Sodium bicarbonate for early lactation cows fed corn silage or hay crop silage-based diets

To compare the effects of NaHCO3 in diets based on different forage sources, 16 Holstein cows, in a split-plot design, were assigned at 2 d postpartum to a total mixed diet of either 30% hay crop silage: 70% concentrate or 40% corn silage: 60% concentrate (dry basis) that contained 0 or 1.25% NaHCO3. Over the first 6 wk postpartum, NaHCO3 increased milk fat percentage in cows fed the corn silage-based diet. During wk 2 through 6 postpartum, NaHCO3 increased milk yield with the hay crop silage-based diet and tended to decrease milk yield with the corn silage-based diet. Sodium bicarbonate increased digestion of NDF with both forages and increased excretion of urinary nitrogen with the corn silage-based diet. Responses to NaHCO3 by cows in early lactation may depend on the nature of the dietary forage component.     

Pigeon peas as a supplement for lactating dairy cows fed corn silage-based diets

Holstein rumen-cannulated cows [n = 7; initial body weight (BW) 640.56 ± 71.43 kg] were fed a corn silage basal diet with 1 of 3 concentrates (C = control; P10 = 10% pigeon peas; P20 = 20% pigeon peas). Cows were randomly assigned to treatments in a replicated 3 × 3 Latin square and individually fed using Calan gates. Each experimental period was 21 d with 7 d for adaption and 14 d for sample collection. Ruminal fluid samples were taken the last day of each experimental period and analyzed for pH, ammonia, long-chain fatty acids, and volatile fatty acids (VFA). Consecutive a.m. and p.m. milk samples were taken during the last 2 wk of the 21-d period and analyzed for fat, protein, long-chain fatty acids, and somatic cell count. Dry matter intake (kg/d) was reduced during the second period and was greater for P10 diets. Milk protein was greater for cows fed P20 compared with P10. Energy-corrected milk was greater for cows fed the control diet compared with P10. Treatment had no effect on milk yield. Ruminal fluid pH decreased over sampling times; however, pH remained at or above 5.5. Diets did not affect ruminal fluid pH; however, pH was different for sampling periods. Ruminal ammonia decreased until 8 h postfeeding at which time it peaked consistent with changes in ammonia concentrations that usually peak 3 to 5 h postfeeding on diets high in plant proteins. Dietary treatments altered ruminal fluid VFA with reduced concentrations of acetate and greater concentrations of propionate for control diet, resulting in reduced acetate:propionate ratio. Isobutyrate exhibited an hour by treatment interaction, in which isobutyrate decreased until 8 h postfeeding and then tended to be greater for P10 than for other treatments. Animals fed the P10 diet had greater concentrations of ruminal isovalerate. Ruminal cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid (CLA) isomers were not affected by dietary treatments. The P10 diet had greatest ruminal synthesis of cis-9,trans-11, but control cows had greatest ruminal synthesis of trans-10,cis-12. Milk CLA isomers were similar among treatments. Trends were observed for greater cis-9,trans-11 and trans-10,cis-12 for the P10 diet. Pigeon peas may be used as a protein supplement in dairy diets without affecting milk production, dry matter intake, or ruminal environment when they replace corn and soybean meal.     

Methane emissions of manure from dairy cows fed red clover- or corn silage-based diets supplemented with linseed oil

The objective of this study was to investigate the effects of forage source (red clover silage: RCS vs. corn silage: CS) and diet supplementation with linseed oil (LO) on CH₄ emissions of manure from dairy cows. For this purpose, 12 lactating cows were used in a 2 × 2 factorial arrangement of treatments. Cows were fed (ad libitum) RCS- or CS-based diets (forage:concentrate ratio 60:40; dry matter basis) without or with LO addition (4% dry matter). Feces and urine were collected from each cow and mixed with residual sludge obtained from a manure storage structure. Manure was incubated for 17 wk at 20°C under anaerobic conditions (O₂-free N₂) in 500-mL glass bottles. Methane emissions and changes in chemical composition of the manure were monitored during the entire incubation period. The total amount of feces and urine excreted by cows was not affected by dietary treatments and averaged 6.6 kg/d of volatile solids (VS). Compared with manure from cows fed RCS-based diets, maximum CH₄ production potential of manure from cows fed CS-based diets was 54% higher (182 vs. 118 L/kg of VS) throughout the incubation period. Maximum CH₄ production potential from manure also increased (by 17%) when cows were fed LO-supplemented diets compared with those fed nonsupplemented diets. Similar to maximum CH₄ production potential, VS degraded during incubation (i.e., VS loss) was higher from manure from cows fed CS-based diets versus cows fed RCS-based diets (30.6 vs. 22.5%), and increased (+3 percentage units, on average) with the addition of LO to the diets. Ammonia concentration in manure was higher when cows were fed CS-based diets compared with RCS-based diets, and declined with LO supplementation to CS and RCS diets. It is concluded that both dietary forage source and fat supplementation affect maximum CH₄ production potential from manure and this should be taken into account when such dietary options are recommended to mitigate enteric CH₄ emissions from dairy cows.     

Phosphorus partitioning during early lactation in dairy cows fed diets varying in phosphorus content

The effect of dietary P content on P partitioning and excretion during early lactation was evaluated in 13 cows fed diets containing 0.34 (no supplementary P), 0.51, or 0.67% P. All cows were fed a common pre-partum total mixed ration (TMR) (0.28% P), followed by common TMR (0.51% P) for 7 d post-partum. On day 7, cows were randomly assigned to one of the three dietary P treatments. All treatment diets contained 16.6% CP, 15.2% ADF, 26.3% NDF, and 0.74% Ca. Total collections of milk, urine, and feces were conducted during weeks 3, 5, 7, 9, and 11 of lactation. Average body weight (591 kg), milk yield (47.9 kg/d), and DMI (25.2 kg/d) throughout the 10-wk trial were not affected by dietary P content. With increasing dietary P, however, linear increases in P intake (84.7, 135.2, and 161.5 g/d), fecal P (42.3, 87.5, and 108.6 g/d), urinary P (0.32, 1.28, and 3.90 g/d), and total P excretion (42.6, 88.8, and 112.5 g/d) were observed. Apparent P digestibility (49.0, 34.4, and 32.8% of P intake) decreased quadratically with increasing dietary P. Phosphorus balance was highly variable, but cows fed the 0.34% P diet were in negative P balance longer than were cows fed diets containing 0.51 or 0.67% P. With increasing dietary P, serum concentrations of inorganic P increased linearly, but serum Ca and Mg concentrations decreased. Increasing dietary P increased fecal and urinary P excretion in early lactation cows. Increased duration of negative P balance and changes in blood mineral concentrations suggest that cows fed low P diets mobilized more P from body reserves than cows on medium- and high-P diets.     

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.     

Evaluation of palm kernel meal and corn distillers grains in corn silage-based diets for lactating dairy cows

The effects of increasing levels of solvent-extracted palm kernel meal (SPKM) and corn distillers dried grains (CDG) in corn silage-based diets on feed intake and milk production were examined in 2 experiments. In Experiment 1, 20 Holstein cows averaging 100 d in milk (DIM) (SD = 61.5) at the start of the experiment were utilized in an 11-wk randomized complete block design with 4 treatments in 5 blocks to study effects of increasing levels of SPKM in the diet. During a 3-wk preliminary period, cows were fed a standard diet. At the end of the preliminary period, cows were blocked by 4% fat-corrected milk yield, parity number (primiparous and multiparous), and DIM, and were assigned randomly to 1 of 4 experimental diets. The total mixed ration (TMR) consisted of (dry matter basis) 40% corn silage, 5% coarsely chopped wheat straw, and 55% concentrate. The increasing dietary levels of SPKM were achieved by replacing protein sources and citrus pulp with SPKM and urea (0, 5, 10, and 15% SPKM and 0.06, 0.22, 0.38, and 0.55% urea for SPKM0, SPKM5, SPKM10, and SPKM15, respectively). In Experiment 2, 18 Holstein cows averaging 93 DIM (SD = 49.1) at the start of the experiment were utilized in an 11-wk randomized complete block design with 3 treatments in 6 blocks to study effects of increasing levels of CDG in the diet. The preliminary period lasted for 2 wk. Assignment of cows to treatments was the same as in Experiment 1. The TMR consisted of (dry matter basis) 40% corn silage, 5% coarsely chopped wheat straw, and 55% concentrate. The increasing dietary levels of CDG were achieved by replacing soybean meal and citrus pulp with CDG and urea (0, 7, and 14% CDG and 0, 0.22, and 0.49% urea for CDG0, CDG7, and CDG14, respectively). There were no significant treatment effects on dry matter intake, milk yield, or milk composition in Experiment 1. Inclusion of SPKM tended to increase protein and lactose contents of milk. The SPKM0 diet promoted body weight loss. There were no treatment effects in Experiment 2, except for milk protein content, which was decreased by CDG. Plasma Lys concentration tended to be affected by SPKM and CDG inclusions. Plasma concentrations of 3-methylhistidine and Leu seemed to be related to body protein degradation/synthesis. The feeding of SPKM up to 15% in the diet decreased feed costs without detrimental effects on productive responses and tended to increase milk protein content. The inclusion of CDG in diets based on corn silage and corn byproducts might decrease milk protein content due to an unbalanced supply of AA, particularly Lys.     

Net energy for lactation of calcium salts of long-chain fatty acids for cows fed silage-based diets.

The NEL of calcium salts of long-chain fatty acids from palm oil was determined in mature Holstein cows. Twelve lactating (fed for ad libitum intake) and six nonlactating (restricted to near maintenance intake) Holstein cows were fed 0 or 2.95% fat supplement in diets formulated to contain 16 or 20% CP in a 2 x 2 factorial arrangement of treatments in a single reversal design within protein level. The fat supplement was substituted for ground corn and minerals. Two 6-d total collection balance trials were conducted during which cows were in open circuit respiration chambers. Intake of OM was lower for lactating cows fed the fat supplement (18.1 vs. 19.1 kg/d), but energy intake did not differ (93.2 Mcal/d). Total long-chain fatty acid intake was increased from 477 to 820 g/d with fat feeding. Apparent digestibility of long-chain fatty acids was increased 11.1 percentage units with increased dietary CP for lactating cows with no difference in fatty acid digestibility for the dry cows. Milk yield was higher (34.3 vs. 32.0 kg/d) with fat feeding, but milk energy yield did not differ (22.6 Mcal/d). The NEL of the fat supplement was estimated from the incremental differences in energy values within cows, assuming NEL of corn replaced by fat to be 1.96 Mcal/kg DM, and was determined to be 6.52 Mcal/kg DM (SE = 1.74). The efficiency of the use of metabolizable energy for lactation from dietary fat was 77.2%. The energy in calcium salts of long-chain fatty acids is utilized efficiently for lactation in mature cows.     

Effect of type and level of dietary fat on rumen fermentation and performance of dairy cows fed corn silage-based diets

The objective of this study was to investigate the effects of tallow and choice white grease (CWG) fed at 0, 2, and 4% of the diet dry matter (DM) on rumen fermentation and performance of dairy cows when corn silage is the sole forage source. Fifteen midlactation Holstein cows were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments were 0% fat (control), 2% tallow, 2% CWG, 4% tallow, and 4% CWG (DM basis). The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (DM basis). Cows were allowed ad libitum consumption of diets fed twice daily as total mixed rations. Cows fed supplemental fat had lower DM intake and produced less milk and milk fat than cows fed the control diet. Feeding 4% fat reduced milk production and milk fat yield relative to feeding 2% fat. Treatments had little effect on the concentration of trans-octadecenoic acids in milk fat. Total trans fatty acids were poorly related to changes in milk fat percentage. Ruminal pH and total volatile fatty acids concentration were not affected by supplemental fat. The acetate:propionate ratio, NH3-N, and numbers of protozoa in the rumen were significantly decreased when fat was added to the diets. Source of dietary fat did not affect rumen parameters. There was no treatment effect on in situ corn silage DM and neutral detergent fiber disappearance. Including fat in corn silage-based diets had negative effects on milk production and rumen fermentation regardless of the source or level of supplemental fat.     

Effect of alfalfa forage preservation method and particle length on performance of dairy cows fed corn silage-based diets and tallow

A study was conducted to evaluate the effect of including alfalfa preserved either as silage or long-stem or chopped hay on DMI and milk fat production of dairy cows fed corn silage-based diets with supplemental tallow (T). Fifteen Holstein cows that averaged 117 DIM were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments (DM basis) were: 1) 50% corn silage:50% concentrate without T (CS); 2) 50% corn silage:50% concentrate with 2% T (CST); 3) 25% corn silage:25% short-cut alfalfa hay:50% concentrate with 2% T (SAHT); 4) 25% corn silage:25% long-cut alfalfa hay:50% concentrate with 2% T (LAHT); and 5) 25% corn silage:25% alfalfa silage:50% concentrate with 2% T (AST). Cows were allowed ad libitum consumption of a TMR fed 4 times daily. Diets averaged 16.4% CP and 30.3% NDF. Including 2% T in diets with corn silage as the sole forage source decreased DMI and milk fat percentage and yield. Replacing part of corn silage with alfalfa in diets with 2% T increased milk fat percentage and yield. The milk fat of cows fed CST was higher in trans-10 C18:1 than that of cows fed diets with alfalfa. No effect of alfalfa preservation method or hay particle length was observed on DMI and milk production. The milk fat percentage and yield were lower, and the proportion of trans-10 C18:1 in milk fat was higher for cows fed LAHT than for cows fed SAHT. Alfalfa preservation method had no effect on milk fat yield. Ruminal pH was higher for cows fed alfalfa in the diets, and it was higher for cows fed LAHT than SAHT. Feeding alfalfa silage or chopped hay appears to be more beneficial than long hay in sustaining milk fat production when 2% T is fed with diets high in corn silage. These results support the role of trans fatty acids in milk fat depression.     

Effects of dietary protein concentration and balance of absorbable amino acids on productive responses of dairy cows fed corn silage-based diets

A cyclical changeover design experiment (3-wk periods; 12-wk total) was conducted to evaluate whether improving the balance of absorbable AA would allow the feeding of less crude protein (CP) without compromising production, thereby reducing the potential environmental pollution from dairy farms. Sixteen multiparous Holstein cows were assigned to 1 of 8 dietary treatments as total mixed rations (TMR) containing [dry matter (DM) basis] 45% corn silage, 5% coarsely chopped wheat straw, and 50% concentrate mixture. The 8 treatments were formulated to differ in dietary CP (14 and 16%; DM basis) and in the balance of absorbable AA achieved by changing the main protein source (MPS) of the concentrate mixtures [replacing soybean meal (SBM) with corn byproducts (CBP), dried corn distillers grains (DDG), and some corn gluten meal], and by adding a mixture of rumen-protected Lys and Met (RPLM). Feeding lactating dairy cows corn silage-based diets with 16% CP promoted significantly higher DM intakes and milk yields, and lower feed N-use efficiency than feeding diets with 14% CP. Replacing SBM with CBP significantly increased milk yields and decreased milk fat and protein concentrations, but had no effect on the efficiency of conversion of feed N into milk N. With 16% CP diets, the addition of RPLM decreased feed N use efficiency. A significant effect was observed for the MPS × RPLM interaction on milk protein concentrations. Plasma Lys concentration was lower with diets based on CBP, and plasma Met increased with RPLM. We did not find clear benefits of RPLM in facilitating a reduction of dietary protein without loss of production.     

Performance and nutrient digestibility by dairy cows treated with bovine somatotropin and fed diets with steam-flaked sorghum or steam-rolled corn during early lactation

This study compared effects of exogenous bovine somatotropin (bST) on the performance of early lactation cows fed diets differing in ruminally degradable starch. Thirty-two Holstein cows (24 multiparous) in early lactation (5 d in milk) were divided into four groups and fed diets containing 39% grain as steam-flaked sorghum or steam-rolled corn with or without exogenous bST for 90 d. Grain processing did not affect dry matter intake as a percentage of body weight or yields of milk, but steam-rolled corn improved efficiency of feed utilization during the first 45 d of the study. Cows receiving bST had lower dry matter intake during the first 45 d of treatment. Milk yield and efficiency of feed utilization were increased by bST treatment, and milk yield response was greater during the first half than during the second half of the study. Milk composition and yield of milk components did not differ among treatments. Flaked sorghum increased in vitro starch hydrolysis and digestibilities of dry matter, organic matter, and starch, but neither method of grain processing nor bST affected digestibilities of crude protein, acid detergent fiber, or neutral detergent fiber. Grain type did not affect milk yield, and responses to bST were lower from 7 to 13 wk than from 1 to 6 wk prepartum.     

Response of early lactation dairy cows fed diets varying in source of nonstructural carbohydrate and crude protein

Seventy-six high producing Holstein cows were randomly assigned in a 2 x 2 factorial to evaluate two sources of nonstructural carbohydrates (corn and barley), which supposedly differed in degradability of starch with two sources of CP degradability (soybean meal and urea) in the concentrate mix during wk 4 through 14 postpartum. Total mixed diets, formulated to be isonitrogenous at 16% CP, contained (DM) 40% corn silage, 10% alfalfa hay, and 50% of the respective concentrate mix. Nonstructural carbohydrate degradability was similar for concentrate mixes containing corn or barley. Production of milk (32.2 and 31.8 kg/d) was similar, but production of 4% FCM (29.1 and 27.4 kg/d) and SCM (29.1 and 27.5 kg/d) was decreased for cows fed barley due to lower percentages of fat (3.39 and 3.22) and SNF (8.65 and 8.59). Percentages of protein (3.09 and 3.08) were similar for cows fed corn and barley diets. Degradability of CP did not affect production of milk (31.9 and 32.0 kg/d), 4% FCM (28.5 and 28.0 kg/d), and SCM (28.4 and 28.2 kg/d) for cows fed soybean meal and urea. Dry matter intake was lower for cows fed barley (20.7 and 19.2 kg/d), but intakes (20.1 and 19.8 kg/d) were similar for cows fed soybean meal and urea. Providing an alternative nonstructural carbohydrate source (barley versus corn) did not increase utilization of a more readily degradable CP source (urea versus soybean meal).     

Effects of various glucogenic sources on production and metabolic responses of dairy cows fed grass silage-based diets

Four rumen cannulated Finnish Ayrshire cows in midlactation were used in an experiment designed as a 4 x 5 incomplete Latin square with 2-wk periods to compare effects of glucogenic substrates on grass silage-based diets. The five treatments were continuous infusions of 1) water (control), 2) casein 300 g/d, 3) glucose 300 g/d, 4) propionic acid 247 g/d, and 5) barley starch 270 g/d. Substrates were infused either into the rumen (propionic acid) or into the abomasum (other substrates). As a basal diet, cows were fed a formic acid treated grass silage ad libitum (digestible organic matter 690 g/kg dry matter [DM], crude protein [CP] 131 g/kg DM) and a barley-rapeseed concentrate (CP 141g/kg DM) at a rate of 7 kg/d. Production responses to glucogenic substrates other than casein were negligible, suggesting that glucose supply of the cows did not primarily limit milk production. However, with casein cows produced significantly more milk, milk protein, and lactose than with other glucogenic substrates. Casein increased urea and essential amino acid (EAA), and decreased nonessential AA (NEAA) in arterial plasma compared with other substrates, suggesting that casein provided precursors both in terms of NEAA for gluconeogenesis and EAA for milk protein synthesis. This puts forward that providing the AA needs of the mammary gland for milk protein synthesis are met, glucose supply may become the next limiting factor for milk protein synthesis in cows fed diets based on restrictively fermented grass silage. The limited supply of AA from the basal diet, and possibly the low production levels of cows partly invalidated the hypothesis of monitoring differing glucogenic substrates for grass silage-based diets.     

Effect of substituting brown rice for corn on lactation and digestion in dairy cows fed diets with a high proportion of grain

The effects of the substitution of brown rice (Oryza sativa L.; BR) for corn (Zea mays L.) in ensiled total mixed ration (TMR) that had a high proportion of grain on feed intake, lactation performance, ruminal fermentation, digestion, and N utilization were evaluated. Nine multiparous Holstein cows (51 ± 9 d in milk) were used in a replicated 3 × 3 Latin square design with 3 dietary treatments: a diet containing 0, 20, or 40% steam-flaked BR and 40, 20, or 0% steam-flaked corn (dry matter basis). Cows were fed ad libitum an ensiled TMR consisting of 40.7% alfalfa silage, 11.8% grass silage, 7.1% soybean meal, and 40.0% steam-flaked grain (dry matter basis). The ensiled TMR was prepared by baling fresh TMR, and then sealed by a bale wrapper and stored outdoors at 5 to 30°C for over 6 mo. Dry matter intake and milk yield were lower for cows fed 40% BR than for cows fed 40% corn. The ruminal pH and total volatile fatty acid concentrations were not affected by dietary treatment. The ruminal ammonia-N concentration decreased as the percentage of BR in the diets was elevated. The proportion of acetate decreased, and that of propionate and butyrate increased with the increasing levels of BR. Plasma urea-N concentrations was lower and glucose and insulin concentrations were higher for cows fed 40% BR than for cows fed 40% corn. The whole-tract apparent digestibility of dry matter, organic matter, and starch increased, and the digestibility of neutral detergent fiber and acid detergent fiber decreased with the increasing BR level in the diet, with no dietary effect on crude protein digestion. As a proportion of N intake, the urinary N excretion was lower and the retention of N was higher for cows fed 40% BR than for cows fed 40% corn, with no dietary effect observed on N secretion in milk and fecal N excretion. These results show that substituting BR for corn decreases urinary N losses and improves N utilization, but causes adverse effects on milk production when cows are fed high-grain diets at 40% of dietary dry matter.     

Effects of dietary protein and starch on intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets

Feed intake, milk production, and milk fatty acid profiles of dairy cows fed corn silage-based diets with different protein and starch concentrations were measured in a 3-period experiment in a changeover design using 12 Holstein cows. Each experimental period lasted for 3 wk. The diet fed as a total mixed ration consisted of 45% corn silage, 5% coarsely chopped wheat straw, and 50% concentrate, on a dry matter (DM) basis. The 4 treatments, formulated to be isoenergetic and to differ in concentrations of dietary crude protein (CP) and starch (DM basis), were as follows: low CP and low starch (LPLS; 14% CP and 15% starch), low CP and high starch (LPHS; 14% CP and 25% starch), high CP and low starch (HPLS; 16% CP and 15% starch), and high CP and high starch (HPHS; 16% CP and 25% starch). The LPLS treatment led to lower DM intake, milk yield, milk protein concentration, and milk lactose yield, probably due to a shortage of both rumen-degradable protein supply to rumen microbes and glucogenic nutrients to the animal. There were no differences between protein-rich diets and LPHS, suggesting that this diet satisfied the rumen-degradable protein requirements of rumen microbes and did not limit feed intake, and the increased supply of glucogenic nutrients spared AA so that the nutrient requirements of mid lactation dairy cows were met. Further increases in CP concentration increased plasma urea concentration and resulted in decreased efficiency of conversion of dietary N into milk N. Milk fatty acid profiles were affected by starch and protein supply, with starch having the largest effect. Additionally, increasing dietary starch concentration decreased the apparent transfer of dietary polyunsaturated fatty acids to milk, suggesting an increased channeling of fatty acids to adipose tissue. The results further suggest that C_15:0 and C_17:0 are synthesized de novo in animal tissues.     

The effects of starch and rapidly degradable dry matter from concentrate on ruminal digestion in dairy cows fed corn silage-based diets with fixed forage proportion

This study investigated the effects of the type (starch vs. nonstarch) and rate of ruminal degradation of carbohydrates from the concentrate on digestion in dairy cows fed corn silage-based diets. Six ruminally cannulated cows were assigned to 6 treatments in a 6 × 6 Latin square design. Treatments were arranged in a 3 × 2 factorial design. Two starch levels [25 and 41% dry matter (DM) for low starch (LS) and high starch (HS) diets, respectively] were obtained by replacing starch-rich feedstuffs by nonstarch feedstuffs. These starch levels were combined with slowly, moderately, and rapidly rumen-degradable feedstuffs to obtain 3 levels of rapidly degradable carbohydrates from concentrate (18, 23, and 28% DM). These levels were estimated from the DM disappearance of concentrate after 4 h of in sacco incubation (CRDM). Wheat and corn grain were used as rapidly degradable and slowly degradable starch feedstuffs, respectively. Soybean hulls and citrus pulp were used as slowly degradable and rapidly degradable nonstarch feedstuffs, respectively. No interaction effect was found between dietary starch content and CRDM on pH range, volatile fatty acid (VFA) range, or VFA profile. Increasing CRDM led to a linear decrease in acetate-to-propionate ratio (from 2.7 to 2.1), and a linear increase in the pH and VFA ranges (from 0.86 to 1.12 pH units and from 34 to 56 mM, respectively). Feeding HS diets decreased acetate-to-propionate ratio (2.6 vs. 2.0) and increased pH range (0.89 vs. 1.04 pH units), but had no effect on VFA range. Increasing CRDM linearly decreased mean ruminal pH in LS diets but linearly increased mean ruminal pH in HS diets. Fibrolytic activity was unaffected in LS diets but decreased strongly in HS diets (from 62 to 50%). These findings suggest that pH regulation differs on a short-term and on a longer-term basis. In the short-term, increasing CRDM increased the rate of VFA production, which may have been partly buffered under LS diets due to the higher cation exchange capacity of nonstarch feedstuffs compared with starch-rich feedstuffs. In the longer term, feeding starch reduced fibrolytic activity, which may have led to lower total VFA production and higher mean pH. The results of this experiment clearly show that both fermentative characteristics of the concentrate and dietary starch content should be taken into account when formulating diets to prevent subacute ruminal acidosis and to predict VFA profile.     

Addition of buffers to high quality alfalfa hay-based diets for dairy cows in early lactation

Beginning 4 wk postpartum, 14 Holstein cows were paired according to expected calving date and lactation number and assigned randomly to one of two treatments in a single reversal experiment designed to study the effects of added buffers to high quality alfalfa hay-based diets. Cows were offered daily 14.5 kg of concentrate containing 0 or 2% sodium bicarbonate and .5% magnesium oxide (as fed), plus free choice high quality alfalfa hay in a ratio of forage:grain approaching 50:50 (dry matter). No differences were in milk production, milk fat percentage, fat-corrected milk, or dry matter intake. Dry matter intake of grain was decreased with addition of buffers. Kilograms fat-corrected milk per kilogram of dry matter intake were 1.41 and 1.45 for control and buffered diets. No differences were significant for rumen pH, ammonia concentration, molar proportions of acetate and propionate, or ratio of acetate: propionate. Concentrations of total volatile fatty acids were higher for cows fed the buffered diet. No differences were in blood acid-base status or in various serum metabolites. Urine pH was 8.11 and 8.20 for control and buffered diets. Fractional urinary excretion of magnesium and sodium was greater when cows consumed the buffered diet. Diet digestibilities and rate of passage were not affected by dietary buffers. Addition of sodium bicarbonate plus magnesium oxide did not improve performance of early lactation cows fed high quality alfalfa hay as the sole forage.     

Effects of replacement of barley with oats on milk fatty acid composition in dairy cows fed grass silage-based diets

This study consists of milk fatty acid (FA) data collected during 2 in vivo experiments. For this study, 8 cows from each experiment were included in a replicated 4 × 4 Latin square design. At the start of experiment 1 (Exp1) cows were at (mean ± standard deviation) 87 ± 34.6 d in milk, 625 ± 85.0 kg of body weight, and 32.1 ± 4.17 kg/d milk yield and at the start of experiment 2 (Exp2) cows were at 74 ± 18.2 d in milk, 629 ± 87.0 kg of body weight, and 37.0 ± 3.2 kg/d milk yield. In Exp1, we examined the effects of gradual replacement of barley with hulled oats (oats with hulls) on milk FA composition. The basal diet was grass silage and rapeseed meal (58 and 10% of diet DM, respectively), and the 4 grain supplements were formulated so that barley was gradually replaced by hulled oats at levels of 0, 33, 67, and 100% on dry matter basis. In Exp2, we examined (1) the effects of replacing barley with both hulled and dehulled oats (oats without hulls) and (2) the effects of gradual replacement of hulled oats with dehulled oats on milk FA composition. The basal diet was grass silage and rapeseed meal (60 and 10% of diet DM, respectively), and the 4 pelleted experimental concentrates were barley, hulled oats, a 50:50 mixture of hulled and dehulled oats, and dehulled oats on dry matter basis. In Exp1, gradual replacement of barley with hulled oats decreased relative proportions of 14:0, 16:0, and total saturated FA (SFA) in milk fat linearly, whereas proportions of 18:0, 18:1, total monounsaturated FA, and total cis unsaturated FA increased linearly. Transfer efficiency of total C18 decreased linearly when barley was replaced by hulled oats in Exp1. In Exp2, relative proportions of 14:0, 16:0, and total SFA were lower, whereas proportions of 18:0, 18:1, monounsaturated FA, and cis unsaturated FA were higher in milk from cows fed the oat diets than in milk from cows fed the barley diet. Moreover, in Exp2, gradual replacement of hulled oats with dehulled oats slightly decreased the relative proportion of 14:0 in milk fat but did not affect the proportions of 16:0, 18:0, 18:1, total SFA, monounsaturated FA, trans FA, or polyunsaturated FA. In Exp2, transfer efficiency of total C18 was lower when cows were fed the oat diets than when fed the barley diet and decreased linearly when hulled oats were replaced with dehulled oats. Predictions of daily CH₄ emissions (g/d) using the on-farm available variables energy-corrected milk yield and body weight were not markedly improved by including milk concentrations of individual milk FA in prediction equations. In conclusion, replacement of barley with oats as a concentrate supplement for dairy cows fed a grass silage-based diet could offer a practical strategy to change the FA composition of milk to be more in accordance with international dietary guidelines regarding consumption of SFA.     

Effects of substitution of different levels of steam-flaked corn for finely ground corn on lactation and digestion in early lactation dairy cows

Eight multiparous Holstein cows, 4 of them fitted with rumen cannulas, were used to test the effects of substitution of steam-flaked corn (SFC) for equal amounts of finely ground corn (FGC) in diets on feed intake and digestion, blood metabolites, and lactation performance in early lactation dairy cows. Cows were fed 4 diets in a replicated 4 × 4 Latin square design. The fistulated cows formed 1 replicate. Each experimental period lasted for 3 wk. The 4 diets contained 0, 10, 20, or 40% SFC and 40, 30, 20, or 0% FGC (dry matter basis), respectively. The milk protein content and yield, milk solid nonfat content and yield, plasma glucose concentration, and dry matter intake increased as the proportion of SFC increased in diets. Apparent total tract digestibilities of dry matter, organic matter, neutral detergent fiber, acid detergent fiber, and average ruminal fluid NH₃-N concentration decreased with increasing levels of SFC. The ruminal fluid pH was not affected by the substitution of SFC for FGC. The 20% SFC substitution improved digestion of crude protein, yield of fat-corrected milk, milk lactose content, fat, and fat yield. The 40% SFC substitution increased urea concentration in both plasma and milk. It was concluded that 20% of SFC substitution for FGC appeared to be an appropriate level in diet for early lactation dairy cows.     

Replacing corn with glycerol in diets for transition dairy cows

Expansion of the biofuels industry has increased the availability of glycerol as an alternative feed for dairy cows. The objective of this study was to determine the effects of glycerol on feed intake, milk production, rumen volatile fatty acids, and metabolic parameters in transition dairy cows. Multiparous Holstein cows were fed diets containing either high-moisture corn (n = 11) or glycerol (n = 12) from −28 to +56 d relative to calving. Glycerol was included at 11.5 and 10.8% of the ration dry matter for the pre- and postpartum diets, respectively. Prepartum feed intake was not changed by glycerol feeding (14.9 vs. 14.6 kg/d, control vs. glycerol) nor did postpartum feed intake differ (19.8 vs. 20.7 kg/d, control vs. glycerol). Overall milk yield did not differ (35.8 vs. 37 kg/d, control vs. glycerol) and milk composition, milk urea nitrogen, somatic cells, and energy balance were not different with glycerol feeding. Blood glucose content was decreased in cows fed glycerol during the prepartum period (59.1 vs. 53.4 mg/dL), and β-hydroxybutyrate concentration was increased (0.58 vs. 0.82 mmol/L, control vs. glycerol). Concentrations of blood nonesterified fatty acids did not differ between the treatment groups, and no response to glycerol for blood metabolites during the postpartum period was observed. Total rumen volatile fatty acid concentrations (mmol/L) did not differ between treatments, but proportions of rumen propionate and butyrate were greater for cows fed glycerol (22.7 vs. 28.6% of propionate, control vs. glycerol; and 11.5 vs. 15.3% of butyrate, control vs. glycerol) at the expense of acetate (61.4 vs. 51.5%, control vs. glycerol). These data indicate that glycerol is a suitable replacement for corn grain in diets for transition dairy cows.