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Department of Animal Science
University of Minnesota
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Beef Cattle Research Abstracts

- 2007 -

Evaluation of human chorionic gonadotropin (hCG) as a replacement for GnRH in an ovulation - synchronization protocol before fixed timed AI

M.G. Burns¹, B.S. Buttrey¹, D.R. Eborn¹, J.E. Larson², B.J. Lovaas², G.C. Lamb², K.C. Olson¹, and J.S. Stevenson¹

Two experiments were conducted to evaluate differences between GnRH and hCG given at the beginning of a timed AI protocol and their effects on fertility. In Exp. 1, beef cows (n = 680) at 6 locations were assigned randomly to treatments based on parity, BCS, and days postpartum. On d –20, and –10, blood was collected to determine progesterone (P4) concentrations and assess cyclicity. Blood also collected for P4 analysis at each subsequent handling of 113 cows. Cattle were treated on d –10 with 200 μg of GnRH or 1,000 IU of hCG and CIDR insert (CO-Synch + CIDR). An injection of PGF_2α (PGF) was given and CIDR inserts were removed on d –3. Cows were inseminated at 62 h (d 0) after CIDR insert removal. Pregnancy was diagnosed at 33 d (range of 32 to 35) after AI to determine pregnancy rate (PR). For cows that were pregnant after the first AI, a second pregnancy diagnosis was conducted 35 d (range of 33 to 37) after the first diagnosis to determine pregnancy survival. In Exp. 2, cattle were assigned randomly to 3 treatments, balanced across 2 treatments applied in Exp. 1. Cows were injected (same doses as in Exp. 1) with GnRH, hCG, or saline 7 d before first pregnancy diagnosis in Exp. 1. Injection of hCG reduced (P < 0.001) PR compared with GnRH (see table), whereas P4 was greater (P = 0.06) 7 d after hCG or GnRH (4.4 vs 3.2 ng/mL). At the time of pregnancy diagnosis, cattle found not pregnant (n = 360) were given PGF and inseminated 56 h later, concurrent with a GnRH injection. Injections of GnRH (n = 107) and hCG (n = 114), compared with saline (n = 107), tended (P = 0.07) to reduce PR at second AI (33, 31, and 41%), respectively. Concentrations of P4 did not differ among GnRH, hCG, or saline 7 d after treatment at pregnancy diagnosis. We concluded that hCG compared with GnRH given before first timed AI reduced PR (Exp. 1). Neither GnRH nor hCG may be necessary to initiate a CO-Synch protocol for cows identified not pregnant at 33 d after first timed AI (Exp. 2).

¹Kansas State University
²University of Minnesota

Effects of human chorionic gonadotropin (hCG) and gonadotropin releasing hormone (GnRH) on follicle and corpus luteum dynamics and concentrations of progesterone in pre-pubertal Angus heifers

C.R. Dahlen¹, J.E. Larson², G. Marquezini², and G.C. Lamb²

We determined the effects of administering human chorionic gonadotropin (hCG) on subsequent follicle and corpus luteum dynamics and concentrations of progesterone in pre-pubertal heifers. Forty-seven purebred, pre-pubertal Angus heifers were stratified by age and weight and assigned randomly to one of three treatments: 1) heifers received a 100 μg injection of GnRH (GnRH; n = 16); 2) heifers received a 1,000 IU injection of hCG (H1000; n = 16); and 3) heifers received a 500 IU injection of hCG (H500; n = 15). From d -1 to 9 relative to treatment daily blood samples were collected to determine concentrations of progesterone and ovaries of each heifer were examined daily by transrectal ultrasonography using a 7.5Mhz transducer. Diameter of all follicles larger than 5 mm and all corpora lutea (CL) were measured and recorded. A greater percentage (P < 0.05) of heifers in the H1000 treatment (87.5%) ovulated compared with GnRH heifers (43.8%), whereas H500 heifers (73.7%) were intermediate. A greater percentage (P < 0.05) of H1000 (87.5%) and H500 (73.3%) heifers developed a CL compared with GnRH heifers (18.8%). The largest follicle present on ovaries of H1000 and H500 heifers was smaller (P < 0.05) from d 2 to 5 than that of GnRH heifers. Heifers treated with H1000 (1.72 ng/ml) had peak concentrations of progesterone that were greater (P < 0.05) than H500 heifers (1.34 ng/ml), which were greater (P < 0.05) than heifers treated with GnRH (0.31 ng/ml). Mean volume of luteal tissue was greater (P <0.05) in H1000 heifers (1.54 cm3) than in H500 heifers (1.15 cm3), which was greater (P< 0.05) than in heifers treated with GnRH (0.23 cm3). We concluded that hCG was more effective than GnRH in its ability to ovulate follicles, increase volume of luteal tissue in the subsequent developing CL and concentrations of progesterone in pre-pubertal heifers. In addition, hCG appears to be more effective when administered at 1,000 IU than 500 IU. Concentrations of progesterone peaked on d 6 for all treatments.

¹Northwest Research and Outreach Center, University of Minnesota, Crookston
²North Central Research and Outreach Center, University of Minnesota, Grand Rapids

Effects of feeding polyclonal antibody preparations against Streptococcus bovis and Fusobacterium necrophorum on rumen in situ starch and fiber disappearance

N. DiLorenzo¹, G.I. Crawford², D. Blini¹, and A. DiCostanzo¹

Avian-derived polyclonal antibody preparations (PAP) against Streptococcus bovis (PAP-Sb) or Fusobacterium necrophorum (PAP-Fn) were effective in reducing counts of target bacteria and improving feed efficiency of steers fed high-grain diets. Sixteen rumen-cannulated steers fed high-grain diets were used in a completely randomized design with a 2 X 2 factorial arrangement of treatments (PAP-Sb or PAP-Fn) to test effects of PAP on rumen in situ starch and fiber fraction disappearance. Diet (DM basis) fed once daily ad libitum was comprised of 83% corn grain, 12% corn silage and 5% supplement, and was formulated to contain (DM basis; 1.39 Mcal NE_g/kg DM, 12.5% CP, 0.65% Ca, and 0.35% P). The supplement delivered 300 mg monensin/d and 90 mg tylosin/d. Polyclonal antibody preparations were top-dressed. No effects were observed on rumen in situ starch disappearance at 3 or 9 h post-incubation. A PAP-Sb x PAP-Fn interaction (P = 0.04) was observed for rumen in situ starch disappearance at 6 h post-incubation. Steers receiving PAP-Sb had lesser (P < 0.05) rumen in situ starch disappearance at 6 h post-incubation than those receiving both or no PAP (45.7 % vs. 52.6 % and 54.2 % for PAP-Sb, both or control respectively). Steers receiving PAP-Sb tended (P = 0.06) to have lesser rumen in situ starch disappearance than those receiving PAP-Fn. No differences were observed in rumen NDF or ADF in situ disappearance after 24 h post-incubation. Previously documented reductions in rumen S. bovis counts observed in this study when feeding PAP-Sb are likely responsible for the reduced rumen in situ starch disappearance at 6 h post-incubation. However, this effect is transient as rumen in situ starch disappearance at 9 h post-incubation was similar among treatments.

¹University of Minnesota, St. Paul
²University of Minnesota Extension Regional Center, Hutchinson

Effects of feeding a polyclonal antibody preparation against selected rumen bacteria on rumen pH of lactating dairy cows

N. Di Lorenzo, C.R. Dahlen, J.E. Larson, R. K. Gill, and A. DiCostanzo

A series of experiments were conducted to evaluate the effects of feeding an avian-derived polyclonal antibody preparation against selected proteolytic, amylolytic and Gram – bacteria (RMT) on rumen pH of lactating dairy cows. Exp 1: 13 rumen cannulated dairy cows in late lactation were used in a cross-over design consisting of a 13-d adaptation period followed by 1 d of sample collection. Cows were fed a basal diet containing 1.72 Mcal NE_l/kg DM, 17.5% CP, 0.65% Ca and 0.35% P. Cows received 10 mL RMT or a preparation made with generic eggs (Control) daily top-dressed at 0900. Rumen pH was measured at 0, 2, 6 and 8 h post feeding on d 14. Exp 2: A batch culture incubation was done using rumen fluid from early lactation donor dairy cows supplemented with RMT or Control (10 ml/d) for 13 d. Flasks (250 mL) were incubated at 39°C with 10% glucose added as substrate. Each flask received 0.5 mL of RMT or Control, and pH was measured over time. Exp 3: Four rumen cannulated dairy cows in early lactation were used in a cross-over design with two 3-d pH-monitoring periods. Cows received 250 mL of RMT or Control solution on d 0 through the rumen cannula. During days -1 to 1, rumen pH was recorded every 20 min by means of an indwelling pH electrode. Exp 1: No significant effects (P > 0.05) of RMT were observed in rumen pH of late lactation dairy cows. Exp 2: pH at 4.5 h (6.04 vs. 5.85) and 6 h (5.20 vs. 5.08) of incubation was greater (P < 0.05) in flasks infused with RMT. Exp 3: mean daily rumen pH (6.07 vs. 5.75) and mean daily maximum rumen pH (6.82 vs. 6.36) were greater (P < 0.05) for cows receiving RMT. Mean daily minimum rumen pH tended (P = 0.06) to be greater for cows receiving RMT (5.48 vs. 5.06). Feeding an avian-derived polyclonal antibody preparation against specific rumen microorganisms was effective at maintaining a greater rumen pH in early lactation dairy cows; this finding may have positive implications on health and performance of dairy cows.

In vitro release of ammonia nitrogen from various nitrogen sources in batch culture

N. Di Lorenzo, and A. DiCostanzo
University of Minnesota, St. Paul

An experiment was designed to evaluate the kinetics of NH₃-N release in batch culture. Rumen fluid was collected from an Angus steer fitted with a rumen cannula at 0900 h prior to feed delivery. The steer was adapted (> 30 d) to receive a diet of 95% corn silage and 5% protein supplement (DM basis). Batch cultures were conducted in 250-mL flasks fitted with a one-way rubber valve, which were inoculated with a 1:4 solution of rumen fluid:nutritive solution. Treatments (sources of N) were: blank (BLK; no N source added), Nitroshure™ (NTS; Balchem Encapsulates, New Hampton, NY), soybean meal (SBM), biuret (BIU), urea (URE), or Fermenten® (FER, Church & Dwight Co., Inc, Princeton, NJ). All flasks except BLK received equal amounts of N (155 mg; equivalent to 2 g of SBM) based on their N content. Ammonia N in rumen fluid was measured at 0, 0.5, 2, 4, 6, 8, 12 and 24 h. The study was analyzed as a completely randomized design with 8 replicates per treatment, and repeated measures over time. A significant treatment x time interaction was observed (P < 0.01). From 4 to 24 h, URE led to greatest (P < 0.05) NH₃-N release, and greater (P < 0.01) NH₃-N release when compared to that elicited by NTS at all times. From 4 to 24 h, BIU had the lowest (P < 0.05) NH3-N concentrations of all the NPN sources, demonstrating the reduced biuretase activity in the rumen of cattle not adapted to biuret. During the first 2 h, FER had the greatest (P < 0.05) NH₃-N release. The release of NH₃-N by FER was greater (P < 0.01) than NTS, BIU, SBM and BLK at all times. The patterns of NH₃-N release by the sources of N tested in vitro showed marked differences. Synchrony between rumen carbohydrate fermentation rates and release of NH₃ is one of the primary goals to maximize microbial crude protein synthesis. Thus, choosing the source of N that best matches the carbohydrate fermentation profile may improve animal performance.

Fixed-time artificial insemination in replacement beef heifers after treatment with human chorionic gonadotropin (hCG), progesterone, and prostaglandin F2α

G.C. Lamb¹, J.E. Larson¹, C.R. Dahlen², and G. Marquezini¹

We determined whether pre-treatment with human chorionic gonadotropin (hCG) 14 d prior to estrous synchronization or replacing GnRH with hCG at the time of CIDR insertion would alter pregnancy rates in replacement beef heifers estrous synchronized with the CO-Synch + CIDR protocol. Five hundred forty seven replacement beef heifers originating from four herds were assigned randomly to one of four treatments in a 2 x 2 factorial design: 1) heifers received a 100 μg injection of GnRH at CIDR insertion (d -7) and a 25 mg injection of PGF_2α at CIDR removal (d 0), followed in 54 h by fixed-time AI (TAI) with a second injection of GnRH (CG; n = 160); 2) CG but the first injection of GnRH was replaced with a 1,000 IU injection of hCG (CH; n = 158); 3) CG, plus heifers received a 1,000 IU injection of hCG 14 d prior to CIDR insertion (HG; n = 116); and 4) CH, plus heifers received a 1,000 IU injection of hCG 14 d prior to CIDR insertion (HH; n = 113). Blood samples were collected on d -24, -14, -7, 0, 2 to determine concentrations of progesterone. Transrectal ultrasonography was used to monitor ovarian structures on d -7 and 0, plus pregnancy status on d 35. Pregnancy rates differed (P < 0.01) among herds. Between pre-treatment factors of control or hCG pregnancy rates were similar, whereas for the factor of GnRH or hCG at CIDR insertion pregnancy rates for the GnRH treated heifers (41%) was greater (P < 0.05) than hCG treated heifers (29%). Heifers treated with hCG had an increased (P < 0.05) occurrence of multiple corpora lutea (38.3% vs. 24.0%) at the time of CIDR removal and had increased concentrations of progesterone at the time of CIDR removal (2.68 ng/ml vs 2.10 ng/ml; P < 0.05) and at TAI (0.56 ng/ml vs. 0.39 ng/ml; P < 0.05). We concluded that presynchronization with hCG 14 d prior to CIDR insertion failed to enhance pregnancy rates and replacing GnRH at CIDR insertion with hCG resulted in decreased pregnancy rates. However, hCG enhanced the incidence of multiple ovulations and concentrations of progesterone at CIDR removal and at TAI.

¹North Central Research and Outreach Center, University of Minnesota, Grand Rapids
²Northwest Research and Outreach Center, University of Minnesota, Crookston

Artificial insemination of superovulated Angus cows using sexed or conventionally frozen semen

G.C. Lamb¹, B.J. Lovaas¹, S.L. Bird¹, A. Martins¹, J.E. Larson¹, J.C. Rodgers¹, D.J. Frank², and D.M. Williams²

We determined whether embryo production characteristics would be compromised in a superstimulation protocol when sexed semen was utilized for insemination of donors. Thirty two, Angus cows from a single herd stratified by age and body condition score before random assignment to a switch-back experimental design: 1) cows received four inseminations of conventionally frozen semen at a minimum concentration of 15 × 106 sperm/straw (Conventional; n = 32); and 2) cows received four inseminations of sexed semen at a minimum concentration of 2.1 × 106 sperm/straw (Sexed; n = 32). Cows were blocked by two separate AI sires. During period 1, 10 d after the marker heat, eight 2× daily injections of FSH were administered to the cows, with cows receiving PGF at the time of the seventh injection of PGF. Cows were inseminated 1× at the time of first detected estrus, 2× 12 hr after onset of estrus, and 1× 24 hr after onset of estrus. Embryos were collected 7 d after first detected estrus and all embryos were assigned a developmental stage and quality grade. After a 30 d adaptation interval, period 2 was initiated and cows were resynchronized and superovulated using the same protocol as for period 1. The total ova per flush was similar between Conventional (11.7 ± 1.8) and Sexed treatments (12.0 ± 1.6), but the number of transferable embryos was greater (P < 0.01) for Conventional (6.5 ± 1.0) than Sexed (4.5 ± 0.9) treatments. In contrast, the mean number of unfertilized ova was greater (P < 0.05) for Conventional (3.1 ± 1.2) and Sexed (6.3 ± 1.0) treated cows. The number of degenerate, Grade 2, and Grade 3 embryos were similar among treatments. There were no differences between Bull 1 (44.4%) and Bull 2 (46.7%) in the percentage of transferable embryos recovered. However, fertilization rates and the percentage of transferable embryos where affected (P < 0.05) by period and donor. We concluded that insemination of superstimulated donor cows with sexed semen will result in lower transferable embryos and an increase in unfertilized ova than those cows inseminated with conventionally frozen semen.

¹North Central Research and Outreach Center, University of Minnesota, Grand Rapids
²ABS Global, Inc.

2006

Effects of feeding a polyclonal antibody preparation against Streptococcus bovison rumen fermentation of heifers switched from a high forage to a high concentrate diet

M. Blanch¹, S. Calsamiglia¹, N. DiLorenzo², and A. DiCostanzo²

The effects of feeding a polyclonal antibody preparation against Streptococcus bovis (PAPSb) were studied in a completely randomized experiment using 12 crossbred heifers (452±20 kg BW) with two groups (6 animals each): control (CTR) and polyclonal antibody treatment (PAPSb, CAMAS Inc., MN). The acidosis induction protocol included 3 periods: 3 months of baseline (100% fescue ad libitum), 10 d adaptation (d 1-10 of the experiment, fed 100% forage + 10 mL of PAPSb top-dressed in treatment group) and 12 d of challenge feeding (d 11-22 of the experiment). The challenge consisted in increasing the concentrate (16% CP) intake 2.5 kg DM per day until 12.5 kg (achieved in 5 days) plus fescue ad libitum. The treatment group received 10 mL of PAPSb daily. Acidosis was declared when pH reached 5.5 or when concentrate intake was reduced more than 50% compared with the previous day. When an animal was considered acidotic it was taken out of the experiment. Samples of ruminal contents were collected at 0h and 6h post feeding to determine pH, and volatile fatty acid and ammonia-N concentrations. Data were analyzed using PROC MIXED of SAS (version 8.2). Differences were declared at P<0.05. PAPSb had higher pH values at 0 h post feeding in days 16 (6.70 vs 6.11), 18 (6.54 vs 5.95) and 19 (7.26 vs 6.59) compared with CTR. PAPSb had higher concentration of acetic acid at 6h post feeding (81.8 vs 90.3 mM for CTR and PAPSb, respectively) and higher total volatile fatty acid concentration (132.9 vs 147.1 mM for CTR and PAPSb, respectively). These results indicate that PAPSb may be effective in reducing acidosis when heifers are abruptly adapted from a high forage to a high concentrate diet.

¹Universitat Autonoma de Barcelona, Bellaterra, Spain
²University of Minnesota, St. Paul

Effects of feeding polyclonal antibody preparations against Streptococcus bovis or Fusobacterium necrophorum on target bacteria populations and pH of steers fed high-grain diets

N. Di Lorenzo, F. Diez-Gonzalez, J.E. Larson, and A. DiCostanzo
University of Minnesota, St. Paul

Three factorial experiments were designed to test the efficacy of avian-derived polyclonal antibody preparations (PAP) against Streptococcus bovis (PAPSb) or Fusobacterium necrophorum (PAPFn) in reducing rumen counts of target bacteria in steers fed high-grain diets with or without feed additives (FA; 300 mg monensin/hd/d and 100 mg tylosin/hd/d). Sixteen rumen cannulated steers were fed a diet comprised of 83% corn grain, 12% corn silage and 5% supplement on DM basis. Diet supplied 1.39 Mcal NE_g/kg DM, 12.5% CP, 0.65% Ca, and 0.35% P. Polyclonal antibody preparations were top-dressed. In Experiment 1, feeding increasing doses of PAPSb reduced S. bovis counts in a cubic response (P < 0.05). Inclusion of FA had no effect (P > 0.15) on rumen S. bovis counts. Counts of F. necrophorum were reduced (P < 0.05) by feeding FA. Feeding PAPSb or FA alone had no effect (P > 0.15) on rumen S. bovis counts, but feeding PAPSb and FA reduced (P < 0.05) rumen S. bovis counts relative to feeding either FA alone (Experiment 2). Rumen pH was greater (P < 0.05) in steers fed PAPSb, FA or both. In Experiment 3, rumen F. necrophorum counts were reduced (P < 0.05) by feeding PAPFn, FA or both. When feeding PAPFn and FA together, counts of F. necrophorum were greater (P < 0.05) than when feeding FA alone. Counts of S. bovis or rumen pH were not affected (P > 0.15) by feeding PAPFn. Total anaerobic counts were not affected (P > 0.15) by feeding either PAP (Experiments 1 and 3). In conclusion, avian-derived PAP were effective in reducing rumen counts of target bacteria. Specificity of the PAP was demonstrated as they did not affect counts of other rumen bacteria measured. Thus, PAP against S. bovis or F. necrophorum could be effective in preventing the pathogenic situations associated with these bacteria, and perhaps enhance animal performance.

Impact of feeding distillers grains on beef tenderness and sensory traits

R.K. Gill¹, D.L. Roeber-VanOverbeke², and A. DiCostanzo¹

Consumers expect quality and wholesome beef, but knowledge regarding quality and sensory traits of beef from cattle fed distillers grains (DG) are limited. Therefore, strip loins from each of the studies conducted at the University of Illinois (Exp. 1) and Iowa State University (Exp. 2) were collected by University of Minnesota personnel to determine the effect of feeding DG on beef quality and sensory traits. Treatment groups evaluated from Exp. 1 were: whole corn-corn silage-soybean meal control, 12.5% dry distillers grains (DDG) plus urea, 25% DDG, 50% DDG, 25% wet distillers grains (WDG), and 50% WDG, while those evaluated from Exp. 2 were: urea control, soybean meal control, 10% DDG, 20% DDG, 40% DDG, 10% WDG, 20% WDG, and 40% WDG. Strip loins from each of four steers in four replicate pens per treatment were tagged, collected post-fabrication, and aged for 13 d at 21°C for subsequent color, tenderness, and palatability evaluation. Color of steaks was measured objectively by using a HunterLab Miniscan XE spectrophotometer and was subjectively measured by a trained panel. Tenderness was measured on a steak from each strip loin at one degree of doneness (70°C) using the Warner-Bratzler shear force instrument. Steaks were thawed for 24 h at 0°C, cooked to 70°C, cooled to room temperature, and then six to ten 1.25 cm cores were removed from each steak parallel to the muscle fiber for shear evaluation. For sensory evaluation, ninety-five consumers evaluated tenderness, flavor, and juiciness in cooked steaks. Panelists evaluated 14 steak samples using a nine-point, end-anchored hedonic scale (1=dislike extremely and 9=like extremely). In Exp. 1, the objective evaluation showed that the 25% WDG treatment had a higher a* value (P < 0.05) than for all other treatments except for the 12.5% DDG treatment. The subjective evaluation in Exp. 2 for the 40% DDG and the 40% WDG treatment groups had a higher percentage (P < 0.05) of steaks that were considered 'moderately unacceptable' than the soybean meal, urea, 10% DDG, 10% WDG, and 20% WDG treatment groups. In Exp. 1 and Exp. 2, no differences (P > 0.05) were documented in shear force values in comparisons within DDG or WDG treatment groups, or among all treatment groups. Shears force values for steaks in Exp. 1 averaged 1.60 ± 1.35 kg and steaks in Exp. 2 averaged 1.60 ± 1.33 kg. Similar to shear force results, there were no differences (P > 0.05) in tenderness, flavor, or juiciness attributes in comparison within DDG or WDG treatment groups, or among all treatment groups. In Exp. 1, steaks averaged 5.7 ± 2.1 for tenderness, 6.0 ± 1.9 for flavor, and 5.6 ± 2.1 for juiciness. Steaks in Exp. 2 averaged 6.2 ± 2.1 for tenderness, 6.2 ± 1.8 for flavor, and 5.8 ± 2.0 for juiciness. We conclude that there was no detrimental impact on shear force or sensory characteristics when DG were fed to dairy-breed steers; therefore, DG may be a viable feed alternative for cattle feeders.

¹University of Minnesota, St. Paul
²Oklahoma State University, Stillwater

Effects of estrous synchronization with a CIDR prior to the breeding in bull-breeding herds on pregnancy rates

G.C. Lamb¹, C.R. Dahlen², K.A. Vonnahme³, G.R. Hansen⁴, J.D. Arseneau⁵, G.A. Perry⁶, J. Clement⁷, and J.D. Arthington⁸

We determined whether insertion of a CIDR prior to the breeding season enhanced pregnancy rates and altered the date of conception in suckled beef cows mated naturally. One thousand seven hundred and fifty suckled beef cows from thirteen locations were randomly assigned to one of two treatments: 1) cows received a CIDR 7 d prior to the breeding season for 7 d (CIDR; n = 866); 2) cows received no treatment (Control; n = 884). On the first day of the breeding season bulls were introduced to the herd at a rate of 15 to 25 cows per yearling bull or 20 to 30 cows per mature bull. Cows were evaluated by transrectal ultrasonography for pregnancy at 56 d and 120 d after initiation of the breeding season to determine pregnancy status and date of conception. Overall pregnancy rates ranged from 59.3 to 98.9% among the 13 locations. Pregnancy rates within the first 30 days of the breeding season were similar between CIDR (64.4%) and Control (64.7%), and overall pregnancy rates were similar between CIDR (89.7%) and Control (89.6%). The average day of conception after initiation of the breeding season was shorter (P < 0.05) for CIDR (20.1 ± 0.8 d) compared to Control cows (23.2 ± 0.8 d). Of cows conceiving during the breeding season, more (P < 0.05) CIDR cows (43%) conceived during the first ten days of the breeding season than Control cows (35%). Body condition score and parity did not affect pregnancy rates or days to conception, whereas pregnancy rates and days to conception were affected (P < 0.01) by location and days postpartum. Days to conception were similar between treatments for cows calving within 50 d of initiation of the breeding season (28.2 ± 1.0 d), whereas cows calving earlier in the calving season treated with a CIDR (16.1 ± 0.9 d) conceived earlier (P < 0.05) than Control cows (20.7 ± 0.9 d). We concluded that insertion of a CIDR prior to the breeding season failed to increase overall pregnancy rates, but did influence the average day of conception in earlier calving cows.

¹North Central Research and Outreach Center, University of Minnesota, Grand Rapids
²Northwest Research and Outreach Center, University of Minnesota, Crookston
³Department of Animal and Range Sciences, North Dakota State University, Fargo
⁴North Florida Research and Education Center, University of Florida, Mariana
⁵Department of Animal Science, Purdue University, West Lafayette
⁶Department of Animal and Range Science, South Dakota State University, Brookings
⁷Clement Cow-Calf Consulting, Mandan, North Dakota
⁸Research and Education Center, University of Florida, Ona

In vitro evaluation of various energy supplements for tropical and temperate forages

R.D.L. Pacheco¹, D.D. Millen¹, N. DiLorenzo², and A. DiCostanzo²

The objective of this study was to evaluate the effects of various energy supplements (Corn Grain, CG; Citrus Pulp, CIP; or Soy Hulls, SH) on IVDMD in two types of forages: Brachiaria decumbens (BD), a tropical forage, or Poa pratensis, (PP) a temperate grass, hay. Energy supplementation level was based on providing 0.2 % corn per kg BW for a 450-kg cow expected to consume a total of 8.1 kg DMI daily. Energy-supplemented diets were isoenergetic and formulated based on the following TDN values: CG = 92%, CIP = 81% and SH = 74%. Forage only (FOR) or forage mixed with respective supplement (DIET) in Ankom fiber bags were incubated in jars in a DaisyII Incubator (Ankom Technology Corp.). Jars containing FOR bags only were added respective supplement in the media. A set of control bags (CTL) contained forage only. Supplementation had no effect on IVDMD of the forage (P > 0.05) regardless of source. Temperate grass hay had greater (P < 0.01) IVDMD values than BD. A supplement type X forage source interaction was observed (P = 0.04) for total diet IVDMD. No differences (P > 0.05) in total diet IVDMD were observed for BD supplementation (CTL = 41.58%, CG = 40.19%, CIP = 42.38%, SH = 42.67%; SEM = 2.42), but greater (P < 0.05) total diet IVDMD values were observed for CTL and CG when compared to SH (CTL = 55.20%, CG = 55.02%, CIP = 53.00%, SH = 51.21%; SEM = 2.42). In conclusion energy supplementation effects on total diet and forage fraction IVDMD were dependent on forage type and supplemental source. At the supplementation level tested, no effect on IVDMD was observed in the forage fraction of the diet for either PP or BD. No effects were observed in IVDMD when supplementing tropical forage (BD) based diets. A reduction in total diet IVDMD was observed when supplementing a PP with soy hulls, when compared to no energy supplementation or supplemented with corn grain.

¹FMVZ/UNESP, Botucatu, Sao Paulo, Brazil,
²University of Minnesota, St. Paul

Influence of a CIDR insert after a fixed-time AI on pregnancy rates and return to estrus of nonpregnant cows

K.N. Thielen¹, J.E. Larson², B.J. Lovaas¹, D.J. Kesler³, J.S. Stevenson⁴, T.T. Marston⁴, and G.C. Lamb¹

We determined whether resynchronization of an ovulatory estrus could be accomplished in nonpregnant cows without compromising pregnancy in cows pregnant from a previous synchronized estrus or to those inseminated to the resynchronized estrus. Ovulation was synchronized in 937 suckled beef cows at 6 locations using a CO-Synch + CIDR protocol (a 100-mg injection of GnRH at the time of CIDR insertion, followed in 7 d by a 25-mg injection of PGF_2α at CIDR removal. At 60 h after PGF_2α, cows received a fixed-time AI [TAI] plus a second injection of GnRH. After initial TAI cows were assigned randomly to 4 treatments; 1) untreated (control; n = 237); 2) CIDR inserted 5 d after TAI and removed 14 d after TAI (CIDR5-14; n = 234); 3) CIDR inserted 14 d after TAI and removed 21 d after TAI (CIDR14-21; n = 232); or 4) CIDR inserted 5 d after TAI and removed 14 d after TAI and then a new CIDR inserted at 14 d and removed 21 d after TAI (CIDR5-21; n = 234). After TAI, cows were observed twice daily until 25 d after TAI for estrus and inseminated according to the AM-PM rule. Pregnancy was determined at 29 and 59 d after TAI to determine conception to first- and second-service AI. Pregnancy rates to TAI were similar for control (55%), CIDR5-14 (54%), CIDR14-21 (48%), and CIDR5-21 (53%). A greater proportion of nonpregnant cows were resynchronized during a 2-d peak period in the CIDR5-21 (76/109, 70%) and CIDR14-21 (77/119, 65%) than controls (44/106, 42%) and CIDR5-14 (39/109, 36%) cows. Although overall pregnancy rates after second AI service were similar, conception rates of nonpregnant cows detected in estrus and inseminated seemed to be compromised (P < 0.05) in CIDR5-21 (41/76, 54%) and CIDR14-21 (71/77, 53%) compared with CIDR5-14 (28/39, 72%) cows, whereas controls (29/44, 66%) were intermediate. Insertion of a CIDR 5 d after a TAI did not compromise or enhance pregnancy rates to TAI, however, conception rates were compromised in nonpregnant cows that were resynchronized with a CIDR from d 5 or 14 until 21 d after TAI.

¹North Central Research and Outreach Center, University of Minnesota, Grand Rapids
²Department of Animal Science, University of Minnesota, St. Paul
³Department of Animal Sciences, University of Illinois, Champaign
⁴Department of Animal Sciences and Industry, Kansas State University, Manhattan