Impacto del nivel de producción, estación de parto y el tipo de servicio sobre la tasa de preñez acumulada a 100 días en vacas lecheras en la Argentina

The aim of this study was to estimate using a multiple logistic regression the relative contribution of factors affecting the probability of getting pregnant at the first 100 days of milk production in Argentine dairy herds. The factors considered were milk production level, lactation number, calving season, type of service used, artificial insemination (AI), natural breeding, or combined, and the interaction between type of service and level of production. The 291 Dairy farms (162.116 lactations) are users of the software Dairy Comp 305 herd-management. This software has a production estimator called 305 mature equivalent to standardize records from different lactation numbers. The analyzed variables in the model were statistically significant. Cows of lower milk production have more chances to get pregnant than those with higher milk production. Cows that calves in colder seasons have more probabilities to get pregnant than those calves in hottest seasons. The relation was quadratic between the probability of getting pregnant at 100 days in milk and the number of lactation. The cumulative pregnancy rate at 100 days was greater with natural service, compared to AI but, the AI was related with greater levels of milk production. Therefore, the results suggest that new reproductive management designs specifically developed for given productive levels could increase the overall reproductive efficiency.El propósito de este estudio fue estimar, a través de una regresión logística múltiple, la contribución relativa de factores que afectan la probabilidad de preñez a los 100 días en lactancia en rodeos lecheros argentinos. Los factores analizados fueron: nivel productivo, estación de parto, número de lactancia,tipo de servicio utilizado inseminación artificial (IA), natural o combinación de ambas y la interacción del nivel productivo y el tipo de servicio. Los 291 tambos (162.116 lactancias) son usuarios del software Dairy Comp305, del cual se obtiene la producción estimada que se espera alcance la vaca adulta(305 equivalente maduro). Todos los factores resultaron estadísticamente significativos. Las vacas con bajo nivel productivo tuvieron mayores chances depreñarse que vacas con niveles productivos mayores. Las vacas con parición en estaciones más frías tuvieron mayores chances de preñarse a los 100 días.La relación resultó cuadrática entre la probabilidad de preñarse a los 100 días y el número de lactancia. Los bovinos que recibieron servicio natural presentaron mayor tasa de preñez acumulada; sin embargo, la IA estuvo asociada a niveles productivos mayores. Los resultados sugieren la necesidad de diseños alternativos y evaluación del manejo reproductivo según niveles productivos específicos, como herramienta para incrementar la eficiencia reproductiva global

Effects of dominant follicle aspiration and treatment with recombinant bovine somatotropin (BST) on ovarian follicular development in Nelore (Bos indicus) heifers

Follicle ablation has been recognized as an efficient method of follicular wave synchronization. Treatment with recombinant bovine somatotropin (BST) has been shown to enhance follicular development in Bos taurus. This experiment assessed the effects of these treatments in Nelore (B. indicus) heifers. Eight cycling Nelore heifers were randomly assigned to 3 different treatments. On Day 2 of a synchronized cycle (Day 0 = day of ovulation), heifers assigned to Treatments 1 and 2 received 2 mL of saline, whereas heifers assigned to Treatment 3 received 320 mg of BST. On Day 5, the first-wave dominant follicle was ablated by ultrasound-guided transvaginal aspiration in heifers in Treatments 2 and 3, and all heifers received an injection of prostaglandin on Day 11. Aspiration of the dominant follicle advanced and synchronized (P < 0.05) the day of second-wave emergence (6.9 ± 0.1 vs. 8.4 ± 0.4) and the day of the pre-wave FSH peak (6.0 ± 0.0 vs. 6.9 ± 0.4), and increased FSH peak concentrations (381 ± 21 vs. 292 ± 30; pg/mL; P < 0.01). Recombinant bovine somatotropin treatment caused a two-fold increase in plasma insulin-like growth factor-I (IGF-I) concentrations (P < 0.001) and resulted in a 36% increase in the number of small follicles (<5 mm; P < 0.001) compared with saline-treated heifers. In summary, in agreement with previous reports on B. taurus, dominant follicle aspiration synchronized ovarian follicular development, and BST treatment increased peripheral concentrations of IGF-I in Nelore heifers. Recombinant bovine somatotropin also increased the number of small follicles, but this response appeared to be inferior to that reported for B. taurus.Fil: Buratini, José. University of São Paulo, São Paulo, BrazilFil: Price, C.A. University of Montreal, St. Hyacinthe, Que., CanadaFil: Visintin, J.A. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Bó, G.A. Department of Pharmacology, Institute of Biosciences, UNESP, Botucatu 18618-000 Sao Paulo, Brazi

Impacto del nivel de producción, estación de parto y el tipo de servicio sobre la tasa de preñez acumulada a 100 días en vacas lecheras en la Argentina Impact of the production level, calving season and type of service on the 100-day cumulative pregnancy rate of dairy cows in Argentina

El propósito de este estudio fue estimar, a través de una regresión logística múltiple, la contribución relativa de factores que afectan la probabilidad de preñez a los 100 días en lactancia en rodeos lecheros argentinos. Los factores analizados fueron: nivel productivo, estación de parto, número de lactancia, tipo de servicio utilizado inseminación artificial (IA), natural o combinación de ambas y la interacción del nivel productivo y el tipo de servicio. Los 291 tambos (162.116 lactancias) son usuarios del software Dairy Comp305, del cual se obtiene la producción estimada que se espera alcance la vaca adulta (305 equivalente maduro). Todos los factores resultaron estadísticamente significativos. Las vacas con bajo nivel productivo tuvieron mayores chances de preñarse que vacas con niveles productivos mayores. Las vacas con parición en estaciones más frías tuvieron mayores chances de preñarse a los 100 días. La relación resultó cuadrática entre la probabilidad de preñarse a los 100 días y el número de lactancia. Los bovinos que recibieron servicio natural presentaron mayor tasa de preñez acumulada; sin embargo, la IA estuvo asociada a niveles productivos mayores. Los resultados sugieren la necesidad de diseños alternativos y evaluación del manejo reproductivo según niveles productivos específicos, como herramienta para incrementar la eficiencia reproductiva global.<br>The aim of this study was to estimate using a multiple logistic regression the relative contribution of factors affecting the probability of getting pregnant at the first 100 days of milk production in Argentine dairy herds. The factors considered were milk production level, lactation number, calving season, type of service used, artificial insemination (AI), natural breeding, or combined, and the interaction between type of service and level of production. The 291 Dairy farms (162.116 lactations) are users of the software Dairy Comp 305 herd-management. This software has a production estimator called 305 mature equivalent to standardize records from different lactation numbers. The analyzed variables in the model were statistically significant. Cows of lower milk production have more chances to get pregnant than those with higher milk production. Cows that calves in colder seasons have more probabilities to get pregnant than those calves in hottest seasons. The relation was quadratic between the probability of getting pregnant at 100 days in milk and the number of lactation. The cumulative pregnancy rate at 100 days was greater with natural service, compared to AI but, the AI was related with greater levels of milk production. Therefore, the results suggest that new reproductive management designs specifically developed for given productive levels could increase the overall reproductive efficiency