Calving sub-season and reproductive efficiency of beef cows

Abstract

1 st to 20 th ). Calving sub-season significantly influenced pregnancy rate. Cows which calved in the initial sub-season showed higher pregnancy rates than cows which calved from the fourth calving sub-season. However this difference did not occur in 1999 and in 2007 since calving rates did not statistically differ among the five sub-seasons. In 1998 and 2004, calving rates were lower and the effects of calving sub-season on pregnancy rates were higher, possibly due to climate variations.In general, pregnancy rate decreases as calving occurs later in the year, particularly in years when the weather adversely affects pasture growth.

Factores ambientales y parámetros genéticos para algunas características reproductivas en bovinos Chacuba

“…In general, the four classes of grouping (by bimester, trimester, quarter and semester of calving) have a major effect on each of the dependent variables mentioned. In another study conducted in Brazil (24) reproductive efficiency was affected by the season of the birth when it was divided into 20-d intervals throughout the year. The effect of period of calving on reproductive variables may be related to variation in the availability and quality of the pastures, which is associated in turn to body condition of cows giving birth and as a result the fertility in the postpartum period (25) , affecting the CPI and the CI (24) .…”

“…De manera general, las cuatro formas de agrupación de contemporáneas (bimestre, trimestre, cuatrimestre o semestre del parto) tienen un efecto importante sobre cada una de las variables dependientes señaladas. En otro estudio realizado en Brasil (24) la eficiencia reproductiva se afectó por la época de parto cuando ésta fue dividida en intervalos de 20 días a lo largo del año. El efecto de la época de parto sobre las variables reproductivas podría estar relacionada con la variación en la disponibilidad y calidad de lo pastos, la cual se asocia a su vez con la condición corporal de las vacas al parto y consecuentemente con la fertilidad en el periodo postparto (25) , afectando el IPC y el IP (24) .…”