Genetic selection of pigs over recent decades has sought to reduce carcass fat content to meet consumer demands for lean meat in many countries (e.g., Australia). Due to the impacts of genetic changes, it is unknown whether the carcass fat measures are still responsive to energy intake. Thus, the present experiment aimed to quantify the relationship between tissue composition and dietary energy intake in finisher pigs selected for low carcass backfat. Intact male and female pigs (n = 56 for each sex; Primegro Genetics, Corowa, NSW, Australia) were fed seven different amounts of an amino acid adequate wheat-based diet containing 14.3 MJ digestible energy (DE)/kg to provide the following daily DE intakes- 25.8, 29.0, 32.6, 35.3, 38.5, 41.5, and 44.2 (ad libitum) MJ DE/d for males, and 25.8, 28.9, 32.0, 35.6, 38.3, 40.9, and 44.5 (ad libitum) MJ DE/d for females between 60 and 108 kg live weight. Body composition of anesthetized pigs was measured using the dual energy X-ray absorptiometry (DXA) method when individual pigs reached 108 kg, and protein, fat, and ash deposition rates were calculated. Pigs were slaughtered on the second day post-DXA scan for carcass backfat measurement. The results showed that the carcass backfat thickness (standardized at 83.7 kg carcass) increased by 0.125 mm for every MJ increase in daily DE intake in male pigs (P = 0.004; R2 = 0.130), but carcass backfat of female pigs (standardized at 85.1 kg carcass) was not responsive to daily DE intake. Whole-body fat composition and fat deposition rate increased linearly (both P < 0.01) in male pigs but quadratically (both P < 0.01) in female pigs in response to DE intake. Every MJ increase of daily DE intake increased the rate of daily protein deposition by 3.8 g in intact male pigs (P < 0.001; R2 = 0.781) and by 2.5 g in female pigs (P < 0.001; R2 = 0.643). In conclusion, the selection for low backfat thickness over the last two decades has altered the response of fat deposition and backfat thickness to energy intake, particularly in female pigs. Despite this change, the linear relationship between DE intake and protein deposition rate was maintained in these modern genetics.

中文翻译：

---

低背膘厚度猪的能量摄入与生长性能和体成分的关系

近几十年来，猪的遗传选择一直致力于降低胴体脂肪含量，以满足许多国家（例如澳大利亚）消费者对瘦肉的需求。由于遗传变化的影响，不知道胴体脂肪测量是否仍然对能量摄入有反应。因此，本实验旨在量化选择低胴体背膘肥育育肥猪的组织成分与日粮能量摄入之间的关系。完整的雄性和雌性猪（每种性别 n = 56；Primegro Genetics，Corowa，NSW，Australia）饲喂七种不同量的含有 14.3 MJ 消化能 (DE)/kg 的氨基酸充足的小麦日粮，以提供以下每日 DE 摄入量 - 男性 25.8、29.0、32.6、35.3、38.5、41.5 和 44.2（随意）MJ DE/d，以及 25.8、28.9、32.0、35.6、38.3、40.9 和 44。5（随意）MJ DE/d，适用于体重在 60 至 108 公斤之间的雌性。当猪个体达到108 kg时，使用双能X射线吸收法（DXA）测量麻醉猪的身体成分，并计算蛋白质、脂肪和灰分沉积率。在 DXA 扫描后第二天屠宰猪以测量胴体背膘。结果表明，公猪每天摄入 DE 摄入量每增加 MJ，胴体背膘厚度（标准化为 83.7 kg 胴体）增加 0.125 mm（P = 0.004；R2 = 0.130），但母猪的胴体背膘厚度（标准化为 85.1 kg 胴体）对每日 DE 摄入量没有反应。响应于 DE 摄入，公猪的全身脂肪组成和脂肪沉积率呈线性增加（均 P < 0.01），而母猪则呈二次方增加（均 P < 0.01）。每日 DE 摄入量每增加 MJ，完整公猪的每日蛋白质沉积率增加 3.8 g（P < 0.001；R2 = 0.781），母猪增加 2.5 g（P < 0.001；R2 = 0.643）。总之，在过去二十年中，低背膘厚度的选择改变了脂肪沉积和背膘厚度对能量摄入的反应，尤其是母猪。尽管发生了这种变化，但在这些现代遗传学中，DE 摄入量与蛋白质沉积率之间的线性关系仍然存在。在过去二十年中，低背膘厚度的选择改变了脂肪沉积和背膘厚度对能量摄入的反应，尤其是母猪。尽管发生了这种变化，但在这些现代遗传学中，DE 摄入量与蛋白质沉积率之间的线性关系仍然存在。在过去二十年中，低背膘厚度的选择改变了脂肪沉积和背膘厚度对能量摄入的反应，尤其是母猪。尽管发生了这种变化，但在这些现代遗传学中，DE 摄入量与蛋白质沉积率之间的线性关系仍然存在。