Freetly H C, Nienaber J A, Brown-Brandl T M
USDA-ARS, U.S. Meat Animal Research Center, Clay Center, NE 68933, USA.
J Anim Sci. 2002 Oct;80(10):2759-63.
The hypothesis of this study is that ewes that have equal body weights, but differ in chronological age due to nutrient restriction, do not differ in metabolic rate. The objective of this study was to determine how reducing growth rate nutritionally alters the relationship between heat production per unit body weight and aging. Fasting heat production of 12 Dorset ewe lambs at 114 +/- 2 d of age was determined, and ewes were assigned to treatments. Treatments consisted of two different feeding levels of the same diet (ME = 2.5 Mcal/kg DM and 16.6% CP). The High treatment was offered 4.5% of their weekly BW per day, and the Low treatment was offered 2.5% of their weekly BW per day. Each treatment consisted of six animals that remained within treatment for the remainder of the study. Indirect-calorimetry measurements were repeated every 6 wk. Treatments differed in both the linear and quadratic term for fasted BW on age (P < 0.001). The rate of BW gain decreased as ewes aged in the High treatment, and the rate of BW gain increased as ewes aged in the Low treatment. The heat production:BW (HP:BW) ratio decreased in the High treatment as ewes aged and was described well by a previously reported prediction equation, but the ratio in the Low treatment was not described by this same equation. Describing the HP:BW ratio on age response with treatment-specific decay functions fit the data better than the pooled treatment function (P < 0.001). The HP:BW ratio decreased rapidly in the Low treatment following feed restriction, but remained elevated compared to the High treatment as animals aged. After excluding the initial measurements in the Low treatment that were taken before nutritional treatments were imposed, the HP:BW ratio was best described by a linear decrease. In conclusion, this study suggests that a previous model taking into account proportion of mature body size is a reasonable predictor for heat production across breeds of sheep growing in nutritionally adequate environments; however, it cannot be extended to sheep that are proportionally smaller in their mature BW due to nutritional restriction.
本研究的假设是，体重相同但因营养限制导致实际年龄不同的母羊，其代谢率并无差异。本研究的目的是确定营养方式降低生长速率如何改变单位体重产热与衰老之间的关系。测定了12只114±2日龄多塞特母羊羔羊的禁食产热，并将母羊分配至不同处理组。处理组由两种不同饲喂水平的相同日粮组成（代谢能=2.5兆卡/千克干物质，粗蛋白含量为16.6%）。高饲喂量处理组每天提供其每周体重的4.5%，低饲喂量处理组每天提供其每周体重的2.5%。每个处理组有6只动物，在研究剩余时间内保持在相应处理组中。每隔6周重复进行间接测热法测量。处理组在禁食体重随年龄变化的线性和二次项上均存在差异（P<0.001）。在高饲喂量处理组中，母羊体重增加速率随年龄增长而下降，而在低饲喂量处理组中，母羊体重增加速率随年龄增长而上升。在高饲喂量处理组中，随着母羊年龄增长，产热:体重（HP:BW）比值下降，且可用先前报道的预测方程很好地描述，但低饲喂量处理组的该比值不能用同一方程描述。用特定处理组的衰减函数描述HP:BW比值随年龄的响应比合并处理组函数更符合数据（P<0.001）。在低饲喂量处理组中，饲料限制后HP:BW比值迅速下降，但随着动物年龄增长，与高饲喂量处理组相比仍保持较高水平。在排除低饲喂量处理组在施加营养处理前的初始测量值后，HP:BW比值最好用线性下降来描述。总之，本研究表明，之前考虑成熟体重比例关系的模型对于营养充足环境下生长的不同品种绵羊的产热是一个合理的预测指标；然而，该模型不能推广到因营养限制而成熟体重成比例较小的绵羊。
