Gunter S A, McCollum F T, Gillen R L
Department of Animal Science, University of Arkansas, Hope 71801-9729, USA.
J Anim Sci. 1997 Feb;75(2):490-501. doi: 10.2527/1997.752490x.
Eight beef steers fitted with esophageal (four steers/pasture) and 12 beef calves fitted ruminal and duodenal (six calves/pasture; beginning BW = 267 +/- 6 kg) cannulas grazed either midgrass prairie rangeland (excellent range condition; MIDGRASS) or plains bluestem (Bothriochloa ischaemum var. Plains) pasture (BLUESTEM) during mid-May, late June, mid-August, and mid-October of 1990 and 1991 in order to compare nutrient intake and digestion. Forage OM intake (OMI) by cattle grazing MIDGRASS or BLUESTEM was similar (P > .05) in June and August. In May and October, cattle grazing MIDGRASS consumed more (P < .05) OM than cattle grazing BLUESTEM. The extent of true ruminal OM digestion was similar (P > .05) between forage types except in October 1991, when the extent of digestion for BLUESTEM was greater (P < .05) than for MIDGRASS. The N intake by cattle interacted by year and forage (P < .05). Nitrogen intake by cattle grazing MIDGRASS tended to be lower in June and August than in May and October. The N intake by cattle grazing BLUESTEM peaked (P < .05) in August during 1990; however, N intake was lowest (P < .05) in August during 1991. Duodenal non-ammonia N (NAN) flow was higher (P < .05) in cattle grazing BLUESTEM than in cattle grazing MIDGRASS from May through August; however, duodenal NAN flow in cattle grazing BLUESTEM was lower (P < .05) in October 1991. Duodenal microbial N synthesis (grams/day) responded quadratically (P < .05) to total ruminal OM digestion (kilograms/day). Extent of true ruminal N digestion of both forages decreased (P < .05) as forage became more mature and lower in total N. Midgrass prairie seemed superior to BLUESTEM in May and October because of higher energy intakes and BLUESTEM seemed to be a good alternative to MIDGRASS during June through August, suggesting that these forages would make excellent complements. Furthermore, these data suggest that, in cattle grazing either forage, duodenal NAN flow was disproportionately high relative to energy intake.
八头装有食管瘘管的肉牛（每块牧场四头）和十二头装有瘤胃和十二指肠瘘管的肉牛犊（每块牧场六头；初始体重 = 267 ± 6 千克）于1990年和1991年的五月中旬、六月下旬、八月中旬和十月中旬分别在中草草甸草原牧场（优良牧场条件；中草牧场）或平原须芒草（Bothriochloa ischaemum var. Plains）牧场（须芒草牧场）放牧，以比较营养物质的摄入量和消化率。在六月和八月，放牧于中草牧场或须芒草牧场的牛的饲草有机物质摄入量（OMI）相似（P > 0.05）。在五月和十月，放牧于中草牧场的牛消耗的有机物质比放牧于须芒草牧场的牛更多（P < 0.05）。除了1991年十月，两种饲草类型的瘤胃真有机物质消化程度相似（P > 0.05），1991年十月须芒草牧场的消化程度比中草牧场更高（P < 0.05）。牛的氮摄入量受年份和饲草的交互影响（P < 0.05）。放牧于中草牧场的牛在六月和八月的氮摄入量往往低于五月和十月。1990年八月，放牧于须芒草牧场的牛的氮摄入量达到峰值（P < 0.05）；然而，1991年八月氮摄入量最低（P < 0.05）。从五月到八月，放牧于须芒草牧场的牛的十二指肠非氨氮（NAN）流量高于放牧于中草牧场的牛（P < 0.05）；然而，1991年十月，放牧于须芒草牧场的牛的十二指肠NAN流量较低（P < 0.05）。十二指肠微生物氮合成（克/天）对瘤胃总有机物质消化（千克/天）呈二次响应（P < 0.05）。随着饲草变得更加成熟且总氮含量降低，两种饲草的瘤胃真氮消化程度均下降（P < 0.05）。由于能量摄入量较高，中草草甸草原在五月和十月似乎优于须芒草牧场，而须芒草牧场在六月至八月似乎是中草牧场的良好替代品，这表明这些饲草将是很好的互补品。此外，这些数据表明，对于放牧这两种饲草之一的牛来说，十二指肠NAN流量相对于能量摄入量过高。
