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Biomedical subjects

L L Larson

Publications and source records attributed to L L Larson.

At least 19 recordsLinked to original sources
PubMed2001

Recent advances in the chemistry of spinosyns.

The spinosyns are a new class of fermentation-derived insect control agents that are effective against a variety of chewing insect pests. The successful introduction of spinosad into the agricultural marketplace represents an important milestone in the use of natural products for commercial pest control. The development of a natural product presents additional limitations relative to a synthetic material. While the latter affords some degree of control in building appropriate physical attributes such as photostability, a natural product, designed to function in a different environment, is often less suited for traditional spray applications. Despite its intrinsic photolability, spinosad is stable enough to perform under field conditions. In an effort to generate analogs with improved physical characteristics, we have developed a variety of conditions for selectively modifying different portions of the molecule, and we have discovered analogs with greater activity against a broader spectrum of pests. The inability to translate improved greenhouse activity to actual field conditions resulted in a detailed study of the effects of formulations and crystallinity on biological activity. Through this effort, measurably improved field performance of synthetic spinosyn analogs relative to the natural product have now been observed.

Animals↗
PubMed1996

Effects of tallow and escape protein on lactational and reproductive performance of dairy cows.

Experiments were performed to determine the effect of energy source and proportion of escape protein on lactational performance, body measurements, and reproductive activity. Sixty-eight lactating Holstein cows were assigned to one of four dietary treatments during wk 2 to 12 postpartum: 1) high fat (3% tallow), high escape protein (5% feather meal:blood meal, 85:15, DM basis); 2) high fat, low escape protein (0% feather meal:blood meal); 3) low fat (0% tallow), high escape protein; and 4) low fat, low escape protein. Diets were similar in energy and CP contents. Overall mean milk yield (32.9 kg/d) was not affected by diet, but efficiency of FCM yield was highest with high fat and high escape protein. Daily DMI and net energy balance were greater for cows fed the diet low in fat and low in escape protein, but days to first ovulation were not different among groups. Total cholesterol in plasma increased as DIM increased, and concentrations were greater for cows fed the high fat diets than for cows fed the low fat diets after 35 DIM. Concentrations of luteal phase progesterone and follicular phase estradiol tended to be greater for cows fed the high fat and low escape protein, but conception rate from first AI was greatest for cows fed the high fat and high escape protein. Supplemental tallow and escape protein did not consistently affect lactational performance but did improve efficiency of FCM yield and conception rate from first AI.

Animal Nutritional Physiological Phenomena↗
PubMed1992

Regulation of estrous cycles in dairy cattle: A review.

Artificial insemination has allowed rapid genetic progress in dairy cattle through the use of semen from genetically superior sires. Detection of estrus and proper timing of insemination remain as major problems limiting reproductive efficiency in dairy herds. Numerous programs for regulating estrous cycles have been examined in this review. While several programs appear promising, results remain variable and the need for accurate detection of estrus has not been eliminated. Nulliparous heifers seem to respond more consistently than lactating cows. Further research is required to develop a successful program that will consistently produce a precise synchrony of estrus and ovulation with normal fertility and be cost effective.

Journal Article↗
PubMed1992

Vitamin A supplementation of Holsteins at high concentrations: progesterone and reproductive responses.

Five trials involving 168 Holstein cows and 20 heifers were conducted to determine the effect of vitamin A supplementation at high concentrations, 1 or 2 million IU, compared with 100,000 IU/d, on peripheral concentrations of progesterone and on several measures of reproductive performance. Supplemental vitamin A at high concentrations had no effect on circulating concentrations of progesterone in either cyclic or pregnant cows or on most measures of reproductive performance examined in trials. Thus, it was concluded that providing vitamin A at these high concentrations is not warranted.

Animals↗
PubMed1992

Effects of isolation of calves on growth, behavior, and first lactation milk yield of Holstein cows.

Holstein (n = 323) calves in the herds of four experiment stations were reared individually (control) or in isolation to 70 d of age to determine whether isolation affected growth, behavior, and first lactation yield. Treatment differences were not observed for average daily gain for BW at d 28, 56 or 70. Postweaning approach distance was measured in two herds (n = 122; n = 28). Detailed pre and post-weaning behaviors were reported in one herd (n = 26). Isolation did not affect subsequent milk yield or culling percentages. In a second experiment, seven pairs of monozygous twins and a set of identical triplet calves were obtained by transferring split embryos into recipients, one member of each pair was reared in a group, and the twin was reared in isolation. Early rearing previously had been found to affect growth, feed intake, dominance rank, and learning ability of calves, and, in our study, the subsequent milk yield of calves reared in isolation tended to average more than for calves in groups. Intraclass correlations between monozygous twin pairs for milk, fat, relative value milk, and relative value fat were lower than anticipated. These data indicate that preweaning isolation did not affect first lactation milk yield traits.

Animal Husbandry↗
PubMed1989

Effect of dietary protein and exogenous gonadotropin-releasing hormone on circulating progesterone concentrations and performance of Holstein cows.

Sixty-three Holstein cows were used in a 2 x 2 factorial arrangement of treatments to determine the effects of dietary protein and exogenous gonadotropin-releasing hormone on performance postpartum and on circulating concentrations of progesterone. The experimental diets, 14 or 20% CP (dry basis), were fed from parturition to 14 wk postpartum. Blood serum urea N was elevated in the cows fed the 20% versus 14% CP diet. Feed intake was increased, but yield and composition of milk were not affected by the higher protein diet. Circulating concentrations of progesterone were lower in cows fed 20% than 14% protein on d 12 of both the synchronized and subsequent estrous cycles. Exogenous gonadotropin-releasing hormone administered on d 12 of the preceding estrous cycle did not increase the concentration of progesterone on d 12 of the subsequent estrous cycle. Luteal phase concentrations of progesterone were reduced by high dietary protein, but were not affected by gonadotropin-releasing hormone given on d 12 of the preceding cycle.

Animals↗
PubMed1988

Endocrine responses and estrous activity in Holstein heifers fed supplemental beta-carotene.

Three trials involving 56 Holstein heifers were conducted to determine the effect of feeding supplemental beta-carotene (BC) on several reproductive parameters. Heifers were maintained in a loose housing system and group fed year-old brome hay ad libitum. All heifers were individually fed 2.73 kg of a concentrate mix daily. Half of the heifers received 300 mg BC/d (Trials 1 and 2) or 600 mg BC/d (Trial 3) blended in the concentrate mix. After 4 wk of dietary treatment, estrus was synchronized to facilitate observation for estrous activity and collection of blood samples. Two weeks after the treatment was initiated, concentrations of BC in blood serum were greater in the heifers that were fed supplemental BC as compared to control heifers. This difference increased to 6 wk. However, feeding supplemental BC had no effect on any of the reproductive parameters measured, including incidence of estrus and changes in progesterone and luteinizing hormone (LH) concentrations after PGF2alpha, intervals from PGF2alpha to estrus and LH peak, estrual activity or first service conception rate. The results indicate that feeding supplemental BC does not alter reproductive performance in Holstein heifers.

Journal Article↗
PubMed1988

Effect of beta-carotene supplementation on reproductive performance of lactating Holstein cows.

Fifty-four lactating Holstein cows were assigned by parity and calving date to a 2 X 3 factorial arrangement of a randomized block design to determine effects of beta-carotene supplementation and ration fiber content on reproduction. Because ration fiber treatments did not differ in their effects on reproductive performance, data for beta-carotene analyses were pooled over the three rations. From 3 to 98 d postpartum, cows were individually fed either 0 or 300 mg supplemental beta-carotene daily by adding it on top of their complete mixed ration. By wk 3 postpartum, concentrations of beta-carotene in blood serum were higher in cows fed supplemental beta-carotene and remained higher throughout the experimental period. Feeding supplemental beta-carotene had no effect on the interval from the time of parturition to uterine involution, ovulation, first observed estrus, or conception. Feeding beta-carotene did not influence incidence of cystic follicles based on palpation, ovarian cyclicity based on blood progesterone patterns, peak progesterone concentrations, or first service conception rate. Cows fed supplemental beta-carotene required fewer treatments for clinical mastitis. Reproductive performance in lactating Holstein cows was not improved by feeding supplemental beta-carotene.

Animals↗
PubMed1988

Effect of supplemental beta-carotene on luteinizing hormone released in response to gonadotropin-releasing hormone challenge in ovariectomized Holstein cows.

Thirteen lactating Holstein cows were assigned randomly to either a control or beta-carotene (600 mg/d) treatment group to determine the effect of long-term beta-carotene supplementation on releasable luteinizing hormone in response to gonadotropin-releasing hormone challenge. The experimental period was 28 wk. Milking was terminated at wk 16, ovariectomy performed at wk 20, and response to gonadotropin-releasing hormone determined at wk 27. Serum beta-carotene concentrations reflected dietary intake and were higher in the cows fed beta-carotene after 2 wk of supplementation and remained higher for the duration of the trial. Feeding supplemental beta-carotene had no effect on circulating progesterone concentration, corpora lutea size or corpora lutea progesterone concentration, or basal concentrations of luteinizing hormone, frequency, and amplitude of luteinizing hormone pulses, or the release of luteinizing hormone in response to gonadotropin-releasing hormone. Thus, pituitary responsiveness to exogenous gonadotropin-releasing hormone was not affected by feeding supplemental beta-carotene.

Animals↗
PubMed1987

Avulsion of the bovine prepuce from its attachment to the penile integument during semen collection with an artificial vagina.

Avulsion of the prepuce (AP) from the penile integument during intromission into an artificial vagina (AV) is the most common injury involving the penis and prepuce of bulls collected for the production of frozen semen at artificial insemination (AI) centers. We observed clinical cases at two AI centers. Because temporary loss of seminal collections from genetically superior bulls occurs and the possibility of impotency exists, the economical loss from AP is significant. Surgery, rather than a nonsurgical procedure, is the preferred method for repair of AP if the diagnosis occurs on the same day as the injury. After injury, seminal collection is avoided. The bull can then begin a conditioning program prior to returning to a normal semen collection schedule. A specific etiology for AP remains undetermined; however, many variables potentially involved in its occurrence are known. Bulls with good libido following 4 to 5 yr of sexual inactivity are particularly susceptible to AP. No genetic predisposition was observed. At present, we believe that AP is caused by many factors and that implementing preventive measures does help.

Journal Article↗
PubMed1987

Growth of masking as a measure of response growth in hearing-impaired listeners.

Growth-of-masking functions were obtained from 19 normal and 5 hearing-impaired listeners using a simultaneous-masking paradigm. When masker and probe frequency are identical, the slope of masking approximates 1.0 for both normal-hearing and impaired listeners. For masker frequencies less than or greater than probe frequency, the slopes for impaired listeners are shallower than those of normals. These findings are consistent with previously reported physiological data (single-fiber rate versus level and AP masking functions) for animals with induced cochlear lesions. Results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears.

Adolescent↗
PubMed1986

Application of ABRs to the hearing-aid selection process: preliminary data.

This paper describes preliminary data on the use of click-evoked ABRs in the hearing aid selection process. Four normal-hearing and 4 hearing-impaired subjects were tested with a hearing aid set at three different frequency response settings. Estimates of gain were calculated using shifts in Wave V thresholds, shifts in Wave V latency-level functions, acoustic-reflex measurements, coupler gain measurements, and measurements of functional gain. Results suggest that the click-evoked ABR does not distinguish between differing amounts of low-frequency gain, although reasonable estimates of high-frequency gain appear possible. Also discussed are technical factors that must be considered when using the ABR in the hearing aid evaluation process.

Adult↗
PubMed1985

Relation between frequency selectivity and speech perception following glycerol-induced cochlear changes.

Changes in auditory threshold, psychophysical tuning curves, and speech perception (in both quiet and noise) were monitored over a 3-hr period following the ingestion of glycerol. All listeners had sensorineural hearing loss secondary to Menière's disease. Findings were characterized by large intersubject variability and in general did not show a clear relation between changes in threshold, frequency resolution, and speech perception.

Adult↗
PubMed1983

Effects of selenium, vitamins, and ration fiber on placental retention and performance of dairy cattle.

One hundred and twenty Holstein cows were assigned to a randomized complete block design to determine effects of selenium, vitamins, and ration fiber on incidence of placental retention and other health and reproductive problems. The selenium treatment (50 mg selenium, 680 IU vitamin E) was administered as a single injection approximately 3 to 4 wk prepartum. The vitamin treatment (3 million IU vitamin A, 450,000 IU vitamin D3, 300 IU vitamin E) consisted of two injections, one administered at 3 to 4 wk prepartum and another at 2 to 3 wk postpartum. Fiber treatments were: control, 15.7% crude fiber; beet pulp, 19.3% crude fiber; and soyhull, 19.0% crude fiber. Feeding of experimental rations was begun 1 day postpartum, and the ration effect on placental retention was examined only at subsequent parturition. The overall placental retention rate of 28% was not affected by either selenium, vitamin, or combined treatments. Ration treatments did not affect the placental retention rate of 42% at subsequent parturition. Cows receiving the soyhull ration required fewer services per conception. Incidence of foot problems tended to be higher in the cows that received the combined selenium and vitamin A, D, E treatments. Supplemental selenium, vitamins A, D, and E, and ration fiber treatments did not reduce incidence of placental retention or improve most other health and reproductive measures.

Animals↗
PubMed1983

Relation of age, season, production, and health indices to iodine and beta-carotene concentrations in cow's milk.

Milk samples were collected from 82 Holstein cows during the 1st yr of a 2-yr study and from 44 of these again in the 2nd yr to determine relationships of iodine and beta-carotene concentrations in milk to age, season, placental retention, uterine infections, clinical mastitis, services per conception, and milk yield. Composite milk samples were collected twice weekly at the morning milking. Milk samples from each cow were pooled prior to analyses for the following three times: 1 to 7 wk and 8 to 14 wk postpartum in yr 1 and 1 to 6 wk postpartum in yr 2. Beta-carotene concentrations of milk were inversely related to milk yield and positively related to milk fat percentage. Concentrations tended to be higher for cows experiencing health problems, probably because of lower milk yields and the concommitent higher milk fat content. The relatively low milk iodine concentrations were not generally related to cow age, season of calving, milk yield, milk fat percentage, or to health and performance measures.

Age Factors↗
PubMed1982

Effect of beta-carotene supplementation on reproductive performance of dairy heifers.

Three trials were conducted to determine the effect of feeding supplemental beta-carotene on reproductive performance of Holstein heifers. In each trial, the animals were randomly assigned to either a control or treatment group. Animals in the treatment groups received 300 mg supplemental beta-carotene daily for the test periods which varied from 6 to 8 weeks in length. To facilitate sample collections and observations, estrus was synchronized with two injections of 25 mg PGF(2alpha) at 11 day intervals. The first injection was after 2 weeks of feeding supplemental beta-carotene. Blood serum beta-carotene concentrations were higher in the heifers fed supplemental beta-carotene as compared to concentrations in control heifers after 1 week of feeding and this difference increased throughout the test periods. The interval from the second injection of PGF(2alpha) to onset of estrus was shorter in the control heifers as compared to that interval in heifers supplemented with beta-carotene (trial 1,44.0 vs 56.0 hr; trial 2, 51.3 vs 70.8 hr; trial 3, 40.7 vs 62.5 hr, respectively). The intervals from PGF(2alpha) administration to the preovulatory LH peak (43.3 vs 61.5 hr) and ovulation (69.3 vs 85.9 hr) were also shorter in the control heifers in trial 3. No significant differences were found among treatments in the number of heifers that expressed estrus, the blood serum progesterone concentrations or the conception rates in any of the three trials.

Journal Article↗
PubMed1980

Relationship between early postpartum blood composition and reproductive performance in dairy cattle.

Blood samples were collected over 1 year from 115 postpartum Holstein cows to determine the relationship between blood composition and reproductive performance. Blood samples were collected from each cow at 14 to 21 days (sample 1) and 38 to 45 days (sample 2) postpartum. These samples were analyzed for packed cell volume, hemoglobin, total protein, calcium, phosphorus, magnesium, copper, zinc, and selenium. Blood composition varied little with lactation number and season, and relationships were not consistent for the two collection periods. Hemoglobin, packed cell volume, total protein and zinc were associated negatively and calcium and magnesium associated positively with at least one measure of milk yield. None of the blood components examined at the two collection periods had a consistent relationship to reproductive performance. The most important relationship was the positive relationship of selenium concentration at first collection period with services per conception and days open.

Animals↗