Publication Date

November 2008

Abstract

Kisspeptin, a neuroendocrine regulator of gonadotropin releasing hormone, is hypothesized to integrate nutrition and hormones critical to metabolism and the regulation of reproduction. Since the negative energy balance of early lactation is associated with reduced fertility via suppression of gonadotropin secretion and enhanced growth hormone (GH) responsiveness, this experiment was designed to determine the effects of stage of lactation and negative energy balance on kisspeptin-10 (Kp-10) stimulated luteinizing hormone (LH) and GH concentrations. Five nonlactating [5.1 ± 0.8 (SEM) years; 577 ± 19 kg body weight (BW)] and five lactating [4.1 ± 0.6 years; 608 ± 11 kg BW] multiparous Holstein cows were utilized. Experiments were conducted on the lactating cows at weeks 1, 5 and 11 after parturition and on the nonlactating cows over the same six month period. Except for lactating cows in the first week of lactation (prior to resumed cyclicity and ovarian activity) all other experiments were conducted on cows in the luteal phase of the estrous cycle. The experimental treatments [physiologic saline (control) and Kp-10 (100 and 400 pmoles/kg BW)] were administered as a bolus via jugular cannula. Treatments were successive with 48 hrs between each Kp-10 treatment. Lactating cows were given all treatments for each experimental week of lactation (1, 5 and 11) and each nonlactating cow received all treatments during only one week. Plasma was collected at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 75 and 90 min relative to treatment and stored until assayed for LH, GH and non-esterified fatty acids (NEFA). Lactation (nonlactating and week of lactation) affected the energy balance of the cows as indicated by peripheral concentration of NEFA. Peripheral NEFA concentrations were highest during week one and five of lactation. Neither dose of Kp-10 stimulated an increase in GH concentration in lactating or nonlactating cows. The low Kp-10 dose significantly increased LH concentrations in the lactating cows only. However, the higher dose of Kp-10 elicited an increase in LH concentrations in all treatment groups and stages of lactation. The incremental area under the curve (iAUC) of LH from 0 to 90 min after treatment with the lower Kp-10 dose was significantly greater than the saline treatment only during week 5 of lactation and the iAUC of LH following the highest dose of Kp-10 was significantly greater in cows in week 5 of lactation than all other lactation and nonlactating groups. These data demonstrate impact of energy balance and lactation on kisspeptin-stimulated gonadotropin increase the opposite response seen in lactating rats. The study of the kisspeptin system during lactation in high producing dairy cows may yield critical insights into the mechanisms for lactation associated infertility.

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