Marketta Rinne

Recent developments in forage evaluation with special reference to practical applications

Systemaattisesti keratyn sailorehuaineiston perusteella tehty yhteenveto osoittaa selvasti ns. virallisen rehuanalyysineli Weenden analyysin biologiset puutteet rehujen ravitsemuksellisen laadun kuvaajana. Analyysi ei kuvaa rehun kemiallisen koostumuksen ja sulavuuden valisia syy-seuraussuhteita. Lisaksi tilastolliset yhteydet vaihtelevat huomattavasti eri kasvimateriaaleilla ja ymparistoolosuhteissa. Weenden analyysin kayttoa ei siis voi suositella karkea- eika vakirehujen laadun kuvaamiseen. In vitro pepsiini-sellulaasiliukoisuus (OMS) ja sulamattoman kuidun (iNDF) pitoisuus sen sijaan ennustivat karkearehujen orgaanisen aineen sulavuuden riittavan tarkasti kaytannon ruokinnansuunnittelua varten, edellyttaen etta analyysitulokset muunnettiin sulavuudeksi rehutyyppikohtaisia korjausyhtaloita kayttaen eli erikseen ensimmaisesta sadosta ja jalkikasvusta tehdyille nurmisailorehuille, palkokasvisailorehuille ja kokoviljasailorehuille. Detergenttikuituanalyysi, joka jakaa rehun kuiva-aineen liukoiseen ja lahes taysin kayttokelpoiseen solunsisallykseen (NDS) seka liukenemattomaan kuituun (NDF), on Weenden analyysia huomattavasti kehityskelpoisempi vaihtoehto. Kun kuituanalyysiin yhdistetaan pitka in situ potsi-inkubaatio, rehun kuiva-aine saadaan jaettua kolmeen biologisesti mielekkaaseen osaan: NDS, potentiaalisesti sulava kuitu (pdNDF) ja iNDF. Rehun D-arvo eli sulavan orgaanisen aineen pitoisuus kuiva-aineessa voidaan ennustaa ns. summatiivisella yhtalolla. Yhtalossa lasketaan yhteen sulanut NDS, joka voidaan maarittaa Lucasin yhtalolla, ja sulanut kuitu (pdNDF-pitoisuus × pdNDF:n sulavuus tai vaihtoehtoisesti NDF-pitoisuus × NDF:n sulavuus). Rehutyyppikohtaiset summatiiviset yhtalot ennustivat karkearehujen D-arvon lahes yhta hyvin kuin OMS ja iNDF. Kun koko aineistoa tarkasteltiin yhdessa, summatiiviset yhtalot olivat parempia kuin iNDF ja erityisesti OMS. Jos D-arvon ennustevirhe halutaan saada pienemmaksi kuin 15 g/kg kuiva-ainetta, on kaytettava rehutyyppikohtaisia yhtaloita riippumatta siita, onko laskennan perusteena OMS, iNDF tai summatiivinen yhtalo. Toinen vaihtoehto tulevaisuudessa on dynaamisten mallien kaytto. Ne pystyvat samanaikaisesti huomioimaan kaksi tarkeaa dynaamista prosessia, jotka rajoittavat rehun sulatusta potsissa eli kuidun virtaus- ja sulatusnopeuden. Dynaamisten mallien kaytto edellyttaa kuitenkin sita, etta rehuista voidaan helposti ja luotettavasti maarittaa iNDF-pitoisuus ja kuidun sulatusnopeus. Maatilarehujen iNDF-maaritys NIRS-menetelmalla toteutuu Suomessa lahiaikoina, mutta kuidun sulatusnopeuden maaritys vaatii viela lisatyota.

Prediction of the relative intake potential of grass silage by dairy cows

Data based on the mean treatment values from production studies in lactating dairy cows were used to estimate relationships between silage composition and silage dry matter intake (SDMI). Data from 21 studies were used to estimate relationships between D-value (g digestible organic matter in kg dry matter (DM)) and crude protein (CP) content, and SDMI. The silages were harvested at different maturities but using the same ensiling techniques within the study. Relationships between silage fermentation characteristics and SDMI were estimated using data from 47 studies. The silages were harvested at the same time from the same sward but using various additives. When factorial designs were used, silage data within each treatment (subexperiment) were recorded separately. The data sets included 125 D-value and 234 fermentation observations. Relationships between SDMI and silage parameters were analyzed using mixed model regression analyses with experiment as a fixed factor and subexperiment within experiment as a random factor. The ranges for silage CP concentration and D-value were 111 to 238 (S.D. 25.2) and 589 to 756 (S.D. 48.5) g/kg DM, respectively. D-value was a much better predictor of SDMI than CP (R2 within experiment 0.71 vs. 0.26). The effect of D-value on SDMI diminished with increasing level of concentrate supplementation (interaction P<0.001). D-value had a greater effect on SDMI when the total DM intake was high. SDMI was negatively correlated with concentrations of ammonia N, lactic acid, individual and total volatile fatty acids and total fermentation acids and positively correlated to the concentration of residual water soluble carbohydrates. Total acid concentration was the best SDMI predictor of individual fermentation parameters (R2 within experiment 0.41) followed by lactic acid and ammonia N. Use of quadratic regressions generally increased the variation accounted for by the model. The best multiple regression accounted for 0.51 of the variation in SDMI within experiment. To facilitate interpretation of data, a theoretical model is presented. An interplay between physical load and capacity to use energy determines SDMI of well-fermented silages over the whole range of D-values. With increasing extent of fermentation SDMI is constrained by nutrient imbalance, most probably amino acid to energy ratio at the tissue level, resulting from reduced microbial protein synthesis in the rumen. Low palatability can further constrain silage DM intake. For advisory silage evaluation the following model predicting relative SDMI is proposed: SDMI index=100+0.151×(D-value−690)−0.000531×(TA2−6400)−4.7650 [Ln(Ammonia N) −Ln(50)], where D-value and total acids (TA) are expressed as g/kg DM and ammonia N as g/kg total N, respectively. Regression coefficients are scaled to a mean SDMI of 10 kg DM/day. The values of 690, 80 and 50 are used as standard D-value (g/kg DM), total acid (g/kg DM) and ammonia N (g/kg N) for high quality restrictively fermented silages. The model parameters were limited to those which are currently available for Finnish farm silage analyses, i.e., by near infra-red reflectance spectra (D-value) and electrometric titration (fermentation parameters).

Grass maturity effects on cattle fed silage-based diets. 1. Organic matter digestion, rumen fermentation and nitrogen utilization

Four silages were harvested at approximately one-week intervals from the same timothymeadow fescue sward. Advanced maturity of the herbage was evidenced by increased neutral detergent fibre [409, 497, 579 and 623 g in 1 kg dry matter (DM)] and decreased nitrogen (N; 29.9, using four ruminally and duodenally cannulated young cattle in a 4 × 4 Latin square experiment. On DM basis (g kg−1), the diet comprised grass silage (700), rolled barley (240) and rapeseed meal (60) and it was given at a rate of 70 g DM (kg live weight)−0.75 per day. Organic matter digestibility decreased in a curvilinear manner (PLINEAR (L) < 0.001, PCUBIC (C) < 0.01) the values being 0.821, 0.816, 0.758 and 0.747 for the diets based on the four silages in the order of harvest date. Rumen pH increased linearly (PL < 0.05) and ammonia N concentration decreased curvilinearly (PL < 0.01, PC < 0.05) as the grass matured. The molar proportion of acetate in the rumen VFA increased (PL < 0.001) and the proportion of butyrate decreased (PL < 0.001) with increased grass maturity. The silage harvest date did not affect the proportion of propionate. The changes in rumen fermentation pattern were associated with a decrease (PL < 0.05) in rumen protozoal number with increasing maturity of grass. N intake decreased significantly (PL < 0.001, PC < 0.01) with the maturity of grass from 167.5 to 118.0 g per day, but duodenal non-ammonia N decreased only from 111.3 to 97.3 g per day indicating greater N losses from the rumen with early-cut silages. The efficiency of microbial protein synthesis in the rumen was not affected by the maturity of grass ensiled. Apparent digestibility of N decreased (PL < 0.001, PC < 0.01) and the degradability of N in the rumen decreased (PL < 0.05) as the grass matured.

Prediction of the digestibility of the primary growth of grass silages harvested at different stages of maturity from chemical composition and pepsin-cellulase solubility

Abstract Relationships between silage chemical components or organic matter (OM) pepsin-cellulase solubility and in vivo organic matter digestibility (OMD) and D -value (digestible OM content in dry matter) were studied. Twenty-five silages were made from primary growth timothy-meadow fescue swards in 6 years (3–6 silages per year) at 6–10 days intervals. The silages were analyzed for chemical composition, in vitro pepsin-cellulase solubility and in vivo digestibility in sheep. Chemical components of silage were highly correlated with OMD and D -value, but the accuracy of the OMD and D -value prediction equations were not satisfactory for ration formulation. Acid detergent fibre was the best single predictor of chemical parameters explaining 0.80 of the variation in OMD (residual mean square error (RMSE) 27.2gkg −1 ). Relationships between crude protein (CP) and lignin were improved, when the effects of year or year × component interaction were included in the model. For CP the intercepts and for lignin the slopes, were different between the years. Pepsin-cellulase solubility was superior to chemical parameters in predicting silage OMD and D -value. The monovariate regression equation between OM solubility and OMD was: OMD (gkg−1)=97+0.87×OM solubility ( R 2 =0.974; RMSE=10.8gkg −1 ). Prediction of D -value was improved by including ash as a second factor in bivariate regression analysis: D -value (gDOM(kgDM)−1)=160+0.818×OM solubility −1.09×ash ( R 2 =0.974; RMSE=9.7gkg −1 ). It was concluded that OM pepsin-cellulase solubility has great potential in predicting silage OMD and D -value both precisely and accurately.

A meta-analysis of feed digestion in dairy cows. 2. The effects of feeding level and diet composition on digestibility.

A meta-analysis based on published experiments with lactating dairy cows fed mainly grass silage-based diets was conducted to study the effects of intake, diet composition, and digestibility at a maintenance level of feeding on the apparent total diet digestibility. A data set that included a total of 497 dietary treatment means from 92 studies was collected and analyzed using mixed model regression analysis with a random study effect. Diet organic matter digestibility (OMD) in dairy cows at a production level (OMD(p)) was positively associated with OMD at maintenance (OMD(m)), but the slope was less than 1 (0.69). Diet OMD(p) decreased as feed intake increased, and diets with high OMD(m) exhibited greater depressions in digestibility with increased intake than did diets with low OMD(m). Digestibility of organic matter and neutral detergent fiber (NDF) increased as dietary crude protein concentration increased, whereas increased concentrate fat decreased digestibility. Replacement of grass silage with whole-crop cereal silage was associated with a quadratic decrease in diet digestibility. Metabolic fecal output, defined as fecal organic matter minus NDF, averaged 95.8 (SE = 0.65) g/kg of dry matter intake, and it was not influenced by intake or diet composition. Variation in OMD(p) in cows fed grass silage-based diets was therefore attributable to variation in dietary NDF concentration and NDF digestibility. Depression in digestibility of organic matter with increased intake was less than predicted by the National Research Council and Cornell Net Carbohydrate and Protein systems. The following 2-parameter model indicates that the difference between OMD estimated in sheep fed at maintenance compared with dairy cows at production level is related both to dry matter intake and digestibility at maintenance level: OMD(p) = 257 (+/-43) + 0.685 (+/-0.054) x OMD(m) (g/kg of dry matter) - 2.6 (+/-0.44) x dry matter intake (kg/d); adjusted residual mean square error = 8.4 g/kg. It was concluded that diet digestibility in dairy cows can be predicted accurately and precisely from digestibility estimated at maintenance intake in sheep by using regression models including animal and dietary factors.

A meta-analysis of feed digestion in dairy cows. 1. The effects of forage and concentrate factors on total diet digestibility.

A meta-analysis based on published experiments with lactating dairy cows was conducted to study the effects of dietary forage and concentrate factors on apparent total diet digestibility. A data set was collected that included a total of 497 dietary treatment means from 92 studies. The diets were based on grass silage or on legume or whole-crop cereal silages partly or completely substituted for grass silage. The silages were supplemented with concentrates given at a flat rate within a dietary comparison. For the statistical evaluation, the data were divided into 5 subsets to quantify silage (digestibility, 42 diets in 17 studies; fermentation characteristics, 108 diets in 39 studies) and concentrate (amount of supplementation, 142 diets in 59 studies; concentration of crude protein, 215 diets in 82 studies; carbohydrate composition, 66 diets in 23 studies) factors on total diet digestibility. The diet digestibility of dairy cows was determined by total fecal collection or by using acid-insoluble ash as an internal marker. Diet organic matter digestibility (OMD) at a maintenance level of feeding (OMD(m)) was estimated using sheep in vivo or corresponding in vitro digestibility values for the forage and reported ingredient and chemical composition values, with tabulated digestibility coefficients for the concentrate components of the diet. A mixed model regression analysis was used to detect the responses of different dietary factors on apparent total diet digestibility. Improved silage OMD(m) resulting from earlier harvest was translated into improved production-level OMD in cows (OMD(p)). The effects of silage fermentation characteristics on OMD(p) were quantitatively small, although sometimes significant. Concentrate supplementation improved total diet OMD(m), but this was not realized in lactating dairy cows because of linearly decreased neutral detergent fiber (NDF) digestibility as concentrate intake increased. Increasing the concentrate crude protein amount quadratically improved OMD(p) in cows, with the response being mostly due to improved NDF digestibility. Replacement of starchy concentrates with fibrous by-products slightly decreased OMD(p) but tended to improve NDF digestibility. The true digestibility of cell solubles (OM - NDF) estimated by the Lucas test both from all data and from the data subsets was not significantly different from 1.00, suggesting that responses in OMD(p) of dairy cows are mediated through changes in the concentration and digestibility of NDF.

Utilization and partition of dietary nitrogen in dairy cows fed grass silage-based diets.

Data from 207 production trials (998 treatment means) were used to study the effects of animal and dietary characteristics on the efficiency of N utilization for milk protein production, and on fecal N, urinary N, and total manure N output. The average efficiency of transferring dietary N to milk N (MNE; milk N/N intake) was 277 (SD = 36.0) g/kg. Nitrogen efficiency was poorly related to milk yield. Dietary concentrations of crude protein (CP) and protein balance in the rumen (PBV) were the best single predictors of MNE. Dietary CP concentration explained variation in MNE better than did N intake. Bivariate models with PBV or metabolizable protein (MP) explained the variation better than CP alone. The effects of protein feeding parameters on MNE were consistent among data subsets from studies investigating the effects of the amount and protein concentration of concentrate supplement, silage digestibility, silage fermentation quality, or substitution of grass silage with legume silage. The model with total dry matter and N intakes as independent variables explained fecal, urinary, and total manure N output more precisely than N intake alone. The model of fecal N output suggested that the true digestibility of dietary N was 0.91, and that metabolic and endogenous N was the major component in fecal N. The proportion of urine N in manure N was strongly related to dietary CP concentration. Including the concentration of dietary carbohydrates only slightly improved the models, indicating that the most effective strategy to improve MNE and to decrease N losses in manure, especially in urine, is to avoid feeding diets with excessively high CP concentration and especially excess ruminally degradable CP.

Effects of feeding grass or red clover silage cut at two maturity stages in dairy cows. 1. Nitrogen metabolism and supply of amino acids.

This study investigated the effects of plant species (red clover vs. timothy-meadow fescue) and forage maturity at primary harvest (early vs. late cut silage) on rumen fermentation, nutrient digestion, and nitrogen metabolism including omasal canal AA flow and plasma AA concentration in lactating cows. Five dairy cows equipped with rumen cannulas were used in a study designed as a 5 x 5 Latin square with 21-d periods. The diets consisted of early-cut and late-cut grass and red clover silage, respectively, and a mixture of late-cut grass and early-cut red clover silages given ad libitum with 9 kg/d of a standard concentrate. Grass silage dry matter intake tended to decrease but that of red clover silages tended to increase with advancing maturity. Milk yields were unchanged among treatments, milk protein and fat concentrations being lower for red clover than for grass silage diets. Rumen fluid pH was unchanged but volatile fatty acid and ammonia concentrations were higher for red clover than for grass silage diets. Intake of N, and omasal canal flows of total nonammonia N (NAN), microbial NAN, and dietary NAN were higher for red clover than for grass silage diets but were not affected by forage maturity. However, microbial NAN flow and amount of N excreted in the feces decreased with advancing maturity for grass diets but increased for red clover diets. Apparent ruminal N degradability of the diets was unchanged, but true ruminal N degradability decreased and efficiency of microbial synthesis increased with red clover diets compared with grass silage diets. Omasal canal flows of AA, except those for Met and Cys, were on average 20% higher for red clover than grass silage diets. Omasal canal digesta concentrations of Leu, Phe, branched-chain, and essential AA were higher but those of Met lower for red clover than for grass silage diets. Plasma AA concentrations, except for His (unchanged) and Met (lower), were higher for red clover than for grass diets. However, none of these AA-related variables were affected by forage maturity. Total digestibility of N and excretion of N in the urine were higher for red clover than for grass diets and decreased with advancing maturity. It was concluded that despite the higher total AA supply of cows fed red clover versus grass silage diets, further milk production responses on red clover diets were compromised by an inadequate supply of Met as evidenced by lower Met concentration in the AA profile of omasal digesta and plasma.

Grass maturity effects on cattle fed silage-based diets. 2. Cell wall digestibility, digestion and passage kinetics

Four silages were harvested at approximately 1-week intervals from the same timothy-meadow fescue sward and studied in a 4 × 4 Latin square experiment with four ruminally and duodenally cannulated young cattle. The diets comprised silage and concentrate (7:3 dry matter (DM) basis) and were fed at a rate of 70 g DM kg−0.75 liveweight in two equal meals per day. Neutral detergent fibre (NDF) digestibility was 0.757, 0.765, 0.692 and 0.686 on diets based on the four silages in order of harvest date. Increasing maturity of grass ensiled showed linear (PL < 0.001) and cubic (PC < 0.01) trends. NDF was separated into digestible (DNDF) and indigestible (INDF) fractions, which differed clearly in their rate of passage from the rumen (on average 0.0141 vs. 0.0258 h−1). The rate of digestion (kd) of DNDF was on average 0.076 h−1 when derived from the rumen evacuations but only 0.036 h−1 when calculated from the disappearance from nylon bags incubated in the rumen. Both methods detected decreased kd of NDF with increasing maturity of grass ensiled. Rate of passage from the rumen increased with increasing maturity of grass both when determined for NDF with rumen evacuation technique and from the faecal excretion of ytterbium calculated with a two-pool model. Mean retention time (MRT) in the non-escapable pool of particles increased (PL < 0.01) with increasing grass maturity, the opposite being true for the escapable pool (PL < 0.05), resulting in no change in the total ruminal MRT. Pool sizes of ruminal DM PL < 0.01) and NDF (PL < 0.001) increased with increasing maturity of grass. Ruminal NDF digestibility was calculated by different methods. When digestion kinetic parameters were derived from rumen evacuations and two-pool models used for passage kinetics, estimated digestibilities were very close to the observed ones.

Evaluation of concentrate factors affecting silage intake of dairy cows: a development of the relative total diet intake index

The aim of this work was to develop an index describing the relative intake of the total diet by dairy cows, and hence the ability to predict intake responses to changes in both forage and concentrate variables. An evaluation of concentrate factors affecting silage dry matter (DM) intake of dairy cows was conducted based on dietary treatment means from milk production experiments. The data were divided into four subsets according to concentrate treatments used within the experiments: the amount of concentrate supplementation (n = 217), protein supplementation (n = 336), carbohydrate composition (n = 114) and fat concentration of the concentrate (n = 29). The data were subjected to mixed-model regression analysis. Increased concentrate DM intake (CDMI) decreased silage DM intake (SDMI) quadratically. The substitution rate (substitution of silage DM for concentrate DM) increased with improved silage intake potential. SDMI increased quadratically with concentrate protein intake, the response being negatively related to the effective protein degradability (EPD) of concentrates. Replacement of starchy concentrate ingredients with fibrous supplements had a small positive effect on silage intake, whereas increased concentrate fat concentration slightly decreased SDMI. The outcome of concentrate factors influencing total DM intake (TDMI) was used to create a relative CDMI index as follows: CDMI index = 100 + 10 × [(CDMI - 0.1629 × CDMI - 0.01882 × CDMI2 - 5.49) + ((0.9474 × CCPI - 0.4965 × CCPI2) - 2.017 × (CEPD - 0.74)) + 0.00225 × (CNDF - 250) - 0.0103 × (40 - Cfat) - 0.00058 × (CDMI - 8.0) × (SDMI index - 100)], where CDMI = concentrate DM intake (kg/day), CCPI = supplementary concentrate CP intake (kg/day; CP>170 g/kg DM), CEPD = concentrate EPD (g/g), CNDF = concentrate NDF concentration (g/kg DM), Cfat = concentrate fat concentration (g/kg DM) and SDMI index is the relative intake potential of silage (Huhtanen, Rinne and Nousiainen 2007. Animal 1, 758-770). TDMI index was calculated as SDMI index + CDMI index - 100 to describe the relative intake potential of the total diet. For the whole data set (n = 943), one TDMI index unit was equivalent to 0.095 kg/day DM intake, i.e. close to the default value of 0.100 kg. The CDMI index explained proportionally 0.88 of the variation in TDMI within a study with a 0.27 kg/day residual mean-square error (n = 616). The corresponding values for the TDMI index were 0.81 and 0.37 kg/day (n = 943), respectively. The residual mean-square errors in cross-validation were marginally higher. The developed TDMI index can be used to estimate the intake responses to diet changes. It provides an improved basis for practical dairy cow ration formulation and economic evaluation.