P. Huhtanen

Effect of dietary fish oil on biohydrogenation of fatty acids and milk fatty acid content in cows

Mechanisms underlying milk fat conjugated linoleic acid (CLA) responses to supplements of fish oil were investigated using five lactating cows each fitted with a rumen cannula in a simple experiment consisting of two consecutive 14-day experimental periods. During the first period cows were offered 18 kg dry matter (DM) per day of a basal (B) diet formulated from grass silage and a cereal based-concentrate (0·6 : 0·4; forage : concentrate ratio, on a DM basis) followed by the same diet supplemented with 250 g fish oil per day (FO) in the second period. The flow of non-esterified fatty acids leaving the rumen was measured using the omasal sampling technique in combination with a triple indigestible marker method based on Li-Co-EDTA, Yb-acetate and Cr-mordanted straw. Fish oil decreased DM intake and milk yield, but had no effect on milk constituent content. Milk fat trans-11 C 18:1 , total trans-C 18 : 1 , cis-9 trans-11 CLA, total CLA, C 18 : 2 (n-6) and total C 18 : 2 content were increased in response to fish oil from 1·80, 4·51, 0·39, 0·56, 0·90 and 1·41 to 9·39, 14·39, 1·66, 1·85, 1·25 and 4·00 g/100 g total fatty acids, respectively. Increases in the cis-9, trans-11 isomer accounted for proportionately 0·89 of the CLA response to fish oil. Furthermore, fish oil decreased the flow of C 18 : 0 (283 and 47 g/day for B and FO, respectively) and increased that of trans-C 18 : 1 fatty acids entering the omasal canal (38 and 182 g/day). Omasal flows of trans-C 18 : 1 acids with double bonds in positions from delta-4 to -15 inclusive were enhanced, but the effects were isomer dependent and primarily associated with an increase in trans-11 C18 : 1 leaving the rumen (17·1 and 121·1 g/day for B and FO, respectively). Fish oil had no effect on total (4·36 and 3·50 g/day) or cis-9, trans-11 CLA (2·86 and 2·08 g/day) entering the omasal canal. Flows of cis-9, trans-11 CLA were lower than the secretion of this isomer in milk. Comparison with the transfer of the trans-9, trans-11 isomer synthesized in the rumen suggested that proportionately 0·66 and 0·97 of cis-9, trans-11 CLA was derived from endogenous conversion of trans-11 C 18 : 1 in the mammary gland for B and FO, respectively. It is concluded that fish oil enhances milk fat cis-9, trans-11 CLA content in response to increased supply of trans-11 C 18:1 that arises from an inhibition of trans-C 18 : 1 reduction in the rumen.

The use of internal markers to predict total digestibility and duodenal flow of nutrients in cattle given six different diets

Six ruminally and duodenally cannulated cattle were used in a 6 × 6 Latin square experiment with a 2 × 3 factorial arrangement of treatments. The cattle were fed diets based on silage or dried grass cut simultaneously from the same sward, each fed with 250, 500 or 750 g concentrate dry matter (DM) kg−1 total DM. The feed components investigated as potential markers to determine total DM digestibility (DMD) were acid insoluble ash (AIA) and acid detergent lignin (ADL), indigestible DM (IDM41), neutral detergent fibre (INDF41) and acid detergent fibre (IADF41) determined by a 288 h ruminal incubation in nylon bags with a pore size of 41 μm, and corresponding indigestible fractions determined by using bags with a pore size of 6 μm were IDM6, INDF6 and IADF6. INDF and IADF were also determined by a 96 h in vitro incubation in rumen fluid (IVINDF, IVIADF). If the criterion of an ideal marker is to predict the digestibility and the differences between the diets, none of the markers met this criterion. Of the markers evaluated, the most suitable was AIA, followed by INDF6, INDF41 and IADF41. ADL was the least acceptable marker. n nThree double-marker systems were used to calculate duodenal flows of organic matter (OM), non-ammonia N (NAN), microbial N and NDF. Cr-mordanted straw, INDF41 and IADF41 were used as particulate markers in conjunction with Co-EDTA as a liquid phase marker. Duodenal OM flows were also estimated using a single-marker system. Double-marker systems reduced variability in duodenal OM flow estimates compared with single-marker systems. The choice of the particulate marker affected (P < 0.001) duodenal flow estimates but there were no indications of marker × diet interactions. Neither was the statistical significance of dietary effects changed. When compared with the values obtained with Cr as a particulate marker, INDF estimated a greater relative increase in NDF flow (0.143) than in OM (0.062) or NAN flow (0.018). This suggests that there may be differences in the distribution of solid phase markers in various particle size fractions. In such cases, if the digesta sample contains different proportions of large and small particles compared with the true digesta, then a double-marker system may not be sufficient to correct unrepresentativeness of digesta sampled from a simple T-shaped cannula.

A meta-analysis of the effects of dietary protein concentration and degradability on milk protein yield and milk N efficiency in dairy cows

Data sets from North American (NA, 739 diets) and North European (NE, 998 diets) feeding trials with dairy cows were evaluated to investigate the effects of dietary crude protein (CP) intake and ruminal degradability on milk protein yield (MPY) and efficiency of N utilization for milk protein synthesis (MNE; milk N / N intake) in dairy cows. The NA diets were based on corn silage, alfalfa silage and hay, corn and barley grains, and soybean meal. The NE diets were based on grass silage, barley and oats grains, and soybean and rapeseed meals. Diets were evaluated for rumen-degradable and undegradable protein (RDP and RUP, respectively) concentrations according to NRC (2001). A mixed model regression analysis with random study effect was used to evaluate relationships between dietary CP concentration and degradability and MPY and MNE. In both data sets, CP intake alone predicted MPY reasonably well. Addition of CP degradability to the models slightly improved prediction. Models based on metabolizable protein (MP) intake predicted MPY better than the CP or the CP-CP degradability models. The best prediction models were based on total digestible nutrients (TDN) and CP intakes. Similar to the MPY models, inclusion of CP degradability in the CP (intake or concentration) models only slightly improved prediction of MNE in both data sets. Concentration of dietary CP was a better predictor of MNE than CP intake. Compared with the CP models, prediction of MNE was improved by inclusion of TDN intake or concentration. Milk yield alone was a poor predictor of MNE. The models developed from one data set were validated using the other data set. The MNE models based on TDN and CP intake performed well as indicated by small mean and slope bias. This meta-analysis demonstrated that CP concentration is the most important dietary factor influencing MNE. Ruminal CP degradability as predicted by NRC (2001) does not appear to be a significant factor in predicting MPY or MNE. Data also indicated that increasing milk yield will increase MNE provided that dietary CP concentration is not increased, but the effect is considerably smaller than the effect of reducing CP intake.

Evaluation of the factors affecting silage intake of dairy cows: a revision of the relative silage dry-matter intake index

An evaluation of the factors affecting silage dry-matter intake (SDMI) of dairy cows was conducted based on dietary treatment means. The data were divided into six subsets based on the silage treatments used in the experiments: concentration of digestible organic matter in dry matter (D-value) influenced by the maturity of grass ensiled (nxa0=xa081), fermentation quality influenced by silage additives (nxa0=xa0240), dry matter (DM) concentration influenced by wilting of grass prior to ensiling (W; nxa0=xa085), comparison of silages made from primary growth or regrowth of grass (nxa0=xa046), and replacement of grass silage with legume (L; nxa0=xa053) or fermented whole-crop cereal (WC; nxa0=xa037) silages. The data were subjected to the mixed model regression analysis. Both silage D-value and fermentation quality significantly affected SDMI. The average effects of D-value and total acid (TA) concentration were 17.0xa0g and -xa012.8 per 1xa0g/kg DM, respectively. At a given D-value, silage neutral-detergent fibre (NDF) concentration tended to decrease SDMI. Silage TA concentration was the best fermentation parameter predicting SDMI. Adding other parameters into the multivariate models did not improve the fit and the slopes of the other parameters remained insignificant. Total NDF intake was curvilinearly related to silage D-value the maximum intake being reached at a D-value of 640xa0g/kg DM. Results imply that physical fill is not limiting SDMI of highly digestible grass silages and that both physical and metabolic factors constrain total DM intake in an interactive manner. Silage DM concentration had an independent curvilinear effect on SDMI. Replacing primary growth silage with regrowth, L or WC silages affected SDMI significantly, the response to regrowth silage being linearly decreasing and to L and WC quadratically increasing. The outcome of factors affecting SDMI was used to update the relative SDMI index as follows: SDMI indexxa0=xa0100+10xa0×xa0[(D-valuexa0-xa0680)xa0×xa00.0170xa0-xa0(TAxa0-xa080)xa0×xa00.0128+(0.0198xa0×xa0 (DMxa0-xa0250)xa0-xa00.00002364xa0×xa0(DM2 -xa0250xa02)) -xa00.44xa0×xa0a+4.13xa0×xa0bxa0-xa02.58xa0×xa0b2+5.90xa0×xa0cxa0-xa06.14xa0×xa0c2 -xa00.0023xa0×xa0(550xa0-xa0NDF)], where a, b and c represent the proportions (0-1) of regrowth, L or WC silages from total silage DM. For the whole data set, one index unit corresponded to the default value of 0.10xa0kg in SDMI. The SDMI index explained proportionally 0.852 of the variation in SDMI with 0.34xa0kg DM per day residual. The updated SDMI index provides improved basis for the practical dairy cow ration formulation and economic evaluation.

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).

Comparison of methods, markers, sampling sites and models for estimating digesta passage kinetics in cattle fed at two levels of intake

Abstract Six ruminally and duodenally cannulated Friesian bulls were used in a switch-back experiment to compare passage models, markers and sampling sites, and duodenal or faecal marker excretion curves and rumen evacuation technique for estimating kinetics of digesta passage. Cr-mordanted and Yb-labelled hay were used as particulate markers and CoEDTA as a liquid-phase marker. The cattle were fed on a dry matter (DM) basis (g kg −1 ) a diet of hay (600), barley (396) and urea (4) at either low or high DM intake (40 and 80 g DM (kg 0.75 live weight) −1 ). Post-duodenal digesta kinetics were estimated by administering the markers (CoEDTA, Cr-mordanted and Yb-labelled duodenal digesta particles) into the duodenum and collecting faecal samples. Digesta kinetic parameters were calculated by linear regression of natural log transformed marker concentrations in ruminal fluid, duodenal digesta or faeces, and by non-linear models with either two age-independent compartments (G1G1) or gamma time dependency in the first compartment (GnG1, n = 2–4). Using the models with gamma age dependency improved the curve fitting which suggested an age-dependent flow. In most cases the error mean squares were smallest with the G3G1 model. Total compartmental retention time (CMRT), transit time (TT) and total mean retention time (TMRT) of the markers decreased as DM intake increased. Regardless of marker, sampling site or model, the relative differences in digesta kinetics between the diets kinetics were similar. Shorter post-duodenal retention time of markers at high compared to low DM intake resulted from both shorter CMRT and TT. Similar post-duodenal kinetics of Co, Cr and Yb indicate that there was no differential passage of liquid and solid digesta in the caecum and proximal colon. Average CMRT was shorter for Yb than for Cr when derived either from duodenal (57.4 vs. 66.8 h) or faecal sampling (61.1 vs. 73.5 h). Faecal sampling resulted in 3.7 h (Yb) and 6.6 h (Cr) longer CMRT than duodenal sampling. Post-duodenal CMRT was only 0.223 (Yb) and 0.146 (Cr) of the retention time in the fast age-dependent compartment derived from faecal sampling. This suggests that preduodenal sites accounted for the major proportion of the retention time in this compartment. The passage rate estimates derived from rumen evacuation were much slower than those calculated from the exponential decline in duodenal and faecal Cr and Yb concentrations, mainly because rumen evacuation derived passage rate includes the retention time in both ruminal compartments. However, when a simple first-order passage rate was calculated from the passage rate from the two ruminal compartments and rate of neutral detergent fibre (NDF) digestion, the values for indigestible NDF, NDF and digestible NDF obtained from the two methods were fairly similar; rumen evacuation: 0.0165, 0.0126 and 0.0095 h −1 ; Cr: 0.0159, 0.0111 and 0.0085 h −1 ; Yb: 0.0179, 0.0123 and 0.0099 h −1 .

The effects of barley, unmolassed sugar-beet pulp and molasses supplements on organic matter, nitrogen and fibre digestion in the rumen of cattle given a silage diet

In a 4 × 4 Latin-square experiment with a 2 × 2 factorial arrangement of treatments, 4 cattle fitted with a rumen and duodenal cannula were given four grass-containing diets [480 g kg−1 of the total dry matter (DM) intake] and barley (BU), barley + molasses (2:1) (BM), sugar-beet pulp (SU) or sugar-beet pulp + molasses (SM). Duodenal flow was estimated using Cr-mordanted straw and CoEDTA as markers, and microbial nitrogen entering the small intestine using purine bases of nucleic acids. n nMolasses-containing diets had a higher (P < 0.01) organic matter (OM) digestibility. The proportion of digestible OM apparently disappearing in the rumen averaged 0.72 and was not significantly affected by the diet. When cattle received molasses, the quantity of microbial N entering the small intestine was higher (P < 0.05) and there was a trend towards a higher efficiency of microbial N synthesis (28.8 vs. 25.6 g N kg−1 OM apparently digested in the rumen). When S diets were consumed, total non-ammonia N flow at the duodenum exceeded N intake by 7.0 g day−1 and when B diets were consumed, it was 0.7 g day−1 less than N intake. Feed N degradability in the rumen and apparent N digestibility of S diets were lower (P < 0.05; P < 0.001) than those of B diets. n nRumen (P < 0.05) and total (P < 0.001) digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) was higher when S diets were given. The proportion of digestible fibre disappearing in the rumen was not affected by the diet. The rate and extent of silage and hay DM degradation were not significantly affected by the diet. However, dietary inclusion of molasses decreased (P < 0.05) the lag time of both hay and silage DM degradation. n nThe rumen dilution rate of liquid averaged 0.097 and that of particles, 0.049; neither was significantly different for either B and S diets or U and M diets. Duodenal liquid flow was higher (P < 0.05) for M diets. n nAverage rumen pH was not affected by the diet, but the molasses diets increased (P < 0.05) the range in rumen pH. The BM diet was associated with higher (P < 0.01) rumen ammonia concentration than the other diets. Low rumen ammonia concentrations (< 2 mM) were observed for long periods between feeds. The molar proportion of butyrate was higher on B diets and there was a trend towards a higher proportion of acetate and propionate on S diets. Molasses tended to increase the molar proportion of propionate and butyrate.

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. n nOrganic 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 nN 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.

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.