Walker R S, Martin R M, Gentry G T, Gentry L R
J Anim Sci. 2015 Feb;93(2):672-84. doi: 10.2527/jas.2014-7702.
Thirty-eight Angus-cross beef cows were used to evaluate differences in DMI, residual feed intake (RFI), and endocrine markers on the basis of cow size and RFI ranking during 2 stages of production. Cows housed in individual pens (2.2 × 9.1 m) were fed, over a 70-d feeding period, 30% Bermuda grass hay and 70% ryegrass baleage diet during lactation (LACT) and a 100% ryegrass hay diet during postweaning (NOLACT). Individual daily feed intake, BW, and BCS were recorded, and hip height was used to determine frame score (FS). Feed intake was used to calculate RFI for each cow, and cow was the experimental unit. Blood samples were obtained on d 0 and 70 and were analyzed for glucose, insulin, leptin, triiodothyronine (T3), and thyroxine (T4). Cows were assigned to a light (LIT) or heavy (HEV) BW groups on the basis of mean BW at the beginning of the LACT period. On the basis of RFI values for each feeding period, cows were placed into a negative (NEG; RFI < 0.00) or positive (POS; RFI > 0.00) RFI group and into a low (LOW; ≤0.2 SD mean RFI), medium (MED; within ±0.19 SD), or high (HI; ≥0.2 SD mean RFI) RFI group. During LACT, DMI was 4.8% greater (P = 0.03) and FS was greater (P < 0.01; 6.4 and 5.5 ± 0.16) for the HEV compared with LIT BW cows. No RFI by day interaction or RFI group main effect occurred for endocrine markers during LACT; however, a negative relationship (P = 0.04) existed between BW group and combined T3 data, and a positive relationship (P = 0.04) existed between RFI and combined insulin data. For both LACT and NOLACT, RFI was similar (P > 0.05) among BW groups; however, DMI was 6.5% and 8.9% greater (P < 0.01) for POS compared with NEG RFI in the LACT and NOLACT periods. In LACT, DMI was greater (P < 0.01) for HI and MED RFI compared with LOW RFI, and in NOLACT, DMI was greater (P < 0.01) for the HI compared with MED and LOW RFI cows and MED compared with LOW RFI cows. During NOLACT, DMI was 8.9% greater (P < 0.01) for the HEV (12.4 ± 0.22 kg) compared with LIT (11.3 ± 0.19 kg) BW cows. Change in BCS was greater (P ≤ 0.03) in higher RFI cows in both RFI groups only in the NOLACT period. Differences in T3 and T4 on d 0 and 70 were 25% and 15% greater (P ≤ 0.04) for the LIT BW group compared with the HEV BW group. A negative correlation existed (P ≤ 0.04) between BW group and T3 and T4, as well as leptin and RFI (P = 0.03). Although cow BW was independent of RFI and T3 and T4 levels tended to be greater in lighter BW cows, DMI was consistently greater for cows with heavier BW and higher RFIvalues.
选用38头安格斯杂交肉牛母牛，以评估在两个生产阶段基于母牛体型和剩余采食量（RFI）排名的干物质采食量（DMI）、剩余采食量及内分泌指标的差异。将母牛饲养在个体栏舍（2.2×9.1米）中，在70天的饲喂期内，泌乳期（LACT）饲喂30%的百慕大草干草和70%的黑麦草青贮料日粮，断奶后期（NOLACT）饲喂100%的黑麦草干草日粮。记录个体每日采食量、体重和体况评分（BCS），并使用髋部高度确定体格评分（FS）。采食量用于计算每头母牛的RFI，以母牛作为实验单位。在第0天和第70天采集血样，分析葡萄糖、胰岛素、瘦素、三碘甲状腺原氨酸（T3）和甲状腺素（T4）。根据泌乳期开始时的平均体重，将母牛分为轻体重（LIT）或重体重（HEV）组。根据每个饲喂期的RFI值，将母牛分为负RFI组（NEG；RFI<0.00）或正RFI组（POS；RFI>0.00），以及低RFI组（LOW；≤0.2标准差平均RFI）、中RFI组（MED；±0.19标准差范围内）或高RFI组（HI；≥0.2标准差平均RFI）。在泌乳期，与轻体重母牛相比，重体重母牛的DMI高4.8%（P=0.03），FS更高（P<0.01；6.4和5.5±0.16）。泌乳期内分泌指标未出现RFI与日的交互作用或RFI组主效应；然而，体重组与合并的T3数据之间存在负相关关系（P=0.04），RFI与合并的胰岛素数据之间存在正相关关系（P=0.04）。在泌乳期和断奶后期，体重组之间的RFI相似（P>0.05）；然而，在泌乳期和断奶后期，正RFI组的DMI比负RFI组分别高6.5%和8.9%（P<0.01）。在泌乳期，高RFI组和中RFI组的DMI比低RFI组高（P<0.01），在断奶后期，高RFI组的DMI比中RFI组和低RFI组高（P<0.01），中RFI组的DMI比低RFI组高（P<0.01）。在断奶后期，重体重母牛（12.4±0.22千克）的DMI比轻体重母牛（11.3±0.19千克）高8.9%（P<0.01）。仅在断奶后期，两个RFI组中较高RFI的母牛体况评分变化更大（P≤0.03）。轻体重组第0天和第70天的T3和T4差异比重体重组分别大25%和15%（P≤0.04）。体重组与T3和T4之间存在负相关（P≤0.04），瘦素与RFI之间也存在负相关（P=0.03）。尽管母牛体重与RFI无关，且较轻体重母牛的T3和T4水平往往更高，但体重较重且RFI值较高的母牛的DMI始终更高。
