Decreasing the Roughage: Concentrate Ratio of a Diet to Determine the Critical Roughage Part for Beef Cattle

The critical roughage part (CRP) of 2 diet types was determined in a cross-over design with 6 double-muscled and 6 normally conformated Belgian Blue bulls fitted with rumen cannulae. The roughage:concentrate ratio was lowered weekly until signs of a lack of physical structure were observed. For diet 1, consisting of maize silage and concentrates, the initial proportion of maize silage was 25% of DM but it decreased weekly with 5% units of DM. For the second diet, consisting of wheat straw and concentrate, 12% straw (DM basis) was provided during the first week and thereafter the proportion of straw decreased weekly with 3% units of DM. Several directly observable parameters (rumen pH, feed intake, bloat, faecal consistency) were evaluated weekly for each bull. Apart from these direct indicators of acidosis, also other parameters, whose results were only available after the end of the trial, were determined (volatile fatty acid profile, lactic acid concentration, chewing time). The roughage part between the part fed when signs of a lack of physical structure was first observed and the part that was fed the week before, was considered as the CRP. Most animals showed no acute signs of clinical acidosis (directly observable parameters) and finished the trial on a 100% concentrate diet. However, in sacco rumen DM-degradabilities of maize silage, grass silage and wheat grain was depressed considerably when low roughage diets were fed. Based on all observed parameters, the mean CRP was calculated to be 14.7% for diet 1 and 8.1% for diet 2. The beef type (double-muscled or not) had no influence on the CRP.     

Carbon balances for in vitro digestion and fermentation of potential roughages for pregnant sows

Ad libitum feeding of pregnant sows requires satiating, intake-restricting feed components to prevent sows from getting excessively fat. Because hindgut fermentation starts only after and proceeds much slower than enzymatic digestion in the small intestine, fermentation products might, as nutrients, induce a prolonged physiological satiation of sows. To simulate hindgut fermentation and determine the fermentative release of short-chain fatty acids (SCFA) in vitro, gas production tests (GPTs) were performed with different raw materials after removal of enzymatically hydrolysable compounds. Fresh feces from sows that received standard sow feed was used as inoculum. Fresh, ensiled, or dehydrated by-products of the food industry (brewers’ grains, liquid yeast feed, maize gluten feed, raw potato chips, potato steam peel, pressed potato pulp, sugar beet pulp (SBP)) and whole-plant products (grass, maize) were tested as individual products.

Balances were drawn up of the in vitro flow of organic carbon (OC) to an “ileal” nutrient fraction, a “hindgut” fraction of SCFA and gas, and “fecal” remnants. The OC balances revealed large variations among raw materials in terms of their contribution to the different fractions. Potato steam peel gave the largest “ileal” nutrient fraction (77% of total OC), the lowest was observed with fresh sugar beet pulp (9% of total OC). In the GPT, SBP, and potato pulp brought about the highest “hindgut” SCFA yields (32–49% of total OC), and together with raw potato chips, the highest amounts of gas. Grass products and liquid yeast feed were slower fermented than most by-products. Moreover, whole-plant materials gave larger “fecal” OC portions than by-products, with the exception of fresh and dehydrated brewer’s grains. Together with straw, the latter were the least degradable of all raw materials tested. Among the grass products, dehydrated grass, and among the by-products, raw potato chips left the least “fecal” residues, i.e. they were nutritionally utilized to the largest extent.     

A decade since ”diversification of ruminants”: has our knowledge improved?

In his landmark 1989 paper, R.R. Hofmann classified ruminants into three categories based upon digestive anatomy and preferred forages, and proposed that divergence of feeding strategies among ruminants is a result of morphological evolution of the digestive tract. Because of the hypothetical nature of these views and the ingrained beliefs that they challenged, several papers were published that reported tests of Hofmann’s predictions. The consensus among these papers was that Hofmann’s predictions were inadequate. I describe the experimental evidence that has been put forth in opposition to the ruminant diversification hypothesis and contend that we have failed to adequately test Hofmann’s predictions. Received: 11 October 1999 / Accepted: 6 April 2000