Comparison of bloat potential between a variety of soft-red versus a variety of hard-red winter wheat forage.

Some aspects of wheat pasture bloat have been researched extensively, but few studies have evaluated the effect of wheat type or variety on bloat. Eight Gelbvieh x Angus ruminally cannulated heifers (515 +/- 49 kg of BW) and 48 Angus heifers (238 +/- 12 kg of BW) grazed 1-ha pastures of hard-red or soft-red winter wheat (Triticum aestivum L.) to evaluate the effect of wheat variety on bloat potential. In Exp. 1, cattle grazed from November 11 to 22 and from November 26 to December 7, 2006, in a crossover design. In Exp. 2, cattle were shrunk for 20 h and then grazed from December 19 to 20, 2006, and from January 19 to 20, 2007. In both experiments, bloat was scored at 1000 and 1600 h daily. Rumen samples were collected at 0600, 1200, and 1800 h during each of the last 2 d of each period in Exp. 1 and during both days of each period of Exp. 2. Rumen samples were evaluated for pH, foam production and strength, and viscosity. In Exp. 1, cannulated heifers grazing soft-red had a greater (P < 0.01) percentage of observed bloat (21.9 vs. 5.6%) than those grazing hard-red winter wheat, but bloat incidence was low (2.1%) for the stocker cattle, with no difference between hard-red and soft-red winter wheat (P = 0.52). Viscosity of the rumen fluid was affected (P = 0.03) by the wheat variety x time interaction, with soft-red at 1200 and 1800 h being more viscous than soft-red at 0600 h and hard-red at all times. Foam strength, as determined by bubbling CO(2) gas through rumen fluid, had a wheat variety x time interaction (P = 0.02) with both wheat varieties similar at 0600 h but soft-red having greater foam strength at 1200 and 1800 h. In Exp. 2, no bloat was observed, and no differences between wheat varieties were observed for any of the rumen foam measures. Therefore, for these 2 varieties, the soft-red winter wheat had a greater bloat potential than the hard-red winter wheat based on results from the cannulated heifers, but no differences were observed in the frequency of bloat in stocker cattle. In this study, shrinking of cattle before grazing wheat pasture did not induce bloat.

Animal performance and economic comparison of novel and toxic endophyte tall fescues to cool-season annuals.

Increased costs of annual establishment of small grain pasture associated with fuel, machinery, and labor are eroding the profitability of stocker cattle enterprises. Interest has therefore increased in development of cool-season perennial grasses that are persistent and high quality. This study occurred on 24 ha (divided into thirty 0.81-ha paddocks) located at the University of Arkansas Division of Agriculture Livestock and Forestry Branch Station, near Batesville. Two tall fescue (Festuca arundinacea Schreb.) cultivars infected with novel endophytes (NE), Jesup infected with AR542 endophyte (Jesup AR542), and HiMag infected with Number 11 endophyte (HM11) were established in September 2002. Jesup AR542 and HM11 were compared with endemic endophyte Kentucky 31 (KY-31) tall fescue; wheat (Triticum aestivum L.) and cereal rye (WR, Secale cereale L.) planted in September 2003, 2004, and 2005; and annual ryegrass [RG, Lolium perenne L. ssp. multiflorum (Lam.) Husnot] planted in September 2004 and 2005. Each year, 3 steers (3.7 steers/ha) were placed on each pasture for fall and winter grazing, and 5 steers (6.2 steers/ha) were placed on each pasture for spring grazing. Animal performance is presented by year in the presence of a year x treatment interaction (P < 0.01). Body weight gain per hectare of steers grazing NE tall fescue was greater (P < 0.01) than those of KY-31 and WR during 2003 to 2004, whereas in 2004 to 2005, BW gain per hectare of steers grazing NE and RG did not differ (P < or = 0.29) and was greater (P < 0.01) than that of WR, which was greater (P < 0.01) than that of KY-31. During 2005 to 2006, BW gain per hectare was greater (P < 0.01) for steers grazing RG than those of NE and WR, which did not differ (P > or = 0.14). Body weight gain per hectare was least (P < 0.01) for steers grazing KY-31. Average net return of NE tall fescue was greater (P < 0.01) than KY-31, but profitability of NE did not consistently differ from cool-season annuals. Across the 3-yr study, NE tall fescue produced net returns per hectare of $219; this level of profitability would require 4 yr for a new planting of NE tall fescue to break even. Novel endophyte tall fescues offer potential benefits related to decreased risk of stand establishment of annual forage crops, longer growing season, and acceptable animal performance.

Incidence of puberty in beef heifers fed high- or low-starch diets for different periods before breeding.

Spring-born Hereford x Angus heifers (n = 206) were used to determine effects of energy supplementation programs and amount of starch in the diet on incidence of puberty. In Exp. 1, heifers (205 +/- 5 kg; n = 68) grazing dormant native pasture were fed 0.9 kg/d (as-fed basis) of a 42% CP supplement from November until February 14. Heifers were stratified by weaning weight and allotted randomly to treatment before breeding (May to July). Treatments were 1) 0.9 kg (as-fed basis) of a 42% CP supplement/d and pasture (control); 2) a high-starch (HS) diet (73% corn; 53% starch) fed in a drylot for 60 d (HS-60); 3) a HS diet fed in drylot for 30 d (HS-30); or 4) a low-starch (LS) diet (49% corn; 37% starch) self-fed on pasture for 30 d (LS-30). The HS-60 and HS-30 heifers were limited-fed to gain 0.9 kg/d, and the LS-30 heifers had ad libitum access to the diet. High-starch-60 and LS-30 heifers were heavier (P < 0.05) than control and HS-30 heifers at the beginning of the breeding season. Thirty-one, 25, and 26% more HS-60 heifers were pubertal (P < 0.05) on May 1 compared with LS-30, HS-30, and control heifers, respectively. At puberty, HS-60 heifers were 24 and 22 d younger (P < 0.05) than LS-30 and control heifers, and 31 kg lighter (P < 0.01) than LS-30 heifers. In Exp. 2, heifers grazed dormant pasture and were fed 0.9 kg (as-fed basis) of a 42% CP supplement/d from weaning in October to late February; then heifers were assigned randomly to treatments for 60 d before the breeding season. In two years, control heifers (n = 46) grazed pasture and received 0.9 kg of SBM supplement/d; LS (n = 46) heifers were self-fed a distiller's grain and soybean hull-based diet in drylot; and HS heifers (n = 46) were limited-fed a corn-based diet in drylot. During treatment, HS and LS heifers had greater weight gains than control heifers. Pubertal BW (313 +/- 6 kg) was not influenced by treatment, but HS and LS heifers were younger (P < 0.03) than control heifers at puberty. During a 60-d breeding period, the incidence of puberty was greater (P < 0.05) for HS and LS heifers than for control heifers and was greater (P < 0.05) in HS than in LS heifers in Year 1. Feeding a LS or a HS diet for 30 d before breeding may be inadequate to stimulate puberty in beef heifers, but feeding a diet with a greater amount of starch for 60 d before breeding may increase the incidence of puberty during breeding of heifers that have inadequate yearling weight.

Efficacy of intramuscular treatment of beef cows with oxytetracycline to reduce mastitis and to increase calf growth.

Spring-calving multiparous Angus x Hereford cows were used to determine the efficacy of intramuscular treatment with oxytetracycline to reduce the incidence of mastitis-causing bacteria, decrease milk somatic cell counts (SCC), and increase calf growth. During 2 yr, milk samples were collected from each quarter from a total of 319 cows at 8 to 14 d after calving and at weaning, to determine the presence of bacteria and SCC. A California mastitis test (CMT) was performed on milk from each quarter of each cow at the initial sample collection. Cows with a CMT score of 1, 2, or 3 in at least one quarter, were randomly assigned to receive either an intramuscular injection of oxytetracycline (n = 63) or the control vehicle (n = 60), and cows with a CMT score of 0 or trace in all four quarters were not treated (n = 196). Calf weights were determined at birth, early lactation, and weaning. The number of somatic cells in milk and the percentage of quarters that were infected increased as CMT score increased (P < 0.01). The presence of mastitis-causing bacteria at calving increased (P < 0.05) the incidence of infection at weaning. The presence of mastitis-causing bacteria at weaning was associated with increased SCC for quarters and average SCC for cows (P < 0.01). Average SCC per cow at weaning increased (P < 0.05) as the number of infected quarters per cow increased. Treatment did not alter (P > 0.10) the percentage of cows or quarters infected with mastitis-causing bacteria or SCC of cows or quarters at weaning. Average SCC per cow was negatively correlated (P < 0.05) with calf weights at early lactation, but not with weaning weights of calves. Treatment did not influence (P > 0.10) calf weights at early lactation or at weaning. Cows with one or more dry quarters after calving had calves that weighed less at early lactation and weaning than cows with four functional quarters (P < 0.01). Intramuscular oxytetracycline treatment of beef cows that had CMT scores of 1 or greater after calving did not reduce intramammary infection rates or increase calf weights at weaning.

Effects of growth rate on carcass composition and lipid partitioning at puberty and growth hormone, insulin-like growth factor I, insulin, and metabolites before puberty in beef heifers.

The effect of three rates of gain on carcass composition, lipid partitioning, age and BW at puberty, and concentrations of growth hormone (GH), IGF-I, insulin, glucose, and NEFA in plasma were evaluated in 38 Angus x Hereford heifers. Heifers were allotted by BW and age to three treatments with a replication in each of 2 yr: full-fed (n = 13; FF) to gain 1.36 kg/d; limit-fed (n = 12; LF) to gain .68 kg/d; maintenance-full-fed (n = 13; MFF) to gain .23 kg/d for 16 wk, then full-fed to gain 1.36 kg/d. Heifers were slaughtered within 10 d after the onset of puberty. At slaughter, kidney, pelvic, and heart fat (KPH) and udder (UDDER) were separated from carcass, as was fat surrounding viscera (OM). After 48 h at 4 degrees C a carcass side was dissected into subcutaneous fat (SC), intermuscular fat (SEAM), soft tissue (SFT = inseparable lean and fat), LEAN, and BONE. In yr 1, LF heifers (431 d) were older (P < .05) than MFF heifers (371 d) at puberty, but age of FF heifers (389 d) did not differ (P > .10) from that of LF and MFF heifers. In yr 2, FF heifers (351 d) were younger (P < .05) than LF and MFF heifers (398 and 434 d, respectively). The FF heifers had greater (P < .05) BW and a greater (P < .01) percentage of lipid in the carcass at puberty than LF and MFF heifers. During the first 16 wk of treatment, concentrations of NEFA were greater in heifers with slower daily gains (MFF > LF > FF; P < .01). Concentrations of NEFA were lesser and concentrations of IGF-I and insulin were greater in plasma of FF than in that of MFF heifers during the 10 wk before puberty. Treatment significantly altered age, BW, carcass composition, and lipid partitioning at puberty in beef heifers. We conclude that the percentage of body fat is not the sole regulator of puberty, and age may be an important modulator in determining the onset of puberty in beef heifers.

Effects of energy or protein supplements and stage of production on intake and digestibility of hay by beef cows.

In two consecutive years, primi- and multiparous, spring-calving Hereford and Hereford x Angus cows (n = 32, yr 1; n = 42, yr 2) were used to determine the effects of supplements and lactational status on forage intake, digestibility, and energy intake. Cows were randomly alloted to treatments after being blocked by age, breed, and weight. Supplements fed during gestation provided .55 kg/d of CP from a 40% CP, soybean meal-based supplement (PROTEIN) or a 20% CP, soybean hull-based supplement (ENERGY). After calving, cows remained on the same supplement or were switched. In yr 2, a 40% CP supplement was also fed postpartum at nearly the same rate as ENERGY to provide twice the supplemental CP and energy as PROTEIN. Prairie hay (< 5% CP) DMI was measured directly and DM digestibility estimated for two 7-d periods during late gestation and early lactation. Gestating cows fed PROTEIN consumed 1 kg/d more hay DM and hay DM digestibility was greater (P < .001) than for cows fed ENERGY. Lactating cows also consumed more hay when fed PROTEIN than when fed ENERGY or HI PROT, but hay DMI was not affected. Total ME intake was similar for cows fed PROTEIN and ENERGY in late gestation or early lactation. Results indicated that ENERGY will decrease low-quality forage digestibility for prepartum cows and can decrease forage intake for both pre- and post-partum cows. Increasing the total energy intake of grazing cattle by feeding supplements is difficult after protein requirements are met.

Effects of feeding energy or protein supplements before or after calving on performance of spring-calving cows grazing native range.

In three consecutive years, spring-calving Hereford and Hereford x Angus cows (n = 348) were used to determine effects of level of supplemental energy or protein before and after calving on cowherd performance. Beginning on November 1, cows were individually fed 1.22 kg/d of a 40% CP (PROTEIN) or 2.44 kg/d of a 20% CP supplement (ENERGY) until calving. After calving, cows remained on the same supplement, were switched to the other supplement, or were fed 2.44 kg/d of a 40% CP supplement (HI PROT). Supplementation ended on April 20, the start of a 65-d breeding season. Cows fed ENERGY during gestation had greater BW gains (9 kg) at calving than PROTEIN-fed cows (P < .01). Calf weaning weight was not affected by supplementation. Cows fed ENERGY before calving had an 11% greater pregnancy rate than the cows fed PROTEIN (P < .002). Cows fed PROTEIN or ENERGY after calving had similar BW gains but cows fed HI PROT after calving lost less BW during supplementation (P < .002). Pregnancy rates were not influenced by treatments fed for a short period after calving. In conclusion, conception rates were significantly improved by feeding greater levels of supplemental energy prepartum but not postpartum. Energy supplements can affect reproduction with minimal effects on BW or condition.

Effects of postweaning diet on age and weight at puberty and mild production of heifers.

One hundred 7-mo-old spring-born beef heifers (215 kg) were used to evaluate effects of level of supplementation and short-term concentrate feeding on age and weight at puberty and milk production. In each of two winters, heifers were individually fed .9 kg/d of a 40% CP supplement (SBM) or 1.8 or 2.7 kg/d of a 20% CP supplement (LOW-20 or HIGH-20, respectively) while grazing dormant native pastures or .9 kg/d of SBM until February, and then fed a high-concentrate diet (NEg = 1.31 Mcal/kg) in drylot to weight the same as HIGH-20 heifers on May 1, the beginning of the breeding season. Weights on May 1 were similar for HIGH-20 and DRYLOT heifers (320 and 314 kg, respectively) and were heavier (P < .01) than those of LOW-20 heifers (289 kg), which were heavier (P < .01) than SBM-fed heifers (278 kg). Pubertal weight was similar for SBM, LOW-20, and DRYLOT (290, 296, and 297 kg, respectively) and heaviest for HIGH-20 heifers (P < .01, 325 kg). DRYLOT heifers reached puberty at 29 d younger (P < .05) than heifers on the other treatments. Percentage of heifers puberal on May 1 were 0, 9, 13, and 72 for SBM, LOW-20, HIGH-20, and DRYLOT heifers, respectively. Pregnancy rates were significantly lower for SBM (67%) than for LOW-20, HIGH-20, and DRYLOT (94, 94, and 86%, respectively). Milk production after first parturition was similar for all treatments. Age and weight at puberty may be altered by short-term feeding of high-concentrate diets.(ABSTRACT TRUNCATED AT 250 WORDS)

GnRH in the infundibular stalk-median eminence is related to percentage body fat in carcasses of beef cows.

Mature Hereford cows (n = 28) were used to determine the effect of percentage body fat on secretion of LH and content of GnRH in the infundibular stalk-median eminence (ISME). Cows were fed to maintain, lose, or gain weight to achieve body condition scores (BCS; 1 = emaciated; 9 = obese) of 3 to 7. Then cows were fed to maintain weight and body condition. Before slaughter, estrus was synchronized using two injections of prostaglandin F2 alpha(PGF) 11 d apart. Five d after the second PGF injection, cows were given 100 micrograms of GnRH (im) and serum samples were obtained. LH was quantified using RIA. The anterior pituitary and ISME were obtained within 45 min of death. Anterior pituitary weight and LH concentration, total GnRH in the ISME, total carcass fat, and percentage carcass fat were determined. BCS of cows at the time of slaughter influenced percentage carcass fat (P less than .001), total GnRH in the ISME (P less than .02), and maximum LH after GnRH treatment (P less than .09), but did not influence pituitary weight or concentration of LH in the pituitary. Content of GnRH in the ISME averaged 76 +/- 12, 32 +/- 14, 27 +/- 13, and 24 +/- 13 ng for cows with BCS of 3, 5, 6, and 7, respectively. BCS was correlated (P less than .001) with percentage carcass fat (r = .94) and total fat in the carcass (r = .92). Total GnRH in the ISME was negatively correlated (P less than .005) with BCS (r = -.54), percentage carcass fat (r = -.55), and total carcass fat (r = -.49).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lactational status on forage intake, digestibility, and particulate passage rate of beef cows supplemented with soybean meal, wheat middlings, and corn and soybean meal.

Sixteen mature, lactating (453 kg) and 16 nonlactating (487 kg) Hereford and Angus x Hereford cows were used to determine effects of different dietary supplements and lactational status on forage intake, digestibility, and particulate passage rate. Supplement treatments and amounts fed (kg/d) were as follows: control, 0; and equal daily amounts of CP from soybean meal (SBM), 1.36; wheat middlings (WM), 3.41; or a blend of corn and soybean meal (corn-SBM; 22% corn and 76% SBM), 3.41. Cows were fed supplements at 0800 and had ad libitum access to prairie hay (4.9% CP) in stalls from 0800 to 1100 and from 1300 to 1600 for three 17-d periods. Lactational status and supplement type did not interact (P greater than .50) for hay DMI, DM digestibility, or particulate passage rate. Cows fed SBM ate more hay DM (P less than .01) and had greater hay DM digestibility (P less than .01) than did cows in other treatment groups. Average hay DMI (kg/100 kg of BW) was 1.95, 2.16, 1.94, and 1.89, and hay DM digestibility was 52, 61, 55, and 53% for control, SBM, WM, and corn-SBM supplements, respectively. Total diet DM digestibility was increased by supplementation (P less than .01), but no differences (P greater than .18) were observed among supplements. Lactating cows ate more (P = .13) hay DM (2.11 vs 1.87 kg/100 kg of BW) and had greater (P less than .05) fecal output (4.6 vs 4.3 kg/d) than did nonlactating cows. Dry matter digestibility and particulate passage rate were not affected (P greater than .35) by lactational status.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of nutrition and body condition on pituitary, ovarian, and thyroid function of nonlactating beef cows.

Nonpregnant Hereford cows (n = 70) were used to determine the effect of nutrient intake and body condition on reproductive and thyroid function. Body condition scores (BCS; 1 = emaciated; 9 = obese) of cows averaged 5.0 +/- .2 on July 1, and cows were fed for 4 mo either to lose weight and BCS (thin; n = 22), to maintain weight and BCS (moderate; n = 24), or to gain weight and BCS (fat; n = 24). After November 1, cows received a complete ration to maintain weight and BCS. Cows were slaughtered in December (six thin, eight moderate, and eight fat cows) or the subsequent March (16 cows per group). Before slaughter, cows were given two injections of prostaglandin F2 alpha (PGF) 11 d apart. Six days after the second PGF injection, cows were simultaneously treated with 100 micrograms of gonadotropin releasing hormone (GnRH; i.m.) and 100 micrograms of thyrotropin releasing hormone (TRH; i.v.) and serum samples were obtained. The BCS of cows at slaughter (8 d after PGF) averaged 3.4, 5.3, and 7.1 (P less than .01) and carcass energy content averaged 243, 432, and 714 Mcal (P less than .01) for thin, moderate, and fat cows, respectively. Wet ovarian (P less than .001) and corpora lutea (P less than .01) weights were heavier for fat cows. Content of LH in the pituitary gland and concentrations of thyroxine (T4) in serum after GnRH/TRH were not influenced by nutrient intake or BCS. However, thin cows had greater concentrations (P less than .05) of LH in serum after GnRH/TRH than did moderate or fat cows. We conclude that nutrient intake and body energy reserves of beef cows influenced ovarian function and LH in serum after treatment with GnRH.

Relationship among weight change, body condition and reproductive performance of range beef cows.

A 5-yr study involving 45 to 78 pregnant Hereford range cows each year evaluated relationships among prepartum nutrition, body condition scores, BW changes and reproductive performance. Four prepartum nutritional treatments were imposed. One group of cows were fed to maintain (M) their November BW until calving in March and April. The other three groups of cows were fed to lose about 5% of their November BW by 8 wk before parturition, then to maintain BW (LM), lose an additional 5% of their BW (LL) or gain 5% of their BW (LG). After calving, all cows were fed to maintain BW. Body condition scores and BW were recorded every 14 d throughout the trial. Linear regression analyses were conducted to examine treatment effects on BW, body condition score and measures of reproductive performance. A discriminant analysis was performed on pregnancy rate and percentage of cows with ovarian luteal activity by 85 d after parturition. The M cows had a greater pregnancy rate (71%) than cows on other treatment groups. The LL cows had a reduced pregnancy rate (42%) compared with LM (51%) and LG (58%) cows. Prepartum nutritional treatment did not affect the days from parturition to conception. Precalving body condition score and November to January BW changes influenced pregnancy rate (P less than .001). A cubic response curve described the relationship between pregnancy rate and precalving body condition score for cows with condition scores of 3 through 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Carcass composition in mature Hereford cows: estimation and effect on daily metabolizable energy requirement during winter.

Seventy-two mature, nonpregnant, nonlactating Hereford cows (400 kg) were utilized in a comparative slaughter trial to investigate the effects of carcass composition on the metabolizable energy (ME) required for maintenance in winter. Body condition score (CS), live weight (LW) and weight:height ratio (WTHT) were evaluated and compared as estimators of carcass composition in cows. Cows ranged in LW, CS and WTHT from 275 to 595 kg, 2.0 to 8.0 units and 2.29 to 4.62 kg/cm, respectively. Live weight, CS and WTHT predicted total carcass energy (TMCAL, r2 = .81, .85 and .83), carcass fat (FAT, r2 = .78, .82 and .80), carcass protein (PRO, r2 = .71, .74 and .70) and carcass water (WAT, r2 = .78, .71 and .77) with similar accuracy. When composition was expressed on a per unit weight basis, CS was superior to LW and WTHT as predictors of TMCAL/hot carcass weight, TMCAL/LW and FAT/hot carcass weight (r2 = .82, .60 and .64; .83, .58 and .62; and .82, .64 and .68, respectively). Forty-seven cows were individually fed a complete diet (2.50 Mcal ME/dry matter) in drylot for 114 d in yr 1 and 115 d in yr 2. Daily feed intakes were adjusted each week to maintain constant LW throughout the winter. Data were analyzed by fitting the model: ME intake = k-1 (carcass energy change) + f(CS)LW.75, where k = efficiency of ME use for carcass energy change and f(CS) = function of CS. Year as a class variable and the expression .1028 + .0234(CS) - .0025(CS)2 accounted for 41% of the variation in Mcal ME for maintenance/LW.75. Condition score was more closely related to carcass composition in mature cows than was LW or WTHT and cows in either a thin (CS = 3) condition or a fat (CS = 7) condition required less (4.4% and 8.9%) Mcal ME/LW.75 for maintenance than cows in moderate (CS = 5) condition.

Effects of corn gluten feed on forage intake, digestibility and ruminal parameters of cattle fed native grass hay.

Thirty-two beef cows (467 kg) were individually fed native grass hay and supplement for two 14-d periods in each of 2 yr. Supplement treatments and amounts fed (kilograms/day) were negative control (NC), 0, or equal amounts of protein from soybean meal (SBM), .7; a blend of soybean meal and corn gluten feed (SBM/CGF), 1.0; or corn gluten feed (CGF) 1.6. Cows received supplement at 0645 and had ad libitum access to native grass hay from 0700 to 1130 and from 1530 to 2000. Compared with NC, all protein supplements increased (P less than .05) ruminal NH3, propionate and butyrate concentrations at 4 and 25 h postfeeding. Ruminal fluid pH, total VFA and acetate concentrations at 4 and 35 h postfeeding were not affected by supplements. All supplements increased (P less than .01) hay intake as well as hay, acid detergent fiber (ADF) and total diet dry matter (DM) digestibility. Compared to supplemental SBM, feeding CGF reduced (P less than .01) hay intake. Calculated daily intakes of metabolizable energy (ME) were 12, 17, 18, and 17 Mcal for NC, SBM, SBM/CGF and CGF, respectively. Hay intake, DM and ADF digestibility and ME intakes tended to be higher for SBM/CGF than for the average of SBM and CGF fed alone. Intakes of digestible DM and ADF were not altered by protein supplements, suggesting that intake responses were due to increased diet digestibility. Corn gluten feed appears to be an effective source of supplemental protein and energy for cows consuming low-quality roughage.

Postpartum weight and body condition loss and performance of fall-calving cows.

A total of 166 mature fall-calving Hereford cows were used to study the effects of weight and body condition losses on the reproduction of cows and on the performance of their calves. This study was conducted before and during the breeding season over a 3-yr period. The cows calved in a good body condition and were assigned to one of the following treatment groups: the MM group to maintain weight from calving (September - October) through breeding (December - January), the LM group to lose up to 10% of the postpartum weight from calving to the beginning of breeding and to maintain the weight during breeding, and the ML group to maintain weitht from calving to the beginning of breeding and to lose 10 - 15% of the postpartum weight during breeding. Weight losses were adjusted by altering daily amounts of protein supplement and forage. Cows in the LM treatment group lost 3, 17 and 6% of their postpartum weight before breeding in yr 1, 2, and 3, respectively, and they had a 10-d longer (P <0.05) interval from calving to first estrus than MM or ML group cows. The percentage of cows with ovarian activity at the beginning of breeding was reduced (37 vs 64%, P <0.01) for LM compared with MM cows. Treatment-by-year interactions were significant for pregnancy rate and ovarian activity at the end of breeding. In Year1, ML cows lost 14% of postpartum weight during breeding and had reduced (P <0.01) pregnancy rates compared with MM or LM cows (50 vs 79 and 88%). Only 41% of ML cows in Year 1 had luteal activity after estrus compared to 93% for MM and 79% for LM cows. During Year 2, LM cows lost 17% of postpartum weight before breeding, while ML cows lost 6% of their postpartum weight before breeding and 11% during breeding. Pregnancy rates tended to be reduced for both LM and ML cows compared to MM cows (53 and 65 vs 87%, P >0.10). The percentage of cows with ovarian activity at the end of breeding was reduced (P <0.05 for the LM treatment group and tended (P >0.10) to be lower for ML than for MM cows. In Year 3, pregnancy rates were greater (89, 84 and 85% for MM, LM and MM, respectively) for all groups. However, the percentage of cows with luteal activity after estrus was greater (P <0.05 for MM (94%) than for LM and ML (64 and 67%). Calf weaning weights (205 d in April) were not significantly influenced by treatment. We conclude that even if cows have adequate energy reserves at calving (good body condition), optimal reproductive efficiency of fall-calving range cows cannot be ensured.

Response of fall-born calves to progesterone-estradiol benzoate implants and reimplants.

Two trials, involving 469 steer and heifer calves, were conducted to evaluate the practices of implanting or reimplanting suckling fall-born calves with progesterone-estradiol benzoate (PE) implants (100 mg of progesterone, 10 mg of estradiol benzoate). Calves having an average initial weight of 67 kg were randomly allocated within sex and location to remain either nonimplanted or to receive a PE implant in the late fall, in the spring just before green grass, or in both fall and spring. All animals grazed good- to excellent-quality native Bluestem range. Nonimplanted calves in Trial 1 gained .57 kg/d during the winter months and PE implants improved growth rate by 7% to .61 kg/d (P less than .05). Growth rate of calves on dry winter range in Trial 2 was only .20 kg/d, and was not affected by PE implants. Average daily gain of nonimplanted calves during the spring and summer months was .96 and .87 kg/d for trials 1 and 2, respectively. Performance of implanted calves during that period was improved an average of 4.3 to 10% (P less than .05) by PE implants in both trials regardless of when the calves were implanted. Growth rate of calves over the entire 8-mo trials was .66 kg/d for nonimplanted calves and was improved (P less than .01) to .70, .70 and .71 kg/d for calves on the two single-implant and reimplant schedules, respectively. Implanted calves gained an average of 10.4 kg more than nonimplanted calves during the study.

Clenbuterol (planipart(trade mark)) for the postponement of parturition in cattle.

Clenbuterol is a highly specific, long-acting (four to eight hours) beta-two sympathomimetic which causes bronchodilation and tocolysis (myometrial paralysis). The tocolytic effect was explored as a means to control parturition and reduce dystocia. Forty-six heifers were injected i.m. with either Clenbuterol or saline placebo in a randomly controlled experiment. Animals were treated when a cervical dilation of five centimeters or more was detected by vaginal examination. Length of first, second and third stages of parturition, ease of parturition, maternal pelvic area and calf viability were compared between treatment groups. Treatment with Clenbuterol increased (P<0.025; 119 vs 468 mins) the time heifers were in Stage I. However, the lengths of Stages II and III, pelvic area at birth and calf viability were not influenced by treatment. Diameter of the cervix at treatment was negatively related to the length of Stage I delay. Pelvic area also significantly affected the length of Stage II. Clenbuterol effectively delays Stage I of parturition with no adverse effects on the fetus or dam.

Preliminary studies on the effect of yeast culture supplementation on nitrate/nitrite induced methemoglobinemia in lambs and steers.

Lambs and steers were fed low-nitrate hay and supplements which supplied 0.045 kg (lambs) or 0.114 kg (steers) of yeast culture/head/day for 14 and 12 days, respectively, prior to feeding high-nitrate sorghum-sudan hay. Nitrate consumption of lambs by 6 hours after feeding the high-nitrate (29,300 ppm NO3) hay was similar among treatments and ranged from 0.3 to 0.5 g/kg body weight/day over 3 challenge days. Similar rates of nitrate consumption occurred with steers. Blood methemoglobin concentrations, used as a measure of nitrate/nitrite exposure in lambs and steers fed yeast culture, were not lower than those of control animals. The results of the study indicate that yeast culture did not decrease the methemoglobinemia produced by consumption of high-nitrate forages by sheep or cattle.