Intrauterine growth restriction (IUGR) is often observed in one of the fetuses carried by well-fed prolific ewes. This condition is the result of an insufficient placental size to cover the nutritional needs of the fetus during the near exponential growth phase of the last trimester. After birth, these IUGR offspring have an elevated appetite and lower maintenance energy requirements, suggesting dysregulation of homeostatic systems governing energy metabolism. It is also unknown whether the consequent increase in fatness occurs similarly in both visceral and carcass fractions. To address these questions, lambs differing in birth size (BS, IUGR vs. Normal, 2.6 ± 0.05 vs. 4.2 ± 0.07 kg, P < 0.001) were offered unlimited amounts of a low fat [LF; 22% of dry matter (DM)] or a high fat (HF; 38% of DM) milk replacer and slaughtered on day 14 of postnatal age (n = 7 to 8 for each BS × Diet); a second group of IUGR lambs (n = 3 for each diet) was slaughtered when they reached 8.5 kg, corresponding to the weight of Normal lambs on day 14. When normalized to body weight (BW), the DM and energy intake of IUGR lambs were higher than those of Normal lambs over the first 14 d of life (BS, P < 0.01), but contrary to expectations, the HF diet did not exacerbate these effects of the IUGR condition. Intrauterine growth restricted lambs had increased viscera fat with both diets (BS and Diet, P < 0.05) but increased carcass fat only with the LF diet (BS × Diet, P = 0.08); the fatness promoting effect of the IUGR condition was increased in both body fractions when lamb groups were compared at the fixed BW of 8.5 kg. A subset of metabolic hormones was analyzed, including the metabolic rate-setting hormone thyroxine (T4) and its possible positive regulator leptin. Plasma T4 was lower in IUGR than in Normal lambs at birth (P < 0.05) but then disappeared by day 7 of postnatal life (BS × Day, P < 0.01). On the other hand, the HF diet had no effect on plasma T4 over the first 3 d but caused an increase, irrespective of BS by day 11 (Diet × Day, P < 0.001). Plasma leptin increased with dietary fat and time (P < 0.06) but bore no relation to the effects of BS or Diet on plasma T4. These data show that IUGR and Normal lambs are similarly unable to adjust caloric intake in early life and that the fatness promoting effects of the IUGR condition are more pronounced in the viscera than in the carcass. These data also reveal dynamic regulation of plasma T4 by BS and Diet in neonatal lambs.

中文翻译：

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出生体重和膳食脂肪对新生羔羊摄入量、身体成分和血浆甲状腺素的影响


宫内生长受限（ IUGR ）经常出现在喂养良好的多产母羊所产的胎儿之一中。这种情况是由于胎盘尺寸不足以满足胎儿在妊娠最后三个月的指数生长期的营养需求而导致的。出生后，这些 IUGR 后代的食欲增加，维持能量需求降低，这表明控制能量代谢的稳态系统失调。还不清楚随之而来的脂肪增加是否在内脏和胴体部分中发生类似的情况。为了解决这些问题，给出生尺寸不同的羔羊（ BS ，IUGR 与正常体重，2.6 ± 0.05 与 4.2 ± 0.07 kg， P < 0.001）提供无限量的低脂[ LF ； 22% 干物质 ( DM )] 或高脂肪 ( HF ；38% DM) 代乳品，并在出生后第 14 天屠宰（每个 BS × 日粮n = 7 至 8）；第二组 IUGR 羔羊（每种饮食n = 3 只）在体重达到 8.5 公斤（相当于第 14 天正常羔羊的重量）时被屠宰。当标准化为体重 ( BW ) 时，IUGR 羔羊的 DM 和能量摄入量在生命的前 14 天内，这些结果均高于正常羔羊（BS， P < 0.01），但与预期相反，HF 饮食并没有加剧 IUGR 状况的这些影响。两种日粮（BS 和日粮， P < 0.05）的宫内生长受限羔羊内脏脂肪均增加，但仅 LF 日粮时胴体脂肪增加（BS × 日粮， P = 0.08);当羔羊体重固定为 8.5 千克时，对两个身体部位进行比较时，IUGR 条件下的增肥效果均有所增加。对代谢激素的一个子集进行了分析，包括代谢率设定激素甲状腺素（ T4 ）及其可能的正调节因子瘦素。 IUGR 羔羊出生时血浆 T4 低于正常羔羊 ( P < 0.05)，但在出生后第 7 天消失 (BS × Day， P < 0.01)。另一方面，HF 饮食在前 3 天内对血浆 T4 没有影响，但在第 11 天时导致血浆 T4 增加，与 BS 无关（饮食 × 天数， P < 0.001）。血浆瘦素随着膳食脂肪和时间的增加而增加（ P <0.06），但与BS或饮食对血浆T4的影响无关。这些数据表明，IUGR 和正常羔羊同样无法调整生命早期的热量摄入，并且 IUGR 条件下的肥胖促进作用在内脏中比在屠体中更明显。这些数据还揭示了新生羔羊血浆 T4 受 BS 和饮食的动态调节。