M. Drost

Embryonic development in superovulated dairy cattle exposed to elevated ambient temperatures between Days 1 to 7 post insemination

Holstein heifers (n = 29) were used to determine whether thermal stress during the first 7 d of embryonic development may increase the incidence of embryonic abnormalities in dairy cattle. Heifers were acclimated to environmental chambers at 20 degrees C for 9 d and superovulated with follicle stimulating hormone-pituitary (FSH-P; 40 mg total), beginning on Days 9 to 11 of the estrous cycle. Prostaglandin F(2)alpha (Lutalyse; 50 mg total) was administered on Day 3 of FSH-P. Heifers were inseminated artificially at estrus and then maintained at either thermal neutrality (20 degrees C) or under hyperthermic conditions (daily exposure up to 16 h at 30 degrees C and 8 h at 42 degrees C) for 7 d beginning at 30 h after the onset of estrus. On Day 7 post estrus, embryos were recovered nonsurgically and evaluated morphologically for stage of development and quality. The distribution of embryos classified as normal, abnormal, retarded or as unfertilized ova, differed (P<0.001) between heat stress and thermoneutral treatments. Only 20.7% of 82 embryos recovered from stressed heifers were normal compared with 51.5% of 68 embryos from thermoneutral animals. Stressed heifers had a higher incidence of abnormal and retarded embryos with degenerate nonviable blastomeres. Responses indicated that thermal stress from 30 h after the onset of estrus to Day 7 post estrus increases the incidence of abnormal and retarded embryos in superovulated heifers.

Effect of environmental heat stress on follicular development and steroidogenesis in lactating Holstein cows.

Lactating Holstein cows were utilized over two replicate periods (July and September, 1990) to examine the effect of summer heat stress on follicular growth and steroidogenesis. On day of synchronized ovulations, cows were assigned to shade (n=11) or no shade (n=12) management systems. Follicular development was monitored daily by ultrasonography until ovariectomy on Day 8 post estrus. At time of ovariectomy, dominant and second largest follicles were dissected from the ovary. Aromatase activity and steroid concentrations in dominant and subordinate follicles were measured. Acute heat stress had no effects on patterns of growth of first wave dominant and subordinate follicles between Days 1 and 7 of the cycle. Compared with shaded cows, the heat stressed cows did not have suppression of medium size (6 to 9 mm) follicles between Days 5 and 7. A treatment x follicle interaction was detected (P<0.01) for follicular diameter and fluid volume at Day 8. Dominant follicles in shade were bigger (16.4>14.5 mm) and contained more fluid (1.9>1.1 ml) than dominant follicles in no shade. Conversely, subordinate follicles in no shade were bigger (10.1>7.9 mm) and contained more fluid (0.4>0.2 ml) than subordinate follicles in shade. Concentrations of estradiol in plasma and follicular fluid were higher (P<0.01) in July than in September. Heat stress appears to alter the efficiency of follicular selection and dominance, and to have adverse effects on the quality of ovarian follicles.

Embryonic development in superovulated dairy cattle exposed to elevated ambient temperatures between the onset of estrus and insemination

Holstein heifers (n = 16) were used to determine whether heat stress prior to ovulation increases the incidence of embryonic abnormalities. Heifers were superovulated with Follicle Stimulating Hormone (FSH-P; 32 mg total), beginning on Days 10 or 11 of the estrous cycle. Prostaglandin F2α (Lutalyse; 60 mg total) was administered on Day 3 of FSH-P treatment. Heifers were maintained at either thermoneutrality (24°C) or under hyperthermic conditions (exposure to 42°C for 10 h) beginning at the onset of estrus. Following artificial inseminations at 15 and 20 h after the onset of estrus, heifers were continuously maintained under environmental conditions of thermoneutrality for 7 days as provided by environmental shade structures. On Day 7 post estrus, embryos were recovered nonsurgically and evaluated morphologically for stage of development and quality. The distribution of embryos classified as normal, retarded and/or abnormal, or as unfertilized ova differed (P < 0.001) between heat stress and thermoneutral treatments. Only 12.0% of 25 embryos recovered from heat-stressed heifers were normal compared with 68.4% of 19 embryos from thermoneutral heifers. Stressed heifers had a higher (P < 0.001) incidence of retarded and/or abnormal embryos with degenerated blastomeres. These data indicate that thermal stress during the periovulatory period increases the incidence of retarded and/or abnormal embryos in superovulated heifers.

New clinical uses of GnRH and its analogues in cattle

Abstract Gonadotropin-releasing hormone (GnRH) and its analogues cause an acute secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) such that concentrations in peripheral blood are elevated for a 3–5 h period. GnRH-induced alterations in the function of the corpus luteum (CL) or follicle appear to be indirect through alterations in LH and FSH secretion. Repeated injections of GnRH during diestrus or single injections late in diestrus will cause acute increases in plasma progesterone and a delay in CL regression. Injections or continual administration of GnRH during early phases of CL development appear to augment CL differentiation and alter subsequent CL function. These effects are attributable to induced increases in LH. Injections of GnRH during the estrous cycle will re-synchronize follicle development owing to ovulation or luteinization of the dominant follicle leading to subsequent recruitment and selection of a new dominant follicle during a 7 day period. Injection of GnRH followed by injection of prostaglandin (PGF 2α ) at 6 or 7 days is a system of estrous synchronization in which follicle development and CL regression are both synchronized and fertility at the induced estrus is good. Injection of GnRH during the luteal phase post-insemination (e.g. Days 12–14) or post-embryo transfer, to alter CL and/or follicular function, has not resulted in a consistent increase in pregnancy rates. An overall assessment of studies that injected GnRH at the time of insemination in first service postpartum cows or in repeat breeders is rather disappointing. Considerable variation existed among studies within both types of cow populations relative to significant differences, directions of pregnancy rate change ( + vs. −), and magnitude of pregnancy rate increases. Recent findings indicate that timing of GnRH injections closer to the onset of estrus may be beneficial in increasing the conception rate. Utilization of GnRH in combination with progesterone and PGF results in an acute treatment sequence to program follicular development, ovulation and a subsequent cycle in cows with follicular cysts. The use of GnRH, with or without PGF, as a reproductive management program in the early postpartum period has not shown a clear improvement in subsequent reproductive efficiency. Development of precise systems to control ovarian function and reproductive efficiency with GnRH and other pharmaceutical agents is possible. However, such advancements must be founded on a clear understanding of GnRH-induced physiological effects and ability to capture any advantage by good management of the farm unit.

Adverse impact of heat stress on embryo production: causes and strategies for mitigation

The production of embryos by superovulation is often reduced in periods of heat stress. The associated reduction in the number of transferable embryos is due to reduced superovulatory response, lower fertilization rate, and reduced embryo quality. There are also reports that success of in vitro fertilization procedures is reduced during warm periods of the year. Heat stress can compromise the reproductive events required for embryo production by decreasing expression of estrus behavior, altering follicular development, compromising oocyte competence, and inhibiting embryonic development. While preventing effects of heat stress can be difficult, several strategies exist to improve embryo production during heat stress. Among these strategies are changing animal housing to reduce the magnitude of heat stress, utilization of cows with increased resistance to heat stress (i.e., cows with lower milk yield or from thermally-adapted breeds), and manipulation of physiological and cellular function to overcome deleterious consequences of heat stress. Effects of heat stress on estrus behavior can be mitigated by use of estrus detection aids or utilization of ovulation synchronization treatments to allow timed embryo transfer. There is some evidence that embryonic survival can be improved by antioxidant administration and that pharmacological treatments can be developed that reduce the degree of hyperthermia experienced by cows exposed to heat stress.

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 (</= 16 cells) and embryos graded as fair to poor quality. Increased pregnancy rate of recipient lactating cows indicates that the bovine embryo is sensitive to maternal heat stress during the first 7 d after estrus. Embryo transfer may bypass this period of embryonic sensitivity and provide an alternative to AI to partially circumvent heat stress-induced infertility in cattle.

Effect of body condition on reproductive efficiency of lactattng dairy cows receiving a timed insemination

Body condition may influence pregnancy rates to a timed insemination (Ovsynch/TAI) protocol and affect the economical performance of dairy farms. The objectives were to compare pregnancy rates using the Ovsynch/TAI protocol for the first service of lactating dairy cows with body condition scores < 2.5 (scale: 1 to 5, low BCS group) versus > or = 2.5 (control group) and to estimate the economic impact of the effect of body condition on reproductive performance. At 63 +/- 3 d post partum, cows were assigned to 2 experimental groups (low BCS = 81; control = 126), and were treated with GnRH at d 0 and with PGF2alpha 7 d later. At 48 h after PGF2alpha, cows received an injection of GnRH and were inseminated 16 h later. Pregnancy rates to the Ovsynch/TAI protocol were lower for the low BCS group than for the control group at 27 d (18.1 +/- 6.1% < 33.8 +/- 4.5%; P<0.02) and at 45 d (11.1 +/- 5.4% < 25.6 +/- 4.1%; P<0.02) after insemination. Economic analysis indicated that reducing the percentage of the herd in low body condition increases net revenues per cow per year. Body condition influenced pregnancy rates to the Ovsynch/TAI protocol.

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.

Effects of postinsemination progesterone supplementation on fertility and subsequent estrous responses of dairy heifers

The objective of Experiment I, replicated twice, was to evaluate whether fertility of estrus-synchronized dairy heifers could be improved by postinsemination progesterone supplementation. Estrous cycles were synchronized using two injections of prostaglandin (PG) F(2alpha) adiministered 11 days apart. Heifers displaying estrus were inseminated and assigned to control (n = 155) and treated (n = 159) groups. Treatment consisted of intravaginal insertion of controlled internal drug release (CIDR) devices for Days 7 to 13 (Day 0 = day of estrus). The conception rate for CIDR-treated heifers (57.9%) did not differ significantly from that of the controls (53.6%). The return-to-estrus rate and pattern of return estruses were not affected by treatment, but indicated that early embryonic mortality may have occurred in some of the heifers diagnosed nonpregnant. The objective of Experiment II was to evaluate if used CIDR devices were effective in resynchronizing returns to estrus in previously synchronized inseminated but nonpregnant and noninseminated heifers. Estrous cycles of dairy heifers of breeding age were synchronized with PGF(2alpha). Heifers displaying estrus were assigned to be inseminated (n = 117) or not inseminated (n = 35). All heifers were treated with 9-day used CIDR devices for Days 17 to 22 after synchronized estrus in order to resynchronize returns to estrus. Of the inseminated but nonpregnant heifers (n = 41), 78.1% were detected in estrus after CIDR removal (versus 94.3% of noninseminated heifers [n = 35]; P < 0.05) and 61.0% of the estruses occurred within 4 days of CIDR removal (versus 91.4% of noninseminated; P < 0.05). Estruses of synchronized inseminated nonpregnant heifers occurred over a longer period compared with those of noninseminated heifers (P < 0.025). The results indicate that response to the resynchronization protocol was altered by the outcome (early embryo death or failed fertilization) of the previous unsuccessful insemination, and support the hypothesis that delayed returns to estrus can be attributable to a pregnancy which was initiated but failed to establish itself. Such factors should be considered when evaluating responses of cattle to treatments designed to enhance fertility.

Effects of administering progesterone at selected intervals after insemination of synchronized heifers on pregnancy rates and resynchronization of returns to service

In 3 separate trials at 2 locations, dairy heifers (n = 396) were treated with a Controlled Internal Drug Release (CIDR) progesterone device for 9 d. On Day 7 of CIDR treatment, all heifers were injected with PGF(2alpha). Synchronized estruses were detected using a tailpaint and chalk (TPC) scoring system. An animals tailhead was painted at device insertion, and this strip was covered with a contrasting color of chalk at device removal. Over all trials, 85.1% of the heifers were detected in estrus and were inseminated at 48 or 72 hours after CIDR removal. These synchronized and inseminated heifers were divided into the following treatment groups: 1) untreated controls, receiving no further treatment (n = 138); 2) post-insemination progesterone supplementation with a new (n = 59) or used (n = 29) CIDR device for Days 1 to 8 or 2 to 9, respectively, following insemination; or 3) resynchronization of return to service with a used CIDR device for Days 17 to 22 after insemination (n = 112). The pregnancy rate to first insemination in the control and resynchronized groups (Groups 1 and 3) was 46.4%, but decreased to 18.2% with the post-insemination progesterone supplementation. Resynchronization of returns to service (estrus detected 1 to 4 d following removal of second CIDR) occurred in 58.9% of all nonpregnant heifers in Group 3. In summary, CIDR devices used in conjunction with PGF(2alpha) effectively synchronize estrus in dairy heifers. Progesterone supplementation within 2 d of first insemination for 7 d suppressed fertility. Used CIDR devices inserted for Days 17 to 22 after first insemination resynchronized heifers not pregnant to first insemination.