Endocrine Changes during Restoration of Estrous Cycles Following Induction of Anestrus by Restricted Nutrient Intake in Beef Heifers1

Abstract

The working hypotheses in this experiment were: 1) that ovarian estradiol would inhibit luteinizing hormone (LH) secretion in heifers that were anestrus as a result of restricted dietary energy intake and 2) the responsiveness of LH secretion to estradiol negative feedback would decrease during the period when restoration of estrous cycles occurred following feeding of diets adequate in energy. Fifteen heifers wei~hin~ 341 • 12 (mean • SE) kg were fed a diet containing 50% of the energy required for maintenance until 40 to 50 d following cessation of estrous cycles. Heifers were assigned to intact control (C, n = 5), ovariectomized (OVX, n = 5) or ovariectomized-estradiol-17[3-implanted (OVX + E 2, n = 5) treatments. Heifers were subsequently provided a high-energy (HE) diet until termination of the study. Progesterone concentrations indicating cessation of corpus luteum function were detected after heifers had lost 71 • 8 kg body weight over 186 • 28 d. Control heifers re-initiated estrous cycles as indicated by increased progesterone concentrations in serum at 49 • 9 d after initiation of feeding the HE diet (360 • 18 kg body weight). Initiation of pulsatile LH secretion was observed in heifers by d 12 following OVX. Estradiol suppressed LH secretion in OVX + E 2 heifers during the period of nutritional anestrus in C heifers. Suppressive effects of E2 on LH secretion continued in OVX heifers after C heifers had initiated corpus luteum function. Therefore, the working hypothesis that LH secretion is inhibited by E2 in the nutritionally anestrous heifer is accepted but responsiveness to estradiol does not subside with re-initiation of estrous cycles, thus this working hypothesis is rejected.

Parturition to resumption of ovarian cyclicity: comparative aspects of beef and dairy cows

“…A decrease in the concentration of LH and a suppression in the frequency of LH pulses had been reported in nutritionally induced anoestrous beef cows (Richards et al, 1989), heifers (Imakawa et al, 1986), and occurs as a result of reduced GnRH secretion from the hypothalamus. Long-term oestradiol pre-treatment during prolonged undernutrition reduced the magnitude of the induced LH surge to just 20% of that observed in lambs not chronically treated with oestradiol, suggesting that low levels of oestradiol have a strong negative feedback effect on undernourished animals.…”

Impact of Dietary Restriction on Follicular Waves in Cattle With Particular Reference to Anoestrus

“…Nutritional restriction has got immediate negative effects on follicular growth and cyclicity (Mackey et al, 1997;1998;. The dietary energy restriction might influence the LH release directly at the pituitary level as well as indirectly through effects on ovarian steroid production (Beal et al, 1978).The energy restriction decreased the incidence of heifers having estrous cycles and the anestrous heifers did not respond to a progestin-estrogen treatment for induction of estrus (Imakawa et al, 1986). Cessation of ovulation observed in nutritionally induced beef heifers by Bossis et al (1999).…”

Concentraciones de LH en periodos de transición reproductiva en cabras criollas x Nubia con diferente condición nutricional

“…Esto, derivado fundamentalmente de un aumento y disminución en la sensibilidad del hipotálamo a la retroalimentación negativa ejercida por los estrógenos (6) . Asimismo, el estrés nutricional también puede ocasionar un aumento en la sensibilidad del hipotálamo a la retroalimentación negativa de los estrógenos en rumiantes domésticos, lo cual afecta negativamente la secreción pulsátil de GnRH/LH y consecuentemente, la actividad cíclica ovulatoria (7,8) . Se considera que en estos animales el mediador del efecto de retroalimentación negativa de los estrógenos sobre la secreción de GnRH/LH, es un grupo neuronal localizado en la región mediobasal del hipotálamo que utiliza a las Kisspeptinas, Neurocinina B y Dinorfina como neuromediadores (neuronas KNDy) (9) .…”

“…This is mainly derived from a hypothalamic increase and decrease in sensitivity to the negative feedback exerted by estrogens (6) . Nutritional stress can also cause an increase in the hypothalamic sensitivity to the negative feedback of estrogens in domestic ruminants, event which in turn negatively affects the pulsatile GnRH/LH secretion and consequently the cyclic ovulatory activity (7,8) . A neuronal group located in the mediobasal hypothalamus, that uses the Kisspeptines, Neurokinin B and Dynorphin as neurotransmitters (KNDy neurons), is considered to be the mediator of the negative feedback effect of estrogens on the GnRH/LH secretion in domestic ruminants (9) .…”