The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform

M.g. Diskin - One of the best experts on this subject based on the ideXlab platform.

  • Effect of calf isolation and restricted suckling on LH secretion in Postpartum suckler cows
    Proceedings of the British Society of Animal Science, 1999
    Co-Authors: D.r. Mackey, J.f. Roche, J.m. Sreenan, M.g. Diskin
    Abstract:

    In suckler cows follicular development resumes early in the Postpartum period, but failure of successive dominant follicles to ovulate results in a prolonged Interval from calving to first ovulation (Postpartum Interval, PPI). Calf isolation and restricted suckling induce ovulation of either the current or subsequent dominant follicle (DF), probably due to changes in LH pulsatility, but this ovulation is generally silent and followed by an 8-10 day cycle due to lack of progesterone priming. The aim of this study was threefold: 1) to examine the acute effects of calf isolation and restricted suckling on LH pulse frequency and PPI, 2) to determine if progesterone priming would eliminate silent heats and short cycles, and 3) to determine if oestradiol treatment would cause atresia of the current dominant follicle and induce new wave emergence providing a “fresh” dominant follicle at progesterone withdrawal.

  • effect of calf isolation on follicular wave dynamics gonadotropin and metabolic hormone changes and Interval to first ovulation in beef cows fed either of two energy levels Postpartum
    Biology of Reproduction, 1998
    Co-Authors: K Stagg, J.f. Roche, J.m. Sreenan, L J Spicer, M.g. Diskin
    Abstract:

    The effects of Postpartum energy intake, restricted suckling, and cow-calf isolation on concentrations of LH, FSH, growth hormone, and insulin-like growth factor-I (IGF-I) and on Postpartum anestrous Interval were determined by randomly allocating beef cows with a mean body condition score of 2.3 +/- 0.1 to receive either 80 MJ metabolizable energy (low-energy diet [L]; n = 51) or 120 MJ metabolizable energy (high-energy diet [H]; n = 52) per cow per day from calving. At 30 days Postpartum, cows within diet were randomized to 1) have continued full access to their calves from birth to weaning (ad libitum suckling: ADLIB), 2) be suckled once-daily with their calves penned adjacent (restricted suckling, adjacent: RESADJ), 3) be isolated from all calves except for a once-daily suckling period (restricted suckling, isolated: RESISO). The mean Postpartum Interval was similar (p > 0.10) for L and H cows (62 and 63 days, respectively). RESADJ cows had a shorter (p 0.10) of diet. FSH secretion pattern was not affected by diet, suckling treatment, sequential follicle wave number, or follicle wave retrospectively realigned to emergence of first ovulatory wave. Within 5 days of suckling restriction and calf isolation, the number of LH pulses increased from 0.18 to 0.48 pulses per hour (p < 0.05). Both mean LH and the mean number of LH pulses increased linearly (p < 0.01) during the six follicle waves up to the first ovulatory wave. From 80 days before, until the time of, first ovulation, growth hormone decreased (p < 0.05) while IGF-I increased (p < 0.05), irrespective of treatment. The results indicate that the "suckling effect" in beef cows is the major factor affecting the duration of the Postpartum Interval and suggests that the maternal bond is more important than suckling in regulating LH pulse frequency, the key endocrine factor determining whether or not a dominant follicles ovulates. Removal of the suckling effect resulted in a rapid increase in LH pulse frequency, which was not dependent on level of Postpartum nutrition, at least within the nutritional limits of this study. Mean concentrations of FSH, unlike LH, did not vary with follicle wave number, suggesting that lack of FSH is not a major factor delaying the resumption of ovulation in Postpartum beef cows.

J.c. Whittier - One of the best experts on this subject based on the ideXlab platform.

  • Effect of 2, 4, and 5-hour Intervals between 2 prostaglandin F2α injections administered with 5-day CO-Synch + CIDR protocol on pregnancy rate in beef cows
    The Professional Animal Scientist, 2012
    Co-Authors: R.k. Peel, George E. Seidel, J.c. Whittier, Jill L. Seabrook, A.v. Grove, Jason K. Ahola
    Abstract:

    The objective of this study was to compare fixed-time AI (TAI) pregnancy rates resulting from Intervals of 2, 4, or 6 h between 2 prostaglandin (PG) F2α injections administered in a 5-d CO-Synch + controlled internal drug-release device (CIDR) estrus synchronization protocol. Angus and Angus-crossbred cows (n = 901) maintained on native pasture at 3 locations were randomly assigned to treatments after blocking for BCS and Postpartum Interval. All cows received gonadotropin-releasing hormone and a CIDR insert on d –5, PG and CIDR removal on d 0, and gonadotropin-releasing hormone with TAI at 72 h. Cows also received a second injection of PG either 2, 4, or 6 h after the first injection of PG. Pregnancy rates were determined by transrectal ultrasonography 40 ± 2 d following TAI. Body condition score and Postpartum Interval did not differ (P > 0.72) between estrus synchronization protocols, averaging 4.3 and 81 d, respectively. Fixed-time AI pregnancy rate was least (P ≤ 0.05) in cows receiving 2 PG injections separated by 2- and 4-h Intervals (average 51%) compared with cows receiving 2 PG injections separated by a 6-h Interval (59.7%). Reducing the Interval between PG injections from 6 to 2 h resulted in a 9-percentage-point (15%) reduction in TAI pregnancy rates for cows synchronized with a 5-d COSynch + CIDR protocol.

  • Use of gonadotropin-releasing hormone at fixed-time artificial insemination at eighty or ninety-seven hours post prostaglandin F2α in beef cows administered the long-term melengestrol acetate select synch.
    The Professional Animal Scientist, 2009
    Co-Authors: Jason K. Ahola, George E. Seidel, J.c. Whittier
    Abstract:

    ABSTRACT In a 2-yr trial, the pregnancy response of 549 Angus-based cows (BCS 5.1 ± 0.56, Postpartum Interval 69.7 ± 19.1 d) was evaluated when estrous cycles were synchronized by feeding melengestrol acetate for 14 d with gonadotropin-releasing hormone (GnRH) given on d 26 and prostaglandin F 2α (PG) on d 33. Of all cows, those observed in estrus within 72 h after PG were inseminated 9.5 ± 4.01 h after estrus was first observed. The remaining cows were fixed-time inseminated (TAI) and randomly assigned to receive or not receive GnRH at TAI, and randomly assigned to be inseminated at 79.7 ± 2.26 h (early) or 96.6 ± 1.94 h (late) post-PG. There were no GnRH × year ( P = 0.47) or GnRH × time of TAI ( P = 0.96) interactions. Cows that received GnRH at TAI had a greater ( P P = 0.07) for a year × time of TAI interaction. In yr 1, late TAI cows had a greater ( P = 0.01) pregnancy rate than early cows; however, in yr 2, pregnancy rate was not different ( P > 0.10) between early and late cows. Results indicate that within the long-term melengestrol acetate Select Synch protocol, pregnancy rate of cows not observed in estrus within 72 h of PG could be increased by adding a second GnRH injection at TAI, whereas the effect of delaying time of TAI until 97 h post-PG on pregnancy rate was inconsistent.

  • effects of a timed insemination following synchronization of ovulation using the ovsynch or co synch protocol in beef cows
    The Professional Animal Scientist, 1998
    Co-Authors: T. W. Geary, J.c. Whittier, F A Thrift, S L Dolezal
    Abstract:

    Abstract This study compared pregnancy rates of suckled beef cows that were time inseminated following synchronization of ovulation using the Ovsynch protocol. Multiparous beef cows (n=771) within each of three locations were stratified by breed type, age, Postpartum Interval, and AI sire, and randomly allotted to receive either the Ovsynch or CO-Synch protocol. The Ovsynch protocol consisted of an injection of GnRH (100 μg) on d 0, an injection of PGF 2α on d 7, another injection of GnRH (100 μg) on d 9, and timed insemination on d 10. The CO-Synch protocol consisted of the same hormone injection schedule as the Ovsynch protocol, but cows were time inseminated on d 9, when the second GnRH injection was administered. Pregnancy rates did not differ between treatments at each location ( P >0.1). However, when data were pooled across location, pregnancy rate was higher ( P =0.02) for cows that received the Ovsynch protocol (57%) than for cows that received the CO-Synch protocol (49%). No difference ( P >0.1) in pregnancy rate due to cow age, Postpartum Interval, body condition score, age by treatment, or Postpartum Interval by treatment was detected among pooled data. Among cows with a body condition score of 6.0 or greater, pregnancy rates were higher ( P =0.04) for Ovsynch treated cows (72%) than for CO-Synch treated cows (53%). These data demonstrate that the Ovsynch and CO-Synch protocols result in acceptable pregnancy rates to a timed insemination in beef cows. Whether the increase in pregnancy rates obtained using the Ovsynch protocol will warrant handling cows a fourth time for insemination will likely vary by management intensity.

  • pregnancy rates of Postpartum beef cows that were synchronized using syncro mate b or the ovsynch protocol
    Journal of Animal Science, 1998
    Co-Authors: T. W. Geary, J.c. Whittier, M.d. Holland, E R Downing, D G Lefever, R W Silcox, T M Nett, G D Niswender
    Abstract:

    We compared pregnancy rates of beef cows subjected to the traditional Syncro-Mate-B protocol or the new Ovsynch protocol and timed insemination. Multiparous Angus cows (n = 436) were stratified by age, Postpartum Interval, and AI sire and were randomly divided into two treatment groups for synchronization of estrus/ovulation. Approximately half of the cows (n = 216) received the traditional Syncro-Mate-B protocol with 48-h calf removal from the time of implant removal until breeding. The remaining cows (n = 220) received the Ovsynch protocol, which consists of an injection of GnRH (100 microg) on d -10, an injection of PGF2alpha (25 mg) and 48-h calf removal on d -3, another injection of GnRH and calf return on d -1, and timed insemination 24 h later (d 0). Blood samples were collected from all cows before treatment to identify anestrous and cyclic females. Pregnancy rates were higher (P < .025) for Ovsynch-treated cows (54%) than for Syncro-Mate-B-treated cows (42%). Pregnancy rates of cyclic Ovsynch-treated cows (59%) were higher (P < .005) than pregnancy rates of cyclic Syncro-Mate-B-treated cows (38%). Pregnancy rates of anestrous cows also tended to favor synchronization with the Ovsynch protocol. From these data, we conclude that the Ovsynch protocol is capable of inducing a fertile ovulation in cyclic and anestrous beef cows and that pregnancy rates to a timed insemination are higher than those obtained with synchronization of estrus using Syncro-Mate-B.

Jeff W. Tyler - One of the best experts on this subject based on the ideXlab platform.

  • Reducing calf losses in beef herds.
    Veterinary Clinics of North America-food Animal Practice, 2005
    Co-Authors: Robert L Larson, Jeff W. Tyler
    Abstract:

    Comprehensive neonatal disease control programs use estrous synchronization and artificial insemination to breed a high percentage of replacement heifers to bulls with high-accuracy expected progeny differences (EPD) for acceptable birth weight. Reducing the incidence of dystocia improves passive transfer of antibodies to calves and reduces likelihood of a prolonged Postpartum Interval to cycling resumption, allowing breeding of first-calf heifers early in the subsequent season. Use of mature cow-herd estrous synchronization systems, nutritional management for optimum body condition, heifer development plans assuring that heifers are cycling before breeding, and breeding soundness examination (BSE) of bulls ensures that a high percentage of cows conceive early, thereby reducing calves exposed to significantly older calves and amplified pathogen loads during the neonatal period.

A Sanz - One of the best experts on this subject based on the ideXlab platform.

Larry V. Cundiff - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of biological types of cattle (Cycle VII): influence of Postpartum Interval and estrous cycle length on fertility.
    Journal of animal science, 2007
    Co-Authors: Robert A. Cushman, M. F. Allan, R. M. Thallman, Larry V. Cundiff
    Abstract:

    Genetic improvement in reproductive efficiency through selection is difficult because many reproductive traits are binomial and have low heritabilities. Before genetic markers can be generated for fertility in cows, greater characterization of reproductive phenotypes is needed to understand the components of the trait. The current study tested the hypotheses that: 1) breeds vary in Postpartum Interval to estrus (PPIE) and estrous cycle length, 2) a longer estrous cycle immediately before breeding increased pregnancy rates, and 3) a greater number of cycles before breeding increased conception rates. The Postpartum Interval to estrus, estrous cycle length, and number of cycles before breeding were examined in F1 cows (n = 519) obtained from mating Hereford, Angus, and MARC III cows to Hereford, Angus, Simmental, Limousin, Charolais, Gelbvieh, and Red Angus sires. Cows were classified as having 0, 1, 2, or 3 observed estrous cycles before breeding. All traits analyzed were adjusted to constant BCS. Sire breed of the cow influenced length of the PPIE and number of cycles before the start of breeding (P

  • Reproductive performance, calf growth, and milk production of first-calf heifers sired by seven breeds and raised on different levels of nutrition
    Journal of animal science, 1998
    Co-Authors: Harvey C. Freetly, Larry V. Cundiff
    Abstract:

    We evaluated heifers crossbred from seven breeds of sires (Hereford, Angus, Belgian Blue, Piedmontese, Brahman, Boran, and Tuli) and three breeds of dams (Angus, Hereford, and MARC III [four-breed composite]). Heifers were mated to Red Poll sires to calve at 2 yr of age. Heifers were placed in two treatments from weaning to breeding and raised on a high nutrition level (15.8 Mcal ME/d) or on 80% of the high nutrition level (12.6 Mcal ME/d). Breeds differed in the age of the heifers at parturition (P = .03). Birth weights of calves differed by maternal grandsire (P < .001) but not by heifer treatment (P = .91) or maternal grandam (P = .19). Heifers differed in their Postpartum Interval to estrus by sire breed (P = .001). Calf age at weaning (P = .02), calf ADG (P < .001), and 205-d weight (P < .001) differed between breeds of maternal grandsires. Milk production from 50 to 200 d of lactation was greatest for heifers of Belgian Blue (1,070 +/- 30 kg) and Brahman (1,029 +/- 38 kg) sires. Milk production did not differ with treatment group (P = .84). This study suggests that over a diverse group of breeds, accelerated rates of gain during the postweaning period within the ranges of this study do not result in increased production efficiency of the cows.