Fertility of Lactating Dairy Cows Administered Recombinant Bovine Somatotropin During Heat Stress

Administration of recombinant bovine somatotropin (bST) to lactating dairy cows during heat stress increases milk yield, but it also can increase body temperature and may therefore compromise fertility. However, it is possible that bST treatment could increase fertility during heat stress because it has been reported to increase fertility in lactating cows. In addition, bST increases secretion of insulin-like growth factor-I (IGF-I) that promotes embryo survival. The purpose of this study was to determine effects of bST on reproductive function in lactating dairy cows during heat stress. The experiment was conducted in southern Georgia from July to November 2005 using lactating Holstein cows (n = 276 for reproductive traits). For first service timed artificial insemination (TAI), cows were presynchronized with 2 injections of PGF(2alpha) given 14 d apart followed by a modified Ovsynch protocol (GnRH and insemination at 72 h following PGF(2alpha) ). Pregnancy was diagnosed by using ultrasonography on d 29 and reconfirmed by palpation between d 45 and 80 post-TAI. Nonpregnant cows were resynchronized with the modified Ovsynch protocol and received a second TAI. Treatment with bST started 1 wk before the start of Ovsynch and continued at 2-wk intervals. Blood samples were collected from a subset of cows to determine IGF-I profiles immediately before the first bST injection, 1 wk later, and at d 35 of bST treatment. Rectal temperatures were assessed on d 29 of bST treatment. Pregnancy rates (d 45 to 80 post-TAI) did not differ between bST and control cows for first- (16.7 vs. 15.2%) or second-service TAI (14.8 vs. 17.2%). Plasma concentrations of IGF-I and milk yield were greater for bST-treated cows following the initiation of bST treatment and bST increased rectal and vaginal temperatures. Body condition score was less for bST-treated cows. In conclusion, treatment with bST during heat stress increased IGF-I concentrations, milk yield over time, and rectal and vaginal temperatures without affecting first- or second-service pregnancy rates. Thus, at least under certain housing conditions, bST can be used to improve milk yield during heat stress without compromising fertility.

Effect of transfer of one or two in vitro-produced embryos and post-transfer administration of gonadotropin releasing hormone on pregnancy rates of heat-stressed dairy cattle

Pregnancy rates following transfer of an in vitro-produced (IVP) embryo are often lower than those obtained following transfer of an embryo produced by superovulation. The purpose of the current pair of experiments was to examine two strategies for increasing pregnancy rates in heat stressed, dairy recipients receiving an IVP embryo. One method was to transfer two embryos into the uterine horn ipsilateral to the CL, whereas the other method involved injection of GnRH at Day 11 after the anticipated day of ovulation. In Experiment 1, 32 virgin crossbred heifers and 26 lactating crossbred cows were prepared for timed embryo transfer by being subjected to a timed ovulation protocol. Those having a palpable CL were randomly selected to receive one (n = 31 recipients) or two (n = 27 recipients) embryos on Day 7 after anticipated ovulation. At Day 64 of gestation, the pregnancy rate tended to be higher (P = 0.07) for cows than for heifers. Heifers that received one embryo tended to have a higher pregnancy rate than those that received two embryos (41% versus 20%, respectively) while there was no difference in pregnancy rate for cows that received one or two embryos (57% versus 50%, respectively). Pregnancy loss between Day 64 and 127 only occurred for cows that received two embryos (pregnancy rate at Day 127=17%). Between Day 127 and term, one animal (a cow with a single embryo) lost its pregnancy. There was no difference in pregnancy rates at Day 127 or calving rates between cows and heifers, but females that received two embryos had lower Day-127 pregnancy rates and calving rates than females that received one embryo (P < 0.03). Of the females receiving two embryos that calved, 2 of 5 gave birth to twins. For Experiment 2, 87 multiparous, late lactation, nonpregnant Holstein cows were synchronized for timed embryo transfer as in Experiment 1. Cows received a single embryo in the uterine horn ipsilateral to the ovary containing the CL and received either 100 microg GnRH or vehicle at Day 11 after anticipated ovulation (i.e. 4 days after embryo transfer). There was no difference in pregnancy rate for cows that received the GnRH or vehicle treatment (18% versus 17%, respectively). In conclusion, neither unilateral transfer of two embryos nor administration of GnRH at Day 11 after anticipated ovulation improved pregnancy rates of dairy cattle exposed to heat stress.

189 PREGNANCY RATES IN HEAT-STRESSED DAIRY CATTLE RECEIVING ONE OR TWO IN VITRO-PRODUCED EMBRYOS IN A TIMED EMBRYO TRANSFER PROGRAM

The objective was to determine whether transfer of two embryos would increase pregnancy rates in heat-stressed dairy recipients receiving an in vitro-produced embryo transferred into the uterine horn ipsilateral to the corpus luteum (CL). Such a treatment would increase the likelihood that the cow receives at least one embryo competent for sustained development. In addition, transfer of two embryos into the ipsilateral uterine horn is likely to increase the amounts of interferon-tau and other embryonic-signaling molecules in the uterus. A total of 32 virgin crossbreed heifers and 26 lactating crossbreed cows were used as timed embryo transfer recipients after being subjected to an ovulation synchronization protocol as follows: GnRH (100 �g) and insertion of previously used progesterone-containing CIDR on Day -10, prostaglandin F2� and CIDR removal on Day -3, and GnRH (100 �g) on Day 0 (day of anticipated ovulation). All recipients had a palpable CL on Day 6 and were randomly selected to receive one (n = 31 recipients) or two (n = 27) embryos on Day 7. At Day 64, the pregnancy rate tended to be higher (P = 0.07) for cows than for heifers. While not significant, heifers that received two embryos tended to have lower pregnancy rates than those that received a single embryo (20% vs. 41%); there was no difference in pregnancy rate in cows (50% for two embryos vs. 57% for one embryo). Pregnancy losses between Day 64 and Day 127 occurred in one group only cows receiving two embryos. In that group, pregnancy rate was 50% at Day 64 but 17% at Day 127. Overall, there was no difference in pregnancy rates at day 127 between cows and heifers, but recipients that received two embryos (17% for cows and 20% for heifers) had lower pregnancy rates (P < 0.03) than recipients that received one embryo (57% for cows and 41% for heifers). Only one animal, a cow, had twin fetuses at day 127. In conclusion, unilateral transfer of two embryos failed to improve pregnancy rates of dairy cattle exposed to heat stress. The fact that fetal loss occurred sooner for heifers than for cows points out the importance of uterine capacity as a limiting factor for maintenance of fetal development of two conceptuses. The suitability of timed embryo transfer was evident from the high pregnancy rates achieved with crossbreed females that received a single embryo. This work was supported by BARD Grant No. US-1551-14, USDA TSTAR Grant No. 2004-14135-14715, Grant No. 2001-12101-11318 from the USDA-IFAFS Program, and CAPES Grant No. 134202-1).

129 INSULIN-LIKE GROWTH FACTOR-I PROMOTES BLASTOCYST DEVELOPMENT OF HEAT-SHOCKED BOVINE EMBRYOS INDEPENDENT OF ITS ANTI-APOPTOTIC EFFECTS REQUIRING P13K SIGNALING

Insulin-like growth factor-I (IGF-I) reduces effects of heat shock on blastocyst development and induction of apoptosis. The present objective was to test whether IGF-I would allow for blastocyst development following heat shock because of its anti-apoptotic effects. Because anti-apoptotic actions of IGF-I require signaling through the phosphatidylinositol 3-kinase (PI3K) pathway, an inhibitor of PI3K (LY 294002) was used in Exp. 1 to determine whether it would prevent the thermoprotective effects of IGF-I on development. Embryos were produced in vitro in KSOM-BE2 medium �100 ng mL-1 of IGF-I. Embryos e16 cells at 5 d post-insemination (dpi) were placed in fresh drops containing the same IGF-I treatment as well as LY 294002 (100 �m) or vehicle (0.1% DMSO) and cultured at either 38.5�C or 41�C for 15 h. All groups were then cultured at 38.5�C until 8 dpi when blastocyst development was assessed (10 replicates; 112 to 142 embryos per treatment). For embryos in DMSO, IGF-I did not increase the percentage that became blastocysts when cultured at 38.5�C (59.1 and 57.1% for control and IGF-I embryos, respectively; SEM = 3.6%). Heat shock reduced blastocyst development (P < 0.01), and IGF-I blocked this decrease (percent blastocyst = 42.0 and 54.7% for control and IGF-I embryos, respectively; SEM = 3.6%). Similar results were obtained for embryos cultured with LY 294002. The percentage of embryos becoming blastocysts for control embryos was 53.5 and 35.5%, respectively, at 38.5 and 41�C, development for IGF-I-treated embryos was, respectively, 55.8 and 49.4% at 38.5 and 41�C (SEM = 4.8%). Analysis of the entire data set revealed an IGF-I � temperature interaction (P < 0.05) but no interactions with inhibitor treatment. Thus, IGF-I protected embryos from heat shock in the presence and absence of LY 294002. In Exp. 2, procedures were similar, except that embryos were cultured with a caspase-3 inhibitor (z-DEVD-fmk; 100 �m) instead of LY 294002 (12 replicates; 114 to 137 embryos per treatment). For embryos in DMSO, blastocyst development was reduced by heat shock (P < 0.06) and increased by IGF-I (P < 0.06). The percentage of embryos becoming blastocysts was 67.0 and 55.8% for control embryos at 38.5 and 41�C, respectively, vs. 74.7 and 70.8% for IGF-I embryos at 38.5 and 41�C, respectively (SEM = 5.2%). For embryos cultured with z-DEVD-fmk, heat shock reduced blastocyst development (P < 0.01), and IGF-I was no longer effective in blocking the reduction in blastocyst development caused by heat shock (IGF-I � inhibitor treatment; P < 0.01). Blastocyst development was 66.4 and 58.7% for control embryos at 38.5 and 41�C, respectively, vs. 61.8 and 48.6% for IGF-I embryos at 38.5 and 41�C, respectively (SEM = 4.6%). Note that z-DEVD-fmk did not protect embryos from the anti-developmental effects of heat shock but exacerbated heat shock effects for IGF-I-treated embryos. In conclusion, the ability of IGF-I to allow heat-shocked embryos to continue development to the blastocyst stage is independent of its anti-apoptotic effects involving the PI3K pathway but may depend on active caspase-3. This work was supported by USDA NRICGP 2002-35203-12664, BARD US-3551-04, and USDA TSTAR 2004-34135-14715.

Factors associated with early and mid-to-late fetal loss in lactating and nonlactating Holstein cattle in a hot climate1

The purpose of this study was to evaluate associations of lactation, somatic cell count score (SCCS) at breeding, milk yield, lactation number, interval from calving to breeding (days open), number of times inseminated, and season of breeding on fetal loss for lactating Holstein females (both first-parity and multiparous cows) and nonlactating Holstein heifers in a hot climate. Females were palpated between d 40 and 50 of gestation and again at d 70 to 80 to determine pregnancy status. Early fetal loss was defined as a loss that occurred after d 40 to 50 but before d 70 to 80. Mid-to-late fetal loss represented losses after d 70 to 80 but before expected calving. Lactating females had higher early (P = 0.055) and mid-to-late fetal loss (P < 0.05) than nonlactating heifers. Those lactating females with increased days open experienced greater early (P < 0.05) and mid-to-late fetal loss (P = 0.055), whereas lactating females with an elevated SCCS encountered greater mid-to-late fetal loss (P < 0.01). Milk yield, lactation number, number of times inseminated, and season were not associated with early or mid-to-late fetal loss. For nonlactating heifers, there were no associations between number of times inseminated, season, or age at breeding on early or mid-to-late fetal loss. In conclusion, lactating females were more likely to suffer early and mid-to-late fetal loss than nonlactating heifers. Also, days open and SCCS at breeding were related to ability of lactating females to maintain pregnancy, but there were no relationships between fetal loss and milk yield, lactation number, number of times inseminated, or season.

Timing of Inhibitory Actions of Gossypol on Cultured Bovine Embryos

Culture of bovine preimplantation embryos with gossypol, a polyphenolic pigment in cottonseed, inhibits development. Neither stage at which embryos are most sensitive to gossypol, nor the mechanism by which development is blocked is known. Our objectives were to characterize stages at which gossypol inhibits embryonic development and evaluate involvement of apoptosis in actions of gossypol. When presumptive 1-cell embryos were cultured continuously in medium containing gossypol at concentrations of 0, 2.5, 5, and 10 microg/mL, cleavage rate was not reduced by any concentration of gossypol, but percentages of 1-cell embryos that became blastocysts 8 d after insemination was reduced by the 10 microg/mL dose of gossypol. Culture of presumptive 1-cell embryos with gossypol at 10 microg/mL for 24 h was not sufficient to block development. Furthermore, gossypol did not affect development to the blastocyst stage when 2-cell embryos were cultured with gossypol at 10 microg/mL for 24 h or 7 d. Culture of embryos > or =16 cells with gossypol at 10 microg/mL for 24 h failed to reduce cell number 24 h later or increase blastomere apoptosis. Results indicate that embryonic development can be disrupted by long-term exposure to gossypol at 10 microg/mL and that exposure at the 1-cell stage is required. Thus, it is likely that the deleterious effects of gossypol involve disruption of events at the 1-cell stage and such effects are reversible if gossypol is removed. After the 1-cell stage, gossypol does not affect development because the critical event that gossypol disrupts occurs at the 1-cell stage only or the embryo develops cytoprotective mechanisms after the 1-cell stage that limit actions of gossypol.

Insulin-like Growth Factor-I as a Survival Factor for the Bovine Preimplantation Embryo Exposed to Heat Shock1

Insulin-like growth factor-I (IGF-I) is a survival factor for preimplantation mammalian embryos exposed to stress. One stress that compromises preimplantation embryonic development is elevated temperature (i.e., heat shock). Using bovine embryos produced in vitro as a model, it was hypothesized that IGF-I would protect preimplantation embryos by reducing the effects of heat shock on total cell number, the proportion of blastomeres that undergo apoptosis, and the percentage of embryos developing to the blastocyst stage. In experiment 1, embryos were cultured with or without IGF-I; on Day 5 after insemination, embryos >or=16 cells were cultured at 38.5 degrees C for 24 h or were subjected to 41 degrees C for 9 h followed by 38.5 degrees C for 15 h. Heat shock reduced the total cell number at 24 h after initiation of heat shock and increased the percentage of blastomeres that were apoptotic. Effects of heat shock were less for IGF-I-treated embryos. Experiment 2 was conducted similarly except that embryos were allowed to develop to Day 8 after insemination. The percentage reduction in blastocyst development for heat-shocked embryos compared with those maintained at 38.5 degrees C was less for embryos cultured with IGF-I than for control embryos. Heat shock reduced the total cell number in blastocysts and increased the percentage of blastomeres that were apoptotic, whereas IGF-I-treated embryos had increased total cell number and a reduced percentage of apoptosis. Taken together, these results demonstrate that IGF-I can serve as a survival factor for preimplantation bovine embryos exposed to heat shock by reducing the effects of heat shock on development and apoptosis.

Effects of varying the holding temperature and interval from collection to freezing on post-thaw development of bovine embryos in vitro

The objective of this study was to evaluate the in vitro development of frozen-thawed bovine embryos held at room temperature or refrigerated for 2, 6 or 12 h prior to freezing. After recovery, embryos were randomly assigned to be placed in holding media for 2 h (n=131), 6 h (n=136) or 12h (n=133) prior to freezing. Approximately one-half of the embryos were refrigerated (5 degrees C; n=203) while the remaining half were held at room temperature (22 degrees C; n = 197) until freezing. Embryos were frozen in 10% ethylene glycol and stored in liquid nitrogen. After thawing, embryos were cultured for 72 h in Ham's F-10 media supplemented with 4% fetal bovine serum. Embryos were evaluated for quality and stage of development prior to freezing and after culture. At the end of culture, it was determined if each embryo had developed beyond the stage recorded prior to freezing and if the embryo had hatched from the zona pellucida. The percentage of embryos that developed during culture was greater (P < 0.001) for Grade 1 (81%) than for either Grade 2 (65%) or Grade 3 (48%) embryos. Likewise, a greater proportion (P < 0.001) of Grade 1 embryos developed to hatched blastocysts (60%) than either Grade 2 (40%) or Grade 3 (24%) embryos. The holding temperature from collection to freezing did not influence embryo development, regardless of the interval from embryo collection to freezing. The proportion of embryos that developed to expanded blastocysts and hatched was greater (P < 0.005) for embryos held 2 h prior to freezing (64%) than for embryos held for 12 h (33%). Hatching rate of embryos held 6 h prior to freezing (54%) tended (P < 0.08) to be lower than the hatching percentage for embryos held for 2 h. Thus, post-thaw embryonic development was impaired the longer embryos were held prior to freezing and temperature during the interval from collection to freezing did not affect post-thaw development.

130INSULIN-LIKE GROWTH FACTOR-1 AND INTERLEUKIN-11 AS POSSIBLE SURVIVAL FACTORS FOR THE BOVINE PREIMPLANTATION EMBRYO EXPOSED TO STRESS

Both IGF-1 and interleukin-11 (IL-11) are survival factors that modify response to cell injury. Moreover, IGF-1 promotes preimplantation development (Mol. Reprod. Dev. 62, 489) and IL-11 has been reported to reduce effects of heat shock on bovine embryos (Theriogenology 59, 343). For this study, it was hypothesized that IGF-1 and IL-11 improve survival of bovine embryos exposed to lethal stimuli. Embryos were produced in vitro and cultured in KSOM medium. Treatment effects were analyzed using least squares ANOVA with the GLM procedure of SAS (SAS Inst., Inc., Cary, NC, USA). In Exp. 1, 100ngmL−1 IGF-1 increased (P&lt;0.01) the percent of oocytes that became blastocyst at 8 days post-insemination (dpi) (19.0% for control v. 24.5% for IGF-1; SEM=1.3%; 7 replicates; 105 embryos/treatment). For Exp. 2, embryos were cultured±100ngmL−1 IGF-1. At 5 dpi, embryos≥16 cells were cultured at either 38.5°C for 24h or 41°C for 9h and then 38.5°C for 15h followed by TUNEL analysis (7 replicates; 86–100 embryos/treatment). At 38.5°C, IGF-1 did not affect total cell number (60.5 v. 64.4 for control and IGF-1, respectively; SEM=2.3) or percent of blastomeres undergoing apoptosis as determined by TUNEL (5.9% v. 5.7%; SEM=0.6%). Heat shock reduced total cell number (P&lt;0.05) and increased the percent of cells that were TUNEL-positive (P&lt;0.001). For heat-shocked embryos, total cell number was 46.0 for control v. 59.8 for IGF-1 (SEM=2.3) and percent of TUNEL-positive blastomeres was 11.6% for control v. 5.9% for IGF-1 (SEM=0.6%). Effects of heat shock were less for IGF-1-treated embryos (temperature×IGF-1, P=0.07 for cell number and P&lt;0.01 for TUNEL). For Exp. 3 (4 replicates; 111–136 embryos/treatment), embryos were cultured±100ngmL−1 IGF-1 beginning at the 1-cell stage in control medium (KSOM), ethanol (1.0%; v/v) or gossypol (10μgmL−1 in 1% ethanol). Percent of blastocysts at 8 dpi was affected by treatment (P&lt;0.01) and IGF-1 (P&lt;0.04). Without IGF-1, least-squares means were 24.6%, 13.6% and 0.9% for control, ethanol, and gossypol, respectively (SEM=1.7%). With IGF-1, least-squares means were 29.3±3.4%, 26.5±1.6%, and 8.7%±1.7% for control, ethanol, and gossypol (control v. ethanol, NS; control v. gossypol, P&lt;0.01). Thus, IGF-1 blocked the effect of ethanol on development. For Exp. 4, putative zygotes were cultured±10ngmL−1 human IL-11 (4 replicates; 201–214 zygotes/treatment). At 3 dpi, embryos remained at 38.5°C or were cultured at 41°C for 9h and then returned to 38.5°C. Heat shock reduced (P&lt;0.01) the percent of putative zygotes and cleaved embryos that became blastocysts at 8 dpi but IL-11 had no effect at either temperature (percent zygotes to blastocysts=25.3% and 25.6% for control and IL-11 at 38.5°C and 14.0% and 11.8% for control and IL-11 at 41°C; SEM=3.4%). In conclusion, IGF-1 blocked induction of apoptosis caused by heat shock and the reduction in development caused by ethanol. Thus, IGF-1 may play an important role in early development by acting as a survival factor. There was no evidence that IL-11 conferred thermoprotection to bovine embryos. (Support: USDA NRICGP 2002-35203-12664, USDA IFAFS #2001-52101-11318, and USDA TSTAR 2001-34135-11150.)

The effects of varying the interval from follicular wave emergence to progestin withdrawal on follicular dynamics and the synchrony of estrus in beef cattle

The objective of this experiment was to examine the effects of varying the interval from follicular wave emergence to progestin (controlled internal drug-releasing insert, CIDR) withdrawal on follicular dynamics and the synchrony of estrus. A secondary objective was to assess the effects of causing the dominant follicle (DF) to develop in the presence or absence of a corpus luteum (CL) on follicular dynamics and the synchrony of estrus and ovulation. The experiment was designed as a 2 x 2 x 2 factorial arrangement of treatments with injection of GnRH or estradiol-17 beta and progesterone (E2 + P4) at treatment initiation, duration of CIDR treatment, and injection of PG (prostaglandin F2 alpha) or saline at the time of CIDR insertion as main effects. Estrous cycles (n = 49) in Angus cows were synchronized, and treatments commenced on d 6 to 8 of the estrous cycle. Cows were randomly assigned to receive a CIDR containing 1.9 g of P4 for 7 or 9 d. Approximately half the cows from each CIDR group received either GnRH (100 micrograms) or E2 + P4 (1 mg of E2 + 100 mg of P4) at CIDR insertion. Cows in GnRH or E2 + P4 groups were divided into those that received PG (37.5 mg) or saline at CIDR insertion. All cows received PG (25 mg) 1 d before CIDR removal. Daily ovarian events were monitored via ultrasound. The intervals from GnRH or E2 + P4 treatment to follicular wave emergence were 1.4 and 3.3 d, respectively (P < 0.05). The interval from follicular wave emergence to CIDR removal was longer (P < 0.05) for cows treated with GnRH (6.6 d) than those treated with E2 + P4 (4.7 d) and longer (P < 0.05) for those fitted with a CIDR for 9 d (6.5 d) than those with a CIDR in place for 7 d (4.8 d). Cows treated with PG or GnRH at CIDR insertion had a larger (P < 0.05) DF at CIDR removal than those treated with saline or E2 + P4. Treatment with a CIDR for 9 d also resulted in a larger (P < 0.07) DF at CIDR removal compared with cows fitted with a CIDR for 7 d. The interval from CIDR removal to estrus was shorter (P < 0.05) in cows treated with PG than those treated with saline. The synchrony of estrus and ovulation was not affected by any of the treatments (P > 0.05). Altering the interval from follicular wave emergence to progestin removal or creating different luteal environments in which the DF developed caused differences in the size of the DF at CIDR removal and the timing of the onset of estrus, but it did not affect the synchrony of estrus or ovulation.

Effects of density on displacement, falls, injuries, and orientation during horse transportation(1)

Three groups of slaughter-type horses, totaling 30 mares and 29 geldings, were used to determine density effects on displacement (distance moved during a stop), falls, injuries, and orientation using a single-deck, open-topped commercial semi-trailer. Each horse was assigned to one of two treatments: high density (1.28 m(2)/horse with 14 horses) or low density (2.23 m(2)/horse with eight horses). Both treatments occurred sequentially on the same day (treatment order was alternated each trial), using the middle 2.44x7.32 m compartment of a large semi-tractor trailer. The horses were transported for two laps around a 7.28-km course, averaging 25 min and 36+/-89 s. Each lap consisted of two 60 degrees turns, four 90 degrees turns, two 120 degrees turns, one 180 degrees turn, six hard brakes, and six rapid accelerations, which were more severe than conditions usually experienced in commercial transport. Displacement, falls, and orientation were recorded for each horse using overhead video cameras. Average displacement between the two densities was not different (P=0.47). The proportion of horses that fell in the high-density treatment (40%) was greater (P=0.046) than the low-density treatment (17%). The proportion of horses injured was greater (P=0.006) in high density (64%) than low density (29%). However, there was not a significant difference in the average severity of injury for the high-density treatment (1.77) versus the low-density treatment (0.92), P=0.48. Overall, the horses did not show a preference (P=0.38) for facing toward (47.5%) or away (40.7%) from the direction of travel and orientation did not differ (P0.18) between the high and low-density treatments. High stocking density of horses during transport increases the incidence of falls and injuries, and made it more difficult to get up when a subject was floored.