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

Abstract

To determine whether non-fibrous carbohydrate (NFC) supplementation improves fiber digestibility and microbial protein synthesis, 18 Corriedale ewes with a fixed intake level (40 g dry matter (DM)/kg BW 0.75 ) were assigned to three (n 5 6) diets: F 5 100% fresh temperate forage, FG 5 70% forage 1 30% barley grain and FGM 5 70% forage 1 15% barley grain 1 15% molasses-based product (MBP, Kalori 3000). Two experimental periods were carried out, with late (P1) and early (P2) vegetative stage forage. For P2, ewes were fitted with ruminal catheters. Forage was distributed at 0900 h, 1300 h, 1800 h and 2300 h, and supplement added at 0900 h and 1800 h meals. Digestibility of the different components of the diets, retained N and rumen microbial protein synthesis were determined. At the end of P2, ruminal pH and N-NH 3 concentration were determined hourly for 24 h. Supplementation increased digestibility of DM ( P , 0.001) and organic matter (OM; P , 0.001) and reduced NDF digestibility ( P 5 0.043) in both periods, with greater values in P2 ( P 5 0.008) for the three diets. Daily mean ruminal pH differed ( P , 0.05) among treatments: 6.33 (F), 6.15 (FG) and 6.51 (FGM). The high pH in FGM was attributed to Ca(OH) 2 in MBP. Therefore, the decreased fiber digestibility in supplemented diets could not be attributed to pH changes. The mean ruminal concentration of N-NH 3 was 18.0 mg/dl, without differences among treatments or sampling hours. Microbial protein synthesis was greater in P2 (8.0 g/day) than in P1 (6.1 g/day; P 5 0.006), but treatments did not enhance this parameter. The efficiency of protein synthesis tended to be lower in supplemented groups (16.4, 13.9 and 13.4 in P1, and 20.8, 16.7 and 16.2 g N/kg digestible OM ingested in P2, for F, FG and FGM, respectively; P 5 0.07) without differences between supplements. The same tendency was observed for retained N: 2.55, 1.38 and 1.98 in P1, and 2.28, 1.23 and 1.10 g/day in P2, for F, FG and FGM, respectively; P 5 0.05). The efficiency of microbial protein synthesis was greater in P2 (P 5 0.007). In conclusion, addition of feeds containing NFCs to fresh temperate forage reduced the digestibility of cell walls and did not improve microbial protein synthesis or its efficiency. An increase in these parameters was associated to the early phenological stage of the forage.

Diurnal changes in water-soluble carbohydrate concentration in lucerne and tall fescue in autumn and the effects on in vitro fermentation

“…Nitrogen (N) compounds of temperate pastures are extensively and rapidly degraded in the rumen (Repetto et al 2005;Fulkerson et al 2007), releasing high amounts of NH 3 to the ruminal environment Cajarville & Pérez et al 2006) that can be utilised by the microbiota. However, the quantity of readily fermentable carbohydrates is often insufficient, leading to low N utilisation and poor animal performance (Elizalde et al 1996;García et al 2000;Tebot et al 2012). This inadequacy is even greater during autumn and early winter, as day length and luminosity are lower, and fewer water-soluble carbohydrates (WSC) are produced by the plants in comparison with late winter and spring (Delagarde et al 2000).…”

Sheep numbers required for dry matter digestibility evaluations when fed fresh perennial ryegrass or forage rape

“…This is comparable to the results reported in other studies. For example, Tebot et al. (2012) reported the SD of pasture (90% oat [ Avena sativa ] and 10% white clover [ Trifolium repens ]) DM content was 17 g/kg for pasture cut in the early vegetative stage and 31 g/kg for pasture cut in the late vegetative stage of the harvest season.…”

Lamb Fattening Under Intensive Pasture-Based Systems: A Review

“…The results of these studies supported the hypothesis that there are benefits on microbial protein synthesis in synchronizing the availability of rumen-fermentable carbohydrates with N in the rumen, but this is not always associated with significant changes in rumen pH and NH 3 -N concentrations. Meanwhile, Tebot et al [43] evaluated three forage diets with non-fibrous carbohydrate supplementation (100% fresh temperate forage, 70% forage + 30 barley grain, and 70% forage + 15% barley + 15% molasses-based product). The results indicated that supplementation with starch (barley) or sugars (molasses) in sheep grazing did not improve ruminal N-ammonia captured for microbial protein synthesis.…”