Walker S L, Smith R F, Jones D N, Routly J E, Dobson H
Department of Veterinary Clinical Science, Faculty of Veterinary Science, University of Liverpool, Leahurst, Neston, Wirral CH64 7TE, UK.
Horm Behav. 2008 Mar;53(3):493-501. doi: 10.1016/j.yhbeh.2007.12.003. Epub 2007 Dec 23.
The objectives of the present study were to determine if lameness, a model for a natural chronic stressor, affects hormone concentrations in milk prior to estrus and/or the subsequent expression of estrus in the postpartum period. Dairy cows>20 days postpartum were scored for lameness and observed for estrus intensity using a weighted scoring system (>100 points=estrus=Day 0). Increasing lameness score was not associated with daily profiles of milk progesterone (throughout Days -18 to 0), estradiol (Days -6 to 2) or cortisol (Days -18 to 2) around estrus, maximum estradiol values or estradiol concentrations on Day 0. However, post hoc pair wise comparisons revealed that prior to estrus, severely lame cows had lower maximum progesterone concentrations compared to nonlame cows (1.3+/-0.1, 1.2+/-0.2, 0.7+/-0.1 ng/ml milk; P=0.042). Furthermore, severely lame cows expressed behavioral estrus with lower intensity (284+/-128 points, n=9) compared to moderately lame (662+/-310 points, n=9) or nonlame animals (583+/-275 points, n=18; P=0.05 and P=0.02, respectively). Resting concentrations of cortisol (Days 20-80 postpartum) did not vary between days postpartum or lameness score. The incidence of behavioral estrus was not affected by increasing lameness score, as 54.2%, 56.2% and 50.0% periods with low progesterone were associated with spontaneous estrus expression, respectively. Concluding, in this biological model of chronic stress, lameness did not affect the incidence of behavioral estrus but did reduce estrus intensity once ovarian cyclicity had resumed after calving. This reduced intensity of estrus was associated with lower maximum progesterone values prior to estrus but not abnormal daily cortisol or estradiol values in milk.
本研究的目的是确定跛行（一种自然慢性应激源的模型）是否会影响发情前牛奶中的激素浓度和/或产后发情的后续表现。对产后超过20天的奶牛进行跛行评分，并使用加权评分系统（>100分=发情=第0天）观察发情强度。发情前后，跛行评分增加与牛奶孕酮（第-18天至第0天）、雌二醇（第-6天至第2天）或皮质醇（第-18天至第2天）的每日变化曲线、最大雌二醇值或第0天的雌二醇浓度无关。然而，事后两两比较显示，发情前，严重跛行的奶牛与非跛行奶牛相比，最大孕酮浓度较低（牛奶中分别为1.3±0.1、1.2±0.2、0.7±0.1 ng/ml；P=0.042）。此外，与中度跛行（662±310分，n=9）或非跛行动物（583±275分，n=18；P分别为0.05和0.02）相比，严重跛行的奶牛表现出发情行为的强度较低（284±128分，n=9）。产后第20至80天皮质醇的静息浓度在产后天数或跛行评分之间没有差异。行为发情的发生率不受跛行评分增加的影响，因为孕酮水平低的时期分别有54.2%、56.2%和50.0%与自发发情表现相关。总之，在这个慢性应激的生物学模型中，跛行不影响行为发情的发生率，但在产犊后卵巢周期恢复后确实会降低发情强度。发情强度降低与发情前较低的最大孕酮值有关，但与牛奶中异常的每日皮质醇或雌二醇值无关。
