Head W A, Hatfield P G, Hallford D M, Fitzgerald J A, Petersen M K, Stellflug J N
New Mexico State University, Las Cruces 88003, USA.
J Anim Sci. 1996 Sep;74(9):2152-7. doi: 10.2527/1996.7492152x.
Targhee ewes (n = 22, average age 5 yr) rearing twin lambs were used to investigate serum growth hormone (GH), IGF-I, triiodothyronine (T3), thyroxine (T4), and prolactin (PRL; ewes only) concentrations associated with selection pressure for lifetime production of kilograms of lamb weaned per ewe. Period 1 started on d 4 after birth and was conducted in confinement. Periods 2, 3, and 4 were conducted on fenced intermountain sagebrush-bunchgrass range starting at an average of 49, 84, and 112 d after birth, respectively. Blood samples were collected hourly for 6 h on d 4, 11, 18, 25, 49, 84, and 112 after lambing. Ewe models included the fixed effect for line, with ewe age, lambing date, and starting weight nested within line as potential covariables. Lamb models included fixed effects for line, sex, and sibling sex, with lamb age and birth weight nested within line tested as possible covariables. Growth hormone concentrations were greater (P = .06) for selected than for control ewes, but lamb GH concentrations did not differ (P = .90) between selected and control lambs. Ewe prolactin concentration tended (P = .13) to be greater for control than selected ewes. Ewe and lamb IGF-I did not differ (P > .55) between selected and control ewes and lambs. Ewe T3 and T4 concentrations did not differ (P > .19) between selected and control ewes; however, lamb T3 and T4 concentrations were greater (P < .01) for control than for selected lambs. Increased GH concentration in selected ewes seemed to be associated with greater milk production. Differences in selected and control lamb T3 and T4 concentrations could be an indicator of receptor sensitivity, metabolic activity, or seasonal reproductive transitions in ewe lambs.
选用正在哺育双羔的塔尔基母羊（n = 22，平均年龄5岁），来研究血清生长激素（GH）、胰岛素样生长因子-I（IGF-I）、三碘甲状腺原氨酸（T3）、甲状腺素（T4）和催乳素（仅针对母羊）浓度，这些浓度与每只母羊一生中断奶羔羊体重的选择压力相关。第1阶段从出生后第4天开始，在圈舍内进行。第2、3和4阶段分别在围栏的山间蒿属植物-丛生禾本科草原上进行，分别从出生后平均49、84和112天开始。在产羔后第4、11、18、25、49、84和112天，每小时采集6小时的血样。母羊模型包括品系的固定效应，母羊年龄、产羔日期和起始体重作为潜在协变量嵌套在品系内。羔羊模型包括品系、性别和同胞性别的固定效应，羔羊年龄和出生体重作为可能的协变量嵌套在品系内进行测试。所选母羊的生长激素浓度高于对照母羊（P = 0.06），但所选羔羊和对照羔羊的生长激素浓度没有差异（P = 0.90）。对照母羊的催乳素浓度倾向于高于所选母羊（P = 0.13）。所选和对照母羊及羔羊之间的IGF-I没有差异（P > 0.55）。所选和对照母羊之间的T3和T4浓度没有差异（P > 0.19）；然而，对照羔羊的T3和T4浓度高于所选羔羊（P < 0.01）。所选母羊中生长激素浓度的增加似乎与产奶量增加有关。所选和对照羔羊T3和T4浓度的差异可能是母羊羔羊受体敏感性、代谢活性或季节性繁殖转变的一个指标。
