Effect of sire and sexual experience on serving capacity of yearling beef bulls.

Two experiments were conducted in successive years on a Kansas ranch to determine 1) if serving capacity could be evaluated in virgin yearling beef bulls under field conditions, 2) the influence of sire on serving capacity, and 3) the effect of sexual experience on subsequent serving capacity for low serving capacity bulls. In Experiments 1 and 2, 70 and 78 Angus bulls 13 to 15 mo old representing four and six different sires, respectively, were used. In both experiments, a pretest session that measured reaction time to service preceded two successive serving capacity tests. Following the first serving capacity test, in Experiment 2, all low serving capacity bulls (n = 23) underwent sexual experience school, which consisted of exposure to nonrestrained estrus-induced females over a 4-d period. Five days after sexual experience school (9 d after the first serving capacity test), all Experiment 2 bulls were retested. In both experiments, sire influenced mean serving capacity scores of sons (P < 0.01, Experiment 1; P < 0.05, Experiment 2). Characteristics measured, including age, weight, scrotal circumference, and reaction time, were all unrelated to bulls serving capacity in both experiments, as well as to breeding soudness examination scores for bulls in Experiment 1. There was a dramatic impact of sexual experience school on subsequent serving capacity, since 85% of sexual experience school bulls moved into the medium or high serving capacity category at the second serving capacity test. It is concluded that serving capacity can successfully be evaluated in yearling beef bulls under field conditions, that sire has a profound impact on bulls serving capacity, and that providing sexual experience to low serving capacity bulls can improve their serving capacity.

Evaluation of a melengestrol acetate and prostaglandin F(2)alpha system for the synchronization of estrus in beef heifers.

This study was conducted to determine the efficacy of feeding melengestrol acetate (MGA) for 14 days and administering prostaglandin F(2)alpha (PGF) 17 days after MGA to synchronize or induce estrus in yearling beef heifers. The study involved 56 Angus (n = 19), Hereford (n = 15) and Simmental (n = 22) heifers that were assigned by breed and pubertal status to either MGA+PGF or to control groups. Heifers in the synchronized group were fed 0.5 mg MGA per head per day for 14 days from a grain carrier and were injected with 25 mg, i.m. PGF 17 days after the last daily feeding of MGA. Control heifers were fed from a grain carrier without MGA and were not treated with PGF. Heifers were classified as pubertal when concentrations of progesterono in the serum exceeded 1 ng/ml in 1 of 2 samples collected prior to the initiation of treatments. Blood samples were collected 7 days before and on the day that treatment with MGA or carrier began and 7 days before and on the day that PGF was administered. Progesterone concentrations in the serum were elevated ( > 1 ng/ml) in 61% (17 28 ) of the MGA+PGF-treated heifers and in 61% (17 28 ) of the control heifers prior to feeding MGA. However, concentrations of progesterone in the serum at the time PGF was administered differed (P<0.05) between MGA+PGF and control groups. Concentrations of progesterone in the serum exceeded 1 ng/ml in 100% (28 28 ) of the MGA+PGF-treated heifers and in 71% (20 28 ) of control heifers at the time PGF was administered (P<0.05). All heifers were inseminated 12 hours after the first detected estrus. Twenty-two of 28 (79%) of the MGA+PGF-treated heifers exhibited estrus within 6 days after PGF compared with 9 of 28 (32%) of control heifers (P<0.05). The conception rate at first service did not differ between MGA+PGF and control groups (64% and 67%, respectively). Synchronized pregnancy rates were higher (P<0.05) for MGA+PGF-treated heifers than for control heifers (14 28 , 50% vs 6 28 , 21%). Increased concentrations of progesterone in serum at the time PGF was administered and higher pregnancy rates during the synchronized period among MGA+PGF-treated heifers demonstrate the efficacy of this treatment for use in estrus synchronization. Moreover, this treatment may have a potential effect on inducing puberty in breeding age heifers.

Reproductive responses of beef heifers after concurrent administration of vaccines, anthelmintic and progestogen.

A study was conducted to determine whether concurrent administration of vaccines for reproductive diseases and an anthelmintic, given immediately prior to estrus synchronization with a progestogen, would affect subsequent estrous response and fertility in beef heifers. Two hundred ninety-five yearling crossbred beef heifers on 3 ranches in Oregon and Kansas were assigned to 1 of 2 treatments. Control heifers were vaccinated and dewormed 30 d prior to the anticipated breeding. Treated heifers received the same vaccination and deworming products 9 d prior to breeding. All heifers in both groups were treated with norgestomet (Syncro-Mate-B) for 9 d to synchronize estrus. The administered vaccine consisted of modified live virus for infectious bovine rhinotracheitis, parainfluenza and bovine viral diarrhea, with 5-way bacterin for leptospirosis and bacterin for vibriosis. Heifers were also administered ivermectin or fenbendazole for deworming. Heifers exhibiting synchronized estrus were artificially inseminated and subsequently exposed to fertile bulls. Pregnancy status was determined at a later date by palpation per rectum. Vaccination and deworming at the time of treatment with progestogen compared with immunizing and deworming 30 d prior to breeding did not impair the expression of behavioral estrus. The percentage of treated heifers conceiving to AI or natural service did not differ from that of the respective control heifers. These data suggest that vaccination, deworming and synchronization of estrus with norgestomet can be performed simultaneously without any detrimental effects upon occurrence of behavioral estrus or fertility.

Synchronization of estrus in yearling beef heifers with the melengestrol acetate/prostaglandin F(2alpha) system: efficiency of timed insemination 72 hours after prostaglandin treatment.

Two experiments were conducted to determine the conception rates of heifers time-inseminated following melengestrol acetate/prostaglandin F(2alpha) (MGA/PG) estrous synchronization treatment. In Experiment 1, timed insemination of heifers at 72 h after the PG injection, without regard for behavioral estrus, tended to improve (P < 0.15) the percentage of heifers pregnant to artificial insemination (AI) compared with that of synchronized heifers bred 12 h after they were first detected in estrus. In the timed-insemination treatment, heifers exhibiting behavioral estrus 48 to 72 h after PG tended to have an increased (P < 0.15) conception rate to AI compared with heifers exhibiting estrus within 48 h of PG administration. In Experiment 2, the number of heifers conceiving to AI following the MGA/PG estrous synchronization regimen was increased by mass insemination of all heifers not exhibiting estrus by 72 h after PG. The pregnancy rate to AI was higher in heifers with serum progesterone (P(4)) concentrations higher than 1 ng/ml compared with that of heifers with concentrations lower than 1 ng/ml. Of heifers with serum P(4) greater than 1 ng/ml, the pregnancy rate to AI tended to be higher when concentrations exceeded 2 ng/ml than when concentrations were 1 to 2 ng/ml. In cyclic heifers, timed insemination can increase the percentage of heifers pregnant after being synchronized with MGA/PG.

Response of prepubertal Bos taurus and Bos indicus x Bos taurus heifers to melengestrol acetate with or without gonadotropin-releasing hormone.

The effectiveness of treatments to induce estrus in prepubertal beef heifers was evaluated. Angus x Hereford (n = 148) and Brahman x Hereford (n = 148) heifers were sorted after weaning by body weight into light and heavy weight blocks. Heifers were assigned to diets, calculated to reach a target weight of 55% or 65% of their projected mature weight by the start of breeding. Cyclicity was determined after a 160-d observation period and from concentrations of progesterone in serum determined 10 d before and on the day that treatments began to induce puberty. The remaining nonpubertal heifers, with concentrations of progesterone in serum of less than 1 ng/ml (0 or 10 d before treatment), were assigned randomly within breed and nutrition group to either a melengestrol acetate + saline (MGA+S) or MGA + gonadotropin-releasing hormone (MGA+GnRH) treatment. Prepubertal Angus x Hereford heifers (n = 11) and Brahman x Hereford heifers (n = 49) were fed 0.5 mg MGA for 7 d. Forty-eight hours after MGA, heifers were injected with 500 ug s.c. GnRH or 5 ml of saline. Blood samples were collected from all prepubertal heifers every 3 d after GnRH or saline for 30 d. There was no difference between treatments in the proportion of heifers that exhibited estrus by Day 7 after treatment. However, a larger (P<0.05) proportion of MGA+S-treated heifers exhibited estrus within 14 d after treatment than MGA+GnRH-treated heifers (87 vs 63%). Among heifers that exhibited estrus during that time period, the proportion with increased progesterone was higher (P<0.10) for the MGA+GnRH group than for the MGA+S group (71 vs 41%, Day 7; 79 vs 54%, Day 14). There was no difference in conception rate at first service between treatment groups. Thirty-seven and 53%, respectively, of the MGA+S and MGA+GnRH-treated heifers had short estrous cycles after treatment, and 44 and 50%, respectively, of those short cycles were repeated. Pregnancy rates at the end of 45 d were numerically higher for MGA+S heifers than for MGA+GnRH treated counterparts (63 vs 53%).

Prolonging the MGA-prostaglandin F2 alpha interval from 17 to 19 days in an estrus synchronization system for heifers.

Our objective was to determine whether extending the interval from 17 to 19 d between removal of melengestrol acetate (MGA) feed and administration of PGF2 alpha would alter conception rates, pregnancy rates and the degree of synchrony in replacement beef heifers. A commercial heifer operation in north-central Kansas purchased 591 Angus x Hereford heifers from 12 sources. Prior to the spring breeding season, 14% of the heifers were culled. The remaining heifers were assigned randomly to 2 MGA-PGF2 alpha synchronization systems. All heifers were fed MGA (0.5 mg/head/d) for 14 d, and PGF2 alpha was administered either 17 or 19 d after the completion of MGA feeding. Heifers were inseminated artificially for 30 d followed by 30 d of natural mating. Based on each source, first-service conception rates ranged from 66 to 90%, whereas overall pregnancy rates ranged from 91 to 100%. Heifers given PGF2 alpha on Day 17 after MGA had first-service conception rates of 75.9% compared with 81.4% for heifers receiving PGF2 alpha on Day 19. In response to the PGF2 alpha injection, 99% of the Day 19 heifers that were detected in estrus were inseminated artificially by 72 h after the PGF2 alpha injection, whereas 74% of the heifers in the Day 17 treatment were inseminated by that time. Average interval to artificial insemination (AI) after PGF2 alpha was greater (P < 0.01) for the Day 17 heifers (73.1 +/- 1.1 h) than for the Day 19 heifers (56.2 +/- 1.1 h). No differences in conception rates or overall pregnancy rates occurred; however, heifers receiving PGF2 alpha on Day 19 after MGA had shorter intervals to estrus, and a greater proportion was inseminated within 72 h after PGF2 alpha, thus possibly facilitating successful timed insemination of the remaining heifers not yet inseminated by that time.

Prostaglandin F(2alpha) and naloxone therapy in the anestrous postpartum beef cow.

Three experiments were conducted, using multiparous crossbred beef cows, to test the ability of exogenous prostaglandin F(2alpha) (PGF) and/or naloxone to reduce the duration of the postpartum interval to estrus and to improve subsequent reproductive performance. In each experiment, postpartum cows were assigned to treatments by calving date. In Experiment 1, cows (n=44) were assigned to 1 of 4 treatment groups: 1) control, 2) PGF on Day 25 post partum, 3) 400 mg naloxone (3 doses) at 12-h intervals on Day 30 post partum, and 4) PGF on Day 25 followed by 3 400-mg doses naloxone at 12-h intervals on Day 30 post partum. In Experiment 2, cows (n=126) were assigned either to 1) control or 2) PGF on Day 30 post partum In Experiment 3, cows (n=67) were again assigned to 1 of 4 treatments 1) control, 2) PGF on Day 30 post partum, 3) PGF on Day 40 post partum, and 4) PGF on Day 30 and 40 post partum. Serum progesterone was used to determine the postpartum interval to estrus in Experiments 1 and 3. In all 3 experiments, serum progesterone was used to determine the proportion of cows that had reestablished estrous cycles at the start of breeding. Pregnancy rate and calving interval were analyzed for all trials. Naloxone had no effect (P > 0.20) on any reproductive variable measured. The postpartum interval to estrus was similar (P > 0.30) for PGF-treated and control cows in Experiments 1 and 3. The proportion of cows cycling at the start of breeding and the calving interval were not affected (P > 0.20) by PGF treatment in any of the experiments. Only the administration of PGF on Day 40 post partum in Experiment 3 improved (P=0.04) the subsequent pregnancy rate. Analysis of data pooled across experiments showed that the pregnancy rate was higher (P=0.03) for cows treated with PGF than for control cows (91.4 and 72.9%, respectively). It was concluded that administration of PGF during the early postpartum period improves subsequent reproductive function in beef cows.

Effect of treatment with ivermectin on reproductive performance of yearling beef heifers.

To determine the effect of treatment with ivermectin on reproductive parameters, 78 fall-born, yearling heifers were allotted to either an ivermectin treatment group or to the control, non-treatment group. The heifers were treated in June and October when they were approximately 7 and 11 mo old, respectively. Ivermectin effectively lowered fecal egg counts in the treated heifers compared with that of the controls. In heifers that were maintained on a marginal plane of nutrition, treatment with ivermectin not only improved weight gains during each recording period but also hastened the onset of puberty and improved the pregnancy rate during a 60-d breeding season. The positive effect of ivermectin on these reproductive characteristics could not be explained by increased weight gain alone, because the correlation between weight gain and puberty was not significant. Treatment with ivermectin positively affected pelvic area but not uterine score when compared with those of the controls.

Evaluating recipient and embryo factors that affect pregnancy rates of embryo transfer in beef cattle.

The objectives of this experiment were to determine the effects of corpus luteum characteristics, progesterone concentration, donor-recipient synchrony, embryo quality, type, and developmental stage on pregnancy rates after embryo transfer. We synchronized 763 potential recipients for estrus using one of two synchronization protocols: two doses of PGF2alpha (25 mg i.m.) given 11 d apart (Location 1); and, a single norgestomet implant for 7 d with one dose of PGF2alpha (25 mg i.m.) 24 h before implant removal (Location 2). At embryo transfer, ovaries were examined by rectal palpation and ultrasonography. Of the 526 recipients presented for embryo transfer, 122 received a fresh embryo and 326 received a frozen embryo. Pregnancy rates were greater (P < 0.05) with fresh embryos (83%) than frozen-thawed embryos (69%). Pregnancy rates were not affected by embryo grade, embryo stage, donor-recipient synchrony, or the palpated integrity of the CL. Corpus luteum diameter and luteal tissue volume increased as days post-estrus for the recipients increased. However, pregnancy rates did not differ among recipients receiving embryos 6.5 to 8.5 days after estrus (P > 0.1). There was a significant, positive simple correlation between CL diameter or luteal tissue volume and plasma progesterone concentration (r = 0.15, P < 0.01 and r = 0.18, P < 0.01, respectively). There were no significant differences in mean CL diameter, luteal volume or plasma progesterone concentration among recipients that did or did not become pregnant after embryo transfer. We conclude that suitability of a potential embryo transfer recipient is determined by observed estrus and a palpable corpus luteum, regardless of size or quality.

Effect of energy intake after weaning on the sexual development of beef bulls. I. Semen characteristics and serving capacity.

Simmental and Hereford bulls were individually fed varying levels of the same diet to determine the effects of energy intake after weaning, degree of fatness, and short-term weight change on reproductive characteristics of yearling beef bulls. For 200 d (ending in May), 29 Simmentals were fed an average of 14.6, 19.2 or 23.8 Mcal and 27 Herefords were fed 13.4, 17.5 or 22.2 Mcal metabolizable energy per bull daily. Bulls then were adjusted to a roughage diet for 10 d before grazing brome pasture for 38 d (ending in June). Energy level did not affect motility or sperm morphology of semen collected with an artificial vagina in May and June. High energy levels were not detrimental to bull performance during a 30-min serving-capacity test in May or June. Backfat thickness was not related to semen characteristics or serving capacity. Amount of weight lost from May to June did not affect the semen quality or serving capacity of Herefords. Those Simmental bulls that had a more positive weight change from May to June had a more favorable change in semen quality from May to June (P less than .05) due to lower semen quality in May (P less than .05). The high level of energy was not detrimental to semen characteristics or serving capacity. Some of the Simmental bulls may have been underfed for maximum semen quality at the beginning of the pasture period. Within the normal range of energy fed to beef bulls from weaning to the beginning of the breeding season as yearlings, it may be more likely to underfeed breeds of large mature size than to overfeed British breeds.

The effect of molybdenum-induced copper deficiency on acute-phase protein concentrations, superoxide dismutase activity, leukocyte numbers, and lymphocyte proliferation in beef heifers inoculated with bovine herpesvirus-1.

This study was conducted to determine the effect of Cu deficiency on acute-phase protein concentrations, superoxide dismutase activity, leukocyte numbers, and lymphocyte proliferation in heifers inoculated with live bovine herpesvirus-1 (BHV-1). Hereford x Angus heifers were allotted by weight and initial liver Cu concentrations into molybdenum (Mo)-supplemented (n = 6) or control (n = 6) groups. Control heifers were fed a basal diet supplemented with Cu-sulfate to achieve a dietary concentration of 8 ppm of Cu. The Mo-supplemented heifers received the basal diet supplemented with Mo to achieve a dietary Mo:Cu ratio of 2.5:1 and with sulfur at .3% of the diet. All treatments were delivered for 129 d, when heifers were inoculated intranasally with BHV-1. To ensure adequate Cu stores before viral challenge, control heifers were given a cupric glycinate injection on d 100 of treatment. On d 129, Mo-supplemented heifers were considered Cu-deficient (liver Cu = 23.2 and 90.1 ppm for Mo-supplemented and control, respectively). Neutrophils were increased (P < .01) on d 129 in Mo-supplemented heifers. Ceruloplasmin, a copper-dependent acute-phase protein, increased (P < .01) by 48 h after challenge in control but not in Mo-supplemented heifers. Fibrinogen, an acute-phase protein not containing copper, increased by 48 h after challenge in Mo-supplemented but not in control heifers. Erythrocyte superoxide dismutase (SOD) activity was less (P < .05) in Mo-supplemented heifers on d 129. Viral challenge had no effect on SOD activity. Lymphocyte proliferative response to phytohemagglutinin stimulation was greater (P < .01) for Mo-supplemented heifers following BHV-1 challenge. No differences were detected when lymphocytes were stimulated with concanavalin-A or pokeweed mitogens. These data indicate that Cu deficiency alters the acute-phase protein response to viral infection and may affect lymphocyte responsiveness to mitogen stimulation.

Endocrine responses and ovarian changes in inseminated dairy heifers after an injection of a GnRH agonist 11 to 13 days after estrus.

Our objective in this study was to determine endocrine responses and changes in ovarian structures after a single injection of a GnRH agonist in Holstein dairy heifers (n = 38). Heifers were inseminated and received (i.m.) either saline or 200 micrograms of fertirelin acetate once on d 11, 12, or 13 after estrus (d 0). Blood was collected at 15- to 30-min intervals for 6 h after the injection to determine concentrations of LH, FSH, estradiol (E), and progesterone (P) in serum and once daily for 8 to 12 d after the injection to determine concentrations of E and P. Pregnancy rates were 58% (11 of 19) in both treatment groups. Diameter of the corpus luteum and numbers and appearance of ovarian follicles were determined by real-time ultrasonography on d-1 through 5 after injection. No treatment-induced ovulations or changes in the number of ovarian follicles were observed after the injection of the GnRH agonist. More (P less than .05) of the largest follicles within heifers receiving fertirelin acetate showed changes in their appearance on at least the 1st d after injection (6 of 10 vs 1 of 9 control heifers). Fertirelin acetate induced release of LH and FSH from the pituitary within 15 min of injection; both hormones reached peak concentrations at 120 min and then returned to pretreatment concentrations by 300 to 360 min after injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnancy rates in beef cattle after administering a GnRH agonist 11 to 14 days after insemination.

The objective of our study was to determine the dose-pregnancy rate response of a GnRH agonist injected once during the luteal phase in virgin heifers (four locations) and suckled beef cows (two locations) during the spring of 1989. The same treatments in virgin heifers were used at one location in the fall of 1989. Heifers and cows were inseminated at a synchronized estrus and then assigned randomly to each of three doses (0, 100, or 200 micrograms) of fertirelin acetate administered in 4 ml of saline in a double-blind study after being blocked by inseminator and service sire. Injections were given (i.m.) once on d 11, 12, 13, or 14 after estrus. Pregnancy rates were determined by palpation of the uterus per rectum and(or) by actual calving dates. Overall pregnancy rates for heifers across five locations were 86/201 (43%), 100/197 (51%), and 100/203 (49%) for the 0, 100, and 200 micrograms doses of fertirelin acetate, respectively. Pregnancy rates for heifers at two locations based on calving data were 28/48 (50%), 31/47 (66%), and 34/52 (65%) for the three doses. Both the 100- and 200-micrograms doses increased (P less than .05) pregnancy rates in heifers based on palpation results, whereas only the 200-micrograms dose tended to increase (P = .10) pregnancy rates based on calving results. Pregnancy rates based on palpation for suckled beef cows at two locations were 36/51 (71%), 30/43 (70%), and 34/51 (67%), and the corresponding pregnancy rates based on calving results were 30/41 (73%), 32/36 (89%), and 31/38 (82%) for the 0, 100, and 200 micrograms doses, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of copper depletion and repletion on lymphocyte blastogenesis and neutrophil bactericidal function in beef heifers.

Thirty-two beef heifers were used to examine the effect of dietary copper depletion and repletion on neutrophil and lymphocyte functions. Heifers allotted to the control group (C+; n = 8) were fed a basal roughage/concentrate diet with Cu-sulfate supplementation (Cu > or = 8 ppm). To induce a Cu deficiency (depletion phase d 0 to 60), treated (T; n = 24) heifers received a diet supplemented with sulfur (.3% of diet) and sodium molybdate to achieve a Cu:Mo ratio of 1:1.5. Liver biopsies were collected on d 0, 27, and 60. Despite random allocation, T heifers had lower initial liver Cu concentrations (P < .01) than C+ heifers. At the start of the repletion phase (d 0, equal to d 60 of depletion), treated heifers were allotted by liver Cu concentration to three treatments (n = 8/treatment): Cu sulfate (S; Cu = 10 ppm), Cu proteinate (P; Cu = 10 ppm), or a negative control (C-) that remained on Mo and S supplementation. During the repletion phase, livers were biopsied on d 0, 14, and 45. By d 45, both S and P heifers had greater (P < .05) liver Cu concentrations than C- heifers. For both depletion and repletion phases, no treatment differences were detected in liver Mo or S concentrations. Jugular blood was collected on d 0, 27, and 55 of the depletion phase and d 0, 13, and 42 of the repletion phase. Neutrophils were isolated and incubated with Staphylococcus aureus to determine neutrophil bactericidal capacity (NBC).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of molybdenum-induced copper deficiency on in vivo and in vitro measures of neutrophil chemotaxis both before and following an inflammatory stressor.

Twelve Angus x Hereford heifers (avg wt = 183.6 kg) were allotted by initial liver copper (Cu) concentrations into one of two treatments. Control (n = 6) heifers were fed a basal diet supplemented to provide a dietary Cu level of 10 ppm. Molybdenum (Mo)-induced Cu-deficient heifers (n = 6) were fed an identical basal diet supplemented with sodium molybdate (Cu:Mo ratio = 1:2.5), with dietary sulfur at .3% of the total diet. Dietary treatments were delivered for 120 d, at which time Mo-supplemented heifers were considered Cu-deficient (286 and 49 ppm liver Cu for control and Mo-induced Cu-deficient, respectively). Peripheral blood neutrophils were enumerated both before and after the administration of an inflammatory stressor, a subcutaneous injection (1.5 mL) of Freund's complete adjuvant. In vitro and in vivo measures of neutrophil chemotaxis were evaluated and the expression of two adhesion molecules, CD18 and L-selectin, were analyzed by flow cytometric procedures. Molybdenum-induced Cu deficiency increased (P < .01) the number of peripheral blood neutrophils; however, in vitro neutrophil chemotaxis was not affected. In vivo neutrophil chemotaxis tended (P < .08) to be increased in Mo-induced Cu-deficient heifers (1.55 vs 2.26 x 10(6) cells/ sponge for control and Mo-supplemented, respectively). No differences in CD18 or L-selectin expression were detected between treatments. However, CD18 expression was decreased (P < .05) in both treatments following adjuvant injection. These data suggest that Mo-induced Cu deficiency results in an increase in peripheral blood neutrophil number, without altering chemotactic ability and adhesion molecule expression.

Effects of natural mating stimuli on serum luteinizing hormone, testosterone and estradiol-17 beta in yearling beef bulls.

The objective of this study was to determine the effect of natural mating stimuli on serum concentrations of LH, testosterone (T) and estradiol-17 beta (E2) in beef bulls. Twenty sexually experienced, yearling beef bulls were bled every 15 min during a 9-h period, 4 h before and 5 h after exposure to estrual females. For exposure, each bull was placed individually in an isolated pen with two restrained estrual heifers for 10 min or until one service was achieved. Timing and number of all behavioral events, including flehmen responses, abortive mounts and services, were recorded for each bull by two independent observers. Of the 20 bulls, 9 bulls mounted and were removed immediately after achieving a service, 8 bulls mounted without achieving a service and 3 bulls exhibited no interest during exposure. Twelve bulls achieved fewer than three and eight bulls achieved three or more flehmen responses during exposure. Postexposure responses in LH, T and E2 were not consistently correlated with number of mounts or presence or absence of a service. However, postexposure LH and T, but not E2, responses were highly correlated with number of flehmen responses achieved (r = .40 to .66; P = .08 to .001). In bulls that achieved three or more flehmen responses, serum LH increased within 30 min after exposure (P = .02) and serum T was increased dramatically within 1 h after exposure (P less than .01), compared with preexposure hormone concentrations, regardless of the number of mounts and regardless of the presence or absence of a service. Natural mating stimuli had no effect on serum E2, and mounting activity alone and mounting that culminated in a service did not necessarily result in increased LH or T in beef bulls. However, number of flehmen responses achieved during exposure to females dramatically influenced postexposure serum LH and T concentrations in beef bulls.

Serving capacity of crossbred yearling beef bulls. I. Single-sire mating behavior and fertility during average and heavy mating loads at pasture.

Eighty crossbred, virgin, yearling beef bulls were subjected to three serving capacity (SC) tests. Ten low SC (LSC) and 10 high SC (HSC) bulls similar in weight (avg wt = 452 kg), testicular size and seminal traits but differing in average services were selected. Objectives were to evaluate the mating behavior and fertility of LSC and HSC bulls at pasture when exposed to an average and a heavy mating load and to determine the effect of sexual activity on body weight and testicular characteristics. One LSC and one HSC bull per block were exposed single-sire to 25 naturally cyclic (N) cows for 3 d and to 9 estrus-synchronized (S) cows for 1 d in a randomized complete block design consisting of 10, 4-d blocks. Bulls were fitted with pedometers to record distance travelled. Behavioral data were collected by periodic visual observation. During the N cow treatment, LSC bulls had fewer (P less than .05) services per cow, total services and a higher mount to service ratio than HSC bulls. During the S cow treatment, LSC bulls showed increased sexual activity, though they achieved fewer (P less than .09) services per cow. Pregnancy rates for LSC and HSC bulls did not differ (P greater than .20) and across SC groups averaged 53.6% for N cows and 31.9% for S cows. Distance travelled also was similar (P greater than .20) between SC groups for both treatments. Sexual activity during pasture exposure had no effect (P greater than .20) on testicular characteristics but resulted in an average decline in body weight of 25.7 kg across SC groups during the 4-d period. Post-exposure SC tests found that LSC bulls had increased (P less than .05) services, decreased mounts and mount to service ratio compared to pre-exposure measurements, but LSC were still lower (P = .06) than HSC bulls for average services. These results suggest that LSC virgin, yearling bulls should be offered sexual experience and retested before their inherent SC can be determined.

Effects of energy and lasalocid on productivity of first-calf heifers.

One hundred forty-three crossbred, fall-calving first-calf heifers were used to determine the effects of two levels of energy and two levels of lasalocid on cow-calf productivity. Diets fed for approximately 110 d prepartum were calculated to provide a daily intake of 15.3 (LE) or 18.0 (HE) Mcal ME; diets fed for approximately 130 d postpartum were calculated to provide a daily intake of 17.8 (LE) or 21.0 (HE) Mcal ME. Two supplements were fed with each energy level to provide a calculated 0 (C) or 200 mg.hd-1.d-1 lasalocid (L). Heifers fed HE gained .06 kg more (P = .08) per day prepartum than LE heifers. There was an interaction (P less than .05) between treatment and prepartum days on trial for heifer weight approximately 2 wk prepartum and body condition at calving. Energy had no effect on heifer weight at 2 wk prepartum or condition score at calving when estimated and compared at 90 d on trial. However, regression estimates for 130 d on trial showed that HE heifers would have been 19 kg heavier (P less than .001) and would have had .4 unit higher condition score (P less than .01) than LE heifers. Energy and lasalocid had no effect (P greater than .05) on hip height or pelvic area at calving or on calf birth weight, calving ease score or gestation length. Cows fed HE weighed 17 kg more (P less than .05) and had .5 unit higher (P less than .001) condition score than LE cows at approximately 130 d postpartum. Lasalocid had little effect on postpartum changes in weight or body condition. Lasalocid supplementation to the LE diet tended to increase milk production and calf weight, whereas supplementation to the HE diet did not. Feeding the LE diet decreased (P less than .05) cycling activity by 18 percentage points and decreased (P less than .01) overall pregnancy rate by 25 percentage points. Lasalocid had no influence on reproductive performance.

The use of ultrasound in monitoring reproductive physiology of beef cattle.

Real-time, B-mode ultrasonography provides the opportunity to improve the methods of evaluation of ovarian function and diagnoses of pregnancy in beef cattle. Determination of the sex of a fetus early in pregnancy (d 55 to 85) and verification of embryo viability by monitoring fetal heartbeat are unique methods involving ultrasound scanning. These techniques and a method for evaluating the technique of artificial insemination can be used to improve reproductive management of cattle. The way in which ultrasound technology may have its greatest impact is as a tool for improving on the method of palpation per rectum for monitoring ovarian function and pregnancy in beef cows and heifers. Determination of fetal sex and monitoring embryo mortality are less likely to be applied regularly in herd management, but these procedures will be valuable in conducting research in reproductive physiology of beef cattle.

Periparturient changes in intake, ruminal capacity, and digestive characteristics in beef cows consuming alfalfa hay.

Four multiparous, ruminally fistulated Angus x Hereford cows (average BW = 568 kg) were bred to the same bull and used to monitor periparturient changes in DMI, ruminal capacity, and digestion and fermentation characteristics. Cows were individually fed alfalfa hay (16.0% CP, 51.3% NDF) at 130% of the average DMI of the previous 5-d period. Ruminal capacity and DM fill were measured once every 2 wk by removing the ruminal contents from each cow and filling the empty rumen with water. Dry matter intake was measured daily. Ruminal VFA, pH, NH3, and total tract DM digestibility (DMD) were measured during three 7-d periods (average of 58 d before calving, 16 d before calving, and 25 d after calving). Ruminal capacity and DM fill varied in a quadratic manner (P < .01); both were least 6 d before calving. Forage DMI (quadratic effect; P = .02) increased moderately during the prepartum period but increased dramatically after parturition. Although postpartum (d 22) ruminal capacity was only 5% greater than at 61 d before calving, postpartum DMI was 69% greater than DMI measured 61 d before calving. Indigestible ADF (IADF) passage rate changed quadratically with period (P = .01); the greatest IADF passage rate was observed 6 d before calving. Ruminal VFA (mM) also tended to change quadratically (P = .08); the highest concentrations occurred 25 d after calving. The acetate:propionate ratio declined linearly with period (P = .01). Ruminal fluid dilution rate, pH, NH3, and DMD did not change significantly over time.(ABSTRACT TRUNCATED AT 250 WORDS)