Effect of recombinant bovine somatotropin on superovulatory response and recipient pregnancy rates in a commercial embryo transfer program

Recombinant bovine somatotropin (rbST) has been shown to increase follicular growth in cattle and some studies have demonstrated an increase in superovulatory response for rbST-treated cows. Pregnancy rates have also been shown to increase when rbST was administered around the time of insemination or prior to embryo transfer. The application of rbST for the purpose of increasing superovulatory responses of donor cows and increasing pregnancy rates of recipient heifers was tested in a commercial embryo transfer program. In Experiment 1, embryo donor cows (n = 56) underwent three cycles of control superovulation (two before and one after weaning) and subsequently underwent up to four additional superovulations while being treated with either rbST (500 mg sustained-release rbST; Posilac, Monsanto, St. Louis, MO; n = 28) or excipient (control; n = 28) once every 14 days. In Experiment 2, lactating embryo donor cows (n = 37) underwent a control superovulation and then underwent a superovulation while lactating and being treated with either rbST (n = 16) or excipient (n = 21). In Experiment 3, embryo recipient heifers that were being implanted with either in vitro or in vivo produced embryos were treated with either rbST (n = 146) or excipient (n = 143) at the time of embryo transfer. Treatment of non-lactating (Experiment 1) or lactating (Experiment 2) donor cows with rbST during repeated superovulation did not affect the number of corpora lutea, the sum of transferable embryos, degenerate embryos, and unfertilized oocytes, or the number of transferable embryos. Treatment of recipient heifers with rbST (Experiment 3) did not affect pregnancy rates for either in vitro or in vivo produced embryos. We conclude that superovulatory response and pregnancy rates (respectively) are similar to control for rbST-treated cows undergoing repeated superovulations and rbST-treated recipient heifers treated at the time of embryo transfer.     

Association between blood plasma urea nitrogen levels and reproductive fluid urea nitrogen and ammonia concentrations in early lactation dairy cows

Two experiments were conducted to study the relationship of blood plasma urea nitrogen (PUN) concentrations with NH3, urea nitrogen, K, Mg, P, Ca, and Na concentrations in fluid of preovulatory follicles (experiment 1) and the relationships of PUN concentration and stage of estrus cycle with ammonia and urea nitrogen concentrations in uterine fluids (experiment 2) in early lactation dairy cows. Mean PUN levels were used to distribute cows into two groups: cows with PUN>or=20 mg/dl (HPUN), and cows with PUN<20 mg/dl (LPUN). In experiment 1, blood and follicular fluids from preovulatory follicles of 38 early lactation dairy cows were collected on the day of estrus (day 0) 4h after feed was offered. Follicular fluid NH3 was higher (P<0.01) in HPUN cows (339.0 micromol/L+/-72.2) compared to LPUN cows (93.9 micromol/L+/-13.1). Follicular fluid urea N was higher (P<0.001) in HPUN cows (22.4 mg/dl+/-0.4) compared to LPUN cows (17.0 mg/dl+/-0.3). PUN and follicular fluid urea N were correlated (r2=0.86) within cows. In experiment 2, blood and uterine fluids were collected from 30 cows on day 0 and on day 7. Uterine fluid NH3 was higher (P=0.05) in HPUN cows (1562 micromol/L+/-202) than in LPUN cows (1082 micromol/L+/-202) on day 7, but not on day 0. Uterine fluid urea N was higher (P<0.001) in HPUN cows than in LPUN cows on day 0 (26.9 mg/dl+/-1.3 and 20.4 mg/dl+/-0.7) and day 7 (26.5 mg/dl+/-1.1 and 21.4 mg/dl+/-1.1). There was a correlation (r2=0.17) between PUN and uterine fluid urea N within cows. The results of this study indicate that high PUN concentrations were associated with elevated NH3 and urea N concentrations in the preovulatory follicular fluids on the day of estrus and in the uterine fluid during the luteal phase of the estrous cycle in early lactation dairy cows. Elevated NH3 or urea N concentrations in the reproductive fluids may contribute to reproductive inefficiency in dairy cows with elevated plasma urea nitrogen due to embryo toxicity.     

Plasma progesterone profiles and factors affecting embryo-fetal mortality following embryo transfer in dairy cattle

The relationship between plasma progesterone (P4) levels and embryo survival, and the value of P4 profiles for the selection of cattle embryo transfer recipients is still a matter of controversy. This study reports a comparison between lactating cows and heifers (n = 407) from a single dairy herd, after transfer of either fresh or frozen-thawed good quality embryos, of their ability to sustain embryo-fetal development to term. Plasma P4 concentrations on the day of estrus (Day 0 = D0), Day 4, Day 7 and on Day 21 were measured and related to embryo survival. Plasma P4 levels on Days 0, 4 and 7 were similar in recipients later found pregnant or open. Plasma P4 levels on Day 7 were significantly higher (P < 0.01) in heifers than in cows, but they were similar in pregnant and nonpregnant heifers and in pregnant and nonpregnant cows. Pregnancy rates for fresh and frozen-thawed embryos were higher in heifers than in cows, but the differences did not reach significance. However, the overall late embryonic mortality was significantly higher (P < 0.01) and the calving rate for frozen-thawed embryos was significantly lower (P < 0.05) in cows than in heifers. As expected, plasma P4 on Day 21 was significantly higher (P < 0.001) in pregnant than in nonpregnant recipients, but there was no difference between pregnant cows and pregnant heifers. Plasma P4 levels on Day 7 of recipients presumed pregnant on Day 21 and later found pregnant or nonpregnant were similar, but plasma P4 levels on Day 21 were significantly higher (P < 0.001) in pregnant than in nonpregnant recipients. The results of this study suggest that plasma P4 levels until the day of transfer, except for the rejection of recipients with abnormal luteal function, are of limited practical use for embryo transfer recipient selection. However, in lactating cows low plasma P4 values on Day 7 might negatively affect embryo survival, while in heifers this effect is not noticeable. Lactating cows are more prone to embryo loss than heifers, especially in the case of frozen-thawed embryos; this is associated with a lower competence of the corpus luteum at Day 7.     

In vitro production of bovine embryos using sex-sorted sperm

The objective of this study was to investigate the suitability of sex-sorted sperm for producing viable in vitro embryos for subsequent transfer into recipient cows and heifers on commercial dairy farms. From August 2002 to June 2003, ovaries were collected from 104 producer-nominated Holstein donor cows on seven Wisconsin farms via colpotomy or at slaughter. Oocytes (N=3526) were aspirated from these ovaries, fertilized 22+/-0.2h later, and cultured to the morula or blastocyst stage. The fluorescence-activated cell sorting ("Beltsville") approach was used to produce (primarily) X-bearing sperm from the ejaculates of three young Holstein sires, and 365 transferable embryos were produced. On average, 3.6+/-0.3 (means+/-S.E.M.) transferable embryos were produced per donor, including 1.4+/-0.2 (Grade 1), 1.5+/-0.2 (Grade 2), and 0.7+/-0.1 (Grade 3) embryos. Number of usable oocytes per donor (33.9+/-3.3) and percent cleavage (51.1+/-1.9) were significant predictors of the number of blastocysts that developed. Mean conception rates for the resulting in vitro embryos were 34.2+/-1.6% in yearling heifer recipients and 18.2+/-0.7% in lactating cow recipients. Additional oocytes (N=3312) from ovaries of anonymous donors (N unknown) collected at a commercial abattoir were fertilized using unsorted sperm, and the percentage of these that developed to blastocyst stage (20.1+/-2.9) was greater (P<0.05) than the corresponding percentage (12.2+/-2.3) achieved with sex-sorted sperm using oocytes (N=1577) from the same source. In summary, we inferred that in vitro embryo production may be a promising application of sex-sorted sperm in dairy cattle breeding, but that the biological causes of impaired embryo development in vitro and compromised conception rates of transferred embryos should be further investigated.     

Factors affecting success of embryo collection and transfer in large dairy herds

Our objective was to evaluate factors that affected the success of embryo transfer programs in large dairy herds. Non-lactating donor cows produced a larger number of ova/embryos (P<0.01) and viable embryos (P<0.01) than lactating cows. The interaction between season and donor class was correlated with the proportion of ova/embryos classified as fertilized (P=0.03), because lactating donors had fewer fertilized ova in the summer. There was no correlation between 305-day mature equivalent milk yield and response to superstimulation. Although the interval between superstimulation protocols was correlated with the number of ova/embryos (P=0.03), there was no correlation with the number of viable embryos. Pregnancy per embryo transfer (P/ET) in heifer recipients was correlated with embryo quality grade (P<0.01), season (P=0.04), and whether embryos were fresh or frozen/thawed (P<0.01). Lactating recipient cows tended to have a lower rate of P/ET during the summer (P=0.12 to P=0.08). Synchronization protocols tended to be (P=0.06; Herd 1) or were (P=0.02; Herd 2) correlated with P/ET. Lactating cows receiving vitrified IVF embryos had a lower (P=0.01) P/ET than those receiving fresh IVF embryos, especially in the summer (P=0.09). Milk yield was not correlated with P/ET. The use of heat abatement systems is critical to improve embryo production and P/ET. Synchronization protocols that optimized synchrony of ovulation may increase fertility of recipient cows and eliminate the need for estrous detection.     

Effects of circulating progesterone and insulin on early embryo development in beef heifers

The aims of this study were to determine the effect on early embryo development of feeding a diet formulated to enhance circulating insulin concentrations and secondly to investigate the association between early embryo development and maternal progesterone concentrations in beef heifers. The study was carried out in 32 Simmental x Holstein Friesian heifers 22-25 months of age weighing 506+/-7kg and in condition score 3.1+/-0.1. Animals were fed two diets that were isoenergetic and isonitrogenous, but that would encourage either propionate (diet A) or acetate (diet B) production in the rumen. The rationale was that propionate would induce a greater insulin release in response to feeding. Animals were fed a 50:50 mix of the two diets for 14 days at 0.8x maintenance, with straw provided ad libitum. Animals were then fed one of the experimental diets for 3 weeks prior to synchronisation of oestrus and insemination and for a further 16 days following mating. All heifers were blood sampled daily from oestrus synchronisation and eight animals on each diet underwent daily transrectal real-time ultrasonography to determine the day of ovulation. All heifers were slaughtered at Day 16 after mating. While feeding of diet A (propionic) caused a significant (P<0.05) increase in the plasma insulin to glucagons ratio differences in insulin were not significantly different. This is probably due to the fact that insulin concentrations were quite high as the heifers used in the present study were in good body condition making further increases in insulin difficult to achieve. Diet did not affect size of ovulatory follicle (DIET A: 15.1+/-0.7mm; diet B: 14.6+/-0.7mm), day of ovulation (diet A: 3.5+/-0.2 days; diet B: 3.4+/-0.2 days), mean plasma progesterone concentration (diet A: 4.7+/-0.4ng/ml; diet B: 5.2+/-0.3ng/ml), corpus luteum weight (diet A: 6.0+/-0.2g; diet B: 6.0+/-0.2g) or pregnancy rate (diet A: 81.3%; diet B: 81.3%). However, the proportion of well-elongated (>10cm) embryos on Day 16 was higher in animals fed diet A than in those fed diet B (84.6% versus 38.5%; P<0.05). While progesterone concentration did not differ between pregnant and non-pregnant heifers, progesterone did show an earlier post-ovulatory rise in heifers with well-elongated (>10cm) embryos with levels in these animals significantly higher on Days 4 and 5 than in heifers with small (<10cm) embryos at slaughter. This study demonstrated an enhancement in early embryo development in animals fed a diet generating an increased insulin:glucagon ratio that was not related to circulating maternal progesterone concentrations. However, across diets, enhanced embryo development was associated with elevated plasma progesterone on Days 4 and 5 following mating.     

Donor category and seasonal climate associated with embryo production and survival in multiple ovulation and embryo transfer programs in Holstein cattle

The present study investigated the effect of Holstein donor category (cows vs. heifers) and climate variation (hot vs. cooler season) on the efficiency of in vivo embryo production programs as well as embryo survival after transferred to Holstein recipient cows. A total of 1562 multiple ovulation (MO) procedures (cows: n = 609, and heifers: n = 953) and 4076 embryo transfers (ETs) performed in two dairy herds were evaluated. Donor cows had greater number of CLs (10.6 ± 0.6 vs. 7.5 ± 0.4; P < 0.0001) and ova/embryos recovered (7.6 ± 0.6 vs. 4.6 ± 0.4; P < 0.0001) compared with donor heifers. However, fertilization rate (47.9 vs. 82.4%; P < 0.0001) and proportion of transferable embryos (31.5 vs. 67.4%; P < 0.0001) were lower in donor cows than heifers, respectively. Regardless of donor category, the proportion of freezable embryos was less (P < 0.001) during hot season than in cooler season (21.4 vs. 32.8%). However, greater decline in the proportion of freezable embryos during the hot season was observed in cows (21.7 vs. 10.7%) compared with heifers (46.2 vs. 38.1%; P = 0.01). In contrast, the season on which the embryo was produced (hot or cool) did not affect pregnancy rate on Day 31 (30.5 vs. 31.7%; P = 0.45) and 45 (25.3 vs. 25.1%; P = 0.64) of pregnancy. Regardless of the season in which the embryos were produced, embryonic survival after transferring embryos retrieved from donor cows was greater on Days 31 (36.0 vs. 30.7%; P = 0.001) and 45 (28.3 vs. 23.1%; P = 0.001) of pregnancy when compared with embryos from donor heifers. In conclusion, MO embryo production efficiency decreased during the hot seasons both in cows and heifers; however, the decline was more pronounced in donor cows. Regardless of the embryo source, similar pregnancy rate was observed in the recipient that received embryos produced during the hot and cooler seasons. Curiously, embryos originating from donor cows had higher embryonic survival when transferred to recipient cows than embryos originating from heifers.     

Embryo yield and plasma progesterone profiles in superovulated dairy cows and heifers.

This study was conducted to compare the superovulatory (SOV) response of dairy cows (n=172) and heifers (n=172), with two SOV treatments started at the mid-luteal-phase of the estrus cycle. Donors were randomly treated either with equine chorionic gonadotrophin (eCG) plus neutra-eCG serum (eCG+N group, n=167) or follicle stimulating gonadotrophin (FSH-P group, n=177).No significant differences were observed among groups in the percentage of superovulatory responsive donors (SR donors; corpora lutea (CL) >/=2), the mean number of total ova, fertilized ova and viable embryos recovered. Cows yielded significantly less total ova and less fertilized ova (P<0.05) and tended to yield less viable embryos (P<0.06) than heifers.Plasma progesterone (P4) concentrations (n=135 donors) on the day of PGF(2alpha) (PGF) injection and on the day of SOV estrus were significantly higher (P<0.01) in eCG+N than in FSH-P donors and, the increase between those 2 days was also significantly higher (P<0.05) in group eCG+N than in group FSH-P, suggesting a higher luteotrophic effect of eCG than FSH-P. SR donors had P4 levels significantly higher (P<0.001) than non-SR donors only on day 5 after the SOV estrus and on the day of embryo recovery. Plasma P4 concentrations at 5 days after the SOV estrus and at embryo recovery correlated significantly (r=0.76, P<0.001).Heifers had significantly higher P4 levels than cows at gonadotrophin injection (P<0.01), PGF injection (P<0.001), 5 days (P<0.01) and 7 days (P<0.001) after the SOV estrus. At day 7 after the SOV estrus, P4 concentrations per ova recovered were significantly higher in heifers than in cows (P<0.01). The increase of plasma P4 per ova recovered, between days 5 and 7 after the SOV estrus, was significantly (P<0.01) higher in heifers than in cows. Also, the increase of plasma P4 between injections of gonadotrophin and PGF was significantly higher (P<0.05) in heifers than in cows.These results suggest that heifers have higher plasma P4 concentrations at diestrus (either before or after the SOV treatment) and this is associated with a higher embryo yield and quality, as compared to lactating cows. These higher plasma P4 concentrations reflect not only differences in ovulation rate as well as the competence of the corpus luteum, which is potentialized by gonadotrophin stimulation.     

The effect of feeding diets high in quickly degradable nitrogen on follicular development and embryo growth in lactating Holstein dairy cows

This study investigated the effect on follicular and embryo development of increasing quickly degradable nitrogen (QDN) intake in lactating Holstein dairy cows. Forty mature post-partum cows were fed one of two diets for a minimum of 10 weeks, starting 10 days before first insemination. The Control diet was a high production dairy ration. The High QDN diet comprised the Control ration plus 250 g urea/head/day. Both diets were formulated to ensure that the energy requirements of the cows were satisfied. The High QDN treatment resulted in a significant increase in milk urea, plasma urea and plasma ammonia concentrations. The highest plasma urea (8.2 mmol/l) and ammonia concentrations (120 micromol/l) were recorded within 7 days of the urea supplement being added to the diet. There was no effect of diet on plasma progesterone or glucose concentration. There was also no significant effect of treatment on follicular development or embryo growth. The results from this study suggest that the lactating cow can adapt to increased intakes of QDN if the increase starts at least 10 days before insemination.     

Bovine somatotropin increases embryonic development in superovulated cows and improves post-transfer pregnancy rates when given to lactating recipient cows

Previous studies indicated that the use of bovine somatotropin (bST) in concurrence with a timed artificial insemination (TAI) protocol increased pregnancy rates. However, the mechanisms for such a bST effect on fertility were not clear. Objectives of this study were to determine the effects of bST on fertilization and early embryonic development after cows received a superovulation treatment, test whether embryos recovered from bST-treated cows were more likely to survive after transfer to recipients, and evaluate whether treatment of recipient cows with bST affects pregnancy rates. Lactating (n = 8) and nonlactating (n = 4) Holstein donor cows were superovulated, inseminated at detected estrus and assigned to a nontreated control group or to a treatment group receiving a single injection of bST (500 mg, sc) at insemination. Embryos were nonsurgically flushed 7 days after AI and frozen in ethylene glycol for direct transfer. Embryos derived from bST-treated (bST-embryos) or control (control-embryos) donors were transferred to lactating Holstein recipient cows that received either bST treatment 1 day after estrus (500 mg, sc; bST-recipients) or were untreated controls (control-recipients). Thus, there were four treatment groups: control-embryos/control-recipients (n = 43), bST-embryos/control-recipients (n = 41), control-embryos/bST-recipients (n = 37), and bST-embryos/bST-recipients (n = 60). Pregnancy was determined by palpation per rectum 33-43 days after embryo transfer. Unfertilized ova per flush was less for bST than for control (1.0 +/- 0.9 < 3.7 +/- 0.9; P < 0.04). Percentage of transferable embryos was greater for bST than for control (77.2% > 56.4%; P < 0.01). Number of blastocysts per flush was greater for bST than for control (2.4 +/- 0.7 > 0.4 +/- 0.7; P < 0.04). Pregnancy rates following embryo transfer were 25.6% for control-recipient/control-embryo, 43.2% for bST-recipient/control-embryo, 56.1% for control-recipient/bST-embryo, and 43.3% for bST-recipient/bST-embryo. Transfer of bST-embryos increased pregnancy rates compared with transfer of control-embryos (P < 0.04). An interaction between embryo and recipient treatments (P < 0.05) indicated that treatment of recipient cows with bST increased pregnancy rates as compared to control-recipients that received a control-embryo. However, there was no additive effect when bST-recipients received a bST-embryo. Administration of bST at AI decreased the number of unfertilized ova, increased the percentage of transferable embryos, and stimulated embryonic development to the blastocyst stage. Moreover, bST affected both early embryonic development and recipient components to increase pregnancy rates following embryo transfer.     

The usefulness of a single measurement of insulin-like growth factor-1 as a predictor of embryo yield and pregnancy rates in a bovine MOET program

The objective was to determine if a single measurement of plasma insulin-like growth factor-1 (IGF-1) could predict the number of viable embryos obtained from donors and the likelihood of pregnancy in recipients in multiple ovulation and embryo transfer (MOET) programs in cattle. The embryo yields from 101 embryo recoveries were examined in maiden Holstein heifers (n=75) and multiparous Holstein cows (lactating cows n=20, dry cows n=6). Donors were super stimulated with FSH and embryo recovery was done non-surgically 7 days after artificial insemination. Embryos were classified according to the IETS criteria. Pregnancy rates in 100 maiden Holstein heifer recipients were analysed. Recipients were on day 7+/-1 of the estrous cycle at transfer. Pregnancy diagnosis was carried out at day 30 (PD 30) and rechecked at day 60 (PD 60) after transfer. Blood samples from coccygeal vessels taken at the time of embryo recovery (donors) and transfer (recipients) were analysed for IGF-1, insulin, beta-hydroxybutyrate (beta-OHB), non-esterified fatty acids (NEFA), urea and cholesterol. There was a negative correlation between the number of viable embryos and insulin (r=-0.33, P=0.025) in donor heifers. In donor cows, the number of viable embryos was correlated with IGF-1 (r=0.43, P=0.028) and cholesterol (r=-0.43, P=0.027). In recipients, PD30 and PD 60 were not affected by any of the circulating parameters analysed. Insulin, IGF-1 and cholesterol only explained 8.9, 13.9 and 15.8% of the variation in the production of viable embryos, respectively. Several factors affect MOET programs and under the circumstances of the present study the usefulness of hormonal and metabolic profiles as predictors of the outcome of this biotechnology was limited.     

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.     

Conception rates after artificial insemination or embryo transfer in lactating dairy cows during summer in Florida

The objective was to compare conception rates to embryo transfer relative to AI, during summer heat stress, in lactating dairy cows. Holstein cows (n = 180; 50 to 120 d postpartum) were allocated randomly to 1 of 3 groups: artificial insemination (AI, n = 84), embryo transfer using either embryos collected from superovulated donors (ET-DON, n = 48), or embryos produced in vitro (ET-IVF, n = 48). Embryos from superovulated donors were frozen in 10% glycerol and were rehydrated in a 3-step procedure, in decreasing concentrations of glycerol in a sucrose medium before transfer. Embryos produced in vitro were frozen in 1.5 M ethylene glycol, thawed and transferred without rehydration. Blood samples were collected from AI and ET recipients on Days 0, 7 and 22 for measurement of progesterone in plasma. Conception rate was estimated for the three groups at Day 22 (progesterone > 1 ng/mL) and confirmed at Day 42 by palpation per rectum. Conception rate estimates at Day 22 did not differ among groups (AI, 60.7%; ET-DON, 60.4%; ET-IVF, 54.2%), but conception rates at Day 42 differed (AI, 21.4%; ET-DON, 35.4%; ET-IVF, 18.8%; AI versus ET: P > 0.10 and ET-DON versus ET-IVF: P < 0.05). In cows considered pregnant at 22 d but diagnosed open at 42 d, the interestrous intervals were 28.8 +/- 2.2, 35.2 +/- 3.5 and 31.6 +/- 2.9 d, respectively, for AI, ET-DON and ET-IVF groups. Transfer of embryos collected from nonheat-stressed superovulated donors significantly increased conception rates in heat stressed dairy cattle. However, transfer of IVF-derived embryos had no advantage over AI. Where appropriate mechanisms are in place to attenuate the effects of heat stress, embryo transfer using frozen-thawed donor embryos increases conception rates.     

Diets enriched in unsaturated fatty acids enhance early embryonic development in lactating Holstein cows

We hypothesized that a diet enriched in alpha-linolenic acid would enhance embryonic development relative to diets enriched in linoleic or saturated fatty acids. Twenty-four lactating Holstein cows (86+/-22 d postpartum) were assigned to one of three diets containing saturated fatty acids (SAT; high in palmitic and stearic acids), whole flaxseed (FLX; high in alpha-linolenic acid) or sunflower seed (SUN; high in linoleic acid). Rations were formulated to provide 750 g supplemental fat/cow/d in all dietary groups. Ovulation (Day 0) was synchronized approximately 20 d after diets began. Ultrasound-guided follicular ablation of all follicles >8 mm was performed 5 d after ovulation; super stimulatory treatments began 2 d after follicular ablation, and embryos were collected non-surgically 7 d after AI. Fertilization rate, numbers of follicles and ovulations, and total and transferable embryos did not differ (P>0.05) among dietary groups. Sixty-one transferable embryos were stained and total blastomere number determined. Blastomere number was affected by diet (P<0.01); without regard to stage of development, embryos collected from cows fed SAT had lower (P<0.01) blastomere numbers (mean+/-S.E.M.; 77.1+/-3.9) than those from cows fed FLX (93.4+/-3.3) or SUN (97.2+/-3.5). Differences were most evident in the expanded blastocyst stage; at this stage, embryos of cows fed FLX and SUN diets had more blastomeres (P<0.02) than those of cows fed SAT (115.4+/-6.3, 132.3+/-8.3, and 89.3+/-9.6 cells, respectively). Although our hypothesis was only partially supported, embryonic development was enhanced in Holstein cows fed unsaturated fatty acids compared to those fed saturated fatty acids.     

Effect of a single growth hormone (rbST) treatment at breeding on conception rates and pregnancy retention in dairy and beef cattle

Initiation of long-term treatment with rbST (Posilac, Monsanto, St. Louis, MO) coincident with first insemination increased pregnancy rates in dairy cattle, but neither the efficacy of using only the initial injection, nor its effects on retention of pregnancy are known. Lactating dairy cows, dairy heifers, and lactating beef cows were assigned at random to treatment (rbST) or control. Dairy cows, dairy heifers, and beef cows received 500 mg rbST (n = 48, 35, 137 inseminations, respectively) at artificial insemination or were left untreated (n = 62, 33, 130 inseminations, respectively). Pregnancy was diagnosed by ultrasonography at 28-36 days. Treatment with rbST at insemination improved conception rates in dairy cows (60.4% versus 40.3%; P < 0.05), but not in dairy heifers or beef cows. Conception rates did not differ in dairy cows at < or =100 days in milk (DIM), but were improved in cows treated with rbST after 100 DIM (64.3% versus 25.8%; P < 0.05). Retention of pregnancy to approximately 60 days and sizes of CL, diameter of follicles > or =5 mm, and crown-rump lengths of embryos were not affected by treatment. The second objective was to examine the effects of rbST at insemination on birth weight and post-natal calf growth in beef cows. However, birth and weaning weights of beef calves were not affected by treatment. In conclusion, a single treatment with rbST at insemination increased conception rates in dairy cows, specifically in those >100 DIM.     

Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows

High protein diets, which lead to excess production of nonprotein nitrogen such as ammonia and urea, have been associated with reduced fertility in dairy cows. In this study we test the hypothesis that diets containing high levels of quickly degradable urea nitrogen (QDN) compromise embryo development. Lactating dairy cows were fed mixed silage and concentrates twice daily. At 60 days postpartum, a synchronized estrus was induced and the cows were subsequently superovulated and inseminated using a standard protocol. On Day 7 after insemination, the uteri were flushed and embryos retrieved. At the start of treatment, cows were randomly allocated into three nutritional groups: control (CONT, n = 8), long (L-) QDN (n = 8) and short (S-) QDN (n = 9). The L-QDN cows were fed a supplement of urea from 10 days before insemination, and the S-QDN cows were fed the supplement from insemination until embryo collection. Both L- and S-QDN diets produced significant increases in plasma ammonia and urea 3 h post-feeding. The S-QDN but not the L-QDN diet was associated with a significant reduction in embryo yield. Embryo quality was also significantly reduced in the S-QDN cows. This study indicates that there is no deleterious effect on the yield and quality of embryos recovered 7 days after breeding when QDN feeding is initiated during the previous midluteal phase. However, introduction of a similar diet 10 days later, at the time of insemination, was deleterious. We suggest that QDN is toxic to embryos but cows can adjust within 10 days.     

Effect of dietary protein on embryo recovery rate and quality in superovulated heifers

For almost 3 decades, superovulation and embryo transfer have been used in cattle breeding to increase the number of offspring from genetically superior female animals. Several factors including nutrition affect the number of transferable embryos recovered. We compared the effects of two different dietary protein levels easily achieved in practical conditions on embryo number and quality in superovulated heifers. Finnish Ayrshire heifers (n = 37) were allocated to isoenergic diets containing either 14% (D14) or 18% (D18) crude protein (CP). Estruses were synchronized, and the heifers were subsequently superovulated and inseminated using a standard FSH-protocol. Embryos were collected 7 days after inseminations (71-72 days after the beginning of the treatment period) by uterine flushing. The number of corpora lutea, and the number and quality of embryos were determined. Protein feeding did not affect superovulatory response, the number of embryos or the number of transferable embryos recovered. Proportionally more poor-quality embryos were found in group D14 than in group D18 (20.2% versus 13.2%, respectively, P = 0.053). It is concluded that a long-term moderate increase in the content of crude protein fed to energy-adequate heifers does not seem to affect superovulatory response and the number of embryos recovered, but it may be advantageous to the quality of embryos.     

Influence of summer heat stress on pregnancy rates of lactating dairy cattle following embryo transfer or artificial insemination

Lactating Holstein cows were used to determine if pregnancy rate from embryo transfer (n = 113) differed from contemporary control cows (n = 524) that were artificially inseminated (AI). Holstein heifers (n = 55) were superovulated with FSH-P (32 mg total) and inseminated artificially during estrus and subsequently managed under shade structures. On Day 7 post estrus, embryos were recovered, and primarily excellent to good quality embryos (90.3%) were transferred to estrus-synchronized lactating cows. Cows were managed under conditions of exposure to summer heat stress. Pregnancy status was determined by milk progesterone concentrations at Day 21 and palpation per rectum at 45 to 60 d post estrus. Pregnancy rates of cows presented for AI (Day 21, 18.0%; Days 45 to 60, 13.5%) were typical for lactating cows inseminated during periods of summer heat stress in Florida. Pregnancy rates of embryo recipient cows were higher (P<0.001) than those of control cows (Day 21, 47.6%; Days 45 to 60, 29.2%). Summer heat stress had no adverse effect on heifer superovulatory response, but it increased (P<0.05) the incidence of retarded embryos (相似文献   

Effect of dietary phosphorus concentration on estrous behavior of lactating dairy cows

The objective of this study was to determine the effect of dietary phosphorus (P) concentrations of 0.38 (adequate) or 0.48% (excess) of the total mixed ration (TMR) (dry matter basis) on estrous behavior of lactating cows as measured by a radiotelemetric system (HeatWatch; De Forest, WI, USA). At calving, 42 Holstein cows (n=21 per treatment) were randomly assigned to one of two dietary P treatments. Cows were milked twice daily and milk weights were recorded. Cows were housed in a free-stall barn and were fitted with a radiotelemetric transmitter 40 days postpartum to record estrous mounting activity. The total number of estruses recorded for the 42 cows were 72 (37 and 35 for cows in the adequate and excess P groups, respectively). The mean duration of estrous cycles was 22 +/- 0.6 days and 21 +/- 0.4 days for cows fed the adequate and excess P diets, respectively (P=0.14). The mean duration of estrus was 8.9 +/- 1.1 h and 8.6 +/- 1.2 h (P=0.86), the average number of mounts during estrus was 7.0 +/- 1.2 and 8.2 +/- 1.7 (P=0.57), and the total mounting time was 27.1 +/- 4.3 s and 30.8 +/- 6.5 s (P=0.64) for cows fed the adequate and excess P diets, respectively. Phosphorus treatment had no significant effect on intensity or duration of estrus.     

Embryo production with sex-sorted semen in superovulated dairy heifers and cows

The aim of this study was to examine the effect of sex-sorted semen on the number and quality of embryos recovered from superovulated heifers and cows on commercial dairy farm conditions in Finland. The data consist of 1487 commercial embryo collections performed on 633 and 854 animals of Holstein and Finnish Ayrshire breeds, respectively. Superovulation was induced by eight intramuscular injections of follicle-stimulating hormone, at 12-hour intervals over 4 days, involving declining doses beginning on 9 to 12 days after the onset of standing estrus. The donors were inseminated at 9 to 15–hour intervals beginning 12 hours after the onset of estrus with 2 + 2 (+1) doses of sex-sorted frozen-thawed semen (N = 218) into the uterine horns or with 1 + 1 (+1) doses of conventional frozen-thawed semen (N = 1269) into the uterine corpus. Most conventional semen (222 bulls) straws contained 15 million sperm (total number 30–45 million per donor). Sex-sorted semen (61 bulls) straws contained 2 million sperm (total number 8–14 million per donor). Mean number of transferable embryos in recoveries from cows bred with sex-sorted semen was 4.9, which is significantly lower than 9.1 transferable embryos recovered when using conventional semen (P ≤ 0.001). In heifers, no significant difference was detected between mean number of transferable embryos in recoveries using sex-sorted semen and conventional semen (6.1 and 7.2, respectively). The number of unfertilized ova was higher when using sex-sorted semen than when using conventional semen in heifers (P < 0.01) and in cows (P < 0.05), and the number of degenerated embryos in cows (P < 0.01), but not in heifers. It was concluded that the insemination protocol used seemed to be adequate for heifers. In superovulated cows, an optimal protocol for using sex-sorted semen remains to be found.