Forage intake by and site and extent of digestion in beef cattle grazing midgrass prairie rangeland or plains bluestem pasture throughout the summer.

Abstract

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.

Influence of advancing season on dietary composition, intake, site of digestion, and microbial efficiency in beef steers grazing season-long or twice-over rotation native range pastures in western North Dakota1

“…The interaction resulted from true ruminal OM digestibility being numerically greater in L-Jul/E-Aug for SL compared with TOR, whereas TOR had increased digestibility in L-Aug and M-Sep. Small intestinal OM digestibility (% of intake) was not different between treatments (P = 0.44) or sampling periods (P = 0.96). However, values were less than those reported by others (Funk et al, 1987a;Gunter et al, 1990Gunter et al, , 1997, suggesting that more ruminal digestion occurred in the present study.…”

“…In addition, forage N flow or microbial N flow were not different (P ≥ 0.27) among treatments or grazing periods. Forage N flow was less than that reported by Gunter et al (1997), possibly due to decreased N intake in the current study compared with theirs. A period × treatment interaction was observed for fecal N output (P = 0.01), with fecal N output being greater (P < 0.01) on SL than TOR during L-Jul/E-Aug and similar at other time points.…”

“…Additionally, Olson et al (1994a) observed an increase in OM intake per unit of BW with advancing season in south central North Dakota. Organic matter intakes observed in the current experiment were similar to those reported by Cline et al, (2009) in western North Dakota and Gunter et al (1997) for cattle grazing mid-grass prairie. Hirschfeld et al (1996) observed greater OM intakes across the season in cattle grazing short-duration pastures compared with SL pastures, with the exception of late summer in the second year of their study when OM intake was similar between treatments.…”

“…However, total tract N digestion decreased (P = 0.01) across the season. Gunter et al (1997) also found total tract N digestion to decline with advancing season when steers were grazing midgrass prairie. Apparent ruminal N digestion was negative during all periods, indicating substantial N recycling.…”

“…Calculations do not account for endogenous N secretions, microbial N, or sloughed epithelial cells. If these effects are considered, digestibility estimates should increase (Gunter et al, 1997). MacRae et al (1979) suggested that, in addition to N recycled to the rumen through the urea found in the blood and saliva, sloughed epithelial cells or secretions from the tract contribute large amounts to the duodenal N flow.…”