Postpartum Reproduction in Protein Restricted Beef Cows: Effect on the Hypothalamic-Pituitary-Ovarian Axis

Abstract

The influence of dietary CP on circulating LH and anterior pituitary and hypothalamic function was examined. In Exp. 1, 28 cows were randomly assigned to four treatment groups: adequate CP (ADQ; .96 kg/d) or deficient CP (DEF; .32 kg/d) beginning at 90, 60 and 30 d before parturition and continued at a 33% increase in feed consumption after parturition. Cows were bled at 15-min intervals for 8 h on d 20, 40 and 60 after parturition. Pituitaries were collected on d 62 to analyze GnRH receptor numbers and gonadotropin content. Frequency of pulsatile LH release increased (P less than .05) from 20 to 60 d in ADQ cows. Basal and mean LH were not affected (P greater than .10) by CP restriction or by days after parturition. Crude protein did not affect pituitary GnRH receptors (P greater than .10), but it did affect pituitary LH content, FSH content and FSH concentration (P less than .05). In Exp. 2, 28 cows were assigned to treatment groups as in Exp. 1. All cows were challenged with GnRH (.22 micrograms/kg BW) at 20, 40 and 60 d after parturition and were bled every 30 min for 6 h. Responsiveness to GnRH increased with increased time after parturition (P less than .07). Deficient CP decreased GnRH-induced LH release (P less than .05). In Exp. 3, 12 cows were randomly assigned to ADQ or DEF CP beginning 120 d before parturition. All cows received 1 mg estradiol-17 beta (E2) on d 19, 39 and 59 after parturition and were bled every 30 min for 14 h beginning 14 h following E2. Response to E2 was unaffected by CP restriction (P greater than .10), whereas time to E2-induced LH peak decreased as time after parturition increased in ADQ cows (P less than .05). Results suggest that delayed return to estrus in CP-deficient postpartum beef cows might be due to reduced gonadotropin release from the anterior pituitary and decreased anterior pituitary responsiveness to GnRH.

Moderate and Severe Nutrient Restriction has Divergent Effects on Gonadotroph Function in Orchidectomized Sheep1

“…These observations are generally consistent with previous work using rodents, postpartum cattle, and ovariectomized (OVX) sheep that demonstrated that chronic nutrient restriction did not significantly alter tissue stores of the gonadotropins or pituitary concentrations of gonadotropin subunit mRNA [27][28][29][30]. Conversely, the concentration of FSH, but not LH, was markedly decreased in pituitary tissue of growth-restricted OVX lambs [31].…”

“…Indeed, we note here that, in the absence of estrogenic inputs, the concenb i-A trations of GnRH receptor and GnRH receptor mRNA in pituitary tissue of wethers did not vary with nutritive status. Tissue concentrations of GnRH receptor were also unaffected by plane of nutrition in OVX sheep [48] and postpartum cattle [29]. Maintenance of tissue concentrations of GnRH receptor during restricted feeding is likely to account, at least in part, for the ability of undernourished animals to respond to exogenous GnRH stimulation [6,42].…”

Protein supplementation on onset of post‐partum ovarian cyclicity of dairy cows: an isotopic immunoassay study

“…However, it is evident from the above results (which are highly statistically significant, P50:05) that the supplemented group of cows took less time (about 40 days) to express their standing oestrus. The above results are inconsistent with those of Nolan et al 3 who suggested that inadequate nutrition causes delayed post-partum ovarian function by preventing gonadotropin release from the pituitary. The influence of nutrient intake causes weight change and hence the body condition at calving and during post-partum period and this could be related to the interval between calving to first post-partum oestrus.…”

Factors Limiting the Pregnancy Rates in Artificially Inseminated Cows in Bangladesh

“…It is found in a number of studies that nutrition manipulation can result in changes in gonadotrophin (GnRH) secretion. The cows deficient in adequate quantity of balanced feed had reduced pituitary responsiveness to a GnRH challenge (Nolan et al, 1988). Thus providing a feed with combination of green grass, straw and concentrate in the present study might have contributed to proper functioning of reproductive hormones resulting in good rate of pregnancy.…”