Julie A. Small

Effects of progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI in beef cattle.

Three experiments were conducted to determine the effects of low-dose progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI (TAI) in beef cattle (GnRH on Day 0, PGF(2alpha) on Day 7, with GnRH and TAI on Day 9, 54-56 h after PGF(2alpha)). Experiments 1 and 2 were 2 x 2 factorials with presynchronization (with or without a once-used CIDR; Days -15 to 0 in Experiment 1 and Days -7 to 0, with PGF(2alpha) at insertion, in Experiment 2), and with or without 400 IU eCG on Day 7 in suckled cows. In Experiment 3, suckled cows and nulliparous heifers were either presynchronized with a twice-used CIDR (Days -5 to 0) and PGF(2alpha) at insertion, or no treatment prior to insertion of a new CIDR (Days 0-7). Presynchronization increased (P<0.05) ovulation rate to GnRH on Day 0 (75.0% vs 48.7%, 76.7% vs 55.0%, and 60.0% vs 36.1% for Experiments 1, 2, and 3, respectively), increased the diameter of the preovulatory follicle in Experiments 1 and 2, and increased the response to PGF(2alpha) (regardless of parity) in Experiment 1 (P<0.01), and in primiparous cows in Experiment 2 (P<0.01). Effects of presynchronization on pregnancy rates (53.4% vs 54.1%, 57.7% vs 45.3%, and 54.3% vs 44.4% for Experiments 1, 2, and 3, respectively) were influenced by parity and eCG (P<0.05). Treatment with eCG had no effect (P>0.05) on the diameter of the preovulatory follicle (Experiment 1), or the response to PGF(2alpha) (Experiments 1 and 2), but tended (P=0.08) to improve pregnancy rates, especially in primiparous cows that were not presynchronized (P<0.01). However, the effects of eCG and presynchronization were not additive.

Implantation-Associated Changes in Bovine Uterine Expression of Integrins and Extracellular Matrix

Abstract Appropriate integrin expression appears to be necessary for successful implantation of human embryos and varies considerably among species. The present study was undertaken to determine the distributions of integrin subunits α1, α3, and α6 as well as the extracellular matrix (ECM) components collagen IV and laminin in implanting bovine trophoblast and endometrium. Immunohistochemical staining of cryostat sections prepared from nonpregnant endometrium, of preattachment through to early villus development pregnant endometrium (Days 18, 21, 24, and 30), and of isolated trophoblast binucleate cells was performed. Trophoblast down-regulated the integrin α1 subunit as attachment proceeded, whereas reactivity scores for α6 antibody tended to increase from Day 18 through 24 and remained high. A subpopulation of trophoblast binucleate cells expressed the α3 integrin subunit. Uterine epithelium constitutively expressed α3 and α6 integrin subunits, but the α1 subunit was down-regulated as the luminal epithelium was modified. Collagen IV and laminin reactivity increased in the basal lamina and underlying subepithelial stroma as pregnancy proceeded. The results suggest that binucleate cell fusion with the maternal epithelium initiates integrin and ECM changes in the subepithelial stroma.

Measurement of vaginal temperature by radiotelemetry for the prediction of estrus in beef cows

Peaks in vaginal temperature were assessed as predictors of estrus in 22 suckled beef cows during 2 breeding seasons. A flexible plastic anchor was used to retain a temperature radiotransmitter within the cow vagina and vaginal temperature was monitored at 4-min intervals. Blood was collected twice weekly for analysis of serum progesterone to confirm the occurrence of estrus and ovarian status was checked weekly using transrectal ultrasonography. Visual observations of estrous behavior were made for 20 min/h between 0400 and 0800 h and casually from 0800 to 1600 h (4 to 6 times). Values for vaginal temperature were available for 47 estrous periods. The prediction of estrus based on vaginal temperature was excellent when an estral peak in vaginal temperature was defined as an increase of at least 0.4 degree C for 3 or more consecutive hours using the corresponding hourly means of a 2 or 3-d baseline. Combining the results of 2 separate years and using a 3-d baseline, a peak in vaginal temperature was found for 42 of 47 confirmed estrus periods (detection sensitivity of 89.4% and prediction power positive of 85.7%). Corresponding detection sensitivity and prediction power positive for visual observations of standing estrus were 53.2 and 96.2%, respectively. The mean maximal increase in vaginal temperature at estrus was 0.9 +/- 0.3 degree C and the mean duration of the estrual peak in vaginal temperature was 6.5 +/- 2.7 h. In addition, vaginal temperature was found to be significantly depressed for 3 d prior to estrus and significantly elevated at mid-cycle.

Effects of low versus physiologic plasma progesterone concentrations on ovarian follicular development and fertility in beef cattle

The objective of this study was to determine the effects of low versus physiologic plasma progesterone concentrations during the ovulatory wave on fertility in cattle. Suckled beef cows (Bos taurus; n=129) and pubertal heifers (Bos taurus; n=150) at random stages of the estrous cycle were given a luteolytic dose of prostaglandin F(2 alpha) (500 microg cloprostenol; PGF) twice, 11 d apart. Ten days after the second PGF treatment, cattle were given estradiol benzoate im (1.5 and 1.0mg for cows and heifers, respectively) and a progesterone-releasing intravaginal device (Cue-Mate) with a single pod containing 0.78 g progesterone (Day 0). Cattle in the low-progesterone group (n = 148) received a luteolytic dose of PGF on Day 0, whereas those in the high-progesterone (i.e., physiologic plasma concentrations) group (n=131) were allowed to retain their corpora lutea. On Day 8, the Cue-Mate was removed, and PGF was given to both groups. Fifty-four hours to 56 h later, cattle received 12.5mg of porcine LH (pLH) im and were concurrently artificially inseminated. The dominant follicle in the low-progesterone group was larger (P<0.001) than that in the high-progesterone group on the day of insemination (14.9+/-0.3mm vs. 12.7+/-0.3mm, mean+/-SEM). At 7 d after ovulation, the low-progesterone group had a larger corpus luteum (24.5+/-0.54 mm vs. 21.9+/-0.64 mm, P<0.01) and higher plasma progesterone concentration (4.0+/-0.3 vs. 3.1+/-0.2, P<0.01) than that of the high-progesterone group. However, pregnancy rates did not differ (79 of 148, 53.4%, and 70 of 131, 53.4%) for low- and high-progesterone groups, respectively). In summary, low circulating progesterone concentrations during the growing phase of the ovulatory follicle resulted in a larger dominant follicle and a larger CL that produced more progesterone, with no significant effect on pregnancy rate.

Comparison of 2 enzyme immunoassays and a radioimmunoassay for measurement of progesterone concentrations in bovine plasma, skim milk, and whole milk

The objective of this study was to compare 2 enzyme immunoassays (EIAs) with a radioimmunoassay (RIA) as to sensitivity and accuracy in the measurement of the progesterone (P4) concentration in bovine plasma, skim milk, and whole milk. The 72 samples from 24 lactating dairy cows expected to have either a high P4 concentration (cows in diestrus or pregnant) or a low P4 concentration (cows in estrus or anestrus) were analyzed by RIA, solid-phase EIA (SPEIA), which included a solvent extraction step, or direct EIA (DEIA) without solvent extraction. The overall mean concentrations of P4 did not differ (P < 0.4) among the assays. However, for the cows that were in diestrus or pregnant, the mean P4 concentrations (and standard error) were higher (P < 0.03), regardless of sample type, with RIA than with SPEIA, at 7.3 (0.7) and 6.1 (0.6) ng/mL, respectively. When only the high-P4 samples analyzed by RIA were compared, the mean P4 concentration was higher (P < 0.001) in whole milk than in skim milk, at 9.8 (1.0) and 4.1 (0.7) ng/mL, respectively. Although the mean P4 concentrations in the low-P4 samples did not differ (P < 0.80) among assays, the proportions of cows with a P4 concentration > or = 1 ng/mL were 3%, 14%, and 44% for RIA, SPEIA, and DEIA, respectively (P < 0.01; DEIA > SPEIA > RIA).

Effects of evening feeding and extended photoperiod on growth, feed efficiency, live animal carcass traits and plasma prolactin of beef heifers housed outdoors during two Manitoba winters

The effects of evening feeding and extended photoperiod on feedlot performance, live animal carcass traits and plasma prolactin were investigated in crossbred beef heifers in two consecutive Manitoba winters (1998–1999; exp. 1 and 1999–2000; exp. 2) using a 2 × 2 factorial design. Heifers were fed in the morning (1000 exp. 1 and 0900 exp. 2) or evening (2000) and exposed to natural winter photoperiod (NP) of <15 h or extended winter photoperiod (EP) of 16–19 h (65 lux exp. 1, 51 lux exp. 2) in outdoor partially covered pens. Heifers (n = 48; 276.9 ± 19.4 kg, mean ± SD) in exp. 1 were given a 60% forage: 40% concentrate backgrounding ration for 56 d followed by a 25% forage: 75% concentrate finishing ration for 70 d. In exp. 2, heifers (n = 48; 228.8 ± 18.8kg) were given the backgrounding ration for 170 d. Mean ambient temperature during the backgrounding and finishing periods in exp. 1 was -13.7 and 0.5°C, respectively. During the backgrounding period of exp. 1, evening feeding increased (P = 0.05) growth...

Time of feeding and growth promotant effects on the winter growth performance and carcass traits of steers

The effects of time of day of feeding and estrogenic growth promotant on growth performance and carcass traits were determined in three experiments conducted over 3 yr (winters 1998–1999, 1999–2000, 2000–2001). Crossbred steers (year 1, n = 144, year 2, n = 128, year 3, n = 144) were assigned at fall weaning on the basis of sire, age (190 ± 21 d, mean ± SD), and body weight (244 ± 34 kg) to one of eight pens in an outdoor lot at the Brandon Research Centre (49°54′N). In years 1 and 2, pens were assigned to either morning-fed (MF, 0900) or evening-fed (EF, 2000) treatments, and steers within pen were assigned to either Synovex Plus® (TAE) or Synovex S® (PE) growth promotants. In year 3, pens were assigned to either TAE or PE treatments and all were evening-fed. Beginning on Nov. 09 (0 d), steers were given a 20% hay, 80% concentrate (79.2% barley, 0.8% premix) mixed ration (88.6% dry matter, 13.7 MJ kg-1 digestible energy, 124 g kg-1 crude protein, 33.6 mg kg-1 lasalocid). Diets were fed, once daily, in am...

The effects of gonadotrophin releasing hormone in prostaglandin F2α-based timed insemination programs for beef cattle

Trials were conducted in the spring (May; n = 324) and fall (October; n = 132) with crossbred continental-type beef cows assigned on the basis of parity and postpartum interval to one of three timed-AI treatments and one of two post-AI treatments. The timed-AI treatments were: (DPG) double (14 d apart) PGF2α (Lutalyse®) and AI (day = 0) 72 h after the second PGF2α (day –3); (OVS) Ovsynch® with the second GnRH (Factrel®) at 48 h and AI at 66 h; and (BRC) the same as OVS except that the second GnRH was given at the time of AI. Half of the cows within each treatment were given GnRH on day 14. Plasma progesterone concentrations were determined for the day of the first injection and on days –3, 0, 14, and 21. Timed-AI pregnancy was diagnosed by ultrasonography at day 42 and confirmed at calving. For DPG, OVS and BRC, PGF2α responder rates were 75.9, 51.4 and 71.3%, respectively, in spring (P 0.05), and AI pregnancy rates were 28.7, 44.9 and 44.4% in spring (P< 0.05...

The effects of bull exposure and lasalocid on the development of replacement beef heifers

At weaning in the fall, crossbred heifers (n = 224), born in either the winter (January–February) or spring (March–April), were assigned on the basis of age, sire-breed and body weight to one of two similar winter housing facilities (with or without sterilized bulls), and to one of two forage-based (87%) diets (with or without lasalocid, 200 mg d−1) within each housing facility. Observations for estrus were made twice daily. Timed AI (66 h after PGF2α) was used to breed heifers for the first time at 14 mo of age. Plasma progesterone concentrations were used to confirm estrus/ovulation and to determine the PGF2α response rate. Bull exposure advanced puberty in winter-born heifers, but delayed puberty in spring-born heifers (P ≤ 0.029). Similarly, timed AI pregnancy for winter-born heifers was higher with than without bull exposure (58.9 vs. 32.5 ± 5.3%; P = 0.017) while the opposite occurred for the spring-born group (27.1 vs. 59.1 ± 4.7%; P < 0.001). Bull-exposed spring-born heifers were the oldest at cal...

Effect of once daily 5-h or 10-h cold-exposures on body temperature and resting heat production of beef cattle

Twelve yearling crossbred beef heifers weighing 454 ± 31 kg were randomly assigned to either 0 h (control), 5 h (5CE; 0800 to 1300) or 10 h (10CE; 0800 to 1800) of cold exposure (-20°C) daily to determine the effect of daily cold exposures of different durations on body core temperature and resting heat production of beef cattle. Treatments were imposed for a 21-d period (seven intervals of 3 d duration) using two replications with two heifers per treatment × replication combination. Heifers were group housed outdoors in a pen with overhead shade at one end and were moved daily at 0800 to a group pen in either a control room or an environmental chamber set at -20°C. After the 21-d period was completed, resting heat production was measured in a thermal neutral environment for 5 h. Vaginal temperature (Tvag) was continuously monitored using radiotransmitters. Treatment did not affect daily maximum, mean or minimum Tvag, the amount of time spent at Tvag exceeding daily mean Tvag, or the variability of Tvag (...