G. A. Perry

Ovarian follicle diameter at timed insemination and estrous response influence likelihood of ovulation and pregnancy after estrous synchronization with progesterone or progestin-based protocols in suckled Bos indicus cows.

The objectives of the present study were to evaluate factors associated with estrous synchronization responses and pregnancy per insemination (P/AI) in Bos indicus beef cows submitted to progesterone-based fixed-time artificial insemination (FTAI) protocols. A total of 2388 cows (1869 Nellore and 519 crossbred NellorexAngus) from 10 commercial farms were evaluated to determine the relationships among breed, body condition score (BCS) on the first day of the FTAI protocol, the occurrence of estrus between progesterone device removal and FTAI, and diameter of largest ovarian follicle (LF) at FTAI on estrous synchronization responses and P/AI. Cows (n=412 primiparous; 1976 multiparous) received an intravaginal device containing progesterone or an ear implant containing norgestomet (a progestin), and an injection of estradiol at the beginning of the estrous synchronization protocol. Body condition was scored using a 1-5 scale on the first day of the FTAI protocol and at 30-60 days postpartum. Females received 300IU of equine chorionic gonadotropin (eCG) and PGF(2alpha) on the day the progesterone device/implant was removed and were inseminated 48-60h later. At insemination, cows (n=2388) were submitted to an ultrasonographic exam to determine the diameter of the LF. Follicles were classified into four categories based on mean and standard deviation (SD) of the LF (LF1=two SD below the mean; LF2=mean minus one SD; LF3=mean plus one SD; LF4=two SD above the mean). Ovulation rate was determined in a subset of cows (n=813) by three consecutive ultrasonographic exams: (1) at time of progesterone device/implant removal, (2) at time of FTAI and (3) 48h after FTAI. Ovulation was defined as the disappearance of a large follicle (>or=8.0mm) that was previously recorded. Estrus was determined in a subset of the cows (n=445) by the activation of a detection of estrous patch placed on the tail head on the day of progesterone device/implant removal. Pregnancy was diagnosed 30 days after FTAI. Pregnancy was influenced (P=0.001) by follicle diameter [LF1=27.5% (81/295), LF2=46.6% (328/705), LF3=57.9% (647/1118), LF4=63.3% (171/270)] and the occurrence of estrus [estrus=67.7% (174/257) and no estrus=36.2% (68/188)]. Follicle diameter at FTAI influenced ovulation rate [LF1=42.5% (34/80), LF2=73.9% (161/218), LF3=95.8% (407/425), LF4=97.8% (88/90)], the occurrence of estrus [LF1=54.8% (51/93), LF2=33.6% (43/128), LF3=68.9% (126/183), LF4=90.2% (37/41)] and P/AI among cows that had ovulations [LF1=32.4% (11/34), LF2=50.3% (81/161), LF3=60.0% (244/407), LF4=68.2% (60/88)]. Improving estrous responses between progesterone device withdrawal and FTAI and increasing the diameter of the LF at FTAI may be important aspects to achieve improved estrous synchronization responses and P/AI following progesterone/progestin and estradiol based FTAI protocols in suckled Bos indicus cows.

Effect of dried corn distillers grains plus solubles compared with soybean hulls, in late gestation heifer diets, on animal and reproductive performance

Dried distillers grains plus solubles (DDGS) contain fat and rumen undegradable intake protein, both of which have been shown to increase reproductive performance in heifers. The mechanisms leading to enhanced reproduction have not been fully defined. The objectives of this research were to evaluate effects of DDGS in late gestation heifer diets on animal and reproductive performance and on blood plasma concentrations of GH, IGF-I, and NEFA. Over 2 yr, 201 heifers were randomly allotted to 1 of 2 diets, which were similar in energy and adequate in rumen degradable intake protein and were fed from d 190 of gestation through calving. Diets were grass hay with DDGS or soybean hulls (SBH) and a supplement. Cow BW and BCS were measured from the beginning of treatment through weaning. Blood samples were collected prepartum on d 71 and 69 of the feeding period and weekly after calving for 4 and 6 wk (d 84 to 105 and d 76 to 111 relative to the feeding period) during yr 1 and 2, respectively. No treatment x year interactions were detected for any of the performance, hormonal, or reproductive dependent variables. Both treatments caused positive BW changes over the feeding period, but DDGS heifers had a greater (P < 0.01) positive BW change compared with SBH heifers. Initial and final BCS and BCS change were similar (P >/= 0.26) between DDGS and SBH treatments. Treatment did not influence (P >/= 0.12) BW or BCS change during the postpartum period. Calving ease, calf vigor, and calf birth weight, weaning weight, and ADG (birth to weaning) were similar (P >/= 0.41) between treatments. The proportion of cows that had initiated estrous cycles (P = 0.46) and the pregnancy distribution (P >/= 0.21) were similar between treatments. However, a greater (P = 0.058) percentage of DDGS cows became pregnant compared with SBH cows (94 and 84%). In both years, there were no effects of treatment (P >/= 0.17) or treatment x time (P >/= 0.52), but time influenced (P </= 0.05) the concentrations of GH, IGF-I, and NEFA. Concentrations of GH were greater (P </= 0.05) at calving and decreased through d 4 after calving. The IGF-I concentrations were greater (P < 0.01) around calving and decreased (P < 0.05) through d 8 or 6 (yr 1 or 2) and remained similar (P > 0.10) for the duration of the sampling period. Concentrations of NEFA increased from calving through d 8 and gradually declined through d 20. Prepartum diets containing DDGS, a source of fat and UIP, benefited pregnancy rates in well-maintained, primiparous beef heifers.

Follicular determinants of pregnancy establishment and maintenance

Synchronization of dominant follicle development and control of ovulation/oocyte retrieval are commonly used assisted reproductive technologies in both cattle and humans. The final maturation of the dominant follicle is intimately tied to the final maturation of the oocyte, preovulatory secretion of estradiol, preparation of follicular cells for luteinization, postovulatory secretion of progesterone and endocrine control of the oviductal and uterine environment for gamete and embryo development. The physiological maturity of a dominant/ovulatory follicle can affect the establishment and maintenance of pregnancy. Premature induction of the ovulatory process can reduce pregnancy rates and increase late embryonic/fetal mortality in cattle, which is likely mediated through inadequate oocyte competence and a compromised maternal environment. Oocyte competence increases with follicular maturity and is dependent upon acquisition of a complete complement of mRNA transcripts and establishment of the appropriate epigenetic marking of the oocyte genome before the preovulatory gonadotropin surge. Preovulatory secretion of estradiol is a reflection of follicular maturity and affects the oocyte, follicular cells, oviduct and uterus. The corpus luteum is a continuation of follicular maturation and rate of progesterone secretion following ovulation is linked to fertility. Advancements in our understanding of how the follicular microenvironment affects pregnancy establishment and maintenance will improve the efficiency of assisted reproductive technologies in all species. The purpose of this review is to discuss how follicular microenvironment, oocyte competence, preovulatory secretion of estradiol and postovulatory secretion of progesterone can affect pregnancy establishment and embryo/fetal survival, with an emphasis on cattle.

Preovulatory estradiol and the establishment and maintenance of pregnancy in suckled beef cows.

In postpartum beef cows, GnRH-induced ovulation of small dominant follicles decreased pregnancy rates and increased late embryonic/fetal mortality. In Exp. 1, single ovulation reciprocal embryo transfer (ET) was used to examine the relationship between preovulatory serum concentrations of estradiol at GnRH-induced ovulation in donor and recipient cows and establishment and maintenance of pregnancy. Suckled beef cows (n = 1,164) were administered GnRH (GnRH1, 100 μg) on d -9 (GnRH1), PGF(2α) on d -2, and GnRH2 (GnRH2, 100 μg) on d 0 (CO-Synch protocol) either with (donors; n = 810) or without (recipients; n = 354) AI. Single embryos (n = 394) or oocytes (n = 45) were recovered from the donor cows (d 7; ET) and all live embryos were transferred into recipients. Serum concentration of estradiol at GnRH2 was positively correlated with follicle size at GnRH2 (r = 0.45, P < 0.01) and progesterone at ET (r =0.34, P < 0.01). Donor cows with greater estradiol at GnRH2 were more likely to yield an embryo than an unfertilized oocyte (P < 0.01). Donor and recipient cows were retrospectively divided into 4 groups [low estradiol (<8.4 pg/mL) or high estradiol (≥8.4 pg/mL)] based on serum concentration of estradiol at GnRH2. Pregnancy rate at d 27 for low-low (n = 78), low-high (n = 80), high-low (n = 91), and high-high (n = 101) groups (donor-recipient, respectively) was 45, 65, 43, and 61% respectively (P < 0.02). Because recipient cows with greater estradiol concentration at GnRH2 had greater pregnancy rates in Exp. 1, the objective of Exp. 2 was to evaluate the effect of estradiol supplementation on pregnancy rate. Ovulation was synchronized in suckled beef cows (n = 600) using the CO-Synch protocol with the insertion of a controlled internal drug release (CIDR; intravaginal progesterone supplement) from d -9 until d -2. Approximately one-half of the cows (n = 297) received an injection of estradiol cypionate (ECP; 0.5 mg intramuscularly) 24 h before AI. Compared with the no treatment (Control) cows, ECP treatment increased (P < 0.01) pregnancy rates of cows induced to ovulate smaller dominant follicles (<12.2 mm). In conclusion, GnRH-induced ovulation of small dominant follicles was associated with reduced serum estradiol, fertilization rate (donor cows), and pregnancy establishment (recipient cows). Furthermore, ECP supplementation during the preovulatory period increased pregnancy rates in cows induced to ovulate smaller dominant follicles.

Dietary selenium and nutritional plane alter specific aspects of maternal endocrine status during pregnancy and lactation

Objectives were to examine effects of selenium (Se) supply and maternal nutritional plane during gestation on placental size at term and maternal endocrine profiles throughout gestation and early lactation. Ewe lambs (n = 84) were allocated to treatments that included Se supply of adequate Se (ASe; 11.5 μg/kg BW) or high Se (HSe; 77 μg/kg BW) initiated at breeding and nutritional plane of 60% (RES), 100% (CON), or 140% (EXC) of requirements beginning on day 40 of gestation. At parturition, lambs were removed from their dams, and ewes were transitioned to a common diet that met requirements of lactation. Blood samples were taken from a subset of ewes (n = 42) throughout gestation, during parturition, and throughout lactation to determine hormone concentrations. Cotyledon number was reduced (P = 0.03) in RES and EXC ewes compared with CON ewes. Placental delivery time tended (P = 0.08) to be shorter in HSe ewes than in ASe ewes, whereas placental delivery time was longer (P = 0.02) in RES ewes than in CON and EXC ewes. During gestation, maternal progesterone, estradiol-17β, and GH were increased (P < 0.05) in RES ewes and decreased (P < 0.05) in EXC ewes compared with CON ewes. In contrast, maternal cortisol, IGF-I, prolactin, triiodothyronine, and thyroxine were decreased in RES ewes and increased in EXC ewes compared with CON ewes during gestation. Selenium supply did not alter maternal hormone profiles during gestation. During parturition and lactation, maternal hormone concentrations were influenced by both Se and maternal nutritional plane. During the parturient process, HSe ewes tended to have greater (P = 0.06) concentrations of estradiol-17β than ASe ewes. Three hours after parturition a surge of GH was observed in ASe-RES ewes that was muted in HSe-RES ewes and not apparent in other ewes. Growth hormone area under the curve during the parturient process was increased (P < 0.05) in ASe-RES vs HSe-RES ewes. Ewes that were overfed during gestation had reduced (P < 0.05) estradiol-17β but greater IGF-I, triiodothyronine, and thyroxine (P < 0.05) compared with RES ewes. Even though ewes were transitioned to a common diet after parturition, endocrine status continued to be affected into lactation. Moreover, it appears that gestational diet may partially affect lactational performance through altered endocrine status.

Triennial Reproduction Symposium: influence of follicular characteristics at ovulation on early embryonic survival.

Reproductive failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. Although fertilization failure occurs, embryonic mortality represents a greater contribution to reproductive failure. Reproductive success varies among species and production goals but is measured as a binomial trait (i.e., pregnancy), derived by the success or failure of multiple biological steps. This review focuses primarily on follicular characteristics affecting oocyte quality, fertilization, and embryonic health that lead to pregnancy establishment in beef cattle. When estrous cycles are manipulated with assisted reproductive technologies and ovulation is induced, duration of proestrus (i.e., interval from induced luteolysis to induced ovulation), ovulatory follicle growth rate, and ovulatory follicle size are factors that affect the maturation of the follicle and oocyte at induced ovulation. The most critical maturational component of the ovulatory follicle is the production of sufficient estradiol to prepare follicular cells for luteinization and progesterone synthesis and prepare the uterus for pregnancy. The exact roles of estradiol in oocyte maturation remain unclear, but cows that have lesser serum concentrations of estradiol have decreased fertilization rates and decreased embryo survival on d 7 after induced ovulation. When length of proestrus is held constant, perhaps the most practical follicular measure of fertility is ovulatory follicle size because it is an easily measured attribute of the follicle that is highly associated with its ability to produce estradiol.

Maternal dietary intake alters organ mass and endocrine and metabolic profiles in pregnant ewe lambs

To determine the impacts of Se supply and maternal dietary intake on ewe organ mass and endocrine and metabolic changes throughout gestation, pregnant first parity ewes (n=77) were allocated to 6 treatments in a 2×3 factorial array. Factors included Se [adequate Se (ASe; 9.5μg/kg BW) vs. high Se (HSe; 81.8μg/kg BW)] initiated at breeding and dietary intake [60% (RES), 100% (CON), or 140% (EXC) of requirements] initiated on d 50 of gestation. Ewes were individually fed and blood samples from the jugular vein were obtained approximately every 14 d from d 50 until parturition. Maternal Se supply did not impact endocrine or metabolic status. There was a nutritional intake by day interaction for NEFA, blood urea nitrogen (BUN), insulin, triiodothyronine (T3), thyroxine (T4), progesterone (P4), and estradiol-17β (E2). As expected, with increased maternal intake, NEFA concentrations were reduced. During the last weeks of gestation, BUN and insulin were elevated in EXC compared with RES ewes. Although the pattern of T3 and T4 differed throughout gestation within a treatment group, as maternal intake increased, circulating T3 and T4 were increased. For P4 and E2, as maternal dietary intake increased, there was a reduction in the steroid concentrations in jugular blood. There was only a main effect of maternal nutrition (P<0.001) for cortisol concentrations with EXC ewes having greater concentrations than RES and CON ewes, which did not differ. Although Se is known to influence thyroid hormone metabolism, supranutritional levels during pregnancy did not alter circulating T3 and T4 concentrations. Alterations in maternal endocrine status may have influenced placental transport of nutrients to the developing fetus, which we have shown previously is affected by maternal dietary Se and intake. In addition, the alterations in mammary gland weight that we observed may explain the impact of maternal nutrition on mammary gland function and colostrum production, thereby further impairing growth of developing neonates.

GnRH treatment at artificial insemination in beef cattle fails to increase plasma progesterone concentrations or pregnancy rates.

Treatment with GnRH at the onset of standing estrus increased pregnancy percentages and circulating concentrations of progesterone in repeat breeder dairy cows. The objective of this study was to determine the effect of treatment with GnRH at AI on concentrations of progesterone and conception rates in beef cattle that exhibited estrus. Two hundred ninety-three heifers at four locations were synchronized with the Select Synch plus CIDR protocol (given GnRH and a CIDR was placed into the vagina, and 7 d later, given PGF(2alpha) and CIDR removed; n=253) or the 14-19 melengestrol acetate (MGA) protocol (MGA fed at 0.5mg/head/d for 14 d, with PGF(2alpha) 19 d after MGA withdrawal n=40) and AI was done after detection of estrus. At Location 1, blood samples were collected on Day 2, 4, 6, 10, 15, and 18 after AI (Day 0=AI). Two hundred and fifty postpartum cows at two locations were synchronized with the Select Synch plus CIDR protocol, and AI was performed after detection of estrus. At AI, cattle were alternately assigned to one of two treatments: (1) treatment with GnRH (100microg) at AI (n=127 heifers and n=108 cows); or (2) non-treated control (n=120 heifers and n=119 cows). Concentrations of progesterone tended to be greater in control heifers compared to GnRH-treated heifers on Days 6 (P=0.08), 10 (P=0.07), and 15 (P=0.11). Overall conception rates were 68% and 66% for GnRH treated and control, respectively, and were not different between treatments (P=0.72). In summary, treatment with GnRH at time of AI had no influence on conception rates in cattle that had exhibited estrus.

Physiology and Endocrinology Symposium: Harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers.

The development of replacement heifers is a major economic investment for all beef and dairy operations. The costs associated with heifer development cannot be recovered if heifers do not conceive and remain productive in the herd; therefore, heifers need to conceive early in the breeding season or risk being culled. Previous research has reported up to a 21% increase in fertility from pubertal estrus to the third estrus of a heifer. The use of reproductive tract scores to determine pubertal status has demonstrated that peripubertal and pubertal heifers have increased pregnancy success to estrous synchronization compared with heifers that were prepubertal. The development of RIA has allowed accurate measurement of peripheral blood hormone concentrations associated with the pubertal process and luteal formation. This basic knowledge has increased our understanding of the mechanisms that control puberty in heifers. In addition, understanding the hormonal changes that occur during the estrous cycle has allowed for the development of estrous synchronization protocols that result in increased control of follicular growth, regression of luteal tissue, and ovulation. Transrectal ultrasonography has increased our understanding of follicular waves; this understanding led to research investigating the endocrine regulation of follicular waves and development of methods to synchronize follicular waves for purposes of fixed-time AI. Current topics of research include the effect of antral follicle count on fertility and the effect of maternal nutrition (on the fetus in utero) on subsequent reproductive potential of a heifer (i.e., fetal programming). Advancements in genomic technologies will likely provide a powerful tool for selecting heifers at birth that will have a greater probability of being reproductively successful if managed correctly. Therefore, knowledge gained through basic research on factors that control puberty has improved and will continue to improve heifer development and fertility.

Influence of inducing luteal regression before a modified controlled internal drug-releasing device treatment on control of follicular development.

At the initiation of most controlled internal drug-releasing (CIDR) device protocols, GnRH has been used to induce ovulation and reset follicular waves; however, its ability to initiate a new follicular wave is variable and dependent on stage of the estrous cycle. The objectives of the current studies were to determine 1) if inducing luteal regression before the injection of GnRH at time of insertion of a CIDR resulted in increased control of follicular development, and 2) if removing endogenous progesterone by inducing luteal regression before insertion of the CIDR decreased variation in LH pulse frequency. In Exp. 1 and 2, Angus-cross cycling beef heifers (n = 22 and 38, respectively) were allotted to 1 of 2 treatments: 1) heifers received an injection of PGF(2α) on d -3, an injection of GnRH and insertion of a CIDR on d 0, and a PGF(2α) injection and CIDR removal on d 6 (PG-CIDR) or 2) an injection of GnRH and insertion of a CIDR on d 0 and on d 7 an injection of PGF(2α) and removal of CIDR (Select Synch + CIDR). In Exp. 3, Angus-cross beef heifers (n = 15) were assigned to 1 of 3 treatments: 1) PG-CIDR; 2) PGF(2α) on d -3, GnRH on d 0, and PGF(2α) on d 6 (PG-No CIDR); or 3) Select Synch + CIDR. Follicular development and ovulatory response were determined by transrectal ultrasonography. Across all experiments, more (P = 0.02) heifers treated with PG before GnRH initiated a new follicular wave after the injection of GnRH compared with Select Synch + CIDR-treated heifers. In Exp. 1, after CIDR removal, interval to estrus did not differ (P = 0.18) between treatments; however, the variance for the interval to estrus was reduced (P < 0.01) in PG-CIDR heifers compared with Select Synch + CIDR heifers. In Exp. 3, there was a tendency (P = 0.09) for LH pulse frequency to be greater among PG-CIDR and PG-No CIDR compared with the Select Synch + CIDR, but area under the curve, mean LH concentrations, and mean amplitude did not differ (P > 0.76). In summary, induction of luteal regression before an injection of GnRH increased the percentage of heifers initiating a new follicular wave. Removal of endogenous progesterone tended to increase LH pulse frequency, and the modified treatment increased the synchrony of estrus after CIDR removal.