Impact of alfalfa maturity and preservation method on milk production by cows in early lactation.

Ninety-six cows in early lactation were used in two experiments to measure the impact of alfalfa maturity (early or midbud vs. early or midbloom) and method of forage preservation (silage vs. hay) on DMI and milk production. Silage diets were fed as TMR, and hay was fed separately from grain. All diets contained 60% alfalfa (dry basis) and were balanced for 19% CP. Maturity had little effect on milk production in either experiment. Adjusted milk production for early cut silage, late cut silage, early cut hay, and late cut hay were 33.6, 33.4, 30.7, and 32.1 kg/d for Experiment 1 and 38.1, 37.0, 35.0 and 35.0 kg/d for Experiment 2. Increased alfalfa maturity tended to reduce DMI. Cows fed the silage diets consumed 1.2 kg more DM and produced an average of 2.1 kg more milk daily in Experiment 1 than those fed the hay diets. All treatment groups consumed similar amounts of DM in Experiment 2; however, cows fed silage produced 2.6 kg/d more milk than those fed hay. Preserving alfalfa as silage and feeding in a TMR to cows in early lactation resulted in greater milk production via increased DMI or improved feed efficiency compared with preserving alfalfa as hay and feeding grain separately.     

Impact of forage fiber content on digestion and digesta passage in lactating dairy cows

Five Holstein cows (5 wk postpartum) were used in a Latin square design (15-d periods) to determine rumen fill and fractional rates of ruminal digestion and passage. Treatments consisted of prebloom, midbloom, and full bloom alfalfa hay, mature bromegrass hay, and corn silage fed in diets containing forage: concentrate in a 60:40 ratio (DM basis) formulated to be isonitrogenous. Intake of DM averaged 4.0% of body weight for prebloom alfalfa and corn silage. Milk yield and DM intake were lower for full bloom alfalfa and bromegrass than for prebloom alfalfa. Digestibility of organic matter was 7.5 percentage units lower for full bloom than for prebloom alfalfa. Weight of DM in the rumen was higher for midbloom and full bloom alfalfa and bromegrass than with prebloom alfalfa. Ruminal retention time of Yb applied to forage was longer for bromegrass than for prebloom alfalfa. Fractional rates of in situ NDF digestion were slower for full bloom alfalfa and bromegrass than for prebloom alfalfa. Results suggest that the point of limitation of feed intake due to gut fill is dependent on forage quality as well as energy demand of the animal. Dry matter fill of the rumen was more closely related to rates of ruminal digestion and passage than to total tract digestibility or maximum digestibility after lengthy in situ fermentation.     

Site and extent of nutrient digestion in lactating dairy cows fed alfalfa protein concentrate or soybean meal

In vivo and in situ trials were conducted to investigate the utilization of alfalfa protein concentrate as a protein supplement for lactating dairy cows. In the in vivo trial, four Holstein cows fitted with ruminal, duodenal, and ileal cannulae were used in a crossover experiment to measure site and extent of nutrient digestion. Isonitrogenous and isoenergetic diets containing alfalfa protein concentrate or soybean meal were fed four times daily. Sixty percent of dietary total N was provided by the test proteins. Ruminal ammonia and total VFA concentrations were lower in cows fed alfalfa protein concentrate. Fractional digestion coefficient of organic matter (52 vs. 43%) and degradation of dietary protein (57 vs. 47%) in the rumen were slightly lower in cows fed alfalfa protein concentrate. The ratio of amino acid flow to the small intestine to dietary intake of amino acid was higher in cows fed alfalfa protein concentrate. In the in situ trial, rate of N disappearance (2.4 vs. 9.5%.h-1) and potential protein degradability (35 vs. 68%) were lower for alfalfa protein concentrate. Results suggest that alfalfa protein concentrate may be more resistant to ruminal degradation than soybean meal and could be utilized as a relatively undegradable protein source for milk production.     

Effects of tallow in diets based on corn silage or alfalfa silage on digestion and nutrient use by lactating dairy cows

Six multiparous Holstein cows (average 31 days in milk; 36.3 kg/d of milk) fitted with ruminal cannulas were used in a 6 x 6 Latin square with 21-d periods to investigate the effects of diets that varied in forage source and amount of supplemental tallow. Isonitrogenous diets in a 2 x 3 factorial arrangement were based on either high corn silage (40:10 corn silage to alfalfa silage, % of dry matter) or high alfalfa silage (10:40 corn silage to alfalfa silage, % of dry matter) and contained 0, 2, or 4% tallow. Intakes of dry matter and total fatty acids were lower when cows were fed the high corn silage diet. Tallow supplementation linearly decreased dry matter intake. Milk yield was unaffected by diet; yields of milk fat and 3.5% fat-corrected milk were higher for the high alfalfa silage diet but were unaffected by tallow. Milk fat percentage was higher for the high alfalfa silage and tended to decrease when tallow was added to the high corn silage diet. Contents of trans-C18:1 isomers in milk fat were increased by high corn silage and tallow, and tended to be increased more when tallow was fed in the high corn silage diet. Ruminal pH and acetate:propionate were lower when high corn silage was fed. Ruminal acetate:propionate decreased linearly as tallow increased; the molar proportion of acetate was decreased more when tallow was added to the high corn silage diet. Ruminal liquid dilution rates were higher for the alfalfa silage diet; ruminal volume and solid passage rates were similar among diets. Total tract apparent digestibilities of dry matter, organic matter, crude protein, starch, energy, and total fatty acids were unaffected by diet. Digestibilities of neutral detergent fiber, acid detergent fiber, hemicellulose, and cellulose were lower when high corn silage was fed. The high alfalfa silage diet increased intakes of metabolizable energy and N, and increased milk energy and productive N. Tallow decreased the amount of N absorbed but had few other effects on utilization of energy or N. Tallow linearly increased concentrations of nonesterified fatty acids and cholesterol in plasma; cholesterol was increased by high alfalfa silage. Overall, forage source had more pronounced effects on production and metabolism than did tallow supplementation. Few interactions between forage source and tallow supplementation were detected except that ruminal fermentation and milk fat content were affected more negatively when tallow was fed in the high corn silage diet.     

Effect of alfalfa maturity on fiber utilization by high producing dairy cows

Six ruminally cannulated cows were used in a replicated 3 x 3 Latin square to study the effect of alfalfa maturity on utilization of DM and fiber. Cows were fed three diets based on alfalfa hay at early vegetative, late bud, or full bloom maturities. Forage:concentrate ratios were: 68:32, 53:47, and 45:55 for diets with early vegetative, late bud, and full bloom hays. Concentrations of NDF in the early vegetative and late bud diets was higher (32.6%) than NDF in the full bloom diet (27.9%) after accounting for feed refusals. Fat-corrected milk yield was similar, but fat percentage was higher for the diet with early vegetative hay than the diets with late bud or full bloom alfalfa. Dry matter intake was higher for the diet with early vegetative hay than the diets with late bud or full bloom hay (26.1, 24.4, and 24.8 kg/d). Ruminal dacron bag incubations of the three hays suggest that the high digestibility of the early vegetative hay was due to more soluble DM, more potentially digestible DM and fiber, and a faster rate of digestion. These factors compensated for the faster passage of the early vegetative hay and resulted in a higher intake and better utilization of DM and fiber.     

Effect of abomasal pectin infusion on digestion and nitrogen balance in lactating dairy cows

Two experiments were conducted to test the hypothesis that increasing carbohydrate fermentation in the large intestine would increase intestinal conversion of blood urea N to microbial protein, thereby reducing urinary N output. In experiment 1, 3 multiparous Holstein cows were used in an incomplete 4 × 4 Latin square with 14-d periods. Cows were fed the same basal diet and treatments were the abomasal infusion of 0, 0.5, or 1 kg/d of citrus pectin, or the addition of 1 kg/d of molasses to the basal diet. Experiment 2 used 6 cows in a double reversal design with four 21-d periods. Cows were fed one basal diet and treatments were the abomasal infusion of either 0 or 1 kg/d of pectin. In experiment 1, pectin infusion linearly decreased basal ration intake from 25.0 to 23.2 kg/d. This was prevented in experiment 2 by restricted feeding, and basal ration intake was 22.2 kg/d. Abomasal pectin caused numeric decreases in total tract apparent digestibility of neutral detergent fiber and neutral detergent solubles in experiment 1 and significantly decreased starch digestibility in experiment 2, suggesting that pectin may have reduced postruminal nutrient digestibility. Pectin infusion did not affect milk yield but decreased milk fat percentage from 3.69 to 3.53% in experiment 2. Increasing abomasal pectin tended to decrease urinary N and increase fecal N in experiment 1 and these effects were significant in experiment 2. For both experiments, urinary N decreased 26 g/d, approximately 10% of daily urine N output. Abomasal pectin did not affect fecal pH or DM content; however, in experiment 2, pectin decreased fecal ammonia from 19.8 to 13.4 mmol/kg of DM and increased fecal purines from 13.8 to 15.8 mmol/kg of DM. In both experiments, excretion of fecal purines was increased from 15 g/d for 0 kg/d pectin to 18 g/d for 1 kg/d pectin, although this increase was only significant in experiment 2. These results suggest that manipulating dairy diets to increase postruminal fermentation may reduce urinary N and consequently manure ammonia losses. However, abomasal pectin tended to decrease both ruminal ammonia concentration and urinary purine derivative output in experiment 2, suggesting that postruminal pectin fermentation may have compromised rumen microbial protein production.     

Starch and stage of maturity of grass silage: site of digestion and intestinal nutrient supply in dairy cows

The interaction between the quality of grass silage and starch supplementation on ruminal digestion was studied in an experiment with a 2 x 2 factorial design using four dairy cows. Treatment factors were grass silage harvested after either 21 or 37 d of regrowth and two concentrations of steam-flaked corn starch (0 or 4 kg/d). Ruminal volume and flow of duodenal digesta were estimated. When forage was harvested at a more mature stage, only minor effects were noted for silage composition and, consequently, ruminal and intestinal digestion. The addition of starch to the diet tended to reduce ruminal digestion of neutral detergent fiber. The reduction in ruminal digestion was not compensated by increased digestion in the large intestine. Starch increased duodenal nonammonia N flow because of an increase in bacterial N flow. The increase in bacterial N was accompanied by a reduction in the escape of feed N from the rumen. Results from this study indicate that the addition of ruminally available starch to diets based on grass silage reduced ruminally degradable neutral detergent fiber and increased the duodenal supply of protein. These effects have to be taken into account to predict production responses to extra starch.     

Effect of alfalfa silage storage structure and rumen-protected methionine on production in lactating dairy cows

The objective of this study was to determine whether production and nutrient utilization differed when lactating cows were fed diets based on 1 of 3 sources of alfalfa silage (AS) and whether performance was altered by feeding rumen-protected Met (RPM; fed as Mepron). Thirty-six lactating Holstein cows were blocked by parity and days in milk, then assigned to a randomized complete block design and fed a 3 × 2 arrangement of diets formulated from alfalfa ensiled in bag, bunker, or oxygen-limited silos, and supplemented with either 0 or 8 g of RPM/d. After feeding a covariate diet for 3 wk, treatment diets were fed for the remaining 12 wk of the trial. Experimental diets averaged [dry matter (DM) basis] 41% AS, 24% corn silage, 24% high-moisture corn, 3.7% soybean meal, 4% roasted soybeans, 2% ground shelled corn, 1.0% minerals and vitamins, 16.7% CP, and 31% NDF. Alfalfa from the oxygen-limited silo was lower in ash, higher in lactate, nonfiber carbohydrate, and in vitro NDF digestibility, had lower pH and ammonia content, and gave rise to greater DM intake and ADF digestibility than silage from the other 2 silos, indicating a more effective fermentation that, in turn, resulted in greater nutrient preservation. However, the more favorable composition, intake, and digestibility of alfalfa from the oxygen-limited silo were not reflected in improved milk production, which was not different among alfalfa sources. There was increased apparent N efficiency and trends for improved feed efficiency and protein yield with RPM supplementation across all 3 silages. The National Research Council (2001) model predicted that feeding RPM reduced Lys:Met ratio from 3.5 to 2.9, indicating that the diets were limiting in Met.     

Ryegrass or alfalfa silage as the dietary forage for lactating dairy cows

Renewed interest exists in using grass forages to dilute the higher crude protein (CP) and lower digestible fiber present in legumes fed to lactating dairy cows. A 3 x 3 Latin square feeding study with 4-wk periods was conducted with 24 Holstein cows to compare ryegrass silage, either untreated control or macerated (intensively conditioned) before ensiling, with alfalfa silage as the sole dietary forage. Ryegrass silages averaged [dry matter (DM) basis] 18.4% CP, 50% neutral detergent fiber (NDF), and 10% indigestible acid detergent fiber (ADF) (control) and 16.6% CP, 51% NDF, and 12% indigestible ADF (macerated). Alfalfa silage was higher in CP (21.6%) and lower in NDF (44%) but higher in indigestible ADF (26%). A lower proportion of the total N in macerated ryegrass silage was present as nonprotein N than in control ryegrass and alfalfa silages. Diets were formulated to contain 41% DM from either rye-grass silage, or 51% DM from alfalfa silage, plus high moisture corn, and protein concentrates. Diets averaged 17.5% CP and 28 to 29% NDF. The shortfall in CP on ryegrass was made up by feeding 7.6% more soybean meal. Intake and milk yields were similar on control and macerated ryegrass; however, DM intake was 8.3 kg/d greater on the alfalfa diet. Moreover, feeding the alfalfa diet increased BW gain (0.48 kg/d) and yield of milk (6.1 kg/d), FCM (6.8 kg/d), fat (0.26 kg/d), protein (0.25 kg/d), lactose (0.35 kg/d), and SNF (0.65 kg/d) versus the mean of the two ryegrass diets. Both DM efficiency (milk/DM intake) and N efficiency (milk-N/N-intake) were 27% greater, and apparent digestibility was 16% greater for DM and 53% greater for NDF and ADF, on the ryegrass diets. However, apparent digestibility of digestible ADF was greater on alfalfa (96%) than on ryegrass (average = 91%). Also, dietary energy content (estimated as net energy of lactation required for maintenance, milk yield, and weight gain) per unit of digested DM was similar for all three diets. Results of this trial indicated that, relative to ryegrass silage, feeding alfalfa silage stimulated much greater feed intake, which supported greater milk production.     

Macromineral digestion by lactating dairy cows: factors affecting digestibility of magnesium

The objectives of this experiment were to determine dietary factors influencing the apparent digestibility of Mg by lactating dairy cows and to compare empirical apparent digestibility values with Mg absorption coefficients used in the dairy cattle nutrient requirement model of the National Research Council (NRC). Data were compiled from 8 experiments with 39 dietary treatments and 162 cows (all lactating Holsteins) in which apparent digestibility of Mg was measured using total collection of feces and urine. The concentration of dietary Mg ranged from 0.20 to 0.36% of DM (mean = 0.27%). On average, 19% of the dietary Mg came from a Mg supplement (MgO or MgSO4). The concentration of dietary K ranged from 1.07 to 2.65% (mean = 1.60%). The mean apparent digestibility of Mg was 0.18 and ranged from -0.04 to 0.33. The average digestibility was 30% lower than the mean value calculated by the NRC model. The primary reason for the low average Mg digestibility was high concentrations of dietary K. At a dietary K concentration of 1%, empirical data agreed with NRC estimates, but apparent Mg digestibility decreased 0.075 (+/- 0.035)/percentage unit of K in the diet. Lactating dairy cows had to consume an additional 18 g of Mg/d for every 1 percentage unit increase in dietary K above 1% to maintain the same intake of digestible Mg as that consumed when fed a diet with 1% K.     

Effect of feeding macerated alfalfa silage on nutrient digestibility and milk yield in lactating dairy cows

Five feeding studies were conducted with 141 lactating Holstein cows comparing macerated and control alfalfa silage harvested at two cuttings in each of 2 yr. Overall, silage made from macerated alfalfa contained more ash (suggesting improved soil contamination); greater fiber and lower nonprotein nitrogen (NPN) content suggested greater fermentation in the silo. In a digestion study, two diets were fed containing [dry matter (DM) basis] 72% of either control or macerated second-cutting alfalfa. Apparent digestibility of neutral detergent fiber and acid detergent fiber (ADF) was increased by maceration, and similar changes in digestibility were observed with Yb or indigestible ADF as marker; indigestible ADF was used as a marker in later studies. Lactation trials were conducted with first- and second-cutting alfalfa from each year. In each study, diets were formulated from alfalfa silage plus concentrate based on processed high moisture ear corn; mean compositions were (DM basis): negative control (61% control alfalfa silage), macerated (61% macerated alfalfa silage), and positive control (50% control alfalfa silage). All diets contained 2% crude protein from either roasted soybeans or low-solubles fish meal; soybean meal was added to make the positive control isonitrogenous (but not equal in ruminal undergraded protein). Milk yield was greater on macerated than negative control in two of four trials but not different in the other two trials. Yields of milk and milk components were not different between macerated and positive control in one of four trials. Versus the negative control, milk fat synthesis was depressed on macerated alfalfa in one trial. Overall performance on macerated versus negative control indicated greater apparent digestibility of organic matter (OM), greater yield of milk, protein, and solids not fat, but lower milk fat content. Yields of milk and milk components were greater overall on positive control versus macerated. Estimation of net energy for lactation (NEL) from maintenance, milk yield, and body weight gain indicated that control and macerated alfalfa silage contained, respectively, 1.36 and 1.42 Mcal of NEL of OM, an increase of about 5% due to maceration of alfalfa in these trials.     

Pelleted beet pulp substituted for high-moisture corn: 2. Effects on digestion and ruminal digestion kinetics in lactating dairy cows

The effects of increasing concentrations of dried, pelleted beet pulp substituted for high-moisture corn on digestion and ruminal digestion kinetics were evaluated using eight ruminally and duodenally cannulated multiparous Holstein cows in a duplicated 4 x 4 Latin square design with 21-d periods. Cows were 79 +/- 17 (mean +/- SD) d in milk at the beginning of the experiment. Experimental diets with 40% forage (corn silage and alfalfa silage) and 60% concentrate contained 0, 6.1, 12.1, or 24.3% beet pulp substituted for high-moisture corn on a dry matter basis. Diet concentrations of neutral detergent fiber (NDF) and starch were 24.3 and 34.6% (0% beet pulp), 26.2 and 30.5% (6% beet pulp), 28.0 and 26.5% (12% beet pulp), and 31.6 and 18.4% (24% beet pulp), respectively. Ruminal dry matter pool decreased and NDF turnover rate increased as dietary beet pulp content increased. Potentially digestible NDF was digested more extensively and at a faster rate in the rumen with increasing beet pulp, resulting in increased total tract NDF digestibility. Passage rates of potentially digestible NDF and of indigestible NDF were not affected by treatment. True ruminal digestibility of starch decreased with increasing beet pulp substitution. This was caused by a linear increase in starch passage rate, possibly because of increasing ruminal fill, and a linear decrease in digestion rate of starch in the rumen, possibly because of reduced amylolytic enzyme activity for lower-starch diets. Although true ruminal starch digestibility decreased when more beet pulp was fed, whole tract starch digestibility was not affected because of compensatory digestion of starch in the intestines. Due to more thorough digestion of fiber in diets containing more beet pulp, whole-tract digestibility of organic matter increased linearly, and intake of digestible organic matter was not affected. Partially replacing high-moisture corn with beet pulp in low-forage diets increased fiber digestibility without reducing whole-tract starch digestibility.     

Macromineral digestion by lactating dairy cows: estimating phosphorus excretion via manure

Data from 8 experiments involving 39 diverse dietary treatments and 162 Holstein cows were used to derive equations that estimate manure excretion of P by lactating dairy cows. Within an experiment, diets were formulated to have similar P concentrations and to meet or slightly exceed standard recommendations for P. The data were generated from total collection digestion trials. The only sources of supplemental P used were dicalcium phosphate and monosodium phosphate. The concentration of dietary P ranged from 0.34 to 0.45% of dry matter (DM). Cows varied in milk production (8 to 59 kg/d), DM intake (12.4 to 30.5 kg/d), and P intake (45 to 133 g/d). Apparent digestibility of P averaged 40.4%, fecal output of P averaged 47 g/d, and apparent P retention averaged 4 g/d. Two equations were derived to estimate excretion of P via manure (g/d): 1) Manure P = -2.5 + 0.64 x P intake, and 2) Manure P = 7.5 + 0.78 x P intake - 0.702 x Milk; where P intake is in g/d and milk is kg/d. Both equations were evaluated using literature data, and both equations had acceptable accuracy for field use. The requirements for P of lactating dairy cows from the National Research Council (NRC) were also evaluated, and for most diets, those requirements were adequate based on retention of P.     

Stay-green ranking and maturity of corn hybrids: 2. Effects on the performance of lactating dairy cows

To address producer concerns that feeding high stay-green (SG) corn hybrids is associated with decreased performance and health problems in dairy cows, this study examined how the performance of cows was affected by feeding hybrids with contrasting SG rankings and maturities. Two near-isogenic corn hybrids with high (HSG; Croplan Genetics 691, Croplan Genetics, St. Paul, MN) and low (LSG; Croplan Genetics 737) SG rankings were grown on separate halves of a 10-ha field, harvested at 27% (maturity 1) or 35% (maturity 2) dry matter (DM) and ensiled in bag silos for 84 and 77 d, respectively. A further treatment involved addition of water (15 L/t) to the HSG maturity 1 hybrid during packing to compound the potential negative effects of excess water in the HSG hybrid. Each of the resulting silages was included in a total mixed ration consisting of 35, 55, and 10% (DM basis) of corn silage, concentrate, and alfalfa hay, respectively. In experiment 1, the total mixed ration was fed for ad libitum consumption twice daily to 30 Holstein cows (92±18 d in milk). This experiment had a completely randomized design and consisted of two 28-d periods, each with 14 d for adaptation and 14 d for sample collection. In experiment 2, the ruminal fermentation of the diets was measured using 5 ruminally cannulated cows on the last day of three 15-d periods. Ruminal contraction rate (2.28±0.14 contractions/min), milk yield (36.7±1.3 kg/d), yield of milk protein (1.1±0.03 kg/d), and concentration of milk protein (2.9±0.03%) were not affected by treatment. Feeding diets containing HSG instead of LSG reduced intake of crude protein (CP) and neutral detergent fiber, digestibility of neutral detergent fiber, and concentrations of ruminal total volatile fatty acids (VFA) and milk fat when the hybrids were harvested at 27% DM but not 35% DM. Across maturity stages, feeding diets containing HSG instead of LSG decreased DM and CP digestibility, increased rectal temperature and plasma ceruloplasmin concentration, and increased the efficiency of milk production. Except for increasing yeast and mold counts, adding water to the HSG hybrid harvested at 27% DM did not have adverse effects but was associated with greater starch intake, CP digestibility, and ruminal total VFA concentration, and decreased acetate to propionate ratio in dairy cows.     

Utilization of kura clover-reed canarygrass silage versus alfalfa silage by lactating dairy cows

The mixture of kura clover (Trifolium ambiguum M. Bieb.) and reed canarygrass (Phalaris arundinacea L.) has proven to be extremely persistent in the northern United States, but information about dairy cow performance on this mixture is lacking. Twenty lactating Holstein cows were used in a crossover design to compare dry matter (DM) intake and milk production from diets containing kura clover-reed canarygrass silage (KRS) or alfalfa (Medicago sativa L.) silage (AS). Forages were cut, wilted, ensiled in horizontal plastic bags, and allowed to ferment for at least 50 d before beginning the feeding experiment. The KRS was approximately 40% kura clover and 60% reed canarygrass. Treatments were total mixed rations formulated with either 57% of total DM from 1) AS or 2) KRS. Experimental periods were 28 d, with the first 14 d for diet adaptation and the last 14 d for measurement of intake and milk production. The neutral detergent fiber (NDF) concentrations of AS and KRS were 37.3 and 47.3%, respectively. The fermentation analyses indicated that both silages underwent a restricted fermentation, producing primarily lactic acid and some acetic acid. Dry matter intake (24.2 vs. 22.8 kg) and 4% fat-corrected milk (32.8 vs. 30.9 kg) were significantly higher for cows fed AS than for cows fed KRS. Cows consumed less NDF (6.7 vs. 8.0 kg) and less digestible NDF (3.0 vs. 4.4 kg) when fed AS diets compared with KRS diets, but the pool of ruminally undegraded NDF was similar (3.7 kg) between diets. Cows produced 1.5 kg of milk/kg of DM consumed regardless of the diet, indicating that digestible NDF of KRS was utilized with similar efficiency as the cell wall constituents of AS, but the intake of cows fed KRS may have been limited by rumen fill. Milk fat concentration tended to be higher for cows fed AS, but the milk true protein concentration and yields of fat and protein did not differ by treatment. Milk urea nitrogen content was higher when cows consumed AS (16.4 mg/ dL) compared with KRS (13.4 mg/dL). The cows fed KRS consumed more NDF but less total DMI, based on the results from this trial with diets formulated to contain approximately 60% of DM as forage, resulting in slightly lower milk yields than cows fed excellent-quality AS. This grass-legume mixture has the potential to be a source of quality forage for dairy cows in regions where alfalfa persistence is a problem.     

Effect of corn particle size on site and extent of starch digestion in lactating dairy cows

Two experiments were conducted to determine the effects of corn particle size (CPS) on site and extent of starch digestion in lactating dairy cows. Animals were fitted with ruminal, duodenal, and ileal cannulas. Dry corn grain accounted for 36% of dry matter intake. In experiment 1, 6 cows were used in a duplicate 3 x 3 Latin square design. Semiflint corn was used. Corn processing methods were grinding, medium rolling, and coarse rolling. The mean particle size of the processed corn was 730, 1807, and 3668 microm, respectively. Rumen digestibility of starch linearly decreased from 59% with ground corn to 36% with coarsely rolled corn. Similarly, small intestine digestibility linearly decreased with increased CPS, and consequently, the amount of starch digested in the small intestine was not affected by corn processing. In experiment 2, 4 cows were used in a 2 x 2 crossover design. Dent corn was used. Corn processing methods were grinding and coarse rolling. The mean particle size of the processed corn was 568 and 3458 microm, respectively. Rumen digestibility of starch decreased from 70% with ground corn to 54% with coarsely rolled corn. Small intestine digestibility of starch was not significantly affected by CPS, and the amount of starch digested in the small intestine tended to be greater for rolled than for ground corn. In both experiments, starch total tract digestibility decreased with increased CPS. In conclusion, CPS is an efficient tool to manipulate rumen degradability of cornstarch. In midlactation cows, the decrease in the amount of starch digested in the rumen between grinding and coarse rolling is partly compensated for by an increase in the amount of starch digested in the small intestine with dent genotype, but with semiflint genotype postruminal digestion is not increased and rumen escape starch is not utilized by the animal.     

Effects of fatty acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on ruminal digestion kinetics, and ruminal and postruminal nutrient digestion. Eight early lactation ruminally and duodenally cannulated cows (77 ± 12 days in milk, mean ± SD) were used in a replicated 4 × 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Saturated FS linearly decreased ruminal digestibility of dry matter and organic matter and linearly decreased ruminal neutral detergent fiber (NDF) digestibility. The reduction in ruminal NDF digestibility was because of a linear decrease in digestion rate and a linear increase in passage rate of potentially digestible NDF with increasing saturated FS. Total tract digestibility of NDF was not different between treatments because of compensatory postruminal digestion. Ruminal fatty acid and C18 fatty acid digestibility tended to increase linearly with increasing unsaturated FS, and postruminal C18 fatty acid digestibility decreased with increasing saturated FS. Saturated FS linearly decreased ruminal organic matter digestibility and decreased intestinal long-chain fatty acid digestibility, although differences in fatty acid digestibility may be partially explained by fatty acid intake.     

Impact of intake water temperatures on reticular temperatures of lactating dairy cows

Automatic temperature recording may allow early detection of disease, estrus, heat stress, and the onset of calving. The phase IV Cattle Temperature Monitoring System (MaGiiX Inc., Post Falls, ID) utilizes a passive bolus equipped with a temperature sensor, a stationary panel reader to query the bolus, and software to collect, analyze, and display data. One potential limitation to collection of reticular temperatures is the effect of water temperature and consumption on recorded temperatures. Two replicated 3 × 3 Latin square experiments were conducted at the Purdue Dairy Research and Education Center to assess the impact of water intake on reticular temperatures using the Cattle Temperature Monitoring System. Nine high-producing, mid-lactation, second-parity cows with low somatic cell counts were selected. Before administering a water treatment, access to feed and water was restricted for at least 2 h. Baseline reticular temperatures were established from measurements before water intake. In experiment 1, treatments were 25.2 kg of hot water (34.3°C ± 1.0), warm water (18.2°C ± 0.4), or cold water (7.6°C ± 0.4). In experiment 2, treatments were 18.9 kg of body-temperature water (38.9°C ± 0.2), cold water (5.1°C ± 0.4), or control (no water). Following water intake, reticular temperatures were collected for 3 h. In experiment 1, an initial dramatic decrease in reticular temperature was observed followed by a gradual increase toward baseline. Least squares means for maximum drop in temperature were 8.5 ± 0.5, 6.9 ± 0.5, and 2.2 ± 0.5°C for cold, warm, and hot water treatments, respectively. Yet at 3 h, reticular temperatures did not return to the baseline. In experiment 2, control cows remained within the baseline confidence interval through the observation period, and cows receiving body temperature water experienced an initial decrease in temperature (0.4 ± 0.2°C) with a return to within the baseline confidence interval within 15 min. Cows receiving cold water did not return to within the baseline confidence interval after a large decrease of 9.2 ± 0.2°C during the 3-h observational period. Moreover, a regression analysis of continued ascent in temperatures predicted that temperatures would return to baseline within 3.5 h. These results demonstrate that, when cows consume large quantities of cold water, the effect of water intake is sizable and sustained. The value of reticular temperatures for daily monitoring in a production setting hinges largely on the implications of this impact.     

Impact of dietary fiber and physical form on performance of lactating dairy cows

Two trials were conducted to study the effects of forage intake and physical form on lactating cow performance. In trial 1, four cows in a 4 X 4 Latin square were fed long alfalfa hay at 28, 36, 45, and 53% of total dry matter plus concentrate. Total dry matter intake was not affected by forage percent. Total chewing time and milk fat percentage increased linearly with increasing forage consumption. Maximum 4% fat-corrected milk production occurred when diets contained 27% neutral detergent fiber and 18% acid detergent fiber. In trial 2, four cows in a 4 X 4 Latin square were fed diets of chopped alfalfa hay and concentrate in proportions to supply 27.4% total ration neutral detergent fiber. Mean particle length measured with an oscillating screen particle separator of the chopped hay was .26, .46, .64, and .90 cm. Total dry matter and forage dry matter intakes and total chewing were not influenced by forage mean particle length. Mean particle length did not affect actual milk or 4% fat-corrected milk production. Depression of milk fat percentage was prevented when forage mean particle length was greater than or equal .64 cm. Apparent digestibility of dietary constituents and rate of passage of hay and concentrate was not influenced by forage intake or physical form.     

Replacing chopped alfalfa hay with alfalfa silage in barley grain and alfalfa-based total mixed rations for lactating dairy cows

The effects of replacing chopped alfalfa hay with alfalfa silage in a fine barley grain and alfalfa-based total mixed ration (TMR) were evaluated. Diets contained (dry matter basis) 53.0% commercial energy supplement, 10.3% commercial protein supplement, and 9.7% corn silage. Diets varied in inclusion of chopped alfalfa hay and alfalfa silage, and contained either 20.0% chopped alfalfa hay and 7.0% alfalfa silage, 10.0% chopped alfalfa hay and 17.0% alfalfa silage, or 27.0% alfalfa silage. Contents of crude protein, neutral detergent fiber (NDF), acid detergent fiber, and minerals did not differ among diets. Replacing chopped alfalfa hay with alfalfa silage decreased dietary dry matter, and increased dietary soluble protein and physical effective NDF calculated as the proportion of dietary NDF retained by the 8- and 19-mm screens of the Penn State Particle Separator (peNDF(NDF)) from 13.3 to 15.6% DM. Replacing chopped alfalfa hay with alfalfa silage did not affect dry matter intake, rumen pH, rumen volatile fatty acids, blood lactate, milk fat, and milk protein percentage, but did decrease blood glucose, tended to increase blood urea, and numerically decreased milk yield and milk protein yield. A wider range in peNDF(NDF) and a higher inclusion of corn silage might have resulted in greater differences in rumen fermentation and milk production among diets. The pH of rumen fluid samples collected 4 h after feeding varied from 5.90 to 5.98, and milk fat percentage varied from 2.50 to 2.60% among diets. These values suggest that mild subacute ruminal acidosis was induced by all diets.