Applying nutrition and physiology to improve reproduction in dairy cattle

Abstract

The establishment and maintenance of pregnancy in lactating dairy cows is a complex biological event that is influenced by a multitude of factors, from the reproductive biology of the cow to managerial aspects of the dairy farm. It is often mentioned in the scientific literature that fertility in dairy cows has declined concurrent with major advances in milk production. Some of this decline is attributed to the negative genetic correlation between milk production and reproduction. In the United States, yearly production per cow has increased steadily at a rate of 1.3% in the last decade and it is likely that this trend will continue in the years to come. At this rate, the average cow in the United States will be producing over 14 tons of milk per year in 2050 and technologies will have to be developed to allow these cows to reproduce to maintain the sustainability of dairy production. Despite high production, it is not uncommon for dairy herds with rolling herd averages for milk yield above 11,000 kg to overcome the challenges of reproduction and obtain satisfactory reproductive performance. Among other things, those herds have been able to mitigate some of the mechanisms that suppress reproduction in dairy cows such as extended postpartum anovulatory period, poor estrous detection, low pregnancy per insemination and, to a lesser extent, the high pregnancy loss. The success of those farms comes from an integrated approach to fertility that includes adequate cow comfort, elaborated transition cow management and nutrition, aggressive postpartum health monitoring program with preventative and curative measures to mitigate the negative effects of diseases on reproduction, and a sound reproductive program that includes manipulation of the ovarian cycle to allow for increased insemination rate. More recently, introduction of fertility traits in selection programs have created new opportunities for improved reproduction without neglecting economically important production traits. Applying nutrition and physiology to improve reproduction in dairy cattle

Synchronisation of ovulation for management of reproduction in dairy cows

“…Allowing 56 h of proestrus helps in additional growth of the ovulatory follicle and increased exposure to oestradiol (Peters and Pursley, 2003), which is thought to be needed to avoid short oestrus cycles after induced ovulation. On the other hand, for cows subjected to the 5-day timed AI programme, which results in smaller ovulatory follicles and reduced concentrations of oestradiol in the plasma around the time of AI compared with the Ovsynch protocol (Santos et al, 2010a), the length of proestrus should be extended to 72 h (Bisinotto et al, 2010b;Ribeiro et al, 2012b). Therefore, a careful balance involving follicle/oocyte maturation and timing between sperm and oocyte availability must be considered so that optimal fertility can be achieved.…”

“…Finally, although ovulation is synchronised between 24 and 32 h after the final GnRH injection (Pursley et al, 1995), not all cows have a synchronised ovulation, which typically averages 85% (Santos et al, 2010a), and this number seems to decline when cows are exposed to heat stress because of the supposed deleterious effects of hyperthermia on ovulation (López-Gatius et al, 2005). Furthermore, herds with increased prevalence of peripartum diseases have reduced response to synchronisation programmes because of increased prevalence of anovular cows, reduced fertilisation and impaired embryo development, which ultimately leads to smaller P/AI and increased pregnancy loss (Santos et al, 2010b;Ribeiro et al, 2013). …”

“…Therefore, a careful balance involving follicle/oocyte maturation and timing between sperm and oocyte availability must be considered so that optimal fertility can be achieved. Extending the duration of the proestrus during the 5-day timed AI programme compensated for a less optimal interval between induced ovulation and insemination, which allowed for the administration of the final GnRH concurrently with AI at 72 h after PGF 2α without rendering P/AI (Bisinotto et al, 2010b). …”

Impacto del balance energético negativo en vacas lecheras tratadas con somatotropina recombinante bovina

“…El ideal establecido para el intervalo parto-parto es de 12 a 13 meses y para que este supuesto se cumpla, la vaca debe quedar preñada en los tres meses siguientes al parto, es decir que la reanudación de la actividad ovárica debe darse lo más pronto posible después del parto 20 . La síntesis y secreción de hormonas, la ovulación de un folículo y el sostenimiento de un embrión en desarrollo presentan costos energéticos mínimos en comparación con los costos de la lactancia, sin embargo, las señales endocrinas y metabólicas involucradas en el balance energético negativo afectan la reanudación de los ciclos ovulatorios, la calidad de los ovocitos y del embrión, así como el establecimiento y mantenimiento de la preñez, disminuyendo la eficiencia reproductiva en los hatos lecheros 30 . La vaca en balance energético negativo está en alto riesgo de presentar anestro anovulatorio debido a que a pesar de que desarrolla un folículo dominante, éste no ovula; los aumentos recurrentes de FSH cada 7 a 10 días después del parto permiten la aparición de ondas foliculares que dan desarrollo al folículo dominante, aunque éste no produce la concentración suficiente de estradiol para inducir un aumento en la hormona liberadora de gonadotropina, lo cual lleva a la disminución en la frecuencia de pulsos de la hormona luteinizante, evitando que se presente la ovulación 29 .…”

“…Los resultados favorables en vacas de primer servicio 30 no se observaron en otros estudios con tratamientos similares 4,26 . Probablemente el tipo de bST, el manejo reproductivo de los hatos y las condiciones ambientales podrían explicar dicha variación, por lo cual su uso en vacas de primer servicio debe validarse en cada condición particular.…”