El periparto en las vacas lecheras: balance energético, actividad ovárica, salud uterina y eficiencia reproductiva

Este trabajo de tesis tuvo cuatro objetivos principales: evaluar la relación entre algunos indicadores de balance energético (BE) alrededor del parto y el reinicio de las ovulaciones postparto (ROP), determinar la asociación entre esos indicadores y el riesgo de presentación de metritis (MET) y de endometritis clínica (EC), analizar si el diagnóstico anticipado de MET y su tratamiento con Ceftiofur (CEF) mejoran la curación y la eficiencia reproductiva, y estimar los efectos de estas dos afecciones uterinas sobre la producción de leche y la eficiencia reproductiva en vacas lecheras de producción comercial. Se realizaron 2 experimentos, en el primero se utilizó un diseño completamente aleatorio con mediciones repetidas en el tiempo en el que la vaca fue la unidad experimental. Se evaluaron la condición corporal (CC), y la concentración plasmática de metabolitos y hormonas metabólicas de 20 vacas multíparas desde 2 semanas anteriores a 9 posteriores al parto. Los datos se analizaron con modelos lineales mixtos y con regresiones logísticas y de riesgos proporcionales de Cox. Se encontró que las vacas que padecen de ovulación retrasada poseen menor CC y mayor nivel de movilización grasa durante el periparto, y que la tasa de riesgo instantáneo de tener ROP está en relación directa con la concentración del factor de crecimiento 1 similar a la insulina (IGF-1) en el preparto y en relación inversa con los niveles de ácidos grasos no esterificados (AGNE) en el postparto. Además, se constató que el riesgo de sufrir ovulación retrasada se incrementa a medida que se elevan las concentraciones de AGNE tanto antes como después del parto. En el segundo ensayo se utilizó un diseño completamente aleatorio con mediciones repetidas en el tiempo en el que la vaca fue la unidad experimental. Se evaluaron la CC, las características del moco vaginal (MV) y la concentración plasmática de metabolitos y hormonas metabólicas de 303 vacas primíparas y multíparas desde 2 semanas anteriores a 7 posteriores al parto. Los datos se analizaron con modelos lineales mixtos y con regresiones logísticas, multinomiales y de riesgos proporcionales de Cox. Se determinó que el riesgo de MET es mayor en las vacas primíparas, en las que tienen problemas al parto y en las que poseen altos niveles de AGNE y bajos de IGF-1 durante el preparto; que la terapia con CEF no es efectiva contra la MET, puesto que no afecta la curación clínica, la producción de leche, ni la eficiencia reproductiva; que la tasa de curación guarda relación directa con las concentraciones de insulina, previas y posteriores al parto, y que aumenta con el tiempo postparto, y que es mayor cuando la MET no se acompaña de fiebre. Además, se demostró que la temperatura rectal (TR) y la CC son herramientas diagnósticas precisas para la MET; que los efectos deletéreos sobre la tasa de preñez y el intervalo entre el parto y la concepción (IPC) son causados principalmente por la MET puerperal, puesto que las vacas con MET clínica se comportan prácticamente igual que las sanas; que la MET posee efectos negativos sobre la producción principalmente al inicio de la lactancia. Asimismo, en el caso de la EC, se demostró que el riesgo es mayor en las vacas que presentan problemas al parto y/o MET y en las que atraviesan un BE más negativo; que las concentraciones de AGNE en el preparto y de B-hidroxibutirato (BHB) en el postparto son útiles para predecir el riesgo de esta enfermedad; que la curación espontánea de EC aumenta con el paso del tiempo durante el postparto; que esta afección causa pérdidas reproductivas por alargar el intervalo a la concepción y por incrementar las chances de rechazo del rodeo, y además que, llamativamente, se acompaña de mayor producción láctea sin afectar el BE de los animales. En conclusión, podría afirmarse que el BE negativo es un factor de riesgo importante para el desarrollo de la ovulación retrasada, de la MET y de la EC, y que los indicadores de BE (i.e.: AGNE y BHB) son útiles para predecir el riesgo de las vacas de padecer estos trastornos a nivel individual. Además, que los problemas al parto (i.e.: distocia y retención de placenta) desempeñan un rol clave en el desarrollo de las dos afecciones uterinas estudiadas, y que el tratamiento antibiótico con CEF no es efectivo contra la MET. Por último, podría expresarse que la MET, especialmente la puerperal, y la EC poseen efectos deletéreos similares sobre la eficiencia reproductiva, en tanto que ejercen acciones contrapuestas sobre la producción de leche debido a que la primera disminuye marcadamente la producción mientras que la segunda la incrementa levemente.Facultad de Ciencias Veterinaria

Relato de un profesor devenido en youtuber : Enseñar fisiología virtualmente en tiempos de cuarentena por la pandemia de COVID-19

Esta nota breve consta de dos partes, la primera, donde cuento las vicisitudes que experimenté creando contenido para YouTube y la segunda, donde comento qué temas desarrollo en los videos y con qué enfoque fisiológico.Sociedad Argentina de Fisiologí

Association between prepartum metabolic status and resumption of postpartum ovulation in dairy cows

Cows transitioning from late gestation to early lactation experience an increase in energy demands, which lead to a negative energy balance (NEB) because the greater energy requirement is not fully synchronized with the intake of dry matter. In this context, there is an increase in plasma NEFA and ghrelin concentrations and a decrease in plasma insulin and glucose-dependent insulinotropic polypeptide (GIP) concentrations. This situation could have a negative impact on the return to cyclicity because some of these variables have been associated with reduced GnRH and LH pulsatility (high NEFA and low insulin concentrations). However, there are no studies showing the relationship between ghrelin or GIP and reproductive performance. It is known that these hormones are related with lipolysis and NEB, with NEB being one of the main determinants of GnRH pulse generator activity. Thus, the objective of the present study was to evaluate the association between plasma NEFA concentration and metabolic hormones (insulin, ghrelin, and GIP) before parturition and their associations with the resumption of postpartum ovulations in dairy cows. A completely randomized block design was used in a commercial dairy herd with sampling day (visit to farm) as the blocking criteria. Holstein cows (n = 92) were screened for plasma NEFA concentration -5 d (+/-2 d) relative to the expected parturition day, and top and bottom quartiles were considered as high (H-NEFA) and low (L-NEFA) NEFA groups. Data were analyzed with correlation, linear regression, and proportional hazard regression models. Plasma NEFA concentration (H-NEFA mean ¼ 294 mM, SD ¼ 141.2; and L-NEFA mean ¼ 122 mM, SD ¼ 25.3) was correlated (P < 0.01) with plasma insulin (r2 = 0.374) and ghrelin (r2 = 0.346) concentrations but not with plasma GIP concentration (P = 0.64). The greater the concentration of insulin, the lesser the prepartum NEFA concentration (for each 1 mU/mL of plasma insulin increase, there is a decrease of 1.223 +/- 0.62 mM of NEFA). Plasma ghrelin and GIP concentrations were not associated with plasma NEFA concentration. Finally, H-NEFA prepartum cows were less likely to resume ovulation than L-NEFA cows (hazard ratio [HR] = 0.563, 95% confidence interval [CI] = 0.314–1.011), whereas high ghrelin cows were more likely to resume ovulation than low ghrelin cows (HR = 1.873, 95% CI = 0.846–4.145). Conversely, resumption of ovulation was not associated with prepartum insulin and GIP concentrations. Prepartum NEFA and possibly ghrelin are associated with the return to postpartum cyclicity; however, insulin and GIP are not related to the resumption of ovulation in dairy cows.Facultad de Ciencias Veterinaria

Uterine infection with bovine herpesvirus type 4 in dairy cows

Diseases of the reproductive tract are a frequent problem in dairy herds. Herpesviruses are uterine pathogens also involved in other clinical diseases; for example, bovine herpesvirus type 4 BoHV-4 induces abortion, enteritis, metritis, pneumonia and vaginitis, but it can also be detected in healthy cows. The role of BoHV-4 in the development of clinical endometritis (CE) or subclinical endometritis (SE) has not clearly been described. Therefore, the objective of this study was to describe the prevalence of uterine BoHV-4 infection and its relationship with clinical, bacteriological and cytological findings in dairy cows 20–30 days after calving. The experiment was performed as a completely randomized block design, with farm (n = 10) as blocking criterion and with cow (n = 397) as the experimental unit. Logistic regression models were used to assess the effect of BoHV-4 infection on CE, SE and reproductive performance. Proportion of cows infected with BoHV-4 was 5.8% (n = 23/397). BoHV-4 was isolated in 11.0% (n = 12/109), 4.8% (n = 4/84) and 3.6% (n = 7/194) of cows diagnosed as CE, SE or healthy, respectively. A logistic model revealed that BoHV-4 infection showed a tendency to increase the risk for CE (AOR = 2.17; p = .10) but significantly reduced both, the odds for artificial insemination within 80 days post-partum (dpp) (AOR = 0.37; p = .035) and for pregnancy within 200 dpp (AOR = 0.13; p = .004). Furthermore, BoHV-4 infection increased the chance for intrauterine infection with Trueperella pyogenes (AOR = 5.55; p < .001) and vice versa (AOR = 5.79, p < .001). In conclusion, BoHV-4 infection is associated with reduced chances for insemination and pregnancy by 200 dpp and showed a trend to be associated with increased risk for CE. Furthermore, BoHV-4 and Trueperella pyogenes infections are strongly related.Facultad de Ciencias Veterinaria

Un tratamiento metafiláctico con doble dosis de oxitetraciclina reduce el riesgo de enfermedad respiratoria bovina en terneros de engorde a corral

The objective of this study was to evaluate the effect of a metaphylactic treatment with oxytetracycline (OTC) in the labeled and double doses on the risk for bovine respiratory disease (BRD) in feedlot calves. This study was conducted in a commercial feedlot where 2,754 calves belonging to high risk groups were enrolled. A randomized complete block design was used, with animals as experimental units and pens (n=10) as blocks. Three experimental groups were assessed: 1- untreated control (CTL), 2- OTC 20 mg/kg SC (OTC20) and 3- OTC 40 mg/kg SC (OTC40). The risk for BRD was evaluated with a mixed logistic regression. Untreated CTL had 2.85 and 7.14 more chances of getting BRD than OTC20 and OTC40 groups, respectively (p<0.001). In conclusion, metaphylactic treatment with OTC is useful to reduce the risk for BRD in feedlot cattle, being protective effect higher at double dose than at labeled one.El objetivo del presente estudio fue evaluar el efecto del tratamiento metafiláctico con oxitetraciclina (OTC), a simple y doble dosis, en bovinos con alto riesgo de padecer enfermedad respiratoria bovina (ERB). El estudio se realizó en un establecimiento de engorde a corral donde se utilizaron 2.754 terneros que fueron considerados de alto riesgo de padecer ERB. Se utilizó un diseño en bloque completamente al azar donde se consideró al animal como la unidad experimental y el corral (n=10) como bloque. Se formaron tres grupos experimentales: 1- control (CTL) el cual permaneció sin tratamiento, 2- recibió OTC 20 mg/kg SC (OTC20) y 3- recibió OTC 40 mg/kg SC (OTC40). El riesgo de ERB fue evaluado a través de una regresión logística. Los animales del grupo CTL tuvieron 2,85 y 7,14 veces más chances de enfermarse de ERB que los animales de los grupos OTC20 y OTC40 respectivamente (p<0,001). En conclusión, el tratamiento metafiláctico con OTC es útil para reducir el riesgo de padecer ERB en engorde a corral, siendo su efecto mayor cuando se aplica a la dosis de 40 mg/kg.Facultad de Ciencias Veterinaria

Association between prepartum metabolic status and resumption of postpartum ovulation in dairy cows

Cows transitioning from late gestation to early lactation experience an increase in energy demands, which lead to a negative energy balance (NEB) because the greater energy requirement is not fully synchronized with the intake of dry matter. In this context, there is an increase in plasma NEFA and ghrelin concentrations and a decrease in plasma insulin and glucose-dependent insulinotropic polypeptide (GIP) concentrations. This situation could have a negative impact on the return to cyclicity because some of these variables have been associated with reduced GnRH and LH pulsatility (high NEFA and low insulin concentrations). However, there are no studies showing the relationship between ghrelin or GIP and reproductive performance. It is known that these hormones are related with lipolysis and NEB, with NEB being one of the main determinants of GnRH pulse generator activity. Thus, the objective of the present study was to evaluate the association between plasma NEFA concentration and metabolic hormones (insulin, ghrelin, and GIP) before parturition and their associations with the resumption of postpartum ovulations in dairy cows. A completely randomized block design was used in a commercial dairy herd with sampling day (visit to farm) as the blocking criteria. Holstein cows (n = 92) were screened for plasma NEFA concentration -5 d (+/-2 d) relative to the expected parturition day, and top and bottom quartiles were considered as high (H-NEFA) and low (L-NEFA) NEFA groups. Data were analyzed with correlation, linear regression, and proportional hazard regression models. Plasma NEFA concentration (H-NEFA mean ¼ 294 mM, SD ¼ 141.2; and L-NEFA mean ¼ 122 mM, SD ¼ 25.3) was correlated (P &lt; 0.01) with plasma insulin (r2 = 0.374) and ghrelin (r2 = 0.346) concentrations but not with plasma GIP concentration (P = 0.64). The greater the concentration of insulin, the lesser the prepartum NEFA concentration (for each 1 mU/mL of plasma insulin increase, there is a decrease of 1.223 +/- 0.62 mM of NEFA). Plasma ghrelin and GIP concentrations were not associated with plasma NEFA concentration. Finally, H-NEFA prepartum cows were less likely to resume ovulation than L-NEFA cows (hazard ratio [HR] = 0.563, 95% confidence interval [CI] = 0.314–1.011), whereas high ghrelin cows were more likely to resume ovulation than low ghrelin cows (HR = 1.873, 95% CI = 0.846–4.145). Conversely, resumption of ovulation was not associated with prepartum insulin and GIP concentrations. Prepartum NEFA and possibly ghrelin are associated with the return to postpartum cyclicity; however, insulin and GIP are not related to the resumption of ovulation in dairy cows.Facultad de Ciencias Veterinaria

Rainfall effect on grass and <i>Lotus glaber mill</i>. mineral composition from Magdalena district

Los excesos hídricos incrementan la absorción de Fe por el forraje y éste puede reducir la captación de Cu y Zn. En el partido de Magdalena en los años donde aumentó el régimen de lluvias se registraron mayores prevalencias de hipocuprosis bovina. El objetivo del presente trabajo es establecer los cambios provocados por el exceso hídrico del suelo sobre la composición mineral del forraje. En doce establecimientos del partido de Magdalena, entre marzo y diciembre de 1997, se tomaron 76 muestras pareadas de Lotus glaber Mill (= Lotus tenuis Waldst. et Kit. ex Wild.) y gramíneas durante períodos secos y húmedos. Las muestras se sometieron a digestión ácida y se determinó el contenido de Cu, Fe, Mn y Zn por espectrofotometría de absorción atómica y el de S por titulación con arsenazo III. Los datos se analizaron mediante test de T y análisis de varianza. El contenido de Fe aumentó significativamente durante los períodos húmedos: 579 vs 206 ppm en L. glaber y 858 vs 104 ppm en gramíneas. El L. glaber presentó mayores concentraciones de Cu y Zn que las gramíneas. El contenido de Cu aumentó significativamente en las gramíneas durante el período húmedo y en el L. glaber no se modificó. El Mn aumentó significativamente en el L. glaber durante el período húmedo.Water excess increases forage Fe absorption, and in turn, Fe can reduce both Cu and Zn uptake by roots. It is known that Cu deficiency prevalence in cattle is higher when annual rainfall in Magdalena district is heavier. Our objective is to assess the changes in forage mineral composition caused by water excess in soil. Seventy six samples of Lotus glaber Mill. (= Lotus tenuis Waldst. et Kit. ex Wild.) and accompanying grass were taken, during dry and wet periods, in 12 beef breeding farms from Magdalena district, from march through December 1997. Samples were acid digested, and Cu, Fe, Mn and Zn concentration was measured by atomic absorption, whereas S content was measured by Arsenaze III tritration. Data were analyzed by T test and variance (p < 0.05). Iron concentration increased during wet periods: 579 vs 206 ppm for L. glaber and 858 vs 104 for grass samples (p: <0.05). L. glaber samples had higher Cu and Zn contents than grass samples. Copper concentration increased in grass samples (p < 0.05). Manganese concentration increased in L. glaber samples during wet periods (p < 0.05).Facultad de Ciencias Veterinaria

Associations of somatic cell count with milk yield and reproductive performance in grazing dairy cows

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.Fil: Rearte, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Corva, S. G.. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: de la Sota, Rodolfo Luzbel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Lacau, Isabel María. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Giuliodori, Mauricio Javier. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentin

Purulent vaginal discharge in grazing dairy cows: risk factors, reproductive performance, and prostaglandin F2α treatment

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.Facultad de Ciencias Veterinaria

Endometrial cytology, biopsy, and bacteriology for the diagnosis of subclinical endometritis in grazing dairy cows

The objectives of this study were to assess the agreement between endometrial cytology and uterine biopsy for the diagnosis of subclinical endometritis (SEND) in grazing dairy cows, the interobserver agreement of the biopsy's readings, and the bacterial population isolated from the uterus of cows having SEND. In experiment 1, lactating Holstein cows (n. = 44) 31 to 59. d in milk (DIM) at sampling were enrolled. Clinical endometritis was diagnosed by direct evaluation of vaginal discharge and SEND by endometrial cytology evaluation. Two hundred cells per smear were counted to determine the percentage of polymorphonuclear neutrophilic leukocytes (PMNL). Cut-off values used were ≥8% PMNL at ≤33 DIM, ≥6% PMNL at 34 to 47 DIM, and ≥4% PMNL at ≥48 DIM. Biopsies were assessed blindly by 2 observers who categorized them into 4 groups according to their inflammatory changes: none, minimal, moderate, and severe inflammatory changes. Data were analyzed using the kappa coefficient and logistic regression. In experiment 2, lactating Holstein cows (n. = 60) 21 to 62 DIM were enrolled. Clinical endometritis and SEND were diagnosed as previously described. Samples were cultured for aerobic and anaerobic bacteria by routine methods of bacteriological testing. Data were analyzed with logistic regression. In experiment 1, little agreement was observed between cytology and biopsy outputs (kappa. = 0.151), and strong agreement between the 2 operators (kappa. = 0.854). The likelihood of having a normal biopsy (no inflammatory change) was greater for healthy cows than for those having SEND (odds ratio. = 13.145). The probability for getting normal uterine tissue decreased 2.1% for every increasing percentage point in PMNL. In experiment 2, no bacteria were isolated from cows with SEND, coagulase-negative staphylococci were commonly isolated from healthy cows, and Trueperella pyogenes was frequently isolated from cows with clinical endometritis. The likelihood of isolating T. pyogenes from uterine samples increased with the percentage of PMNL (odds ratio. = 1.100). In conclusion, biopsy showed low agreement with cytology for the diagnosis of SEND. Nevertheless, fertility trials using uterine biopsies to predict pregnancy outcomes are needed to determine its diagnostic usefulness. Finally, bacteriology would not be recommended as a diagnostic tool because no bacteria were isolated from cows with SEND.Facultad de Ciencias Veterinaria