Christensen R A, Malinowski K, Scanes C G, Hafs H D
Department of Animal Science, Rutgers-The State University of New Jersey, New Brunswick 08903, USA.
J Anim Sci. 1997 Oct;75(10):2770-7. doi: 10.2527/1997.75102770x.
Our goal was to establish a time of day and(or) interval from feeding that would avoid the refractory period after a somatotropin (ST) surge and optimize the responsiveness of horses to ST secretagogues. Two experiments were conducted with eight geldings conditioned to consume grain at 0800 and 1600 daily. In Exp. 1, during a 24-h period, these geldings averaged 3.2 +/- .3 pulses of ST with peak amplitude of 4.2 +/- .4 ng/mL, pulse duration of 55 +/- 6 min, and interpeak interval of 400 +/- 57 min. No ST peaks occurred within 2 h after either grain feeding. In Exp. 2, eight geldings were given 50 micrograms of ST-releasing factor (STRF) at 0800. Two geldings that had a pulse of ST between 0700 and 0800 failed to respond to STRF, but the other six responded with a pulse of ST at 37 +/- 3 min; peak amplitude was 4.6 +/- 2.2 ng/mL and duration was 123 +/- 25 min. Experiments 3 and 4 were with mares aged 20 to 26 yr and conditioned to be fed grain at 0800 daily. In Exp. 3, blood was sampled for 8 h beginning at 0500. Seven of the eight mares had a ST pulse in progress at 0500. Five additional pulses were detected, all from 0740 to 0940, but none from 0600 to 0700 or from 1000 to 1300. In Exp. 4, four of the same eight mares were given 50 micrograms of STRF at 0700 and the other four at 1300. Three of the four treated at 0700 and all four treated at 1300 responded to STRF with ST peaks at 20 +/- 5 min; peak amplitude was 12.7 +/- 9.5 ng/mL and duration was 69 +/- 6 min. In Exp. 5, nine mares aged 20 to 26 yr were fed grain at 0800 and 1600 as in Exp. 1 and 2 and given a nonpeptidal ST secretagogue (STS, Merck L-163,255) i.v. at 0, 1, or 5 mg/kg (n = 3 mares/dose) at 1300. No mare had a pulse of ST during the 1 h before treatment. All six mares given STS responded with ST pulses. The ST responses to STS at 1 and 5 mg/kg did not differ (P > .05); time to ST peak was 35 +/- 4 min, pulse amplitude was 24.0 +/- 6.3 ng/mL, and pulse duration was 100 +/- 9 min. We conclude that mares and geldings fed grain once or twice daily usually have a period of 2 to 5 h after feeding with no ST pulses. When horses are fed grain at 0800, one may give a ST secretagogue at 1300 to avoid a refractory period and improve the probability of an ST response.
我们的目标是确定一天中的某个时间和/或距喂食的时间间隔，以避开生长激素（ST）分泌高峰后的不应期，并优化马匹对ST促分泌素的反应性。我们对8匹已适应于每天08:00和16:00采食谷物的去势公马进行了两项试验。在试验1中，在24小时期间，这些去势公马平均有3.2±0.3次ST脉冲，峰值幅度为4.2±0.4 ng/mL，脉冲持续时间为55±6分钟，峰间间隔为400±57分钟。在任何一次谷物喂食后的2小时内均未出现ST峰值。在试验2中，8匹去势公马于08:00给予50微克的ST释放因子（STRF）。在07:00至08:00之间有一次ST脉冲的2匹去势公马对STRF无反应，但其他6匹在37±3分钟时出现一次ST脉冲反应；峰值幅度为4.6±2.2 ng/mL，持续时间为123±25分钟。试验3和试验4的对象是年龄在20至26岁之间且已适应于每天08:00喂食谷物的母马。在试验3中，从05:00开始采血8小时。8匹母马中有7匹在05:00时正处于一次ST脉冲过程中。又检测到5次额外的脉冲，均在07:40至09:40之间，但在06:00至07:00或1
