Acetylcholinesterase mutation in diazinon-resistant Haematobia irritans (L.) (Diptera: Muscidae).

Acetylcholinesterase (AChE) cDNA from individual field-collected diazinon-resistant horn flies was amplified by RT-PCR. Sequencing of the amplification products revealed that 8/12 of the diazinon-resistant horn flies contained a point mutation previously associated with resistance to organophosphates in house flies and Drosophila, strongly suggesting that this cDNA encodes the AChE that is the target site for organophosphate (OP) pesticide. The point mutation (G262A) resulted in a shift from glycine to alanine in the mature HiAChE amino acid sequence at position 262. Allele-specific PCR and RLFP assays were developed to diagnose the presence or absence of the G262A mutation in individual flies. Use of the allele-specific assays each demonstrated the presence of the G262A mutation in 10 of 12 individual field-collected flies, demonstrating higher sensitivity than direct sequencing of RT-PCR amplification products. The G262A mutation was found in additional fly populations previously characterized as OP-resistant, further supporting that this AChE is the target site for OP pesticide. The allele-specific assay is a useful tool for quantitative assay of the resistance allele in horn fly populations.

Effect of horn fly (Haematobia irritans) control on growth and reproduction of beef heifers.

The influence of horn fly control with commercially available ear tags was studied on beef replacement heifers (n = 670) for growth and reproductive performance. The study was conducted at five sites in Louisiana over 3 yr. Heifers used were yearling replacement females that were exposed to fertile bulls during a limited spring breeding season that coincided with the horn fly season. In mid to late May of each year, heifers were randomly assigned to one of two horn fly treatments: untreated and treated for horn fly control. The trial continued each year until September or October at the end of fly season. Pregnancy status was determined by rectal palpation. Horn fly populations were controlled on the treated heifers at moderate levels (84%). Total weight gain of treated heifers was 14% greater than for untreated heifers. Horn fly treatment had no effect on pregnancy rate (78% and 75% for untreated and treated heifers, respectively). Treatment differences for weight gain were of greater magnitude for heifers failing to conceive than for heifers that became pregnant. Weight gains of nonpregnant treated heifers were 33% greater than for nonpregnant untreated heifers, whereas weight gains of pregnant treated heifers were 8% greater than for pregnant untreated heifers. In conclusion, horn fly control on yearling beef replacement heifers improved weight gain but had no effect on first exposure reproduction.

Effect of horn fly and internal parasite control on growth of beef heifers.

The effects of horn fly and gastrointestinal nematode control on body weight gain of yearling Angus-Brangus cross heifers were evaluated in three separate studies during the years 1999, 2000 and 2002. In each year, the studies started in late May and lasted for 150, 148 and 123 days, respectively. In all three studies, the tag treatment (10% lambdacyhalothrin+13% piperonyl butoxide impregnated ear tags) provided excellent horn fly control. In the three studies, the average weekly horn fly counts for tagged heifers were 1, 3, and 0 flies per side while the average on untreated heifers was 52, 163 and 90 flies per side. In studies 1 and 2, there was no difference (P>0.1) in weight gain between tagged and untreated heifers, but in study 3, tagged heifers gained 50% more weight (P<0.001) than the untreated heifers. For gastrointestinal nematode control, ivermectin (IVM) was administered on Day 0 in studies 1 and 3 using a sustained release bolus and on Day 0 and subsequent 56-day intervals in study 2 using either the injectable or pour-on formulation. Heifers treated with IVM in studies 1 and 3 had significantly lower (P<0.05) GI nematode fecal egg counts compared to control heifers. In study 2, IVM treated heifers also had significantly lower GI nematode fecal egg counts compared to control heifers, except for Day 90 when no differences in fecal egg counts were observed between IVM pour-on treated and control heifers. Weight gain of heifers that received IVM was significantly greater (P<0.005) than untreated heifers in each of the three studies. IVM treated heifers gained 45, 61 and 184% more weight than the untreated heifers during the three studies. There was no interaction (P>0.1) between the main treatment effects of fly control and gastrointestinal nematode control.

Insulin-like growth factor-I, insulin-like growth factor-binding proteins, and gonadotropins in the hypothalamic-pituitary axis and serum of nutrient-restricted ewes.

Body condition scores (BCS) of ovariectomized estradiol-treated ewes were controlled to examine effects of suboptimum BCS on insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBPs), and LH in the anterior pituitary gland, hypophyseal stalk-median eminence (SME), and circulation. Serum LH increased in ewes with BCS (1 = emaciated, 9 = obese) > 3 (HIGH-BCS), but not in ewes with BCS

Effects of extruded corn or grain sorghum on intake, digestibility, weight gain, and carcasses of finishing steers.

We conducted two trials to evaluate the effects of extruding vs dry-rolling either corn or grain sorghum on intake, digestibility, and performance of finishing steers. In Trial 1, 92 crossbred steers (average BW 413 kg) were used in a 2 x 2 factorial design. Diets contained either dry-rolled corn (RC), extruded corn (EC), dry-rolled grain sorghum (RGS), or extruded grain sorghum (EGS). Diets were fed for 110 d and contained 78.6% of the respective grain, 9% alfalfa pellets, 8.2% molasses, and 4.2% protein-mineral supplement. Daily gain was highest (P < .049) for steers fed RC, and the ADG of steers fed RGS was higher than that of steers fed extruded diets; there was no difference in ADG between steers fed EC and those fed EGS. Steers fed dry-rolled diets consumed more DM (P = .001) than steers fed extruded diets. Feed efficiency was not affected (P = .18) by processing method, but steers fed corn utilized the diets more efficiently (P = .006) than steers fed grain sorghum. Except for carcass weight, carcass data were not affected by grain type (P > .20). Dressing percentage, quality grade, and longissimus muscle area were lower (P < .09) in steers that received extruded grain than in those that received dry-rolled grain. In Trial 2, five ruminally cannulated crossbred steers (average BW 518 kg) were used in a 4 x 4 + 1 Latin square design to evaluate the ruminal and total tract digestion characteristics of the diets used in Trial 1. Type of grain had no effect (P > .16) on intake, total tract digestibility, or ruminal pH. Extruding corn or grain sorghum decreased intake (P < .001) but increased (P < .074) DM and starch digestibility compared with dry rolling; steers fed extruded diets had lower (P < .032) ADF and NDF digestibilities. Ruminal in situ DM and starch disappearance were higher (P < .03) and ruminal pH was lower (P < .052) in steers fed extruded grains than in those fed dry-rolled grains. Data from this study indicate that extruded corn and extruded grain sorghum are highly degradable feeds; however, decreased DM intake and lower ruminal pH levels resulted in lower performance.

Intake and digestion of low-, medium-, and high-quality grass hays by lambs receiving increasing levels of corn supplementation.

Thirty wether lambs (52.5 +/- 1.5 kg) were used in a replicated 3 x 5 factorial treatment arrangement and four periods to determine dietary intake and digestibility of three ground forages with increasing levels of supplemental ground corn. Forages were a mature, low-protein grass hay (LQH; 5.2% CP), an immature, medium-protein grass hay (MQH; 10.2% CP), and an immature, high-protein grass hay (HQH; 14.2% CP). Supplementation treatments were no supplement (NS), a protein supplement (PS), protein plus .25% BW of corn (LC), protein plus .5% BW of corn (MC), and protein plus .75% BW of corn (HC). Crude protein intake (1.4 g/kg BW) from supplements was equalized with soybean meal and corn gluten meal. Lambs were housed in metabolism crates. Supplements were fed at 0700 each morning after orts from the previous day's feeding were removed. Hay was subsequently offered at approximately the previous day's consumption plus 25%. Each of the four periods lasted 21 d. Sixteen days were allowed for diet adaptation. Feces were collected with fecal bags during d 17 to 21. Lambs receiving LQH and PS had higher forage (P < .04) and total DMI (P < .001) than lambs fed LQH and NS. Corn supplementation decreased forage intake (quadratic effect; P = .08), total intake (quadratic effect; P = .08), and increased apparent DM digestibility (linear effect; P < .04) with lambs receiving LQH. Protein supplementation did not affect forage or total DMI (P > .11), and corn supplementation did not affect total DMI (P > .20) with either MQH or HQH.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute glucose antagonism on hypophyseal hormones and concentrations of insulin-like growth factor (IGF)-I and IGF-binding proteins in serum, anterior pituitary, and hypothalamus of ewes.

The objectives of this study were to determine whether 2-deoxy-D-glucose (2DG), a metabolic inhibitor of glucose, 1) differentially affected release of LH, growth hormone (GH) and prolactin (PRL); 2) decreased anterior pituitary response to GnRH; and 3) altered concentrations of insulin-like growth factor I (IGF-I) and intensity of 125I-IGF-I binding to proteins (IGFBPs) in serum, anterior pituitary (AP), and hypothalamus (preoptic are [POA], medial basal hypothalamus [MBH], and stalk median eminence [SME]). In trial 1, mature, ovariectomized, crossbred ewes were treated with a single s.c. injection of either saline (n = 5) or 2DG (n = 5; 0.1 g/kg BW). Administration of 2DG suppressed (p < 0.05) concentrations of LH but did not affect (p > 0.05) serum concentrations of GH or PRL. In trial 2, ovariectomized ewes received injections of saline or 2DG, and each group was subdivided to receive either saline or GnRH analog (5 micrograms; Des-Gly10-[D-Ala6]) 2 h later. Administration of 2DG suppressed (p < 0.05) serum concentrations of LH before administration of GnRH; however, release of LH in response to exogenous GnRH was greater (p < 0.05) in ewes that received 2DG. Treatment with 2DG did not affect (p > 0.05) concentrations of FSH before or after administration of GnRH. In trial 3, 10 ovariectomized ewes were slaughtered 2 h after treatment with saline (n = 5) or 2DG (n = 5). Serum and tissues collected at slaughter (AP, MBH, SME, and POA) were analyzed for concentrations of IGF-I by RIA and intensity of 125I-IGF-I binding to proteins by ligand blotting.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of increasing levels of corn or beet pulp on utilization of low-quality crested wheatgrass hay by lambs and in vitro dry matter disappearance of forages.

Two trials were conducted to evaluate the effects of corn or dried beet pulp on intake and digestibility of forage by lambs and on IVDMD. In Trial 1, 16 lambs (average BW = 41 +/- .9 kg) were used in a randomized complete block design with eight lambs per block. Lambs were fed a crested wheatgrass hay (7.5% CP) and received either no supplement (NS), a protein supplement (PS), or protein supplements with various levels of corn or beet pulp. Corn supplements supplied 1.75 (PCL), 3.5 (PMC), and 5.25 (PHC) g of corn/kg of BW, whereas beet pulp supplements supplied 2.1 (PLBP), 4.2 (PMBP), and 6.3 (PHBP) g of beet pulp/kg of BW. All supplemented lambs received .128 g of CP/kg of BW. Hay DMI decreased linearly (P < .03) as the level of corn and beet pulp increased in the supplement. Total DMI decreased linearly (P = .013) as the level of corn increased; however, beet pulp did not affect total DMI (P > .71). Supplemental corn increased (P = .03) apparent diet DM digestibility (DMD), whereas supplemental beet pulp did not affect (P > .32) diet DMD. Lambs whose diet was supplemented with beet pulp had greater (P = .010) estimated hay DMD than lambs whose diet was supplemented with corn. In Trial 2, 48-h IVDMD was determined on each of three forages mixed with either corn or beet pulp. The crude protein content of the three forages was 4.9, 9.4, and 12.2% for low-, medium-, and high-quality forages, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of body composition of mature ewes with condition score and body weight.

Fourteen mature, ovariectomized, western-range ewes with an initial mean BW of 72 +/- 4.5 kg and mean condition score (CS) of 7.5 +/- .3 were used to evaluate the relationship between CS and body composition. Diets of chopped straw and alfalfa hay were formulated to provide either maintenance energy or less than maintenance energy (100 or 60% of ME) to induce changes in BW and CS. After 180 d, ewes were weighted, scored for body condition, and slaughtered. All carcass components, viscera, and organs were analyzed for lipid, DM, and ash, and protein was determined by difference. Body weight and CS values were related by regression analysis to percentage of composition and weights of carcass components, carcass, and empty body. Body weight and CS were highly correlated (r = .89) and analysis indicated that each increase in CS resulted in an increase of 5.1 kg of BW. Condition score accounted for more variation of percentage of lipid in the empty body (R2 = .95) and carcass (R2 = .90) than did BW (R2 = .84 and .80, respectively). In contrast, BW accounted for more of the variation in carcass weight (R2 = .97) and empty BW (R2 = .99). Inclusion of both BW and CS in regression models did not increase the variation accounted for with the single best predictor. With mature western-range ewes in this study, CS was highly related to carcass lipids and could be used to describe energy reserves available to ewes.

Intake and digestion of low-quality meadow hay by steers and performance of cows on native range when fed protein supplements containing various levels of corn.

Two trials were conducted to evaluate the effects of corn in protein supplements fed to cattle receiving low-quality forages. In Trial 1, four ruminally cannulated steers (avg BW 500 kg) and four intact steers (avg BW 270 kg) were used in a replicated latin square to determine intake and digestibility fo a low-quality meadow hay (4.3% CP) when fed no supplement (NS), 1.12 g CP/kg BW (PS), 1.12 g CP/kg BW with corn supplying 1.98 g starch/kg BW (PLC) or 1.12 g CP/kg BW with corn supplying 3.96 g starch/kg BW (PHC). Hay DMI decreased (P = .001) and total diet DMI increased (P = .001) quadratically as supplemental corn increased. Diet DM digestibility increased (P = .004) and forage DM and hemicellulose digestibility decreased (P less than or equal to .018) quadratically as level of corn in the diet increased. In Trial 2, 135 cows received either ear corn (1.16 kg TDN and 127 g CP.hd(-1).d(-1), ear corn plus protein (1.16 kg TDN) and 290 g CP g CP.hd(-1).d(-1) or protein (.72 kg TDN and 290 g CP.hd(-1.d(-1) while grazing native Sandhills winter range for 112 d and while receiving hay (10% CP) during the following 60-d calving period. Cows that received ear corn lost (P less than .001) more weight than cows fed ear corn plus protein supplement, which lost more weight than cows fed only protein supplement (-54, -18 and 6 kg, respectively) during the 112-d winter grazing period. Cows that received ear corn and ear corn plus protein gained more (P less than .001) weight during calving and summer grazing (after supplement wa withdrawn) than protein-supplemented cows. Reproductive performance was not affected (P greater than .705) by treatments.

Value of a molasses mixture containing natural protein as a supplement to brood cows offered low-quality forages.

In a 4-yr study, molasses (M; 6% CP), molasses-urea (MU; 17.5% CP; 92% molasses, 4% urea and 4% water) and molasses-cottonseed meal-urea (MCSM; 17.5% CP; 73% molasses, 25% cottonseed meal, 1% urea and 1% water) were compared as winter supplements for Braford cows (514 matings) consuming low-quality forage. Cows were fed 1.35, 1.50 and 1.27 kg.head-1.d-1 of the respective supplements for 127 d beginning in December. Cows were wintered on bahiagrass pasture (avg 8% CP) and stargrass hay (avg 5% CP). Quantity of hay offered averaged 7.6 kg.cow-1.d-1 over 109 d. Cows were exposed to bulls for 90 d beginning on March 1. Supplementation treatment did not affect cow live weight, live weight change or condition score (P greater than .05). However, pregnancy rate was higher (P less than .05) for cows fed MCSM (79.0%) than for cows fed M (67.8%). The pregnancy rate of cows fed MU (76.3%) was intermediate to, but not different (P greater than .05) from, that of cows fed either M or MCSM. Supplementation treatment did not affect calf performance as measured by birth weight, survival rate or weaning weight (P greater than .05). However, calves from cows fed MCSM were 6 d older (P less than .05) at weaning than calves from cows fed M. For 3-yr-old cows, pregnancy rate was considerably higher (P less than .05) for cows fed MCSM (69.6%) than for cows fed M (37.5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Intake and digestibility of low-quality meadow hay by cattle receiving various levels of whole shelled corn.

Two trials were conducted to evaluate the effects of whole shelled corn supplementation on intake and digestibility of low-quality meadow hay by cattle. In Trial 1, four ruminally cannulated steers (avg BW 418 kg) were used in a latin square design with four treatments (no corn or corn fed at .25%, .50% or .75% of BW). Hay DMI decreased (P = .002) linearly .43 g for each gram of increase in corn intake. In contrast, total diet DMI increased (P = .001) linearly as level of corn supplementation increased. Apparent DM digestibility of the diet increased (P = .026) linearly, whereas hay DM digestibility was not affected (P greater than .05) by supplemental corn, although the DM digestion coefficient for hay alone was 24% higher than for hay fed with corn at .75% of BW. Ruminal ammonia concentration and pH were not affected (P greater than .05) by treatments; however, ratio of acetate:propionate and acetate:butyrate responded (P less than or equal to .097) quadratically to increased corn supplementation. Corn supplementation resulted in a cubic (P less than or equal to .081) decrease in meadow hay NDF disappearance from nylon bags suspended in the rumen at all incubation intervals after 4 h. In Trial 2, 45 crossbred, nonlactating, pregnant cows (avg BW 474 kg) were used in a completely randomized design with three treatments (no corn, .91 and 1.81 kg corn.hd-1.d-1). Cow performance was not altered (P greater than .05) by treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Forage intake by lactating beef cows differing in potential for milk production.

Two feeding trials (early and late lactation) were conducted to measure ad libitum forage intake by beef cows from three breed groups of similar mature weight, but with different milk production potential. Twenty-four cow-calf units, eight from each milk production level (low, medium and high) were grouped (two/pen) based on similarity of cow weight and previous weigh-suckle-weigh and calf weaning weight data. Each pair of cow-calf units was confined to separate pens and allowed ad libitum access to chopped native Sandhills meadow hay. Dry matter intake, cow and calf BW and calf milk consumption were determined. Daily DMI (kg/hd) and milk consumption showed a positive linear response (P less than .05) among low, medium and high milk-producing cows. When cow DMI was expressed as g/unit mean cow BW during the trial, both a positive linear (P less than .05) and a quadratic response (P less than .01) expressed the relationship among production levels during early and late lactation. Calf forage intake, birth weight and adjusted 181- and 205-d weaning weight had no linear or quadratic relationship (P greater than .10) to milk production levels. However, June 1 calf weight, actual calf weaning weight and calf rate of gain (birth to weaning) had a positive linear (P less than .07) relationship. Best fit regression models with DMI as the dependent variable were developed for each trial based on R2 and CV values of the potential models. The best fit model (R2 = .94, SE = .33) for early lactation included production level as a class variable with cow BW.75 and calf birth weight as independent variables. The best fit model (R2 = .92, SE = .53) for late lactation included actual weaning weight in addition to the variables used during early lactation.

Effects of long-term consumption of sewage solids on blood, milk and tissue elemental composition of breeding ewes.

Fine-wool ewes received for 2 yr a complete pelleted basal diet (11% protein) or the basal diet fortified with 3.5% cottonseed meal (CSM; 12% protein) or gamma-irradiated (1 megarad) dried solids (SS; 12% protein) from primary (undigested) sewage (Las Cruces, New Mexico, municipal sewage). Five ewes fed each diet were sampled to determine Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb and Zn in blood, milk and tissues. Tissues and blood were sampled at slaughter 40 d after weaning of lambs. Mean whole blood mineral concentrations were similar (P less than .05) among treatments 3 d postpartum; however, at 42 d after lambing (mean +/- SE) both basal- (54 +/- 2 micrograms/ml) and sewage-fed (54 +/- 2 micrograms/ml) ewes had elevated (P less than .05) blood Ca compared with ewes fed CSM (46 +/- 2 micrograms/ml). No biologically important differences were detected in the concentrations of elements in milk. Ewes fed SS had lower (P less than .05) blood Fe than animals in the other groups. Sewage-fed ewes also had higher (P less than .05) liver Fe (1,092 +/- 100 micrograms/g) than basal-fed ewes (626 +/- 100 micrograms/g); whereas Fe in CSM-fed ewes (873 +/- 100 micrograms/g) was similar to both. Basal-fed animals had 1.1- to 1.3 times more (P less than .05) liver Mg and two- to threefold higher liver Na than CSM or SS. Livers from SS-fed ewes had higher concentrations (P less than .05) of Cd (1.5- to 1.6-times) and Pb (1.4- to 1.9-times) than livers from CSM- or basal-fed ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary sewage solids on feedlot performance, carcass characteristics, serum constituents and tissue elements of growing lambs.

Twenty fine-wool wether lambs were allotted randomly at weaning to be fed a conventional diet (CD) formulated for growing lambs, or the same basal mixture plus dried gamma-irradiated solids from primary sewage sludge (SS) incorporated as 7% of the dry matter. Feedlot performance and chemical elements in whole blood were monitored during 90 d, after which lambs were slaughtered and carcass data were collected. Concentrations of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb and Zn were measured in livers, kidneys, bones, spleens and muscles. Sewage solids in the diet did not affect performance appreciably, although dressing percentages from lambs fed SS were 4% lower than CD-fed animals (P less than .05). Rib eye areas, fat thicknesses, quality and yield grades were similar (P greater than .05). Element concentrations in whole blood at weaning, after 56 d of the feeding trial and at slaughter did not differ (P greater than .05) between dietary groups. Serum chemistry determinations showed no biologically meaningful patterns related to diets. Lambs fed SS had higher (P less than .05) concentrations of Cu in livers (51.1 vs 34.3 +/- 3.8 micrograms/g, mean +/- SE) and Pb in kidneys (4.0 vs 2.2 +/- .3 micrograms/g) and lower (P less than .05) Mg in kidneys (.69 vs .72 +/- .01 mg/g). None of the elements in spleen and muscle tissue differed (P greater than .05) between diet groups. Lambs fed SS had elevated (P less than .05) bone Co, Cu, Fe, K and Na compared with those of CD.(ABSTRACT TRUNCATED AT 250 WORDS)