Reticulo-rumen temperature as a predictor of calving time in primiparous and parous Holstein females.

The objective of this research was to define and analyze drops in reticulo-rumen temperature (Trr) as an indicator of calving time in Holstein females. Data were collected from 111 primiparous and 150 parous Holstein females between November 2012 and March 2013. Between -15 and -5 d relative to anticipated calving date, each female received an orally administered temperature sensing reticulo-rumen bolus that collected temperatures hourly. Daily mean Trr was calculated from d -5 to 0 relative to using all Trr values (A-Trr) or only Trr values ≥37.7°C (W-Trr) not altered by water intake. To identify a Trr drop, 2 methodologies for computing the baseline temperature were used. Generalized linear models (GLM) were used to estimate the probability of calving within the next 12 or 24 h for primiparous, parous, and all females, based on the size of the Trr drop. For all GLM, a large drop in Trr corresponded with a large estimated probability of calving. The predictive power of the GLM was assessed using receiver-operating characteristic (ROC) curves. The ROC curve analyses showed that all models, regardless of methodology in calculation of the baseline or tested category (primiparous or parous), were able to predict calving; however, area under the ROC curve values, an indication of prediction quality, were greater for methods predicting calving within 24 h. Further comparisons between GLM for primiparous and parous, and using baseline 1 and 2, provide insight on the differences in predictive performance. Based on the GLM, Trr drops of 0.2, 0.3, and 0.4°C were identified as useful indicators of parturition and further analyzed using sensitivity, specificity, and diagnostic odds ratios. Based on sensitivity, specificity, and diagnostic odds ratios, the best indicator of calving was an average Trr drop ≥0.2°C, regardless of methodology used to compute the baseline or category of animal evaluated.

BEEF SPECIES SYMPOSIUM: Beef production without mature cows.

Nutrients in animal feed get partitioned to growth, lactation, pregnancy, fat accretion, and/or maintenance. For mature beef cows, >80% of nutrients consumed annually go to unproductive maintenance. Integrated over the entire U.S. beef cattle production system, nearly one-half of the nutrients consumed go to maintenance of cow herds. This accounts for much of the inefficiency of beef production and can be minimized by the single-calf heifer system, in which heifers are fattened and slaughtered after having their first calf. We propose a modification, use of sexed semen, so that most heifers replace themselves with a heifer calf. This greatly decreases the size of the inherently inefficient cow herd required for beef production and greatly increases efficiency of beef production in terms of nutrients consumed and waste produced, such as methane, by increasing the ratio of nutrients used for growth to those used for maintenance. Additional management is required including AI, early weaning, and the attention required when calving 2-yr-old heifers. Low conception rates with sexed semen and less efficient growth of females than males also must be considered. However, these issues seem greatly outweighed by the benefits of increased efficiency from decreasing cow herd size while eliminating the need for breeding back lactating first-calf heifers, the need for castration, and health problems inherent in older cows such as mastitis and lameness. Moreover, the decreased generation interval can greatly accelerate genetic progress.

Effects of pain mitigation and method of castration on behavior and feedlot performance in cull beef bulls.

The objectives of this study were to evaluate the effects of castration method (banding vs. surgical) and use of analgesia on behavior and feedlot performance in cull bulls. Angus, Hereford, and Angus-crossbred bulls (n = 20; initial BW = 384 ± 59.3 kg; 336 ± 20.1 d old) were housed in feedlot pens equipped with the ability to measure individual daily feed intake. A balanced randomized block design using a 2 × 2 factorial arrangement of treatments was used. A multimodal analgesia (MMA) protocol was used and consisted of sutcutaneous ketamine stun containing butorphanol (0.01 mg/kg BW), xylazine (0.02 mg/kg BW), ketamine (0.04 mg/kg BW), and a local 2% lidocaine hydrochloride anesthetic block of the spermatic cords (10 mL/cord) and scrotum (10 mL) on d 0. Flunixin meglumine (1.2 mg/kg) was administered intravenously on d 0, 1, 2, and 3 to MMA cattle. Cattle were stratified to treatments based on breed, BW, age, and a temperament score. Treatments included 1) band castration without analgesia (BND), 2) band castration with analgesia (BND-MMA), 3) surgical castration without analgesia (SURG), and 4) surgical castration with analgesia (SURG-MMA). All castrations were performed on d 0. Chute exit velocity (EV) and time in chute (TIC) were collected on d -9, 0, 1, 2, and 13. Willingness-to-enter-chute (WTE) score, rectal temperature (TEMP), heart rate (HR), and respiration (RESP) were collected on d 0, 1, 2, 3, and 13. Cattle were weighed on d -9 and 13 while feeding behaviors were collected continuously for 57 d precastration and 28 d postcastration. There was a tendency (P < 0.09) for ADG to be greater in cattle receiving analgesia. Both SURG treatments exhibited elevated TEMP on d 1 (P < 0.001) and 2 (P < 0.05) compared to BND treatments. Postcastration DMI was greater (P = 0.02) in MMA treatments compared with nonmedicated treatments throughout the trial. Meal duration was greater (P < 0.05) in BND than SURG castrates during the first week postcastration. Results suggest that pain mitigation reduces the impact of castration on ADG and DMI.

Impact of oral meloxicam administration before and after band castration on feedlot performance and behavioral response in weanling beef bulls.

Two experiments evaluated the effects of band castration and oral administration of an analgesic in association with castration on performance and behavioral and physiological responses in yearling beef bulls. In Exp. 1 Angus and Charolais-crossbred bull calves (n = 127; 309.8 ± 59.04 kg BW) and in Exp. 2 Hereford, Angus, and Hereford × Angus crossbred bulls (n = 30; 300.8 ± 4.96 kg BW) were stratified by BW and randomly assigned to 1 of 3 treatments: 1) band castration (BAND), 2) band castration with oral administration of meloxicam (BAND-MEL), and 3) sham castration (SHAM). The BAND and SHAM procedures were completed on d 0. The SHAM treatment consisted of all animal manipulations associated with band castration without band application. Meloxicam was administered on d -1, 0, and 1 (1.0, 0.5, and 0.5 mg/kg, respectively) via an oral bolus. Body weight and a subjective chute score (CS) were collected on d -1, 0, 1, 7, 14, and 21 (d 28 Exp. 1 only). In Exp. 2, jugular blood samples were collected immediately before castration and 24 h postcastration for substance P (SP) analysis. In Exp. 2, video documentation on d 0 was used to determine range of vertical head motion (DIST) on a subset of animals during treatment administration. In both experiments, ADG was similar (P ≥ 0.50) between BAND and BAND-MEL, but ADG in SHAM cattle was greater (P < 0.001) and tended (P = 0.07) to be greater than castrates in Exp. 1 and 2, respectively. In Exp. 1, CS did not differ (P ≥ 0.26) between BAND and BAND-MEL on any day, but castrates exhibited less desirable CS on d 1 and 28 than SHAM cattle. In Exp. 2, CS was not affected (P ≥ 0.41) by castration or the presence of meloxicam. In Exp. 2, DIST did not differ (P = 0.57) between BAND and BAND-MEL, but when pooled, castrates exhibited greater (P = 0.04) DIST than SHAM. In Exp. 2, plasma SP concentrations were similar between BAND and BAND-MEL (P = 0.81) and between castrates vs. sham cattle (P = 0.67). Results indicate no impact of meloxicam administration on performance or behavioral and physiological responses to band castration. However, there was a negative impact of castration on ADG and DIST.

Administration of a GnRH analog on day 9 of a 14-day controlled internal drug release insert with timed artificial insemination in lactating beef cows.

Many estrus synchronization protocols aim to induce a new follicular wave to improve response and enhance pregnancy rate. Our objectives were to determine the effectiveness of GnRH analog administered d 0 and 9 during an extended controlled internal drug release (CIDR) protocol to produce 2 follicular waves, induce cyclicity in anestrus cows, and evaluate the efficacy of a single 50-mg dose of PGF2α to initiate luteal regression on CIDR removal. Lactating beef cows (n = 779) at 3 locations (n = 247, location 1; n = 395, location 2; n = 137, location 3) were randomly assigned to 1 of 3 treatments. Cows in the 14-d 50 PG treatment received a CIDR (1.38 g progesterone) with 100 µg GnRH analog intramuscularly (i.m.) on d 0, 100 µg GnRH analog i.m. on d 9, and CIDR removal concurrent with 50 mg PGF2α i.m. on d 14. Cows in the 14-d 6-h PG treatment were assigned the same protocol as the 14-d 50 PG treatment except that 25 mg PGF2α i.m. was given on d 14 plus 25 mg PGF2α i.m. 6 ± 1 h later. Cows in the control treatment, 5-d CO-Synch + CIDR (5-d CO-Synch), received a CIDR concurrent with 100 µg GnRH analog i.m. on d 9, CIDR removal concurrent with 25 mg PGF2α i.m. on d 14, and 25 mg PGF2α i.m. 6 ± 1 h after first F2α injection. Cows in all treatments received 100 µg GnRH analog i.m. and timed AI (TAI) 72 ± 3 h after CIDR removal. Pregnancy status to TAI was determined by ultrasonography 37 to 40 d after TAI. Averaged over all locations, pregnancy rates to TAI for 14-d 50 PG, 14-d 6-h PG, and 5-d CO-Synch treatments were 58.2%, 46.8%, and 41.9%, respectively. Pregnancy rates to TAI were greater (P < 0.05) in 14-d 50 PG treatment than 14-d 6-h PGF2α and 5-d CO-Synch treatments. Cycling status at 2 locations (n = 243, location 1; n = 391, location 2) was determined from blood collected on d -7 and 0; cows with serum progesterone concentrations >1 ng/mL at either (or both) bleeding date were considered cyclic. Averaged over the 2 locations, there was a tendency (P = 0.06) for a greater number of cyclic animals to become pregnant to TAI in the 14-d 50 PG treatment (64.4%) than 5-d CO-Synch treatment (50.2%). The 14-d CIDR with GnRH analog on d 0 and 9 and a single 50-mg dose of PG i.m. at CIDR removal was a more efficacious protocol to maximize TAI pregnancy rates than the standard 5-d CO-Synch.

Effect of copper, zinc, and manganese supplementation and source on reproduction, mineral status, and performance in grazing beef cattle over a two-year period.

Crossbred, multiparous beef cows (n = 178 in Year 1; n = 148 in Year 2) were used to evaluate the effects of Cu, Zn, and Mn supplementation and source on reproduction, mineral status, and performance in grazing cattle in eastern Colorado over a 2-yr period. Cows were stratified by expected calving date, age, BW, BCS, and liver mineral status and assigned to the following treatments: 1) control (no supplemental Cu, Zn, or Mn); 2) organic (ORG; 50% organic and 50% inorganic Cu, Zn, and Mn); and 3) inorganic (ING; 100% inorganic CuSO4, ZnSO4, and MnSO4). Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Zn, and Mn from 82 d (Year 1) and 81 d (Year 2) before the average calving date of the herd through 110 d (Year 1) and 135 d (Year 2) after calving. At the end of Year 1, supplemented cows had greater liver Cu (P < 0.01), Zn (P < 0.05), and Mn (P < 0.01) concentrations compared with controls, whereas liver Cu concentration was greater (P < 0.01) in ORG vs. ING cows. At the end of Year 2, supplemented cows had greater (P < 0.01) liver Cu concentrations relative to controls, whereas control cows had greater (P < 0.02) liver Mn concentration than did supplemented cows. In Year 1, pregnancy rate to AI in control cows did not differ (P = 0.47) from supplemented cows, but there was a trend (P < 0.08) for pregnancy rate to be higher for ORG than ING cows. In Year 2, supplemented cows had a higher (P < 0.02) pregnancy rate to AI than controls. In both years, when cows were inseminated after an observed estrus, supplemented cows had a higher (P < 0.04) pregnancy rate than did controls. Also, for both years, overall 60-d pregnancy rate tended (P = 0.10) to be higher for supplemented cows than for controls. In Year 1, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and kilograms of calf weaned per cow exposed was greater (P < 0.01) in ING than ORG treatments. However, in Year 2, kilograms of calf weaned per cow exposed was greater (P < 0.02) in controls than in supplemented cows, and tended (P = 0.09) to be greater in ORG than ING treatments. Results indicate that supplementation and source of trace minerals affected mineral status and kilograms of calf weaned per cow exposed in grazing beef cows. Supplementation also improved pregnancy rate to AI compared with cows not supplemented with Cu, Zn, or Mn for more than 1 yr. Furthermore, mineral source may influence pregnancy rate to AI.

Effect of fish meal supplementation on plasma and endometrial fatty acid composition in nonlactating beef cows.

Seven nonlactating mature Angus cows (4 to 10 yr old) were used to examine the effects of fish meal supplementation on plasma and endometrial fatty acid composition. Cows were fed a corn silage-based diet supplemented with either fish meal, a rich source of the n-3 fatty acids, eicosapentaenoate and docosahexaenoate (n = 3; 5.1% of dietary DM), or corn gluten meal (n = 4; 8.5% of dietary DM) for approximately 64 d. Cows were given 25 mg of PGF2alpha (i.m.) on d 11 and 25 of supplementation to synchronize estrous cycles. On d 18 postestrus of the second estrous cycle, cows were slaughtered, and caruncular endometrium was dissected from uteri immediately after slaughter. Jugular blood samples were collected immediately before supplementation was initiated (d 0) and at 7-d intervals for 35 d of the study. Plasma eicosapentaenoic and docosahexaenoic acids did not differ between treatment groups on d 0 (P > 0.10); however, these fatty acids were greater in cows supplemented with fish meal over the first 35 d of supplementation compared with cows supplemented with corn gluten meal (P < 0.05). Endometrial docosahexaenoic acid did not differ (P = 0.12), whereas eicosapentaenoic acid was greater (P < 0.05) in cows supplemented with fish meal than in cows supplemented with corn gluten meal. These results indicate that dietary fish meal alters plasma and endometrial n-3 fatty acid composition in beef cows.

Synchronization of ovulation using GnRH or hCG with the CO-Synch protocol in suckled beef cows.

The objectives of this study were to evaluate replacing GnRH with hCG and the effects of 48-h calf removal (CR) on pregnancy rates of cows synchronized with the CO-Synch protocol. Suckled beef cows (n = 467) at two locations were assigned to treatment by breed, age, and calving date. Treatment included either GnRH with (n = 121) or without CR (n = 117) or hCG with (n = 115) or without CR (n = 114) using the CO-Synch protocol. On d 0 and 9, cows received either hCG (2,500 IU, i.m.) or GnRH (100 microg, i.m.), and on d 7 all cows received PGF2alpha (25 mg). At one location, blood samples were collected from all cows (n = 203) on d -14, -7, 0, 7, 9, and 16. Calves were removed on d 7 and returned on d 9 (48 h) from approximately half of the cows that received GnRH or hCG. Cows that were detected in estrus between d 6 and 9 were bred approximately 12 h later and received no further injections. Cows not observed in estrus by d 9 received a second injection of either GnRH or hCG and were timed-inseminated. The AI pregnancy rates for GnRH-treated cows with or without CR and hCG-treated cows with or without CR were 46, 49, 35, and 34%, respectively (P = 0.44). Pregnancy rates of cows differed by treatment x age interaction (P = 0.07), hormone (P = 0.09), and hormone x age (P = 0.01) but not by CR (P = 0.66) or CR x age (P = 0.33). Among 2-yr-olds, pregnancy rates were higher for cows treated with hCG without CR than for cows that received GnRH with calf removal, whereas cows treated with hCG with CR and GnRH without CR were intermediate. In addition hCG-treated 2-yr-olds had higher pregnancy rates than GnRH-treated 2-yr-olds regardless of calf presence, but the reverse was true for older cows. Overall, GnRH-treated cows (48%) had a higher (P = 0.09) pregnancy rate than hCG-treated cows (34%). Among anestrous cows, GnRH and hCG were similar (P = 0.40) in their ability to induce ovulation and corpus luteum formation after the first and second injections of GnRH (31 and 76%, respectively) or hCG (39 and 61%, respectively). More (P = 0.001) hCG-treated cows exhibited short estrous cycles following timed AI. We conclude that hCG is not a suitable replacement for GnRH to synchronize ovulation with the CO-Synch protocol in multiparous cows, although further evaluation among primiparous cows is warranted using hCG with the CO-Synch protocol.

Calf removal improves conception rates to the Ovsynch and CO-Synch protocols.

Beef cows (n = 473) from two locations were stratified by breed, postpartum interval, age, and AI sire and were randomly allotted to one of four treatments for synchronization of ovulation. Ovulation synchronization protocols included the Ovsynch protocol with (n = 114) or without (n = 123) 48-h calf removal from d 7 to 9 (d 0 = 1st GnRH injection) or the CO-Synch protocol with (n = 119) or without (n = 117) 48-h calf removal from d 7 to 9. The Ovsynch protocol included administration of GnRH (100 microg; i.m.) on d 0, PGF2alpha (25 mg; i.m.) on d 7, GnRH (100 microg; i.m.) on d 9, and timed insemination on d 10. The CO-Synch protocol included administration of GnRH (100 microg; i.m.) on d 0, PGF2alpha (25 mg; i.m.) on d 7, and GnRH (100 microg; i.m.) with timed insemination on d 9. Blood samples were collected from all cows on d -10 and d 0 for analysis of serum progesterone. Cows with at least one serum progesterone concentration greater than 1 ng/mL were considered to be cyclic at the time of treatment. Conception rates of cows that received the CO-Synch + calf removal, Ovsynch + calf removal, CO-Synch, or Ovsynch protocol (63, 61, 54, and 52%, respectively) were not different (P = 0.50). Conception rates were not different (P = 0.80) among CO-Synch- and Ovsynch-treated cows; however, both estrual status and 48-h calf removal affected conception rates. Conception rates of cyclic cows (66%) were greater (P = 0.01) than those of anestrous cows (53%), regardless of which synchronization protocol was used. When data were pooled across synchronization protocol, conception rates of cows with 48-h calf removal (62%) were greater (P = 0.09) than conception rates of cows without calf removal (53%). The CO-Synch + calf removal protocol induces a fertile ovulation in cyclic and anestrous cows, requires handling cattle just three times, results in high conception rates from timed insemination, and should be a useful program for synchronization of ovulation in beef cows.

Effect of anthelmintic treatment on sexual maturation in prepubertal beef heifers.

Heifers treated with ivermectin at weaning have been reported to reach puberty at a younger age and lighter weight than untreated heifers. We tested the hypothesis that heifers administered ivermectin would respond with earlier follicular development and a greater LH response to a 1-mg estradiol-17beta challenge (E2C) than untreated heifers. Fall-born Angus heifers (n = 32) were randomly assigned on 284 +/- 9 d of age (215.5 +/- 20.8 kg) to receive ivermectin (IVR) or albendazole (ALB), IVR + ALB, or to remain as untreated controls (CONT). Each group (n = 8) was housed separately in adjacent pens throughout the trial and managed to gain .8 kg/heifer on a ration containing 13.2% CP, 58.8% TDN, and 49.9% DM. The CONT heifers received an additional 2.27 kg/heifer of corn silage and 1.59 kg/heifer of corn daily to maintain ADG at comparable levels. Individual body weight was recorded weekly, and nematode eggs per gram (EPG) of feces were measured every 21 d. Ultrasonography was performed on alternate days starting 2 wk prior to E2C to characterize follicular wave patterns. Follicles were separated into classes (C1 [3 to 5 mm], C2 [6 to 9 mm], and C3 [10 mm]) and sizes (largest [LF], second [SLF], third [TLF], and fourth largest follicles [FLF]). The sizes of the regressing dominant follicle 1 (DF1) and the progressing dominant follicle 2 (DF2) were also determined. Serum concentrations of LH were determined from hourly jugular blood samples collected 8 to 24 h after injection of E2C. The IVR + ALB treatment group had more C3 follicles than ALB and CONT (P < .07). The IVR-treated heifers had larger TLF than ALB and CONT (P < .04). The IVR- and IVR + ALB-treated heifers had larger FLF and DF2 than ALB and CONT (P < .1). Least squares means for DF2 were 9.5 +/- .5, 8.0 +/- .4, 9.5 +/- .3 and 8.3 +/- .3 mm, for IVR, ALB, IVR + ALB and CONT, respectively (P = .02 for treatment effect). The E2C-induced serum LH concentration did not differ with respect to treatment. We conclude that heifers administered IVR display increased follicular development, supporting our earlier investigations regarding reduced age at puberty in heifers treated with IVR near weaning.

Performance of beef cows receiving cull beans, sunflower meal, and canola meal as protein supplements while grazing native winter range in Eastern Colorado.

A 2-yr grazing performance study was conducted in Eastern Colorado to evaluate the effects of feeding raw cull beans (Phaseolus vulgaris) or canola meal, compared to sunflower meal, to beef cows grazing dormant, native winter range on body weight and body condition score (BCS) change, reproductive performance, and calf performance. Ninety-five pregnant, spring-calving crossbred cows (541 +/- 51 kg) in 1995 to 1996 and 65 cows (602 +/- 60 kg) in 1996 to 1997 were randomly assigned to one of five treatments (19 and 13 cows per treatment in 1995 to 1996 and 1996 to 1997, respectively): 1) unprocessed Great Northern beans to supply 182 g/d of CP (GNB); 2) canola meal to supply 182 g/d of CP (CM); 3) a mixture of Great Northern beans and sunflower meal, each to supply 91 g/d of CP, for a total of 182 g/d of CP (MIX); 4) sunflower meal to supply 182 g/d of CP (SFM+); and 5) sunflower meal to supply 91 g/d of CP (SFM-). Cow weight and body condition performance were broken into a gestation and a lactation phase in 1995 to 1996; calves were weighed at birth, at the end of the lactation phase in April, and at weaning the following September. Only gestation performance was monitored in 1996 to 1997, and subsequent calf birth and weaning weight were recorded. The SFM- group lost more weight during the gestation phase than other treatments (P < .05), yet no differences were detected for gestation phase daily BCS change, calf birth weight, lactation phase daily weight change, lactation phase daily BCS change, first-service conception rate to AI, or overall pregnancy rate. Off-test calf weight was higher in April for calves from dams of the SFM+ and CM treatments than for calves from dams on the GNB or SFM- treatments (P < .05), and calves from cows on the CM treatment were heavier in April than calves from cows on the MIX treatment (P < .05). No differences in calf weight were present at weaning. Consumption of beans by cows on the GNB treatment was low because of palatability problems. Mixing the beans with sunflower meal in the MIX treatment eliminated this problem. Canola meal, Great Northern beans, or a combination of sunflower meal and Great Northern beans were comparable to sunflower meal as protein supplements for beef cows grazing native winter range, despite obvious palatability problems with the beans.

Pregnancy rates of postpartum beef cows that were synchronized using Syncro-Mate-B or the Ovsynch protocol.

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

Use of short-term progestin treatment to resynchronize the second estrus following synchronized breeding in beef heifers.

Two trials were conducted to evaluate the efficacy of short-term progestin administration to resynchronize the second estrus after artificial insemination in yearling beef heifers. In Trial 1 crossbred yearling heifers (n = 208) were synchronized with Syncro-Mate-B (SMB) and artificially inseminated (AI) between 48 and 54 h following implant removal. Implant removal is defined as Day 1. Following AI, the heifers were randomly assigned to 1 of 2 experimental groups. Group 1 heifers were fed melengestrol acetate (MGA) daily from Day 17 to 21 at a rate of 0.5 mg/head, while Group 2 control received no exogenous progestin during this period. Synchrony of estrus was defined as the 3-d period in which the highest number of heifers expressed behavioral estrus in each group. There was no difference (P < 0.05) in the pregnancy rate during the second estrus due to MGA supplementation. More MGA-treated heifers (P < 0.01) expressed estrus in a 3-d period than the controls. In Trial 2, yearling heifers (n = 108) were synchronized with 2 injections of PGF(2alpha) (second PGF(2alpha) injection is designated as Day 1) administered 14 d apart with AI 12 h after the onset of behavioral estrus. The heifers were then randomly assigned to 1 of the following 3 treatment groups after initial AI: 1) MGA fed at 0.5 mg/head daily from Days 17 to 21; 2) norgestomet administered in 6.0-mg implants from Days 17 to 21; 3) untreated control heifers. Blood samples were collected on Day 21 and analyzed for progesterone (P(4)). Elevated P(4) (> 1 ng/ml) on Day 21 indicated pregnancy to the first insemination. Synchrony among the 3 groups of heifers was similar (P > 0.10); however, the second estrus was less (P < 0.05) variable in the MGA and norgestomet treated heifers. During the resynchronized second estrus, conception rates were not affected by progestin treatment (MGA 40%, norgestomet 64%, and control 62%; P > 0.10). However, a proportion of heifers treated MGA 10% 4 36 and norgestomet 3% 1 36 expressed behavioral estrus during second estrus even though they were diagnosed as pregnant from first service by elevated P(4) levels on Day 21. We conclude that short-term use of progestin from Days 17 to 21 following AI causes closer synchrony of estrus; however, inseminating pregnant heifers that exhibit behavioral estrus may cause abortion.

Effects of ionophore feeding and anthelmintic administration on age and weight at puberty in spring-born beef heifers.

Two hundred eighty-eight heifer calves in two 1-yr replications were used to test the hypothesis that ionophore (ION) feeding, anthelmintic (ANT) administration, or the combination (COMB) would cause heifers to express pubertal estrus at a younger age than control (CONT) heifers. Heifers were assigned randomly within three weight blocks in a randomized complete block design with a 2 x 2 factorial arrangement of treatments. A high-fiber diet was fed for 172 d during yr 1 (Y1) and 199 d during yr 2 (Y2). Monensin sodium (200mg.animal-1.d-1) was fed to ION and COMB treatments and ivermectin (200 micrograms/kg of BW) was given to ANT and COMB groups at weaning and 84 d later. Rate of gain was monitored every 21 d and diet intake was adjusted to obtain equal rates of gain across treatments. Fecal samples were collected from one-third of the heifers in each group and analyzed for internal parasite egg counts every 21 d. Serum progesterone samples taken twice weekly were used to estimate onset of puberty. There was no treatment x year interaction in any parameter measured and the data were pooled across both years. Total weight gain was similar (P > .10) for all treatments. Fecal egg output decreased (P < .01) after initial application of anthelmintic. The ANT, ION, and COMB heifers had greater (P < .05) gain:feed ratios than did CONT (.132, .142, and .148 vs .125 kg for ANT, ION, COMB, and CONT, respectively). Age and weight at puberty were different (P < .05) for ION (425 d, 351.8 kg), COMB (425 d, 349.5 kg), and ANT (424 d, 348.8 kg) compared with CONT (433 d, 362.5 kg). There was no difference (P > .10) in age and weight at puberty between COMB, ION, or ANT heifers. During Y1, but not Y2, there were a greater (P < .05) number of COMB, ION, and ANT heifers pubertal before the breeding season. Additionally, there was a tendency (P = .12) for higher first-service conception in the COMB, ION, and ANT heifers than in the CONT heifers. Final pregnancy rates among treatments were similar (P > .10).

Relationship between circulating progesterone and conception at the first postpartum estrus in young primiparous beef cows.

The objective of this study was to determine whether patterns of change in concentration of progesterone in circulation of primiparous beef cows were related to conception rates at the first postpartum estrus. Data were collected over 2 yr from crossbred primiparous 2-yr-old cows (n = 77). Cows were artificially inseminated when estrus was detected between 3 and 20 (yr 1) or 3 and 23 (yr 2) wk after parturition. Cows were exposed to intact bulls for 32 (yr 1) or 21 d (yr 2) after the periods of AI, and estrus detection also occurred during the period when natural mating occurred. After parturition, blood samples were collected twice weekly to determine time of transient (less than 1 wk) and sustained increases (more than 1 wk) in progesterone of more than 1 ng/mL of serum. Mean times from parturition to transient increase in progesterone, first estrus, conception, and sustained increase in progesterone were 91, 100, 108, and 105 d, respectively. Sixty-four percent of the cows conceived as a result of AI at the first estrus that was detected after parturition, 32% conceived at a subsequent estrus, and 4% failed to conceive. In 31.1% of the cows, a transient increase in progesterone was not detected before the first estrus after calving. Conception as a result of AI at the first estrus after calving was less if a transient increase in progesterone did not precede estrus (76 vs 41%; P < .01). These data indicate that the majority of cows have increases in progesterone before the first postpartum estrus. If the transient pre-estrus increase in progesterone occurs in postpartum cows, there seems to be an enhanced conception rate as compared with cows without the increase in progesterone before their first estrus following parturition.

Weight gain and reproductive performance of spring-born beef heifer calves intraruminally administered oxfendazole.

The effect of oxfendazole (Synanthic) on weight gain and reproductive performance of spring-born heifer calves was evaluated at five locations (IL, IN, MI, MO, ND). Three hundred thirty-eight mixed-breed beef heifers (293.4 kg) blocked by weight and age were randomly allotted to one of two treatments. Treatment 1 heifers were dewormed via intraruminal injection of oxfendazole. Treatment 2 heifers served as a control. Heifers were comingled during the winter phase in semi-confinement during the period from late January to late May (winter phase). Heifers were sorted by treatment at the beginning of the grazing season (approximately May 24, 1991) and remained separate until the end of the study (approximately July 31, 1991; summer phase). Dewormed heifers received oxfendazole (4.5 mg/kg BW) in late January and again 28 and 56 d after the beginning of the grazing season. Fecal samples were taken every 21 d from January through September and assayed for gastrointestinal parasite eggs. Fecal egg counts were similar across treatments at the beginning of the trial (P = .34). Deworming decreased fecal egg counts throughout the trial. Twenty-eight days after initial deworming a significant treatment effect on fecal egg counts was observed (P < .01). Winter ADG was significantly higher (P < .01) for dewormed heifers than for controls (.60 vs .52 kg, respectively). Summer ADG was not different between treatments. Dewormed heifers were 7.4 kg heavier than controls (P < .05) at the end of the trial. Age of puberty was not affected by treatment (P = .64). First-service conception and final pregnancy rates were not different between treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive response of yearling beef heifers to a melengestrol acetate-prostaglandin F2 alpha estrus synchronization system.

A study was designed to evaluate estrus response and fertility after treatment with melengestrol acetate (MGA) and prostaglandin F2 alpha (PGF2 alpha) in yearling beef heifers. Three hundred four heifers at three locations were allotted to one of two treatments: Treatment 1 served as a nonsynchronized control (CON); and heifers in Treatment 2 received .5 mg of MGA.animal-1.d-1 for 14 d and 25 mg of prostaglandin F2 alpha (PGF2 alpha) 17 d after MGA (MGA-PGF). Heifers in CON and MGA-PGF groups were artificially inseminated 12 h after observed estrus for 21 and 6 d after PGF2 alpha, respectively. Blood samples were collected from each heifer 10 d before and on the day MGA feeding began and 10 d before and on the day PGF2 alpha was administered. Heifers with concentrations of serum progesterone greater than 1 ng/mL on either date before administration of MGA or PGF2 alpha were considered pubertal. More (P = .02) prepubertal heifers that received MGA attained puberty by initiation of breeding than did CON heifers (72 vs 45%, respectively). The proportion of heifers that displayed estrus within 6 d after PGF2 alpha was greater (P less than .001) for MGA-PGF than for CON heifers (77 vs 25%, respectively) but was also influenced by location (P = .03). Conception rate at first service for MGA-PGF heifers that attained puberty during MGA feeding and before PGF2 alpha was not different (P = .50) from that of CON that attained puberty during the same period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a prostaglandin F2 alpha injection 96 hours after introduction of intact bulls on estrus and calving distribution of beef cows.

Most estrus synchronization schemes facilitate the use of artificial insemination; however, combining estrus synchronization with natural service also offers several benefits to beef producers. This experiment was designed to study the effectiveness of one injection of prostaglandin F2 alpha (PGF2 alpha) 96 h after introduction of intact bulls on estrus synchronization and calving distribution of beef cows and heifers. Three hundred sixty beef cows and 45 beef heifers in seven trials were allotted by age, breed, and prior calving date to one of two treatments. Within each subclass, one group was injected with an appropriate dose of PGF2 alpha and the second group at each location received 5 ml of saline (SAL). Cows were classified as estrual or anestrual at the start of breeding based on serum progesterone levels and were observed for behavioral estrus regularly during the first 25 d of the breeding season in two of the trials (d 0 = day before bull turn-in). Pregnancy data and calving dates were recorded in each of the studies. All cows were palpated per rectum for pregnancy approximately 70 d after the introduction of bulls. During d 5 to 9 after treatment, the percentage of cows exhibiting behavioral estrus (P = .02) and the pregnancy rate (P = .02) obtained was greater for PGF2 alpha-treated cows than for SAL-treated cows. There were 6.5% more (P = .05) calves born during the overall calving period from animals treated with PGF2 alpha compared with those in the SAL group. In summary, treatment of cows and heifers with PGF2 alpha 96 h after bull turn-in was effective in synchronizing behavioral estrus of beef cows and heifers and increasing the calving rate during the subsequent calving season.