Intake, Site, and Extent of Nutrient Digestion of Lactating Cows Grazing Pasture

Abstract

The objective of this study was to determine intake and site and extent of nutrient digestion of lactating cows grazing pasture with or without energy supplementation. Four dual-cannulated (rumen and proximal duodenum) cows were randomly assigned to two groups to graze mixed cool season grass legume pasture with either no supplement or with 6.4 kg of cracked corn and mineral mix daily in a switchback design with three 2-wk periods. Markers (Cr2O3 and Co-EDTA) were used to estimate intake, duodenal flow, fecal output, and fractional rates of passage from the rumen. Daily OM intake was similar between diets, but OM intake of pasture was lower when cows were fed corn. Apparent OM and NDF digestibilities in the rumen and total digestive tract were lower when cows were supplemented with corn than when they consumed pasture only. Supplemental corn decreased ruminal NH3 N (22 vs. 17 mg/dl) and increased N recovery at the duodenum (86% vs. 75% of N intake). Nonammonia, nonmicrobial N flowing to the duodenum was 67% of the total NAN flow. Corn increased energy intake of grazing cows, but decreased herbage intake and digestibility.

Supplementation with non-fibrous carbohydrates reduced fiber digestibility and did not improve microbial protein synthesis in sheep fed fresh forage of two nutritive values

“…It has been shown that fermentable carbohydrate supplementation reduces ruminal N-NH 3 increasing its capture by microorganisms and its subsequent use in protein synthesis (Berzaghi et al, 1996). However, Wiedmeier et al (1992), comparing the effect of molasses and a molasses by-product on digestibility and rumen fermentation in hay-fed cattle, obtained N-NH 3 concentrations similar to those reported in this study without significant differences between treatments.…”

Milk Production and Composition, Rumen Fermentation Parameters, and Grazing Behavior of Dairy Cows Supplemented with Different Forms and Amounts of Corn Grain

“…Intake of orchard grass hay while in the dirt lot, approximately 1 kg/d, was not accounted for in this intake estimation. Average estimated DMI was numerically higher in wk 1 of the study (18.6 DIM, and milk yield and composition (2,6). Grain supplementation was slightly higher (7.2 to 7.6 kg/d DM) in the study of Holden et al (6) compared with the present study.…”

“…When CSH was regressed against measured herbage DM yields (kg/ha of DM) the equation (Figure 1) was obtained: Alfalfa-orchardgrass was grazed during the last week of June (wk 7) through the third week of July (wk 10) for 3 h each morning. 2 Average nutrient composition of orchardgrass hay during the study. Ether extract, ash, and macro and micro minerals of OG hay were obtained from NRC (20).…”

“…High quality pastures are usually characterized by high concentrations of CP, which is highly degradable in the rumen (2). This results in transport of large amounts of NH 3 -N across the rumen wall that is converted primarily to urea in the liver.…”

Nutritional Strategies to Improve Nitrogen use Efficiency by Grazing Dairy Cows

“…Cows consuming only pasture had a NUE of 21.0 ± 6.1% while supplemented grazing cows improved their NUE, storing in the milk 24.6 ± 3.8% of the ingested N, showing a positive effect of CHO supplementation on NUE (Van Vuuren et al, 1993;Berzaghi et al, 1996;Carruthers and Neil, 1997;Robaina et al, 1998;Reis and Combs, 2000;Walker et al, 2001;Bargo et al, 2002;Steinshamn et al, 2006). This improvement may be due to a decrease in CP content of the diet and to an increase of microbial protein synthesis.…”