locations, such as the mediastinum and retroperitoneum. All patients died and in four of them an autopsy was performed. The histological diagnosis was confirmed by immunohistochemical studies on four cases. The alveolar rhabdomyosarcoma has a poor prognosis and can have a variable clinical presentation and morphology, simulating lymphomas, leukemias and systemic metastatic disease with an unknown primary neoplasm, such as in the cases here in reported.

Breeding soundness evaluation of extensively managed bulls in Costa Rica.

This paper describes the results of single breeding soundness evaluations (BSE) in 898 Bos indicus, Bos taurus and B. indicus x B. taurus bulls, 1 to 12 yr old, extensively reared in different climatic regions of Costa Rica and representing approximately 2% of the total breeding bull population. Thirty-three percent (n = 296) of the bulls were classified as unsound for breeding owing to clinical problems (9.1%, n = 82), low scrotal circumference (SC) being the most common finding, followed by unsatisfactory sperm morphology (23.9%, n = 214). The prevalence of bulls unsound for breeding was lowest in Bos indicus (29%, P < 0.01), intermediate in B. taurus (41%), and highest in B. indicus x B. taurus (48%). The percentages of abnormal sperm heads, acrosomes and midpieces tended to be higher in the ejaculates of bulls with softer testicular consistency (P < 0.001), a long scrotum (P < 0.01) or a low SC (P < 0.05), and such bulls were more often classified as being unsound for breeding (P < 0.05). Frequencies of sperm abnormalities were higher in bulls < 2 yr of age than in older males (P < 0.01) and were highest in B. indicus x B. taurus bulls (P < 0.001). The results confirm differences between species in their adaptability to a tropical environment and support earlier evidence of an association between SC, testicular consistency and scrotal length clinical parameters, and testicular function in bulls.

Seasonal variation in live weight, testes size, testosterone, LH secretion, melatonin and thyroxine in Merino and Corriedale rams in a subtropical climate.

In the present investigation we studied the seasonal changes in live weight and testes and pituitary activity in Merino and Corriedale rams in a subtropical climate. Testes activity was measured as scrotal circumference (SC), plasma concentration of testosterone (T) and release of testosterone after exogenous GnRH injection. LH pulsatility and pituitary LH responsiveness to exogenous GnRH was measured as an index of pituitary activity. In addition, we wanted to characterize the seasonal pattern of thyroxine (T4) secretion and the 24 h secretory pattern of melatonin (M) at the winter and summer solstices in the 2 breeds. Nine Corriedale and 7 Merino adult (4-6 years) rams were kept on native pasture and managed in one group. Twice a month live weight (LW) and scrotal circumference (SC) were measured. To monitor plasma concentration of testosterone (T), and thyroxine (T4), 5 animals of each breed were bled every month except during autumn (March-May), when blood samples were collected with 15 day intervals and in spring (October) with 10 day intervals. To monitor pulsatile LH secretion, 3 rams of each breed were bled at 15 min intervals for 6 h at the winter and summer solstices and spring and autumn equinoxes. Pituitary LH and testicular testosterone response to GnRH injection was performed bimonthly from 2 animals of each breed. No effect of breed was found on any of the variables investigated. An interaction between breed and sampling date was found in LW (p < 0.001) and total T response after GnRH challenge (p < 0.001). Sampling date had a significant effect (p < 0.001) on all the variables studied. In both breeds SC decreased during autumn and increased during spring with minimum T concentrations in late autumn and maximum in mid-summer/early autumn. The lowest (p < 0.05) number of LH pulses were observed in winter (June) and the highest (p < 0.05) in early autumn (March). The highest LH and testosterone response to GnRH challenge was observed in autumn (April) (p < 0.05) in both breeds. Baseline concentrations of M were similar in both breeds at the winter and summer solstices and high concentrations were observed during the dark period on both occasions. In both breeds thyroxine was high at the end of winter/spring (February-April) and low from the end of summer to mid-autumn (August-November). The results show that Corriedale and Merino rams under subtropical conditions have annual reproductive cycles. There was an association (p < 0.001) between changes in LW and SC in the 2 breeds and this relationship was stronger in Merino rams (R2 = 0.68) than in Corriedale (R2 = 0.33) which indicates that nutritional factors may have more influence on the reproductive cycle of Merino than Corriedale rams.

Biostimulatory effects of estrous cows and bulls on resumption of ovarian activity in postpartum anestrous Zebu (Bos indicus) cows in the humid tropics.

Suckled postpartum Zebu (Bos indicus) cows were exposed either to estrous females alone or together with bulls to determine if this regimen would stimulate the resumption of ovarian activity. The study was carried out on 60 Zebu cows. The animals were allocated at parturition to 1 of 3 treatment groups. Group FB cows (n = 14) were exposed to progestogen treated females (approximately 3 cows per progestogen treated cow) and a bull for 42 d. Group F cows (n = 31) were exposed to progestogen treated females and after 21 d a bull was introduced and remained with the group until the end of the experiment 21 d later. Estrus was induced with Syncro Mate B treatment and the cows were in estrus when introduced into Groups FB and F. Group N cows (n = 15) were introduced to a bull 21 d after the treatments had begun in Groups FB and F, and the bull remained with these cows until the end of the study. On average, resumption of ovarian activity occurred in 57% (8/14), 19% (6/31) and 7% (1/15) of the cows in Group FB, F and N, respectively, within 21 d after the start of treatments. The difference was significant between Group FB and Groups F and N (P < 0.05). During the second part of the experiment, in which the bull was introduced to Groups F and N, an additional 32% (10/31) of the cows in Group F and 33% (5/15) in Group N resumed ovarian activity. No cows in Group FB resumed ovarian activity during this period. There were significant differences in body condition between cows that resumed ovarian activity and those that remained in anestrus (P < 0.05). We conclude that biostimulation effectively enhanced resumption of ovarian activity in anestrous suckled Zebu cows. This technique offers a potentially useful and practical way to improve reproductive efficiency in anestrous Zebu cattle in the tropics.