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The objective of this study was using a wide range of dietary concentrate levels to investigate the major effects of limit-feeding on heifers. Twenty-four Holstein heifers were blocked into six groups and fed with one of four diets containing different levels of concentrate (20%, 40%, 60% and 80% on a dry matter (DM) basis) but with same intakes of metabolizable energy for 28 days. Increasing levels of dietary concentrate caused decreased (P ≤ 0.02) intakes of dry matter (DMI) and neutral detergent fiber and total rumination time, but increased (P < 0.01) nonfiberous carbohydrates intake, ruminal concentrations of NH 3 -N, propionate and butyrate, and digestibility of DM and crude protein. Dietary concentrate levels had no significant effect on most plasma concentrations and body measurements. The corrected average daily gain (CADG) and feed efficency (ADG/DMI, CFE) were linearly increased (P < 0.01) with increasing dietary concentrate levels when gut fill impact was removed. In conclusion, heifers limit-fed high concentrate diets increased most ruminal fermentation parameters, CADG and CFE with similar body growth and blood metabolites as heifers fed low concentrate diets, and had the potential to be used as an effective feeding strategy in dairy heifers., (© 2017 Japanese Society of Animal Science.)

Postpartum dairy cows can develop nutritional diarrhea when their diet is abruptly changed for milk production. However, it is unclear whether nutritional diarrhea develops as a result of gut acidosis and/or dysbiosis. This study aimed to uncover changes in the gastrointestinal microbiota and its fermentation parameters in response to nutritional diarrhea in postpartum dairy cows. Rumen and fecal samples were collected from twenty-four postpartum cows fed with the same diet but with different fecal scores: the low-fecal-score (LFS: diarrheic) group and high-fecal-score (HFS: non-diarrheic) group. A microbiota difference was only observed for fecal microbiota, with the relative abundance of Defluviitaleaceae_UCG-011 and Lachnospiraceae_UCG-001 tending (p < 0.10) to be higher in HFS cows compared to LFS cows, and Frisingicoccus were only detected in HFS cows. The fecal bacterial community in LFS cows had higher robustness (p < 0.05) compared to that in HFS cows, and also had lower negative cohesion (less competitive behaviors) and higher positive cohesion (more cooperative behaviors) (p < 0.05) compared that in to HFS cows. Lower total volatile fatty acids and higher ammonia nitrogen (p < 0.05) were observed in LFS cows' feces compared to HFS cows. The observed shift in fecal bacterial composition, community networks, and metabolites suggests that hindgut dysbiosis could be related to nutritional diarrhea in postpartum cows. [ABSTRACT FROM AUTHOR]

Rosemary extract (RE) is characterized as an antioxidant, and it has the potential to reduce methane emission and change microbial fermentation. Hence, to the extent of the evaluation of RE in ruminant nutrition, the in vitro fermentation technique was used to investigate the effects of RE on the fermentation characteristics of a total mixed ration (TMR) fed to dairy cows. Different doses of RE were added to the TMR to obtain different concentrations of antioxidants, including 0 (CON), 0.05 (LRE), and 0.10 g/kg (HRE). A total of 500 mg ground TMR was incubated in buffer solution and rumen fluid for 48 h at 39 °C. Nutrient degradability, gas production parameters, gas composition, fermentation parameters, and microbial composition were analyzed. The results showed that nutrient degradability and total volatile fatty acid concentration were not affected by the treatments. Furthermore, total methane production and proportion were depressed in a dose-dependent way. The RE increased the propionate concentration and proportion linearly and decreased the acetate concentration and proportion linearly. Finally, microbial diversity analysis showed that the richness and evenness indexes were unchanged by different treatments, while Prevotella_1 was decreased and Prevotella_7 was increased with RE supplementation. In conclusion, RE is an effective inhibitor of methane emission of microbial fermentation and changed the profile of volatile fatty acids with no disadvantageous effects on diet utilization. [ABSTRACT FROM AUTHOR]

Deoxynivalenol (DON) is a type B trichothecene mycotoxin produced by Fusarium fungi. To investigate its ruminal degradability and its effect on rumen fermentation, a 2 × 5 factorial experiment was conducted in vitro with two feed substrates with different forage levels (high forage (HF), forage-to-concentrate = 4:1; low forage (LF), forage-to-concentrate = 1:4) and five DON additions per substrate (0, 5, 10, 15, and 20 mg/kg of dry matter). After 48 h incubation, the DON degradability in the HF group was higher than in the LF group (p < 0.01), and it decreased along with the increase in DON concentrations (p < 0.01), which varied from 57.18% to 29.01% at 48 h. In addition, the gas production rate, total VFA production and microbial crude protein decreased linearly against the increase in DON additions (p < 0.05). Meanwhile, the proportion of CH4 in the fermentation gas end-products increased linearly, especially in the HF group (p < 0.01). In brief, rumen microorganisms presented 29–57% of the DON degradation ability and were particularly significant under a high-forage substrate. Along with the increasing DON addition, the toxin degradability decreased, showing a dose-dependent response. However, DON inhibited rumen fermentation and increased methane production when it exceeded 5 mg/kg of dry matter. [ABSTRACT FROM AUTHOR]

This study evaluated the effects of different dietary n-6/n-3 polyunsaturated fatty acid (PUFA) ratios on in vitro ruminant fermentation. Methane production, fatty acid composition, and microbial profiles were compared after the in vitro fermentation of rumen fluid collected from cows that had been fed isoenergetic and isoproteic experimental diets at three different n-6/n-3 ratios: 3.04 (HN6, high n-6 source), 2.03 (MN6, medium n-6 source), and 0.8 (LN6, low n-6 source). The fermented rumen fluid pH and total volatile fatty acid (VFA) levels were significantly decreased (p < 0.05) in the HN6 group as compared with those in the MN6 and LN6 groups. Additionally, the HN6 group produced a significantly lower (p < 0.05) proportion of methane than the MN6 group during in vitro fermentation. The MN6 and LN6 groups had significantly increased (p < 0.05) levels of C18:2n6 and C18:3n3 in the fermented rumen fluid, respectively, as compared with the HN6 group. The Chao 1 diversity index value was lower (p < 0.05) in the HN6 group than in the MN6 and LN6 groups. The observed species richness was significantly lower (p < 0.05) in the HN6 group than in the MN6 group. The reduced relative abundances of Lachnospiraceae UCG-006 and Selenomonas in the HN6 group resulted in lower pH and VFA levels (i.e., acetate, propionate, butyrate, and total VFA) during in vitro fermentation. Furthermore, n-6 and n-3 PUFAs were toxic to Butyrivibrio_2 growth, resulting in high levels of incomplete biohydrogenation. Taken together, the study findings suggest that supplementation of high-forage diets with high levels of n-6 PUFAs could reduce methane emissions, whereas both VFA concentration and pH are reduced. [ABSTRACT FROM AUTHOR]

Aims: This study aims to investigate the effect of hydroxy‐selenomethionine supplementation on the in vitro rumen fermentation characteristics and microorganisms of Holstein cows. Methods and Results: Five fermentation substrates, including control (without selenium supplementation, CON), sodium selenite supplementation (0.3 mg kg−1 DM, SS03), and hydroxy‐selenomethionine supplementation (0.3, 0.6 and 0.9 mg kg−1 DM, SM03, SM06 and SM09, respectively) were incubated with rumen fluid in vitro. The results showed that in vitro dry matter disappearance and gas production at 48 h was significantly higher in SM06 than SM03, SS03 and CON; propionate and total volatile fatty acid (VFA) production was higher in SM06 than CON. Moreover, higher species richness of rumen fluid was found in SM06 than others. Higher relative abundance of Prevotella and Prevotellaceae‐UCG‐003 and lower relative abundance of Ruminococcus‐1 were detected in SM06 than CON. Besides, higher relative abundance of Ruminococcaceae_UCG‐005 was found in CON than other treatments. Conclusions: It is observed that 0.6 mg kg−1 DM hydroxy‐selenomethionine supplementation could increase cumulative gas production, propionate, and total VFAs production by altering the relative abundance of Prevotella, Prevotellaceae‐UCG‐003, Ruminococcaceae_UCG‐005 and Ruminococcus‐1, so that it can be used as a rumen fermentation regulator in Holstein cows. Significance and Impact of the Study: This study provides an optimal addition ratio of hydroxy‐selenomethionine on rumen fermentation and bacterial composition via an in vitro test. [ABSTRACT FROM AUTHOR]

Simple Summary: The rumen microbiota plays an important role in maintaining microbiota homeostasis and promoting milk production synthesis through utilizing amino acids and non-protein nitrogen. Furthermore, various nitrogen sources have shown distinct effects on microbial growth rates. The methionine dipeptide (MD) is a bioactive peptide consisting of two methionine (Met) residues linked by a peptide bond. Although the role of MD in milk protein synthesis is established, little is known about its role in bacterial fermentation. The present study demonstrates that the various nitrogen sources could reshape microbiota differently, and MD could be more efficient than free Met in the rumen to support acetate producer growth. Our study provides some new insights into the relationship between ruminal microbiota of dairy cows and small peptides and points to potential strategies to effectively enhance the health condition and digestion ability of dairy cows. It is well known that the methionine dipeptide (MD) could enhance the dairy cows milking performance. However, there is still a knowledge gap of the effects of MD on the rumen fermentation characteristics, microbiota composition, and digestibility. This experiment was conducted to determine the effect of different nitrogen sources with a total mixed ration on in vitro nutrient digestibility, fermentation characteristics, and bacterial composition. The treatments included 5 mg urea (UR), 25.08 mg methionine (Met), 23.57 mg MD, and no additive (CON) in fermentation culture medium composed of buffer solution, filtrated Holstein dairy cow rumen fluid, and substrate (1 g total mixed ration). Nutrient digestibility was measured after 24 h and 48 h fermentation, and fermentation parameters and microbial composition were measured after 48 h fermentation. Digestibility of dry matter, crude protein, neutral detergent fiber (NDF), and acid detergent fiber (ADF) in the MD group at 48 h were significantly higher than in the CON and UR groups. The total volatile fatty acid concentration was higher in the MD group than in the other groups. In addition, 16S rRNA microbial sequencing results showed MD significantly improved the relative abundances of Succinivibrio, Anaerotruncus, and Treponema_2, whereas there was no significant difference between Met and UR groups. Spearman's correlation analysis showed the relative abundance of Succinivibrio and Anaerotruncus were positively correlated with gas production, NDF digestibility, ADF digestibility, and acetate, propionate, butyrate, and total volatile fatty acid concentrations. Overall, our results suggested that the microbiota in the fermentation system could be affected by additional nitrogen supplementation and MD could effectively enhance the nutrient utilization in dairy cows. [ABSTRACT FROM AUTHOR]

Simple Summary: Weaning is very important for young ruminants. At this stage, calves' main source of nutrients is transferred from milk into solid feed, such as starter and roughage. At the same time, the rumen function of calves undergoes tremendous changes, such as bacteria, which are the main players in rumen function. Our research found that the rumen bacteria network of post-weaning calves was more complex. The fermentation end products, such as acetate, propionate, and butyrate, were higher in the post-weaning calves than the pre-weaning group. However, digestive enzymes such as protease, carboxymethyl cellulase, cellobiohydrolase, and glucosidase were lower in the post-weaning calves than the pre-weaning calves. These findings provided useful information for reference regarding the feeding management of calves. To better understand the transition of rumen function during the weaning period in dairy calves, sixteen Holstein dairy calves were selected and divided into two groups: pre-weaning (age = 56 ± 7 day, n = 8) and post-weaning (age = 80 ± 6 day, n = 8). The rumen fluid was obtained by an oral gastric tube. The rumen fermentation profile, enzyme activity, bacteria composition, and their inter-relationship were investigated. The results indicated that the post-weaning calves had a higher rumen acetate, propionate, butyrate, and microbial crude protein (MCP) than the pre-weaning calves (p < 0.05). The rumen pH in the post-weaning calves was lower than the pre-weaning calves (p < 0.05). The protease, carboxymethyl cellulase, cellobiohydrolase, and glucosidase in the post-weaning calves had a lower trend than the pre-weaning calves (0.05 < p < 0.1). There was no difference in α and β diversity between the two groups. Linear discriminant analysis showed that the phylum of Fibrobacteres in the post-weaning group was higher than the pre-weaning group. At the genus level, Shuttleworthia, Rikenellaceae, Fibrobacter, and Syntrophococcus could be worked as the unique bacteria in the post-weaning group. The rumen bacteria network node degree in the post-weaning group was higher than the pre-weaning group (16.54 vs. 9.5). The Shuttleworthia genus was highly positively correlated with MCP, propionate, total volatile fatty acid, glucosidase, acetate, and butyrate (r > 0.65, and p < 0.01). Our study provided new information about the rumen enzyme activity and its relationship with bacteria, which help us to better understand the effects of weaning on the rumen function. [ABSTRACT FROM AUTHOR]

To understand the effects of diet and age on the rumen bacterial community and function, forty-eight dairy cattle at 1.5 (M1.5), 6 (M6), 9 (M9), 18 (M18), 23 (M23), and 27 (M27) months old were selected. Rumen fermentation profile, enzyme activity, and bacteria community in rumen fluid were measured. The acetate to propionate ratio (A/P) at M9, M18, and M23 was higher than other ages, and M6 was the lowest (p < 0.05). The total volatile fatty acid (TVFA) at M23 and M27 was higher than at other ages (p < 0.05). The urease at M18 was lower than at M1.5, M6, and M9, and the xylanase at M18 was higher than at M1.5, M23, and M27 (p < 0.05). Thirty-three bacteria were identified as biomarkers of the different groups based on the linear discriminant analysis (LDA) when the LDA score >4. The variation partitioning approach analysis showed that the age and diet had a 7.98 and 32.49% contribution to the rumen bacteria community variation, respectively. The richness of Succinivibrionaceae_UCG-002 and Fibrobacter were positive correlated with age (r > 0.60, p < 0.01) and positively correlated with TVFA and acetate (r > 0.50, p < 0.01). The Lachnospiraceae_AC2044_group, Pseudobutyrivibrio, and Saccharofermentans has a positive correlation (r > 0.80, p < 0.05) with diet fiber and a negative correlation (r < −0.80, p < 0.05) with diet protein and starch, which were also positively correlated with the acetate and A/P (r > 0.50, p < 0.01). The genera of Lachnospiraceae_AC2044_group, Pseudobutyrivibrio, and Saccharofermentans could be worked as the target bacteria to modulate the rumen fermentation by diet; meanwhile, the high age correlated bacteria such as Succinivibrionaceae_UCG-002 and Fibrobacter also should be considered when shaping the rumen function. [ABSTRACT FROM AUTHOR]

Simple Summary: The rumen is a large fermentation chamber that enables dairy cows to utilize otherwise indigestible plant polymers and compounds for their nutrition, highlighting a crucial difference between ruminants and monogastrics. The key point in this process is the pool of enzymes secreted by microorganisms. Hence, exogenous enzymes from additives are important for high-production dairy cows to improve the utilization of feeds. In this study, we used the Aspergillus oryzae and Aspergillus niger co-cultivation extract (AOAN) to improve the digestibility of roughage and total mixed ration in vitro. Our results indicated that the digestibility of nutrients in feeds was significantly increased by AOAN supplementation, except for the digestibility of crude protein in the total mixed ratio (TMR). Furthermore, the diversity of the bacteria in TMR and oat hay was increased with AOAN supplementation. Although broad effectiveness of AOAN was established, regardless of roughage types, the mechanism may be different according to roughage types. AOAN may provide enzymes to improve the digestibility of feeds and enhance rumen fermentation. This study determined the effects of AOAN on digestibility, fermentation characteristics, and bacterial composition using in vitro gas recording fermentation system. A total of 30 mg of AOAN was supplemented into 500 mg of TMR, corn silage, oat hay, and alfalfa hay. Fermentation parameters and bacterial communities were determined after 48 h fermentation, and digestibility was determined after 7, 24, 30, and 48 h fermentation. Gas production and dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) digestibility were significantly increased by AOAN supplementation at 48 h (p < 0.05), except for digestibility of CP of the TMR (p > 0.05). AOAN increased starch digestibility in corn silage (p < 0.05) and tended to increase that in TMR (0.05 < p < 0.10). AOAN supplementation increased total volatile fatty acid production (p < 0.05). The molar proportions of acetate and acetate to propionate ratio of oat hay and alfalfa hay were increased (p < 0.05). The 16S rRNA analysis revealed that the microbial richness of TMR and oat hay, and microbial evenness of TMR were increased (p < 0.05). AOAN did not affect the α diversity, β diversity, and bacterial composition of the corn silage. The relative abundance of Prevotella was increased and Ruminococcus was decreased in TMR, oat hay, and alfalfa hay. In conclusion, results suggest that AOAN has the potential to improve the utilization of diets differently, including providing enzymes with changing microbiota (TMR, oat hay, and alfalfa hay) or providing enzymes alone (corn silage). [ABSTRACT FROM AUTHOR]

Simple Summary: Cassava processing and utilization generates many byproducts, such as cassava residue. On one hand, this residue still contains many nutrients like starch, fiber and minerals. On the other hand, it pollutes the environment if not be utilized properly. Lactating dairy cows need to control the body weight for smooth calving, but too much high energy feed material like maize can influence their lipid metabolism. Cassava residue may be a good option for them since it can be used not only as roughage, but also can provide energy for dairy cows. Therefore, this study was conducted to investigate the effect replacing high energy feedstuff crushed maize with cassava residue on in vitro fermentation characteristics of dairy cows in mid-lactation. This may help provide further in vivo tests with data support, which finally, could alleviate feed shortages, reduce environmental pollution and improve economic benefits of dairy farming. This study was conducted to investigate the effect of using cassava residue to replace crushed maize on in vitro fermentation characteristics of dairy cows at mid-lactation and provide guidance for its utilization. The study included seven treatments with four replicates, which used 0% (control, CON), 5%, 10%, 15%, 20%, 25% and 30% cassava residue to replace crushed maize (air-dried matter basis), respectively. A China-patented automated trace gas recording system was used to perform in vitro gas tests; rumen fluids were collected from three dairy cows at mid-lactation. In vitro dry matter digestibility (IVDMD), gas production (GP), pH, ammonia–N (NH3-N) and microbial protein (MCP) content were analyzed after in vitro incubating for 3, 6, 12, 24 and 48 h, respectively; volatile fatty acid (VFA) content was analyzed after in vitro culturing for 48 h. The results showed that with the increase of substitution ratio of cassava residue, the asymptotic gas production (A) increased quadratically (p < 0.05), cumulative gas production at 48 h (GP48) and the maximum rate of substrate digestion (RmaxS) increased linearly and quadratically (p < 0.05), the time at which the maximum gas production rate is reached (TRmaxG) increases linearly (p < 0.05). In addition, asymptotic gas production in 30% was significantly higher than the other treatments (p < 0.05), RmaxS in 25% and 30% were significantly higher than CON, 5% and 10% (p < 0.05). In addition, with the increase of substitution ratio of cassava residue, when in vitro cultured for 6 h and 12 h, NH3–N content decreased linearly and quadratically (p < 0.05). NH3–N content in 30% was significantly lower than the other treatments except 20% and 25% (p < 0.05) after cultivating for 6 h. Moreover, the content of iso-butyrate, iso-valerate, valerate and total VFA (tVFA) decreased linearly and quadratically (p < 0.05), acetate decreased quadratically (p < 0.05) with the increase of substitution ratio of cassava residue. In conclusion, when the cassava residue substitution ratio for crushed maize was 25% or less, there were no negative effects on in vitro ruminal fermentation characteristics of dairy cows at mid-lactation. [ABSTRACT FROM AUTHOR]

Simple Summary: The present study comparatively investigates the inhibitory difference of nitroethane (NE), 2-nitroethanol (NEOH), and 2-nitro-1-propanol (NPOH) on in vitro rumen fermentation, microbial populations, and coenzyme activities associated with methanogenesis. The results showed that both NE and NEOH were more effective in reducing ruminal methane (CH4) production than NPOH. This work provides evidence that NE, NEOH, and NPOH were able to inhibit methanogen population and dramatically decrease methyl-coenzyme M reductase gene expression and the content of coenzymes F420 and F430 with different magnitudes in order to reduce ruminal CH4 production. Nitroethane (NE), 2-nitroethanol (NEOH), and 2-nitro-1-propanol (NPOH) were comparatively examined to determine their inhibitory actions on rumen fermentation and methanogenesis in vitro. Fermentation characteristics, CH4 and total gas production, and coenzyme contents were determined at 6, 12, 24, 48, and 72 h incubation time, and the populations of ruminal microbiota were analyzed by real-time PCR at 72 h incubation time. The addition of NE, NEOH, and NPOH slowed down in vitro rumen fermentation and reduced the proportion of molar CH4 by 96.7%, 96.7%, and 41.7%, respectively (p < 0.01). The content of coenzymes F420 and F430 and the relative expression of the mcrA gene declined with the supplementation of NE, NEOH, and NPOH in comparison with the control (p < 0.01). The addition of NE, NEOH, and NPOH decreased total volatile fatty acids (VFAs) and acetate (p < 0.05), but had no effect on propionate concentration (p > 0.05). Real-time PCR results showed that the relative abundance of total methanogens, Methanobacteriales, Methanococcales, and Fibrobacter succinogenes were reduced by NE, NEOH, and NPOH (p < 0.05). In addition, the nitro-degradation rates in culture fluids were ranked as NEOH (−0.088) > NE (−0.069) > NPOH (−0.054). In brief, the results firstly provided evidence that NE, NEOH, and NPOH were able to decrease methanogen abundance and dramatically decrease mcrA gene expression and coenzyme F420 and F430 contents with different magnitudes to reduce ruminal CH4 production. [ABSTRACT FROM AUTHOR]

Simple Summary: With its drought tolerant and high productive characteristics, Zhang hybrid millet is becoming an important food source for both humans and animals. Whole plant Zhang hybrid millet has great potential in lowering feed cost while providing relatively high crude protein, vitamin, and mineral content. This study aimed to disclose whether harvest time and microbial anaerobic fermentation can improve ruminal degradability and intestinal digestibility of whole Zhang hybrid millet, and explore the effect of microbial anaerobic fermented whole Zhang hybrid millet as feedstuff on milk yield and milk quality. Results showed that the interaction effect of harvest time and microbial anaerobic fermentation had significant influence on the crude ash, Acid detergent fiber (ADF), water-soluble carbohydrate (WSC), and neutral detergent insoluble protein (NDIP) content and effective degradability of dry matter (EDDM) of whole Zhang hybrid millet. Early harvested whole Zhang hybrid millet with microbial anaerobic fermentation appeared to have a better chemical profile with lower content of crude ash, Neutral detergent fiber (NDF), ADF, and higher content of WSC, and a better ruminal degradability with lower EDDM, effective degradability of neutral crude protein EDCP, and effective degradability of neutral detergent fiber (EDNDF). Microbial anaerobic fermented whole Zhang hybrid millet as feedstuff did not significantly affect milk components, but significantly reduced somatic cell count (SCC) compared with controls. Milk yield was numerically higher in whole Zhang hybrid millet groups. Collectively, harvest time and microbial anaerobic fermentation could further improve the nutritive value of whole Zhang hybrid millet. Microbial anaerobic fermented whole Zhang hybrid millet as an alternative feedstock for dairy diet was safe and feasible. This study assessed whether harvest time and microbial anaerobic fermentation could affect ruminal degradability and intestinal digestibility of whole Zhang hybrid millet, and estimate the effect of microbial anaerobic fermented whole Zhang hybrid millet as feedstuff on milk yield and milk quality. Protein degradation and intestinal digestion were determined using in situ nylon bag technique and three-step in vitro method, respectively. Results showed that harvest time, microbial anaerobic fermentation, or their interaction significantly affected EDDM, EDCP, and EDNDF (p < 0.05). In vitro fermentation was significantly influenced by harvest time. Early harvested samples appeared to have higher Total volatile fatty acid (TVFA) and lower acetate: propionate ratio than late harvested ones (p < 0.01). However, significant effect of harvest time and fermentation was failed to find in the estimation of rumen-undegradable protein (RUP) (p > 0.05). Microbial anaerobic fermented whole Zhang hybrid millet as feedstuff provided similar milk compositions compared with controls, and it significantly reduced SCC (p = 0.04). Milk yield was numerically higher in whole Zhang hybrid millet groups. In conclusion, harvest time and microbial anaerobic fermentation could further improve ruminal utilization of whole Zhang hybrid millet. Whole Zhang hybrid millet could be an alternative feedstock for dairy cows with acceptable safety profile and potential benefit in milk production. [ABSTRACT FROM AUTHOR]

• In the short-term, calves sorted for the familiar feed components after transition to a total mixed ration. • Feed familiarity established early in life does not affect diet selection and rumen fermentation over the long term. • In long-term, feeding the same feed components in a TMR eventually override the effect of feed sources early in life. Feed sorting is a common issue on dairy farms. Cows prefer smaller grain particles over long forage particles, leading to increased volatile fatty acids (VFA) and consequently subacute ruminal acidosis (SARA). The purpose of this study was to investigate the short and long-term effects of early life exposure to different feed sources on feed sorting and rumen fermentation of calves. Forty newborn female Holstein calves were randomly assigned at birth (38.5 ± 2.4 kg of BW) to 1 of 2 treatments: (1) the provision of concentrate (CON) only or (2) provision of hay (HAY) only as the source of solid feed during the milk-feeding stage (d 1–56). Afterward, all calves were offered a total mixed ration until the end of the experiment (d 57–196). Calves were raised in individual hutches from d 1–70. The calves were then transferred into a heifer barn with pens and housed in pairs (2 calves/pen) as per the previous treatments. Rectal temperature, feed intake, body weight and body structural measurements were recorded throughout the study. Fresh feed and orts were sampled daily in the first two weeks (d 57–70) of feeding TMR and in the last week of the experiment (d 190–196) to analyze feed sorting behaviour. Rumen fluid samples were collected from d 14–190 for detecting VFA concentrations. Our findings showed that early feed exposure did not influence calf health and growth performance but affected feed sorting over a short period. Upon transition to the same mixed diet, differences were found in the sorting of different particle fractions between treatments. In the first two weeks (wk 9 and 10) after transition to TMR, calves exposed to concentrates early began to sort for fine particle and against the long particle fractions. In contrast, calves fed hay early sorted for the long particle and against the fine particle fractions, resulting in a higher preference for fine particle fractions (P < 0.01) and a lower preference for long particle fractions (P < 0.01) in calves fed concentrate early than those fed hay early. However, no carryover effects were observed, such that differences between treatments in sorting for long (P = 0.43) and fine (P = 0.45) particle fractions faded away by the last week (wk 28) of the experiment. All calves sorted for short and fine particle fractions and against long and medium particle fractions. Although the pattern of feed sorting initially differed between treatments, rumen fermentation parameters, such as total VFA (P = 0.54), acetate (P = 0.83), propionate (P = 0.21), butyrate (P = 0.20), were not altered once all calves transitioned to a total mixed ration. These results suggested that the feed familiarity established early in life would not affect diet selection and rumen fermentation in heifer later in life. Moreover, the effect of feeding a total mixed ration after transition could eventually override the effect of feeding concentrate or hay early in life. [ABSTRACT FROM AUTHOR]