Cai W, Casey D S, Dekkers J C M
Department of Animal Science, Iowa State University, Ames, Iowa 50011, USA.
J Anim Sci. 2008 Feb;86(2):287-98. doi: 10.2527/jas.2007-0396. Epub 2007 Nov 12.
Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between the observed feed intake and that predicted from the average requirements for growth and maintenance. The objective of this study was to evaluate the response in a selection experiment consisting of a line selected for low RFI and a random control line and to estimate the genetic parameters for RFI and related production and carcass traits. Beginning with random allocation of purebred Yorkshire littermates, in each generation, electronically measured ADFI, ADG, and ultrasound backfat (BF) were evaluated during a approximately 40- to approximately 115-kg of BW test period on approximately 90 boars from first parity and approximately 90 gilts from second parity sows of the low RFI line. After evaluation of first parity boars, approximately 12 boars and approximately 70 gilts from the low RFI line were selected to produce approximately 50 litters for the next generation. Approximately 30 control line litters were produced by random selection and mating. Selection was on EBV for RFI from an animal model analysis of ADFI, with on-test group and sex (fixed), pen within group and litter (random), and covariates for interactions of on- and off-test BW, on-test age, ADG, and BF with generations. The RFI explained 34% of phenotypic variation in ADFI. After 4 generations of selection, estimates of heritability for RFI, ADFI, ADG, feed efficiency (FE, which is the reciprocal of the feed conversion ratio and equals ADG/ ADFI), and ultrasound-predicted BF, LM area (LMA), and intramuscular fat (IMF) were 0.29, 0.51, 0.42, 0.17, 0.68, 0.57, and 0.28, respectively; predicted responses based on average EBV in the low RFI line were -114, -202, and -39 g/d for RFI (= 0.9 phenotypic SD), ADFI (0.9 SD), and ADG (0.4 SD), respectively, and 1.56% for FE (0.5 SD), -0.37 mm for BF (0.1 SD), 0.35 cm(2) for LMA (0.1 SD), and -0.10% for IMF (0.3 SD). Direct phenotypic comparison of the low RFI and control lines based on 92 low RFI and 76 control gilts from the second parity of generation 4 showed that selection had significantly decreased RFI by 96 g/d (P = 0.002) and ADFI by 165 g/d (P < 0.0001). The low RFI line also had 33 g/d lower ADG (P = 0.022), 1.36% greater FE (P = 0.09), and 1.99 mm less BF (P = 0.013). There was not a significant difference in LMA and other carcass traits, including subjective marbling score, despite a large observed difference in ultrasound-predicted IMF (-1.05% with P < 0.0001). In conclusion, RFI is a heritable trait, and selection for low RFI has significantly decreased the feed required for a given rate of growth and backfat.
剩余采食量（RFI）是衡量饲料效率的一个指标，定义为观察到的采食量与根据生长和维持的平均需求预测的采食量之间的差值。本研究的目的是评估在一个选择实验中的反应，该实验包括一个选择低RFI的品系和一个随机对照品系，并估计RFI以及相关生产和胴体性状的遗传参数。从纯种约克夏同窝仔猪的随机分配开始，在每一代中，在体重约40至约115千克的测试期内，对低RFI品系的约90头初产公猪和约90头经产母猪的后备母猪进行电子测量的平均日采食量（ADFI）、平均日增重（ADG）和超声背膘厚（BF）评估。在对初产公猪进行评估后，从低RFI品系中选择约12头公猪和约70头后备母猪来生产下一代的约50窝仔猪。通过随机选择和配种产生约30窝对照品系仔猪。选择基于对ADFI进行动物模型分析得出的RFI的估计育种值（EBV），其中测试组和性别（固定）、组内栏和窝（随机），以及测试期和测试期外体重、测试期年龄、ADG和BF与世代的相互作用的协变量。RFI解释了ADFI中34%的表型变异。经过4代选择，RFI、ADFI、ADG、饲料效率（FE，即饲料转化率的倒数，等于ADG/ADFI）以及超声预测的BF、眼肌面积（LMA）和肌内脂肪（IMF）的遗传力估计值分别为0.29、0.51、0.42、0.17、0.68、0.57和0.28；基于低RFI品系平均EBV的预测反应分别为：RFI（=0.9个表型标准差）为-114克/天、ADFI（0.9个标准差）为-202克/天、ADG（0.4个标准差）为-39克/天，FE为1.56%（0.5个标准差），BF为-0.37毫米（0.1个标准差），LMA为0.35平方厘米（0.1个标准差），IMF为-0.10%（0.3个标准差）。基于第4代经产的92头低RFI和76头对照后备母猪对低RFI品系和对照品系进行直接表型比较，结果表明选择显著降低了RFI 96克/天（P = 0.002）和ADFI 165克/天（P < 0.0001）。低RFI品系的ADG也低33克/天（P = 0.022），FE高1.36%（P = 0.09），BF薄1.99毫米（P = 0.013）。尽管超声预测的IMF存在很大的观察差异（-1.05%，P < 0.0001），但LMA和其他胴体性状，包括主观大理石花纹评分，没有显著差异。总之，RFI是一个可遗传的性状，选择低RFI显著降低了给定生长速度和背膘所需的饲料量。
