Effects of forage source and amount of concentrate on rumen and intestinal digestion of nutrients in late-lactation cows

Effects of high-grain diet feeding on fatty acid profiles in milk, blood, muscle, and adipose tissue, and transcriptional expression of lipid-related genes in muscle and adipose tissue of dairy cows

BACKGROUND

High-grain (HG) diets affect lipid metabolism in the liver and mammary tissue of dairy cows, but its effects on muscle and adipose tissue have not been wide evaluated. Thus, the aim of this study is to clarify this issue.

METHODS

Twelve Holstein cows were randomly divided into two groups: conventional diet group (CON, n = 6) and the HG diet group (n = 6). On day 7 of week 4, rumen fluid was sampled to measure pH, milk was sampled to measure components, and blood was sampled to measure biochemical parameters and fatty acid composition. After the experiment, cows were slaughtered to collect muscle and adipose tissue for fatty acid composition and transcriptome analysis.

RESULTS

HG feeding decreased the ruminal pH, milk's fat content and long-chain fatty acid proportion (P < 0.05) and increased the proportion of short- and medium-chain fatty acids in the milk (P < 0.05) as compared with CON diets. The concentrations of blood cholesterol, low-density lipoprotein, and polyunsaturated fatty acids in the HG cows were lower than those in CON cows (P < 0.05). In muscle tissue, HG feeding tended to increase the triacylglycerol (TG) concentration (P < 0.10). Transcriptome analysis revealed changes in the biosynthesis of the unsaturated fatty acids pathway, the regulation of lipolysis in the adipocytes pathway, and the PPAR signalling pathway. In adipose tissue, HG feeding increased the concentration of TG and decreased the concentration of C18:1 cis9 (P < 0.05). At the transcriptome level, the fatty acid biosynthesis pathway, linoleic acid metabolism pathway, and PPAR signalling pathway were activated.

CONCLUSION

HG feeding leads to subacute rumen acidosis and a decreased milk fat content. The fatty acid profiles in the milk and plasma of dairy cows were changed by HG feeding. In muscle and adipose tissue, HG feeding increased TG concentration and up-regulated the expression of genes related to adipogenesis, while down-regulated the expression of genes related to lipid transport. These results complement our knowledge of the fatty acid composition of muscle and adipose tissue in dairy cows and expand our understanding of the mechanisms by which HG diets affect lipid metabolism in muscle and adipose tissue.

Comparative digestibility and rumen fermentation of camels and sheep fed different forage sources

The present study evaluated the effects of forage sources on dry matter (DM) intake, digestibility, and fermentation parameters in camels vs. sheep. The study was arranged as a 2 × 3 factorial experiment in a completely randomized design by using two animal species (three ruminally cannulated female camels and three male sheep) and three forage sources. The forages were (1) alfalfa hay; 164 and 479 g/kg DM for crude protein (CP) and neutral detergent fiber (NDF), respectively, (2) berseem hay; 121 and 513 g/kg DM for CP and NDF, respectively, and (3) wheat straw (27.5 and 723 g/kg DM for CP and NDF, respectively). Higher DM intake [g/kg body weight (BW)] was noted in sheep compared to camel when alfalfa hay (p < 0.05) and berseem hay (p < 0.05) were fed but was similar between both species when they were fed wheat straw. Forage type rather than animal species had more effect on metabolic intake. Lower digestibility was noted in sheep with wheat straw (p < 0.05). Similar in situ degradability values for crude protein and DM were noted between camels and sheep. In situ degradability of NDF was higher (p < 0.05) in camel than sheep. Greater ruminal pH (p < 0.05) was noted in sheep vs. camels when berseem hay and wheat straw were fed. Lower ruminal passage rate (p < 0.05) was noted in camels and higher total mean retention time. It was concluded that sheep and camels had similar digestion capacities when fed berseem hay and alfalfa hay, however, camels are more efficient than sheep when fed wheat straw.

Digestibility, lactation performance, plasma metabolites, ruminal fermentation, and bacterial communities in Holstein cows fed a fermented corn gluten-wheat bran mixture as a substitute for soybean meal

The purpose of this research was to investigate the effects of replacing soybean meal (SBM) with a fermented corn gluten-wheat bran mixture (FCWM) on nutrient digestibility, lactation performance, plasma metabolites, ruminal fermentation, and bacterial communities in Holstein cows. Nine healthy multiparous (parity = 3) Holstein cows with similar body weights (624 ± 14.4 kg), days in milk (112 ± 4.2), and milk yields (31.8 ± 1.73 kg; all mean ± standard deviation) were used in a replicated 3 × 3 Latin square design with 3 periods of 28 d. Cows were fed 1 of 3 dietary treatments in which FCWM replaced SBM as follows: basal diet with no replacement (0FCWM); 50% replacement of SBM with FCWM (50%FCWM); and 100% replacement of SBM with FCWM (100%FCWM). The diets were formulated to be isocaloric and isonitrogenous. The results showed that the total-tract digestibility of dry matter and crude protein increased linearly with increased dietary FCWM, and we found a trend for increased total-tract neutral detergent fiber and potentially digestible NDF digestibility. Milk yield tended to increase in a linear manner as more FCWM was consumed, and energy-corrected milk production was significantly increased with FCWM supplementation as a result of increased milk protein and lactose yields. Plasma glucose and IgG concentrations increased linearly with increasing FCWM supplementation, but plasma malondialdehyde concentration decreased linearly. Concentrations of total volatile fatty acids and propionate showed a linear increase with increasing FCWM supplementation, leading to a linear decrease in pH. The relative abundance of ruminal Prevotellaceae, Veillonellaceae, and Prevotella 1 increased linearly with increasing FCWM supplementation, and the relative abundance of ruminal Succinivibrionaceae and Muribaculaceae decreased linearly. The relative abundance of fecal Ruminococcaceae, Prevotellaceae, and Ruminococcaceae UCG-005 increased linearly with increasing FCWM supplementation, but the relative abundance of fecal Peptostreptococcaceae decreased linearly. Overall, the replacement of SBM with FCWM altered the composition of the ruminal bacterial community and improved nutrient digestibility, lactation performance, and ruminal fermentation in cows, providing a data reference for the use of FCWM in dairy production.

Feeding diets varying in forage proportion and particle length to lactating dairy cows: I. Effects on ruminal pH and fermentation, microbial protein synthesis, digestibility, and milk production

Physically effective neutral detergent fiber (peNDF) content of dairy cow diets was modified by varying the theoretical chop length of alfalfa silage and forage:concentrate (F:C) ratio, and effects on nutrient intakes, ruminal fermentation, site and extent of digestion, microbial protein synthesis, and milk production were evaluated. Estimates of dietary peNDF contents were compared with recommendations, and predictions of ruminal pH from peNDF and the recently developed physically adjusted neutral detergent fiber (paNDF) system were compared with observed pH. The experiment was designed as a triple 4 × 4 Latin square using 12 mid-lactating dairy cows with 4 intact, 4 ruminally cannulated, and 4 ruminally and duodenally cannulated cows. Site and extent of digestion and microbial protein synthesis were measured in a single 4 × 4 Latin square. Treatments were a 2 × 2 factorial arrangement; 2 forage particle lengths (FPL) of alfalfa silage (short and long) were combined with low (35:65) and high (60:40) F:C ratios [dry matter (DM) basis]. The peNDF contents were determined by multiplying the proportion (DM basis) of total mixed ration retained on 2 (8 and 19 mm; peNDF_8.0) or 3 (1.18, 8, and 19 mm; peNDF_1.18) sieves of the Penn State Particle Separator by the neutral detergent fiber content of the diet. The dietary peNDF contents ranged from 10.7 to 17.5% for peNDF_8.0 or from 23.1 to 28.2% for peNDF_1.18. Interactions between F:C ratio and FPL content were few. Increasing peNDF content of diets by increasing F:C ratio decreased DM intake, milk yield, and milk protein yield, whereas apparent total-tract DM digestibility and milk efficiency improved. Increasing F:C ratio improved ruminal pH status but decreased total volatile fatty acid concentration and microbial protein synthesis. Increasing peNDF content of diets via dietary FPL increased mean ruminal pH, but did not affect DM intake, total-tract digestibility, or milk production. The results indicate that feeding dairy cows a low F:C diet helps increase DM intake, milk production, and microbial protein synthesis, but may adversely affect feed digestibility and milk efficiency due to increased risk of subacute ruminal acidosis. Increased FPL improved ruminal pH status, but had minimal effects on feed intake, ruminal fermentation, nutrient digestibility, and milk production. The results indicate a trade-off between reducing the risk of subacute ruminal acidosis and maximizing ruminal fermentation, feed digestibility, and milk production of dairy cows. The paNDF model showed improvement in the predictability of ruminal pH over the peNDF model, but the accuracy of predictions varied depending upon the diet and ruminal fermentation variables considered in the equations.

Feeding diets varying in forage proportion and particle length to lactating dairy cows: II. Effects on duodenal flows and intestinal digestibility of amino acids

A study was conducted to evaluate the effects of forage-to-concentrate (F:C) ratio and forage particle length (FPL) on intake, duodenal flow, and digestibility of individual AA in the intestine of lactating dairy cows. The experiment was designed as a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments using 4 lactating dairy cows (parity 2) with ruminal and duodenal cannulas. Low (35:65) and high (60:40) F:C ratios (dry matter basis) were combined with 2 FPL of alfalfa silage (short vs. long; 7.9 vs. 19.1 mm). Few interactions between F:C and FPL for duodenal flow and intestinal digestibility of AA occurred, but interactions were detected for intakes of several AA. Intake of essential AA and nonessential AA decreased with increasing F:C, and the intake of several individual AA increased or decreased with increasing FPL. Increasing F:C decreased duodenal flows of essential AA, nonessential AA, and microbial AA due to consistent decreased flows of most individual AA (except Glu). Degradability of most individual AA in the rumen was not affected by F:C ratio or FPL except that the degradability of His was greater with high than low F:C diets, and the degradability of Ser was greater with long versus short FPL diets. However, the degradability of individual AA within diet varied considerably. Overall, F:C ratio and FPL did not affect intestinal digestibility of AA and rumen undegradable protein AA, whereas the digestibility of individual AA in the intestine varied considerably regardless of dietary treatment. These results indicate that increasing F:C ratio decreased AA supply due to decreased flow of AA to the duodenum but altering FPL did not affect AA supply. The results also revealed the necessity to consider both the flows and digestibility of individual AA when optimizing ration formulation to meet AA requirements of dairy cows.

Effect of dietary energy source and level on nutrient digestibility, rumen microbial protein synthesis, and milk performance in lactating dairy cows

This study was conducted to examine the effects of dietary energy source and level on intake, digestion, rumen microbial protein synthesis, and milk production in lactating dairy cows, using corn stover as a forage source. Eight multiparous Holstein cows, 4 of which were fitted with rumen cannulas, were evaluated in a replicated 4 × 4 Latin square design, with each period lasting 21 d. The cows were randomly assigned into 4 treatment groups: low-energy (LE) ground corn (GC), LE steam-flaked corn (SFC), high-energy (HE) GC, and HE SFC. Changes to ruminal energy degradation rates were induced by feeding the cows diets of either finely ground corn or SFC as components of diets with the same total energy level. Milk yield, milk protein content and yield, and milk lactose yield all increased in response to higher levels of dietary energy, whereas contents of milk fat and lactose were unaffected. Cows fed HE diets had a higher crude microbial protein yield and total-tract apparent digestibility than those receiving LE diets. Milk yield, milk protein yield, and microbial protein yield were also higher when SFC replaced GC as the main energy source for lactating cows fed LE diets. These results suggest that an increased dietary energy level and ruminal degradation rate are beneficial to milk protein production, which we suggest is due to increased yields of microbial proteins, when cows are fed corn stover as a dietary forage source.

Effects of forage sources on rumen fermentation characteristics, performance, and microbial protein synthesis in midlactation cows

Eight multiparous Holstein cows (632±12 kg BW; 135±16 DIM) were used in a replicated 4×4 Latin square design to evaluate the effects of forage sources on rumen fermentation characteristics, performance, and microbial protein (MCP) synthesis. The forage portion of the diets contained alfalfa hay (AH), oat hay (OH), Leymus chinensis (LC), or rice straw (RS) as the primary source of fiber. Diets were isonitrogenous and isocaloric, and cows were fed four corn silages based total mixed rations with equivalent nonfiber carbohydrate (NFC) and forage neutral detergent fiber (NDF). Dry matter intake was not affected by the source of dietary forages, ranging from 18.83 to 19.20 kg/d, consequently, milk yield was similar among diets. Because of the numerical differences in milk fat and milk protein concentrations, 4% FCM and ECM yields were unchanged (p>0.05). Mean rumen pH, NH₃-N content, and concentrations of volatile fatty acids in the rumen fluid were not affected by the treatments (p>0.05). Dietary treatments did not affect the total tract apparent digestibility of dry matter, organic matter, and crude protein (p>0.05); however, digestibility of NDF and acid detergent fiber in RS diet was higher compared with AH, OH, and LC diets (p<0.05). Total purine derivative excretion was higher in cows fed AH, OH, and LC diets compared with those fed RS diet (p<0.05), consequently, estimated MCP synthesis was 124.35 g/d higher in cows fed AH diet compared with those fed RS diet (p<0.05). The results indicated that cows fed AH, OH, LC, and RS diets with an equivalent forage NDF and NFC have no unfavourable effect on the ruminal fermentation and productive parameters.

Effect of dietary forage sources on rumen microbiota, rumen fermentation and biogenic amines in dairy cows

BACKGROUND

Fifteen lactating Holstein dairy cows were assigned to three diets in a 3 × 3 Latin square design to evaluate the effects of dietary forage sources on rumen microbiota, rumen fermentation and biogenic amines. Diets were isonitrogenous and isocaloric, with a forage/concentrate ratio of 45:55 (dry matter basis) but different main forage sources, namely cornstalk (CS), Leymus chinensis (LC) or alfalfa hay (AH).

RESULTS

Pyrosequencing of the V3-V6 hypervariable coding region of 16S rRNA revealed that the rumen microbiota was significantly affected by forage sources. AH feeding increased the proportion of genera Prevotella and Selenomonas compared with the CS diet, while CS feeding increased the proportion of genera Anaerotruncus, Papillibacter, Thermoactimoyces, Bacillus and Streptomyces compared with the LC or AH diet. AH and LC feeding both increased the propionate concentration compared with the CS diet. AH feeding decreased the concentrations of tyramine, putrescine and histamine compared with the LC diet.

CONCLUSION

These results indicate that a high proportion of alfalfa hay in the ration is beneficial for milk yield and a healthy and balanced rumen microbiota in lactating cattle. This can be attributed to the higher degradation of rumen organic matter and the more balanced carbohydrates and proteins for optimal rumen microbial growth.

Milk fatty acid profiles in Holstein dairy cows fed diets based on corn stover or mixed forage

In this study the influence of modulated concentrate-to-roughage ratio on the fatty acid profile of milk fat was investigated in dairy cows. Therefore, corn stover was compared with better-quality roughages. Two groups of in total 24 Holstein dairy cows (136 ± 37 days in milk) received either a high-forage diet (Diet MF, forage-to-concentrate ratio [F:C] = 60:40) with alfalfa hay, corn silage and Chinese wild rye as forage sources, or a low-forage diet with corn stover as forage source (Diet CS, F: C = 40:60) for an experimental period of nine weeks. During the study, milk yield as well content and fatty acid profiles of milk fat were examined. Dietary treatments had no effect on milk yield and milk fat content, whereas dry matter intake (p < 0.01) and milk fat yield (p < 0.05) were higher for Diet MF than for Diet CS. Compared with Diet CS, feeding Diet MF increased the daily intake of total unsaturated fatty acids and the C18:0 and C18:3 contents (p < 0.01) in milk fat, whereas the total content of fatty acids <16C was decreased (p < 0.05). No influence on total saturated, monounsaturated and polyunsaturated fatty acids in milk was observed. The ratio of total unsaturated fatty acids in milk fat to its daily intake was substantially lower for Diet MF compared with Diet CS, suggesting that the high proportion of roughage resulted in a high rate of biohydrogenation in the rumen.

Effects of dietary forage sources on rumen microbial protein synthesis and milk performance in early lactating dairy cows

The objective of this study was to evaluate the effects of dietary forage sources on milk performance, rumen microbial protein synthesis, and N utilization in early lactation dairy cows. Twelve primiparous Chinese Holstein dairy cows (45 ± 6.0 DIM) were used in a 3 × 3 Latin square design. Diets were isonitrogenous and isocaloric, with a forage-to-concentrate ratio of 45:55 [dry matter (DM) basis] and contained similar concentrate mixtures. Different forage sources were then added (on a DM basis): 21% corn silage, 19% corn stover, and 5% alfalfa hay (CS); 19% corn silage, 21% Chinese wild rye hay and 5% alfalfa hay (CWR); or 19% corn silage, 9% Chinese wild rye hay, and 17% alfalfa hay (AH). Each period lasted for 21 d, with the first 14 d for an adaptation period. Dry matter intake was not affected by the source of dietary forage. Milk yield was higher for cows fed AH than those fed CS, with an intermediate value for CWR. Milk protein content was higher in the cows fed AH compared with CWR (3.02 vs. 2.92%), with CS (2.95%) at an intermediate position. The contents of milk fat and lactose were not different among the treatments. However, milk efficiency (milk yield/DM intake) was higher for cows fed AH than those fed CS, with those fed CWR intermediate. Cows fed AH had higher microbial protein yield and metabolizable protein than those fed CS or CWR. The concentrations of urea N in the urine, blood, and milk were decreased for cows fed AH, indicating an increased N conversion. The results indicated that corn stover could replace Chinese wild rye grass in the diets for lactating cows and that a high proportion of alfalfa hay in the diet is beneficial for milk protein production by increasing microbial protein yield. This can be attributed to the improving the supply of rumen-available energy.

Ruminal degradability and whole-tract digestibility of protein and fibre fractions in fenugreek haylage

Doepel, L., Montgomery, J. E., Beauchemin, K. A., King, J. R. and Acharya, S. N. 2012. Ruminal degradability and whole-tract digestibility of protein and fibre fractions in fenugreek haylage. Can. J. Anim. Sci. 92: 211–217. The purpose of this study was to evaluate the digestibility of fenugreek forage compared with alfalfa in dairy cows. Alfalfa and two genotypes of fenugreek, Quatro and F70, were harvested and prepared as plastic-wrapped high-moisture bales. Fourteen weeks after baling, forage samples were obtained for determination of ruminal degradation and whole-tract digestibility. To determine ruminal degradation, forage samples were placed in polyester bags and incubated in the rumen for various time points (up to 168 h) in lactating Holstein cows. Digestibility in the rumen, intestine and the whole digestive tract was estimated by incubating samples in the rumen, followed by measurements of intestinal digestibility using the mobile bag technique in two non-lactating Holstein cows. Effective ruminal degradability of DM was lower for F70 than for alfalfa, while for ADF and NDF it was equivalent in all forages. Whole-tract disappearance of DM, CP, ADF and NDF was lower for F70 than Quatro. In general, Quatro and alfalfa were similar in terms of ruminal degradation and digestion in the rumen, intestine and whole-tract, while F70 tended to be of lower quality.

Modeling the adequacy of dietary fiber in dairy cows based on the responses of ruminal pH and milk fat production to composition of the diet

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

Altering Physically Effective Fiber Intake Through Forage Proportion and Particle Length: Digestion and Milk Production

Intake of physically effective neutral detergent fiber (peNDF) of dairy cows was altered by adjusting the proportion of forage in the diet and forage particle length, and effects on nutrient intake, site and extent of digestion, microbial N synthesis, and milk production were measured. The experiment was designed as a triplicated 4 x 4 Latin square using 12 lactating dairy cows, with 4 that were ruminally and duodenally cannulated, 4 that were ruminally cannulated, and 4 that were intact. Thus, the site and extent of digestion, and microbial N synthesis were measured in a single 4 x 4 Latin square. Treatments were arranged in a 2 x 2 factorial design; 2 forage particle lengths (FPL) of alfalfa silage (short and long) were combined with low (35:65) and high (60:40) forage:concentrate (F:C) ratios (dry matter basis). Dietary peNDF content was determined from the sum of the proportion (dry matter basis) of dietary dry matter retained either on the 2 screens (8- and 19-mm) or on the 3 screens (1.18-, 8-, and 19-mm) of the Penn State Particle Separator multiplied by the neutral detergent fiber content of the diet. An increased F:C ratio reduced intakes of dry matter and starch by 9 and 46%, respectively, but increased intake of fiber from forage sources by 53%. Digestibility of dry matter in the total tract was not affected, whereas total digestion of fiber and N was improved by increasing the F:C ratio. Improved total fiber digestion resulted from higher ruminal digestion, which was partially due to a shift in starch digestion from the rumen to the intestine with the increased F:C ratio. Actual milk yield was decreased but production of 4% fat-corrected milk was similar between the low and high F:C diets because of increased milk fat content. Increased FPL increased intake of peNDF, especially when the high F:C diet was fed. However, nutrient intakes, N metabolism in the digestive tract, and milk production were not affected. Digestibility of neutral detergent fiber in the total tract was increased because of improved fiber digestion in the rumen with increased FPL. These results indicate that feeding dairy cows a low F:C diet is beneficial in terms of increasing feed intake, microbial N synthesis, and milk production. However, low F:C diets do not maximize feed digestion and production efficiency because of the effects of subacute ruminal acidosis. Increased FPL improves fiber utilization with minimal effects on the digestion of other nutrients and milk production. Increasing dietary peNDF, through an increased proportion of forage or increased FPL, improves fiber digestion because of improved rumen function.

Effect of forage: concentrate ratio on ruminal metabolism and duodenal flow of fatty acids in beef steers

The objective of this study was to determine the proportion of forage in the diet which would maximize duodenal flow of unsaturated fatty acids in beef steers supplemented with linseed oil. A second objective was to determine how diets differing in forage content, but equal in nitrogen (N), energy and lipid supply, would affect the duodenal flow of C18:1and conjugated linoleic acid (CLA) isomers. Eight Hereford×Friesian steers (533±13·6 kg), prepared with rumen and duodenal cannulae were offered one of four forage:concentrate (F:C) ratios: F80C20; F60C40; F40C60 and F20C80 on a dry-matter (DM) basis. All diets were offered at 0·013 body weight and designed to be isonitrogenous and isoenergetic with total lipid made up to 0·06 DM intake with linseed oil. The experimental design was a replicated incomplete 4×4 Latin square with three periods. Increasing the concentrate component in the diet from 0·20 to 0·60 reduced rumen pH from 6·58 to 6·37 and caused a small but significant shift in volatile fatty acid molar proportions, decreasing the non-glucogenic ratio. Rumen ammonia-nitrogen concentration was also significantly reduced with increasing concentrate, from 156·8 to 101·0 mg N per l on F80C20 and F20C80, respectively. Microbial nitrogen (MN) and the efficiency of microbial protein synthesis was significantly elevated as forage level decreased from 51·6 to 72·4 g/day and 17·2 to 27·3 g MN per kg organic matter apparently digested in the rumen, respectively for F80C20 and F20C80. Intake and duodenal flow of C18:1n-9 and C18:2n-6 were significantly higher with increasing concentrate level in the diet whereas C18:3n-3 intake and flow was not different, averaging 143·6 and 6·37 g/day, respectively. There were no differences in the flows of total C18:1transor CLA (47·7 and 1·79 g/day, respectively) across the diets. However, although not significantly different in duodenal flow there were trends (P<0·1) for an increasing proportion of trans-10 and a decreasing proportion oftrans-11 when increasing the concentrate in the diet. Biohydrogenation of C18:2n-6 decreased from 0·91 to 0·85 when increasing concentrate in the diet from 0·20 to 0·40 but further increases had no effect. F:C ratio had little effect on the flow of unsaturated fatty acids, C18:1transand CLA to the duodenum of beef steers, and this may relate to the ability of the rumen to buffer the large changes in concentrate intake.

Milk production and composition from cows fed high oil or conventional corn at two forage concentrations

Twelve multiparous Holstein cows (63 +/- 24 d in milk) were used in a replicated 4 x 4 Latin square with 28-d periods to evaluate conventional and high oil corn grains when fed at two different forage-to-concentrate ratios. Dietary treatments consisted of conventional or high oil corn supplementing a diet with a 25:25:50 mixture of corn silage: alfalfa: concentrate mix, or a high forage diet with a 30:30:40 mixture of corn silage: alfalfa: concentrate mix. Dry matter intake (28.1, 28.7, 26.9, and 26.2 kg/d for normal diets with conventional and high oil corn, and high forage diets with conventional and high oil corn, respectively) and milk yields (36.8, 37.2, 35.5, and 35.2 kg/d) were similar for conventional and high oil corn diets and were lower with the high forage diet, regardless of corn source. Milk fat concentrations were greater when cows were fed diets containing 60% forage (4.03 vs. 3.88%, for the 60 and 50% forages, respectively), but milk protein concentrations were not affected by forage content. Corn source did not affect milk fat or protein concentrations. Long-chain fatty acid concentrations, unsaturated fatty acid concentrations, and total 18:1 fatty acid concentrations were greater when cows were fed high oil corn but were unaffected by forage content of the diet. Concentrations of transvaccenic acid (0.58, 0.81, 0.62, and 0.69 g/100 g of fatty acids) and cis-9, trans-11 conjugated linoleic acid (0.28, 0.39, 0.32, and 0.33 g/100 g of fatty acids) were greater when cows were fed high oil compared with conventional corn when fed 50% forage but were similar for both corn sources at 60% forage. Total n-3 fatty acids were not affected by corn source or forage content. High forage diets decreased milk production and increased milk fat concentration. Feeding high oil corn increased concentrations of long-chain, unsaturated, transvaccenic, and conjugated linoleic fatty acids in milk; however, production of transvaccenic and conjugated linoleic acids were attenuated by high forage diet.

Effects of substituting barley grain with corn on ruminal fermentation characteristics, milk yield, and milk composition of Holstein cows

The influence of corn or barley, or the equal mixture of both, on digestion characteristics and dairy cow performance was evaluated in metabolic and production experiments. Three rumen-cannulated early-lactation cows were used in a 3 x 3 Latin square design experiment to study the effect on ruminal fermentation characteristics and whole-tract digestion of substituting barley grain with corn. Production responses were determined by the use of 27 early-lactation Holstein cows. Cows in the production study were fed the test diets for 12 wk after a 2-wk covariate period. Results from the metabolic study indicated the effects of grain source on ruminal and total-tract digestion to be minimal. Total ruminal volatile fatty acids and acetate concentrations decreased linearly, butyrate increased linearly, and pH and lactic acid concentration were not affected by increasing levels of corn. Apparent digestibility of DM and organic matter showed a quadratic response with increasing the corn level in the diet, with no dietary effect on neutral detergent fiber, acid detergent fiber, and cellulose digestion. Ruminal fermentation characteristics suggest that substitution of barley grain with corn may alter the site of digestion and the end products of digestion that are absorbed by the animal. Multiparous cows failed to respond to treatment, whereas primiparous animals showed the greater response in milk yield and milk-component yield to diets that contained an equal mixture of corn and barley. These results probably reflect a more optimal synchronization of dietary protein and energy for dairy cows fed the 50:50 barley/corn diet.