Microbial Protein Yield Research Articles

The effect of the form of nitrogen in the diet on ruminal fermentation and the yield of microbial protein in sheep consuming diets of grass silage supplemented with starch or sucrose

Three experiments were conducted to investigate the influence of the type of carbohydrate in the supplement on responses of microbial protein synthesis (MPS, calculated from the urinary output of purine derivatives) in the rumen to dietary addition of ruminal sources of peptides and amino acids in sheep consuming grass silage. In Experiment 1, incubations of rumen liquor in vitro indicated that bacteria fermenting sucrose grew better when ammonia was the only source of added nitrogen than did bacteria utilizing starch. These results led to the hypothesis that bacteria fermenting sucrose might be less dependent on performed amino acids and peptides for their growth than are bacteria fermenting starch. Experiment 2 was designed to test this hypothesis by measuring the response of MPS to inclusion of rapeseed meal, as a source of ruminal amino acids and peptides, in supplements of sucrose or starch given to sheep given a basal diet of grass silage. There was no difference between the carbohydrate treatments in the response of MPS to the inclusion of rapeseed meal, but also, there was no difference in MPS between the sucrose and starch supplements when given without added protein. Experiment 3 examined the effect of the level of starch (0.20 and 0.38 of DM) in the diet on the response of MPS to isonitrogenous dietary additions of urea or casein. The hypothesis tested was that the addition of protein would lead to a greater increase of MPS with the higher level of starch because amylolytic bacteria require preformed peptides and amino acids for maximal growth. However, this was not the case because the response of MPS to inclusion of casein as opposed to urea was greater at the lower level of starch. These results question the generalization that amylolytic bacteria require preformed peptides and amino acids for growth and highlight the need for more information on the influence of diet composition in determining the types of amylolytic bacteria that dominate the ruminal fermentation, there being evidence in the literature that at least one potentially dominant organism, Ruminobacter amylophilus, mainly uses ammonia for growth with only very limited incorporation of organic nitrogen.

Effects of Rumen-undegradable Protein and Feed Intake on Purine Derivative and Urea Nitrogen: Comparison with Predictions from the Cornell Net Carbohydrate and Protein System

Six multiparous Holstein cows were used in a 6 × 6 Latin square to investigate the ability of the Cornell Net Carbohydrate and Protein System to predict accurately rumen microbial yield, plasma urea N, and milk urea N. Estimations for microbial protein yield were compared with the measured excretion of purine derivative N in urine. A 3 × 2 factorial arrangement of treatments was adopted. Three concentrations of a rumen-undegradable protein (RUP) supplement (4.5, 14.9, and 29.1% of dry matter intake) and two levels of feed restriction (90 and 80% of ad libitum intake) were the corresponding factors. No effect of concentration of RUP supplement or feed restriction was detected on the excretion of purine derivative N in urine (mean, 18.5 g/d). Conversely, the Cornell system predicted a linear decrease in metabolizable protein from bacteria as the concentration of the RUP supplement increased. The Cornell system also predicted a significant reduction in metabolizable protein of microbial origin as feed restriction was increased. Measured values and values derived from the Cornell system for plasma and milk urea N increased linearly as the concentration of the RUP supplement increased. The Cornell system overpredicted milk urea N for cows consuming the highest RUP concentration. Predictions by the Cornell Net Carbohydrate and Protein System were of limited value because the empirical nature of the model is insufficiently rigorous to yield accurate predictions under the conditions described herein.

A review of current nutritional models: what we need to measure

AbstractA common feature of nutritional models developed in the last three decades is that estimates of energy and protein are generally made independent of each other, even though interactions between them are recognized.Most of the energy systems have adopted metabolizable energy (ME) or net energy (NE) as the unit for energy evaluation. Accurate measurement of the ME content of a food requires in vivo digestibility measurements using cattle or sheep, with methane losses either measured or predicted. This approach is clearly unsuitable for routine food evaluation and most systems predict the ME content from chemical analyses, using regression equations derived from calorimetric measurements.The new generation of protein systems recognize the need to consider, separately, the energy and nitrogen requirements of the rumen micro-organisms and the protein requirements of the host animal. Despite this common base, systems differ markedly in estimates of energy supply to rumen bacteria, the degree to which dietary protein is degraded in the rumen, microbial protein yield and the digestibility of the microbial and undegraded dietary protein.Although empirically based, current protein systems contain dynamic elements relating to rates of fermentation and protein degradation. In most cases, data have been derived using the in situ nylon bag technique, although this has major limitations. Recent developments in the gas production technique suggest that this approach has the potential for describing fermentation and degradation rates of individual foods.To be effective, energy and protein systems need to describe foods in units that are both easily understood by non-specialists and can be measured using procedures that are rapid, reliable and cost effective. Near infra-red reflectance spectroscopy (NIRS) can be both rapid and cost effective and there is evidence that it may be able to predict not only proximate analyses but also dynamic characteristics of foods.

The effect of asynchronous diets on the function of the rumen in the lactating dairy cow

Sinclair et al. (1993) found that a diet formulated to be synchronous with regard to hourly release of nitrogen and energy increased microbial protein synthesis by 14% in sheep. Dairy cows in early lactation experience a shortfall of energy and protein, with available protein determining the overall efficiency of metabolism (MacRae and Lobley, 1986) and subsequent milk production. It is therefore necessary to maximise microbial protein yield during this period. In this study diets were designed for lactating dairy cows to contain the same feed ingredients, but to release nitrogen and energy in the rumen at different times. Rumen fermentation parameters, nutrient flows to the small intestine and production performance were investigated.

The effect of asynchronous diets on the function of the rumen in the lactating dairy cow

Sinclair et al. (1993) found that a diet formulated to be synchronous with regard to hourly release of nitrogen and energy increased microbial protein synthesis by 14% in sheep. Dairy cows in early lactation experience a shortfall of energy and protein, with available protein determining the overall efficiency of metabolism (MacRae and Lobley, 1986) and subsequent milk production. It is therefore necessary to maximise microbial protein yield during this period. In this study diets were designed for lactating dairy cows to contain the same feed ingredients, but to release nitrogen and energy in the rumen at different times. Rumen fermentation parameters, nutrient flows to the small intestine and production performance were investigated.

Effects of supplementation with foliage from the tree legumes Acacia angustissima, Cajanus cajan, Calliandra calothyrsus and Leucaena leucocephala on feed intake, digestibility and nitrogen metabolism of sheep given maize stover ad libitum

Foliage (leaves, small-diameter stems and flowers and fruits if present) was harvested in March 1994 from Acacia angustissima, Cajanus cajan, Calliandra calothyrsus and Leucaena leucocephala and given as a supplement at four levels (0, 50, 100 and 150 g dry matter/day) to a diet of maize stover fed ad libitum to sheep. Sixteen sheep were used and divided into four groups of four, each with a mean weight of 18 kg. Each group was allocated at random to one of the legumes. Four 4 × 4 Latin square design experiments were carried out using 14-day periods and during the second week of each period feed intake, digestibility, nitrogen balance and microbial protein yield were measured. For each legume, other than C. calothyrsus, there was a significant increase ( P < 0.05) in dry matter intake as the level of supplement increased. For all four legumes, there was a significant increase ( P < 0.05) in digestibility of organic matter, nitrogen balance (NB) and microbial protein yield as the level of supplement increased. As judged by increases in intake of digestible organic matter and NB, A. angustissima gave the best response, followed by C. calothyrsus and L. leucocephala which were similar and then C. cajan gave the poorest response.

Effects of Supplementation of Energy or Ruminally Undegraded Protein to Lactating Cows Fed Alfalfa Hay or Silage

Alfalfa was harvested as silage or hay and fed in two 12-wk trials with a 4×4 Latin square design that used 12 (trial 1) or 24 (trial 2) multiparous lactating cows (4 ruminally cannulated cows per trial). Diets contained (dry matter basis) 75 or 50% alfalfa plus 24 or 40% high moisture corn (trial 1) or 50% alfalfa, 44 or 41% high moisture corn, with (3%) or without fish meal (trial 2). Experiments were conducted to evaluate the responses of cows fed alfalfa hay or alfalfa silage diets to an increase in protein supply from microbial protein synthesis (trial 1) or from the supplementation of ruminally undegraded protein (RUP) (trial 2). In trial 1, the increase in high moisture corn in the diet increased both milk protein and microbial crude protein yields (estimated from the excretion of purine derivatives) to a greater extent for the cows fed the alfalfa silage diets (170 and 337 g/d, respectively) than for the cows fed the alfalfa hay diets (100 and 100 g/d, respectively). In trial 2, RUP supplementation (as fish meal) increased milk protein yield 100 g/d for cows fed alfalfa silage diets and 20 g/d for cows fed alfalfa hay diets. These results indicated that protein status was poorer and, thus, more responsive to absorbable protein from microbial protein (trial 1) or RUP (trial 2) for cows that consumed alfalfa conserved as silage versus those that consumed alfalfa conserved as hay.

Effect of ammoniation or protein supplementation of barley straw on digestion and purine derivative excretion in sheep

AbstractAn experiment was conducted to examine the effect of ammonia treatment or soya-bean meal supplementation on rumen and lower tract digestion and urinary purine-derivative excretion in sheep given barley straw-based diets. Four wethers each fitted with simple rumen and duodenal cannulae were randomly allocated to four diets in a 4×4 Latin-square design. The diets were, untreated barley straw + molasses meal (diet 1), ammonia-treated barley straw + molasses meal (diet 2), untreated barley straw + soya-bean meal + molasses meal (diet 3) and ammonia-treated barley straw + soya-bean meal + molasses meal (diet 4). Dry-matter (DM) intake, total tract neutral- and acid-detergent fibre apparent digestibility and faecal nitrogen (N) output were higher for diets 2 and 4. Microbial protein yield, determined from total urinary purine-derivative excretion, was also high in sheep on diets 2 and 4. However, supplementation with soya-bean meal in diet 4 reduced DM and fibre digestion but increased intake and microbial synthesis. Despite the lower microbial protein synthesis for diet 3, total tract N digestion was high for the diet, an indication of higher nutrient absorption in the lower tract. The above results indicated that there was a substantial increase in rumen microbial N yield from ammoniated straw-based diets. However, not all the N was made available to the animals. Some of the microbial N absorbed in the lower tract may have been overestimated by the use of the purine derivative-microbial N evaluation method. On the other hand, when protein supplements were given the amount of microbial protein available to the ruminant through absorption in the lower tract may have been underestimated by urinary purine derivatives.

The addition of lactose to the diets of dairy cows fed protected fats

Rumen inert fats are often included in dairy rations to increase the metabolisable energy (ME) supply whilst maintaining rumen function. Protected fat supplements have been shown to increase milk yields and fat content but with an associated and undesirable reduction in protein content. A reduced intake of rumen available energy (FME) may limit the microbial protein yield and so reduce the supply of amino acids to the mammary gland. Lactose supplements have been shown to increase the flow of microbial protein to the intestines (Chamberlain et al, 1993) and to reduce the effect of protected fats on milk protein content during early lactation (Garnsworthy, 1996). A trial was conducted to determine whether lactose supplementation could reduce the effects of protected fats on milk protein content during mid lactation.

Yield of microbial protein in sheep fed diets differing in protein degradability

Modern protein systems for ruminants require estimates of microbial protein yield relative to the amount of energy fermented in the rumen. In the Metabolizable Protein (MP) System (Webster 1992) this is expressed by the ratio of microbial nitrogen to fermented metabolizable energy (MiN:FME). However uncertainty as to the estimation of MiN yield both in absolute terms and relative to rumen degradable N (RDN) generates further uncertainty as to the efficiency of capture of quickly and slowly degraded N (QDN and SDN). Moreover the MP system assumes no capacity to recapture recycled undegraded N (UDN). This experiment measures increments in excretion of purine derivatives by sheep to explore the effects of varying relative and absolute supply of QDN, SDN and UDN on relationships between FME utilisation and yield of microbial N from the rumen.

Effects of feeding lactose with protected fat and protein on milk production of cows in mid lactation

Protected fats are very useful for increasing the energy concentration of diets fed to high-yielding dairy cows without adverse effects on rumen fermentation. However, in previous studies, it has been found that although high-fat diets usually increase yields of milk and milk constituents, they can lead to a depression in milk protein content. This can be partially overcome by increasing the supply of fermentable carbohydrates, using lactose, thereby increasing microbial protein yield (Garnsworthy, 1996), or by increasing undegradable protein supply (Garnsworthy, unpublished). The objective of this experiment was to study the response of cows in mid lactation to a product containing protected fat and protein (MegaPro, Volac International) fed with or without lactose.

Effects of feeding lactose with protected fat and protein on milk production of cows in mid lactation

Protected fats are very useful for increasing the energy concentration of diets fed to high-yielding dairy cows without adverse effects on rumen fermentation. However, in previous studies, it has been found that although high-fat diets usually increase yields of milk and milk constituents, they can lead to a depression in milk protein content. This can be partially overcome by increasing the supply of fermentable carbohydrates, using lactose, thereby increasing microbial protein yield (Garnsworthy, 1996), or by increasing undegradable protein supply (Garnsworthy, unpublished). The objective of this experiment was to study the response of cows in mid lactation to a product containing protected fat and protein (MegaPro, Volac International) fed with or without lactose.

Effects of the composition of grass silages on milk production and nitrogen utilization by dairy cows

AbstractSixteen varied grass silages metabolizable energy (ME): 9·76 to 11·99 MJ/kg ethanol-corrected toluene dry matter (TDM); crude protein (CP: 149 to 211 g/kg TDM; lactic acid: 3·5 to 134·7 g/kg TDM; butyric acid 0·4 to 46·7 g/kg TDM) were offered ad libitum to early-lactation dairy cows (12 per experiment) along with a fixed allocation of 7 kg/day of a standard concentrate. Four silages were offered in each of four incomplete change-over design experiments with three 21-day periods. This design meant that each cow was allocated to receive three of the four silages evaluated in that experiment. ME intake ranged from 108 to 262 MJ/day (mean 177 (s.d. 30·2)). Similar variation was obtained with milk yields (mean 26·5 (s.d. 4·36) kg/day), fat content (mean 37·7 (s.d. 5·60) g/kg) and protein content (mean 29·0 (s.d. 2·36) g/kg). Urinary purine derivative/creatinine ratio (PD/C), an index of microbial protein measured in spot samples (two per day) averaged 2·92 (s.d. 0·757) mol/mol. Allantoin made up an almost constant molar proportion of PD excretion (mean 0·876 (s.d. 0·0377)), with a small but significant (P &lt; 0·001) decline of 0·0132 (s.d. 0·003) per unit increase in PD/C.Maximal utilization of silage nitrogen occurred with silages having higher ME and lower CP concentrations. Urinary PD/C suggested that microbial protein yield varied in a way which would not be predicted in current schemes and that it was a major source of variation in milk protein yield under the conditions of the present experiment. Principal components regression confirmed independent effects of ME supply and MP supply (indexed by urinary PD/C) on milk protein yield. Further work should pursue the possibility of using the urinary PD/C technique to refine protein feeding at the farm level.

Effects of sources of carbohydrate and protein given at low levels with grass silage ad libitum on the performance of lactating dairy cows

An effective strategy for milk production is to supplement silage with small amounts of high-protein concentrate based on mixed carbohydrate sources and fish and soyabean meals (Aston et al 1992). Recent work at Trawsgoed by Sargeant and McAllan (1993) using growing steers given high-digestibility grass silage supplemented with rapeseed meal (a source of highly rumen degradable protein) produced similar live-weight gains to those obtained with fish meal. Jacobs and McAllan (1992) concluded that microbial protein yield is greater when the more degradable protein source is given, indicating a better balance in the supply of nitrogen and energy nutrients within the rumen. Lactating cows given grass silage diets have a high requirement for Metabolisable Protein (MP). The source of rumen fermentable carbohydrate may be important when MP supply is derived from degradable dietary protein and hence microbial growth. This study therefore examined the effects of varying the sources of carbohydrate and protein in low levels of concentrate given with high-digestibility grass silage. The main effects observed in the milk production experiment are presented here.

Relationship between urinary purine derivative excretion and milk protein yield by dairy cows

The ability to predict microbial protein yield in any feeding situation is important in maximising the utilisation of feed nitrogen since it will guide decisions as to whether to take steps to improve rumen function or provide supplementary undegradable protein (UDP). The UK Metabolisable Protein (MP) system (Agricultural and Food Research Council, 1992) predicts the yield of microbial protein from the rumen according to the supply of Fermentable Metabolisable Energy (FME). This has led to an improved understanding of responses seen on farms, though there remains uncertainty about microbial protein yield. The excretion of purine derivatives (PD), allantoin and uric acid, in urine has been used as a non-invasive index of microbial protein flow to the duodenum (Chen et al, 1990) and might form the basis of an on-farm diagnostic test. In earlier work, with spot sampling of urine (Dewhurst et al, 1994), we have shown a relationship between milk protein yield and urinary PD excretion; the current work extended these studies by utilising 6-day total collections of urine.

Effects of sources of carbohydrate and protein given at low levels with grass silage ad libitum on the performance of lactating dairy cows

An effective strategy for milk production is to supplement silage with small amounts of high-protein concentrate based on mixed carbohydrate sources and fish and soyabean meals (Aston et al 1992). Recent work at Trawsgoed by Sargeant and McAllan (1993) using growing steers given high-digestibility grass silage supplemented with rapeseed meal (a source of highly rumen degradable protein) produced similar live-weight gains to those obtained with fish meal. Jacobs and McAllan (1992) concluded that microbial protein yield is greater when the more degradable protein source is given, indicating a better balance in the supply of nitrogen and energy nutrients within the rumen. Lactating cows given grass silage diets have a high requirement for Metabolisable Protein (MP). The source of rumen fermentable carbohydrate may be important when MP supply is derived from degradable dietary protein and hence microbial growth. This study therefore examined the effects of varying the sources of carbohydrate and protein in low levels of concentrate given with high-digestibility grass silage. The main effects observed in the milk production experiment are presented here.

Relationship between urinary purine derivative excretion and milk protein yield by dairy cows

The ability to predict microbial protein yield in any feeding situation is important in maximising the utilisation of feed nitrogen since it will guide decisions as to whether to take steps to improve rumen function or provide supplementary undegradable protein (UDP). The UK Metabolisable Protein (MP) system (Agricultural and Food Research Council, 1992) predicts the yield of microbial protein from the rumen according to the supply of Fermentable Metabolisable Energy (FME). This has led to an improved understanding of responses seen on farms, though there remains uncertainty about microbial protein yield. The excretion of purine derivatives (PD), allantoin and uric acid, in urine has been used as a non-invasive index of microbial protein flow to the duodenum (Chen et al, 1990) and might form the basis of an on-farm diagnostic test. In earlier work, with spot sampling of urine (Dewhurst et al, 1994), we have shown a relationship between milk protein yield and urinary PD excretion; the current work extended these studies by utilising 6-day total collections of urine.

Effects of calcium salts of long-chain fatty acids on ruminal digestibility, microbial protein yield and lactation performance

Effects of calcium salts of long-chain fatty acids on ruminal digestibility, microbial protein yield and lactation performance

Diurnal variation in urinary purine derivative excretion of dairy cows on different feeding patterns

Diurnal variation in the yield of microbial protein from the rumen may limit the use of urinary purine derivatives (PD) to estimate microbial protein yield from the rumen when assessed using spot samples. Chen, Grubic, Ørskov and Osuji (1992) found only small differences in the urinary PD excretion in young steers, and even less variation when PD excretion was estimated as a ratio to urinary creatinine. Lactating dairy cows have a much higher feed intake than steers and as a consequence may exhibit greater diurnal variation in urinary PD excretion. An examination of data from three experiments was undertaken to assess the effects of diurnal variation in rumen microbial protein yield on urinary PD excretion.

The fermentable metabolisable energy in grass silage

The UK metabolisable protein system (AFRC, 1992) requires the measurement of fermentable metabolisable energy (FME) to determine the potential yield of microbial crude protein in the rumen. FME is defined as:The objective of this work was to measure the ME , ether extract and volatile fatty acid components of first cut grass silages to assess the range of FME and non-fermentable fractions and hence the range of fermentabilities (FME:ME).Eighty-four clamp grass silages, predominantly first-cut rye grass, were analysed for modified acid detergent fibre (MADF), individual volatile fatty acids, oil (ether extract) and oven dry matter. ME was predicted from the MADF after correction for oven dry matter. The gross energy of the lactic, acetic, propanoic, butyric and valeric acid were taken to be 15.2, 14.6, 20.8, 24.9, and 28.0 MJ/kg DM, and for the Ether Extract fraction of grass 38.5 MJ/kg DM. The energy content of the volatile fatty acids in the silage were summed and FME was calculated as described above. The fermentability of the silage was the expressed as the proportion of FME to ME.