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Biomedical subjects

R D Randel

Publications and source records attributed to R D Randel.

At least 127 records · Page 7Linked to original sources
PubMed1985

Effect of lasalocid on growth and puberal development in Brahman bulls.

Twenty-four half-sib Brahman bulls (171 to 276 d of age; 140.9 to 243.2 kg) were paired by age and weight and randomly allotted to one of two treatment groups (12 bulls/treatment) with two replicates (six bulls/replicate). Control treatment (C) was a 4:1 corn (IFN 4-02-931):cotton-seed meal (IFN 3-01-621) diet fed at 1% of the average body weight plus Coastal bermudagrass hay (IFN 1-00-716) ad libitum. Lasalocid treatment (L) was the control diet with the addition of 200 mg lasalocid X head-1 X d-1. Lasalocid resulted in lower acetate and butyrate with higher propionate and no change in total ruminal volatile fatty acids. Lasalocid-fed bulls tended to gain more weight (L = 153.6 +/- 8.5 kg, C = 138.4 +/- 7.9 kg; P less than .08), tended to have a greater average daily gain (ADG; L = .78 +/- .05 kg/d, C = .71 +/- .04 kg/d; P less than .09) and had greater feed conversion (11.5% less feed/kg gain) than did the control bulls. Lasalocid did not affect bull height (HT), weight:height ratio, length (LE) or heart girth (HG) at any time tested during puberal development. Lasalocid bulls exhibited a greater increase in HG through 175 d on treatment (L = 27.6 +/- 1.0 cm, C = 24.3 +/- 1.8 cm; P less than .05) and through first detected sperm (FS) in an ejaculate (L = 30.1 +/- 2.2 cm, C = 26.1 +/- 1.4 cm; P less than .05), but the increase in HG from the start of the trial through puberty was not different between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows.

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.

Journal Article↗
PubMed1984

Postpartum nutrient intake and body condition: effect on pituitary function and onset of estrus in beef cattle.

From calving through first estrus, 30 Brangus females were assigned equally to one of three diets to study the effect of postpartum nutrient intake and body condition on the ability of the pituitary to release luteinizing hormone (LH) and on the postpartum interval to estrus (PPI). The postpartum diets were calculated to achieve a 1) low [90% of the National Research Council (NRC) recommendations], 2) maintenance (100% of the NRC recommendations), or 3) high (110% of the NRC recommendations) level of nutrient intake. The females were group-fed within a treatment and calves were allowed to suckle ad libitum. Cow weight, body condition score and calf weight were recorded 24 h aftercalving, d 20 postpartum and at first behavioral estrus. On d 21 postpartum, blood samples were collected via jugular cannulae at 15-min intervals for 4 h, followed by a 100-micrograms im injection of gonadotropin-releasing hormone (GnRH) and continued sampling at 15-min intervals for an additional 6 h to determine serum LH. Although there was a significant decrease in PPI with increasing levels of nutrient intake (low = 57.5 +/- 8.8 d; maintenance = 40.3 +/- 6.6 d; high = 34.7 +/- 5.1 d), there were no differences in any of the observed LH characteristics (or variables) due to treatment. There were, however, marked differences in both the PPI and LH characteristics when data were analyzed on the basis of ability to maintain body condition from calving through 20 d postpartum, regardless of calculated dietary treatments. Cows that maintained body condition (MBC) had a shorter PPI [MBC, 31.7 +/- 2.8 vs lost (LBC) 60.0 +/- 7.5 d; P less than .01], higher basal levels of endogenous LH (MBC, .83 +/- .09 vs LBC, .61 +/- .04 ng/ml; P less than .025), higher GnRH-induced peak LH concentration (MBC, 58.99 +/- 11.15 vs LBC, 38.86 +/- 8.37 ng/ml. P less than .10), higher LH levels throughout the GnRH-induced LH surge (P less than .001), and greater release curve areas for the endogenous (MBC, 124.6 +/- 13.3 vs LBC, 91.7 +/- 5.6 units; P less than .025), GnRH-induced (MBC, 4370.8 +/- 699.5 vs LBC, 3039.7 +/- 683.3 units; P less than .10) and total (MBC, 4510.7 +/- 706.7 vs LBC, 3141.9 +/- 684.7 units; P less than .10) LH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Ovarian and uterine morphology and function in Angus and Brahman cows.

Ovarian characteristics, daily serum progesterone (P4) and estradiol-17 beta (E2) concentrations (d 7 through 17) and uterine luminal secretory protein components and histological variables were evaluated in parous Bos taurus (Angus, n = 20) and Bos indicus (Brahman, n = 19) cows. Cows were slaughtered on d 17 (estrus = d 0) for measurement of ovarian structures, flushing of uteri and removal of uterine tissue for histological evaluation. Cows were placed into one of three reproductive categories: nonpregnant, remnant (flushings contained remnants of embryonic tissue) or pregnant. For ovarian and uterine variables, there were only a few differences among reproductive categories within breeds. For combined categories, weight of the active ovary (containing the corpus luteum) was similar between breeds, but inactive ovarian (P less than .001) and follicular fluid (P less than .01) weights, stromal weight (P less than .01) and number of follicles less than 5 mm in diameter (P less than .01) for both ovaries combined were greater in Brahman than Angus cows. Corpus luteum weight (P less than .001), luteal P4 content (P less than .08) and number of follicles greater than 5 mm in diameter for both ovaries combined (P less than .05) were greater for Angus than for Brahman cows. Overall, mean serum P4 concentrations were greater in nonpregnant (P less than .05), pregnant (P less than .005) and combined (P less than .025) reproductive categories for Angus than corresponding categories of Brahman cows and mean serum E2 concentrations were greater in remnant (P less than .025) and combined (P less than .05) reproductive categories for Angus than corresponding categories of Brahman cows. Mean total uterine luminal protein was greater (P less than .05) in Angus than in Brahman cows for pregnant (23.4 vs 14.7 mg, respectively) and combined reproductive categories (22.4 vs 16.1 mg, respectively). Using electrophoretic analyses, percentage composition of three uterine specific cathode migrating protein bands and quantitative estimates of proteins with molecular weights (MW, X 10(-3)) of 9, 15.5, 34.2, 41.3, 46.2 and 183.1 were greater (P less than .05 to P less than .001) in uterine flushings from Angus than from Brahman cows. Uterine, myometrial and endometrial thicknesses, number of glands/microscopic field and uterine luminal epithelial cell height variables were generally greater (P less than .05 to P less than .001) in pregnant and combined reproductive categories for Angus than for Brahman cows.

Animals↗
PubMed1984

Immunosuppressive effect of uterine secretory protein from Angus and Brahman cows upon lymphocytes in vitro.

Uterine luminal protein collected on d 17 (estrus = d 0) from Angus (n = 20) and Brahman (n = 19) cows of varying reproductive status was evaluated for immunosuppressive activity in vitro. Reproductive status consisted of the following categories: nonpregnant (uterine flushing was devoid of embryonic material); remnant (uterine flushing contained obvious degenerative fragments of embryonic tissue) and pregnant (uterine flushing contained an intact conceptus). Uterine protein was tested for suppressor activity in both phytohemagglutinin (PHA) and mixed lymphocyte culture (MLC) systems. Incorporation of [3H]-thymidine into 1 X 10(6) Angus or Brahman lymphocytes for PHA cultures and 5 X 10(5) lymphocytes from each breed for MLC experiments served as the index for lymphocyte blastogenesis. For all experiments, uterine luminal protein from nonpregnant, remnant and pregnant Angus and Brahman cows suppressed (P less than .01) lymphocyte blastogenesis for Angus and Brahman lymphocytes, respectively. In two lymphocyte-uterine protein specificity experiments containing PHA, uterine protein from Angus cows suppressed (P less than .01) blastogenesis of Brahman lymphocytes and uterine protein from Brahman cows suppressed (P less than .01) blastogenesis of Angus lymphocytes. Within and between breed comparisons of suppressor activity were evaluated when expressing uterine protein culture data as percentages of control (no test protein) cultures. At 200, 400 and 800 micrograms/ml of uterine protein, suppressor activity was consistently greater in secretions from pregnant than from nonpregnant cows for each breed. For between breed comparisons, there were nonsignificant trends toward greater suppressor activity for nonpregnant Angus than for nonpregnant Brahman cows at 200, 400 and 800 micrograms/ml of protein. Suppressor activity was greater (P less than .10) for pregnant Angus than for pregnant Brahman cows at 400 micrograms/ml of protein and tended to be greater for pregnant Angus than for Brahman cows at 800 micrograms/ml of protein. These data indicate that uterine secretory protein collected on d 17 from Angus and Brahman cows exerted immunosuppressive activity in vitro. Further, suppressor activity in each breed was greater in pregnant than in nonpregnant cows and suppressor activity tended to be greater for Angus than for Brahman cows.

Animals↗
PubMed1983

Effect of epinephrine, norepinephrine and(or) GnRH on serum LH in prepuberal beef heifers.

Forty prepuberal Simmental X Brahman-Hereford heifers were utilized to determine the effects of epinephrine (E), norepinephrine (NE), gonadotropin releasing hormone (GnRH) or combinations of GnRH + E and GnRH + NE on serum luteinizing hormone (LH) concentrations. Animals were assigned randomly to one of five treatments with four replicates/treatment. Treatments consisted of I) 100 micrograms GnRH at time 0 (n = 8); II) 50 mg NE at time -15 and 0 (n = 8); III) 50 mg E at time -15 and 0 (n = 8); IV) 100 micrograms GnRH at time 0, plus 50 mg NE at time -15 and 0 (n = 8) and V) 100 micrograms GnRH at time 0, plus 50 mg E at time -15 and 0 (n = 8). All treatment compounds were administered im in 2 ml physiological saline and blood samples were collected via tail vessel puncture at -30, -15, 0, 15, 30, 45, 60, 90, 120, 180, 240, 300 and 360 min from GnRH injection. Treatment with NE or E alone had no effect (P greater than .10) on serum LH during the sampling period. The initial LH release to GnRH was altered (P less than .05) by concomitant treatment with NE (treatment IV) or E (treatment V). Magnitude of the LH release was reduced (P less than .01) by treatment V. Area under the LH surge was reduced (P less than .05) by treatment IV (NE) and V (E).

Animals↗
PubMed1982

Auto and heterotransplantation of the ovary to the uterus or parotid region in beef cows and prepuberal heifers.

Eighteen mature estrous cycling beef cows and 9 prepuberal heifers were stratified by breed, age and weight to determine the effect of ovary-transplantation to a proximal site (right uterine horn) (U) and distal site (parotid region) (P) upon ovarian activity. Active ovaries (AO), ovaries with the corpus luteum (CL), were autotransplanted to the myometrium of the U in 3 cows and to the muscles of the P in 2 cows and their inactive ovaries (IO), ovaries without a CL, remained. Active ovaries of 6 cows were removed and heterotransplanted to 6 prepuberal heifers and their 10 were heterotransplanted to the U or the parotid (3). Six heifers received either a mature AO in the U or in the parotid. Three heifers were ovariectomized and their ovaries were heterotransplanted to 6 cows, 3 per site. Cows and heifers were slaughtered randomly 2 months after surgery and their ovaries were collected for microscopic and histological analysis. The transplants were successfully accomplished in 94% of the cows and in 83% of the heifers. Both of the unsuccessful heterotransplantations were located in the uterus. More estrous activity was found (P<.025) in cows than in heifers with their own ovaries in situ . All prepuberal ovaries in situ showed follicular development when mature AO were transplanted to either the U or parotid. The same trend was found in prepuberal ovaries transplanted to mature cycling cows. Cows with an IO in situ and AO transplanted to either site had more estrous activity than did ovariectomized cows with an IO transplanted to either site. Pregnancy rates in mature cycling cows with an least one ovary in situ were higher (P<.005) in cows with an ovary in the parotid region than cows with an ovary transplanted to the uterus.

Journal Article↗
PubMed1982

Effect of several biogenic amines on in vitro progesterone secretion by the bovine corpus luteum.

1. The effect of several biogenic amines on secretion of progesterone (P4) was examined using bovine corpora lutea (n = 6), removed on day 13 of the oestrus cycle, enzymatically dispersed and cultured in vitro. 2. Luteal cell cultures were co-incubated with 0, 10, 50 or 100 ng of luteinizing hormone (LH) and 50 ng of epinephrine (EPI), norepinephrine (NOR), dopamine (DOPA), melatonin (MEL), N-acetyl-50H-serotonin (N-acetyl-50H-tryptamine; NacS), serotonin (50H-tryptamine; 5HT) or saline control. 3. EPI, NOR and DOPA decreased baseline release of P4. 4. The magnitude of the response of P4 to LH was depressed when cells were co-incubated with DOPA, EPI and 5HT and stimulated when cells were co-incubated with MEL and NacS. 5. These data indicate that the biogenic amines might modulate ovarian steroidogenesis supplementary to hypothalamic-hypophyseal hormonal mechanisms.

Animals↗
PubMed1982

Effect of monensin on the estrogen-induced LH surge in prepuberal heifers.

The effect of dietary monensin on the luteinizing hormone (LH) surge following estradiol-17 beta (E2) injection was investigated in prepuberal Simmental X Brahman-Hereford heifers. Ten heifers, weighing approximately 260 kg and approximately 10 mo of age, were equally divided by age and weight into two groups: control (C) heifers each received 1.8 kg/d of a concentrate diet plus Coastal bermudagrass hay ad libitum; monensin (M) heifers each received the same diet plus 200 mg monensin/d. All heifers were maintained in dry lots on their respective diets for 14 d before the E2 challenge. On d 15, all heifers were injected in with 5 mg of E2 in corn oil. Blood samples were collected via tail vessel puncture immediately before E2 injection and at 2-h intervals until 48 h after the E2 injection. The samples were processed for serum and stored at -20 degrees C until LH concentrations were measured by radioimmunoassay. Mean concentrations of LH in serum differed (P less than .005) between C and M heifers and with time after E2 injection. A treatment X sampling period interaction (P less than .10) indicated that maximum serum concentrations of LH (LH surge) were detected earlier (P less than .001) for M (17.2 +/- 1.8 h) than C (27.0 +/- 6.0 h) heifers after the E2 injection. When the data were arrayed relative to the time of the LH surge, treatment (P less than .05) and sampling period (P less than .001) effects were significant, but a treatment X sampling period interaction was not detected. Peak LH concentration was 23.1 +/- 3.0 ng/ml for M heifers and 21.6+/- 4.2 ng/ml for controls (P greater than .10). Duration of the LH surge was 8.0 +/- .9 h in M heifers and 4.8 +/- 1.6 h in C heifers (P less than .001). Area under the LH surge was greater (P less than .001) in M heifers than in control heifers. We conclude that dietary monensin altered the estrogen-induced LH surge in prepuberal heifers.

Animals↗
PubMed1982

Evidence for seasonal and nutritional modification of ovarian and pituitary function in crossbred heifers and Brahman cows.

Alterations in endocrine response in the bovine female after consumption of monensin or exposure to changes in season were observed in two experiments. Thirty-three monensin-fed (M) or control (C) crossbred heifers in Exp. 1A were given a porcine follicle stimulating hormone (FSH-P) challenge on d 16 to 21 postestrus. Nine M heifers ovariectomized (OVX) on d 11 after the FSH-challenged estrus had a greater number of smaller corpora lutea (CL; P less than .005) than did nine d 11 OVX C heifers. Serum progesterone (P4) concentrations were greater in M on d 5 through 13 following the FSH-challenged estrus (P less than .001). Seven M and seven C Brahman cows in Exp. 1B given an identical FSH challenge had similar increases in CL number and size. In Exp. 2, blood samples were obtained from 14 M and 13 C Brahman cows during winter (WI), early spring (ESp) and late spring (LSp) to characterize the preovulatory LH surge. During each seasonal period, blood samples were taken hourly from estrus through 24 h postestrus for each cow. Only one of five WI-C cows had a preovulatory LH surge compared to five of five WI-M cows (P less than .01). No differences were found in the number of cows having an LH surge in ESp or LSp groups. Analysis of combined WI and ESp group values indicated a difference in timing of the LH surge by M or C treatment. Of those cows that had an LH surge, only three of 10 C had peak LH values later than the first sample taken, compared with 10 of 15 M (P less than .10). A heightened LH response was detected in M cows in all comparisons of LH surge profiles (P less than .005). Concurrent with changes in season from WI to ESp was an increase in number of C cows having an LH surge (one of five vs nine of 10; P less than .005), and elevated LH values in ESp-C and M groups compared with WI-C and M groups (P less than .05). Midluteal blood samples taken after every estrus indicated P4 to be greatest in February M cows (P less than .10) and P4 tended to be greater in February and lower in January for all groups. Conclusions are that monensin affects the FSH-P-induced ovulation rate of bovine females of all ages. Seasonal effects occurring between the shortest and longest days of the year exert their greatest influence on the preovulatory LH surge and P4 concentrations in Brahman cows between January and March. Seasonal effects appear to be partially modulated by nutritional factors.

Animals↗
PubMed1981

Serum luteinizing hormone levels in Brangus cows following variable suckling intensity and administration of various levels of estrogen.

Fifty Brangus cows were randomly allotted to suckled (S) or nonsuckled (NS) treatment groups on day 20 postpartum. Suckled cows were nursed at 6 hr intervals for 72 hours. Nonsuckled cows were separated from their calves for the entire 72 hours. At 24 hr after initial separation from calves, S and NS cows were given an I.M. challenge of 0, 0.5, 1.0, 2.0 or 4.0 mg estradiol-17beta (E2) to induce a luteinizing hormone (LH) surge (five cows per treatment group). Blood samples were taken at the time of E2 injection and at 2 hr intervals until hr 48 post-injection. Blood serum was analyzed for LH content via radioimmunoassay. Suckled and NS cows manifesting an LH surge after receiving less than 4 mg E2 were 2 of 15 vs 9 of 15 (P<.01), or 4 mg E2 dose were 5 of 5 vs 5 of 5, respectively. Greater serum LH concentrations in NS than S cows were found with dose levels of 0, 0.5 and 1.0 mg E2 (P<.005), but there was no difference by period. Differences by treatment (P<.05) and by period (P<.005) were found at the 2 mg E2 dose. Suckled and NS cows having an LH surge at less than a 4 mg E2 challenge had no differences in LH concentration or timing parameters. Four mg E2 hastened the time of onset of the LH surge (P<.025), time till peak height of the surge (P<.025) and completion of the surge (P<.10). No differences in postpartum interval or conception rate were found between S and nonsuckled. Suckling impairs hypothalamic/pituitary response to low E2 challenge dose and elicits changes in timing parameters in response to high E2 dosage.

Journal Article↗
PubMed1981

Interrelationships of serum corticosteriods, LH, and testosterone in male bovine.

Temporal interrelationships of endogenous peripheral blood concentrations of corticosteriods (CS), luteinizing hormone (LH), and testosterone(T) were evaluate in bulls. Concentrations of CS, LH, and T were quantitated in blood samples collected at hourly intervals via jugular cannula from four bulls during a single 24-hr period in January and again in June. Alterations in hormone profile characteristics were noted within bulls between January and June. An increased number of LH peaks and increased area beneath entire 24-hr LH profile suggested that LH secretion was higher during the June sampling period than the January sampling period. However, no significant alteration in T secretion in June was observed. as number of T peaks and area under T peaks were essentially unchanged relative to January. An inconsistent relationship between secretion of LH and T was observed in June, with only 47% of LH peaks associated with elevations in concentration of T whereas in January 80% of LH peaks were associated with T peaks. A higher lag correlation over all bulls between concentration of LH at one hour and concentration of T at the subsequent hour for all such combinations throughout the 24-hr period (LAG-LHTCORR) in January (r = 0.45, p less than 0.001) than in June (r = 0.12, p less than 0.24) also indicated that the temporal relationship between LH and T changed between these two periods of time. Coincident with the area beneath entire 24-hr CS profile and the height of CS peaks were greater in June. Prolonged elevations in concentration of CS were observed to be coincident with basal concentrations of LH and T and a negative value was obtained for LAG-CSTCORR in June (r = -0.10) but not in January (r = 0.06). Results of this study indicate that the major effect of LH upon blood concentration if T in the bull is usually exerted within 1 hr of a LH surge. However, failure of some LH peaks to be followed by T peaks suggests that the secretion of LH and T in the bull may be subject to modulation by adrenocortical hormones and other intrinsic and extrinsic factors.

Adrenal Cortex Hormones↗
PubMed1980

Effect of bleeding stress and variable suckling intensity upon serum luteinizing hormone in Brangus heifers.

In the first experiment, the effect of the stress of blood collection (via tail vessel puncture) on serum luteinizing hormone (LH) was evaluated in six nonsuckled first calf Brangus heifers. The animals were bled on days 22 and 31 postpartum at 15 minute intervals for a period of two hours. Blood was processed to yield serum and analyzed for LH via radioimmunoassay (RIA). There were no significant differences or fluctuations in serum LH levels between bleeding periods or between cows. Serum LH concentrations in nonsuckled cows were not affected by the stress of blood collection. In the second experiment, 24 first calf Brangus heifers were randomly assigned to one of four treatment groups. Treatment 1 cows were suckled once daily for approximately 30 min starting day 21 postpartum. Treatment 2 cows were suckled twice daily for approximately 30 min each time, starting 21 days postpartum. Treatment 3 cows were suckled once daily for approximately 30 min starting 30 days postpartum. Treatment 4 cows were suckled twice daily for approximately 30 min each time starting 30 days postpartum. Each cow was bled via tail vessel puncture on days one and nine following the start of each treatment. The blood sampling regime was similar to that used in Experiment 1 and consisted of four presuckling samples taken at 15 min intervals, one midsuckling sample (the calf was allowed to suckle for 15 min) and four postsuckling samples taken at 15 min intervals. Blood was collected, processed to yield serum and assayed for LH via RIA. Suckling intensity (SI) was found to have a significant effect on serum LH levels. The once daily suckled cows had higher (P<.01) mean serum LH levels than did the twice daily suckled cows (1.70 +/- .03 and 1.53 +/- .03 ng/ml, respectively). The LH concentrations decreased (P<.01) from the first to last bleeding time (BT). The mean serum LH levels for the presuckling, midsuckling and the first postsuckling samples were higher (P<.05) than the last postsuckling sample. The mean serum LH level for the first time period prior to suckling was higher (P<.05) than the last postsuckling sample. The mean serum LH level for the first time period prior to suckling was higher (P<.05) than the last two periods after suckling (1.73 +/- .08 ng/ml vs 1.51 +/- .06 and 1.41 +/- .06 ng/ml). Bleeding day (BD) and weaning day (WD) did not alter serum LH levels. The interactions found to be significant (P<.01) were SIxBD, SIxWD, BDxWD and BTxSIxBDxWD.

Journal Article↗
PubMed1980

Effect of variable suckling intensity and estrogen administration upon serum luteinizing hormone in Brahman cows.

Ten mature Brahman cows were randomly allotted within calving intervals to either a suckled (S) or nonsuckled (NS) treatment group. All cows received a 20 mg intramuscular injection of estradiol-17beta (E2), suspended in 2 ml of corn oil, to determine the effect of suckling on the estrogen induced LH surge. Starting on day 21 postpartum the S cows were suckled at six hour intervals for 24 hours, at which time they were challenged with a 20 mg E2 injection. The suckling regimen was continued for 48 hours postinjection. The NS cows were separated from their calves on day 21 postpartum and received no suckling stimulus for 72 hours. At 24 hours after calf separation, the NS cows were challenged with a 20 mg E2 injection. Blood samples were removed at two hour intervals beginning 10 hours post E2 injection until 36 hours postinjection, at which time blood samples were removed at four hour intervals until 48 hours postinjection. Blood samples were processed to yield serum and assayed for luteinizing hormone (LH) via radioimmunoassay. The injection of a 20 mg dose of E2 induced an LH surge in all cows. The NS cows were found to exhibit a longer (P<.05) duration of the estrogen induced LH surge than the S cows, 15.6 +/- .98 and 12.4 +/- .75 hours, respectively. The timing parameters (time to start of LH surge, time to peak LH value and time to end of surge) and LH concentration parameters (LH concentration at start of LH surge, peak value of LH surge and LH concentration at end of LH surge) were not different between suckling regimens. No blockage of the LH response to estrogen challenge was found on day 22 postpartum. Suckling did depress the duration of the LH surge indicating some blockage due to suckling stimuli.

Journal Article↗
PubMed1980

Effect of monensin on gain and forage utilization by calves grazing bermudagrass.

Two trials were conducted to determine the influence of monensin on live weight gain and efficiency of forage utilization of calves grazing Bermudagrass. In trial 1, 32 calves, weaned at an average age of 238 days and 250 kg, were grazed on "Coastcross I" Bermudagrass from July 20 to October 13. Eight steers and eight heifers were randomly assigned to one of two treatments: 200 mg monensin/head/day or 0 mg monensin/head/day fed in a .01 kg/head/day diet of pelletized 14% protein feed. Both groups were stocked at 15.3 head/ha. Monensin-fed calves gained .52 kg/head/day, while the control-fed calves gained .42 kg/head/day (P < .10). Average daily gains (ADG) of steers (.54 kg) were greater (P < .05) than those of heifers (.40 kg). Forage to gain ratio estimates were 15:1 and 19:1 for calves on monensin and control paddocks, respectively. In trial 2, 48 steer calves, averaging 265 days of age and 260 kg, were randomly assigned to each of two replicates of the following grazing treatments: common Bermudagrass only (P), Bermudagrass + .91 kg/head/day 14% protein feed (PF) or Bermudagrass + .91 kg/head/day feed + 200 mg monensin/head/day (PFM). ADG were .45, .47 and .68 kg for steers fed P, PF and PFM, respectively. The monensin-fed calves showed a 45% improvement in ADG (P < .05). Estimated forage to gain ratios for calves fed P, PF and PFM were 20:5:1, 19:1 and 13:1, respectively. The use of 200 mg monensin/head/day improved calf gains by 23 to 45% and increased estimated feed efficiencies by 21 to 36% on Bermudagrass pastures. The improvement in gain for heifers fed monensin was 28.6%, while steers gained 18.4% more when fed monensin.

Animal Feed↗
PubMed1980

Effect of dietary monensin on ovarian response following gonadotropin treatment in prepuberal heifers.

Twenty prepuberal Charolais X Brahman-Hereford heifers were randomly assigned to be fed a concentrate containing either 0 mg (C) or 200 mg (M) monensin sodium/head/day. Coastal bermudagrass hay was fed ad libitum. Average daily gain was similar for the two groups. Each heifer received 1 mg of porcine follicle stimulating hormone (FSH-P) (Armour) at 0800 and 2000 hr on days 22 through 26 (10 mg total) and 2,500 IU human chorionic gonadotropin (HCG) on day 27. Flank laparotomy was performed on day 30, for examination of ovaries, and ovariectomy was performed on day 37. The average ovarian size +/- standard error at day 15 ws 3,730 +/- 66 mm3 and 1,848 +/- 55 mm3 for groups M and C, respectively (P < .025), as measured by rectal palpation. Numbers of ovulation sites measured on day 30 were 9.1 +/- 2.2 and 4.9 +/- 1.8 per heifer for groups M and C, respectively (P < .01). After ovariectomy on day 37, heifers fed M were found to have greater ovarian weight (P < .05), more corpora lutea (CL) (P < .05), greater total luteal weight (P < .05), more follicles (P < .01) and greater weight of follicular fluid (P < .05) and stroma (P < .025) than controls. CL were analyzed for progesterone content by spectrophotometric procedures. Heifers fed M had slightly larger CL (P < .10) with progesterone concentrations similar to those in CL from controls. This resulted in more luteal progesterone per CL and more luteal progesterone per heifer in the M heifers than in the controls. Prepuberal heifers fed M, which caused the expected shifts in rumen fermentation and volatile fatty acid production, exhibited an enhanced ovarian response to gonadotropins compared to that exhibited by controls.

Animals↗