Effect of timing of artificial insemination on gender ratio in beef cattle

Foal sex in Thoroughbred horses: related factors

Reproductive biotechniques in the equine species have advanced in the last decade and horse breeders have started to question the possibilities of interfering in the determination of foal sex. The aim of the present study was to verify whether the variables mares and stallion's age, side of the ovary containing the preovulatory follicle, preovulatory follicle diameter, time between breeding and ovulation, and ovulation inducing hormones influence the sex of the foal. A total of 259 reproductive cycles of 160 mares and 22 Thoroughbred stallions were used. Statistical analysis was performed using R software, including Pearson's chi-square test and logistic regression. Of the total foals born, 136 were males (52.51%) and 123 were females (47.49%). In mares that ovulated with -24h after ovulation induction, 104 foals (54.74%) were males and 86 (45.26%) were females, while in mares that ovulated with +24h, 32 foals (46.38%) were males and 37 (53.62%) were females. Stallions up to 15 years old had 44.14% (n=49) females and those over 15 years had 49.66% (n=73) females. The simple logistic regression model showed that mares and stallions under 15 years old, mares with ovulation time less than 24 hours and treated with Deslorelin had a higher probability of having male foals, but the Pearson's chi-square test showed that foals gender were not influenced by the variables studied.

Evaluation of age, weaning weight, body condition score, and reproductive tract score in pre-selected beef heifers relative to reproductive potential

Background

Artificial insemination is a preferred breeding method for beef heifers as it advances the genetic background, produces a predictive and profitable calving season, and extends the heifer's reproductive life span. As reproductive efficiency in heifers is key for the success of beef cattle production systems, following artificial insemination, heifers are exposed to a bull for the remainder of the breeding season. Altogether, up to 95% of heifers might become pregnant in their first breeding season. Heifers that do not become pregnant at the end of the breeding season represent an irreparable economical loss. Additionally, heifers conceiving late in the breeding season to natural service, although acceptable, poses serious losses to producers. To minimize losses due to reproductive failure, different phenotypic parameters can be assessed and utilized as selection tools. Here, we tested the hypothesis that in a group of pre-selected heifers, records of weaning weight, age at weaning, age at artificial insemination, and age of dam differ among heifers of varied reproductive outcomes during the first breeding season.

Results

None of the parameters tested presented predictive ability to discriminate the heifers based on the response variable ('pregnant to artificial insemination', 'pregnant to natural service', 'not pregnant'). Heifers categorized with body condition score = 6 and reproductive tract score ≥ 4 had the greatest proportion of pregnancy to artificial insemination (49% and 44%, respectively). Furthermore, it was notable that heifers presenting body condition score = 6 and reproductive tract score = 5 presented the greatest pregnancy rate at end of the breeding season (89%). Heifers younger than 368 d at the start of the breeding season did not become pregnant to artificial insemination. Those young heifers had 12.5% chance to become pregnant in their first breeding season, compared to 87.5% if the heifers were older than 368 days.

Conclusion

Our results suggest that beef heifers with body condition score = 6 and reproductive tract score ≥ 4 are more likely to become pregnant to artificial insemination. Careful assessment should be undertaken when developing replacement heifers that will not reach 12 months of age by the beginning of the breeding season.

Transcriptome profiles in peripheral white blood cells at the time of artificial insemination discriminate beef heifers with different fertility potential

Background

Infertility is a longstanding limitation in livestock production with important economic impact for the cattle industry. Female reproductive traits are polygenic and lowly heritable in nature, thus selection for fertility is challenging. Beef cattle operations leverage estrous synchronization in combination with artificial insemination (AI) to breed heifers and benefit from an early and uniform calving season. A couple of weeks following AI, heifers are exposed to bulls for an opportunity to become pregnant by natural breeding (NB), but they may also not become pregnant during this time period. Focusing on beef heifers, in their first breeding season, we hypothesized that: a- at the time of AI, the transcriptome of peripheral white blood cells (PWBC) differs between heifers that become pregnant to AI and heifers that become pregnant late in the breeding season by NB or do not become pregnant during the breeding season; and b- the ratio of transcript abundance between genes in PWBC classifies heifers according to pregnancy by AI, NB, or failure to become pregnant.

Results

We generated RNA-sequencing data from 23 heifers from two locations (A: six AI-pregnant and five NB-pregnant; and B: six AI-pregnant and six non-pregnant). After filtering out lowly expressed genes, we quantified transcript abundance for 12,538 genes. The comparison of gene expression levels between AI-pregnant and NB-pregnant heifers yielded 18 differentially expressed genes (DEGs) (ADAM20, ALDH5A1, ANG, BOLA-DQB, DMBT1, FCER1A, GSTM3, KIR3DL1, LOC107131247, LOC618633, LYZ, MNS1, P2RY12, PPP1R1B, SIGLEC14, TPPP, TTLL1, UGT8, eFDR≤0.02). The comparison of gene expression levels between AI-pregnant and non-pregnant heifers yielded six DEGs (ALAS2, CNKSR3, LOC522763, SAXO2, TAC3, TFF2, eFDR≤0.05). We calculated the ratio of expression levels between all gene pairs and assessed their potential to classify samples according to experimental groups. Considering all samples, relative expression from two gene pairs correctly classified 10 out of 12 AI-pregnant heifers (P = 0.0028) separately from the other 11 heifers (NB-pregnant, or non-pregnant).

Conclusion

The transcriptome profile in PWBC, at the time of AI, is associated with the fertility potential of beef heifers. Transcript levels of specific genes may be further explored as potential classifiers, and thus selection tools, of heifer fertility.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4505-4) contains supplementary material, which is available to authorized users.

Effect of timing of artificial insemination after synchronization of ovulation on reproductive performance in Holstein dairy cows

The objective of this study was to determine the effect of timing of artificial insemination on pregnancy rates, calving rates, abortion rates, twinning rates, and calf gender ratio after synchronization of ovulation with Ovsynch protocol in Holstein dairy cows. The ovulation of 219 lactating Holstein dairy cows was synchronized using the Ovsynch protocol. Therefore, cows received an injection of GnRH followed by an injection of prostaglandin F(2α) 7 days later and a second treatment with GnRH 2 days later. Cows were artificially inseminated at 0, 12, or 24 h after the second injection of GnRH. Reproductive performance did not differ between cows inseminated at 0 h (n = 82), 12 h (n = 66), or 24 h (n = 71) after the last injection of GnRH (pregnancy rate: 0 h 48 %, 12 h 47 %, 24 h 52 %; abortion rate: 0 h 5 %, 12 h 0 %, 24 h 11 %; calving rate: 0 h 43 %, 12 h 47 %, 24 h 41 %; twinning rate: 0 h 2 %, 12 h 0 %, 24 h 0 %; calf gender ratio (F/M): 0 h 61:39 %, 12 h 48:52 %, 24 h 39:61 %; P > 0.05). Pregnancy rates for cows inseminated in postpartum times of 50-75, 76-100, and >100 days within the first and ≥ 3 parities were statistically similar (P > 0.05), but pregnancy rates for cows inseminated at different postpartum times of 50-75, 76-100, and >100 days within the second parity were different (P < 0.01). In general, pregnancy rates of cows inseminated at different postpartum times (P < 0.01) and parities (P < 0.001) differed. The findings of the current study showed that rates of pregnancy, abortion, calving, and twinning of Holstein dairy cows subjected to artificial insemination at different times after synchronization were similar. These results also indicate that the timing of artificial insemination after synchronization did not influence calf gender ratio. Furthermore, pregnancy rates of Holstein dairy cows inseminated after synchronization were significantly influenced by postpartum time and parity number.

Intrafollicular testosterone concentration and sex ratio in individually cultured bovine embryos

Recent studies have suggested a relationship between bovine follicular fluid testosterone concentration and the likelihood of the oocyte being fertilised by an X- or Y-bearing spermatozoon; however, this theory has been challenged. To further test this hypothesis, follicles were dissected from the ovaries of slaughtered heifers, measured and carefully ruptured. The cumulus–oocyte complex (COC) was removed and the follicular fluid collected and testosterone concentration determined by radioimmunoassay. COCs were matured, fertilised and cultured in an individually identifiable manner; all cleaved embryos (2- to 4-cell stage, n = 164) had their sex determined by PCR. Testosterone concentrations were positively skewed. There was no significant difference between follicular fluid testosterone concentrations in male and female embryos (mean ± s.e.m. 51.5 ± 5.59 and 49.5 ± 7.42 ng mL–1, respectively). Linear, quadratic and cubic logistical regression showed that follicular testosterone concentration could not reliably predict the sex of the embryo with odds ratios of 1.001, 1.013 and 1.066, repectively, and coefficient of determination (R2) values of 0.0003, 0.0126 and 0.0567, respectively. Follicular size and testosterone concentration were not related (R2 = 0.087). Finally, follicular size had no influence on embryo sex determination (P = 0.70). In conclusion, under the conditions of the present study, the likelihood of an oocyte being fertilised by an X- or Y-bearing spermatozoon was not affected by the size of the follicle from which it was derived, nor by the testosterone concentration in the follicular fluid.

Effect of duration of oocyte maturation on the kinetics of cleavage, embryo yield and sex ratio in cattle

The aim of the present study was to examine the effect of maturation for 16 v. 24 h on the kinetics of development and the sex ratio of bovine embryos. Oocytes were inseminated at 16 or 24 h after the beginning of maturation using frozen–thawed bull semen. Two-cell embryos at 24, 28, 32, 36, 40, 44 and 48 h post-insemination (hpi) and blastocysts at Days 6, 7 and 8 from both groups were snap-frozen individually and stored at –80°C until determination of embryo sex. Insemination at 16 h resulted in a lower cleavage rate at 48 hpi than insemination at 24 h (70.6% v. 77.1%, respectively, P < 0.05). In terms of the evolution of cleavage divisions, insemination at 24 h resulted in a typical pattern of cleavage such that by 32 hpi, ~58% of presumptive zygotes had cleaved. In contrast, first cleavage following insemination at 16 h was significantly slower such that by 32 hpi, ~35% of presumptive zygotes had cleaved. Duration of IVM did not affect blastocyst yield (~37%). The overall sex ratio of 2-cell embryos at 48 hpi differed from 1 : 1 in favour of males in both groups (24 h: 55.9 v. 44.1%; 16 h: 59.1 v. 40.9%, P < 0.05). Similarly, the overall sex ratio of blastocysts differed from 1 : 1 in both groups (24 h: 59.7 v. 40.3%; 16 h: 58.5 v. 41.5%, P < 0.05). In conclusion, timing of gamete interaction and maturity of the oocyte at the time of the interaction can affect the kinetics of the early cleavage divisions but has no effect on the sex ratio of the embryos produce.

Relationships among estrous behavior, superovulatory response and grade 1 embryo sex ratio in superovulated Holstein heifers

In this study, we first attempted to determine whether the timing of artificial insemination affects the sex ratio of seven-day-old embryos in superovulated Holstein heifers. The superovulatory treatment consisted of eight decreasing doses of FSH for 4 days and 2 doses of PGF(2alpha) given with the last two doses of FSH. The superovulated heifers were given a GnRH analogue 48 h after the first PGF(2alpha) treatment and were artificially inseminated 48 h (n=10) or 56 h (n=8) after the first PGF(2alpha) treatment. There were no significant differences in the percentages of unfertilized ova and transferable embryos (grades 1 to 3) between the two groups. The proportions of female grade 1 embryos did not significantly differ from the expected ratio of 50:50 (49.3% at 48 h and 52.5% at 56 h). We then compared the estrous behavior and superovulatory responses of the heifers with a proportion of female embryos of 50% or less (n=7, Low group) to those of the heifers with a proportion of female embryos of more than 50% (n=9, High group). The Low group had a longer duration of estrus and a higher superovulatory response than the High group. These findings offer little encouragement for prediction of the population of female embryos collected from superovulated heifers. Further studies are necessary to evaluate to what degree maternal hormone levels are related to estrus duration and sex ratio.

Effect of time of artificial insemination on embryo sex ratio in dairy cattle

The objective of the present study was to examine whether different intervals between insemination and ovulation have an influence on the sex of seven-day-old embryos in dairy cattle. Cows were inseminated once with semen of one of two bulls of proven fertility between 36 h before ovulation and 12 h after ovulation. Time of ovulation was assessed by ultrasound at 4-h intervals. In total, 64 embryos were determined to be male or female. Of these 64 embryos, 51.6% were female. The sex ratio in the various insemination-ovulation intervals (early: between 36 and 20 h before ovulation; intermediate: between 20 and 8 h before ovulation; late: between 8 h before and 12 h after ovulation) did not significantly differ from the expected 1:1 sex ratio (50, 50 and 55% females, respectively). Bull (Bull A and B) and Parity (primiparous and multiparous) had no influence on the expected 1:1 sex ratio either. The number of cell cycles was similar for male and female (P = 0.23) embryos when quality of the embryo (P < 0.0001) was included in the model. The results of this study indicate that, in cattle, the interval between insemination and ovulation does not influence the sex ratio of seven-day-old embryos.

Repeated in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure affects male gonads in offspring, leading to sex ratio changes in F2 progeny

The effects of in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male rat offspring (F1) and the sex ratio of the subsequent generation (F2) were examined. Female Holtzman rats were gavaged with an initial loading dose of 400 ng/kg TCDD prior to mating, followed by weekly maintenance doses of 80 ng/kg during mating, pregnancy, and the lactation period. Maternal exposure to TCDD had no significant effects on fetus/pup (F1) mortality, litter size, or sex ratio on gestation day (GD) 20 or postnatal day (PND) 2. The TCDD concentration in maternal livers and adipose tissue on GD20 was 1.21 and 1.81 ng/kg, respectively, and decreased at weaning to 0.72 in the liver and 0.84 in the adipose tissue. In contrast, the TCDD concentration in pup livers was 1.32 ng/kg on PND2 and increased to 1.80 ng/kg at weaning. Ventral prostate weight of male offspring was significantly decreased by TCDD exposure on PND28 and 120 compared with that of controls. Weight of the testes, cauda epididymides, and seminal vesicle, and sperm number in the cauda epididymis were not changed by TCDD exposure at PND120. TCDD- or vehicle-exposed male offspring were mated with unexposed females. The sex ratio (percentage of male pups) of F2 offspring was significantly reduced in the TCDD-exposed group compared with controls. These results suggest that in utero and lactational TCDD exposures affect the development of male gonads in offspring (F1), leading to changes in the sex ratio of the subsequent generation (F2).

Effect of the interval between estrus onset and artificial insemination on sex ratio and fertility in cattle: a field study

We have carried out a field trial in cattle to study the effect of the interval between the onset of estrus and AI on sex ratio and fertility. Data were obtained from 716 cows that had been inseminated at different times between 8 and 44 h from the visual detection of estrus. Before analyzing the data, it was grouped in three intervals considering the time between estrus onset and AI (8-18, 18-30, and > or = 30 h). Our results show that the percentage of calved females (73.05%) is significantly superior for early inseminations (8-18 h), and it decreases 1.85% per hour from the onset of estrus. Delayed AIs (> or = 30 h) produce a significant deviation of the sex ratio towards the males (72.06%); nevertheless, fertility (percentage of successful pregnancies) diminishes significantly, from 66.19% (8-18 h) to 45.35% (> or = 30 h). In conclusion, variations in the interval between the onset of estrus and AI modify sex ratio. However, we must consider its effect on fertility.

Maternal diet and other factors affecting offspring sex ratio: a review

Mammals usually produce approximately equal numbers of sons and daughters, but there are exceptions to this general rule, as has been observed in ruminant ungulate species, where the sex-allocation hypothesis of Trivers and Willard has provided a rational evolutionary underpinning to adaptive changes in sex ratio. Here, we review circumstances whereby ruminants and other mammalian species, especially rodents and primates, appear able to skew the sex ratio of their offspring. We also discuss some of the factors, both nutritional and nonnutritional, that potentially promote such skewing. Work from our laboratory, performed on mice, suggests that age of the mother and maternal diet, rather than the maternal body condition per se, play directive roles in controlling sex ratio. In particular, a diet high in saturated fats but low in carbohydrate leads to the birth of significantly more male than female offspring in mature laboratory mice, whereas when calories are supplied mainly in the form of carbohydrate rather than fat, daughters predominate. As the diets fed to the mice in these experiments were nutritionally complete and because litter sizes did not differ between treatments, dietary inadequacy seems not to be the cause for sex-ratio distortion. A number of mechanisms, all of which are testable, are discussed to provide an explanation for the phenomenon. We conclude the review by discussing potential implications of these observations to human medicine and agriculture.

Sex related embryo development

Although sexual dimorphic development in the mammalian embryo prior to differentiation of the gonad has been documented, there are many seemingly conflicting observations and gaps in our understanding of this process. Conditions that influence the process include gamete interaction, that might give one sex and advantage in the fertilization process and in rates of blastomere cleavage that would allow one sex to accumulate cells at a faster rate. In this scenario, males could accumulate more cells within a defined window of development. Another key difference between males and females is the number of copies of genes located on the sex chromosomes. Transcripts from the Y-chromosome are thought to function as transcription factors, which could accelerate development. Conversely, the X-chromosome contains genes that code for rate limiting steps in pathways key to embryo metabolism and stress reduction. It can be envisioned that prior to X-chromosome inactivation in females, elevated levels of transcripts for such genes may enable greater protection from environmental stress and regulate growth. As we gain a better understanding of how males and female develop we will be able to exert greater control over the manipulation of the sex ratio for the offspring of domestic animals.