Serum and plasma metabolites associated with postpartum ovulation and pregnancy risks in suckled beef cows subjected to artificial insemination.

Two experiments were conducted to determine relationships of blood metabolite concentrations, BW, BCS, and rump fat depth with postpartum ovulation and pregnancy risks, as well as their utility in predicting those outcomes in suckled beef cows. In experiment 1, plasma glucose collected 10 and 3 d before AI of suckled beef cows at seven locations did not differ between cows that had resumed estrous cycles (ovulated) before AI compared with anovulatory cows, whereas plasma glucose 3 d before AI was greater (P < 0.01) in cows that became pregnant compared with nonpregnant cows. Serum beta-hydroxybutyrate (BHB) tended (P = 0.09) to be less in ovulatory cows compared with anovulatory cows 10 d before AI, but was unrelated to pregnancy status. Receiver-operator derived true-positive (sensitivity) and false-positive (1-specificity) risks were determined for plasma glucose and serum BHB as predictors for postpartum ovulation and pregnancy status. Serum BHB 3 d before AI produced true-positive and false-positive risks of 82% and 37%, respectively, when predicting ovulatory status before AI. Serum BHB 10 d before AI produced a true-positive and false-positive risks of 92% and 25%, respectively, when predicting pregnancy status. In experiment 2, blood was collected weekly for 12 wk from multiparous suckled beef cows to assess blood metabolite concentrations in addition to concurrent weekly assessments of BW, BCS, and rump fat. When blood metabolites and physical measures were normalized to parturition reflecting changes occurring during the first 6 wk after calving, we observed reduced (P < 0.05) concentrations of serum BHB and NEFA, and greater (P < 0.05) rump fat and BCS in cows that ovulated before first AI, whereas reduced (P < 0.05) plasma glucose was characteristic of cows that became pregnant. When blood metabolites and physical measures were normalized to the onset of the AI program reflecting changes during 6 wk before AI, ovulatory cows had increased (P < 0.05) BCS and lower (P < 0.05) NEFA from 3 to 6 wk before the onset of the AI program compared with anovulatory cows. With all predictor variables in regression models, some multiple correlation coefficients (R2) exceeded 50% when predicting postpartum ovulatory status, but those for predicting pregnancy risk were less than 25%. Although measures of BCS and BHB during 6 wk after calving were related to postpartum ovulation risk, rump fat, glucose, BCS, and NEFA were associated with cows that were ovulatory and pregnant.

Two split-time artificial insemination programs in suckled beef cows.

Our objective was to determine which of 2 split-time AI programs applied to suckled beef cows would result in greater pregnancy risk. Suckled beef cows (n = 1,062) at 12 locations in 4 states (CO, KS, MY, and WA) were enrolled. Cows were treated on d -7 with a progesterone insert concurrent with 100 µg GnRH and on d 0 with 25 mg PGF plus removal of the insert. Estrus-detection patches were affixed to cows at insert removal. The study was designed as a completely randomized experiment of 2 treatment combinations. Within location and balanced for parity (primiparous vs. multiparous), cows were assigned randomly to 2 treatment times (55 vs. 65 h after CIDR insert removal) at which time estrus-detection patches were assessed. Estrus was defined to have occurred when an estrus-detection patch was > 50% colored (activated). Cows determined to be in estrus were inseminated at either 55 or 65 h, whereas the residual nonestrous cows in both treatment times received GnRH at 55 or 65 h but were inseminated 20 h later at 75 or 85 h, respectively. Pregnancy outcomes were determined at 36 d after AI and at the end of the breeding season. Thus, pregnancy outcomes of interest were compared between the 55 + 75-h treatment combination and that of the 65+85-h combination. Expression of estrus was greater ( = 0.001) by 65 h after PGF than by 55 h (62.0% vs. 41.9%), respectively, and this proportion was influenced by parity (time x parity interaction; = 0.006). As a result, proportionally more ( < 0.001) cows received the timed AI at 75 than 85 h (59.4% vs. 40.6%). Similar proportions of cows not in estrus by 55 or 65 h were detected in estrus by 75 or 85 h (40.1% vs. 39.3%), respectively. The cumulative proportion of cows in estrus by 75 h was less ( < 0.001) than that by 85 h (66.7% vs. 76.7%), respectively. Pregnancy risks at 36 d differed among treatments, with cows detected in estrus and inseminated at 55 or 65 h having greater pregnancy risks than their time-inseminated herd mates at 75 or 85 h (62.3% vs.49.7%), respectively. Overall pregnancy risk for cows in the 65+85-h treatment combination was greater at 36 d than for cows in the 55 + 75-h treatment combination (61.0% vs. 51.4%), respectively. We conclude that the 65 + 85-h treatment combination produced more pregnancies than the 55 + 75-h combination, but its implementation may be somewhat less convenient in terms of cow handling times.

Gonadotropin-releasing hormone increased pregnancy risk in suckled beef cows not detected in estrus and subjected to a split-time artificial insemination program.

We hypothesized that GnRH would increase pregnancy risk (PR) in a split-time AI program for cows in which estrus was not detected. A total of 1,236 suckled beef cows at 12 locations in 3 states (Colorado, Kansas, and North Dakota) were enrolled. Before applying the fixed-time AI program, BCS was assessed. Cows were treated on d -7 with a progesterone insert concurrent with 100 µg GnRH and on d 0 with 25 mg PGF plus removal of the insert. Estrus-detection patches were affixed to cows at insert removal. Estrus was defined to have occurred when an estrus-detection patch was >50% colored (activated). Cows in estrus by 65 h ( = 758; 61.3% of all cows) were randomly allocated to 2 treatments: 1) 100 µg GnRH and early + GnRH (E+G; = 373) or 2) AI only at 65 h (early - no GnRH [E-G]; = 385). The remaining cows were randomly allocated to 2 treatments: 1) 5(L+G; = 252) or 2) AI only at 84 h (late no GnRH [L-G]; = 226). Pregnancy was determined 35 d after AI via transrectal ultrasound. Pregnancy risk did not differ ( = 0.68) between E+G and E-G cows (61.9 vs. 60.4%, respectively). Conversely, for cows inseminated at 84 h, PR was greater ( = 0.01) in cows that received GnRH (L+G) compared with their herd mates not receiving GnRH (L- G; 41.7 vs. 30.8%, respectively). Of those cows not detected in estrus by 65 h, 42.1% were detected by 84 h, for a total expression of estrus by all cows of 77.6%. Administration of GnRH increased ( < 0.01) PR in cows not detected in estrus by 84 h (+GnRH = 33.4% [ = 146] vs. no GnRH = 15.0% [ = 128]) but had no effect in cows expressing estrus by 84 h (+GnRH = 65.3% [ = 103] vs. no GnRH = 61.7% [ = 97]). Neither estrus expression by 65 or 84 h nor PR was influenced by BCS, parity, or days postpartum at AI. Cows had greater PR when they had been detected in estrus before AI, and PR was improved by administration of GnRH at 65 h after insert removal in cows that were not detected in estrus and inseminated at 84 h.

Using estrus detection patches to optimally time insemination improved pregnancy risk in suckled beef cows enrolled in a fixed-time artificial insemination program.

A multilocation study examined pregnancy risk (PR) after delaying AI in suckled beef cows from 60 to 75 h when estrus had not been detected by 60 h in response to a 7-d CO-Synch + progesterone insert (CIDR) timed AI (TAI) program (d -7: CIDR insert concurrent with an injection of GnRH; d 0: PGF injection and removal of CIDR insert; and GnRH injection at TAI [60 or 75 h after CIDR removal]). A total of 1,611 suckled beef cows at 15 locations in 9 states (CO, IL, KS, MN, MS, MT, ND, SD, and VA) were enrolled. Before applying the fixed-time AI program, BCS was assessed, and blood samples were collected. Estrus was defined to have occurred when an estrus detection patch was >50% colored (activated). Pregnancy was determined 35 d after AI via transrectal ultrasound. Cows ( = 746) detected in estrus by 60 h (46.3%) after CIDR removal were inseminated and treated with GnRH at AI (Control). Remaining nonestrous cows were allocated within location to 3 treatments on the basis of parity and days postpartum: 1) GnRH injection and AI at 60 h (early-early = EE; = 292), 2) GnRH injection at 60 h and AI at 75 h (early-delayed = ED; = 282), or 3) GnRH injection and AI at 75 h (delayed-delayed = DD; = 291). Control cows had a greater ( < 0.01) PR (64.2%) than other treatments (EE = 41.7%, ED = 52.8%, DD = 50.0%). Use of estrus detection patches to delay AI in cows not in estrus by 60 h after CIDR insert removal (ED and DD treatments) increased ( < 0.05) PR to TAI when compared with cows in the EE treatment. More ( < 0.001) cows that showed estrus by 60 h conceived to AI at 60 h than those not showing estrus (64.2% vs. 48.1%). Approximately half (49.2%) of the cows not in estrus by 60 h had activated patches by 75 h, resulting in a greater ( < 0.05) PR than their nonestrous herd mates in the EE (46.1% vs. 34.5%), ED (64.2% vs. 39.2%), and DD (64.8% vs. 31.5%) treatments, respectively. Overall, cows showing estrus by 75 h (72.7%) had greater ( < 0.001) PR to AI (61.3% vs. 37.9%) than cows not showing estrus. Use of estrus detection patches to allow for a delayed AI in cows not in estrus by 60 h after removal of the CIDR insert improved PR to TAI by optimizing the timing of the AI in those cows.

Phenotypic relationships between docility and reproduction in Angus heifers.

The objective of this study was to elucidate the phenotypic relationships between docility and first-service AI conception rate in heifers. Data ( = 337) collected from 3 cooperator herds in Kansas at the start of synchronization protocol included exit velocity (EV), chute score (CS), fecal cortisol (FC), and blood serum cortisol (BC). Data were analyzed using logistic regression with 30-d pregnancy rate as the dependent variable. The model included the fixed effect of contemporary group and the covariates FC, BC, EV, CS, BW, and age. Correlation coefficients were calculated between all continuous traits. Pregnancy rate ranged from 34% to 60% between herds. Blood cortisol positively correlated with EV ( = 0.22, < 0.01), negatively correlated with age ( = -0.12, < 0.03), and tended to be negatively correlated with BW ( = -0.10, = 0.09). Exit velocity was positively correlated with CS ( = 0.24, < 0.01) and negatively correlated with BW ( = -0.15, < 0.01) and age ( = -0.12, < 0.03). Chute score negatively correlated with age ( = -0.14, < 0.01), and age and BW were moderately positively correlated ( = 0.42, < 0.01), as expected. Older, heavier animals generally had better temperament, as indicated by lower BC, EV, and CS. The power of our test could detect no significant predictors of 30-d pregnancy for the combined data from all ranches. When the data were divided by ranch, CS ( < 0.03) and BW ( < 0.01) were both significant predictors for 30-d pregnancy for ranch 1. The odds ratio estimate for CS has an inverse relationship with pregnancy, meaning that a 1-unit increase in average CS will reduce the probability of pregnancy at ranch 1 by 48.1%. Weight also has a negative impact on pregnancy because a 1-kg increase in BW will decrease the probability of pregnancy by 2.2%. Fertility is a complex trait that depends on many factors; our data suggest that docility is 1 factor that warrants further investigation.

Altered progesterone concentrations by hormonal manipulations before a fixed-time artificial insemination CO-Synch + CIDR program in suckled beef cows.

We hypothesized that pregnancy outcomes may be improved by inducing luteal regression, ovulation, or both (i.e., altering progesterone status) before initiating a timed-artificial insemination (TAI) program in suckled beef cows. This hypothesis was tested in two experiments in which cows were treated with either PGF2α (PG) or PG + GnRH before initiating a TAI program to increase the proportion of cows starting the program in a theoretical marginal (<1 ng/mL; experiment 1) or elevated (≥1 ng/mL; experiment 2) progesterone environment, respectively. The control was a standard CO-Synch + controlled internal drug release (CIDR) program employed in suckled beef cows (100 µg GnRH intramuscularly [IM] [GnRH-1] and insertion of a progesterone-impregnated intravaginal CIDR insert on study Day -10, 25 mg PG and CIDR insert removal on study Day -3, and 100 µg GnRH IM [GnRH-2] and TAI on study Day 0). In both experiments, blood was collected before each injection for later progesterone analyses. In experiment 1, cows at nine locations (n = 1537) were assigned to either: (1) control or (2) PrePG (same as control with a PG injection on study Day -13). The PrePG cows had larger (P < 0.05) follicles on study Day -10 and more (P < 0.05) ovulated after GnRH-1 compared with control cows (60.6% vs. 36.5%), but pregnancy per TAI was not altered (55.5% vs. 52.2%, respectively). In experiment 2, cows (n = 803) at four locations were assigned to: (1) control or (2) PrePGG (same as control with PG injection on study Day -20 and GnRH injection on study Day -17). Although pregnancy per TAI did not differ between control and PrePGG cows (44.0% vs. 44.4%, respectively), cows with body condition score greater than 5.0 or 77 or more days postpartum at TAI were more (P < 0.05) likely to become pregnant than thinner cows or those with fewer days postpartum. Presynchronized cows in both experiments were more (P < 0.05) likely than controls to have luteolysis after initial PG injections and reduced (P < 0.05) serum progesterone; moreover, treatments altered the proportion of cows and pregnancy per TAI of cows in various progesterone categories before the onset of the TAI protocol. In combined data from both experiments, cows classified as anestrous before the study but with elevated progesterone on Day -10 had increased (P < 0.05) pregnancy outcomes compared with anestrous cows with low progesterone concentrations. Progesterone concentration had no effect on pregnancy outcome of cycling cows. In summary, luteal regression and ovulation were enhanced and progesterone concentrations were altered by presynchronization treatments before the 7-day CO-Synch + CIDR program, but pregnancy per TAI was not improved.

Effects of equine chorionic gonadotropin on follicle development and pregnancy rates in suckled beef cows with or without calf removal.

Two experiments were conducted to evaluate the effects of eCG, temporary 72-h calf removal (CR), or both on dominant follicle (DF) diameter and pregnancy rates (PR) in suckled beef cows. For Exp. 1, we hypothesized that CR, eCG, or both at PGF2α administration concomitant with synchronization of ovulation protocol would increase DF diameter and alter patterns of LH, estradiol (E), and progesterone (P4) secretion. Thirty-five multiparous, suckled crossbred beef cows were assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 µg GnRH and a controlled internal drug release (CIDR) insert containing 1.38 g of P4 (d -7) followed in 7 d by 25 mg PGF(2α) and CIDR removal (d 0) followed in 72 h by GnRH and fixed-time AI (d 3; Control; n = 9); 2) similar to control, but calves were removed from their dams for 72 h between d 0 and 3 (COCR; n = 9); 3) similar to control, but cows received 400 IU eCG on d 0 (COeCG; n = 9); and 4) similar to COCR, but cows received 400 IU eCG on d 0 (eCGCR; n = 8). Blood sample collection and ovary scans were performed on d -14, -7, 0, 1, 2, 3, 4, and 10. Pregnancy rate, ovulation response by d 4, and peak concentrations of LH before 72 h after PGF(2α) were greater (P < 0.05) for cows exposed to CR (COCR and eCGCR) than for cows not exposed to CR (Control and COeCG). Follicle diameter on d 3 was greater (P = 0.02) for cows receiving eCG (COeCG and COeCG; 14.9 ± 0.5 mm) than for cows receiving no eCG (Control and COCR; 13.1 ± 0.5 mm). Concentrations of E were greater (P < 0.05) at 32 h for COCR (8.2 ± 1.0 pg/mL) and eCGCR (8.5 ± 0.9 pg/mL) than in Control (4.9 ± 1.2 pg/mL) and COeCG (4.6 ± 1.1 pg/mL) and at 44 h after PGF(2α) for eCGCR (11.7 ± 1.6 pg/mL) compared with Control (6.9 ± 1.7 pg/mL), COCR (7.1 ± 1.5 pg/mL), and COeCG (7.5 ± 1.7 pg/mL). In Exp. 2, we determined whether administration of 200 IU eCG improved PR in suckled beef cows. The Control (n = 261) and COeCG (n = 252) treatments were similar to those previously described in Exp. 1; however, the interval from PGF(2α) to fixed-time AI was 66 h and 200 IU of eCG were administered to the COeCG group. Pregnancy rates did not differ (P > 0.10) between COeCG (43%) and Control (50%). We conclude that eCG increased DF diameter and CR resulted in a greater percentage of cows experiencing LH peak before 72 h after PGF(2α) and ovulation response; however, eCG failed to improve PR to timed AI.

Effects of feeding a single or sequence of beta-adrenergic agonists on cull cow meat quality.

Sixty cull cows were implanted and assigned to four treatments: C = concentrate ration only; RH = supplemented with ractopmaine-HCl (8.33 mg/kg of feed) for 25 d; ZH = supplemented with zilpaterol-HCl (ZH) (200mg head (-1)d(-1)) for the last 20 d; and RH + ZH = supplemented with RH for 25 d followed by ZH for 20 d. All cows were fed a concentrate ration for 74 d. Infraspinatus steaks from cows supplemented with RH and/or ZH had lower (P<0.05) shear force than steaks from C cows. Longissimus (LM) steaks from the 6-8th rib section of ZH and RH+ZH cows had decreased (P<0.0001) desmin degradation at 10 and 21 d postmortem compared to steaks from C and RH cows. Collagen solubility of the LM was increased (P<0.05) by ZH and RH+ZH compared to C. There were no treatment differences in 12th rib LM tenderness when enhanced with calcium lactate. Color and sensory traits of meat from RH+ZH cows were not different from C but flavor intensity was greater and off-flavor less than for C cows.

Determination of the appropriate delivery of prostaglandin F2α in the five-day CO-Synch + controlled intravaginal drug release protocol in suckled beef cows.

The objective of this experiment was to determine if 2 doses of prostaglandin F(2α) (PGF) administered concurrently at controlled intravaginal drug release (CIDR) removal was an efficacious method for delivery of PGF in the 5-d CO-Synch + CIDR protocol. Postpartum beef cows (n = 2,465) from 13 herds in 8 states were enrolled in the 5-d CO-Synch + CIDR protocol and assigned to receive 2 doses of PGF (25 mg/dose) 8 h apart with the initial injection given at CIDR insert removal (8h-PGF), 2 doses (25 mg/dose) of PGF delivered in 2 injection sites, both administered at CIDR insert removal (Co-PGF), or a single 25-mg dose of PGF at CIDR insert removal (1x-PGF). Cows were fixed timed-artificially inseminated (FTAI) 72 h after CIDR removal concurrent with GnRH administration. Estrus-cycling status (54% cyclic) was determined by evaluation of progesterone in 2 blood samples collected before CIDR insertion. Determination of pregnancy was performed by transrectal ultrasonography 39 ± 0.1 d after FTAI and at least 35 d after the conclusion of the breeding season. Fixed timed-AI pregnancy rates were greater (P < 0.05) for the 8h-PGF (55%) than the 1x-PGF (48%) treatment, with the Co-PGF (51%) treatment intermediate and not different (P > 0.10) from the other treatments. Contrast analysis demonstrated that cows receiving 50 mg of PGF (8h-PGF and Co-PGF) had greater (P < 0.05) FTAI pregnancy rates than those receiving 25 mg (1x-PGF). Pregnancy rates to FTAI were greater (P < 0.05) in cyclic (55%) than noncyclic (47%) and greater (P < 0.05) in multiparous (≥3 yr of age; 54%; n = 1,940) than primiparous cows (40%; n = 525). Luteolysis after PGF treatment was assessed in a subset of cows (n = 277) and treatment tended (P = 0.09) to affect the proportion of cows having luteolysis. The percentage of cows that had luteolysis was least in the 1x-PGF treatment (89%) and greatest in the 8h-PGF treatment (97%), with the Co-PGF treatment (94%) being intermediate. Breeding season pregnancy rate (88%) did not differ (P > 0.10) among treatments but was greater (P < 0.01) in multiparous (90%) than primiparous (78%) cows. In summary, 50 mg of PGF was required in the 5-d CO-Synch + CIDR protocol to maximize pregnancy rates; however, pregnancy rate did not differ when 50 mg of PGF was administered simultaneously with CIDR removal or split with 25 mg administered at 0 and 8 h after CIDR removal.

Endogenous prostaglandin F2α concentrations in bovine whole semen, seminal plasma, and extended semen.

A series of experiments were conducted to quantify PGF2α in bovine semen, seminal plasma, and extended semen, and to determine if PGF2α was synthesized or released during extension of bovine semen. Concentrations of PGF2α were measured in paired samples of whole and extended semen from beef and dairy bulls. Concentrations of PGF2α did not differ between beef and dairy (mean±SEM, 273.8±42.8 vs. 210.3±18.5 pg/mL, respectively; P=0.12), but tended (P=0.08) to be greater for whole compared with extended semen (255.5±29.8 vs. 194.5±17.0 pg/mL). Whole semen was extended at eight dilution rates (regardless of initial sperm concentration), using a diluent consisting of two fractions. Samples collected after each dilution step resulted in four subsamples. Concentrations of PGF2α in subsamples decreased (P<0.001) at higher dilution rates and later steps of extension. Subsequently, whole semen and seminal plasma were extended at three dilution rates. Initial PGF2α concentration was greater (P<0.001) for whole semen compared with seminal plasma. During extension, PGF2α synthesis or release resulted in less disparity, but the amount synthesized or released was greater (P=0.03) for semen compared with seminal plasma. We concluded that synthesis or release of PGF2α during extension resulted in concentrations similar to whole semen.

Effects of sequential feeding of ß-adrenergic agonists on cull cow performance, carcass characteristics, and mRNA relative abundance.

The objectives of this study were to determine the effects of supplementation with a single ß-adrenergic agonist (ß-AA) or a sequence of ß-AA on cow performance, carcass characteristics, and mRNA relative abundance of cull cows implanted and fed a concentrate diet. Sixty cull cows were implanted with Revalor-200 (200 mg of trenbolone acetate and 20 mg of estradiol) and assigned to 1 of 4 treatments (n = 15/treatment): CON = fed a concentrate diet only; RH = supplemented with ractopamine-HCl for the last 25 d before slaughter; ZH = supplemented with zilpaterol-HCl for 20 d before a 3-d withdrawal before slaughter; RH + ZH = supplemented with RH for 25 d, followed by ZH for 20 d before a 3-d withdrawal before slaughter. Ractopamine-HCl was supplemented at a dose of 200 mg·animal(-1)·d(-1), and ZH was supplemented at 8.33 mg/kg (100% DM basis) of feed. All cows were fed a concentrate diet for 74 d. Each treatment had 5 cows per pen and 3 replicate pens. Body weights were collected on d 1, 24, 51, and 72. Muscle biopsies from the LM were collected on d 24, 51, and at slaughter from a subsample of 3 cows per pen. Carcass traits were evaluated postslaughter. The 2 ZH treatments averaged 15.3 kg more BW gain, 0.20 kg greater ADG, and 7.8 cm(2) larger LM area than CON and RH treatments, and 21 kg more HCW than CON, but these differences were not significant (P > 0.10), likely due to a sample size of n = 15/treatment. The sequence of RH followed by ZH tended to optimize the combination of HCW, LM area, percent intramuscular fat, and lean color and maturity compared with the ZH treatment. Abundance of ß(2)-adrenergic receptor (AR) mRNA was not altered in the RH + ZH treatment during RH supplementation from d 24 to 51 of feeding. However, the abundance of ß(2)-AR mRNA increased (P < 0.05) the last 23 d of feeding for the RH treatment and tended (P = 0.10) to increase in ZH cows during ZH supplementation. For all cows, abundance of type IIa myosin heavy chain (MHC-IIa) mRNA decreased (P < 0.05) after 24 d of feeding. Abundance of MHC-IIx mRNA increased (P < 0.05) for ZH and RH + ZH treatments the last 23 d of feeding during ZH supplementation. Although few significant differences were observed in performance or carcass traits, mRNA quantification indicated that ß-AA supplementation elicited a cellular response in cull cows. Implanting and feeding cull cows for 74 d, regardless of ß-AA supplementation, added economic value by transitioning cows from a cull cow to what is referred to in industry as a white cow market in which cows have white fat resulting from grain feeding.

Escherichia coli O157:H7 shedding in vaccinated beef calves born to cows vaccinated prepartum with Escherichia coli O157:H7 SRP vaccine.

Extensive research, intervention equipment, money, and media coverage have been directed at controlling Escherichia coli O157:H7 in beef cattle. However, much of the focus has been on controlling this pathogen postcolonization. This study was conducted to examine the performance, health, and shedding characteristics of beef calves that were vaccinated with an E. coli O157:H7 SRP bacterial extract. These calves had been born to cows vaccinated prepartum with the same vaccine. Cows and calves were assigned randomly to one of four treatments: (i) neither cows nor calves vaccinated with E. coli O157:H7 SRP (CON), (ii) cows vaccinated with E. coli O157:H7 SRP prepartum but calves not vaccinated (COWVAC), (iii) calves vaccinated with E. coli O157:H7 SRP but born to cows not vaccinated (CALFVAC), (iv) cows vaccinated with E. coli O157:H7 SRP prepartum and calves also vaccinated (BOTH). Calves born to vaccinated cows had significantly higher titers of anti-E. coli O157:H7 SRP antibodies (SRPAb) in circulation at branding time (P < 0.001). Upon entry to the feedlot, overall fecal E. coli O157:H7 prevalence was 23 % among calves, with 25 % in the CON treatment group, 19 % in the CALFVAC group, 32 % in the COWVAC group, and 15 % in the BOTH group (P > 0.05). Fecal shedding of E. coli O157 on arrival to the feedlot was not correlated with fecal shedding at slaughter (Spearman's rho = -0.02; P = 0.91). No significant effects of cow or calf E. coli O157:H7 SRP vaccination treatment were found on feedlot calf health or performance (P > 0.05), prevalence of lung lesions or liver abscess (P > 0.05), or morbidity, retreatment, or mortality numbers (P > 0.05). The findings of this study indicate that the timing of vaccination of calves against E. coli O157:H7 may be an important consideration for maximizing the field efficacy of this vaccine.

Effects of mineral-supplement delivery system on frequency, duration, and timing of supplement use by beef cows grazing topographically rugged, native rangeland in the Kansas Flint Hills.

The effects of mineral-supplement delivery system on patterns of supplement use by grazing beef cows were measured in 2 studies. Study 1 was conducted on 4 pastures grazed by pregnant, mature beef cows (BW = 562 ± 38 kg) from February to May. Study 2 was conducted on 4 pastures grazed by lactating beef cows (BW = 579 ± 54 kg) and their calves from May to September. Treatments were mineral delivered in salt-based, granular form (salty) or mineral provided in a low-protein, cooked, molasses-based block (sweet); both were fed ad libitum. The salty supplement was supplied to cattle via a covered mineral feeder; the sweet supplement was supplied via an open-topped barrel. Both salty and sweet supplements were deployed in each pasture. No additional salt was supplied to cattle. Forage use in the vicinity of each supplement-deployment site and the frequency and duration of herd visits to each supplement-deployment site were measured during four 14-d periods during study 1 and seven 14-d periods during study 2. Supplements were moved to new locations within pastures at the beginning of each period. Consumption of the sweet supplement was greater than salty during each data-collection period in study 1; however, relative differences in consumption diminished over time (treatment × time, P = 0.03). In study 2, sweet consumption was greater than salty in periods 1, 6, and 7 but was not different from salty during periods 2, 3, 4, and 5 (treatment × time, P < 0.01). Increased consumption of the sweet supplement in study 1 translated to greater frequency of herd visits to supplement-deployment sites compared with the salty sites (2.82 vs. 2.47 herd visits/d; P = 0.02) and longer herd visits to supplement-deployment sites compared with the salty sites (125.7 vs. 54.9 min/herd visit; P < 0.01). The frequency of herd visits to mineral feeding sites in study 2 was similar (P > 0.10) between treatments for periods 1 through 6; however, herds visited the sweet sites more often than salty during period 7 (P < 0.01). Herd visits to the sweet sites were longer than those to the salty sites in study 2 (83.8 vs. 51.4 min/herd visit; P < 0.01). Forage disappearance within 100 m of supplement-deployment sites was not influenced (P ≥ 0.54) by treatment in either study. Results were interpreted to suggest that the sweet supplement influenced the location of grazing cattle more strongly than the salty supplement and may be more effective for luring cattle into specific areas of pasture during the winter, spring, and early fall but not during summer.

Effects of implanting and feeding zilpaterol hydrochloride on performance, carcass characteristics, and subprimal beef yields of fed cows.

Sixty crossbred cull cows were used to determine the combined effects of a trenbolone acetate-estradiol implant and feeding zilpaterol hydrochloride on performance, carcass characteristics, and subprimal yields of mature cows fed for 70 d. Cows were assigned to 1 of 5 treatments: 1) grazing native grass pasture (G); 2) concentrate-fed (C) a grain sorghum-sorghum silage diet; 3) concentrate-fed and implanted (CI) with Revalor-200 (trenbolone acetate-estradiol); 4) concentrate-fed and fed Zilmax (zilpaterol hydrochloride) beginning on d 38 of the feeding period (CZ); and 5) concentrate-fed, implanted, and fed Zilmax beginning on d 38 (CIZ). The concentrate diet consisted primarily of ground grain sorghum and sorghum silage. During the last 34 d of the feeding trial, concentrate-fed (C, CI, CZ, and CIZ) cows had greater (P < 0.05) gains than G cows. Hot carcass weights and dressing percentages were greater (P < 0.05) for the concentrate-fed cows than for G cows. Longissimus muscle area was largest (P < 0.05) for CIZ cows, whereas subprimal weights from the chuck were heavier (P < 0.05) from CIZ cows than C and G cows, and carcasses from CI and CZ cows had heavier (P < 0.05) chuck subprimal weights than G cows. Rib and round subprimal weights were heavier (P < 0.05) for concentrate-fed cows compared with G cows. In addition, carcasses from CIZ cows had heavier (P < 0.05) total subprimal weights, and total subprimals were a greater percentage of their initial BW than C cows. Rib cut-out and total soft tissue weights from the 9-10-11th rib were less (P < 0.05) for G cows than concentrate-fed cows. Feeding cull cows a concentrate diet increased carcass weight, dressing percentage, and subprimal yields compared with feeding cows a grass-based pasture diet, and the combination of a trenbolone acetate-estradiol implant and feeding zilpaterol hydrochloride can maximize trimmed beef yields from cull cows fed a high-concentrate diet.

Ovarian function in ewes after treatment with mifepristone early during the oestrous cycle.

The aim of this study was to determine whether endogenous progesterone regulates synthesis and secretion of luteal oxytocin. In Expt 1, mature ewes (n = 5 per group) were assigned randomly to control or mifepristone (RU486) treatment groups. Ewes were injected s.c. twice a day with vehicle or 10 mg RU486 on days 5-7 of the oestrous cycle (oestrus = day 0). On day 8, after an i.v. injection with prostaglandin F(2alpha) (250 microg cloprostenol), venous blood samples were collected at frequent intervals to determine plasma oxytocin concentrations. Plasma oxytocin concentrations of RU486-treated ewes were not significantly different from those of control ewes. In Expt 2, ewes were injected s.c. each day with vehicle or 175 mg RU486 on days 2-5 of the oestrous cycle followed by administration of prostaglandin F(2alpha) on day 6. Four of five RU486-treated ewes showed 'split-oestrus' (oestrous behaviour for 36 h and then again at 84-108 h after the onset of initial oestrus). There was no significant difference in mean plasma oxytocin or progesterone concentrations between treatment groups. The mean masses of mature corpora lutea from control and RU486-treated ewes on day 6 of the oestrous cycle did not differ significantly (394.8 +/- 28.8 versus 319.5 +/- 48.3 mg). RU486-treated ewes contained mature corpora lutea, new corpora lutea (two of four ewes) and preovulatory follicles (>or= 10 mm, two of four ewes). The average interoestrous interval for RU486-treated ewes was 9 days more than that for control animals (26.2 +/- 2.9 versus 17 +/- 0.5 days; P < 0.025).

Cryptic vicariance in the historical assembly of a Baja California peninsular desert biota.

We use analyses of phylogeographic population structure across a suite of 12 mammalian, avian, amphibian, and reptilian species and species-groups to assess the role of Late Miocene to Pleistocene geological history in the evolution of a distinct Baja California Peninsular Desert biota. Comparative examination of phylogroup distributions provides support for previously hypothesized vicariant events produced by: a middle Pleistocene midpeninsular seaway, a late Pliocene northward transgression of the Sea of Cortéz, and a Pliocene seaway across the southern peninsular Isthmus of La Paz. Most of this phylogeographic architecture is cryptically embedded within widespread taxonomic species and species-groups, such that the unique evolutionary history of the Peninsular Desert has been obscured and ignored. The Peninsular Desert can no longer be considered a subset of the Sonoran Desert-it is a separate regional desert with its own unique evolutionary history, ecological arena, and conservation value.

Influence of supplemental alfalfa quality on the intake, use, and subsequent performance of beef cattle consuming low-quality roughages.

Three experiments were conducted to evaluate influences of supplemental alfalfa quality on intake and use of low-quality meadow grass roughages (MG) by beef cattle. In Exp. 1, 15 steers (250 kg) were assigned to three treatments: 1) MG (5.2% CP), no supplement; 2) MG plus high-quality alfalfa (18.8% CP); and 3) MG plus low-quality alfalfa (15.2% CP). High- and low-quality alfalfa supplements were fed at .45 and .55% BW, respectively. Total DMI was greater (P < .01) for alfalfa-supplemented steers than for MG. Likewise, intake of digestible DM, DM digestibility (DMD), and ruminal ammonia level were greater (P < .01) for supplemented steers. In Exp. 2, 96 pregnant Hereford x Simmental cows (537 kg; body condition [BC] score 4.86) were assigned to the same treatments as in Exp. 1. For d 0 to 42, cows grazed on 19.1 ha of stockpiled MG (4,539 kg/ha; 6.8% CP), whereas, on d 43 to 84, cows received MG hay (5.2% CP). Supplemented cows gained more BW (P < .01), BC score (P < .01), and had heavier calf birth weight (P < .01) than nonsupplemented cows. However, there were no treatment effects (P > .10) on cow cyclicity, pregnancy rate, or calving interval. In Exp. 3, 90 pregnant Angus x Hereford cows (475 kg; BC score 4.59) were assigned to three treatments: 16.1%, 17.8% or 20.0% CP alfalfa supplement, with levels of .63, .55, and .50% of BW, respectively. Weight gain and BC score for the 84-d study displayed a quadratic response (P < .10), yet represented only 7 kg BW and .2 units of BC score. In conclusion, alfalfa hay supplementation was effective in increasing DMI and digestibility. However, alfalfa hay quality did not dramatically affect BW, BC score, and(or) calf birth weight, when fed on an isonitrogenous basis.

Luteinizing hormone release and reproductive traits in anestrous, estrus-cycling, and ovariectomized cattle after tyrosine supplementation.

The role of rumen-protected L-tyrosine as a nutritional signal altering LH release and other reproductive traits in cattle was studied. In Exp. 1, 28 suckled crossbred cows were assigned randomly to five treatments (0 or 40 g of tyrosine daily in feed for 3 d followed by a single i.v. injection of 200 micrograms of GnRH or 1 mg/kg of naloxone on d 26 +/- 1 postpartum; no tyrosine plus an injection of saline was the control). Peak LH after GnRH was greater (P < .001) in GnRH-treated cows regardless of tyrosine supplementation. Compared to cows receiving saline, days to first postpartum ovulation were reduced (P < .05) by naloxone, tyrosine, and GnRH. In Exp. 2, 47 suckled crossbred cows were assigned randomly to six treatments (0, 20, or 40 g of tyrosine daily for 3 d before GnRH or saline was injected i.m. on d 23 +/- 1 postpartum). Injection of GnRH increased (P < .001) LH. An interaction (P = .08) of tyrosine and GnRH tended to reduce days to first postpartum ovulation. In Exp. 3, tyrosine (40 g) administered once daily for 3 d to ovariectomized cows (six cows per treatment) had no effect on any characteristic of LH before or after estradiol-17 beta. In Exp. 4, suckled cows (n = 136) were allotted randomly to two treatments (0 or 30 g of tyrosine daily for 3 d before a PGF2 alpha-synchronized estrus). Tyrosine increased (P = .05) the percentage of cows in estrus after PGF2 alpha but reduced (P = .05) AI conception rate. These results fail to support the thesis that tyrosine alters LH release in cattle. Supplemental tyrosine increased expression of estrus in suckled cows after PGF2 alpha and tended to reduce intervals to first postpartum ovulation.

Detection of estrus by visual observation and radiotelemetry in peripubertal, estrus-synchronized beef heifers.

The effectiveness of two estrus-detection methods (visual observation and radiotelemetric, pressure-sensitive, rump-mounted devices) was compared in peripubertal, crossbred yearling beef heifers. Heifers (n = 50) were fitted with a pressure-sensitive device affixed to their rumps to which a battery-operated radio transmitter was connected. Activation of the sensor sent a radiotelemetric signal to a microcomputer via a fixed radio antenna. Heifer identification, date, time, and duration of standing events were recorded. Estrus was synchronized by feeding melengestrol acetate (MGA) for 14 d and then injecting PGF2 alpha 17 d after the last daily dose of MGA. Following the injection of PGF2 alpha, heifers were observed visually for signs of estrus at 0730 and 1630 (45 min each). Estrus was detected in 41 of 49 heifers (one lost the device) by visual observation and(or) the radiotelemetric device. Number of standing events during estrus, determined by the radiotelemetric device, averaged 50.1 +/- 6.4 per heifer, with the duration of estrus ranging from 2.6 to 26.2 h (average = 14 +/- .8 h). Visual observation failed to detect 11 of 41 heifers (37%) that were detected by the radiotelemetric device. Heifers with fewer standing events (19.3 vs 60.5; P < .001) and estrus of shorter duration (8.4 vs 15.6 h; P < .001) were those not identified by visual observation. Based on intervals between the first detected standing event of estrus and time of insemination, a wide window of fertility seems to exist in some heifers. Radiotelemetric devices were useful in identifying a greater (P < .05) proportion (100%) of heifers in estrus (increased efficiency) compared with visual observation (73%). However, accuracy of both methods was similar.