Biomedical subjects

B W McBride

Publications and source records attributed to B W McBride.

At least 19 recordsLinked to original sources

PubMed2007

Technical note: A system for continuous recording of ruminal pH in cattle.

Continuous recording of ruminal pH in cannulated cattle has been practiced to study rumen metabolism. However, most systems reported did not permit animal mobility during pH recording. Therefore, the objective of this study was to develop a continuous rumen pH data acquisition system that permitted animal mobility during data acquisition. A further objective was to compare the pH readings obtained using the continuous recording system to readings obtained at the same time using spot sampling. The continuous recording system was composed of a heavy-duty electrode and a data logger. The electrode was attached to a 0.5-kg weight to help maintain the electrode in the ventral sac of the rumen. The electrode was connected via a 0.5-m cable to a lightweight data logger that was mounted on the animal's back using a belt wrapped around the girth. The data logger was battery powered and could hold over 13,000 pH data values. A personal digital assistant was used to configure and download data from the data logger during the experiment. Ruminal pH was continuously recorded (every 10 s) using a dry Holstein cow fed alfalfa hay ad libitum in a 3-d experiment to compare the performance of the continuous system to spot samples taken from the ventral sac of the rumen, the same location as the continuous electrode. The spot samples were collected 3 times per d for 3 d. At every sampling time, 3 replicate samples were collected, pH was determined immediately using a handheld pH meter, and readings were averaged (n = 3) and compared with the average of the 3 pH readings recorded using the continuous system at the same time. The pH recorded by spot sampling (6.63 +/- 0.04) was greater (P = 0.009) than that of the continuous system (6.56 +/- 0.03), with a correlation of r = 0.88 (P = 0.002). The continuous recording system has the potential to facilitate measurement of ruminal pH in free-roaming cattle.

Animals↗

PubMed2006

Fatty acid composition of ruminal bacteria and protozoa, with emphasis on conjugated linoleic acid, vaccenic acid, and odd-chain and branched-chain fatty acids.

Knowledge of the fatty acid profile of microbial lipids is of great nutritional importance to the animals and, subsequently, their products. This study was conducted to examine the fatty acid profiles of mixed rumen bacteria and protozoa. Bacterial and protozoal cells were isolated by differential centrifugation of rumen contents. The main fatty acids were palmitic (16:0) and stearic (18:0) in both the bacterial and protozoal fractions. Palmitic acid was 74% greater in the protozoal fatty acids than in the bacterial fatty acids, whereas bacteria had 2.25-times greater stearic acid (18:0) proportions compared with protozoa. The total odd-chain plus branched-chain fatty acids were 16.5% of bacterial fatty acids and 11.0% of protozoal fatty acids. The anteiso-17:0 proportions in bacterial and protozoal fatty acids were 1.4 and 2.9%, respectively. The most abundant trans-18:1 isomer, vaccenic acid (18:1 trans-11), was 6.6% of total fatty acids in protozoa and 2.0% of total fatty acids in bacteria. The cis-9, trans-11 CLA was 8.6-times greater in the protozoal fraction (1.32% of total fatty acids) than in the bacterial fraction (0.15%). These results suggest that the presence of protozoa in the rumen may increase the supply of CLA and other unsaturated fatty acids for lower gut absorption by ruminants.

Animals↗

PubMed2006

Effects of mild heat stress and grain challenge on acid-base balance and rumen tissue histology in lambs.

The effect of heat stress (HS) and grain challenge (GC) on acid-base balance and rumen tissue histology in lambs was investigated using 24 yearling wether lambs (58 +/- 4.5 kg of BW) in a 2 x 2 factorial experiment with repeated measures for day (10, 14, and 17) of sampling. The factors were temperature [thermoneutral zone (TN) vs. HS] and diet (control vs. GC). Lambs were blocked by BW and assigned to 1 of 4 treatments in temperature-controlled rooms: 1) TN (temperature = 18 to 20 degrees C; relative humidity = 30%; 2) TN + GC; 3) HS (temperature = 35 degrees C for 9 h/d, 20 degrees C for 15 h/d; relative humidity = 40%); and 4) HS + GC. Venous blood samples were collected at 1800 on the first day of GC (d 10), in the middle of GC (d 14), and at the end of the trial (d 17) by jugular venipuncture and analyzed for pH, gases, hematocrit, plasma ions, and total protein. After all measurements in live animals were taken on d 17, lambs were slaughtered, and tissue samples were obtained from the ventral sac of the rumen for histological assessment. Except for the concentration of plasma glucose (P = 0.04) and total protein (P < 0.01), there were no (P > 0.05) diet x temperature interactions. With HS, the concentration of Na+ and Cl- in the control group decreased at d 14 and then increased by d 17, and respiration rates in the control group decreased linearly (P < 0.05). Compared with the control group, respiration rates and the concentration of Cl- in the GC lambs increased linearly over time, whereas the concentration of Na+ decreased linearly (P < 0.05) across time. Under HS, the partial pressure of carbon dioxide, total carbon dioxide, the partial pressure of oxygen and oxygen saturation, and the concentration of Mg2+, glucose, and HCO3- showed quadratic (P < 0.05) responses with time. In both treatments, DMI, base excess of extracellular fluid, base excess of blood, and standard bicarbonate increased linearly (P < 0.05), and hematocrit, plasma protein, Ca2+, anion gap, and plasma strong ion difference decreased linearly (P < 0.05) across day. Compared with the control group, the GC group had decreased papillae count in the ruminal ventral sac (1.3 vs. 1.5; P < 0.05). These results suggest that under HS the acidifying effects of GC on acid-base balance in lambs were counteracted in the short-term through respiratory adaptation.

Acid-Base Equilibrium↗

PubMed2006

Effect of ruminally protected methionine on splanchnic metabolism of amino acids in lactating dairy cows.

The effect of ruminally protected Met (RPM) on splanchnic metabolism was measured in 3 primiparous and 3 multiparous Holstein cows. Doses of RPM (0, 36, and 72 g/d) were tested in a replicated 3 x 3 Latin square design, over 3 consecutive 14-d experimental periods. A mixed ration was fed in 12 equal meals per d (average dry matter intake: 17.5 +/- 0.08 kg/d). Indwelling catheters were surgically implanted in the mesenteric artery and the portal and hepatic veins for blood collection, as well as in 2 distal branches of the mesenteric vein for infusion of p-aminohippurate to determine blood flow. On d 14 of each period, a temporary catheter was inserted into a mammary vein and 6 hourly blood samples were collected to determine plasma concentrations of metabolites, hormones, and their respective fluxes across the splanchnic bed and mammary glands. Yields of milk (32.8, 32.0, and 32.9 +/- 0.92 kg/d) and protein (1,028, 1,053, and 1,075 +/- 28.7 g/d) were unaffected by level of RPM. However, the true protein content in milk from primiparous cows increased linearly (2.92, 3.09, and 3.34 +/- 0.077%). The addition of RPM linearly increased the net flux of Met across the portal-drained viscera, which resulted in increased arterial Met concentrations (25, 29, and 40 +/- 1.1 microM). Although it had no significant effect on net portal and hepatic fluxes of other essential amino acids, RPM resulted in a linear increase in the total splanchnic output of Ile, Leu, Phe, and Thr. These results suggest that feeding RPM triggered a homeostatic response resulting in less utilization of certain essential amino acids through the gastrointestinal tract and liver. Net mammary uptake of Met did not change with the addition of RPM. However, mammary extraction of Met decreased in a linear fashion in response to increased arterial inflow.

Amino Acids↗

PubMed2006

Acetyl CoA carboxylase shares control of fatty acid synthesis with fatty acid synthase in bovine mammary homogenate.

The objectives of this research were to determine the flux control coefficients for acetyl CoA carboxylase and fatty acid synthase using an in vitro preparation of bovine mammary homogenate. For an enzyme to be considered rate limiting with the use of metabolic control analysis, its control coefficient would be equal to unity. The hypothesis for this experiment was that the control coefficient for acetyl CoA carboxylase was not equal to unity, and that this enzyme was not, therefore, the rate-limiting step. Mammary tissue was isolated from lactating Holstein cows at slaughter and frozen in liquid nitrogen. Tissue was ground, homogenized, and centrifuged to obtain a postmitochondrial supernatant for use in in vitro incubations containing labeled acetate. Specific inhibitors for acetyl CoA carboxylase and fatty acid synthase were used to fractionally inhibit de novo synthesis for the calculation of flux control coefficients. The composition of fatty acids synthesized in the absence of enzyme inhibitors was similar to the composition of fatty acids in the presence of inhibitors. Calculations following avidin inhibition of acetyl CoA carboxylase determined the flux control coefficient was 0.63 +/- 0.15, which means that 63% of the control of fatty acid synthesis is exerted by acetyl CoA carboxylase. The remaining control (37%) was from fatty acid synthase, which indicates a significant degree of control over the flux of acetate in de novo synthesis resides with this enzyme. The rate-limiting status ascribed to acetyl CoA carboxylase was not supported, because the flux control coefficient was less than unity. Metabolic control analysis, through its use of pathway product measurements, allows for potential interactions in the pathway such as feedback inhibition contribution to the flux control coefficients, which would not otherwise be considered in studies measuring enzyme kinetics with purified enzymes.

Acetates↗

PubMed2006

Effects of rumen acid load from feed and forage particle size on ruminal pH and dry matter intake in the lactating dairy cow.

The objective of this study was to evaluate the effects of level of concentrate acidogenic value (AV) and forage particle size on ruminal pH and feed intake in lactating dairy cows. Two isoenergetic (net energy for lactation = 1.5 +/- 0.01 Mcal/kg) and isonitrogenous (crude protein = 17.4 +/- 0.1% dry matter) concentrates with either a low AV or high AV were formulated and fed in a total mixed ration with either coarsely or finely chopped corn silage and alfalfa haylage ad libitum. Four rumen-fistulated cows (114 +/- 14 d in milk) were randomly assigned to 1 of the 4 treatments in a 4 x 4 Latin square with a 2 x 2 factorial treatment arrangement. Each period consisted of 3-wk (14-d treatment adaptation and 7-d data collection). Increasing the concentrate AV decreased the mean pH (from 6.07 to 5.97) and minimum pH (from 5.49 to 5.34). Cows fed high-AV diets spent a longer time below pH 5.6 (135.1 vs. 236.7 min/d; low-AV diet vs. high-AV diet, respectively) and pH 5.8 (290.0 vs. 480.6 min/d; low-AV diet vs. high-AV diet, respectively) than cows fed low-AV diets. Increasing forage particle size had no effect on the mean and minimum ruminal pH. There was an interaction between concentrate AV and forage particle size on maximum ruminal pH. Increasing forage particle size increased the maximum pH for cows fed the high-AV concentrate (6.69 vs. 6.72; low-AV diet vs. high-AV diet, respectively) and had no effect on the maximum pH for cows fed the low-AV concentrate (6.98 vs. 6.76; low-AV diet vs. high-AV diet, respectively). Increasing the concentrate AV did not affect dry matter intake but reduced neutral detergent fiber intake from 9.7 to 8.8 kg/d. Milk fat content was negatively correlated with time and area below pH 5.6 (time below, r = -0.51; area below, r = -0.56) and pH 5.8 (time below, r = -0.42; area below, r = -0.54). These results suggest that coarse forage particle size can attenuate drops in ruminal pH. However, the ameliorating effects of forage particle size on drops in ruminal pH were more apparent for high-AV diets than for low-AV diets. The AV approach combined with physically effective neutral detergent fiber would therefore improve the formulation of diets and help to mitigate subacute ruminal acidosis in dairy cows.

Animal Feed↗

PubMed2005

Effects of monensin and stage of lactation on variation of blood metabolites within twenty-four hours in dairy cows.

Effects of prepartum administration of a monensin controlled release capsule (CRC) and stage of lactation on variation of blood metabolites within 24 h were determined in 16 dairy cows. Cows were fed a total mixed ration ad libitum twice daily at 0700 and 1300 h. At calving, cows were switched from a close-up dry cow diet to a lactating cow diet. Cows were blood sampled every 3 h for 24 h at 3 stages of lactation, including 1 wk before calving (wk -1), 1 wk after calving (wk 1), and 6 wk after calving (wk 6). Serum concentrations of glucose, beta-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA), and urea exhibited significant variation within 24 h. Glucose and NEFA were, respectively, 0.09 and 0.08 mM lower between 1030 and 2230 h than between 2230 and 1030 h. beta-Hydroxybutyrate and urea were, respectively, 95.1 and 0.49 mM higher between 1030 and 2230 h than between 2230 and 1030 h. Monensin did not significantly affect glucose, NEFA, and urea in this study. Monensin reduced BHBA at wk 1, but not at wk -1 or wk 6. Glucose was lower and BHBA and NEFA were higher at wk 1 compared with wk -1 and wk 6. Urea was higher at wk 6 compared with wk -1. The variation within 24 h of glucose, BHBA, and NEFA were not affected by monensin and stage of lactation. Diurnal variation of urea was affected by stage of lactation, but not by monensin.

3-Hydroxybutyric Acid↗

PubMed2004

The effects of subacute ruminal acidosis on sodium bicarbonate-supplemented water intake for lactating dairy cows.

Four multiparous ruminally fistulated Holstein dairy cows were used in an 8-wk experiment utilizing a repeated measures block design to determine the effects of subacute ruminal acidosis (SARA) on supplemented water intake. Animals were subjected to SARA, which was induced by replacing 25% of the ad libitum intake of the total mixed ration (dry matter basis) with 50:50 wheat:barley pellets utilizing a grain challenge model. Cows had free choice from 2 water bowls. One bowl contained water with sodium bicarbonate (SB) supplemented at 2.5 g/L. The other bowl contained unsupplemented water. Ruminal pH was monitored continuously during the trial using indwelling pH probes. The induction of SARA reduced daily mean ruminal pH and increased the duration when ruminal pH was below 6. The total mixed ration intake by the cows decreased during the SARA periods. The overall preference for SB-supplemented water did not change, as the preference ratio was similar during the control and SARA periods. During the period of greatest ruminal pH depression, total water intake was higher during the SARA periods than during the control periods. During SARA, there was no difference in the preference of a SB water source to unsupplemented water. During the period of day with the most severe ruminal pH depression, the lactating dairy cows subjected to SARA increased their total water intake.

Acidosis↗

PubMed2004

Effects of monensin on ruminal forage degradability and total tract diet digestibility in lactating dairy cows during grain-induced subacute ruminal acidosis.

The effects of monensin premix supplementation on ruminal pH characteristics and forage degradability, and total tract diet digestibility during grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows receiving a total mixed ration were investigated. Six multiparous, rumen-fistulated Holstein cows were used in a 2-treatment, 2-period (5 wk per period) crossover design. During wk 5 (d 29 to 35) of each period, SARA was induced using a grain challenge model, and ruminal pH was measured continuously using indwelling pH probes. Ruminal degradation of corn silage and alfalfa haylage was determined using the in situ (nylon bag) technique, and total tract diet digestibility was determined by total fecal collection during wk 5. Monensin supplementation did not affect dry matter intake, milk yield, and composition, and ruminal pH characteristics under these experimentally induced SARA conditions. Rates of ruminal forage fiber degradability were similar between control and monensin-treated cows; however, monensin supplementation increased total tract fiber digestion. This study indicates that monensin altered total tract nutrient digestion by increasing fiber digestion at postruminal sites.

Acidosis↗

PubMed2003

Effect of combinations of fish meal and feather meal on milk fatty acid content and nitrogen utilization in dairy cows.

The effect of supplemental fishmeal in combination with feathermeal at two different proportions in the diet on milk docosahexaenoic acid (DHA) content was investigated. Recently, benefits to human health have been attributed to the consumption of this fatty acid, which is normally present in marine lipids. Six Holstein cows past peak lactation were used in a Latin square design with a 2 x 3 factorial arrangement of treatments. Fish- and feathermeals were prepared as pellets at 4:1 and 1:4 combinations and offered at 3.75, 11.75, and 27% of the diet. The supplements were top-dressed onto a basal diet based on corn silage that was progressively replaced by supplement. Nitrogen balance measures were made during the experiment because of the wide range in crude protein content of experimental diets. Milk protein content increased with level of supplementation in the diet reflecting the protein quality of the supplements used. There was overall higher milk DHA content when cows consumed the supplement containing more fishmeal than feather meal. Milk DHA content increased in a quadratic fashion, as more of either supplement was included in the diet. Apparent transfer efficiency of DHA from diet to milk declined with increasing amount of DHA in the diet. Results from this experiment suggest that transfer of docosahexaenoic acid from diet to milk may depend on diet composition and quantity present in the diet.

Animals↗

PubMed2003

Short communication: Effects of subacute ruminal acidosis on free-choice intake of sodium bicarbonate in lactating dairy cows.

The effect of inducing subacute ruminal acidosis (SARA) on the free-choice intake of sodium bicarbonate (SB) was investigated in four midlactation Holstein cows in a switchover experiment with four 1-wk periods. The SARA was induced by replacing 25% of the ad libitum intake of total mixed ration (TMR) with pellets containing 50% ground wheat and 50% ground barley and restricting access to TMR from 0700 to 1700 h. Control consisted of feeding TMR ad libitum. Powdered SB was provided for ad libitum consumption. Rumen pH was measured continuously using indwelling pH probes. Induction of SARA reduced (P < 0.05) the average daily rumen pH from 6.08 to 5.87, increased (P < 0.05) the average duration of rumen pH below 6 from 547 min x d(-1) to 916 min x d(-1), and increased (P < 0.05) the average duration of rumen pH below 5.6 from 132 min x d(-1) to 397 min x d(-1) (P < 0.05) but did not significantly affect SB intake. Average intake of SB was 26.8 g x d(-1) during SARA and 34.5 g x d(-1) during control. These low SB intakes must not have substantially affected rumen pH. Sodium bicarbonate intake differed significantly (P < 0.05) between cows. These data indicate that cows did not select SB in order to attenuate SARA.

Acidosis↗

PubMed2003

Physical and processing properties of milk, butter, and cheddar cheese from cows fed supplemental fish meal.

Physical, chemical, sensory and processing properties of milk produced by feeding a rumen-undegradable fish meal protein supplement to Holstein cows were investigated. The supplement contained (as fed basis) 25% soft-white wheat, 60% herring meal, and 15% feather meal. The total fat level in the milk decreased to 2.43%. For both pasteurized and ultra-high temperature processed drinking milk, no difference was found between fish meal (FM) milk and control milk in terms of color, flavor and flavor stability; in particular, no oxidized flavor was observed. Cheddar cheese made from FM milk ripened faster after 3 mo of ripening and developed a more desirable texture and stronger Cheddar flavor. The yield efficiencies for FM and control cheese, 94.4 (+/- 2.44 SE) and 96.4 (+/- 2.26 SE), respectively, were not different. Relative to controls, average fat globule size was smaller in FM milk and churning time of FM cream was longer. FM butter had softer texture and better cold spreadability, and butter oils from FM enriched milk had lower dropping points compared to control butter oil (average 32.89 versus 34.06 degrees C). These differences in physical properties of butter fat were greater than expected considering that iodine values were not different. This study demonstrates the feasibility of producing high quality products from milk naturally supplemented with FM, but the results also show that dietary changes affect processing properties.

Animal Feed↗

PubMed2003

Effects of replacing chopped alfalfa hay with alfalfa silage in a total mixed ration on production and rumen conditions of lactating dairy cows.

The effects of replacing chopped alfalfa hay with alfalfa silage in a total mixed ration containing barley grain and corn silage on production and rumen conditions were investigated. Cows received three diets that all contained (dry matter basis) 38.5% barley grain-based energy supplement, 30.5% corn silage, 17.0% protein supplement, and 4.2% sunflower seeds. One diet contained (dry matter basis) 9.8% of chopped alfalfa hay and no alfalfa silage. One diet contained (dry matter basis) 4.9% chopped alfalfa hay and 4.9% alfalfa silage. One diet contained (dry matter basis) 9.8% of alfalfa silage and no chopped alfalfa hay. Contents of crude protein, neutral detergent fiber, acid detergent fiber, and starch, averaged across diets, were 16.7, 41.3, 21.1, and 24.4% DM, respectively, and did not differ significantly among diets. Replacing chopped alfalfa hay with alfalfa silage decreased the proportion of dietary DM passing through the 8-mm screen of the Penn State Particle Separator from 61.9 to 55.2% dry matter and significantly increased dietary physical effective NDF (peNDF) content, calculated as the NDF retained by the two screens of the Penn State Particle Separator, from 20.1 to 23.3% DM. Replacing chopped alfalfa hay with alfalfa silage also reduced dietary DM content, increased rumen pH from 6.27 to 6.47, reduced volatile fatty acid concentrations, numerically increased milk fat concentration and milk fat yield. Milk yield, milk protein concentration, dry matter intake, and rumen ammonia concentration were not affected.

Animal Nutritional Physiological Phenomena↗

PubMed2003

Short communication: Effects of a monensin premix on milk fatty acid content during subacute ruminal acidosis in dairy cows.

The effects of a monensin premix on milk fatty acid content during grain-induced subacute ruminal acidosis (SARA) in Holstein cows receiving a total mixed ration was investigated. Six multiparous, rumen-fistulated Holstein cows were used in a two-treatment, two-period crossover design with 6-wk periods. Experimental treatments were either a monensin premix or a placebo premix. At the beginning of wk 4, SARA was induced in experimental cows for a 10-d period using a grain challenge model. The administration of a monensin premix elevated milk fat proportion of total short-chain saturated fatty acids (sum of C4 to C15). Milk fat proportions of conjugated linoleic acid isomers were unaffected. Linolenic acid (C18:3n3) proportion in milk fat of monensin-treated cows were lower when compared with placebo-treated cows during the SARA period. Results from this study indicate that dietary supplementation with monensin during SARA had little effect on milk fatty acid content.

Acidosis↗

PubMed2002

Short communication: Effect of subacute ruminal acidosis on in situ fiber digestion in lactating dairy cows.

Subacute ruminal acidosis (SARA) was induced by replacing 25% of the total mixed ration intake [dry matter (DM) basis] with pellets consisting of 50% wheat and 50% barley. This reduced dietary forage content (DM basis) from 39.7 to 29.8% and increased the dietary concentrate content from 60.3 to 70.2%. Induction of SARA reduced the 24- and 48-h in situ neutral detergent fiber (NDF) degradabilities of grass hay numerically from 31.5% to 24.6% (P = 0.29) and from 51.3% to 36.9% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of legume hay were reduced from 35.3 to 26.3% (P < 0.05) and from 49.0 to 35.8% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of corn silage were reduced from 44.0 to 37.2% (P < 0.05) and from 56.1 to 44.8% (P < 0.05), respectively. This study suggests that induction of SARA by excess feeding of wheat/barley pellets reduces the rumen digestion of NDF from grass hay, legume hay, and corn silage.

Acidosis↗

PubMed2002

Inhibition of fatty acid synthesis in bovine mammary homogenate by palmitic acid is not a detergent effect.

Supplemental fat fed to dairy cows affects the fat composition of milk by reducing the yield of mammary synthesized fatty acids. The effect has been attributed to a potential allosteric inhibition of acetyl coenzyme-A, a key enzyme in fatty acid synthesis. In vitro experiments have demonstrated an inhibition of fatty acid synthesis when long-chain fatty acids are added to incubations. However, in vitro inhibition can result from a nonspecific detergent effect arising from an inherent physical property of fatty acids. An allosteric role for palmitic acid has not been tested in bovine mammary tissue. The objective of this experiment was to test the hypothesis that palmitic acid is an allosteric inhibitor of fatty acid synthesis in mammary tissue. We tested for a detergent effect by including a synthetic detergent, sodium dodecyl sulfate, under identical incubation conditions. A subcellular supernatant fraction of mammary tissue was used for incubations in the present experiment. The incubation system produced free fatty acids in a linear fashion for time and protein content. Results indicated that fatty acid synthesis was affected by the addition of palmitic acid to the incubations but not by caprylic acid, a short-chain fatty acid. Sodium dodecyl sulfate did not affect fatty acid synthesis at the concentrations used. The results of the present experiment indicate that palmitic acid inhibited fatty acid synthesis, and the effect was not the result of a detergent effect.

Acetyl Coenzyme A↗

PubMed2002

Effects of dietary protein solubility on nitrogen losses from lactating dairy cows and comparison with predictions from the Cornell Net Carbohydrate and Protein System.

This experiment determined the effects of dietary protein solubility on amount, form, and route of nitrogen loss in lactating Holstein dairy cows, and the ability of the Cornell Net Carbohydrate and Protein System (CNCPS) to accurately predict rumen microbial yield, serum urea N (SUN), milk urea N (MUN), and fecal N. Eighteen multiparous Holstein cows were assigned randomly to one of three dietary treatments that were similar in crude protein (17.7%) content but differed in their content of soluble intake protein (SIP). Dietary contents of SIP, as % of total CP were 30, 36, and 48%. The experimental period was 21 d, and total N balance collections were done during the last 5 d. As dietary content of SIP increased, excretion of urinary N increased quadratically, and it was the primary route of N excretion. Urinary excretion of purine derivatives (PD) responded quadratically as dietary SIP content increased. The CNCPS predicted a quadratic decrease in total metabolizable protein (MP) supply. No effect of dietary content of SIP was detected on MUN and SUN. The CNCPS predicted a quadratic decrease in SUN and MUN as dietary SIP increased. Results from this study indicated that changing the dietary content of SIP altered routes of N excretion in dairy cows, but had no effect on total N balance. The CNCPS did not adequately predict changes in SUN and MUN for cows fed diets varying in SIP.

Animals↗

PubMed2002

Effects of a subacute ruminal acidosis model on the diet selection of dairy cows.

Two experiments were conducted to study the effects of a subacute ruminal acidosis (SARA) model on diet choice in dairy cows. In the first experiment, 25% of the ad libitum dry matter intake (DMI) of the total mixed ration (TMR) was replaced with wheat-barley pellets (WBP, 50% ground wheat, 50% ground barley). Rumen pH was measured continuously via in-dwelling probes in 4 mid to late lactation cows. This diet change reduced rumen pH by 0.14 +/- 0.02 pH units (mean +/- SE) and increased time below pH 6.0, from 319 +/- 36 min(-1) to 641 +/- 36 min(-1). Hence, the nutritional model successfully induced SARA. The second experiment determined if inducing SARA increases the feed preference for long alfalfa hay compared with alfalfa pellets. The 2 wk of inducing SARA were separated by 1 control wk. Four cows on either SARA and control diets were given a choice of 2 feeds, 2 times per d, for 30 min. The preference ratios (PR = Amount of Hay consumed/Amount of Hay + Pellets consumed) for alfalfa hay during two SARA weeks was greater (0.85 +/- 0.03) compared with the control week (0.60 +/- 0.03). In SARA weeks, average rumen pH was 0.23 +/- 0.03 units lower, and time below pH 6.0 and 5.6 was higher compared to control. These results suggest that when given a choice of feeds, dairy cows alter their diet selection to attempt to attenuate SARA.

Acidosis↗