Impact of trace mineral source on beef replacement heifer growth, reproductive development, and biomarkers of maternal recognition of pregnancy and embryo survival.

Trace minerals are known to play important roles in early embryo development. The study objective was to determine effects of trace mineral source on heifer reproductive performance. Beef heifers (n = 129) were randomly assigned to one of two treatments. From weaning through breeding, all heifers were individually fed a basal diet supplemented with cobalt (Co), copper (Cu), manganese (Mn), and zinc (Zn) either from organic sources (COMP; Cu, Mn, and Zn amino acid complexes and Co glucoheptonate; Availa-4, Zinpro Corporation, Eden Prairie, MN) or inorganic sources (INORG; Cu, Mn, and Zn hydroxychlorides; Intellibond C, M, and Z, Micronutrients, Indianapolis, IN) and Co as CoSO4. Blood samples and a reproductive tract score (RTS) were collected to determine pubertal status. All animals were synchronized and artificially inseminated. Pregnancy status was determined by lymphocyte gene expression, circulating concentrations of pregnancy-associated glycoproteins (PAGs), and by transrectal ultrasonography after artificial insemination. Embryonic loss was defined as when a previously pregnant animal was subsequently diagnosed not pregnant. Data were analyzed using the MIXED procedure in SAS. Puberty (P = 0.44), pelvic area (P = 0.74), RTS (P = 0.49), and estrus expression (P = 0.82) were not influenced by treatment. There was no effect of treatment (P = 0.37) or treatment by time (P = 0.19) on pregnancy, but there was a tendency (P = 0.13) for decreased embryonic loss among COMP heifers (27 ± 6%) compared to INORG heifers (38 ± 6%). There was a treatment by pregnancy status by time interaction (P < 0.01) on circulating PAG concentrations with PAG concentrations tending (P = 0.08) to be greater on day 25 among heifers in the COMP treatment compared to heifers in the INORG group. In summary, source of trace mineral did not affect puberty, RTS, pelvic area, or overall pregnancy success, but feeding complexed trace minerals tended to increase circulating PAG concentrations and embryo survival.

Effect of progesterone supplementation in a resynchronization protocol on follicular dynamics and pregnancy success.

The objective of this study was to evaluate the necessity of a controlled internal drug releasing device (CIDR) in a fixed-time AI resynchronization protocol as well as to compare a commercially available blood pregnancy test with transrectal ultrasonography for Day 28 pregnancy detection. Over a two-year period, beef cows and heifers from twelve herds were inseminated using the 7-day CO-Synch + CIDR protocol. On Day 21 following the first insemination, the protocol was repeated, with animals receiving either a CIDR or no CIDR. Pregnancy status (AI1) was determined on Day 28 by both transrectal ultrasonography and the IDEXX Rapid Visual Pregnancy Test. Non-pregnant animals by both methods (CIDR: n = 190 cows, n = 228 heifers; no CIDR: n = 185 cows, n = 223 heifers) received an injection of Prostaglandin F2alpha and were inseminated at the appropriate time or bred following detection of estrus. Corpora lutea (CL) number and largest follicle diameter were recorded on a subset of non-pregnant animals (CIDR: n = 66 cows, n = 46 heifers; no CIDR: n = 76 cows, n = 41 heifers) at time of pregnancy diagnosis on Day 28. Final pregnancy status was determined a minimum of 31 days following the second AI (AI2). The GLIMMIX procedure of SAS was utilized for estrus and pregnancy data; while the MIXED procedure was utilized for analyses of CL number and largest follicle diameter. There was no effect (P ≥ 0.55) of treatment on AI1 pregnancy, AI2 pregnancy, or overall pregnancy rates. The presence of a CIDR during the resynchronization increased (P < 0.001) estrus expression prior to AI2. There was an effect of treatment by age on AI2 pregnancy (P < 0.01); heifers that received a CIDR had greater AI2 pregnancy rates than heifers that did not receive a CIDR (P = 0.04), but there was no difference between cows with and without a CIDR. Treatment had no effect (P > 0.10) on embryonic loss (between the first and second pregnancy diagnosis), CL number, or follicle diameter. Although, there was a tendency for the interaction of treatment by age on follicle size (P = 0.07), with cows having larger follicles than heifers in the no CIDR group but not the CIDR group. In conclusion, use of a CIDR in this resynchronization protocol increased estrus expression, increased AI2 pregnancy for heifers, but did not improve pregnancies in cows, and did not influence overall pregnancy or embryonic loss.

Role of preovulatory concentrations of estradiol on timing of conception and regulation of the uterine environment in beef cattle.

The ability to induce ovulation with an injection of GnRH facilitated the development of fixed-time artificial insemination (AI) protocols. However, animals that exhibit estrus prior to fixed-time AI have greater pregnancy success. Thus, the objectives of the present experiments were to determine the impact of estrus expression prior to fixed-time AI on timing of conception and to characterize the role of preovulatory estradiol in regulating changes in expression of uterine genes. In experiment 1, data were collected from 4,499 beef cows inseminated by fixed-time AI in 31 different herds. Animals that did not conceive to AI but exhibited estrus before timed-AI were more likely to conceive during cycle 1 after AI, and overall conceived earlier in the breeding season compared to animals that did not exhibit estrus. In experiment 2, beef cows were synchronized using a fixed-time AI protocol. Uterine horn biopsies and blood samples were collected on Day 0, 5, 10, or 16. Concentrations of estradiol on Day 0 did not influence expression of progesterone receptor, ER beta, or oxytocin receptor. Increased concentrations of estradiol on Day 0 increased expression of ER alpha from Days 0 to 5 of the estrous cycle. Furthermore, cows with increased concentrations of estradiol on Day 0 had increased expression of inhibin beta A, and uterine milk protein precursor. Thus, animals that do not exhibit estrus prior to fixed-time AI had decreased breeding season pregnancy success and conceived later in the breeding season, and preovulatory concentrations of estradiol likely play a major role in this establishment of pregnancy, not only directly by regulating uterine gene expression, but also indirectly throughout the subsequent estrous cycle.

Influence of Sexcel™ (gender ablation technology) gender-ablated semen in fixed-time artificial insemination of beef cows and heifers.

Previous research has indicated that gender-sorted semen has decreased conception rates compared to conventional semen. A new method to skew the gender ratio of semen has been developed that does not use traditional sorting technology. Thus, the objective of this study was to evaluate the use of gender-ablated semen in a fixed-time AI protocol. Beef heifers and cows (n = 878) from six herds were synchronized with the 7-d CO-Synch plus CIDR protocol, and artificially inseminated (AI) after CIDR removal (cows 60-66 h; heifers 52-56 h). Estrus detection aids were applied at CIDR removal and estrus activity was determined at time of AI. Animals remained separated from bulls for at least 10 d after AI. Pregnancy success and fetal age were determined between d 28 and 70 after AI. Semen from five sires was utilized in this study, with two sires used in each herd. Sire 1 was used in all herds and the use of the second sire varied by herd (both conventional and gender-ablated semen from each sire was used in each herd). Data were analyzed using the GLIMMIX procedure in SAS and included the influence of semen type, estrus expression, semen type by estrus expression, dam age, and sire in the model. Herd was included as a random variable. Overall, conventional semen had greater conception rates compared to gender-ablated semen (P < 0.01; 67% vs 52%), and cows that had fully activated patches and partially activated patches had greater conception rates compared to animals that had not exhibited estrus (P < 0.01; 69%, 65%, and 45%). There was no semen type by estrus expression interaction (P = 0.24). Conception rates tended to be greater for conventional semen among animals that had activated patches (P = 0.06; 73% vs 65%) and partially activated patches (P = 0.06; 72% vs 59%). Conception rates were greater for conventional semen (P < 0.01; 56% vs 33%) among animals that did not exhibit estrus. There was no effect of dam age (P = 0.40) or sire (P = 0.92) on conception rates. In conclusion, Sexcel™ gender-ablated semen can successfully be used in fixed-time AI protocols among animals that exhibit estrus, but caution should be used among animals that do not exhibit estrus.

Oxylipin concentrations in bovine corpora lutea during maternal recognition of pregnancy.

The objective was to determine the effects of pregnancy status on oxylipin profiles and eicosanoid metabolizing enzymes and in corpora lutea (CL) or endometrial (caruncle; CAR and intercaruncle; IC) tissues. Angus crossed cattle were synchronized with the CO-Synch protocol and artificially inseminated (AI). Sixteen days after AI, cattle were euthanized, and reproductive tracts collected from 6 non-pregnant and 6 pregnant cows. Oxylipin profiles and concentrations of progesterone (P4) were obtained from CL tissues. The activity of cytochrome P450 1A (CYP1A) and UDP-glucuronosyltransferase (UGT) enzymes were determined using specific luminogenic substrates. Data were analyzed using the MIXED procedure of SAS, and the model included pregnancy status. Corpora lutea of pregnant cattle contained greater (P < 0.05) concentrations of 9,10-DiHODE, 15,16-DiHODE, and 9,10-DiHOME. These oxylipins have been observed to increase cellular proliferation and vasodilation. Activity of CYP1A in the CL and UGT in CAR and IC was not different (P > 0.05) between pregnant and non-pregnant cattle. In the CL, activity of UGT was decreased (P < 0.05) in pregnant vs. non-pregnant cattle. The decrease in CL UGT activity during pregnancy indicates alterations in local hormone metabolism, while no differences in CL weight nor amount of P4 in CL were different between pregnant and non-pregnant cattle. Moreover, the increase in specific concentrations of oxylipins in the CL may indicate a novel pathway of steroid and eicosanoid metabolism during maternal recognition of pregnancy.

Brangus cows have ovarian reserve parameters more like Brahman than Angus cows.

Bos indicus females have more surface antral follicles than Bos taurus females; however, histological studies demonstrated no difference in total number of primordial follicles between these two biological types of cattle. Primordial follicle density in the ovary was less in Nelore ovaries compared to Angus ovaries, but no studies have examined the primordial follicle density in Bos indicus cross-bred females. It, therefore, was hypothesized that primordial follicle density in the ovary would decrease as percentage Bos indicus increased. Ovaries were collected from cross-bred Angus (n = 32, no Bos indicus influence), Brangus (n = 15), or Brahman (n = 9) cows and prepared for histological evaluation. There was no difference in total number of primordial follicles per ovary between breeds (P > 0.10). When numbers of primordial follicles were expressed on a per gram of ovarian tissue basis, there were fewer primordial follicles per gram of ovarian tissue in Brangus and Brahman cows than in Angus cows (P < 0.05). Brangus cows did not differ from Brahman cows in primordial follicle density (P > 0.10). Differences in primordial follicle density could indicate differences in capacity of ovarian stroma to produce factors necessary for oogonial proliferation and primordial follicle formation among breeds. Identifying these factors could improve the aprroach for culturing pre-antral follicles of cattle. Furthermore, these results explain why ultrasonographic antral follicle counts may need to be adjusted to a greater threshold to predict size of the ovarian reserve and determine ovarian reserve related reproductive traits in Bos indicus females.

Comparison of two bovine serum pregnancy tests in detection of artificial insemination pregnancies and pregnancy loss in beef cattle.

Blood tests for early detection of pregnancy in cattle based on pregnancy-associated glycoproteins (PAGs) are commercially available. The objective of these studies were to compare the accuracy of blood tests to transrectal ultrasonography in detecting AI pregnancies, and to compare the accuracy of blood tests in predicting pregnancy loss. Beef cattle from 6 herds were synchronized using a recommended CIDR based protocol (Study 1: n = 460; Study 2: n = 472). Pregnancy status was determined by transrectal ultrasonography between days 28-40 following AI, blood samples were collected at this time. In study 2 a final pregnancy determination was performed at the end of the breeding season to determine pregnancy loss. Each serum sample was examined for PAG concentrations using a microtiter plate reader and/or scored by two technicians blind to pregnancy status and pregnancy loss. For study 1 Cohen's kappa statistics were calculated to assess the agreement between each test and transrectal ultrasonography. For study 2 data was analyzed using the GLIMMIX procedure of SAS with herd as a random effect, and loss, age, and their interaction included in the model. Agreement was good to very good for each test. There was no difference (P = 0.79) in sensitivity, but a difference (P<0.01) in specificity of the assays (88%, 64%, 87%, 90%) and in the overall percent correct (93%, 84%, 93%, 93%). There was an effect of pregnancy loss (P = 0.04), age (P = 0.0002), and their interaction (P = 0.06) on PAG concentrations. In conclusion both pregnancy tests were accurate at detecting AI pregnancies, and were in very good agreement with transrectal ultrasonography. Both tests detected differences in PAGs among females that maintained and lost pregnancy; however, prediction proved to be difficult as most females were above the threshold and would have been considered pregnant on the day of testing.

Maternal age influences the number of primordial follicles in the ovaries of yearling Angus heifers.

The number of antral follicles detectable by ultrasonography in heifers is influenced by age of the dam, because daughters of primiparous cows have fewer antral follicles than daughters of mature cows. We, therefore, hypothesized that heifers with primiparous dams would have fewer primordial follicles in their ovaries than heifers born to mature (4+ y) cows. Angus heifers (n = 464) were submitted for ultrasonographic evaluation of antral follicle number at 325, 355, and 385 d of age. Ovaries were collected from a random subset of heifers (n = 79) and processed for histological evaluation to determine number of primordial follicles. A greater percentage of heifers with primiparous dams had a corpus luteum at first ultrasonographic examination; however, a greater percentage of heifers with multiparous dams had ovulated by the start of breeding (P < 0.01). Heifers with primiparous dams had fewer antral follicles detectable by ultrasonography (P < 0.01). Heifers with primparous dams had fewer surface antral follicles on their ovaries (P < 0.01), and the number of primordial follicles per histological section was less for heifers with primiparous dams (P = 0.02). These data indicate that the lesser number of antral follicles detectable by ultrasonography in heifers with primparous dams is due to less ovarian follicle reserves. Selecting replacement heifers from mature dams may result in daughters with greater fertility and reproductive longevity; however, further research is necessary to determine if interactions between size of the ovarian follicle reserve and age at puberty influence fertility and reproductive longevity in replacement heifers.

Influence of GnRH supplementation at CIDR removal on estrus expression and interval to estrus in beef cattle.

Previous research has indicated that multiple small doses of GnRH following CIDR removal increased circulating concentrations of estradiol. Therefore, our objective was to determine if a single small dose of GnRH (5 µg or 10 µg) at CIDR removal would impact expression of estrus and/or interval to estrus. Beef cows and heifers (n = 1620; n = 1057 cows, n = 563 heifers) were synchronized using the 7-day CO-Synch + CIDR protocol, and randomly assigned to one of three treatments (0, 5, or 10 µg of a GnRH analog at CIDR removal). Animals were inseminated following detection in estrus. Interval to estrus was calculated for each animal that exhibited estrus (INTERVAL 1). Animals that did not exhibit estrus were administered 100 µg of GnRH at the time of AI and their interval to estrus was designated at 120 h (INTERVAL 2). There was a treatment by age interaction (P = 0.05) on INTERVAL 1. Heifers treated with 5 µg of GnRH tended to have a shorter interval to estrus (P = 0.07; 47 ±â€¯1.4 h) compared to 0 µg (50 ±â€¯1.5 h) and did have a shorter interval compared to 10 µg (P < 0.01; 52 ±â€¯1.5 h). There were no differences between treatments in interval to estrus among cows (P > 0.34). When animals that did not exhibit estrus by 120 h were included in the analysis there was no treatment by age interaction (P = 0.49). This is likely due to the fact that treatment (P < 0.01), but not age (P = 0.96) or treatment by age (P = 0.74) influenced expression of estrus. In addition, there tended to be a treatment by estrus interaction (P = 0.08) on pregnancy success. There was no difference in pregnancy success between treatments among animals that exhibited estrus (P > 0.30). In summary, 5 µg of GnRH at CIDR removal tended to decrease the interval to estrus and increased expression of estrus among heifers but not cows, and 10 µg of GnRH at CIDR removal did not improve estrus expression and lengthened the interval to estrus in comparison to the control.

Effects of preovulatory estradiol on uterine environment and conceptus survival from fertilization to maternal recognition of pregnancy.

Preovulatory estradiol is known to impact embryo quality and survival. The objective of this study was to determine the effects of preovulatory estradiol on the uterine environment and conceptus survival through maternal recognition of pregnancy. Beef cows/heifers were AIed following induced ovulation. Cows were grouped into high and low preovulatory estradiol. Conceptuses were collected on day 16 nonsurgically (Rep 1; n = 20), or following slaughter (Rep 2; n = 29). Blood was collected to determine plasma glucose concentrations, and uterine luminal fluid (ULF) was analyzed for protein, glucose, and interferon tau (IFNT) concentrations. Total cellular RNA was extracted from caruncular (CAR) and intercaruncular (INCAR) endometrial tissue. There was no effect of preovulatory estradiol on conceptus recovery rate (P = 0.38) or on apoptosis rate in the trophectoderm (P = 0.64). Cows in which a conceptus was recovered had greater concentrations of protein in the ULF (P = 0.04). Animals with elevated preovulatory estradiol had greater endometrial abundance of SLC2A1 (P = 0.05) and SLC5A1 (P = 0.04) in both INCAR and CAR tissue. Presence of a conceptus also tended to increase (P = 0.10) abundance of SLC5A1 in INCAR. In CAR tissue, cows with a conceptus had decreased SLC2A4 abundance (P = 0.05). In summary, conceptus recovery rates, apoptosis in the trophectoderm, IFNT, glucose, and protein concentration in ULF did not differ between cows that did or did not have an increase in preovulatory estradiol concentrations. Thus, there is no indication of increased conceptus survival to day 16 of pregnancy based on estradiol concentrations.