Effects of Controlled Heat Stress on Ovarian Function of Dairy Cattle. 1. Lactating Cows

Abstract

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29 degrees C, 60% relative humidity) or thermoneutral (n = 11; 19 degrees C, 60% relative humidity) treatment. For cows undergoing heat stress, ambient temperature (19 degrees C) was increased from d 11 to 13 of the estrous cycle (3.3 degrees C/d increase) and remained at 29 degrees C until d 21. Beginning on d 11, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography. Blood was collected daily by coccygeal venipuncture for measurement of serum concentrations of progesterone and estradiol. The second wave dominant follicle was more likely to ovulate in cows in the thermoneutral treatment than in cows undergoing heat stress (91 vs. 18% ovulation, respectively). Patterns of follicular growth in cows under-going heat stress were associated with decreased serum estradiol from d 11 to 21 and on the day of luteolysis. The average day of luteolysis was delayed by 9 d in heat-stressed cows. Conclusions were that follicular growth and development and luteolytic mechanisms were compromised in heat-stressed cows; as a result, luteolysis was delayed, and second wave dominant follicles did not ovulate.

Induction of ovulation with GnRH and PGF2a in lactating Bos taurus × Bos indicus cows

“…Although it has been demonstrated that suckling, BCS and heat stress affect ovarian activity, the results obtained in the present trial were acceptable, despite the fact that the cows were suckling their calves, had a low BCS and experienced heat stress due to high ambient temperatures. Although heat stress diminishes particularly the number of small follicles (Wolfenson et al, 1995) and delays luteolysis in cows (Wilson et al, 1998), this was not observed in the present study; on the contrary, PGF 2α induced luteolysis in all cows that had a CL, and the follicles that consequently developed were small (3 to 5 mm) but great in number.…”

Progesterone profiles and oestrous cycle changes following superovulatory treatment of Holstein-Friesian dairy cows in a tropical environment

“…Ronchi et al (2001) found P4 concentration to be lower in heat-stressed cows, while others have observed higher concentrations of P4 (Wilson et al, 1998). In contrast, Wolfenson et al (1995) found no differences in P4 concentrations between heat-stressed and cooled cows.…”

El estrés calórico afecta el comportamiento reproductivo y el desarrollo embrionario temprano en bovinos

“…Por ejemplo, Wilson et al, (1998b) La dinámica folicular es afectada por el estrés calórico, el efecto de dominancia decrece, hay una emergencia temprana del folículo preovulatorio y carencia en la regresión de los folículos subordinados (Wolfenson et al, 1995).El efecto del estrés calórico sobre la dominancia en el desarrollo de ondas foliculares fue también confirmado por Trout et al, (1998). En un experimento in vitro, donde se cultivaron fragmentos ováricos durante 7 días, el complejo cúmulus-ovocito (COC) y ovocitos aislados fueron sometidos a estrés calórico durante las primeras 12 horas del experimento.…”

“…Se estima que los efectos del estrés calórico sobre la dinámica ovárica tienen consecuencias en el corto y largo plazo y que para que la dinámica ovárica se normalice deben pasar de 2 a 3 ciclos estrales desde la última afectación por calor (Roth, 2015). Wilson et al (1998b) encontraron que la vida del cuerpo lúteo en vacas cíclicas en condiciones de estrés calórico es más larga y que las concentraciones de progesterona se mantienen significativamente más altas del día 17 al 21 del ciclo estral. El comportamiento del cuerpo lúteo de vida larga observado en vacas bajo estrés calórico, fue el mismo obtenido cuando la evaluación se realizó con novillas, la única diferencia es que las concentraciones altas de progesterona fueron de los días 16 al 20 del ciclo estral.…”