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The objective of this experiment was to compare two progestins and three treatments for synchronizing follicular wave emergence and ovulation in protocols for fixed-time AI in beef heifers. On d 0 (beginning of the experiment), Angus and Angus-Simmental cross beef heifers at random stages of the estrous cycle either received a CIDR-B device (n = 257) or were started on 0.5 mg*[animal.sup.-1]*[d.sup.-1] melengestrol acetate (MGA; n = 246) and were randomly assigned to receive i.m. injections of 100 [micro]g GnRH, 12.5 mg porcine LH (pLH), or 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4). The last feeding of MGA was given on d 6 and on d 7, CIDR-B devices were removed and all heifers received 500 [micro]g cloprostenol (PG). Consistent with their treatment groups on d 0, heifers were given either 100 [micro]g GnRH or 12.5 mg pLH 48 h after PG (and were concurrently inseminated) or 1 mg EB 24 h after PG and were inseminated 28 h later (52 h after PGF). Estrus rate (combined for both progestins) in heifers receiving EB (92.0%) was greater (P < 0.05) than that in heifers receiving GnRH and pLH (combined) and a CIDR-B device (62.9%) or MGA (34.3%). Although the mean interval from PG treatment to estrus did not differ among groups (overall, 47.8 h; P = 0.85), it was less variable (P < 0.01) in MGA-fed heifers (SD = 2.5 h) than in CIDR-B-treated heifers (SD = 8.1 h). Pregnancy rates (determined by ultrasonography approximately 30 d after AI) did not differ (P = 0.30) among the six treatment groups (average, 58.0%; range, 52.5 to 65.0%). Although fixed-time AI was done, pregnancy rates were greater in heifers detected in estrus than in those not detected in estrus (62.6 vs 51.9%; P < 0.05). In conclusion, GnRH, pLH, or EB treatment in combination with a CIDR-B device or MGA effectively synchronized ovulation for fixed-time AI, resulting in acceptable pregnancy rates in beef heifers. Key Words: Estradiol, Fixed-Time AI, GnRH, LH, Progestins, Synchronization

This study was conducted to determine the live weights at which large-, medium-, and small-framed feeder steers and heifers attain a degree of finish associated with a carcass quality grade of low Choice and to examine the relationship of feeder cattle muscle thickness to carcass yield grade traits. Feeder steers (n = 401) and heifers (n = 463) representing three age classes (calf, yearling, long yearling) were selected randomly at a commercial feedlot to exhibit wide ranges in frame size and muscularity. Individual weights were recorded and a panel of five experienced evaluators scored each animal for frame size, muscle thickness, and flesh condition. The cattle were finished on a high-concentrate finishing diet and harvested at an estimated carcass fat thickness of 10 mm. Final weights and USDA carcass grade data were collected for all cattle. Frame size scores effectively predicted finished weight at a marbling end point of [Small.sup.00] for both heifers ([r.sup.2] = 0.89, SE = 16 kg) and steers ([r.sup.2] = 0.94, SE = 13 kg). For heifers, the Small/Medium and Medium/ Large frame score intersects corresponded to live weights of 460 kg and 520 kg, respectively. For steers, the Small/Medium and Medium/Large frame score lines corresponded to live weights of 504 kg and 577 kg, respectively. These weights were greater than weights specified in the 1979 USDA grade standards. Evaluations of feeder cattle muscling, based on 1979 USDA Standards, were associated (P < 0.05) with differences in longissimus muscle area but were not related (P = 0.08) to differences in numerical carcass yield grades. An alternative muscle thickness classification scheme, involving the use of four thickness classes, was effective for stratifying feeder cattle according to eventual differences (P = 0.004) in carcass yield grade. Our findings suggest that USDA feeder cattle grade standards developed in 1979 are no longer adequate for describing today's population of feeder cattle. Key Words: Beef, Carcasses, Meat Grades, Muscle Weight

Two experiments were conducted to evaluate performance and physiological responses of heifers and lambs to Neotyphodium coenophialum-infested tall fescue hay fed under European rearing conditions. Endophyte-free (E-) or 100% endophyte-infested (E+) hay was derived from the same cultivar (cv. Clarine) so that the effect of the endophytic fungus could be clearly separated from a possible cultivar effect. In Exp. 1, starting in June 1996, 20 age- and body weight-paired Holstein dairy heifers were assigned for 97 d to one of two treatments consisting of ad libitum access to either E- or E+ hay, corresponding to 0 and .41 mg/ kg ergovaline, respectively. During the experimental period, no significant difference (P > .20) in forage consumption, rectal temperature, or behavioral status of the animals was observed between the two treatments. The E+ diet induced a 10% apparent decrease in ADG and a clear reduction in prolactin (PRL) plasma concentration compared to the E- diet. When animals were all reassigned to a common endophyte-free diet, the E+ group recovered body weight and PRL to levels similar to those in animals fed E- after 7 wk. In Exp. 2, 30 Texel ram lambs were assigned to two treatments consisting of dietary E- or E+ tall fescue hay. The E- and E+ hays were harvested from the same plots as used in Exp. 1 and contained 0 and .96 mg/kg ergovaline, respectively. No effect of the end0phyte was found on intake or carcass or testicle weight (P > .20) after the 95-d feeding period. The E+ treatment resulted in a slight reduction in BW at slaughter, mainly explained by a lower ruminal fill (P < .01). In E+ treated animals, prolactin concentrations dropped significantly (P < .001) from d 27. Hay assessment in both experiments showed no difference in chemical composition and IVDMD. The endophytic fungus strongly lowered the palatability of the E+ hay, although there was no effect on intake with heifers (Exp. 1) or with lambs (Exp. 2). The potential of severe heat stress, as expressed by the temperature humidity index, was not high in our experimental conditions, although they were considered rather unusually stressful for the western part of northern Europe. Yet, no economic effect on cattle was observed, in disagreement with results obtained in many previous U.S. studies. Key Words: Festuca arundinacea, Endophytes, Intake, Performance, Cattle

An experiment was conducted to determine whether feeding rumen-protected fatty acids (FA) to postpartum heifers would increase plasma concentrations of linoleic acid and PGF(sub 2 alpha) metabolite (PGFM), shorten the interval from calving to first increase in plasma concentrations of progesterone (P(sub 4)), and increase pregnancy rate relative to controls. Hereford x Angus heifers (346 kg) were assigned randomly to treatments containing either lipid or barley supplemented diets for the first 30 d postpartum. Lipid was .23 kg-heifer(super -1).d(super -1) of calcium salts of FA (CSFA; n = 20), and an isocaloric amount of barley served as the control (n = 19). Supplements, with .23 kg of barley as a vehicle, and a basal diet of meadow and alfalfa hays were pen fed to heifers (5/pen). Heifers were bled on alternate days (d 1 to 30) and twice weekly (d 30 to 2 wk after first estrus) for RIA of plasma PGFM and P(sub 4), respectively. Weight percentage of major FA in plasma on d 1 and 7 was determined with gas chromatography. First behavioral estrus was detected by use of intact bulls and confirmed by an increase in plasma P(sub 4). On d 7, but not d 1, plasma from heifers fed CSFA had altered proportions of major FA (P < .01), including an increase in linoleic acid compared with those of controls (29.1 vs 25.6% of total FA; SE = .75; P < .01). Analysis of variance of contrast variables revealed an effect of treatment on direction of change in PGFM from d 3 to 5 (P < .01). By d 7 and on d 9, plasma concentrations of PGFM were greater in heifers fed CSFA than in controls (P = .02 and P = .06, respectively). There was no difference in plasma concentration of PGFM between treatments on d 1, 3, 5, 11, 13, and 15 postpartum (P = .80, .17, .52, .82, .46, and .77, respectively). Days to first estrus with ovulation, pregnancy rate, and calving interval were not affected by treatments (P = .58, .52, and .24, respectively). Although supplemental lipid fed to primiparous beef heifers increased plasma levels of linoleic acid and production of PGFM in the early postpartum period, it did not improve the fertility of these heifers in the subsequent breeding season. Key Words: Prostaglandins, Fatty Acids, Postpartum Period, Beef Cows, Heifers

Eight cows ( 7 to 9 yr old, 522 kg) and six heifers (10 mo old, 169 kg) were fed either alfalfa hay (18.7% CP) or mature brome hay (5.1% CP) to determine the effect of cattle age on apparent forage utilization. Cattle were fitted with ruminal and duodenal cannulas and were individually fed once daily (ad libitum intake, 1000). The split-plot design consisted of age (whole-plot) and two sampling periods feeding alfalfa or brome hay (subplot). Each period consisted of 28 d: d 1 to 13 for adaptation, d 13 to 20 for feed intake determination, and d 20 to 28 for sampling. Nylon bags containing NDF substrate from alfalfa or brome hay were incubated ruminally for 0, 3, 6, 12, 24, 48, 96, and 192 h to determine the rate and extent of fiber degradation. Ruminal liquid dilution rate and fermentation characteristics were conducted on 2 27. Ruminal fill was determined by total evacuation at 0800 on d 28. Cows consumed more feed (BW(super.75),P < .01) and had greater ruminal OM fill (P = .04) but had similar fluid fill (P = .88) compared with heifers. Ruminal liquid dilution rate was greater in cows than in heifers (P < .01). The rate of in situ NDF degradation was 3 and .5% per hour greater in cows than in heifers when alfalfa and brome hay were fed, respectively (age x hay, P < .01). Ruminal NDF digestibility as a percentage of intake was greater in cows than in heifers (P < .01). Numbers of ruminal cellulolytic bacteria were not affected by treatment (P > .21). These data indicate that mature cows have a smaller ruminal fluid fill that turns over more rapidly, and this may be responsible for a faster rate of ruminal fiber degradation in cows than in young heifers. Key Words: Beef Cows, Heifers, Forage, Intake, Digestibility

Prolonged infusions of bacterial lipopolysaccharides (LPS) are known to model Gramnegative bacterial infections, but the basic mechanisms of the LPS effects on feed intake and metabolism and their potential interdependence are largely unknown. The aim of the present study was to distinguish and to better characterize the feeding suppressive and metabolic effects of LPS. Six heifers were infused intravenously for 100 min with either 1 ) LPS (2 mu g/kg BW) with free access to feed, 2) saline with free access to feed, or 3) saline with feeding restricted to the amount of feed consumed after LPS infusion. Feed intake, body temperature, plasma concentrations of various metabolites and hormones, and the respiratory quotient and heat production were measured. The LPS reduced feed intake and induced pronounced changes in metabolic energy turnover and fat and carbohydrate metabolism that were largely independent of the concomitant feed intake reduction. Some of the metabolic changes were biphasic; the first phase resembled a stress response with increases in plasma glucose and cortisol, and the second phase reflected a beginning energy deficit with low plasma glucose and enhanced lipolysis. The coincidence of a short-term surge of plasma insulin with marked transient decreases in plasma FFA, glycerol, and beta-hydroxybutyrate as well as with the transition from hyper- to hypoglycemia indicates that insulin plays a role in some of the metabolic responses to LPS. The failure of LPS to clearly increase energy expenditure despite the increase in body temperature suggests that anaerobic mechanisms of heat production and, perhaps, a reduced peripheral blood flow contributed to the fever. Many of the initial metabolic responses occurred before and, therefore, independent of, an increase in circulating tumor necrosis factor-alpha. Key Words: Ruminants, Lipopolysaccharides, Tumor Necrosis Factor, Metabolism,Insulin, Heat Production

The objective of this study was to determine whether reconstituting field-dried and early-harvested sorghum grain affected the fermentation characteristics and feed value of the ensiled grain when fed to feedlot heifers. In Trial 1, sorghum grain was harvested at 14% moisture, rolled, and reconstituted to 25, 30, or 35% moisture, then ensiled in laboratory-scale silos. Lactic acid concentration increased (d 5 to 90) and pH decreased more rapidly (d 3 to 90) as moisture level increased (P < .05). Acetic acid concentration increased (P < .05) with moisture and day postfilling. Concentration of ethanol was highest (P < .05) in the 30 and 35% moisture grains from d 1 to 5, but by d 90 the ethanol concentration in the 25% moisture grain exceeded (P < .05) that of the two higher-moisture grains. Ammonia N concentration was lowest (P < .05) in the 25% moisture grain at all sampling times postfilling. In Trial 2, 288 heifers (BW = 286 [+ or -] 83 kg) were used to compare the feeding value of rolled, ensiled sorghum grain harvested at 25% moisture to the same grain reconstituted to 30 or 35% moisture. A steam-flaked corn (SFC) diet served as the control. Final live weight; ADG; hot carcass weight; backfat depth; marbling score; kidney, pelvic, and heart fat; and liver abscess score were not affected by grain treatment (P > .10). Dry matter intake was highest (P < .10) for heifers fed the 25 or 30% moisture sorghum grain diets and lowest for those fed the SFC diet; DMI for heifers fed the 35% moisture sorghum grain diet was intermediate. Feeding 35% moisture sorghum grain improved gain efficiency (P < .10) compared with feeding 25 or 30% moisture sorghum grain by 9.0 and 5.7%, respectively. We conclude that reconstituting sorghum grain beyond the typical moisture levels of 25 to 30% would enhance the fermentation characteristics of the ensiled grain and improve gain efficiency in feedlot heifers. Key Words: Sorghum, Moisture Content, Silage Making, Reconstituted Products, Feedlots, Performance

Heifers produced from sires of seven breeds (Hereford, Angus, Belgian Blue, Piedmontese, Brahman, Boran, and Tuli) and Angus, Hereford, and MARC III (four-breed composite) cows were evaluated. Weaned heifers were placed in three treatment groups of moderate nutrition (15.8 Mcal ME/d), 80% of moderate nutrition (12.6 Mcal ME/d), or fed as a mixed-breed group (16.3 Mcal ME/d). Average daily gain (ADG) from 228 d of age through breeding was measured. There was a sire breed x group interaction (P < .0001) for ADG in the drylot. Sire breeds differed in their 365-d BW (P < .0001), and 365-d BW of heifers in the low group (315 [+ or -] 4 kg) were lighter (P < .0001) than those of heifers in the high group (346 [+ or -] 4 kg). During breeding, heifers that had been in the low group in the drylot had a higher ADG (.58 [+ or -] .02 kg/d) than heifers in the high group (.39 [+ or -] .03 kg/d). Age of heifers at puberty did not differ (P = .06) between the low (362 [+ or -] 5 d) and high groups (357 [+ or -] 5 d). Heifers from MARC III (358 [+ or -] 5 d) and Angus (358 [+ or -] 6 d) dams reached puberty at a younger age than did heifers with Hereford dams (380 [+ or -] 9 d). Age at which puberty was expressed differed with sire breed (P < .001). The proportion of heifers that were pregnant at palpation (.90) did not differ between sire breeds (P = .24), dam breeds (P = .40), or group (P = .56). Breed differences in postweaning ADG and in the manner in which the population expresses puberty allow for selection of breed types that will optimize cow herd performance. Key Words: Beef Cattle, Heifers, Puberty, Pregnancy

Three trials with 156 crossbred heifers were used to determine the effects of dietary energy and bovine somatotropin administration on subsequent heifer productivity. In Trial 1, heifer calves were weaned from their dams (n = 28; 113 [+ or -] 13 d of age) and assigned to a 2 x 2 factorial arrangement of moderate (MDE) or high dietary energy (HDE) and injections of vehicle (VEH) or 250 mg of bovine somatotropin (bST) every 14 d. Heifer calves in Trial 2 (n = 28; 123 [+ or -] 20 d of age) and Trial 3 (n = 100; 134 [+ or -] 22 d of age) nursed their dams while grazing pasture and received no creep feed (MDE) or ad libitum access to creep feed (HDE) and received VEH or bST as in Trial 1. Treatments were administered for 112 d and heifers within trial were managed alike after that time. There were no dietary treatment x bST treatment interactions for any of the variables analyzed (P > .05). Dietary energy did not affect daily gain in Trial 1; however, heifers receiving HDE in Trials 2 and 3 had greater weight, hip height growth, and fat thickness (P Key Words: Supplemental Feed, Lactation, Mammary Tissue, Insulin-Like Growth Factor

Three studies were designed using a 2 x 2 factorial arrangement of treatments within each experiment to evaluate the effects of various management techniques on growth and carcass traits of once-calved heifers. In Exp. 1, 33 yearling (16 control [C] and 17 prenatally androgenized [PA]) and 39 once-calved (20 C and 19 PA) nonpregnant heifers were used to evaluate the effects of age and PA. Once-calved heifers were approximately 31 kg heavier (P < .03) on-test, initially consumed 11% more (P < .01) DM, and gained 11% faster (P < .08), but had similar (P = .44) gain to feed ratios (.138 vs. .131) as yearlings. Growth performance was not affected by PA. The yearling and once-calved heifers were then slaughtered at approximately 707 and 1,080 d of age, respectively. Despite maturity differences (P < .01), marbling scores (P = .26) and percentage of choice carcasses (P = .27) were similar. However, on the basis of newly accepted grading changes, percentage of once-calved heifer carcasses grading choice decreased from 57.3 to 34.4%. Organoleptic properties did not differ. Experiments 2 and 3 were then conducted to evaluate effects of commercially available products (melengestrol acetate [MGA] and Synovex-H[R]) on feedlot characteristics of heifers following weaning of their first calf. In Exp. 2, 48 once-calved Simmental-based heifers were fed during the summer to a constant compositional fat thickness of .8 cm. Experiment 3 was conducted in the late fall and early winter, during which 52 moderately sized heifers were fed for 116 d postweaning and slaughtered. Performance of heifers in Exp. 2 was not affected by MGA. However, heifers fed MGA in Exp. 3 gained 9% faster (P < .05) than controls. In Exp. 2, Synovex-H tended to improve ADG (P < .09) and feed efficiency (P < .07), but did not affect performance in Exp. 3. Most carcass traits were not affected by either treatment. Nonpregnant, once-calved heifers seem to have a large capacity for efficient weight gain as compared with yearling heifers. However, hormonal compounds, such as testosterone propionate provided pre- or postnatally (Synovex-H), and MGA do not appear to provide the consistent, positive responses often seen with younger, more typical feedlot heifers. Key Words: Heifers, Androgens, Estradiol, Melengestrol, Performance, Carcass

Thirty-two beef heifers were used to examine the effect of dietary copper depletion and repletion on neutrophil and lymphocyte functions. Heifers allotted to the control group (C+; n = 8) were fed a basal roughage/concentrate diet with Cu-sulfate supplementation (Cu [greater than or equal to] 8 ppm). To induce a Cu deficiency (depletion phase d 0 to 60), treated (T; n = 24) heifers received a diet supplemented with sulfur (.3 % of diet) and sodium molybdate to achieve a Cu: Mo ratio of 1:1.5. Liver biopsies were collected on d 0, 27, and 60. Despite random allocation, T heifers had lower initial liver Cu concentrations (P < .01) than C+ heifers. At the start of the repletion phase (d 0, equal to d 60 of depletion), treated heifers were allotted by liver Cu concentration to three treatments (n = 8/ treatment): Cu sulfate (S; Cu = 10 ppm), Cu proteinate (P; Cu = 10 ppm), or a negative control (C-) that remained on Mo and S supplementation. During the repletion phase, livers were biopsied on d 0, 14, and 45. By d 45, both S and P heifers had greater (P < .05) liver Cu concentrations than C- heifers. For both depletion and repletion phases, no treatment differences were detected in liver Mo or S concentrations. Jugular blood was collected on d 0, 27, and 55 of the depletion phase and d 0, 13, and 42 of the repletion phase. Neutrophils were isolated and incubated with Staphylococcus aureus to determine neutrophil bactericidal capacity (NBC). Lymphocyte blastogenic response (LBR) was monitored during the repletion phase by measuring the amount of [3H] thymidine incorporated when isolated lymphocytes were incubated with pokeweed mitogen, phytohemagglutinin, and concanavalin A. During Cu depletion and repletion, no differences in NBC and LBR were detected. Analysis of whole blood constituents showed no treatment effects for red blood cell count or hematocrit during Cu depletion and repletion. Hemoglobin values were numerically greater for C+ heifers on d 13 and 42 of repletion. These data indicate that the degrees of Cu depletion or repletion achieved in this experiment did not affect neutrophil or lymphocyte function in growing beef heifers. Key Words: Copper, Neutrophils, Lymphocytes, Heifers

Four hundred fifty-two (452) weanling heifer calves (192 [+ or -] 23 kg) were used to determine the effect of postweaning weight gain on subsequent reproductive performance and lactation. Heifers grazed stockpiled tall fescue pastures and were fed a high (H) or low (L) amount of ground corn supplement (3.68 and 2.99 kg/[animal-d], respectively) during a postweaning treatment period of 136 d. Postweaning gain of heifers receiving L and H was .43 and .62 kg/d, respectively. These treatments resulted in a range of postweaning gain from .07 to 1.17 kg/d. Heifers receiving H were 26 kg heavier (P [less than] .01), had .15 cm more fat thickness (P [less than] .01), 5% greater pelvic area (P [less than] .01), and tended (P = .08) to have greater hip height than heifers receiving L at yearling. More heifers in the H group were pubertal before the start of the breeding season (70.9 vs 61.3%) (P [less than] .05). No significant differences were found in pregnancy rate or first-service calving rate between treatment groups. Mean milk production was 10% greater for H- than for L-fed heifers (P [less than] .01) and resulted in heavier calves at 54, 104, and 153 d of age (P [less than] .05). Regression analysis revealed that as weaning weight and post-weaning gain increased, so did the probability for reaching puberty before the breeding season. Increasing weaning weight also increased the probability of calving to the first AI service. As heifer weaning weight and postweaning gain increased, subsequent milk production also increased. Increasing postweaning weight gain of lightweight heifers from .07 to 1.17 kg/d increased both reproductive and lactation performance. Key Words: Beef Cattle, Heifers, Supplementary Feeding, Gain, Milk Production, Fertility

Our objectives were to determine the effects of incremental increases in dietary gossypol on metabolic homeostasis and reproductive endocrine function in postpubertal beef heifers and the long-term effects of elevated dietary gossypol on various metabolic and reproductive endocrine characteristics in mature cows. In Exp. 1, heifers (n = 6/group) were fed either 0, .5, 2.5, 5, 10, or 20 g|center dot~|animal.sup.-1~|center dot~|d.sup.-1~ of dietary free gossypol for 62 d. Erythrocyte membrane osmotic fragility was increased (P |is less than~ .0001) in both the 10- and 20-g groups. Slight alterations in plasma concentrations of sorbitol dehydrogenase and K+ were also detected in the latter group. Treatment did not affect ADG, body condition scores, or concentrations of progesterone during the estrous cycle; however, mean concentrations of LH were higher (P |is less than~ .001) in heifers fed 20 g/d of gossypol than in heifers in all other groups. In Exp. 2, lactating cows (n = 17) exhibiting regular estrous cycles were fed a control (no gossypol, n = 8) or high-gossypol (20 mg|center dot~kg |BW.sup.-1~|center dot~|d.sup.-1~ free gossypol, n = 9) diet for 33 wk. Mean BW and body condition scores did not differ during the feeding period. Erythrocyte membrane fragility was greater (P |is less than~ .05) in the high-gossypol than in the control group. Magnitude of the preovulatory LH surge, luteal phase concentrations of progesterone, follicular fluid concentrations of estradiol and progesterone, in vitro granulosa cell estradiol production, and 60-d pregnancy rates were similar between groups. The amounts of gossypol fed in these experiments are not likely to affect reproductive performance adversely in beef heifers or cows.

The effects of sorghum type on amino acid digestion were determined by feeding heifers (230 kg) equipped with ruminal, duodenal, and ileal cannulas bird-resistant (BR) or non-BR grains that had a normal or waxy endosperm (NORMAL-BR, WAXY-BR, NORMAL, WAXY). Dry-rolled grain diets were fed at 2% of BW in a 4 x 4 Latin square design. Total (TAA), essential (EAA), and nonessential (NAA) amino acid intake (grams/day) tended to be greater for BR than for non-BR grains. Feed (plus endogenous) amino acids reaching the duodenum were calculated by subtracting amino acids of microbial protein from total flow. Flow (grams/day) of total and feed TAA, EAA, NAA, and proline-rich-protein (sum of aspartate, glutamate, glycine, and proline) to the duodenum was greater (P < .05) for BR than for non-BR grains. The ratio between feed proline-rich-protein and NAA reaching the duodenum was similar to that noted with feed intake. Amino acid disappearance (grams/day) from the small intestine was unchanged (P > .10) by sorghum type, although the digestibility (percentage of duodenal flow) of TAA, EAA, NAA, and most individual amino acids was decreased (P < .05) for BR varieties. Amino acid flow to the cecum (grams/day) was generally greater for NORMAL-BR than for WAXY-BR (P < .10) or for NORMAL (P < .01) and greater (P < .10) for WAXY-BR than for WAXY. Condensed tannins in BR sorghum grain seem to decrease small intestinal amino acid digestibility by increasing indigestible feed protein flow to the duodenum, rather than by increasing the supply of endogenous protein or inhibiting digestive enzymes. Key Words: Sorghum Grain, Digestion, Amino Acids, Beef Cattle

Sixteen crossbred beef heifers were used to determine the efficacy of serum clinical profiles as diagnostic tools for detection of early stages of locoweed toxicity and to test the ability of two mineral supplements for prevention or therapy of toxicosis. Dietary treatments were (DM basis) 1) 100% sorghum sudangrass hay, 2) 80% sorghum sudangrass hay:20% locoweed plus 100 g of Silent Herder Mineral Mix (a mineral supplement reported to alleviate locoweed toxicity), and 4) 80% sorghum sudangrass hay:20% locoweed plus 100 g of clinoptilolite (a natural zeolite clay). Diets were fed at 1.5% of BW for 28 d, after which heifers had ad libitum access to sorghum sudangrass hay for 14 d. Jugular blood was sampled before feeding every 7 d, and at 2, 4, 6, and 8 h after feeding on d 28. Compared with controls, heifers fed locoweed had elevated (P < .01) serum alkaline phosphatase activities from d 7 through 35. On d 42, alkaline phosphatase activities in heifers previously fed locoweed were lower (P < .05) than in control heifers. Serum glutamic oxaloacetic transaminase activities were elevated (P < .01) in heifers fed locoweed from d 7 through 42 compared with control heifers. In heifers fed locoweed, serum Fe concentrations were less (P < .01) on d 7 through 28, but no treatment effects were noted (P > .10) on d 35 or 42. On d 28, serum somatotropin, prolactin, and melatonin concentrations did not differ (P > .10) among treatments, but insulin was lower (P < .05) in heifers fed Silent Herder and clinoptilolite than in heifers fed only locoweed. Diets containing 20% locoweed altered the serum concentrations of alkaline phosphatase, glutamic oxaloacetic transaminase, and Fe; these serum constituents may serve as indices of early stages of locoweed toxicosis. Neither Silent Herder nor clinoptilolite ameliorated the toxic effects of locoweed.

Early-weaned Angus x Simmental heifers were used to evaluate the effects of postweaning nutritional management on feedlot performance, carcass merit, and the relationship of intramuscular and subcutaneous fat deposition to the feed efficiency among heifers fed for a high-quality market. Sixteen heifers were weaned at 73 [+ or -] 5.5 d of age and grazed on endophyte-infected tall fescue for 18 mo before entering the feedlot (early-weaned-P). Eighty heifers from the following year's calf crop were weaned at 71 [+ or -] 5.5 d of age and allowed either ad libitum access to a 25% concentrate diet (early-weaned-25C) or limit-fed a 90% concentrate diet (early-weaned-90C) to achieve a similar ADG. Following a 119-d growing period, 16 early-weaned-90C and 16 early-weaned-25C calves were paired based on BW and growth rate and individually fed during the finishing period along with the early-weaned-P heifers. Ultrasound measurements of s.c. and i.m. fat were recorded at approximately 60-d intervals throughout the finishing period. Feed efficiency was regressed against s.c. and i.m. fat, and i.m. fat was regressed on s.c. fat. Despite a similar ADG, early-weaned-90C calves gained more efficiently (P [is less than or equal to] 0.05) in the feedlot than early-weaned-25C calves. Heifers finished as yearlings tended (P [is less than or equal to] 0.10) to gain faster but gained less efficiently (P [is less than or equal to] 0.01) than early-weaned-90C heifers finished as calves. The rate of s.c. and i.m. fat deposition was similar between early-weaned-90C and early-weaned-25C heifer calves. The calves were grouped together for comparison to yearlings. Feed efficiency decreased quadratically (P [is less than or equal to] 0.01) as s.c. fat cover increased. The rate at which feed efficiency decreased relative to increasing s.c. fat cover was similar regardless of age at feedlot entry. However, heifers finished as calves gained more efficiently (P [is less than or equal to] 0.01) than yearlings at any given fat thickness. Feed efficiency decreased linearly (P [is less than or equal to] 0.01) as i.m. fat increased among heifers finished as calves. Additionally, heifers finished as calves deposited i.m. fat at a faster rate relative to s.c. fat (P [is less than or equal to] 0.01) than yearlings. These data suggest that heifers finished as calves produce high-quality carcasses with less s.c. fat cover while gaining more efficiently than heifers finished as yearlings. Key Words: Feed Efficiency, Heifers, Ultrasound, Weaning

The objectives of this study were to evaluate the effects of pre- and postpartum undegraded intake protein (UIP) supplementation on body condition score (BCS), BW, calf weight, milk production, serum IGF-I concentrations, and postpartum interval in primiparous beef heifers (n = 44). Heifers were maintained on endophyte-free stockpiled tall fescue (11.7% CP, 38% ADF) and individually fed supplement daily beginning 60 d prepartum. Pre- and postpartum supplements provided 19.3% CP, 83.4% TDN (UIP); 14.1% CP, 84.1% TDN (Control); 21.5% CP, 81.5% TDN (UIP); and 14.6% CP, 81.4% TDN (Control); respectively. Blood meal (146 g/d) was the source of UIP. Six heifers were removed from the study due to calf loss unrelated to treatment; therefore, postpartum measurements are based on 19 animals per treatment. Statistical analyses using ANOVA and a split-plot design revealed no effects of treatment (P [is greater than] 0.2) on BCS, BW, calf weight, milk production, or postpartum interval. There tended to be a treatment x time interaction on BCS (P [is less than] 0.09) with UIP heifers having higher BCS than Control at wk 5, 7, and 9 postpartum. There was a treatment x time interaction on serum IGF-I (P [is less than] 0.06) during the first 35 d postpartum. In UIP heifers, serum IGF-I was greater at calving compared with Control heifers (117.5 vs 92.4 ng/mL, respectively); however, these differences were not related to changes in BCS or BW. Although serum IGF-I concentrations were increased at calving in heifers receiving UIP, there were no treatment effects on postpartum interval (P [is greater than] 0.7). During the first 30 d postpartum, IGF-I differed (P [is less than] 0.01) among heifers with postpartum intervals defined as short, [is less than] 50 d (128.9 ng/mL); medium, 51 to 65 d (115.2 ng/mL); and long, 66 to 130 d (52.9 ng/mL). When analyzed as a regression, a 1 ng/mL increase in IGF-I (UIP and Control heifers) at calving (P [is less than] 0.05) and throughout the postpartum period (P [is less than] 0.01) corresponded to a decrease in postpartum interval of 0.13 d. Based on the results of this study, the inclusion of UIP in diets for primiparous heifers and its effects on postpartum interval warrant further evaluation. Key Words: Bred Heifers, Protein Digestibility, Reproduction

The effect of an undegradable intake protein (UIP) source on performance, diet digestibility, and forage intake of yearling heifers grazing flood-meadow pastures was studied over 2 consecutive summers (1999 and 2000) at Logan, Utah. Crossbred yearling beef heifers composed of varying proportions of Angus, Hereford, Tarentaise, and Gelbvieh (n=48 in 1999; n=47 in 2000) were blocked according to weight, age, and breed into one of two treatments (control, receiving no supplement; and supplement, receiving a mixture of 0.906 kg per d of ground corn and 0.453 kg per d of Soybest[R]). Heifers were weighed at 28 d intervals. The rumen evacuation technique was used to collect diet samples. Diet digestibility was estimated using indigestible acid detergent fiber as an internal marker. In 1999, fecal output was estimated using chromic oxide from sustained release boluses as an external marker. Forage intake was calculated from fecal output and diet digestibility. Diet and fecal sampling were conducted in 2 periods (early July and September). Data were analyzed in a completely randomized design. Total organic matter intake expressed as kg per d did not differ among treatments (P>0.15), but was higher in the control group on a percentage of body weight basis (P=0.03). Supplementation did not affect organic matter digestibility (OMD) in July 1999, but increased OMD in July 2000. Supplementation increased OMD in September 1999, but decreased OMD in September 2000. Supplementation did not affect NDF digestibility in July 1999, but increased NDF digestibility in September 1999 (P Key Words: Beef heifers, Protein supplementation, Meadow pastures

One thousand five hundred fifty-eight heifers (345 kg) were randomly allotted to one of three treatments (18 pens; 6 reps/trt) in a commercial feedlot. Heifers were implanted with Ralgro[R] d 0, and reimplanted with Synovex Plus (SynPlus), Finaplix-H (FinH) or Revalor-H (RevH) 95 d prior to slaughter. MGA was fed to all treatments. Heifers were fed a steam-flaked corn-based diet for 139 d. Dry matter intake was higher (9.2, 9.1 vs. 8.8 kg/d; P Key Words: Finishing, Heifers, Implants

Holstein heifers (n = 20; BW = 270 kg) were used in three randomized complete block experiments to determine the effects of various supplements on digestibility of low-quality fescue hay-based diets. Heifers were restrained in individual tie-stalls and fed fescue hay (Festuca arundinacia Shreb.; (8.7% CP, 39.7% ADF) ad libitum. In trial 1, heifers were fed supplemental DIP at 0, .05, .10, .15, or .20% BW/d. Soybean meal (53.3% CP, DIP = 65% of CP) was used to deliver DIP. Total tract digestibility of NDF (TNDFD) was unaffected (P > .10) by supplemental DIP. Conversely, total tract ADF digestibility (TADFD) tended to increase in quadratic fashion (P = .07) with increasing supplemental DIP. In trial 2, heifers were fed supplemental NDF at rates of 0, .16, .33, .49, or .65% BW/d. Soybean hulls (58.5% NDF) were used to deliver supplemental NDF. Soybean hull supplementation increased (P < .01) TNDFD and TADFD compared to no supplementation. Moreover, TNDFD increased quadratically (P < .01) and TADFD increased linearly (P < .01) with increasing soybean hull supplementation. In trial 3, heifers were fed supplemental ruminally-degradable starch (RDS) at rates of 0, .10, .20, .30, or .40% BW. Dry-rolled corn (72% starch, 75% ruminally degradable) was used to deliver supplemental RDS. Supplemental starch did not affect TNDFD (P > .10); however, TADFD by supplemented animals tended to be lower (P = .07) than unsupplemented animals. Results were interpreted to suggest that DIP or fiber supplementation positively influenced digestibility of the fiber components of fescue hay-based diets fed to heifers. Conversely, supplemental RDS appeared to have negative affects on ADF digestibility. Key Words: Supplementation, Digestion, Forage