Calibration and validation of a carbon oxidation system and determination of the bicarbonate retention factor and the dietary phenylalanine requirement, in the presence of excess tyrosine, of adult, female, mixed-breed dogs,.

Carbon oxidation methods have been used as rapid and sensitive methods to determine whole-body AA requirements in multiple species. The objectives of the current studies were to validate complete CO recovery, determine the bicarbonate retention factor, and estimate the Phe requirement, in the presence of excess Tyr, in adult dogs using the direct oxidation technique. In this series of studies, 2 oxidation chambers were constructed and calibrated to ensure accurate collection of breath CO. First, 104.6 ± 7.1% CO was recovered from chambers and suggests that the chambers were appropriately designed for complete and efficient CO recovery. Second, we determined bicarbonate retention in 5 dogs using repeated oral dosing of a bicarbonate tracer (NaHCO) with small meals. At isotopic and physiological steady state, 102.5 ± 2.6% of the delivered NaHCO was recovered in breath. Third, the Phe requirement, when Tyr was supplied in excess, was determined by the rate of appearance of CO in the breath (CO). Dogs ( = 5) were fed test diets with different concentrations of Phe ranging from deficient to excessive for 2 d prior to conducting the tracer studies. The mean Phe requirement (when Tyr was supplied in excess) was 0.535% of diet (upper 95% confidence interval = 0.645% diet) on an as-fed basis or 0.575% of diet (upper 95% confidence interval = 0.694% of diet) on a DM basis and was based on a calculated (modified Atwater calculation) dietary ME density of 3.73 Mcal/kg DM. These data support the use of carbon oxidation methods and oral dosing of isotope to measure whole-body requirements of indispensable AA in adult dogs and suggest the current recommendations may be low.

Effect of graded inclusion of dietary soybean meal on nutrient digestibility, health, and metabolic indices of adult dogs.

Two studies were conducted using adult dogs to evaluate the effect of increasing the inclusion of soybean meal (SBM) in an adult dog food on body composition, hematological and biochemical blood analyses, and total tract nutrient digestibility. Nutritionally complete and balanced diets were formulated with commercial-grade SBM (48% CP) to replace 0, 10, 20, or 30% of the protein provided by dried chicken protein resulting in final SBM inclusion of 0, 6.0, 11.5, and 17.0% (as-fed basis), respectively. In study 1, diets were fed during a 24-wk feeding trial using 36 female (spayed), adult hounds to evaluate food intake, BW, body composition, and blood measurements. There were no diet-related differences in food intake or BW. Body composition responded in a quadratic manner to increased dietary SBM inclusion with the percentage (%) of lean mass responding positively (P < 0.05) and absolute amounts of fat mass and percent body fat responding negatively (P < 0.05). All diagnostic blood components remained within normal physiological ranges for healthy, adult dogs. Serum concentrations of C-reactive protein and IGF-1 were similar among diets. In study 2, diets were evaluated in a digestibility study using 12 adult dogs in a 4 × 4 Latin square design. Increased SBM inclusion was associated with linear increases in the digestibility of CP (P < 0.05) and fat (P < 0.05) and CP retention (P < 0.05). Linear reductions in fecal DM content (P < 0.01) and increased fecal output (P < 0.05) were noted with increased SBM inclusion. All diets were similar in DE and ME content, but a quadratic trend was noted with increased SBM inclusion when DE (P = 0.083) and ME (P = 0.062) were expressed per unit of metabolic body size. Overall, it can be inferred from these results that the partial replacement of dried chicken protein with SBM in a nutritionally complete and balanced diet does not compromise the nutritional status and long-term health of adult dogs.

Oral and intravenous l-[1-13 C]phenylalanine delivery measure similar rates of elimination when gastric emptying and splanchnic extraction are accounted for in adult mixed hounds.

There are few reported estimates of amino acid (AA) kinetics in adult mammals and none exist in adult dogs. The study objectives were to evaluate the use of oral isotope delivery in contrast to the more commonly used intravenous (IV) delivery to estimate AA kinetics in adult dogs and to estimate splanchnic extraction and gastric emptying using a commonly accepted mathematical model. Dogs received 25 × 1/2-hourly meals (13 g/kg BW/day) and either an oral or IV bolus of l-[1-(13) C]Phe (12 mg/kg BW). Blood samples were taken immediately before each feeding. Concentrations of plasma Phe were measured using liquid chromatography-tandem mass spectrometry. There were no differences in baseline plasma Phe concentrations (34 µm ± 0.61), Phe distribution volume, Phe pool size and rate constants between dogs when the tracer was administered IV or orally (p > 0.25). Decay curve for plasma l-[1-(13) C]Phe differed between IV and oral dosing protocols with IV dosing fit best using a two-compartment model. Phe disappeared from plasma at a mean rate of 2.8%/min. Estimates of gastric emptying and splanchnic extraction did not differ based on oral or IV tracer dosing when the decay curves were fit with the two-compartment model (p > 0.40). The half-life for gastric emptying was 18 min, and first-pass Phe extraction by the splanchnic bed was 24% of the dietary Phe. These results suggest that oral isotope dosing can be used as an alternative to IV isotope dosing in studies that utilize a primed, constant dosing approach to measure protein and amino acid kinetics.

Effect of dietary protein on lean body wasting in dogs: correlation between loss of lean mass and markers of proteasome-dependent proteolysis.

To determine the effect of dietary protein intake on lean body wasting in adult canines a study was undertaken to investigate the Ubiquitin Proteasome (UP) pathway and concurrent changes in lean and fat body mass of canines fed variable sources and concentrations of dietary protein. Purpose-bred, intact female canines (56) between the ages of 2 and 3 years were fed either 12 or 28% protein diet for 10 weeks. Each diet contained variable amounts of corn gluten meal and chicken protein sources in ratios of 100 : 0, 67 : 33, 33 : 67 and 0 : 100 per cent (w/w), respectively. All diets were isocaloric with calories coming from protein : fat : carbohydrate at the respective ratios of 12 : 40 : 48% for the 12% diets, and 28 : 40 : 32% for the 28% diets. Standard dual energy X-ray absorptiometry was performed to assess total body lean and fat mass at weeks 0 and 10 of the dietary trial. Muscle biopsies were also taken and processed for protein determination and standard gel electrophoresis with subsequent Western blotting for 20S proteasome and PA700 regulatory cap subunit p31. Statistical analysis revealed a moderate degree of correlation between increasing quantities of corn gluten, which is low in essential amino acids (i.e. lysine, tryptophan), and increasing loss of lean body mass over the 10-week study (R = 0.56). Furthermore, a moderate degree of correlation was observed between increasing concentrations of corn gluten protein and decreased expression of the p31 subunit of the 26S proteasome (R = 0.49). Additionally, the dogs consuming the 12% protein diets had a significant increase in fat mass regardless of the protein source. These findings suggest that lean body wasting in adult canines can be associated with the consumption of low protein diets consisting of predominantly corn gluten, which is likely due to imbalances or subclinical deficiencies of specific essential amino acids, and that low protein diets may augment accumulation of adipose tissue. Although the mechanisms remain unclear, alteration of molecular targets of skeletal muscle proteolysis, specifically involving the UP pathway occur.

Effect of dietary protein on calpastatin in canine skeletal muscle.

The cysteine proteinases, mu- and m-calpain, along with their inhibitor, calpastatin, have been hypothesized to play a role in skeletal muscle protein degradation. Because nutrition has previously been shown to influence the expression of calpastatin, the working hypothesis of this study was that the quantity and source of dietary protein could influence regulation of the calpain system in muscle. The objectives to support this hypothesis were to determine the effects of dietary protein (amount and source) on the expression of calpastatin in canine skeletal muscle. This study comprised eight diets with seven dogs per diet. A biopsy was taken from the biceps femoris of all 56 dogs before and after 10 wk on their respective diets. This experimental design allowed examination of change within individual dogs. Diets 1 to 4 contained 12% total protein derived from chicken and/or corn gluten meal in ratios of 100:0, 67:33, 33:67, and 0:100%, respectively. Diets 5 to 8 contained 28% total protein with protein sources and ratios identical to Diets 1 to 4. Differences in calpastatin were examined qualitatively using SDS-PAGE and immunoblotting, and semiquantitatively with densitometric analyses. The majority of the calpastatin blots showed three distinct calpastatin bands, the uppermost appearing at approximately 110 kDa. Diet 5 (28% CP, 100% chicken) resulted in an increase in the expression of the 110-kDa calpastatin band compared with the other two lower molecular weight bands in the same samples. Muscle from dogs fed Diet 5 showed greater increase in (P < 0.05) calpastatin intensity of the topmost band than those fed Diet 8 (0:100; chicken:corn gluten meal). Diet 5 (100:0; chicken:corn gluten meal) showed greater total calpastatin intensity than Diet 8 (0:100; chicken:corn gluten meal). These data suggest that dogs fed a diet containing a higher total percentage of chicken protein may have a greater potential to regulate calpain-mediated degradation of muscle protein than dogs fed diets containing corn gluten meal.

Effect of diet on hunting performance of English pointers.

A study was conducted to evaluate the influence of diet on hunting performance of English pointers during the quail-hunting season in southwest Georgia. Twenty-three trained dogs were assigned to two commercially available diets (i.e., Diet A = Eukanuba Premium Performance Formula, The Iams Company, Lewisburg, OH; Diet B = Diamond Premium Adult Dog Food, Diamond Pet Foods, Meta, MO). Results showed that dogs fed Diet A maintained or gained weight and body condition throughout the hunting season while dogs fed Diet B lost body weight and body condition (P < .05). Dogs fed Diet A demonstrated superior hunting performance (P < .05) compared with those fed Diet B based on total finds per hunt and on the number of birds located per hour of hunting. All blood variables were within normal ranges for adult healthy dogs throughout the season. These results imply that diet can affect the overall performance of hunting dogs and should provide useful information to trainers, handlers, and clinicians who are concerned with promoting the best performance and health in hunting dogs and other canine athletes.

Effects of dietary protein on whole-body protein turnover and endocrine function in young-adult and aging dogs.

Thirty-six adult female Beagles averaging 2 (young-adult) or 8 (geriatric) yr of age were used to assess the effects of graded levels of dietary protein (16, 24, or 32%) on endocrine-controlled regulation of whole-body protein turnover. Rates of whole-body protein synthesis (WBPS) and whole-body protein degradation (WBPD) were estimated using orally administered 15N-glycine and total excreta collection. Although N balance was similar for all dogs, N flux through the metabolic pool increased linearly (P < 0.05) as protein intake increased. Rates of WBPS, WBPD, or the difference between them were not influenced by age (P > 0.10). A quadratic increase (P < 0.05) in WBPS and WBPD was observed in response to dietary protein. Serum insulin-like growth factor-I (IGF-I), IGF-I-binding protein 3, and total IGF-I-binding proteins were higher (P < 0.05) in geriatric dogs than in young-adult dogs regardless of protein intake. These results indicate that dietary protein in excess of 16% may not be required to maintain N balance in young-adult and aging dogs despite the linear increase in N flux through the metabolic pool. Furthermore, age-induced changes in endocrine functionality may differ between dogs and other species.

Abomasal nitrogen flow affects the relationship between dietary nitrogen and insulin-like growth factor-I in growing lambs.

Twelve abomasally cannulated wether lambs were fed isocaloric diets containing 9, 12 or 15% crude protein to determine insulin-like growth factor-I (IGF-I) responses to altered abomasal nitrogen flow and nitrogen status. Lambs were offered 1100 g/d of their respective diets. Voluntary feed consumption was not affected by nitrogen intake. Ruminal and total tract digestibilities of dry matter, organic matter and nitrogen increased linearly (P < 0.05) with increased dietary nitrogen. Abomasal flows of total, bacterial and rumen escape nitrogen increased (linear, P < 0.01), whereas dry matter and organic matter flows decreased (linear, P < 0.01). Total amino acid flow was greater (linear, P < 0.01) in lambs fed additional nitrogen due to increased (linear, P < 0.01) flows of essential and nonessential amino acids. Nitrogen retention and blood urea nitrogen increased linearly (P < 0.01). Serum IGF-I concentrations and relative hybridization intensity of hepatic IGF-I mRNA increased (linear, P < 0.05) as lambs consumed more nitrogen. Serum IGF-I and hepatic IGF-I mRNA were correlated positively (P < 0.05) with nitrogen intake and abomasal flows of nitrogen and various amino acids. These data provide evidence of a relationship between abomasal amino acid flow, as influenced by nitrogen intake, and hepatic gene expression and serum concentrations of IGF-I in growing lambs.

Effect of dietary protein and estradiol-17 beta on growth and insulin-like growth factor I in cattle during realimentation.

Forty-eight medium-framed, crossbred steers (average BW = 268 +/- 20 kg) were limit-fed a 35% concentrate diet to gain approximately .10 kg/d during a 66-d restriction (REST) period. This was followed by a 98-d realimentation (REAL) period in which steers were allotted to a 3 x 2 factorial arrangement of treatments. Treatments were 80% concentrate diets containing 9, 12, or 15% CP, and implantation of one-half of the steers with 24 mg/steer of estradiol-17 beta (E2; Compudose). The allotted steers were distributed across four pens (12 steers/pen) with each pen containing two replicates of each treatment combination. Individual feed intakes were monitored using a Calan gate system. Each steer had ad libitum access to its respective diet. Longissimus muscle area and fat thickness at the 12th rib were measured using real-time ultrasound. Dry matter intake was not affected by CP or E2 through d 56. Steers fed 9% CP weighed less (quadratic, P < .05) after d 14 than steers fed 12 or 15% CP due to slower (quadratic, P < .05) gains during this initial period. Implantation increased (P < .05) ADG from d 15 to 56 resulting in heavier BW (P < .05) on d 56 and 98. Increasing concentrations of dietary CP resulted in linear (P < .05) increases in longissimus muscle area on d 28 and 56, and fat thickness on d 98. Serum IGF-I concentrations were lowest on d -21 of REST and highest on d 28 of REAL (quadratic, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and endocrine responses of cattle to implantation of estradiol-17 beta during continuous or discontinuous grazing of high- and low-endophyte-infected tall fescue.

Forty-eight Angus x Hereford steers (initial BW = 336 +/- 8.3 kg) were used in a 56-d study to evaluate growth and endocrine responses to continuous or discontinuous grazing of high-endophyte-infected Kentucky-31 (K; > 57% infestation rate) or low-endophyte-infected Johnstone tall fescue (J; < 1% infestation rate) and implantation with 0 or 24 mg/steer of estradiol-17 beta (E2; Compudose). Steers were allotted by weight to eight 3-ha paddocks (four paddocks of each fescue variety) with six steers per paddock. Two paddocks of each variety were grazed continuously (KK and JJ), whereas steers on the remaining four paddocks were rotated every 14 d from K to J (KJ) or from J to K (JK). Three steers in each paddock were implanted with E2 on d 0. The study extended from May 25, 1988 to July 20, 1988 with steers exposed to potential heat-stress conditions for 52 d of the 56-d study. Body weights were obtained on d 0, 28, and 56, and blood samples were taken on d 28 and 56. Overall ADG, serum prolactin, and serum alkaline phosphatase activity were greater (P < .05) in JJ than in KK steers. Rotation from K to J did not increase overall ADG, prolactin, insulin-like growth factor I (IGF-I), or alkaline phosphatase activity compared with the continuously grazed KK, whereas JK steers had lower (P < .10) ADG, prolactin, and alkaline phosphatase activity than JJ steers. Estradiol-17 beta increased (P < .10) IGF-I in JJ, KJ, and JK steers but not in KK steers.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic and endocrine responses of lambs fed Acremonium coenophialum-infected or noninfected tall fescue hay at equivalent nutrient intake.

Ten Hampshire x Western wether lambs (means weight = 30.1 kg) equipped with ruminal and abomasal cannulas were fed either low-Acremonium coenophialum (AC) Kentucky-31 (less than 1% infected) or high-AC G1-307 (greater than 95% infected) varieties of tall-fescue (TF) hay of similar nutrient composition in a completely randomized design. Lambs were housed in metabolism crates at 21 +/- 1 degrees C and fed 552 g DM/d of ground hay at 0800 and 2000. A 10-d adaptation preceded 7 d of sample collection. Levels of water and DM voluntarily consumed by the low-AC group during the adjustment period were held constant for both treatment groups throughout the collection period by intraruminal insertion of unconsumed DM and water. Fixed water intake markedly reduced voluntary water intake but it alleviated previous depressions in voluntary DM intake in lambs fed high-AC. Mean daily respiration and heart rates, rectal temperature and hematocrit were not affected (P greater than .10) by treatment. Compared with high-AC, lambs fed low-AC retained a greater (P less than .10) amount of N (1.8 vs 1.1 g/d) and a greater (P less than .10) percentage of their N intake (16.4 vs 9.9%). Abomasal total and bacterial N flow and ruminal digestion of cell wall components were not affected (P greater than .10) by treatment. Total tract digestion of DM, NDF and ADF was lower (P less than .01) for high- than for low-AC. Serum prolactin concentration was higher (P less than .10) for lambs fed low- than for those fed high-AC TF, but serum cortisol and thyroxine concentrations were not affected (P greater than .10) by treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance and plasma amino acids of growing calves fed corn silage supplemented with ground soybeans, fishmeal and rumen-protected lysine.

A 100-d growth study was conducted to evaluate performance and plasma amino acid (AA) responses of 96 crossbred beef calves (220 kg) with ad libitum access to corn silage and supplemented with ground soybeans (GSB) with or without added fishmeal (FM) and (or) rumen-protected lysine (Lys). Calves were allotted by breed, sex and weight to four treatments with three replicate pens of eight calves per pen. The treatments were: GSB, GSB + Lys, GSB + FM and GSB + FM + Lys. The isonitrogenous supplements were top-dressed on corn silage once daily at a level of 2.27 kg/hd, with FM providing one-half of the supplemental N in FM-containing supplements. The Lys-containing supplements provided a daily intake of 6.0 g/hd of rumen-protected Lys. Dry matter intake was similar (P less than .10) for all treatments. Overall ADG and feed efficiency of GSB calves averaged .83 kg/d and 7.39 kg feed/kg gain, respectively, and were 14% lower than the mean of calves fed supplements containing FM and(or) Lys. Lysine was not the principal factor limiting growth because the inclusion of Lys alone in the GSB-containing supplements did not improve (P greater than .10) ADG, feed efficiency or plasma AA concentrations. In contrast, FM supplementation increased (P less than .05) ADG, feed efficiency and plasma concentrations of total AA, total essential AA and total nonessential AA. The inclusion of Lys in the GSB + FM-containing supplement resulted in no further improvement (P greater than .10) in performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioavailability of magnesium in beef cattle fed magnesium oxide or magnesium hydroxide.

Two experiments were conducted to compare Mg bioavailability from Mg oxide (MgO) vs Mg hydroxide (Mg(OH)2) fed in either a completely mixed diet or a mineral supplement. In Exp. 1, these Mg sources were incorporated into completely mixed diets and offered to 15 steers (282 kg) allotted to three treatments: control diet containing .19% Mg, control plus .2% added Mg as MgO, or control plus .2% added Mg as Mg(OH)2. Each calf was fed 5 kg/d of the respective diet during 10-d adjustment and 7-d collection periods. Blood samples were collected on d 1, 3 and 7. Mg supplementation increased (P less than .01) fecal and urinary Mg excretions, whereas apparent Mg absorption (%) and retention were similar (P greater than .10) for all treatments. Plasma Mg concentrations were similar (P less than .10) for calves supplemented with MgO and Mg(OH)2 but were higher (P less than .05) for Mg supplemented than for control calves on d 7. In Exp. 2, these Mg sources were incorporated into mineral supplements and offered free choice to 30 spring-calving beef cows gazing tetany-inducing pastures from March 6 to May 1. Each of three groups of 10 cows was assigned to a 5.7-ha tall fescue pasture and offered either a control supplement or a supplement containing 40% MgO or Mg(OH)2. Blood samplers were collected on d 0, 7, 14, 28, 42 and 56. Plasma Mg concentrations were not different (P greater than .10) for cows offered MgO and Mg(OH)2 but were higher (P less than .01) for Mg-supplemented than for control cows on d 28, 42 and 56.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrogen metabolism and somatotropin secretion in beef heifers receiving abomasal arginine infusions.

Twelve Angus x Hereford heifer calves (233 kg) were fitted with abomasal infusion cannulas and used to study N and endocrine responses to abomasally infused arginine (Arg). Heifers were allotted randomly to three treatment groups and received continuous abomasal infusions (2 liters/d) of water (CON) or Arg solutions providing .33 g Arg.HCl/kg BW (LOW) or .50 g Arg.HCl/kg BW (HIGH) each day. A 12-d dietary adjustment period preceded a 7-d infusion and collection period. Each calf received 4,544 g DM/d of a basal diet in equal portions at 0600, 1200, 1800 and 2400. Calves were housed in individual metabolism crates and fitted with urinary bladder catheters for total excreta collection. On d 1 and 5, blood samples were collected at 15-min intervals for 8 h between 1200 and 2000. Single samples were obtained at 1400 on remaining days. The infusion of Arg increased the quantity of N retained by heifers (P less than .01) and the percentage of total N retained (P less than .10); however, no differences were observed between LOW and HIGH heifers. Increased (P less than .01) urinary N excretion by Arg heifers was associated with greater (P less than .05) quantities of urinary urea N and ammonia N. Blood urea N and serum Arg concentrations were highest (P less than .05) in Arg heifers, whereas total serum AA concentrations were lower (P less than .05) in Arg heifers than in CON heifers. Serum glucose and insulin concentrations were not affected (P greater than .10) by treatment. Characterization of somatotropin (STH) profiles revealed that amplitude and frequency of STH pulses were not affected (P greater than .10) by treatment, whereas mean (P less than .10) and basal (P less than .05) STH concentrations were elevated in HIGH compared to LOW heifers on d 1 and 5. The similar N retention responses of LOW and HIGH heifers and similar STH profiles of CON and LOW heifers suggest that the stimulatory effect of the HIGH dose on STH secretion occurred only after tissue N requirements had been satisfied.

Nitrogen metabolism and somatotropin secretion in lambs receiving arginine and ornithine via abomasal infusion.

Sixteen wether lambs (25 kg) were fitted with abomasal infusion cannulas and used to study N and endocrine responses to abomasal infusions of arginine (ARG) or ornithine (ORN). Lambs were randomly allotted to four treatment groups and abomasally infused with solutions of water (CON), ARG, ORN or UREA. The ARG solution provided .50 g ARG.HCl/kg BW and was equimolar with ORN.HCl (.40 g/kg). UREA (.28 g/kg) was isonitrogenous with ARG and served as a positive N control. Lambs were housed in metabolism crates for excreta collection and received 729 g DM/d of a 13.7% CP diet in equal portions four times daily. Following a 7-d dietary adjustment period, lambs were infused continuously (2 liters/d) with water for a 5-d preliminary collection period (Period 1), which immediately preceded a 7-d infusion and collection period (Period 2). Sequential blood samples were taken at 15-min intervals for 8 h between 1200 and 2000 on d 4 of both periods. Single samples were obtained at 1500 on remaining days. Nonrepeated measurements were analyzed as a completely randomized design, whereas repeated measurements were analyzed as a split-plot over time. Period 2 measurements were adjusted using covariance techniques if differences among treatment groups were observed for Period 1. Contrasts used in determining treatment effects were: CON vs UREA, CON vs ARG + ORN, and ARG vs ORN. Nitrogen retention was similar for all treatment, suggesting that dietary N was not limiting. Arginine and ORN increased serum ornithine (P less than .05), blood urea N (BUN; P less than .10) and urinary urea N excretion (P less than .01), whereas ARG increased (P less than .05) serum arginine and UREA increased (P less than .01) BUN and urinary urea N. Serum insulin and glucose were not affected by treatment. Compared with CON, ARG and ORN increased (P less than .05) mean somatotropin (STH) concentration (13.8 vs 16.9 and 18.4 ng/ml) and amplitude of STH pulses (9.8 vs 15.1 and 17.8 ng/ml), whereas CON and UREA were similar. Abomasal infusions of ARG and ORN were equally efficacious in stimulating ovine STH secretion when dietary N intake was not limiting.

Physiological responses of cattle consuming tall fescue to environmental temperature and supplemental phenothiazine.

The influence of supplemental phenothiazine (P) on growth and physiological criteria was studied in parasite-controlled calves consuming endophyte (Acremonium coenophialum)-infected tall fescue (TF). In Exp. 1, nine Angus heifer calves (312 kg) were supplemented with 227 g corn-mineral (CM) mix twice daily and allowed ad libitum access to either high-endophyte (HE) G1-307 (greater than 90% infected) or low-endophyte (LE) Kenhy (less than 1% infected) tall fescue hay, or HE G1-307 plus 2 g/d P in the daily supplement. Calves were kept in temperature-controlled rooms for 12 d at 21 degrees C followed by 7 d at 34 degrees C. In Exp. 2, 48 Angus steer calves (312 kg) were assigned to treatment groups consisting of calves grazing HE Kentucky-31 (57% infected) or LE Johnstone (less than 1% infected) TF, and supplemented daily with either .91 kg of a control CM mix or .91 kg of the CM mix containing 2 g P. The 112-d experiment was initiated on May 4 with BW and rectal temperature (RT) measurements and blood collected at 28-d intervals. In both experiments, calves receiving HE TF had lower (P less than .01) serum prolactin concentrations (PRL) at elevated ambient temperature and lower (P less than .01) serum alkaline phosphatase activities (AP) but higher (P less than .01) RT than calves consuming LE TF regardless of ambient temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary protein level on nitrogen metabolism in the growing bovine: II. Diffusion into and utilization of endogenous urea nitrogen in the rumen.

Six Angus heifer calves (234 kg) were assigned to either a high (HP; 126.1 g N/d) or low (LP; 66.5 g N/d) protein intake to evaluate ruminal criteria associated with movement of blood urea-N (BUN)-derived NH3-N from the rumen wall into interior ruminal digesta. Calves received 4.8 kg DM/d of diets containing 30% cottonseed hulls and 70% cornsoybean meal in equal portions at 4-h intervals. Following single i.v. injections of 15N-urea, ruminal fluid was collected serially for 4 h postinjection from digesta located adjacent to the rumen wall (wall-proximate digesta; WPD) and from the center of the rumen digesta mass after manual agitation (center mixed digesta; CMD). Mean ruminal NH3-N (RAN) concentrations were higher (P less than .05) for HP than for LP, but were not affected (P greater than .05) by digesta sampling site. Ruminal urease activity was higher (P less than .05) for LP than for HP and tended (P = .14) to be higher for WPD than for CMD. Area under the 15N enrichment curve (AUC) ratios between sampling sites (WPD/CMD x 100) for RAN were greater (P less than .05) for LP than for HP. However, AUC ratios for bacterial N were not affected (P greater than .05) by protein level. Whereas BUN-derived 15NH3 appeared to thoroughly equilibrate with RAN in interior ruminal digesta with HP, there appeared to be a declining enrichment gradient for RAN from the rumen wall to the interior ruminal digesta with LP. Data are interpreted to suggest that bacteria at or near the rumen wall may preferentially utilize some BUN-derived NH3-N entering through the rumen wall in calves fed LP diets.

Effect of soybean lipid on growth and ruminal nitrogen metabolism in cattle fed soybean meal or ground whole soybeans.

Three experiments were conducted to determine the effect of soybean lipid on ruminal proteolysis of soybean meal (SBM) and ground whole soybeans (GSB). Experiment 1 was a 92-d growth experiment using 120 calves (206 kg) allotted to 12 pens of 10 calves each. Three replicate pens were assigned to each of the treatment supplements: low SBM (LSBM), low GSB (LGSB), high SBM (HSBM) and high GSB (HGSB). Calves received ad libitum amounts of corn silage top-dressed with the respective supplement (.81 kg/head). High protein supplements produced greater (P less than .05) gains than low protein supplements, with HSBM calves gaining faster (P less than .05) than HGSB calves and LSBM and LGSB calves having similar (P greater than .10) gains. In Exp. 2, 15 ruminally cannulated Angus X Hereford heifers (380 kg) fed corn silage were used to determine ammonia-N release from the treatment supplements: ground corn (control), GSB, SBM and SBM coated with soybean oil (SBMO). Heifers fed the control supplement had lower (P less than .05) ruminal NH3-N concentrations than those consuming soybean protein. Ruminal NH3-N concentrations were similar (P greater than .10) for GSB and SBM; whereas, SBMO had lower (P less than .10) concentrations than SBM through 3 h. In Exp. 3, two ruminally cannulated Angus X Jersey steers (250 kg) were used to determine in situ disappearance of SBM, GSB and SBMO. Total and feed N disappearances were greater (P less than .001) for GSB than SBM or SBMO.(ABSTRACT TRUNCATED AT 250 WORDS)