H. Steingass

Modeling the Adequacy of Dietary Fiber in Dairy Cows Based on the Responses of Ruminal pH and Milk Fat Production to Composition of the Diet

The main objective of this study was to develop practical models to assess and predict the adequacy of dietary fiber in high-yielding dairy cows. We used quantitative methods to analyze relevant research data and critically evaluate and determine the responses of ruminal pH and production performance to different variables including physical, chemical, and starch-degrading characteristics of the diet. Further, extensive data were used to model the magnitude of ruminal pH fluctuations and determine the threshold for the development of subacute ruminal acidosis (SARA). Results of this study showed that to minimize the risk of SARA, the following events should be avoided: 1) a daily mean ruminal pH lower than 6.16, and 2) a time period in which ruminal pH is <5.8 for more than 5.24 h/d. As the content of physically effective neutral detergent fiber (peNDF) or the ratio between peNDF and rumen-degradable starch from grains in the diet increased up to 31.2 +/- 1.6% [dry matter (DM) basis] or 1.45 +/- 0.22, respectively, so did the daily mean ruminal pH, for which a asymptotic plateau was reached at a pH of 6.20 to 6.27. This study also showed that digestibility of fiber in the total tract depends on ruminal pH and outflow rate of digesta from reticulorumen; thereby both variables explained 62% of the variation of fiber digestibility. Feeding diets with peNDF content up to 31.9 +/- 1.97% (DM basis) slightly decreased DM intake and actual milk yield; however, 3.5% fat-corrected milk and milk fat yield were increased, resulting in greater milk energy efficiency. In conclusion, a level of about 30 to 33% peNDF in the diet may be considered generally optimal for minimizing the risk of SARA without impairing important production responses in high-yielding dairy cows. In terms of improvement of the accuracy to assessing dietary fiber adequacy, it is suggested that the content of peNDF required to stabilize ruminal pH and maintain milk fat content without compromising milk energy efficiency can be arranged based on grain or starch sources included in the diet, on feed intake level, and on days in milk of the cows.

Energy and protein evaluation of tropical feedstuffs for whole tract and ruminal digestion by chemical analyses and rumen inoculum studies in vitro

Abstract A range of tropical feedstuffs used in feeding ruminants were analysed for metabolisable energy ( ME ) and nitrogen fractions. The ME content was predicted from the extent of fermentation in in-vitro incubation with rumen inoculum and N was evaluated based on solubility in borate-phosphate buffer, protease enzyme and acid detergent solution. The range in predicted ME content and the rate of organic matter fermentation for grains, byproduct feeds, cultivated fodders and nonlegume straw were respectively, 11.8–13.9 and 0.05–0.11; 6.0–13.7 and 0.05–0.15; 7.1–9.4 and 0.05–0.13; 5.7–7.7 and 0.02–0.04. Potentially digestible N was more than 90% for most feedstuffs with the exception of finger millet grains (73.9%), rice bran (88.0%), napier grass (79.3%), spear grass (82.6%) and nonlegume straw (66.0–88.6%). N insolubility in protease enzyme (PIN) was maximum in rice bran, solvent extracted (s.e.) (56.6%) and minimum in sesame meal (3.3%), with cottonseed meal and rapeseed meal > sunflower meal, coconut meal, groundnut meal, s.e. > groundnut meal, expeller (exp). However, the buffer insoluble N soluble in protease enzyme (considered as slowly degraded N) was found to be maximum in sesame meal (90.6%), followed by coconut meal (60.2%), cottonseed meal (50.6, 61.6%), sunflower meal (45.7%), groundnut meal, s.e (45.1%) and groundnut cake, exp. (22.7%). In situ N undegradability reported in the literature for similar feedstuffs indicated too wide a range making it difficult to take these values as standards for comparison with any of the N fractions obtained from the laboratory analysis.

Laboratory variation of 24 h in vitro gas production and estimated metabolizable energy values of ruminant feeds

Intra- and inter-laboratory variation of in vitro gas production and calculated metabolizable energy (ME, MJ/kg DM) values were studied using 16 test feeds in 7 laboratories. Intra-laboratory variation was low, with six of the seven laboratories having very high relationships in gas production between runs (R 2 ≥ 0.96) and slopes that did not differ from unity. Inter-laboratory differences were higher with highly significant ( P< 0.001) differences among laboratories in both gas production and calculated ME values. Three of the six test laboratories generated predicted ME values that did not differ from the seventh (reference) laboratory. Combining intra-laboratory variation in gas production and inter-laboratory variation in predicted ME values, three of the six test laboratories were judged acceptable overall. ME values predicted by the gas production technique by laboratories in different parts of the world cannot be considered absolute.

Digesta characteristics of dorsal, middle and ventral rumen of cows fed with different hay qualities and concentrate levels

The influence of fibre content of hay (H) and concentrate level (C) on local differences in the composition of ruminal digesta (ratio of solid to fluid digesta, DM, NDF, ADF and ADL content), particle size (MPL), specific gravity (SG) and fermentation (pH and concentrations of SCFA and bicarbonate) have been tested on two ruminally cannulated Friesian cows (520 kg BW) which were fed restricted, using individual cows as experimental units. Digesta samples were collected via cannula from three rumen layers: 5 to 10 cm (top) and 25 – 35 cm beneath the top of the particle mat (middle) and 5 – 10 cm above the rumen floor (bottom). For a main plot treatment (H·C), repeated samples were collected at four time intervals (1 h before and 2, 5 and 10 h after morning feeding) on each of two days. From top to bottom rumen the share of solid digesta mass (SM), DM and NDF contents of squeezed digesta fluid (SRF) and concentration of SCFA decreased (P < 0.05); pH and bicarbonate concentration increased (P < 0.05), while DM, NDF, ADF and ADL contents in SM, MPL and SG did not differ. Higher NDF content of hay (from 47 – 62%) increased SM, fibre fractions in SM, MPL, pH and concentration of bicarbonate in ruminal digesta, especially when 50% concentrate was given, while SG decreased. When the concentrate level was enhanced from 20 to 50%, digesta SM, MPL and the content of DM and NDF in SRF increased, while pH, concentrations of SCFA and acetate decreased when low-fibre hay was given. With longer time after feeding the digesta SM was reduced and fibre content in SM increased. The increase of the fibre content of hay reduced the possible negative effect of high concentrate level on the stratification of ruminal digesta. The decrease of the fibre content of hay promised better conditions for fibre digestion in the rumen when concentrate availability is limited.

A model to optimise the requirements of lactating dairy cows for physically effective neutral detergent fibre

This study modelled multiple physiological responses of dairy cows to physical and chemical characteristics of a diet aiming to optimise their requirements for physically effective neutral detergent fibre, expressed inclusive of particles-dry matter > 8 mm (peNDF>8). Extensive research data, comprising a wide range of feeding conditions (n = 64 studies and 257 different dietary treatments), were used to parameterise the model, while statistical modelling was used to account for the inter- and intra-experiment variation as well as to derive the model estimates. Physiological thresholds and ‘safety limits’ of peNDF>8 for maintaining different physiological variables were derived using non-linear statistical modelling. Results showed that peNDF>8 content in the diet is a key factor stimulating rumination activity, maintaining optimal ruminal pH and promoting fibre digestion. Modelling data with regard to the association of fibre digestion and time duration of ruminal pH < 5.8 and dietary peNDF>8 suggests that feeding of less than 13.7% peNDF>8 (the lower ‘safety limit’) is critical to prevent depression of fibre digestion in dairy cows. The study also indicated that the beneficial effects of peNDF>8 on ruminal pH and fibre digestion can be at the expense of the dry matter intake (DMI) level of high-producing cows when the peNDF>8 threshold of 14.9% in the diet is exceeded. In terms of the optimisation of peNDF>8 requirements, the modelling data suggest that feeding of 17–18.5% peNDF>8 can be beneficial in maintaining ruminal pH, while allowing a relatively high DMI (22.3–22.7 kg · d−1) for average high-producing dairy cows.

Prediction of the net energy content of raw materials and compound feeds for ruminants by different laboratory methods.

In this study three different laboratory procedures were compared as predictors of net energy content of raw materials and compound feeds for ruminants. Laboratory measurements included an enzymatic technique (pepsin-cellulase method) and a rumen fluid technique (Hohenheim gas test). An estimate based on crude nutrients only was also tested. A total of 98 feed samples with known in vivo digestibility were available. By multivariate regression analysis equations for the prediction of the net energy content were calculated. The results suggest that in case of compound feeds for dairy the cellulase technique and the gas test are suitable in vitro techniques. With both procedures the relationships between energy contents estimated in vitro and energy contents measured in vivo showed residual errors of less than 4 percent. However for the evaluation of raw materials the gas test was superior. Compared to the cellulase technique the risk of extreme under- or overestimations is apparently reduced and this was found to be the case for own prediction equations as well as equations from literature. Crude nutrients proved to be very poor predictors for all feed samples.

Supplementation of wheat straw with sesbania on voluntary intake, digestibility and ruminal fermentation in sheep

The study was conducted to investigate the effect of supplementation of sesbania (Sesbania aculata) on the voluntary intake, digestibility and ruminal fermentation characteristics in sheep. Digestion trials were conducted with four Cameroon wethers fed ad libitum wheat straw alone (T0), wheat straw supplemented on dry matter (DM) basis with 10 (T1) and 20% (T2) dried sesbania in 3×3 Latin square design. Three rumen fistulated Merino sheep were also used under same feeding and management conditions for rumen parameter studies. Daily total DM intake (g/kg BW0.75) was significantly increased (P<0.01) by 50 and 71% by 10 and 20% sesbania. Straw DM intake (g/kg BW0.75) was increased 36% by 10 and 20% sesbania. Digestibility of the nutrients was improved with increasing levels of sesbania compared to feeding wheat straw diet alone. Average daily gain (g) of the sheep receiving T1 (−23±43) and T2 (139±31) diets was significantly (P<0.05) higher than those with T0 (−84±68) diet. Rumen fluid pH declined linearly (P<0.05) with increasing sesbania while concentration of rumen ammonia was not significantly affected. Total volatile fatty acids (VFA) was higher (P<0.05) in sheep fed T1 and T2 diets than those fed T0 diet. It was concluded that wheat straw was better utilized by sheep when sesbania was supplemented at the level of 20%.

Preliminary observations on the relationship between gas production and microbial protein synthesis in vitro

The relationship between gas production and microbial protein synthesis was studied in vitro using the method of MENKE et al. (1979). 150 mg starch or cellulose or a mixture of 10% glucose, 40% starch and 50% cellulose was used as the carbohydrate source. The microbial protein synthesis and gas production occurring during 2 hrs after the 5th, 10th, and 23rd hr of incubation were studied. Total and net microbial synthesis were estimated using 32P as a microbial marker and by the net disappearance of NH3-N respectively. The data indicate that the type of carbohydrate and the rate of carbohydrate fermentation influence microbial protein synthesis per unit volume of gas produced. However, the relationship between total synthesis and cumulative gas production (up to 8 hrs incubation) with carbohydrate mixture as the substrate was linear. With reference to these observations, the possibilities and difficulties in using cumulative gas production as an index of microbial growth potential of the feedstuffs are discussed.

Influence of Apple and Citrus Pectins, Processed Mango Peels, a Phenolic Mango Peel Extract, and Gallic Acid as Potential Feed Supplements on in Vitro Total Gas Production and Rumen Methanogenesis

Several food processing byproducts were assessed as potential feed and feed supplements. Since their chemical composition revealed a high nutritional potential for ruminants, the Hohenheim in vitro gas test was used to investigate total gas, methane, and volatile fatty acid production as well as protozoal numbers after ruminal digestion of different substrate levels. Processing byproducts used were low- and high-esterified citrus and apple pectins, integral mango peels, and depectinized mango peels. In addition, the effect of a phenolic mango peel extract and pure gallic acid was investigated. The highest decrease in methane production (19%) was achieved by supplementing high levels of low-esterified citrus pectin to the hay-based diet. Interestingly, total gas production was not affected at the same time. Showing valuable nutritional potential, all byproducts exhibited, e.g., high metabolizable energy (11.9-12.8 MJ/kg DM). In conclusion, all byproducts, particularly low-esterified citrus pectin, revealed promising potential as feed and feed supplements.

Effects of long-term supplementation of chestnut and valonea extracts on methane release, digestibility and nitrogen excretion in sheep.

The long-term effects of adding chestnut (CHE; Castanea sativa) and valonea (VAL; Quercus valonea) tannin-rich extracts to sheep feed were investigated. In Experiment 1, sheep (65 kg BW) were fed 842 g/day of a ryegrass-based hay. The control-treated animals (CON) received 464 g/day of concentrate, and tannin-treated animals received the same amount of concentrate additionally containing 20 g of the respective tannin-rich extract. Hay and concentrates were offered together in one meal. After the onset of treatment, methane release was measured in respiration chambers for 23.5-h intervals (nine times) in a 190-days period. Faeces and urine were collected three times (including once before the onset of the tannin treatment) to assess digestibility and urinary excretion of purine derivatives. Based on the results obtained from Experiment 1, a second experiment (Experiment 2) was initiated, in which the daily tannin dosage was almost doubled (from 0.9 (Experiment 1) to 1.7 g/kg BW0.75). With the exception of the dosage and duration of the treatment (85 days), Experiment 2 followed the same design as Experiment 1, with the same measurements. In an attempt to compare in vitro and in vivo effects of tannin supplementation, the same substrates and tannin treatments were examined in the Hohenheim gas test. In vitro methane production was not significantly different between treatments. None of the tannin-rich extract doses induced a reduction in methane in the sheep experiments. On the 1st day of tannin feeding in both experiments, tannin inclusion tended to decrease methane release, but this trend disappeared by day 14 in both experiments. In balance period 3 of Experiment 1, lower dry matter and organic matter digestibility was noted for tannin treatments. The digestibility of CP, but not NDF or ADF, was reduced in both experiments. A significant shift in N excretion from urine to faeces was observed for both tannin-rich extracts in both experiments, particularly in Experiment 2. In balance period 2 of Experiment 2, an increased intake of metabolisable energy for VAL was observed. The urinary excretion of purine derivatives was not significantly different between treatments, indicating that microbial protein synthesis was equal for all treatments. Thus, we concluded that both tannin-rich extracts temporary affect processes in the rumen but did not alter methane release over a longer period.