PSII-7 Feed Intake and Behavioral Responses of Mature Rams Provided Feed Containing Phenylthiocarbamide

Bitter taste perception has been studied in various species, including humans, using the synthetic compound phenylthiocarbamide (PTC). Human perception of PTC is linked to the ability to taste bitter foods. Sheep express varying levels of aversion to PTC delivered in drinking water. The objective of this study was to determine the effects of PTC delivered in feed on dietary intake and behavior in mature rams. We hypothesized that rams previously classified into PTC-taster categories using PTC-spiked drinking water would rank similarly when PTC was added to feed. Mature Targhee, Rambouillet, Polypay, and composite-breed rams, previously classified as either super- (n = 3), intermediate- (n = 5), or non-PTC tasters (n = 4), were subjected to 4-d acclimation and 6-d test phases. Alfalfa (70%), corn (15%), and beat pulp (15%) meal were mixed with ethanol (150 g/kg, as fed) only (control) or PTC solubilized in ethanol (150 g/kg, as fed) to create three pelleted (6.3 mm) test diets (110, 220 and 330 mg PTC/kg feed, as fed). Rams received control and PTC diets (0.87% BW) daily for 30 min in a side-by-side presentation, which was replicated for each PTC concentration. Feeding duration, number of bucket approaches and switches, sniffs, drinks, lip smacks and licks, and head bobs, jerks, and shakes were recorded throughout the trial using video surveillance. For each PTC concentration, consumption of PTC and control diets was similar (P = 0.22) when measured as a percentage of total diet (control + PTC) consumed. Individual PTC diet intakes ranged from 1.5 to 89.8% of total diet consumed. The CV for intake of 110, 220 and 330 mg/kg diets increased from 22.4 to 34.1 to 36.1%, respectively. Intake of total diet offered decreased (P = 0.01) between 110 mg/kg (80.9 ± 3.2%) and 330 mg/kg (72.3 ± 3.2%), while 220 mg/kg (78.4 ± 3.2%) was intermediate (P ≥ 0.06). Rams were classified by average PTC diet consumption relative to ± 1.0 SD of the population mean (50.2 ± 7.5%). Using this method, only 7 of the 12 rams were classified similarly to the former classification established when PTC was added to drinking water. Total feeding duration was less (P ≤ 0.03) when rams were offered 330 mg/kg (805.4 ± 18.2 s) compared with 110 (858.1 ± 19.3 s) and 220 mg/kg (862.7 ± 19.5 s). Rams switched between the control and PTC diets more (P ≤ 0.02) when offered 110 mg/kg (21.2 ± 10.0) than the 220 (16.4 ± 7.8) and 330 mg/kg (18.4 ± 8.4). These results suggest that sheep perceive and exhibit variable responses to PTC when incorporated into a pelleted feed. More research is needed to identify mechanisms by which sheep perceive bitter-tasting feeds.

Protein Supplementation and Grazing Behavior for Cows on Differing Late-Season Rangeland Grazing Systems

Simple Summary

Cattle grazing late-season dormant rangeland are subject to impaired production due to reduced forage digestibility and a longer residence time of forage in the rumen, leading to reduced forage intake. It is a common practice to provide supplemental protein to help counteract these effects and to improve animal well-being and livestock production. Yet, the usage of supplements has been shown to interrupt and reduce the time spent grazing. These behavioral changes may vary with climate and the frequency and timing of strategic supplementation. The objective of this study was to evaluate how protein supplementation altered grazing behavior when used in both rotationally and continuously grazed dormant pastures. We utilized accelerometers (used in rockets to measure velocity in three directions and in smart phones to rotate the screen) to evaluate cattle behavior (via head movements) every 5 s on a 24 h basis. The cattle altered their grazing behavior in response to climate, supplementation status, and the grazing system. Cattle that were deprived of the protein supplement and stayed in the same continuously grazed pasture showed more restlessness in their behavior, spending more time walking from midnight to 8 a.m. Additionally, the harvest rate of dormant forage increased for the supplemented cattle.

Abstract

The objective was to determine if low- or high-residual feed intake (LRFI or HRFI, n = 24 for each) Hereford × Angus cows on continuously or rotationally grazed rangeland altered their grazing behavior when provided a protein supplement in late autumn. Treatments included continuously grazed, control (CCON, n = 12); continuously grazed, supplemented (CTRT, n = 12); rotationally grazed, control (RCON, n = 12); and rotationally grazed, supplemented pastures (RTRT, n = 12). Cows in each treatment had grazing time (GT), resting time (RT), and walking time (WLK) measured for 2 years with accelerometers. Bite rate (BR) was also measured. Time distributions of GT and RT differed by year (p < 0.05), being influenced by colder temperatures in 2016. Cattle in 2016 spent more time grazing during early morning and late evening (p < 0.05) and rested more during the day (p < 0.05). In 2017, cattle in the CCON treatment walked more (p < 0.05) during early morning time periods than did the CTRT cattle, indicative of search grazing. All supplemented cattle had greater BR (p < 0.05) than control cattle in 2017. Cattle with increased nutritional demands alter grazing behavior in a compensatory fashion when grazing late-season rangelands.

Grazing behavior and production for lactating cows differing in residual feed intake while grazing spring and summer rangeland

The objectives were to determine if previously classified, efficient (LRFI, low-residual-feed intake, n = 12 × 2 yr) vs. inefficient (HRFI, high-residual-feed intake, n = 12 × 2 yr) lactating 2-yr-old Hereford × Angus cows differed in grazing behavior, body weight (BW), body condition score (BCS), and calf weaning weight while grazing rugged rangeland pastures. Cows were fitted with grazing halters containing both an accelerometer and a global positioning system (GPS) data logger during June 14 to July 4, 2016, August 2 to 25, 2016, May 23 to June 12, 2017, and August 5 to 28, 2017. GPS data were recorded at 7-min intervals in 2016 and 4-min intervals in 2017 and accelerometer data recorded at 25 times/s. Grazing time (GT), resting, walking, bite rate (BR), daily travel distance (DTD), elevation, and slope were analyzed with a mixed model that included fixed effects of RFI group, day, and RFI group × day and cow within treatment as the random effect. Cow BW, BCS, and calf weaning weight were analyzed by analysis of variance with treatment as the main effect. There were no differences (P > 0.10) due to RFI detected for BW, BCS, or calf weaning weights. During periods of mild heat load (MHL), HRFI cows spent more (P < 0.05) time resting during the day at lower elevations (P < 0.05) than LRFI cows. During a 6-d period in spring with only 2 h MHL, HRFI cows grazed 1.7 h/d longer than LRFI cows (P < 0.05); commencing grazing earlier in the morning and extending the grazing bout later. During the summer with > MHL, LRFI cows grazed more than HRFI cows 18% of the time (P < 0.10). The HRFI cows had greater GT than LRFI cows only 3% of the time (P < 0.10) during summer. There was no difference (P > 0.10) in BR between HRFI and LRFI cattle. The DTD tended (P < 0.10) to be greater for LRFI cattle during summer 2017. Over all sample periods, HRFI had greater walking than LRFI 15% of the time and LRFI exceeded HRFI cattle for walking 3% of the time (P < 0.10). The greater walking for HRFI was assumed to be associated with more search grazing. Metabolic heat load on hot summer days for HRFI cattle is presumed to have contributed to differences observed in grazing behavior. These results suggest that lactating cows with low-RFI phenotypes appear to be better adapted to grazing rugged rangelands in late summer during periods of MHL.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F_2α (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278. Fertile bulls were placed in pastures with heifers of the three NS treatment groups for a 65-day period which began 10 days after progestin treatments (MGA or CIDR) ended. Heifers in FTAI treatment groups were administered PG (25 mg, IM) 16 days after CIDR removal or 19 days following MGA withdrawal, respectively, and FTAI was performed at 66 (CIDR-PG) or 72 h (MGA-PG) after PG. Gonadotropin-releasing hormone (GnRH; 100 μg, i.m.) was administered at FTAI. Pregnancy status was determined at the end of a 65-day breeding period. Pregnancy rates on Days 21 and 65 of the breeding period differed among treatment groups based on pre-treatment pubertal status (P ≤ 0.02) and body weight (P ≤ 0.05) but did not differ by group. These data highlight the need for continued research efforts to improve reproductive management of Bos indicus-influenced females.

Intake behaviors of yearling steers grazing irrigated pasture and receiving either a free-choice salt-based mineral or a low-moisture molasses-based tub mineral

Mineral intake in grazing cattle is highly variable and research evaluating behavioral aspects of intake are minimal. Development of the GrowSafe System to monitor feed intake allows researchers to record individual feeding behaviors of cattle 24 h per day. In the current experiment conducted during June and July, the GrowSafe System was utilized to evaluate intake behaviors of grazing steers during a short-term free-choice supplementation of either salt-based loose minerals (LM; n = 24; 408 ± 57 kg) or low-moisture molasses-based tub minerals (TUB; n = 24; 396 ± 64 kg). Each treatment was randomized to two of the four irrigated pastures (~5 ha each) consisting of orchard grass (Dactylis glomerat L.), red clover (Trifolium pretense L.), and smooth brome (Bromus inermis). Individual intake was evaluated over three 7-d periods: d – 7 to 0 (adaptation period; AP), d 1 to 7 (period 1; P1), and d 15 to 22 (period 2; P2) of the experiment. The LM mineral mix contained 28% salt during the AP and more salt was added at the initiation of P1 to prevent excessive mineral intake observed during the AP. The LM mineral mix contained 38% salt during P1 and P2. Daily bunk attendance was greater (P < 0.001) for LM (93%) than TUB (67%) steers for the AP. Whereas there was a treatment × period effect (P < 0.001) on daily bunk attendance across P1 (LM: 92%; TUB: 64%) and P2 (LM: 91%; TUB: 82%). Daily mineral intake (as-fed) was greater (P < 0.001) for LM (568 g) than TUB (283 g) during the AP. For P1 and P2, there were no treatment (P = 0.46) and period (P = 0.77) effects on daily mineral intake (LM, 370 g vs. TUB, 343 g), but LM (3.1 visits) had more (P < 0.001) bunk visits per day than TUB (2.0 visits). During the AP, LM (8.5 min) had a greater (P = 0.04) duration of mineral intake per day than TUB (5.6 min); whereas during P1 and P2, TUB (P1 = 8.6; P2 = 12.8 min) had a greater (P ≤ 0.05) duration of mineral intake per day than LM (P1 = 4.9; P2 = 5.7 min). In conclusion, mineral delivery method significantly affected bunk attendance, number of bunk visits per day, and time spent consuming mineral. These results provide additional evidence that mineral type and associated feeding behaviors contribute to the significant variation observed in daily mineral intake in grazing cattle.

Effect of increased inclusion of dried distillers grain supplement on adaptation, intake, digestibility, and rumen parameters in steers consuming bermudagrass round bale silage

Eight ruminally cannulated beef steers were used to evaluate forage intake and physiological response during adaptation to a diet consisting of bermudagrass round bale silage (RBS) and dried distillers grains (DDG) and in a second experiment the effect of level of DDG supplementation on RBS forage intake, digestibility, and rumen parameters. The adaptation experiment was designed to simulate a 14-d step-up process. Initially steers received ad libitum RBS, on d 4 steers were offered 1.13 kg of DDG daily and every 4 d daily DDG offered was increased by 1.13 kg. Blood and rumen fluid samples were collected before feeding (0 h) and 6, 12, 24 (before feeding), and 36 h after every diet change. The digestibility experiment was conducted as an 8 × 4 Latin square with four periods. Treatments included RBS only and DDG supplement levels of 0.33%, 0.66%, and 1.0% of body weight (RBS + 0.33, +0.66, and 1.0, respectively). Collection periods consisted of 21 d to determine dry matter intake [DMI], digestibility, and collect rumen fluid samples. During adaptation, level of DDG did not (P = 0.42) affect RBS DMI. Mean ruminal pH was greater (P < 0.05) for RBS only compared with diets with DDG. When steers were offered 3.39 or 4.52 kg/d of DDG rumen NH₃-N concentration was greater (P ≤ 0.05) compared with other levels of DDG or RBS alone. Mean nonesterified fatty acid and plasma urea N concentrations varied among levels of DDG offered. In the digestibility experiment forage DMI, total DMI, and total tract apparent digestibility exhibited a quadratic (P ≤ 0.05) response to level of DDG offered. Mean ruminal pH responded in a quadratic manner (P = 0.03) and was greater for RBS only compared with RBS plus DDG at any level. Mean ruminal NH₃-N concentration tended (P = 0.07) to respond in a cubic manner as DDG amount offered increased. Physiological responses during adaptation to DDG over 14 d resembled responses previously observed after long-term DDG supplementation. Offering DDG up to 1% of body weight did depress forage DMI and ruminal pH but increased total DMI, diet digestibility, and ruminal NH₃-N concentration.

Comparison of wet brewers' grains or dried distillers' grains as supplements to conserved bermudagrass forage as winter feeding options for beef cows

The objective of this study was to examine the use of 2 byproduct supplements and conserved warm-season forage as winter feeding options for primiparous beef cows. Gestating Angus ( = 48) and Brangus ( = 24) 2-yr-old cows were stratified by BW and breed to 1 of 12 pens. Pens were randomly assigned 1 of 2 supplements, wet brewers' grains (WBG) or dried distillers' grains (DDG). Coastal bermudagrass hay or round bale silage (RBS) was fed free choice (6 pens each) and cows received WBG or DDG supplements at a daily rate of 0.05% BW (DM basis) prorated for feeding 3 d/wk. Total BW and BCS changes did not differ ( = 0.65 and = 0.93, respectively) between DDG- and WBG-supplemented cows. Total amount of forage DM offered and mean calculated daily forage DM offered did not differ ( = 0.59 and = 0.20, respectively) between supplement treatments. Estimated daily mean and total supplement DM offered was greater ( < 0.001) for WBG than for DDG treatments. The same 2 supplements and forage sources were used in an unbalanced 6 × 4 design to measure intake, digestibility, and rumen parameters in ruminally fistulated steers. Supplement did not affect forage DMI of hay ( = 0.31) or RBS ( = 0.63). Total DMI was not different ( = 0.37 and = 0.73) for hay-based and RBS-based diets, respectively. Total tract digestibility tended to be greater ( = 0.06) for DDG than for WBG in hay diets but was not different ( = 0.76) for RBS diets. Daily mean ruminal pH was greater ( = 0.03) for WBG than for DDG when supplemented to hay-based diets. In RBS diets, a supplement × hour interaction ( = 0.05) existed for ruminal pH. Daily mean ruminal ammonia N concentration was greater ( < 0.001) for WBG-supplemented diets compared with DDG-supplemented diets. A supplement × hour interaction existed for ruminal ammonia in hay- ( < 0.001) and RBS- ( = 0.09) based diets. Ruminal pH and ammonia N concentrations stayed in ranges adequate to support ruminal metabolism and cattle performance. Marginal differences in ruminal measures between high-moisture and dry byproduct supplements resulted in no differences in cow performance when offered with hay or high-moisture forage. High-moisture forage sources can be coupled with high-moisture byproduct supplements.

Select Synch and Co-Synch protocols using a CIDR yield similar pregnancy rates after a fixed-time insemination in suckled Bos indicus × Bos taurus cows

Primiparous and multiparous suckled Bos indicus × Bos taurus cows were used to compare a Select Synch + controlled internal drug release (CIDR) and timed artificial insemination (AI) protocol (SSC) to a modified CO-Synch + CIDR protocol (COS). Five separate groups of cows were utilized (n = 659) and within a group, cows were allotted to two treatments on the basis of body condition score (BCS) taken 10 days before and days postpartum at CIDR insertion (Day 0). Blood samples were collected on Day -10 and 0 for assessment of circulating concentrations of progesterone to determine estrous cycling status. Cows in both treatments received intramuscular (im) GnRH (100 μg) and a CIDR inserted on Day 0. On Day 7, the SSC treatment had CIDR removed and received im PGF2α (25 mg), whereas COS treatment had CIDR removed and received im PGF2α (25 mg) on Day 7.5. In the SSC treatment, estrus was detected daily at 0700 and 1700 hours for 72 hours after PGF2α administration, and cows were artificially inseminated 8 to 12 hours after a detected estrus. Cows failing to exhibit estrus were subjected to timed-AI and received im GnRH (100 μg) 76 ± 4 hours after PGF2α administration. In the COS treatment, cows received im GnRH (100 μg) and were fixed-time artificially inseminated at 64 ± 4 hours after PGF2α administration. Although group differences (P < 0.05) existed for synchronized AI pregnancy rates, there were no significant interactions of group with any variable analyzed; hence, groups were pooled for further evaluation. Within the SSC treatment, the 72-hour estrous response was 50.6% (168 of 332). Conception rate of cows in estrus was 66.1% (111 of 168), and timed-AI pregnancy rate for nonresponders was 32.3% (53 of 164). Overall synchronized AI pregnancy rates were similar (P > 0.05) for SSC (49.4%; n = 164 of 332) and COS (47.1%; n = 154 of 327). Estrous cycling status and days postpartum did not (P > 0.05) influence synchronized AI pregnancy rates but BCS did (P < 0.05). Cows with a BCS greater than or equal to 5 had synchronized AI pregnancy rates of 50% compared to 39% for cows with BCS lesser than 5.0. In summary, the modified COS protocol yielded similar synchronized AI pregnancy rates compared to the SSC protocol, and it appears that the modified COS protocol has the potential to be an effective timed-AI protocol in suckled Bos indicus × Bos taurus cows.

Subspecies differences in early fetal development and plasma pregnancy-associated glycoprotein concentrations in cattle

Inclusion of Bos indicus genetics improves production traits of cattle maintained in hot climates. Limited information exists detailing pregnancy-specific events as influenced by variable amounts of Bos indicus genetics. Three experiments were completed to examine the effect of Bos taurus and Bos indicus genotypes on fetal size and plasma pregnancy-associated glycoprotein (PAG) concentrations. In all experiments, cows were bred by AI after synchronization of ovulation. Fetal measurements were completed by transrectal ultrasonography and plasma PAG concentrations were quantified from plasma harvested the day of each fetal measurement. In Exp. 1, fetal size and plasma PAG concentrations were measured at d 53 of pregnancy in cows composed of various fractions of Angus and Brahman (n = 9 to 21 cows/group). Fetus size was greater in cows containing >80% Angus genetics compared with cows containing <80% Angus influence (3.40 ± 0.28 vs. 2.86 ± 0.28 cm crown-rump length; P < 0.01). Plasma PAG concentrations were reduced (P < 0.01) in cows containing >80% Angus genetics when compared with their contemporaries (6.0 ± 1.5 ng/mL vs. 9.4 ± 1.5 ng/mL). In Exp. 2, fetal measurements and plasma PAG concentrations were determined at d 35 and 62 of pregnancy in Angus and Brangus cows. Breed did not affect fetus size at d 35, but Angus cows contained larger fetuses than Brangus cows at d 62 [3.0 ± 0.03 vs. 2.8 ± 0.03 cm crown-nose length (CNL; P > 0.01)]. Plasma PAG concentrations were not different between breed at d 35 and 62 (P > 0.1). In Exp. 3, fetal measurements and plasma samples were collected at d 33/34, 40/41, 47/48, and 54/55 post-AI in Angus and Brangus cows. Fetus size was not different (P > 0.05) between genotypes on d 33/34, 40/41, and 47/48. Angus fetuses were larger than Brangus fetuses at d 54/55 (2.1 ± 0.03 vs. 1.9 ± 0.03 cm CNL; P = 0.001). Plasma PAG concentrations were less in Angus than Brangus cows at each time point (average 4.9 ± 0.9 vs. 8.2 ± 0.9 ng/mL; P = 0.005). In conclusion, these studies determined that the Bos taurus × Bos indicus genotype impacts fetal size and rate of fetal development by 7 wk of gestation. Plasma PAG concentrations were increased in cattle with Bos indicus genetics in 2 of 3 studies, suggesting that genotype is one of several determinants of PAG production and secretion in cattle.

Effects of acclimation to handling on performance, reproductive, and physiological responses of Brahman-crossbred heifers

The objective of this study was to evaluate the effects of acclimation to handling on growth, plasma concentrations of progesterone (P4) and cortisol, temperament, and reproductive performance of Brahman-crossbred heifers. Over 2 consecutive years, 37 Braford and 43 Brahman x Angus heifers were initially evaluated, within 30 d after weaning, for BW and puberty status via transrectal ultrasonography and plasma P4 concentrations (d 0 and 10), and for temperament by measurements of chute score, pen score, and exit velocity (d 10 only). On d 11, heifers were stratified by breed, puberty status, temperament score, BW, and age and randomly assigned to receive or not (control) the acclimation treatment. Acclimated heifers were exposed to a handling process 3 times weekly (Mondays, Wednesdays, and Fridays) for 4 wk (d 11 to 39 of the experiment). The acclimation treatment was applied individually to heifers by processing them through a handling facility, whereas control heifers remained undisturbed on pasture. Heifer puberty status, evaluated via plasma P4 concentrations and transrectal ultrasonography, and BW were assessed again on d 40 and 50, d 80 and 90, and d 120 and 130. Blood samples collected before (d 10) and at the end of the acclimation period (d 40) were also analyzed for plasma concentrations of cortisol. Heifer temperament was assessed again on d 40 of the study. No interactions containing the effects of treatment, breed, and year were detected. Acclimated heifers had reduced (P < 0.01) ADG compared with control heifers (0.50 vs. 0.58 kg/d, respectively). Attainment of puberty and pregnancy, however, was hastened (P = 0.02 and 0.04, respectively) in acclimated heifers compared with control. Acclimated heifers had reduced chute score (P < 0.01) and concentrations of cortisol (P < 0.01) and P4 (P = 0.03; prepubertal heifers only) compared with control heifers after the acclimation period (1.37 vs. 1.84 for chute score; 37.8 vs. 50.5 ng/mL of cortisol; 0.52 vs. 0.78 ng/mL of P4). Results from this study indicated that, although acclimation to handling decreased ADG, it resulted in decreased chute score, reduced plasma concentrations of cortisol and prepubertal P4, and enhanced reproductive performance of Brahman-crossbred heifers.

Response to GnRH on day 6 of the estrous cycle is diminished as the percentage of Bos indicus breeding increases in Angus, Brangus, and Brahman×Angus heifers

Angus (n=6), Brangus (5/8 Angus x 3/8 Brahman, n=6), and Brahman x Angus (3/8 Angus x 5/8 Brahman, n=6) heifers exhibiting estrous cycles at regular intervals were used to determine if the percentage of Bos indicus breeding influenced the secretory patterns of LH in response to a GnRH treatment on Day 6 of the estrous cycle. Heifers were pre-synchronized with a two-injection PGF(2 alpha) protocol (25 mg i.m. Day -14 and 12.5 mg i.m. Day -3 and -2 of experiment). Heifers received 100 microg GnRH i.m. on Day 6 of the subsequent estrous cycle. Blood samples were collected at -60, -30, and -1 min before GnRH and 15, 30, 60, 90, 120, 150, 180, 240, 300, 360, 420, and 480 min after GnRH to determine concentrations of serum LH. Estradiol concentrations were determined at -60, -30, and -1 min before GnRH. On Day 6 and 8, ovaries were examined by ultrasonography to determine if ovulation occurred. On Day 13, heifers received 25 mg PGF(2 alpha) i.m. and blood samples were collected daily until either the expression of estrus or Day 20 for heifers not exhibiting estrus to determine progesterone concentrations. There was no effect (P>0.10) of breed on ovulation rate to GnRH as well as size of the largest follicle, mean estradiol, and mean corpus luteum volume at GnRH. Mean LH was greater (P<0.05) for Angus (7.0+/-0.8 ng/mL) compared to Brangus (4.6+/-0.8 ng/mL) and Brahman x Angus (2.9+/-0.8 ng/mL), which were similar (P>0.10). Mean LH peak-height was similar (P>0.10) for Brangus (13.9+/-3.4 ng/mL) compared to Angus (21.9+/-3.4 ng/mL) and Brahman x Angus (8.0+/-3.4 ng/mL), but was greater (P<0.05) for Angus compared to Brahman x Angus. Interval from GnRH to LH peak was similar (P>0.10) between breeds. As the percentage of Bos indicus breeding increased the amount of LH released in response to GnRH on Day 6 of the estrous cycle decreased.

Insulin-like growth factor (IGF) family genes are aberrantly expressed in bovine conceptuses produced in vitro or by nuclear transfer

Embryos produced through somatic cell nuclear transfer (NT) or in vitro production (IVP) are often associated with increased abortion and abnormalities thought to arise from disruptions in normal gene expression. The insulin-like growth factor (IGF) family has a major influence on embryonic, fetal and placental development; differences in IGF expression in NT- and IVP-derived embryos may account for embryonic losses during placental attachment. In the present study, expression of IGF-I, IGF-II, IGF-I receptor (IGF-IR), and IGF-IIR mRNAs was quantitated in Day 7 and 25 bovine embryos produced in vivo, by NT, IVP, or parthenogenesis, to further understand divergent changes occurring during development. Expression of the IGF-I gene was not detected in Day 7 blastocysts for any treatment. However, there were no differences (P>0.10) among Day 7 treatments in the amounts of IGF-IR, IGF-II, and IGF-IIR mRNA. For Day 25 conceptuses, there was higher expression of IGF-I mRNA for NT and IVP embryonic tissues than for in vivo embryonic tissues (P<0.05). Furthermore, embryonic tissues from NT-derived embryos had higher expression of IGF-II mRNA than IVP embryonic tissues (P<0.05). Placental expression of IGF-IIR mRNA was greater for NT-derived than in vivo-derived embryos (P<0.05). There were no differences in IGF-IR mRNA across all treatments and tissues (P>0.10). In conclusion, these differences in growth factor gene expression during early placental attachment and rapid embryonic growth may directly or indirectly contribute to increased losses and abnormalities in IVP- and NT-derived embryos.

Efficacy of either a single or split treatment of PGF2α after a 14 day melengestrol acetate treatment to synchronize estrus and induce luteolysis in Bos indicus×Bos taurus heifers

Two experiments evaluated a modified delivery of prostaglandin F2alpha (PGF2alpha) after a melengestrol acetate (MGA) treatment in Angus and Bos indicus x Bos taurus (BI) heifers. Experiment 1 was replicated three times with yearling BI heifers (n = 695). Heifers received MGA (0.5 mg head(-1) day(-1)) for 14 days. In Replications 1 and 2, heifers received either 25 mg of PGF2alpha im 19 days after MGA (single) or 12.5 mg of PGF2alpha im 19 and 20 days after MGA (split). In Replication 3, heifers received the same treatments, with PGF2alpha initiated either 18 or 19 days after MGA. Estrus was detected for 72 h after PGF2alpha, with AI commencing 8-12 h after a detected estrus. Heifers not observed in estrus by 72 h were timed-AI concomitant with GnRH (100 microg im). Heifers from Replication 2 (n = 146) had blood samples collected at the initial PGF2alpha and at timed-AI to determine corpus luteum (CL) regression by evaluating plasma progesterone concentrations. The interval from MGA withdrawal to PGF2alpha did not have a significant effect on any variable in Replication 3 and there were no treatment by replication effects for any variables, therefore data were pooled. Modifying the PGF2alpha treatment from a single treatment to two treatments on consecutive days increased (P < 0.05) 72 h estrous response (43.2% versus 50.1%), timed-AI (23.9% versus 33.5%) and total-AI pregnancy rates (34.5% versus 42.5%), and CL regression (79.1% versus 92.5%), respectively. In Experiment 2, yearling Angus (n = 66) and 2-year-old BI (n = 68) heifers were synchronized as per Experiment 1 (with the initial PGF2alpha 19 days after MGA). Neither breed nor PGF2alpha treatment effected (P > 0.05) 72 h estrous response, total-AI pregnancy rate, or CL regression rate. In conclusion, treating yearling BI heifers with split treatments of PGF2alpha (given on two consecutive days) improved estrous response and pregnancy rates by increasing PGF2alpha-induced luteolysis.

Synchronization of Bos indicus x Bos taurus cows for timed artificial insemination using gonadotropin-releasing hormone plus prostaglandin F2alpha in combination with melengestrol acetate

Nonlactating Bos indicus x Bos taurus cows were used in three herds to determine the efficacy of different PGF2alpha treatments in combination with GnRH and melengestrol acetate (MGA) for a timed artificial insemination protocol. The start of the experiment was designated as d 0, at which time cows were assigned a body condition score and received 100 microg of GnRH. Cows were fed MGA (0.5 x mg x cow(-1) x d(-1)) on d 1 to 7. On d 7, cows received either a single injection of PGF2alpha (Lutalyse sterile solution; 25 mg; n = 297), a single injection of cloprostenol sodium (Estrumate; 500 microg; n = 297), or half the recommended dose of PGF2alpha (12.5 mg; n = 275) on d 7 and 8. On d 10, all cows were artificially inseminated and received 100 microg of GnRH. Pregnancy rates to the timed artificial insemination (39%) were not affected by treatment, herd, or treatment x herd. There was an effect (P < 0.01) of artificial insemination sire on timed artificial insemination pregnancy rate for one herd, but not the other two herds. Herd influenced (P < 0.05) 30-d pregnancy rates, but there were no treatment or treatment x herd effects as 72.3% of the cows became pregnant during the first 30 d of the breeding season. Results indicate that the type of PGF2alpha treatment administered 7 d after GnRH did not influence timed artificial insemination pregnancy rates in nonlactating Bos indicus x Bos taurus cows.

Environmental, genetic and social factors affecting the expression of estrus in beef cows

Genetic, social and environmental factors affecting behavioral estrus were evaluated in Angus (n = 10), Brahman (n = 10) and Senepol (n = 10) cows during a PGF2alpha synchronized estrus and subsequent spontaneous estrus. Cows were equally stratified by breed to two groups of 15. Both groups were pre-synchronized with a modified two-injection PGF2alpha protocol. At the start of the experiment, cows were treated with 25 mg PGF2alpha followed by a second and third administration of 12.5 mg PGF2alpha, 11 and 12 days later to induce synchronized estrus. The subsequent estrus was designated as spontaneous estrus. Behavioral estrus data including the onset and end of estrus, estrous duration and the total number of mounts received for the synchronized and spontaneous estruses were collected using HeatWatch". Interval from the third PGF2alpha, treatment to the onset of a HeatWatch" estrus occurred earlier (P < 0.05) in Angus (31 +/- 5 h) than Brahman (53 +/- 7 h) or Senepol (53 +/- 4 h) cows, with dominant Senepol and Brahman cows taking longer to exhibit estrus after PGF2alpha than subordinate cows. The duration of the synchronized estrus tended to be shorter (P < 0.06) in Senepol (12 +/- 3 h) than in Angus (19 +/- 2 h) or Brahman (17 +/- 2 h) cows. Behavioral estrus data between the two periods were confounded by greater temperature-humidity index (THI) values during spontaneous estrus. The THI during spontaneous estrus appeared (P = 0.09) to affect the duration of estrus (9 +/- 1 h versus 16 +/- 1 h) and did affect (P < 0.0001) the total number of mounts received (8 +/- 4 mounts versus 34 +/- 4 mounts) during spontaneous estrus compared to synchronized estrus. Breed had no effect (P > 0.10) on the duration and total number of mounts received during synchronized and spontaneous estruses. In conclusion, type of estrus (synchronized or spontaneous), THI, social dominance and breed exerted significant effects on characteristics associated with behavioral estrus in beef cattle in subtropical environments.

Efficacy of an intravaginal progesterone insert and an injection of PGF2alpha for synchronizing estrus and shortening the interval to pregnancy in postpartum beef cows, peripubertal beef heifers, and dairy heifers

The objective was to test the efficacy of an intravaginal progesterone insert and injection of PGF2alpha for synchronizing estrus and shortening the interval to pregnancy in cattle. Cattle were assigned to one of three treatments before a 31-d breeding period that employed artificial insemination. Control cattle were not treated, and treated cattle were administered PGF2alpha or an intravaginal progesterone-releasing insert (CIDR) for 7 d and treated with PGF2alpha on d 6. The treatments were applied in one of three experiments that involved postpartum beef cows (Exp. 1; n = 851; 56+/-0.6 d postpartum), beef heifers (Exp. 2; n = 724; 442.5+/-2.8 d of age), and dairy heifers (Exp. 3; n = 260; 443.2+/-4.5 d of age). Luteal activity before treatment was determined for individual cattle based on blood progesterone concentrations. In Exp. 1, there was a greater incidence of estrus during the first 3 d of the breeding period in CIDR+PGF2alpha-treated cows compared with PGF2alpha-treated or control cows (15, 33, and 59% for control, PGF2alpha, and CIDR+PGF2alpha, respectively; P < 0.001). The improved estrous response led to an increase in pregnancy rate during the 3-d period (7, 22, and 36% for control, PGF2alpha, and CIDR+PGF2alpha, respectively; P < 0.001) and tended to improve pregnancy rate for the 31-d breeding period for cows treated with CIDR+PGF2alpha, (50, 55, and 58% for control, PGF2alpha, and CIDR+PGF2alpha, respectively, P = 0.10). Improvements in rates of estrus and pregnancy after CIDR+PGF2alpha, were also observed in beef heifers. Presence of luteal activity before the treatment period affected synchronization and pregnancy rates because anestrous cows (Exp. 1) or prepubertal heifers (Exp. 2) had lesser synchronization rates and pregnancy rates during the first 3 d of the breeding period as well as during the entire 31-d breeding period. The PGF2alpha, and CIDR+PGF2alpha but not the control treatments were evaluated in dairy heifers (Exp. 3). The CIDR+PGF2alpha-treated heifers had a greater incidence of estrus (84%) during the first 3 d of the breeding period compared with the PGF2alpha-treated heifers (57%), but pregnancy rates during the first 3 d or during the 31-d breeding period were not improved for CIDR+PGF2alpha compared with PGF2alpha-treated heifers. In summary, the concurrent treatment of CIDR and PGF2alpha improved synchronization rates relative to PGF2alpha alone or control. Improved estrus synchrony led to greater pregnancy rates for beef cows and beef heifers but failed to improve pregnancy rates for dairy heifers.

Effectiveness of GnRH plus prostaglandin F2alpha for estrus synchronization in cattle of Bos indicus breeding

Postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding at three locations were studied to determine the efficacy of GnRH + PGF2alpha combinations for synchronization of estrus and(or) ovulation. Cows were equally distributed to each of three treatments by body condition score at the start of the experiment (d 0). All cows received 100 microg of GnRH on d 0 and 25 mg of PGF2alpha 7 d later. The three insemination protocols included 1) AI 12 h after exhibiting estrus during d 7 to 12 of the experiment (Select-Synch; n = 197); 2) timed-AI + 100 microg of GnRH on d 9 of the experiment (CO-Synch; n = 193); 3) AI 12 h after exhibiting estrus during d 7 to 10 of the experiment. Cows not exhibiting estrus by d 10 were timed-AI and injected with 100 microg of GnRH on d 10 of the experiment (Hybrid-Synch; n = 200). The percentage of cows exhibiting estrus during d 7 to 12 of the experiment was lower (P < 0.05) for CO-Synch (17.6%) cows than for Select-Synch or Hybrid-Synch (45.2 and 33.0%, respectively) cows, which did not differ (P > 0.05). For the Select-Synch and Hybrid-Synch cows that exhibited estrus during d 7 to 10 of the experiment and were artificially inseminated, conception rates were similar across treatments (50.5%). Pregnancy rates were greater (P < 0.01) for CO-Synch and Hybrid-Synch (31.0 and 35.5%, respectively) cows than for Select-Synch (20.8%) cows. A greater (P < 0.01) percentage of cycling cows became pregnant (34.5%) than noncycling cows (25.9%) across all treatments. The CO-Synch and Hybrid-Synch synchronization protocols resulted in greater pregnancy rates compared with the Select-Synch protocol in postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding.

Ovulation and estrus characteristics in crossbred Brahman heifers treated with an intravaginal progesterone-releasing insert in combination with prostaglandin F2alpha and estradiol benzoate

Crossbred Brahman heifers (n = 60) were studied to determine the effect of a 7-d intravaginal progesterone-releasing insert (INSERT) in combination with PG (Lutalyse; 25 mg i.m.) and estradiol benzoate (EB; .5 mg i.m.) on time of ovulation and estrous behavior. In Phase I, heifers at unknown stages of the estrous cycle were assigned by BW and body condition score to one of the three treatments on d 0: 1) INSERT for 7 d and PG on d 7 (CONTROL; n = 10); 2) INSERT for 7 d, PG on d 7, and EB 24 h after INSERT removal (EB24; n = 10); or 3) INSERT for 7 d, PG on d 7, and EB 48 h after INSERT removal (EB48; n = 10). Blood samples were collected every 8 h after INSERT removal. Also, blood sampling and ultrasonography began 8 h after the onset of estrus, determined with HeatWatch devices, and every 4 h thereafter to detect ovulation. In Phase II, Phase-I treatments (n = 10/treatments) were replicated, but only behavioral estrus data were collected to minimize handling of heifers. Frequent handling of heifers did not influence (P > .1) the interval from INSERT removal to the onset of HeatWatch and visual estrus and duration of estrus, so behavioral estrus data were combined for Phases I and II. Interval from INSERT removal to HeatWatch estrus was decreased (P < .05) in EB24 (45.5 h) vs EB48 (55.9 h) and CONTROL (59.2 h). Interval from INSERT removal to ovulation differed (P < .04) between CONTROL, EB24, and EB48 (93.5, 74.5, and 78.9 h, respectively). Ovulatory follicle size was similar (P > .1) between CONTROL, EB24, and EB48 (14.4, 12.5, and 14.1 mm, respectively). Duration of estrus was similar for CONTROL, EB24, and EB48 (14.0, 15.1, and 17.6 h, respectively). No difference (P > . 1) was observed in number of mounts received between CONTROL, EB24, and EB48 (28.0, 25.7, and 39.4, respectively), but number of mounts received increased in Phase II vs Phase I (40.0 and 22.2, respectively; P < .05). In conclusion, EB hastened the interval from INSERT removal to ovulation without altering duration of estrus or number of mounts received. Frequent handling of heifers did not affect interval to first mount received after INSERT removal or duration of estrus, but it decreased the total number of mounts received.

Expression of an inter-alpha-trypsin inhibitor heavy chain-like protein in the pig endometrium during the oestrous cycle and early pregnancy

In pigs, changes in an unidentified endometrial glycoprotein, pGP30, are temporally associated with rapid trophoblast elongation and initial placental attachment on day 12 of gestation. Identification of endometrial pGP30 was undertaken through protein purification, NH2-terminal amino acid sequencing and cDNA sequencing of products generated through reverse transcription-polymerase chain reaction. Sequencing of 35 amino acids from the NH2-terminal end of pGP30 revealed that the 30 kDa glycoprotein is a cleavage product from the C-terminal region of inter-alpha-trypsin inhibitor heavy chain 4 (I alpha IH4), previously known as inter-alpha-trypsin inhibitor heavy chain-like protein. I alpha IH4 is unique compared with the three other inter-alpha-trypsin inhibitor heavy chains as it does not contain a binding site for bikunin that has serine protease inhibitory activity and is sensitive to cleavage by kallikrein. Endometrial gene expression of I alpha IH4 was detected during the oestrous cycle (days 0-18) and early pregnancy (days 10-18). Gene expression of I alpha IH4 appeared to be enhanced during the midluteal phase (days 12 and 15) of the oestrous cycle and the period of trophoblast attachment (days 12-18). Expression of I alpha IH4 was not detected in day 12 conceptus tissue mRNA. Endometrial expression of I alpha IH4 in pigs may function as an acute phase protein for protection of the uterus from the inflammatory response induced by conceptus attachment to the uterine epithelium.

Regulation of conceptus development and attachment in pigs

Implantation/placentation in domestic pigs is preceded by synthesis of oestrogen by the conceptus to maintain functional corpora lutea throughout pregnancy and a rapid morphological transformation of conceptuses from spherical to long filamentous thread-like structures. Initial conceptus expansion, reaching a metre in length, not only delineates the surface area for placental attachment, but also provides the mechanism for delivery of oestrogen to signal events necessary for placentation throughout the uterine horn. Timing for conceptus gene expression to induce trophoblast expansion and attachment in pigs is temporally associated with downregulation of progesterone receptors and increase in oestrogen receptors within the uterine epithelium. Within the confines of the uterine lumen, pig conceptuses normally do not erode or invade through the uterine epithelial surface. However, the pig conceptus possesses extensive proteolytic activity as it is highly invasive outside the uterine lumen of the pig. Initial release of oestrogen by the elongating pig conceptus induces endometrial release of cytokines and a variety of protease inhibitors. Recently, endometrial expression for the inter-trypsin inhibitor (I alpha I) family of protease inhibitors has been detected in the pig endometrium during conceptus elongation and attachment. It is possible that I alpha Is may function to inhibit trophoblast invasion and also serve as targets for adhesion molecules, such as integrins and heparin, to aid in placental attachment to the uterine epithelium.

Endometrial responsiveness to oxytocin during diestrus and early pregnancy in pigs is not controlled solely by changes in oxytocin receptor population density

These studies were performed to test the hypotheses that: 1) endometrial responsiveness to oxytocin (OT) in pig endometrium is associated with changes in OT receptor (OTr) population density resulting from corresponding regulation of OTr gene transcription, 2) endometrial responsiveness to OT is controlled solely through a mechanism involving changes in OTr population density, and 3) OTr population density and endometrial responsiveness to OT differ between diestrus and early pregnancy in pigs. In experiment 1, OTr population density and dissociation constant (Kd) in cyclic pigs were constant on Days 10-16 but increased (p < 0.05) between Days 10 and 12 of pregnancy before decreasing (p < 0.05) through Day 16. OT induced phosphoinositide (PI) hydrolysis and prostaglandin (PG) F2 alpha secretion in cyclic pigs only on Day 16 (p < 0.05), and during pregnancy only on Day 12 (p < 0.05). Activation of G protein by aluminum fluoride (AIF4-) treatment maximally stimulated (p < 0.05) PI hydrolysis and PGF2 alpha secretion in cyclic pigs on all days, indicating that downstream from the OTr, the PGF2 alpha secretory pathway was fully functional. During pregnancy, PI hydrolysis and PGF2 alpha secretion in response to AIF4- decreased (p < 0.01) on Days 14 compared to Days 10 and 12, and AIF4- did not stimulate PGF2 alpha release on Day 16. In experiment 2, abundance of OTr mRNA in cyclic pigs decreased between Days 0 and 5 before increasing between Days 5 and 12 (p < 0.05), but it was higher (p < 0.05) on Days 10-15 of pregnancy than on equivalent days in cyclic gilts. These results indicate that control of PGF2 alpha secretion in cyclic pigs appeared to occur primarily at the level of OTr coupling to G protein because changes in OTr number were not associated with increased sensitivity to OT or G-protein activation by AIF4-. During pregnancy, control was exerted at multiple levels, which included the OTr, G protein, phospholipase C, and subsequent aspects of the secretory pathway. The present study also indicated that endometrium was responsive to OT during luteolysis in cyclic pigs but not during corpus luteum maintenance in pregnant pigs.

Ontogeny of elongation and gene expression in the early developing porcine conceptus

Early porcine conceptus development is characterized by rapid trophoblastic elongation between Days 11 and 12 of pregnancy, a period of embryonic loss in the pig. Growth factors and steroids secreted by the conceptus and uterus, as well as ligand receptors produced by the conceptus, are thought to regulate trophoblastic elongation. Therefore, the objectives of this study were to characterize conceptus gene expression for the steroidogenic enzymes 17alpha-hydroxylase and aromatase and the mesodermal marker brachyury, as well as the expression of receptors for fibronectin (integrin beta-1), progesterone, estrogen, oxytocin, prostaglandin F2alpha, and leukemia inhibitory factor (LIF), prior to and during trophoblastic elongation. Total RNA was extracted from individual conceptuses from Day 10 to Day 12 of pregnancy. Gene expression was determined by reverse transcription polymerase chain reaction on conceptuses having 2- to 4-, 5-, 6-, 7-, 8-, 9-, and 10- to 12-mm spherical, 13- to 25-mm tubular, and > 100-mm filamentous morphologies. There was a stage of development effect on both 17alpha-hydroxylase (p < 0.001) and aromatase (p < 0.003) gene expression. Initial 17alpha-hydroxylase gene expression was detected in early spherical conceptuses (2-4 mm), increasing abruptly through to 7-mm conceptuses. Aromatase gene expression increased dramatically in 6- to 7-mm conceptuses, with increased expression throughout development. Gene expression for LIF receptor (LIFR) (p < 0.02) was similar to that for 17alpha-hydroxylase, while brachyury gene expression began in 6-mm conceptuses and increased (p < 0.001) throughout development. Integrin beta-1 was expressed at all stages of development. Conceptus gene expression was not detected for progesterone, estrogen, oxytocin, and prostaglandin F2alpha receptors. Prior to elongation, dynamic changes in gene expression are occurring that appear to be associated with estrogen production and preparation of the conceptuses for elongation. LIFR expression is highly associated with steroidogenic enzyme production with an initial peak preceding rapid trophoblastic elongation, suggesting that LIF may be involved in early conceptus development in the pig.

Detection of transcripts for retinoic acid receptors, retinol-binding protein, and transforming growth factors during rapid trophoblastic elongation in the porcine conceptus

Early conceptus development (Days 10-12) in the pig is characterized by rapid remodeling and elongation of the trophoblastic membrane. Endometrial synthesis and secretion of retinol-binding protein (RBP; transporter of retinol) into the uterine lumen parallels the rapid morphological transformation of the conceptus. Hence, retinoic acid, a powerful morphogen, may serve a critical function in trophoblastic remodeling and conceptus elongation through the various isoforms of retinoic acid receptor (RAR). We hypothesize that various transcripts for RAR will be expressed, possibly differentially, in the early developing porcine conceptus on Days 10-12 of gestation. Conceptuses were collected from pregnant gilts and individually frozen in liquid nitrogen after classification for morphological size. A total of 36 conceptuses (4 groups of 9) representing spherical (2-9 mm), early tubular (10-12 mm), late tubular (13-60 mm), and filamentous (> 100 mm) morphologies were assembled for qualitative assessment of mRNA for RAR alpha, RARbeta, RARgamma, RBP, and transforming growth factor beta (TGFbeta)-2 and -3 with reverse transcription polymerase chain reaction (RT-PCR). RBP gene expression was affected by stage of conceptus development (p < 0.05) as RBP expression increased in a linear fashion from 2-mm to 8-mm spherical conceptuses, decreased slightly in the tubular stage, and increased dramatically in filamentous conceptuses. RAR alpha, RARbeta, and RARgamma gene expression was evident at all stages of conceptus development. RAR alpha gene expression increased (p < 0.05) in a linear fashion from 2- to 8-mm spherical conceptuses, and expression plateaued in the 9- to 12-mm conceptuses. Expression of RAR alpha declined slightly at the tubular stage but dramatically increased in filamentous conceptuses. RARbeta gene expression was present across all stages of conceptus development although in diminutive amounts. RARgamma gene expression was evident in all stages of conceptus development but was not affected (p > 0.05) by developmental stage. Gene expression for TGFbeta-2 was not detected by RT-PCR at any stage of conceptus development, whereas TGFbeta-3 expression increased (p < 0.05) from the 2- to 8-mm conceptuses and remained high throughout trophoblastic elongation into the filamentous stage. The presence of mRNA for the RAR alpha, RARbeta, and RARgamma in elongating porcine conceptus provides evidence that RAR, particularly RAR alpha, may function as an important acceptor for retinoic acid and possibly regulate gene expression prior to and during rapid trophoblastic elongation in the porcine conceptus.

Persistence of the dominant follicle during melengestrol acetate administration and its regression by exogenous estrogen treatment in beef cattle

Experiments were conducted to test the hypothesis that estrogen treatment will regress a persistent dominant follicle developed during melengestrol acetate (MGA) treatment in the absence of a functional corpus luteum (CL) with normal fertility following development and ovulation of a newly recruited follicle. In Exp. 1, nonlactating beef cows (n = 31) were administered .5 mg.cow-1.d-1 of MGA (d 0) for 14 d with 25 mg of prostaglandin F2 alpha (PGF2 alpha) administered on d 6 and 8 to regress the CL. On d 11 of treatment, approximately half the MGA-treated cows received 5 mg of estradiol valerate (EV) i.m. (MGAEV, n = 14) and the remainder were maintained on MGA (n = 17). Ovaries were checked with ultrasound on d 8, 10, 12, and 14 of MGA treatment and every day until ovulation. A persistent dominant follicle developed in 90% of the MGA-treated cows by d 10 of treatment. Most of the MGA-treated cows ovulated the persistent dominant follicle (n = 13/17), whereas EV treatment regressed the persistent dominant follicle (n = 10/14) with the recruitment of a new follicle that ovulated (n = 8/10). Diameter of the ovulatory follicle was larger (P < .05) for the MGA (19.8 +/- .6 mm) than for the control (15.1 +/- .8 mm) and MGAEV (14.8 +/- .7 mm) cows. In Exp. 2, nonlactating, multiparous beef cows (n = 97) and yearling heifers (n = 38) were equally allotted to either a control, MGA alone, or MGA + estradiol-17 beta (MGAE) group with the same dose of MGA as administered in Exp. 1. The 1st d of MGA feeding was the 1st d of treatment. On d 10 of treatment half the MGA-treated animals were injected i.m. with 5 mg of estradiol-17 beta. In controls, behavioral estrus was detected and animals were artificially inseminated (AI) for 5 d (d 10 to 14 of experiment). All controls not exhibiting estrus by d 15 of experiment were injected with 25 mg of PGF2 alpha. The remaining controls and all MGA cows were observed for behavioral estrus and AI commenced for 7 d following withdrawal of MGA (d 15 to 21 of experiment). More (P < .05) controls (90.3%) than MGA (84.8%) or MGAE (63.6%) cows showed estrus within 7 d after MGA withdrawal. The percentage of animals conceiving to the synchronized estrus did not differ (P > .05) among treatments. The data support our hypothesis that a persistent dominant follicle developed and can be regressed with exogenous estrogen treatment followed by the recruitment and ovulation of a new follicle after MGA withdrawal and fertility of that estrus does not seem to be significantly compromised.

Luteinizing hormone, growth hormone, insulin-like growth factor-I, insulin and metabolites before puberty in heifers fed to gain at two rates

Fall born Angus x Hereford heifers were allotted to treatments at 9 mo of age to achieve the following growth rates: 1) fed to gain 1.36 kg/d (n = 10; HGAIN); and 2) fed to gain 0.23 kg/d for 16 wk, then fed to gain 1.36 kg/d (n = 9; LHGAIN). Growth hormone (GH), insulin-like growth factor-I (IGF-I0, insulin, glucose, nonesterified fatty acids (NEFA), and progesterone were quantified in twice weekly blood samples until onset of puberty. Body weight, hip height, and pelvic area were recorded every 28 d. Frequent blood samples (n = 8 heifers/treatment) were collected every 14 d, commencing on day 29 of treatment until onset of puberty to evaluate secretion of luteinizing hormone (LH) and GH. The HGAIN heifers were younger (369 d; P < 0.001), were shorter at the hip (115 cm; P < 0.05) and had smaller pelvic area (140 cm2; P < 0.10), but body weight (321 kg) did not differ at puberty compared with LHGAIN heifers (460 d; 119 cm; 155 cm2; 347 kg, respectively). The HGAIN heifers had greater (P < 0.05) concentrations of LH, IGF-I, and insulin in serum and glucose in plasma during the first 84 d of treatment than LHGAIN heifers, whereas LHGAIN heifers had greater (P < 0.05) concentrations of GH in serum and NEFA in plasma than HGAIN heifers. On day 68 of treatment, HGAIN heifers had less mean GH (P < 0.01) and greater (P < 0.05) LH pulse frequency than LHGAIN heifers, whereas LH pulse amplitude and mean LH did not differ (P < 0.10) between treatments. Treatment did not influence secretion of LH and GH at 1 and 3 wk before puberty. Mean GH concentrations in serum and GH pulse amplitude in all heifers were greater (P < 0.05) 2 to 9 d (12.9 and 40.7 ng/ml, respectively) than 16 to 23 d (10.4 and 20.0 ng/ml, respectively) before puberty. Nutrient restriction decreased LH pulse frequency and delayed puberty in beef heifers. Furthermore, dramatic changes in mean concentration and amplitude of GH pulses just before puberty in beef heifers may have a role in pubertal development.

Ovarian response after gonadotropin treatment of heifers immunized against gonadotropin-releasing hormone

Angus x Hereford heifers were used to determine whether the ovaries of heifers immunized against GnRH would respond to exogenous gonadotropins. Heifers (n = 23; 24 mo; 491 +/- 23 kg) were assigned to a 2 x 2 factorial experiment: immunization against GnRH conjugated to human serum albumin (GnRH-IMM) or human serum albumin alone (HSA-IMM), and treatment with gonadotropins (GTH) or saline. The GTH treatment was 2,000 IU PMSG + 1,000 iu hCG, and control heifers were given saline (s.c.). Immunization against GnRH (GnRH-IMM) caused cessation of ovulation (progesterone < 1 ng/mL plasma for 3 wk) and GTH treatment began within 3 to 5 wk after heifers became anovulatory. Heifers immunized against HSA (HSA-IMM) were treated between d 9 and 11 of the estrous cycle. All heifers were given PGF (i.m.) on d 2 (d 0 = start of GTH treatment) and 2,000 IU of hCG (i.m.) on d 4. Ovaries of heifers were evaluated by ultrasound. Blood was sampled daily from d 0 to d 8 and every second day through d 24 to quantify progesterone and estradiol. Concentrations of estradiol increased with time after GTH but the response was reduced by GnRH-IMM (IMM x GTH x day, P < .01). Number of follicles > or = 6 mm (d 0 to 14) was increased after GTH (GTH x day, P < .001) but was decreased (P < .03) by GnRH-IMM. Immunization against GnRH reduced total follicles > or = 6 mm on d 4 in heifers on both saline and GTH treatments. Treatment with gonadotropins increased the number of follicles > or = 16 mm on d 14 compared with control heifers. The number of CL was increased by GTH (GTH x day, P < .001) but the response was reduced (P < .03) in GnRH-IMM heifers compared with HSA-IMM heifers. We conclude that treatment with gonadotropins will induce follicular growth and ovulation in heifers that are anovulatory due to immunization against GnRH.

Effects of growth rate on carcass composition and lipid partitioning at puberty and growth hormone, insulin-like growth factor I, insulin, and metabolites before puberty in beef heifers

The effect of three rates of gain on carcass composition, lipid partitioning, age and BW at puberty, and concentrations of growth hormone (GH), IGF-I, insulin, glucose, and NEFA in plasma were evaluated in 38 Angus x Hereford heifers. Heifers were allotted by BW and age to three treatments with a replication in each of 2 yr: full-fed (n = 13; FF) to gain 1.36 kg/d; limit-fed (n = 12; LF) to gain .68 kg/d; maintenance-full-fed (n = 13; MFF) to gain .23 kg/d for 16 wk, then full-fed to gain 1.36 kg/d. Heifers were slaughtered within 10 d after the onset of puberty. At slaughter, kidney, pelvic, and heart fat (KPH) and udder (UDDER) were separated from carcass, as was fat surrounding viscera (OM). After 48 h at 4 degrees C a carcass side was dissected into subcutaneous fat (SC), intermuscular fat (SEAM), soft tissue (SFT = inseparable lean and fat), LEAN, and BONE. In yr 1, LF heifers (431 d) were older (P < .05) than MFF heifers (371 d) at puberty, but age of FF heifers (389 d) did not differ (P > .10) from that of LF and MFF heifers. In yr 2, FF heifers (351 d) were younger (P < .05) than LF and MFF heifers (398 and 434 d, respectively). The FF heifers had greater (P < .05) BW and a greater (P < .01) percentage of lipid in the carcass at puberty than LF and MFF heifers. During the first 16 wk of treatment, concentrations of NEFA were greater in heifers with slower daily gains (MFF > LF > FF; P < .01). Concentrations of NEFA were lesser and concentrations of IGF-I and insulin were greater in plasma of FF than in that of MFF heifers during the 10 wk before puberty. Treatment significantly altered age, BW, carcass composition, and lipid partitioning at puberty in beef heifers. We conclude that the percentage of body fat is not the sole regulator of puberty, and age may be an important modulator in determining the onset of puberty in beef heifers.

Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate and PGF2α

A total of 402 two suckled postpartum beef cows at 2 locations (CSU and ECRC) were utilized in 3 trials to evaluate the effectiveness of a combination melengestrol acetate (MGA)-PGF2alpha estrus synchronization system in spring-calving cows. The cows were allocated by days post partum, body condition score (1 = emaciated; 9 = obese), sire breed, and dam age at the beginning of treatment to 1 of 2 treatments within location and trial: MGA-PGF2alpha (0.5 mg MGA/head/d for 14 d with 25 mg of PGF2alpha injected 17 d after MGA withdrawal), and unsynchronized controls. All cows were observed for estrus at 12-h intervals for at least 5 d post injection. Cows observed in standing estrus were inseminated 12 to 18 h later. There was a location effect on response to treatment that was attributed to differences in body condition score between locations so data were analyzed within a location. Body condition score at the CSU location was 5.7 compared with 4.0 at the ECRC location. The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 5-day estrus and 5-d pregnancy rates (78.6 and 61.0%, respectively) than the CSU controls (11.1 and 6.9%, respectively). Similar results for 5-d estrus and pregnancy rates but of decreased magnitude were also observed for the ECRC MGA-PGF2alpha treated (31.6 and 21.4%, respectively) cows compared with that of the ECRC controls (11.9 and 8.5%, respectively). The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 25- and 60-d pregnancy rates (82.5 and 94.8%) than the CSU controls (65.3 and 87.5%). The 25- and 60-d pregnancy rates were similar between the ECRC MGA-PGF2alpha treated cows and ECRC control cows. The MGA-PGF2alpha estrus synchronization system appears to contribute to pregnancy early in the breeding season in postpartum beef cows, although its effectiveness is limited by cow body condition.

Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate, 48-hour calf removal and PGF2α

One hundred and sixty-five suckled postpartum beef cows were utilized to evaluate the effectiveness of 2 estrus synchronization systems for the initiation and synchronization of estrus. The treatment groups consisted of 1) melengestrol acetate (MGA)-PGF2alpha (cows were given 0.5 mg MGA/head/day for 14 d with 25 mg PGF2alpha injected 17 d after the last day of MGA administration); 2) MGA-48-h calf removal (CR)-PGF2alpha (cows were given 0.5 mg MGA/head/day for 14 d with 48-h calf removal starting on the second day after completion of the MGA regimen plus 25 mg PGF2alpha administered 17 d after the last day of MGA); and 3) unsynchronized controls. Cows were assigned to treatments by the numbers of days post partum, body condition, age, and breed of sire. The cows were observed for estrus at 12-h intervals for 5 d after PGF2alpha administration and were artificially inseminated 12 to 18 h after the observed estrus. Both the MGA-PGF2alpha and MGA-CR-PGF2alpha treatments (64.8 and 61.8%) had greater (P < 0.05) 5-d estrus rates than the control treatments (34.5%). The synchronized pregnancy rate was greater (P < 0.05) for the MGA-CR-PGF2alpha than the control treatment.(52.7 vs 30.9%, respectively). The MGA-CR-PGF2alpha cows had a higher 25-d pregnancy rate than either the MGA-PGF2alpha (P < 0.05) or control cows (P < 0.08). Of the anestrous cows at the beginning of treatment, more MGA-CR-PGF2alpha (P = 0.1) and MGA-PGF2alpha cows were cyclic posttreatment than control cows (58.7 and 55.1 vs 44.7%, respectively), suggesting that treatment initiated estrous cycles in only a small number of the anestrous cows. Both MGA-PGF2alpha and MGA-CR-PGF2alpha treatments appear to be effective methods of synchronizing estrus in suckled postpartum beef cows. However, MGA-CR-PGF2alpha was more effective in establishing pregnancy earlier in the breeding season than MGA-PGF2alpha.