Nitrogen metabolism and rumen microbial enumeration in lactating cows with divergent residual feed intake fed high-digestibility pasture
Nitrogen metabolism and rumen microbial enumeration in lactating cows with divergent residual feed intake fed high-digestibility pasture
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DOI：
10.3168/jds.2012-5392
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发表时间：
2012-09-01
影响因子：
3.5
通讯作者：
Sikkema, E.
中科院分区：
文献类型：
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作者：
Rius, A. G.;Kittelmann, S.;Sikkema, E.
选择负残余采食量（n-RFI；高效）的奶牛应在保持生产的同时减少哺乳期间的干物质采食量，因为饲料消化和营养物质的有效利用得到改善。本研究的目的是在泌乳早期短时间内测定氮(N)的消化率和瘤胃微生物群落组成。因此，N -RFI奶牛的N表观消化率高于正RFI （p-RFI；低效）奶牛，以弥补分化选择过程中确定的较低干物质采食量。选取16头3岁瘤胃空心泌乳奶牛（56 +/- 10 d），分别饲喂n- rfi （n = 8）和p-RFI (n = 8)，饲养于代谢栏内，以新鲜营养性黑麦草（Lolium perenne L.）牧草作为唯一饲粮，进行8 d消化率研究。测定营养物质的摄入量和乳、粪、尿的排泄量。通过去除、称重和取样食糜以及钴- edta稀释来确定瘤胃参数。氮、干物质、有机质及其组分的采食量与RFI无显著差异。与p-RFI奶牛相比，N - rfi奶牛氮的表观消化率更高（77.2比75.5%），干物质和有机物消化率也有更高的趋势。与p-RFI奶牛相比，N - rfi奶牛的粪氮排泄量较低（126比138 g/d），饲料氮与粪氮的比例较低（23.1比24.7%）。我们没有发现不同表型之间氮分配给尿氮或乳粗蛋白的差异，但确实观察到N - rfi奶牛分配给乳酪蛋白的氮较少的趋势（16.8%对17.9%）。两组的瘤胃食糜质量相似，尽管计算出的液体流出率分数不同，而且两种表型组的大多数细菌、古细菌、原生动物和真菌群落相似。综上所述，饲喂高消化率新鲜黑麦草时，两种表型动物的干物质采食量和瘤胃功能相似，但高效（N - rfi）奶牛对饲粮氮的表观消化率更高。未来的研究应该测量不同RFI奶牛在饲喂不同化学成分日粮（如不同粗蛋白质含量）时的消化参数。
Dairy cattle selected for negative residual feed intake (n-RFI; efficient) should maintain production while reducing dry matter intake over a lactation because of improvements in feed digestion and efficient use of nutrients. The objective of this study was to measure nitrogen (N) digestibility and rumen microbial community composition over a short period during early lactation in lactating Holstein-Friesian cows selected previously for divergent RFI. It was proposed that n-RFI cows would have greater apparent digestibility of N than the positive RFI (p-RFI; inefficient) animals, to compensate for the lower dry matter intake determined during selection for divergence. Sixteen 3-yr-old rumen-cannulated, lactating cows (56 +/- 10 d in milk) selected for n-RFI (n = 8) and p-RFI (n = 8) were housed in metabolism stalls and fed fresh vegetative ryegrass (Lolium perenne L.) pasture ad libitum as a sole diet during an 8-d digestibility study. Intake of nutrients and outputs of milk, feces, and urine were determined. Rumen parameters were determined by removing, weighing, and sampling digesta, and by cobalt-EDTA dilution. Intakes of N, dry matter, organic matter, or its components did not differ with RFI. Compared with p-RFI cows, n-RFI cows had a greater apparent N digestibility (77.2 vs. 75.5%), and a tendency toward greater dry matter and organic matter digestibilities. The n-RFI cows had a lower fecal N output (126 vs. 138 g/d) and a lower partition of feed N to fecal N (23.1 vs. 24.7%) compared with p-RFI animals. We found no differences between phenotypes in the partition of N to urinary N or milk crude protein but did observe a trend for n-RFI cows to partition less N to milk casein (16.8 vs. 17.9%). Rumen digesta mass was similar for both groups, despite differences in calculated fractional liquid outflow rates, and most bacterial, archaeal, protozoal, and fungal communities were similar for both phenotype groups. In conclusion, dry matter intake and rumen function were similar for both phenotypes when the animals were fed highly digestible fresh ryegrass, but apparent digestibility of dietary N was higher in the efficient (n-RFI) cows. Future research should measure digestion parameters in cows with divergent RFI when fed diets differing in chemical composition (e.g., divergent crude protein contents).