Abstract
The influence of fiber content of hay (low-fiber 47% NDF and high-fiber 62% NDF of DM) and concentrate level (high 50% and low 20% of ration DM) on chewing activity, passage rate and nutrient digestibility were tested on four restrict-fed (11.1 to 13.7 kg DM/d) Holstein cows in late lactation. Aspects of ruminal fermentation and digesta particle size distribution were also investigated on two ruminally cannulated (100 mm i.d.) cows of the same group of animals. All digestion parameters studied were more affected by the fiber content of the hay and its ratio to non structural carbohydrates than by the concentrate level. Giving a diet of high-fiber (62% NDF) hay and low concentrate level (20%) increased chewing activity but decreased solid passage rate and total digestibility of nutrients due to a limited availability of fermentable OM in the late cut fiber rich hay. A supplementation of high-fiber hay with 50% concentrate in the diet seems to improve the ruminal digestion of cell contents, whilst a depression of the ruminal fiber digestibility was not completely avoided. Giving a diet of low-fiber (47% NDF) hay and high concentrate level (50%) reduced markedly the chewing and rumination activity, affected negatively the rumen conditions and, consequently, the ruminal digestion of fiber. A reduction of the concentrate level from 50 to 20% in the diet of low-fiber hay improved the rumen conditions as reflected by an increase of the ruminal solid passage rate and of fiber digestibility and in a decrease of the concentration of large particles and of the mean particle size of the rumen digesta and of the faeces. Generally, it can be summarised that, (i) concentrate supplementation is not a strategy to overcome limitations of low quality (fiber-rich) hay, and (ii) increase of the roughage quality is an effective strategy in ruminant nutrition, especially when concentrate availability for ruminants is limited.
Highlights
Roughage quality is an important factor affecting for the intake and utilization of forage and for the reducing the use of concentrates in ruminant feeds
For a main plot (H⋅C), repeated digesta samples for ruminal fermentation and particle size distribution were collected at four times intervals (1 h before and 2, 5 and 10 h after the morning feeding) on two days (4 sampling times ×2 days = 8 measurements for each animal and treatment)
The data of ruminal fermentation and of particle size distribution in the rumen digesta were analysed by MIXED procedure of SAS (SAS, Release 8.2, 2001) using a split-plot model for repeated measures according to Littell et al (1998)
Summary
Roughage quality is an important factor affecting for the intake and utilization of forage and for the reducing the use of concentrates in ruminant feeds. Higher fiber content is usually associated with a higher degree of lignification (Van Soest, 1994; Krause and Pell, 2003) and, with a low degradation rate and availability of fiber in the rumen, which leads to a prolonged chewing time and to a decrease of passage rate, of total digestibility of fiber and of voluntary roughage intake. These effects of fiber on digestive processes are confounded by the amount and characteristics of concentrate in the diet.
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