RESUMEN

Poor udder health status can have a detrimental effect on milk yield and reproductive performance, leading to reductions in the dairy farm profit. The objective of this retrospective longitudinal study was to assess the associations of somatic cell count (SCC) with daily milk yield and reproductive performance. A database with 1,930,376 lactations from 867 Argentinean grazing dairy herds records collected for 14 years was used. The association of the evolution of SCC (healthy vs. new case vs. cured vs. chronic; with 150,000 SCC/mL as threshold) and of the severity of SCC [mild (150,000--400,000 SCC/mL) vs. moderate (400,000-1,000,000 SCC/mL) vs. severe (>1,000,000 SCC/mL)] with the odds for conception were estimated. Finally, the associations of the linear score of SCC (LS-SCC) with daily milk yield were estimated depending on parity and milk production quartile. The odds ratios (CI 95%) for conception at first service were 0.921 (0.902-0.941), 0.866 (0.848-0.884), and 0.842 (0.826-0.859) for the new case, cured, and chronic cows compared with healthy cows, respectively. Also, the odds ratios (CI 95%) for conception were 0.902 (0.881-0.925), 0.837 (0.808-0.866) and 0.709 (0.683-0.736) for mild, moderate and severe cases compared with healthy cows, respectively. An increase of one point of LS-SCC was associated with decreases of 0.349, 0.539, and 0.676 kg in daily milk yield for first-, second-, and third-lactation cows, respectively. In conclusion, SCC is negatively associated with the risk for conception and with daily milk yield in grazing dairy cows. This negative relationship with conception is higher when SCC increase occurs after the service date and it is influenced by severity of mastitis, and in the case of milk yield, the negative association is influenced by parity, milk production quartile, and severity of mastitis.

Asunto(s)

Enfermedades de los Bovinos , Mastitis Bovina , Animales , Bovinos , Recuento de Células/veterinaria , Industria Lechera , Femenino , Lactancia , Estudios Longitudinales , Leche , Embarazo , Estudios Retrospectivos

RESUMEN

Different therapeutic strategies have been used with the objective of improve luteal function to reduce embryonic losses. The objective of this work was to study the effect of the administration of GnRH or hCG at Day 4 post fixed time artificial insemination (FTAI) on reproductive efficiency in Merino sheep during the breeding season in North Patagonia. Estrus of multiparous Merino ewes (n = 288) was synchronized by two injections of prostaglandins (PG; 125 µg, Cloprostenol), 14 days apart. Cervical FTAI was performed 53-56 h after the second PG with a dose of fresh semen (100 × 106 spermatozoa) from five Merino rams. In all ewes body condition score (BCS) was determined at FTAI. At 4 days post FTAI ewes were randomly assigned into three experimental groups: GnRH group (4 µg, Buserelin; n = 99), hCG group (300 IU, hCG; n = 92) and Control group (1 ml, saline solution; n = 97). Pregnancy and pregnancy losses were evaluated by ultrasonography on Days 33 and 90 post FTAI. Additionally, embryo crown-rump length (CRL) was measured by ultrasonography (n = 12 single-pregnant ewes by experimental group) at the first ultrasound. Date of birth, litter size and lamb weight were recorded (n = 111 pregnant ewes). Pregnancy rate on Days 33 and 90 post FTAI did not differ among treatment groups (P > 0.05). Pregnancy losses at Day 33 post FTAI were lower in the hCG group compared to the GnRH and Control groups (0, 3, 7.2%, respectively; P < 0.05). Pregnancy losses between Days 33 and 90 after FTAI were negligible (P > 0.05). The embryo CRL at Day 33 post FTAI was not increased by the hormonal treatments (P > 0.05). Moreover, it was lower in GnRH group compared to Control group (P < 0.05). Litter size tended to be greater in the GnRH group compared to the hCG and Control groups (P < 0.1). The birth weight of twin lambs tended to be higher in the GnRH group compared to the Control group (P < 0.1). The birth weight of single lambs was not affected by treatments (P > 0.05). Ram fertility and BCS of ewes at FTAI influenced the effect of hormonal treatments on reproductive parameters. In conclusion, administration of hCG or GnRH at Day 4 post FTAI does not improve pregnancy rate but treatment with hCG reduces pregnancy loss on Day 33 post FTAI. GnRH treatment improves litter size and twin lambs birth weight.

Asunto(s)

Gonadotropina Coriónica/farmacología , Hormona Liberadora de Gonadotropina/farmacología , Inseminación Artificial/veterinaria , Ovinos , Aborto Veterinario , Animales , Peso al Nacer/efectos de los fármacos , Largo Cráneo-Cadera , Desarrollo Embrionario/efectos de los fármacos , Sincronización del Estro , Femenino , Inseminación Artificial/métodos , Tamaño de la Camada/efectos de los fármacos , Embarazo , Índice de Embarazo , Ultrasonografía Prenatal/veterinaria

RESUMEN

The objective of the present study was to assess the relationship between individual cow milk yield and fertility, accounting for the contextual effect of the herd. A data set including 657,968 lactations from 677 dairy herds in Argentina from 2001 to 2012 was used. The odds of pregnancy by 100 d in milk (DIM) were assessed by a multilevel logistic model (with cow as the first and herd as the second hierarchical level), and time to pregnancy was assessed by a proportional hazards regression model. Multilevel logistic models included the fixed effects of milk yield by 80 DIM, parity, year, and calving season at cow level and quartiles of herd milk yield by 80 DIM as a contextual effect. The proportional hazards model included the effect of daily cow-level milk yield as time-dependent variable, with milk yield at herd level as the stratification variable. Cows producing 1 standard deviation over the mean milk yield of their herd had 1.3 percentage point lower pregnancy by 100 DIM (from 31.4 to 30.1%; odds ratio = 0.942) when in herds in the top quartile of milk yield, whereas they increased 0.5 percentage points (from 27.9 to 28.4%) when in herds in the lowest quartile of milk yield. Only 4% of the observed variation in pregnancy by 100 DIM was explained by the random effect of the herd. Similarly, cows producing 1 standard deviation (8 kg/d) greater than the herd mean daily milk had 1.3% lower hazard of pregnancy (hazard ratio = 0.987) at 63 DIM in herds in the top quartile of milk yield, whereas they had 14.8% higher hazard (hazard ratio = 1.148) in herds in the lowest quartile of milk yield. The magnitude of the negative association between the cow's daily milk yield and the hazard of pregnancy increased with DIM. In conclusion, the relationship between milk yield and reproductive performance is statistically significant, but the effect size is practically small and is modulated by herd production level.

Asunto(s)

Bovinos/fisiología , Industria Lechera , Lactancia/fisiología , Reproducción/fisiología , Animales , Argentina , Femenino , Leche , Embarazo

RESUMEN

AIMS: To determine the effect of providing water within the area grazed by dairy cows on milk yield and quality, compared to requiring cows to walk to a distant water trough, on a dairy farm in the Pampa region of Argentina during summer. METHODS: Holstein dairy cows were allocated to two herds with similar parity, days in milk and milk production. They were grazed in one paddock that was divided in two, with a fixed water trough at one end. Cows were moved twice daily to grazing plots within the paddock. Control cows (n=66) could only access water from the fixed trough, whereas supplemented cows (n=67) also received water from a mobile trough within the grazing plot. Milk production of each cow, and water consumption of the two herds were measured daily over 62 days. Milk composition for each herd was determined weekly from Days 18 to 60 of the study, and grazing behaviour was observed between 08:00 and 16:00 hours on Days 11-15, 19-22 and 39-43. RESULTS: Over the 62 days of the study, supplemented cows produced 1.39 (SE 0.11) L/cow/day more milk than Control cows (p=0.027). Estimated mean daily water intake was 50.4 (SE 2.1) L/cow/day for supplemented cows and 58.2 (SE 2.7) L/cow/day for Control cows (p=0.004). Percentage total solids in milk was higher for supplemented (12.5 (SE 0.06)%) than Control (12.4 (SE 0.04)%) cows (p=0.047). During the periods of behavioural observation, a higher percentage of cows in the water supplemented than the Control herd were observed in the grazing area (p=0.012). CONCLUSIONS AND CLINICAL RELEVANCE: This preliminary study demonstrated that provision of water to dairy cows within the grazing plot was beneficial for milk production and composition, and may be associated with longer periods spent within the grazing area, during hot weather in the Pampa region of Argentina.

Asunto(s)

Bovinos/fisiología , Agua Potable , Lactancia/fisiología , Leche/fisiología , Animales , Argentina , Industria Lechera , Suplementos Dietéticos , Femenino

RESUMEN

The objectives of this study were to assess the association of a 4-point scale of vaginal discharge score (VDS) with time to pregnancy to define criteria for a practical case of purulent vaginal discharge (PVD) in dairy cows, to test the risk factors for PVD, and, finally, the effect of a dose of PGF2α on cure and reproductive performance. In experiment 1, grazing Holstein cows (n = 2,414) had their vaginal discharge scored at ∼32 d in milk (DIM) on a 4-point scale, the effect of VDS on the hazard of pregnancy by 300 DIM was then assessed to derive a case definition of PVD. Risk factors for PVD and self-cure were also assessed. In experiment 2, grazing Holstein cows (n = 6,326) from 5 herds were checked for PVD at ∼30 DIM. Cows with PVD were assigned to receive one dose of 500 µg of PGF2α analog (Cloprostenol; Ciclase, Syntex SA, Buenos Aires, Argentina) per cow (odd ear tag number) or to remain untreated (even tag number). Cure was declared if cows presented clear normal vaginal discharge (VDS-0) at visit 2 (∼62 DIM). Data were analyzed with Cox's regression and mixed logistic models. In experiment 1, cows with VDS ≥1 had lower hazard of pregnancy and longer calving to pregnancy interval than cows with VDS-0. This finding was not affected by the time at which the diagnosis was performed. Therefore, a cow ≥21 DIM and having VDS ≥1 was used to define a case of PVD. The odds of PVD were greater in primiparous cows compared with multiparous, in cows with abnormal calving compared with those with normal calving, and in those losing BCS peripartum. In experiment 2, PGF2α treatment tended to slightly increase the hazard of pregnancy (adjusted hazard ratio = 1.13). Conversely, PGF2α had no effect on the odds of cure of PVD [adjusted odds ratio (AOR) = 1.19], pregnancy at first service (AOR = 1.03), or pregnancy by 100 DIM (AOR = 0.89) or 200 DIM (AOR = 1.27). In conclusion, cows with VDS ≥1 can be considered to have PVD because of their lower hazard of pregnancy and longer calving to pregnancy interval (up to 48 d). Important risk factors are parity, calving, and body condition score loss peripartum. Optimal time of diagnosis is ≥28 to 35 DIM because cows experience a high self-cure rate. Self-cure is also affected by parity, prepartum BCS, and VDS. Finally, as treatment with one dose of PGF2α had a small effect on the hazard of pregnancy and no effect on clinical cure, its therapeutic use in grazing dairy cows with PVD is not recommended.

Asunto(s)

Dinoprost/uso terapéutico , Endometritis/veterinaria , Animales , Bovinos , Enfermedades de los Bovinos/diagnóstico , Femenino , Factores de Riesgo , Excreción Vaginal/veterinaria

RESUMEN

Mammary ductal morphogenesis during prepuberty occurs mainly in response to insulin-like growth factor-1 (IGF-1) and estradiol stimulation. Dairy heifers infected with gastrointestinal nematodes have reduced IGF-1 levels, accompanied by reduced growth rate, delayed puberty onset, and lower parenchyma-stroma relationship in their mammary glands. Immunohistochemical studies were undertaken to determine variations in cell division rate, IGF-1 system components, and estradiol receptors (ESR) during peripubertal development in the mammary glands of antiparasitic-treated and untreated Holstein heifers naturally infected with gastrointestinal nematodes. Mammary biopsies were taken at 20, 30, 40, and 70 wk of age. Proliferating cell nuclear antigen immunolabeling, evident in nuclei, tended to be higher in the parenchyma of the glands from treated heifers than in those from untreated. Insulin-like growth factor binding proteins (IGFBP) type 2 and type 3 immunolabeling was cytoplasmic and was evident in stroma and parenchyma. The IGFBP2-labeled area was lower in treated than in untreated heifers. In the treated group, a maximal expression of this protein was seen at 40 wk of age, whereas in the untreated group the labeling remained constant. No differences were observed for IGFBP3 between treatment groups or during development. Immunolabeling for α ESR (ESR1) was evident in parenchymal nuclei and was higher in treated than in untreated heifers. In the treated group, ESR1 peaked at 30 wk of age and then decreased. These results demonstrate that the parasite burden in young heifers negatively influence mammary gland development, affecting cell division rate and parameters related to estradiol and IGF-1 signaling in the gland.

Asunto(s)

Proliferación Celular , Receptor alfa de Estrógeno/metabolismo , Proteína 2 de Unión a Factor de Crecimiento Similar a la Insulina/metabolismo , Proteína 3 de Unión a Factor de Crecimiento Similar a la Insulina/metabolismo , Glándulas Mamarias Animales/metabolismo , Infecciones por Nematodos/veterinaria , Animales , Antihelmínticos/farmacología , Bovinos/parasitología , Estradiol/metabolismo , Receptor alfa de Estrógeno/genética , Femenino , Fenbendazol/farmacología , Tracto Gastrointestinal/parasitología , Proteína 2 de Unión a Factor de Crecimiento Similar a la Insulina/genética , Proteína 3 de Unión a Factor de Crecimiento Similar a la Insulina/genética , Factor I del Crecimiento Similar a la Insulina/genética , Factor I del Crecimiento Similar a la Insulina/metabolismo , Ivermectina/farmacología , Levamisol/farmacología , Glándulas Mamarias Animales/citología , Nematodos , Transducción de Señal

RESUMEN

The objectives of this study were to assess the risk factors for metritis, its effects on milk yield and on reproductive performance, and the efficacy of ceftiofur therapy in Holstein dairy cows. Cows (n=303) from a commercial dairy herd in Argentina were studied. Cows were scored for body condition, and blood samples were collected on d -14, 7, 21, 31, 41, and 50 relative to parturition. Cows having a watery, purulent, or brown, and fetid vaginal discharge (VD) and rectal temperature ≤ 39.2°C were diagnosed as having clinical metritis, and those having a similar VD and rectal temperature >39.2°C were diagnosed as having puerperal metritis. Both clinical and puerperal metritis cows were randomly assigned to control (no treatment) or ceftiofur group (2.2mg/kg×3 consecutive days). Cure was declared if clear VD was observed at 21 d in milk (DIM). Blood samples were analyzed for nonesterified fatty acids, ß-hydroxybutyrate, and blood urea nitrogen using commercial kits, and for insulin-like growth factor-1, insulin, and leptin by RIA. Data were analyzed with PROC MIXED, GENMOD, PHREG, and LIFETEST from SAS (SAS Institute Inc., Cary, NC). The risk for metritis increased with dystocia, retained fetal membranes, and dead calf [AOR (adjusted odds ratio)=2.58, 95% CI: 1.189-5.559], and as prepartum nonesterified fatty acids levels increased (AOR=1.001, 95% CI: 0.999-1.002). Conversely, risk decreased as prepartum insulin-like growth factor-1 increased (AOR=0.65, 95% CI: 0.349-1.219). Cows having either clinical or puerperal metritis produced less milk by 90 DIM than did healthy cows (2,236 ± 172 vs. 2,367 ± 77 vs. 2,647 ± 82 kg, respectively). Cows with puerperal metritis had lower risk for pregnancy by 100 DIM (AOR=0.189, 95% CI: 0.070-0.479) and a lower hazard rate for pregnancy by 150 DIM (hazard rate: 0.753, 95% CI: 0.621-0.911), and took longer to get pregnant (129 vs. 111 vs. 109 d, for puerperal metritis, clinical metritis, and healthy cows, respectively). Ceftiofur treatment was not associated with cure rate or milk yield but was related to increased risk for pregnancy at timed artificial insemination (AOR=2.688, 95% CI: 0.687-10.832), and for lower risk of reproductive cull (AOR=0.121, 95% CI: 0.014-1.066). In conclusion, abnormal calving and negative energy balance are associated with increased risk for metritis. Metritis, especially puerperal metritis, correlates with reduced milk production and poor reproductive performance. Finally, the likelihood for having a normal VD (indicative of cure) increased 2.6% for every day of increase in postpartum time and was 2 times higher for cows with clinical metritis than for those with puerperal metritis.

Asunto(s)

Enfermedades de los Bovinos/diagnóstico , Endometritis/veterinaria , Reproducción , Animales , Antibacterianos/uso terapéutico , Argentina , Bovinos , Enfermedades de los Bovinos/tratamiento farmacológico , Enfermedades de los Bovinos/fisiopatología , Cefalosporinas/uso terapéutico , Industria Lechera , Endometritis/diagnóstico , Endometritis/tratamiento farmacológico , Femenino , Lactancia , Embarazo , Infección Puerperal/diagnóstico , Infección Puerperal/veterinaria , Factores de Riesgo , Excreción Vaginal

RESUMEN

The objectives of this study were to assess the clinical and metabolic risk factors for clinical endometritis, the likelihood for having a normal vaginal discharge during postpartum, and the effects of endometritis on milk yield, reproductive efficiency, and metabolic status in Holstein cows. The study was conducted in a commercial dairy herd (Cordoba, Argentina) where 303 Holstein cows were enrolled. Cows were body condition scored (1 to 5) and tail bled on -14, 7, 21, 31, 41, and 50 d relative to parturition. Cows having a vaginal discharge with presence of pus between 21 and 41 d postpartum (dpp) were diagnosed as having clinical endometritis. Plasma blood samples were analyzed for nonesterified fatty acids (NEFA), ß-hydroxybutyrate (BHBA), and blood urea nitrogen using commercial kits and insulin-like growth factor 1, insulin, and leptin by RIA. Data were analyzed with PROC MIXED, PROC GENMOD, and PROC PHREG of SAS (SAS Institute Inc., Cary, NC). Abnormal calving and puerperal metritis increased the risk for endometritis [adjusted odds ratio (AOR)=2.21 for both]. High prepartum NEFA and high postpartum BHBA increased the risk for endometritis (AOR=1.003 and 1.001, respectively), whereas high prepartum blood urea nitrogen reduced it (AOR=0.853). Cut-offs of 456.6 µM NEFA and 402.5 µM BHBA had sensitivities of 0.69 and 0.58, and specificities of 0.88 and 0.86, respectively. The likelihood for having normal vaginal discharge increased with time (∼1% × dpp) and with normal calving. Cows with endometritis had higher milk yield than normal herdmates (27.8±0.9 vs. 25.7±0.4 kg/d), lower risk for pregnancy by 100 dpp (AOR=0.10), higher nonpregnancy risk by 200 dpp (AOR=2.87), and higher risk for culling than normal cows (AOR=2.28). Cows with endometritis had a lower hazard rate (0.44) for pregnancy and had approximately 70 d longer calving-to-conception intervals. Finally, endometritis had no effect on metabolic hormones. In conclusion, the risk for clinical endometritis increases with abnormal calving and puerperal metritis, as prepartum NEFA and postpartum BHBA concentrations increase. Prepartum NEFA and postpartum BHBA could be useful for the prediction of endometritis. Last, clinical endometritis has detrimental effects on reproductive efficiency, as affected cows take longer to get pregnant and are at higher risk for culling.

Asunto(s)

Enfermedades de los Bovinos/etiología , Endometritis/veterinaria , Ácido 3-Hidroxibutírico/sangre , Animales , Argentina , Nitrógeno de la Urea Sanguínea , Bovinos , Enfermedades de los Bovinos/metabolismo , Enfermedades de los Bovinos/fisiopatología , Endometritis/etiología , Endometritis/metabolismo , Endometritis/fisiopatología , Ácidos Grasos no Esterificados/sangre , Femenino , Insulina/sangre , Factor I del Crecimiento Similar a la Insulina/análisis , Lactancia/fisiología , Leptina/sangre , Embarazo , Reproducción/fisiología , Factores de Riesgo

RESUMEN

Development of resistance to anthelmintic drugs has motivated the search for diagnostic methods to identify animals for targeted selective treatments. We compared three methods for the diagnosis of nematode infection in relation to milk production in a fully grazing dairy herd of 150 cows in the humid Pampa (Argentina). Animals had feces, blood and milk sampled during the first postpartum month for EPG, pepsinogen and anti-Ostertagia antibody determination, respectively. With the results obtained two groups of cows, divided in high and low parasite burden, were conformed for each method, and milk production was then compared between groups. When cows were separated by the EPG method (EPG=0 (N=106) vs. EPG>0 (N=44)) a difference of nearly 800 l of milk per cow per lactation was found (P<0.05). On the other hand, milk production between groups separated by Pepsinogen (mUtyr ≤ 1000 vs. mUtyr > 1000) or by anti-Ostertagia (ODR ≤ 0.5 vs. ODR > 0.5) results did not differ. Interestingly, proportion of cows in each group differed between methods (P<0.0001), and the anti-Ostertagia method yielded significantly more cows in the high index group compared to results using the EPG or Pepsinogen method. No correlations were found between parasite indexes determined by the different methods. High parasite burden estimation found may be ascribed to the production system, fully grazing all year round, and to the sampling time, at the beginning of lactation with cows in negative energy balance and depressed immunity. The fact that the cows were born and reared outside, on pasture with continuous nematode larvae exposure, may also account for the results obtained. In conclusion, EPG counting during the first postpartum month may be a useful tool for the diagnosis of production impairment induced by high nematode burden in adult grazing dairy cows. The anthelmintic treatment of only the EPG-positive recently calved cows would improve milk production, while reducing selective pressure on nematode population for the development of resistance.

Asunto(s)

Enfermedades de los Bovinos/diagnóstico , Enfermedades Gastrointestinales/veterinaria , Lactancia , Nematodos/inmunología , Infecciones por Nematodos/veterinaria , Animales , Anticuerpos Antihelmínticos/sangre , Argentina , Bovinos , Enfermedades de los Bovinos/metabolismo , Enfermedades de los Bovinos/parasitología , Industria Lechera/métodos , Heces/parasitología , Femenino , Enfermedades Gastrointestinales/diagnóstico , Enfermedades Gastrointestinales/metabolismo , Enfermedades Gastrointestinales/parasitología , Nematodos/aislamiento & purificación , Infecciones por Nematodos/diagnóstico , Infecciones por Nematodos/metabolismo , Ostertagia/inmunología , Ostertagia/aislamiento & purificación , Ostertagiasis/diagnóstico , Ostertagiasis/parasitología , Ostertagiasis/veterinaria , Recuento de Huevos de Parásitos/veterinaria , Carga de Parásitos/veterinaria , Pepsinógenos/sangre

RESUMEN

Parasitism in cattle is known to impair growth and development. Recent findings suggest that productivity of adult animals is also affected, but little is known about the physiological mechanisms involved. Furthermore, development of nematode resistance to drugs makes imperative the search of management practices that avoid whole herd treatment. We undertook an epidemiological and endocrine study in a grass based dairy farm in Argentina to study the effect of parasites on milk production and the underlying mechanisms involved, and identify individual animals that would benefit from antiparasitic treatment. All the cows in the dairy were followed monthly for egg parasite output in feces. Samples were cultured for genera determination. Milk production and reproductive results were recorded and periodical bleedings for hormone determination were performed. Nematode egg output (EPG) was maximal in late Summer and Autumn and minimal in Spring in coincidence with the Ostertagia inhibition-disinhibition cycle as this genus had the highest prevalence in all the study. The highest proportion of positive samples was found in the high producing herd and maximal counts were found in the peripartal period. Milk production did not correlate with EPG mean values but, when cows were grouped by EPG positivity around parturition, a significant difference in total milk production between EPG null and positive cows was observed. Positive cows produced 7%, 12% or 15% less milk than null EPG cows, depending on the sampling month/s chosen for classification. The highest difference was seen when both prepartum and postpartum samples were taken into account. No difference in lactation length and a marginal effect on partum to first service interval were encountered. Endocrine studies revealed a decrease in serum growth hormone (GH), type I insulin-like growth factor (IGF-I) and prolactin during lactation in cows with positive EPG in the first postpartum sample with respect to null EPG cows at that time. GH levels decreased and prolactin and IGF-I levels increased in both groups of cows from month 0 to 6 in milk. Serum insulin levels remained stable throughout lactation and were similar in both groups of cows. In conclusion, EPG around parturition may be a useful tool for identifying cows that will have a decrease in productivity due to parasite effects and would possibly benefit from an antiparasitic treatment. Besides, our results suggest that detrimental effect of parasites on milk production may be mediated by GH, IGF-I and prolactin serum levels.

Asunto(s)

Enfermedades de los Bovinos/metabolismo , Enfermedades de los Bovinos/parasitología , Enfermedades Gastrointestinales/veterinaria , Leche/metabolismo , Nematodos/metabolismo , Infecciones por Nematodos/veterinaria , Animales , Argentina , Bovinos , Distribución de Chi-Cuadrado , Heces/parasitología , Femenino , Enfermedades Gastrointestinales/metabolismo , Enfermedades Gastrointestinales/parasitología , Hormona del Crecimiento/sangre , Hormona del Crecimiento/metabolismo , Insulina/sangre , Insulina/metabolismo , Factor I del Crecimiento Similar a la Insulina/líquido cefalorraquídeo , Factor I del Crecimiento Similar a la Insulina/metabolismo , Lactancia , Infecciones por Nematodos/metabolismo , Infecciones por Nematodos/parasitología , Recuento de Huevos de Parásitos/veterinaria , Periodo Periparto , Prolactina/sangre , Prolactina/metabolismo , Estaciones del Año

RESUMEN

Female Holstein calves were treated with ivermectin from birth to first oestrus to study the effect of parasitic burden and anthelmintic treatment on reproductive and productive performance. First oestrus, age at first service and age at calving were advanced by 30, 70 and 110 days, respectively (P<0.05), in ivermectin-treated animals compared with controls. No significant differences were observed in the conception rate, the number of services and the characteristics of the newborn calves and any problems at calving between the two groups. Daily milk yield, fat content in milk during first lactation, and the concentrations of growth hormone, insulin-like growth factor type 1, insulin and prolactin in serum were similar in both groups of cows. Culling during the first lactation was more common in untreated (47 per cent) than in treated (11 per cent) cows (P<0.05).

Asunto(s)

Antihelmínticos/farmacología , Enfermedades de los Bovinos/prevención & control , Helmintiasis Animal/prevención & control , Ivermectina/farmacología , Lactancia/efectos de los fármacos , Reproducción/efectos de los fármacos , Factores de Edad , Animales , Cruzamiento , Bovinos , Estro/efectos de los fármacos , Femenino , Lactancia/fisiología , Leche/química , Leche/metabolismo , Distribución Aleatoria , Reproducción/fisiología

RESUMEN

Leptin is a new plausible candidate for the molecular link between nutritional status and the reproductive axis. In previous studies we described that continuous natural nematode infections in heifers retarded growth and delayed the onset of puberty, and that the insulin-like growth factor I (IGF-I) was involved. In the present study we monitored the leptin levels during development in heifers naturally parasitized versus those chronically treated with ivermectin and we investigated whether growth hormone (GH) accounted for the differences in IGF-I previously noted. Insulin levels were also measured. Prolactin hormone was recorded as an indicator of immune system activation. We found a direct correlation between leptin and body weight during development and a prepubertal surge of the hormone 2 weeks before the first progesterone peak that indicates the onset of puberty. This suggests that leptin may act as a signal for this event. Insulin did not vary during growth and prepuberty. On the other hand, GH as not responsible for diminished IGF-I levels in parasitized animals as levels were similar in both groups. The GH levels were high at birth and then diminished rapidly and remained constant during development and puberty. The last hormone studied, prolactin, followed seasonal changes of sunlight duration and presented sporadic bursts in infected animals. These were related to high nematode infection and are probably involved in the immune response of the host.

Asunto(s)

Enfermedades de los Bovinos/fisiopatología , Bovinos/fisiología , Leptina/biosíntesis , Infecciones por Nematodos/veterinaria , Maduración Sexual/fisiología , Animales , Antinematodos/administración & dosificación , Peso Corporal , Bovinos/metabolismo , Bovinos/parasitología , Enfermedades de los Bovinos/metabolismo , Heces/parasitología , Femenino , Hormona del Crecimiento/sangre , Insulina/sangre , Factor I del Crecimiento Similar a la Insulina/metabolismo , Ivermectina/administración & dosificación , Leptina/sangre , Nematodos/crecimiento & desarrollo , Infecciones por Nematodos/metabolismo , Recuento de Huevos de Parásitos/veterinaria , Progesterona/sangre , Prolactina/sangre

RESUMEN

Continuous treatment with ivermectin from birth to puberty advanced sexual maturation by 3.7 wk in Holstein heifers grazing pastures naturally infected with nematodes. Every 14 d jugular blood samples were taken from birth to 45 wk of age from all heifers. No differences in serum FSH, estradiol, or thyroxine levels were observed during the trial between the treated and untreated group. Mean LH levels were diminished in untreated heifers 4 wk before the first estrus and the amplitude of LH pulses was augmented in treated heifers when puberty was reached. Serum IGF-I levels increased from birth to 22 wk of age and then reached a plateau in both groups, but levels were consistently higher in treated heifers from 26 wk of age onward. Body weight gain was retarded in parasitized heifers and IGF-I values were positively correlated with body weight only during the first 20 wk of life. We suggest that enhanced prepubertal IGF-I levels in conjunction with increased prepubertal LH levels and pubertal LH pulse amplitude might be involved in the accelerated somatic maturation and in puberty advancement observed in ivermectin-treated heifers.

Asunto(s)

Antinematodos/farmacología , Bovinos/crecimiento & desarrollo , Ivermectina/farmacología , Maduración Sexual/efectos de los fármacos , Animales , Industria Lechera , Estradiol/sangre , Femenino , Hormona Folículo Estimulante/sangre , Factor I del Crecimiento Similar a la Insulina/metabolismo , Hormona Luteinizante/sangre , Recuento de Huevos de Parásitos/veterinaria , Progesterona/sangre , Radioinmunoensayo/veterinaria , Tiroxina/sangre , Aumento de Peso

RESUMEN

The effect of continuous ivermectin treatment from birth to puberty on growth and reproductive performance was studied in Holstein heifer calves grown on pastures in comparison to naturally nematode-infected, untreated animals. Ivermectin effectively abated the presence of nematode eggs in feces. Eggs per gram (EPG) in parasitized animals increased rapidly from wk 12 to 18 of age and then decreased. Animals treated with ivermectin grew faster than untreated ones, and differences in body weight became significant at 6 wk of life, even before eggs appeared in the feces of either treatment group. Ivermectin-treated heifers reached puberty 3 wk earlier than infected ones as assessed with serum progesterone concentrations (ivermectin, 30.4 +/- .8 vs untreated, 33.7 +/- 1.3 wk of age). This delay was not directly related to body weight. In addition, pelvic area at 39 wk and at 15 mo of age was increased in treated heifers (8 and 11%, respectively) compared with parasitized animals. No differences in the wither heights were observed. We conclude that ivermectin treatment in dairy heifers may increase growth rate during development, advance the onset of ovarian function, and positively affect yearling pelvic area.

Asunto(s)

Antihelmínticos/uso terapéutico , Bovinos/crecimiento & desarrollo , Industria Lechera/métodos , Ivermectina/uso terapéutico , Animales , Antihelmínticos/administración & dosificación , Bovinos/parasitología , Enfermedades de los Bovinos/parasitología , Enfermedades de los Bovinos/prevención & control , Heces/parasitología , Femenino , Ivermectina/administración & dosificación , Masculino , Infecciones por Nematodos/parasitología , Infecciones por Nematodos/prevención & control , Recuento de Huevos de Parásitos/veterinaria , Estaciones del Año , Maduración Sexual/efectos de los fármacos

RESUMEN

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 13 rams (four Corriedale, nine Australian Merino) during the late spring and autumn. Rams were weighed and testis size was estimated by orchimetry at each time period. Sperm production was estimated during a 2-week period, 2 months before blood collection and during each week following every blood collection. There was no relationship between testicular size and sperm production measured at the same time, nor between live weight and sperm production. In contrast, testicular volume during the late spring was correlated with sperm production in the autumn (r = 0.65; P = 0.02). The autumn serum LH was higher in Corriedale than in Merino rams. LH pulsatility was unaffected by season, but LH pulse frequency tended to be higher in Corriedale than in Merino rams, particularly in the late spring (2.37 versus 1.56 pulses/6 h; P = 0.08). Serum testosterone concentration was similar in both breeds and seasons. FSH levels were higher in the late spring than in the autumn in both breeds (Corriedale: 2.83 +/- 0.48 versus 2.17 +/- 0.24 ng x mL(-1); Merino: 2.23 +/- 0.24 versus 1.88 +/- 0.17 ng x mL(-1)). FSH and testosterone concentrations during the late spring were positively correlated with autumn sperm production (P = 0.07 and P = 0.03, respectively). In conclusion, the present experiment suggests that LH secretion is not a good parameter for the prediction of sperm production. In contrast, in our conditions (breeds and native pastures) testicular size and testosterone or FSH concentrations from the late spring may be used to predict sperm production in the autumn.

Asunto(s)

Hormona Folículo Estimulante/sangre , Hormona Luteinizante/sangre , Ovinos , Espermatogénesis , Testículo/anatomía & histología , Testosterona/sangre , Animales , Peso Corporal , Masculino , Estaciones del Año , Especificidad de la Especie

RESUMEN

The present experiments were designed in order to elucidate the participation of the developing hypophysis in determining the changing sensitivity of gonadotrophins to gonadotropin-releasing hormone (GnRH) during ontogeny in the rat. To that end, we chose two well defined developmental ages that differ markedly in sexual and ontogenic characteristics of hypophyseal sensitivity to GnRH, 15 and 30 d. In order to study sex differences and the role of early sexual organization of the hypothalamus, experiments were carried out in males, females, and neonatally androgenized females (TP females). We evaluated (1) the characteristics of pituitary GnRH receptors, and (2) associated changes in GnRH-induced mobilization of intracellular Ca2+ (a second messenger involved in gonadotropins exocytosis). We measured binding characteristics of the GnRH analog D-Ser(TBu)6-des-Gly10-GnRH ethylamide in pituitary homogenates. We found that Kds did not vary among the different sex groups. Total number and concentration of receptors decreased in the female rat from 15-30 d of age, whereas in the male and TP female, receptors/pituitary increased, and the concentration/mg tissue did not change. Also, at 30 days of age, males presented higher content and concentration of receptors than females, and higher content than TP females. In order to evaluate if developmental and sexual differences in pituitary sensitivity to GnRH might be expressed through variations in the intracellular Ca2+ signal, we studied the mobilization of intracellular Ca2+ induced by GnRH (1 x 10(-8) to 1 x 10(-11) M) in a suspension of dispersed pituitary cells in the six groups. In cells from 15-d-old females, Ca2+ response was greater than in 30-d-old females at the doses of 10(-8) to 10(-10) M, indicating that in the infantile female rat activation of highly concentrated GnRH receptors is reflected in an increase in signal transduction mediated by Ca2+. In males and in female rats androgenized at birth, there was also a decrease in the magnitude of intracellular, Ca2+ mobilization induced by GnRH (10(-8) to 10(-10) M) from 15-30 d of age, even though the concentration of GnRH receptors did not change in the same period. In conclusion, the present results suggest that high sensitivity to GnRH, which has been described in the female infantile rat, may be related to elevated concentration of hypophyseal receptors coupled to an increase of intracellular calcium response to GnRH, both parameters decreasing as the rat matures. In males, the greater sensitivity that has been described for GnRH at 30 d in comparison to 15 d is paralleled by an increase in the total number of GnRH receptors per pituitary (and not in their concentration), but not in an increase in the magnitude of Ca2+ mobilization induced by GnRH. On the other hand, neonatal sexual organization of the hypothalamus is involved in the differential expression of GnRH receptors, but does not modulate mobilization of intracellular Ca2+ induced by the decapeptide.

Asunto(s)

Calcio/metabolismo , Adenohipófisis/crecimiento & desarrollo , Adenohipófisis/metabolismo , Receptores LHRH/fisiología , Caracteres Sexuales , Envejecimiento , Animales , Buserelina/metabolismo , Femenino , Hormona Liberadora de Gonadotropina/farmacología , Radioisótopos de Yodo , Masculino , Adenohipófisis/efectos de los fármacos , Ratas , Ratas Sprague-Dawley

RESUMEN

Marked sexual and ontogenic differences have been described in gonadotropin regulation in the rat. These could arise from events occurring both at the hypothalamic or hypophyseal levels. The present experiments were designed to evaluate the capacity of the hypothalamus in releasing GnRH in vitro, basally and in response to depolarization with KCl, during ontogeny in the rat. To that end we chose two well-defined developmental ages that differ markedly in sexual and ontogenic characteristics of gonadotropin regulation, 15 and 30 days. We compared GnRH release from hypothalami of females, neonatal androgenized females and males. Mediobasal hypothalami were perifused in vitro, and GnRH measured in the effluent. Basal secretion of the decapeptide increased with age in the three groups with no sexual differences encountered. When studying GnRH release induced by membrane depolarization, no differences within sex or age were encountered. On the other hand FSH serum levels decreased with age in females and increased in males, and in neonatal androgenized females followed a similar pattern to that of females. LH levels were higher in infantile females than in age-matched males or androgenized females. Such patterns of gonadotropin release were therefore not correlated to either basal or K+-induced GnRH release from the hypothalamus. We conclude that sexual and ontogenic differences in gonadotropin secretion in the developing rat are not dependent on the intrinsic capability of the hypothalamus to release GnRH in response to membrane depolarization. The hormonal differences observed during development and between sexes are probably related to differences in the sensitivity of the GnRH neuron to specific secretagogue and neurotransmitter regulation, and/or to differences in hypophyseal GnRH receptors and gonadotrope sensitivity.

Asunto(s)

Envejecimiento/metabolismo , Hormona Liberadora de Gonadotropina/metabolismo , Hipotálamo/metabolismo , Caracteres Sexuales , Animales , Animales Recién Nacidos , Femenino , Hormona Folículo Estimulante/sangre , Técnicas In Vitro , Hormona Luteinizante/sangre , Masculino , Potasio/farmacología , Ratas , Ratas Sprague-Dawley , Testosterona/farmacología

RESUMEN

Polyamines play an essential role in tissue growth and differentiation, in body weight increment, in brain organization, and in the molecular mechanisms of hormonal action, intracellular signaling, and cell-to-cell communication. In a previous study, inhibition of their synthesis by alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase, during development in female rats, was followed by prolonged high follicle-stimulating hormone (FSH) serum level and a delayed puberty onset. Those changes were relatively independent of body mass and did not impair posterior fertility. The present work studies the mechanisms and site of action of polyamine participation in FSH secretion during development. DFMO was injected in female rats between Days 1 and 9 on alternate days. At 10 days of age, hypothalami from control and DFMO rats were perifused in vitro, and basal and potassium-induced gonadotropin-releasing hormone (GnRH) release were measured. The response to membrane depolarization was altered in DFMO hypothalami. Increased GnRH release in response to a low K+ concentration was evidenced. Adenohypophyses of the same treated prepubertal rats were perifused in vitro and the response to GnRH pulses was checked. In DFMO-treated rats, higher FSH release was observed, with no changes in LH or PRL secretion. Finally, pituitary GnRH receptor number in adenohypophyseal membranes from treated and control groups was quantified. A significant reduction in specific binding was evident in hypophyses from DFMO-treated rats when compared with binding in the control group. In summary, DFMO treatment in a critical developmental period in the female rat impacts the immature GnRH neuronal network and immature gonadotropes. A delay in maturation is evidenced by a higher sensitivity to secretagogs in both pituitary glands and hypothalamic explants. These events could explain the prolonged high FSH serum levels and delayed puberty onset seen in this experimental model.

Asunto(s)

Eflornitina/farmacología , Hormona Folículo Estimulante/metabolismo , Hormona Liberadora de Gonadotropina/metabolismo , Animales , Femenino , Hormona Folículo Estimulante/sangre , Hormona Luteinizante/sangre , Hormona Luteinizante/metabolismo , Adenohipófisis/metabolismo , Potasio/farmacología , Prolactina/sangre , Prolactina/metabolismo , Ratas , Ratas Sprague-Dawley , Receptores LHRH/metabolismo , Tasa de Secreción/efectos de los fármacos

RESUMEN

Serotonin (5-HT) receptors can be classified into at least three, possibly up to seven, classes of receptors. They comprise the 5-HT1, 5-HT2, and 5-HT3 classes, the "uncloned' 5-HT4 receptor and the recombinant receptors 5-ht5, 5-ht6 and 5-ht7. We investigated the role of different serotonin receptor types in a neuroendocrine response to the activation of the serotonergic system. Female immature rats were chosen as an experimental model as it has been shown that during the 3rd week of life, and not at later developmental stages, 5-hydroxytryptophan (5-HTP, a serotonin precursor) induces gonadotropin release in females and not in males. Besides, at this age, serotonin releases prolactin in both sexes. 5-HTP (50 mg/kg) released prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) as expected. Ketanserin (5-HT2A antagonist) and methysergide (5-HT2C antagonist) blocked 5-HTP-induced prolactin release, but did not block the LH or FSH responses. Ondansetron (5-HT3 receptor antagonist) did not modify prolactin response to 5-HTP, whereas it blocked 5-HTP-induced LH and FSH release. Propranolol (5-HT1 and beta-adrenergic antagonist) blocked prolactin, LH and FSH release induced by 5-HTP. The 5-HT2C agonist 1-(3-chlorophenyl)piperazine dihydrochloride released prolactin, without modifying LH or FSH release. Methyl-quipazine and phenylbiguanide (5-HT3 agonists) increased both LH and FSH levels, without altering prolactin secretion. The present experiments indicate that serotonin acting at the 5-HT3 receptor mediates LH and FSH release in infantile female rats, whereas 5-HT2C or 2A receptor types participate in the release of prolactin at this age. 5-HT1 receptor type may be involved in the release of the three hormones, though a beta-adrenergic component of the response cannot be discarded.

Asunto(s)

5-Hidroxitriptófano/farmacología , Hormona Folículo Estimulante/metabolismo , Hormona Luteinizante/metabolismo , Prolactina/metabolismo , Receptores de Serotonina/fisiología , Animales , Femenino , Ketanserina/farmacología , Metisergida/farmacología , Ondansetrón/farmacología , Propranolol/farmacología , Ratas , Ratas Sprague-Dawley , Antagonistas de la Serotonina/farmacología , Agonistas de Receptores de Serotonina/farmacología

RESUMEN

We have used the nonpeptide angiotensin II (ANG II) receptor antagonists losartan (receptor subtype AT1) and PD-123319 (AT2) to determine the participation of ANG II receptor subtypes in luteinizing hormone-releasing hormone (LHRH)-induced prolactin release in a perifusion study using intact pituitaries in vitro. LHRH (1.85 x 10(-7) M) released prolactin consistently, whereas losartan (10(-5) M) abolished prolactin response without modifying basal prolactin or luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release. PD-123319 (10(-5) M) had no effect on basal or LHRH-induced prolactin, LH, or FSH release. We also determined that the effect of ANG II on prolactin release was mediated by the same receptor subtype. In adenohypophysial cells dispersed in vitro ANG II (10(-8) M) released prolactin. Losartan (10(-7) and 10(-6) M), but not PD-123319, inhibited this effect. We conclude that in intact hypophyses of 15-day-old female rats the effect of LHRH on prolactin release is readily demonstrated. LHRH-induced prolactin release appears to be mediated by ANG II acting in a paracrine manner on AT1 receptors located on lactotrophs.

Asunto(s)

Angiotensina II/farmacología , Hormona Liberadora de Gonadotropina/farmacología , Hipófisis/metabolismo , Prolactina/metabolismo , Receptores de Angiotensina/fisiología , Antagonistas de Receptores de Angiotensina , Animales , Compuestos de Bifenilo/farmacología , Femenino , Imidazoles/farmacología , Técnicas In Vitro , Losartán , Perfusión/métodos , Hipófisis/citología , Piridinas/farmacología , Ratas , Ratas Sprague-Dawley , Tetrazoles/farmacología