Heifer development: reproduction and nutrition.

The nutritional development of heifers from birth to the time they become pregnant with their second calf is a critical component of cowherd management. Veterinarians can use targeted body weights and condition scores to monitor progress and gauge future reproductive success throughout heifer development. Meeting Nutrient Requirements of Beef Cattle recommendations for net energy and metabolizable protein is the single most successful strategy for maximizing reproductive performance from birth through the second pregnancy. Supplementation with fat, minerals, and additional undegraded intake protein has not been consistently reported to enhance the reproductive function of heifers.     

Simulation study of the competitive ability of erect, semi-erect and prostrate cowpea (Vigna unguiculata) genotypes

Ecophysiological simulation models provide a quantitative method to predict the effects of management practices, plant characteristics and environmental factors on crop and weed growth and competition. The INTERCOM interplant competition model was parameterised, calibrated by monoculture data for three cowpea (Vigna unguiculata) genotypes that differed in growth habit, common sunflower (Helianthus annuus) and common purslane (Portulaca oleracea), and used to simulate competition of cowpea cover crops with sunflower or purslane. The simulation results were compared with observations from field competition experiments in 2003 and 2004. INTERCOM more accurately simulated actual field data for the competition of cowpea genotypes and sunflower than companion field experiments for the competition of cowpea and purslane. The validated simulation model of cowpea and sunflower at two densities was used to study the effects of cowpea growth habit on final biomass production of cowpea and sunflower. The model suggested that erect growth habit was more competitive than semi‐erect and prostrate growth habit, when cowpea genotypes were grown with sunflower. Cowpea leaf area distribution was important to higher cowpea biomass production, while cowpea height growth was important to reduce sunflower biomass. Our simulation approach is suggested as a method for crop breeders to gauge the likely success of selection for competitive crops before undertaking expensive long‐term breeding experiments.     

High-yield preparation of purified Anaplasma marginale from infected bovine red blood cells

Purification of Anaplasma marginale from infected bovine RBC was achieved through enzyme treatment and density-gradient centrifugation. A relative yield of 41.6% was obtained by dividing the number of organisms in the final purified preparation by the number of A marginale-infected RBC. Purified parasites were verified as A marginale by light microscopy, electron microscopy, and immunologic tests. The purified parasites reacted positively with calf and rabbit anti-A marginale sera in interfacial and slide agglutination tests. Anti-bovine RBC serum did not agglutinate purified A marginale, indicating absence of any contaminating RBC stroma. Anaplasma marginale was antigenic, but did not cause infection when the preparation was inoculated into a susceptible calf. The density of A marginale was determined to be 1.19 g/ml and cell diameters ranged from 0.25 to 0.63 micron. This method provided procedures for obtaining A marginale free of bovine RBC antigens for accurate biochemical assays and vaccine production.     

Performance of ponderosa pine seedlings under four herbicide regimes in northeast Oregon

The herbicide, hexazinone, was applied four ways over ponderosa pine, 2–0 seedlings planted in northeast Oregon. The four treatments were two broadcast applications, a single broadcast application, a large spot application, and a small spot application. Seedling survival and growth were monitored for five growing seasons. Results indicate that survival more than doubled with either large or small spot applications compared to no application, and either one or two broadcast applications can increase survival an additional 30% over spot applications. Differences in stem volume were substantial, with two broadcast applications yielding more than twice the volume of a single broadcast treatment and more than five times the volume of seedlings treated with spot applications. Trees in small spots were still three times bigger than surviving seedlings in the control. These results are consistent with the concept of competition threshold. Management implications were considered in terms of cost of established seedlings. Although broadcast applications cost more per acre than spot applications, gains in seedling survival, growth and quality offset the additional cost and translate into lower established seedling costs. The cost effectiveness of broadcast applications also may be seen in the elimination of replanting or in-planting requirements and increases in long-term growth potential of the established trees.     

Anatomy of the primary-secondary transition zone in stems of Populus deltoides

Summary The transition from primary to secondary stem tissues occurs as a continuum, and a precise anatomical definition of the transition does not exist. A definition was derived for Populus deltoides based on the birefringent properties of the fiber wall. This definition was quantitatively reproducible in the 9 plants tested, and the secondary transition was found to occur in the internode associated with the first mature leaf from the apex. The primary-secondary transition did not occur uniformly around the periphery. It was first observed in the vascular bundles opposite the incoming trace, and from there it progressed in a counter-clockwise direction. Within the transition internode, each vascular bundle and each tissue comprising the bundle differentiated in accord with the physiological age and the phyllotactic disposition of the developing leaf to which it led. Within any one vascular bundle, differentiation occurred first in the metaxylem vessels and associated fibers, followed closely by extension of fibers into the interfascicular regions and centripetal differentiation of the phloem fibers. The ontogenetic sequence of differentiation for each of the principal tissues of the secondary transition zone is described.The technical assistance of Mr. Gary Buchschacher with the ultramicrotomy and photomicrography is gratefully acknowledged.     

Gonadotropin‐induced Puberty Does Not Impair Reproductive Performance of Gilts over Three Parities

The aim of this study was to evaluate the reproductive performance of three parities of gilts treated or not treated with gonadotropin to induce puberty. Sixty gilts received 600 IU of equine chorionic gonadotropin (eCG) followed by 2.5 mg of porcine luteinizing hormone (LH) 72 h later. Fifty‐nine other gilts were exposed only to a mature boar for 15 min twice daily. Artificial insemination (AI) was performed at 0, 12 and 24 h after the detection of oestrus, and gestation was confirmed by ultrasound after 35 days. Sows were inseminated at the first post‐weaning oestrus. The total numbers of piglets born, piglets born alive, stillborn, mummified foetuses, as well as pregnancy and farrowing rates were evaluated for each of the three parities. Culling rates, farrowing intervals and weaning‐to‐oestrous intervals (WEI) were also analysed. Mean age at puberty and oestrous manifestation were not significantly different between treatments (p = 0.0639; 179.20 ± 17.52 compared with 173.96 ± 16.94, 91.66% compared with 94.92%) across the experimental period. However, females that underwent puberty induction showed modest increases both in the number of total pigs born and in the number of piglets born alive. In conclusion, puberty induction through exogenous gonadotropin administration in field conditions did not induce a more concentrated first oestrous manifestation, but trended to a modest increase in the number of pigs born alive in the first parity and a reduced culling rate during the first gestation.