The importance of maternal lineage on milk yield traits of dairy cattle

Estimation of direct and maternal covariance along with genetic and phenotypic trends of reproduction traits in Murrah buffalo

The research utilized data from 662 Murrah buffaloes meticulously recorded over 24 years (1996-2019) from historical pedigree sheets maintained at the buffalo farm of the Department of Livestock Production and Management (LPM) at Lala Lajpat Rai University of Veterinary and Animal Sciences (LUVAS), Hisar. A series of six univariate animal models were employed to calculate estimates of (co)variance components and heritability for first lactation reproduction traits. Among these models, Model 2 was identified as the best fit for age at first calving (AFC) and calving interval (CI), while Model 1 proved optimal for service period (SP) and conception rate (CR). The heritability estimates for AFC, SP, CR and CI across the models were ranged between 0.11 and 0.32, 0.01 and 0.03, 0.05 and 0.06, and 0.01 and 0.06, respectively. Maternal effects (m2 ) were observed in AFC and CI, ranging from 0.10 to 0.20 and 0.01 to 0.03, respectively. Across all three traits, there was a consistent negative genetic correlation (-0.75 to -0.92) between direct additive and maternal effects. The breeding values for AFC, SP, CR and CI varied within specific ranges from -32.85 to 44.33 days, -15.61 to 28.42 days, -7.41 to 6.48% and -20.64 to 35.79 days, respectively. Significantly, Spearman's rank correlation analysis revealed highly significant relationships (p < .01) between the breeding values of different models, indicating strong and consistent associations within these traits. These findings underscore the stable and reliable connections observed within the breeding values for these essential reproductive traits across the various models used in the study. The majority of reproductive traits showed favourable negative trends, indicating a positive outcome. A decrease in AFC, SP and CI suggests an extended economic life for the animals. Additionally, the upward trends in CR reflect positive indications of effective management practices and skilled operational procedures.

Genetic analysis of persistency indices of milk yield in Jersey crossbred cattle

The study reported in this Research Communication was conducted to estimate genetic parameters for different lactation persistency indices and their association with reproductive traits in Jersey crossbred cattle. Data on lactation traits (part lactation yields and 305-days milk yield) comprising all lactations as well as reproductive traits viz. calving interval, conception rate and gestation length of 378 Jersey crossbred cattle, maintained at National Dairy Research Institute, Kalyani, West Bengal, India, were collected over a period of 35 years (1982-2016). Five lactation persistency indices of animals (P21, P31, P32, P4 and P5) were calculated using ratio method. A total of six different animal models, ignoring or including maternal genetic or permanent environmental effects, were fitted for all persistency traits. The best model was chosen after testing the improvement of the log-likelihood values. The estimates of direct heritability were low in magnitude and ranged from 0.02 to 0.14 for the studied traits under the best fitted animal model. The permanent maternal environmental (c2) effects of different lactation persistency indices accounted for 2-9% of the total phenotypic variance in this study. Estimated genetic correlations of lactation persistency indices with all studied reproductive traits were low to moderate and negative (-0.11 to -0.68), except for calving interval. Phenotypic correlations of lactation persistency measures with studied reproductive traits were low (0.01 to 0.15). The low heritability estimates of all the persistency indices indicate some limited scope of genetic improvement of lactation persistency of animals through selection under the prevailing management conditions.

Impact of additive direct and maternal heritability on production efficiency traits in Jersey crossbred cattle

Variance components, direct and maternal heritability were estimated for milk production efficiency traits namely, milk yield per day of lactation length (MY/LL) and milk yield per day of calving interval (MY/CI) in Jersey crossbreds maintained at Eastern Regional Station of ICAR-National Dairy Research Institute, West Bengal (India). Data analyses were done using restricted maximum likelihood (REML) method with six alternative animal models (direct and including or excluding maternal associated effects). The best model was chosen after testing the improvement of the log-likelihood values and it revealed direct heritability estimates as 0.47 and 0.25 for MY/LL and MY/CI traits, respectively. Maternal heritability (0.14) was found to be important for MY/LL trait and permanent environmental maternal effect contributed 12% to the total phenotypic variance of the MY/CI. Direct heritability estimates were high (0.47) for MY/LL and moderate for MY/CI (0.25) trait suggesting that there is ample scope of improvement through selection for milk production efficiency traits in Jersey crossbred maintained at organizedherds.

Estimation of genetic parameters and genetic trends for milk yield traits in Jamunapari goats in semiarid tropics

•

The heritability for milk yield traits were moderate to high.

•

The repeatability estimates were moderate to high for milk yield traits.

•

The genetic trends for milk yield traits were positive.

•

Phenotypic trends for MY90, MY140 and TMY were positive.

The Jamunapari goats are reared as dairy animals in semi-arid conditions, therefore it is necessary to evaluate the genetic potential for the genetic improvement of milk production traits. The data comprised of 2217 phenotypic records for milk yield at 90 days (MY90) and 140 days (MY140), total milk yield (TMY) and lactation length (LL) obtained from the progeny of 173 sires and 446 dams during the period 1990–2013. The data were analysed using mixed linear models exploring random effects due to direct additive, maternal and permanent environment variance due to animal. The most appropriate genetic models for milk yield traits were those that included permanent environment effects due to the animal. The direct additive heritability estimates were 0.15 ± 0.05, 0.26 ± 0.07, 0.25 ± 0.08 for MY90, MY140 and TMY, respectively. The additive heritability estimate for LL was low and non-significant at 0.02 ± 0.03. The repeatability estimates were moderate to high ranging from 0.68 to 0.73 for milk yield traits. The repeatability for lactation length was 0.20 ± 0.03. Maternal variances were low ranging from 0.03 for MY90 to 0.13 for TMY. There was an increase in mean milk yield of 0.25, 0.70 and 0.72 kg/year respectively at 90 and 140 days, and for TMY. Genetic trends and phenotypic trends for MY90, MY140 and TMY were positive and indicated significant improvement in milk traits due to selective breeding.

Cloned foal derived from in vivo matured horse oocytes aspirated by the short disposable needle system

Transvaginal ultrasound-guided follicle aspiration is one method of obtaining recipient oocytes for equine somatic cell nuclear transfer (SCNT). This study was conducted: (1) to evaluate the possibility of oocyte aspiration from pre-ovulatory follicles using a short disposable needle system (14-G) by comparing the oocyte recovery rate with that of a long double lumen needle (12-G); (2) to investigate the developmental competence of recovered oocytes after SCNT and embryo transfer. The recovery rates with the short disposable needle vs. the long needle were not significantly different (47.5% and 35.0%, respectively). Twenty-six SCNT embryos were transferred to 13 mares, and one mare delivered a live offspring at Day 342. There was a perfect identity match between the cloned foal and the cell donor after analysis of microsatellite DNA, and the mitochondrial DNA of the cloned foal was identical with that of the oocyte donor. These results demonstrated that the short disposable needle system can be used to recover oocytes to use as cytoplasts for SCNT, in the production of cloned foals and for other applications in equine embryology.

Effects of cow families on type traits in dairy cattle

The component of variance attributable to maternal lineage for type traits in the UK Holstein Friesian dairy population was estimated. First lactation type classification records of 33 325 contemporary cows, classified between 1996 and 1998 were used in the analysis. Maternal pedigree records were traced back to 1960 to establish maternal lineages. The tracing resulted in cows being assigned to 10 332 cow families with more than one cow per family. Sixty-six percent of the cows were in families of less than five. The traits comprised 16 linear type traits, a total score trait, four composite scores and measures of temperament and ease of milking. Univariate analysis of each trait was performed using residual maximum likelihood, with and without a maternal lineage component. A principal component analysis used a scree test to determine the number of independent traits being considered in-order to establish a level of significance for the test statistic. It was found that eight principal components were responsible for the variation in type. The composite body score trait was found to have a 1·5% component of maternal lineage variance, significant at the 5% level. No other traits showed a significant maternal lineage variance component.

Estimation of variance of maternal lineage effects at the Langhill dairy herd

Evidence to support the existence of a maternal lineage variance component for production and food intake traits at the Langhill experimental dairy herd was investigated. Maternal pedigree records of the herd were traced back to the points of cytoplasmic origin using herd book records. Cytoplasmic origin was defined as the earliest maternal ancestor of a cow and used to assign cows to maternal lineages. This was either a grade-up cow or an ancestor traced back to 1920. The tracing resulted in the cows being assigned to 56 maternal lineages, ranging in size from one to 72 cows. A total of 1118 records of 517 cows, all with a first lactation record, were used in the analysis. Traits analysed were daily milk, fat and protein yield, fat %, protein %, food dry-matter intake, net energy of milk production, a measure of milk production efficiency, average condition, and calving condition, all averaged over the first 26 weeks of lactation. The analysis was performed using a residual maximum likelihood animal model with and without a random component for maternal lineage. Possible bias, due to the fact that the sires were a select sample from the population, was also examined. No significant effect was found in the analysis of the full data set that could be assigned to maternal lineage. Fat yield was the only trait to show a variance component approaching a 5% significance level with a magnitude of 4% of phenotypic variance. However, when maternal lineages of at least five cows were considered, a significant 4% maternal lineage component of phenotypic variance was found for fat yield. The power of the analysis to detect a variance component of less than 4% was shown to be poor. No evidence was found for a maternal lineage component of food intake traits or condition score. Treating sire as a fixed effect or regressing data on sire EBV made little difference to the maternal lineage component.

Efeitos da origem e da linhagem do DNA mitocondrial sobre características produtivas e reprodutivas de bovinos leiteiros da raça Gir

Avaliou-se a influência do DNA mitocondrial sobre características de produção e reprodução em rebanho Gir. Foram analisados, segundo a origem mitocondrial (indicus ou taurus) e linhagem citoplasmática (fêmeas fundadoras), 3385 registros de produção total de leite (PT), produção de leite até os 305 dias de lactação (P305) e de período de lactação (PL); 2394 registros de intervalo de parto (IP) e de produção de leite por dia de intervalo de partos (PIP) e 618 registros de idade ao primeiro parto (IPP). A origem mitocondrial foi incluída no modelo como efeito fixo para a idade ao primeiro parto, por ter, em análise prévia, demonstrado ser significativa somente para essa característica. A estimação dos componentes de variância e parâmetros genéticos bem como a predição dos valores genéticos foram realizadas a partir de dois modelos animais; com e sem a inclusão da variável aleatória, linhagem citoplasmática, com o programa MTDFREML, pelo método da máxima verossimilhança restrita com algoritmo livre de derivadas. A linhagem citoplasmática explicou 1,6%; 1,5%; 1,2%, 0%, 0% e 0%, da variância fenotípica das características PT, P305, PL, IP, PIP e IPP, não obstante não se mostrou significativa no teste de razão de máxima verossimilhança. As correlações de postos entre os valores genéticos obtidos a partir dos modelos com e sem a inclusão da linhagem citoplasmática foram próximas à unidade para todas as características. O modelo que não incluiu a linhagem citoplasmática viesou apenas as tendências genéticas das características PT, P305 e PL. A origem mitocondrial, indicus ou taurus, somente foi significativa (P<0,05) para a variação da idade ao primeiro parto. A linhagem citoplasmática não contribuiu significativamente para a variância fenotípica de quaisquer das características deste estudo.

Autologous somatic cell nuclear transfer in pigs using recipient oocytes and donor cells from the same animal

The objective of the present study was to examine the feasibility of the production of autologous porcine somatic cell nuclear transfer (SCNT) blastocysts using oocytes and donor cells from slaughtered ovaries. Therefore, we attempted to optimize autologous SCNT by examining the effects of electrical fusion conditions and donor cell type on cell fusion and the development of SCNT embryos. Four types of donor cells were used: 1) denuded cumulus cells (DCCs) collected from in vitro-matured (IVM) oocytes; 2) cumulus cells collected from oocytes after 22 h of IVM and cultured for 18 h (CCCs); 3) follicular cells obtained from follicular contents and cultured for 40 h (CFCs); and 4) adult skin fibroblasts. The DCCs showed a significantly (p < 0.01) lower rate of fusion than the CCCs when two pulses of 170 V/mm DC were applied for 50 µsec (19 ± 2% vs. 77 ± 3%). The rate of DCC fusion with oocytes was increased by the application of two DC pulses of 190 V/mm for 30 µsec, although this was still lower than the rate of fusion in the CCCs (33 ± 1% vs. 80 ± 2%). The rates of cleavage (57 ± 5%) and blastocyst formation (1 ± 1%) in the DCC-derived embryos did not differ from those (55 ± 6% and 3 ± 1%, respectively) in the CCC-derived SCNT embryos. Autologous SCNT embryos derived from CFCs (5 ± 2%) showed higher levels of blastocyst formation (p < 0.01) than CCC-derived autologous SCNT embryos (1 ± 0%). In conclusion, the results of the present study show that culturing cumulus and follicular cells before SCNT enhances cell fusion with oocytes and that CFCs are superior to CCCs in the production of higher numbers of autologous SCNT blastocysts.

Negative influence of high maternal milk production before and after conception on offspring survival and milk production in dairy cattle

There is a paucity of studies on the effect of intrauterine conditions on subsequent progeny performance in dairy cows. Using a large national data set on Irish Holstein-Friesian dairy cows, the objective of this study was to determine if intrauterine conditions, quantified by a maternal genetic variance component, significantly affected milk production, age at first calving, calving interval, somatic cell score (natural logarithm of somatic cell count) and survival in first-, second-, and third-parity female offspring. Maternal genetic variance for each trait in each parity was estimated in a linear mixed model which included, other than fixed effects, direct additive genetic, maternal genetic, cytoplasmic and permanent environmental effect of the dam, and residual component. A covariance was also estimated between the direct additive and maternal genetic components where possible. Because calves in Irish dairy herds are separated from dams at birth, a significant maternal genetic variance (with all other random effects in the model) indicates a prepartum maternal effect. A significant maternal genetic variance was estimated for 305-d milk yield in first and third lactation, somatic cell score in first lactation, and survival to second lactation from 188,144 lactations on 80,881 animals. Where estimated, a negative correlation existed between the direct additive and maternal genetic components. Regression of maternal mixed model solutions on dam milk production at different stages relative to conception revealed that greater milk yield preconception and during gestation was associated with reduced survival and milk yield and greater somatic cell count in the progeny. This study suggests that offspring survival and performance are affected by prepartum conditions that offspring experience as an oocyte, embryo, or fetus, one of which is mediated through milk production (or factors related to milk production) of the dam.

Effect of oocyte mitochondrial DNA haplotype on bovine somatic cell nuclear transfer efficiency

The development capability of reconstructed bovine embryos via ovum pick-up (OPU)-somatic cell nuclear transfer (SCNT) technique has been influenced by the maternal lineage of oocyte cytoplasm, but the underlying mechanism remains unclear. Since mitochondria are the richest maternal-inherited organelle, in this study, we intended to clarify the effect of mtDNA haplotypes on cloning efficiency. By PCR-RFLP method, we identified mtDNA haplotypes A and B, differing in six restriction sites. Reconstructed embryos with haplotype A cytoplast achieved better fusion and blastocyst formation rate (64.6% and 39.4%), as compared with haplotype B (53.6% and 26.3%; P < 0.05). To further evaluate the role of mitochondria, the quantity of mtDNA, ATP content, and mRNA level of mtDNA-encoded COXI, COXIII in both oocytes were measured. Our data indicated that mtDNA copy number in haplotype A oocyte was significantly higher than that in haplotype B oocyte, both at the GV (10(5.03 +/- 0.69) vs. 10(4.81 +/- 0.86) copies/oocyte) and MII stages (10(5.31 +/- 0.71) vs. 10(5.13 +/- 0.63) copies/oocyte; logarithmically transformed values; P < 0.05). ATP content in type A oocyte was also greater at the GV (1.67 +/- 0.09 vs. 1.27 +/- 0.1 pmol) and MII stages (5.18 +/- 0.07 vs. 2.68 +/- 0.03 pmol; P < 0.05). Similarly, the mRNA expression level of mtDNA-encoded COXI and COXIII in haplotype A oocyte was significantly higher comparing to haplotype B oocyte (3.3 +/- 2.0 x 10(3) vs. 0.68 +/- 0.45 x 10(3); 24.9 +/- 10.5 x 10(3) vs. 9.4 +/- 3.3 x 10(3), respectively; P < 0.05). The data suggest that mitochondrial structure, quantity, and function may significantly affect the developmental competence of reconstructed embryos.

Mitochondrial DNA Polymorphism and Determination of Effects on Reproductive Trait in Pigs

The purposes of this study were to investigate single strand conformation polymorphisms (SSCP) in the D-loop region of pig mitochondrial DNA (mtDNA) and to determinate their association with the reproductive traits of meishan pigs. A total of four types of band patterns, designed SSCP band pattern A, B, C and D, were identified. A type of SSCP band pattern was present in all European-American breeds, but not in East Asian breeds. This result showed the diversified sequence in the D-loop region between European-American and East Asian populations. Two types of band patterns, B and C, were found in Meishan pigs. The average body weight at day 21 of piglets from B type dams was significantly heavier than the body weight of C type (p < 0.05). We also tested whether the SSCP patterns would be suitable for paternity testing in a family group and found that bands of all the offspring were derived from their maternal parent. Therefore, we conclude that SSCP may be a marker for identification of maternal ancestors.

Prenatal Maternal Effects on Body Condition Score, Female Fertility, and Milk Yield of Dairy Cows

In this study, maternal effects were described as age of dam at first and second calving, first-lactation body condition score (BCS) of the dam during gestation, and milk yield of the dam. The impact of these effects on first-lactation daughter BCS, fertility, and test-day milk yield was assessed. The effect of milk yield of dam on daughter 305-d yield in the latter's first 3 lactations was also investigated. The proportion of total phenotypic variance in daughter traits accounted for by maternal effects was calculated. Dams calving early for the first time (18 to 23 mo of age) had daughters that produced 4.5% more first-lactation daily milk, had 7% higher BCS, and had their first service 3 d earlier than cows whose dams calved late (30 to 36 mo). However, daughters of dams that calved early had difficulties conceiving as they needed 7% more inseminations and had a 7.5% higher return rate. Cows from second calvings of relatively young (36 to 41 mo) dams produced 6% more first-lactation daily milk, had 2% higher BCS, and showed a significantly better fertility profile than cows whose dams calved at a late age (47 to 55 mo). High maternal BCS during gestation had a favorable effect on daughter BCS, nonreturn rate, and number of inseminations per conception. However, it was also associated with a small decrease in daughter daily milk yield. Changes in dam BCS during gestation did not affect daughter performance significantly. Maternal effects of milk yield of the dam, expressed as her permanent environment during lactation, adversely affected daughter 305-d milk, fat, and protein yield. However, although the effect was significant, it was practically negligible (<0.3% of the mean). Finally, overall maternal effects accounted for a significant proportion of the total phenotypic variance of calving interval (1.4 +/- 0.6%) and nonreturn rate (1.1 +/- 0.5%).

Short- and long-term skin graft survival in cattle clones with different mitochondrial haplotypes

In contrast to nuclear DNA, cytoplasmic genes may differ among cloned animals due to the presence of polymorphic mitochondrial DNA haplotypes in the host oocytes, raising doubts about histocompatibility among clones. Three bovine clones were generated by nuclear transfer; dermal fibroblasts from a fetus were used as donor cells, whereas oocytes from abbatoir-derived ovaries were used as recipient cells. The mitochondrial DNA (sequencing of coding and non-coding regions) and nuclear DNA (13 microsatellite markers) of cloned and control animals were characterized to identify potential polymorphisms. Skin auto- and allografts were transplanted on the adult clones and a non-related animal as a measure of immunological reactivity. Nuclear DNA of cloned animals was genetically identical but differed in all microsatellites of the non-related control. Amounts of donor cell mitochondrial DNA in the skin ranged from 1 to 2.6% among clones. Few differences in heteroplasmy were observed between skin and WBC of the clones, indicating limited mitochondrial DNA segregation in tissues during pre- and post-natal development to adulthood. Sequencing of the remaining oocyte-derived mitochondrial DNA haplotype identified polymorphisms in coding and non-coding regions, confirming their origin from unrelated maternal lineages. Nonetheless, skin transplants between clones were accepted for the 92 d study period, whereas third-party grafts were rejected. In conclusion, the nuclear transfer-generated adult bovine clones used in this study were immunologically compatible with one another despite differences in their mitochondrial DNA haplotypes.

Improving in vitro development of cloned bovine embryos with hybrid (Holstein–Chinese Yellow) recipient oocytes recovered by ovum pick up

In the present study, oocytes from F1 hybrid cattle, as well as their parental lines, were recovered by ovum pick up (OPU) and used as recipient cytoplasm for somatic cell nuclear transfer (SCNT). Four F1 hybrid (Holstein dam x Chinese Yellow sire), 10 Holstein and four Chinese Yellow cattle were subjected to OPU once weekly. There were no significant differences among breeds for number of recovered oocytes per session (overall average, 7.8+/-0.5; mean+/-S.E.M.), quality of the recovered oocytes, or oocyte maturation rate (72-73%). Matured oocytes were all used as recipient cytoplasm (without selection) and a single batch of cumulus cells collected from a Holstein cow were used as donor cells. Although reconstructed embryos initiated cleavage sooner when the recipient cytoplasm was from hybrid cattle versus the two parental breeds, the overall cleavage rate was indistinguishable among breeds. At Day 8, the blastocyst rate from the cleaved embryos (51% versus 37% and 27%), the total number of cells per blastocyst (135+/-4.1 versus 116+/-3.6 and 101+/-4.2), and the percentage of Grade-A (excellent quality) blastocysts (54% versus 42% and 29%) in the hybrid group were all higher than that of Holstein and Yellow groups. Furthermore, the proportion of blastocysts obtained at Day 7 (as a percentage of the total number of blastocysts) was greater in the hybrid group than in Holstein and Yellow groups (89% versus 71% and 63%). In conclusion, the use of F1 hybrid oocytes as recipient cytoplasm significantly improved in vitro development of cloned bovine embryos relative to oocytes derived from the parental lines.

Heteroplasmy in bovine fetuses produced by intra- and inter-subspecific somatic cell nuclear transfer: neutral segregation of nuclear donor mitochondrial DNA in various tissues and evidence for recipient cow mitochondria in fetal blood

Varying degrees of mitochondrial DNA (mtDNA) heteroplasmy have been observed in nuclear transfer embryos, fetuses, and offspring, but the mechanisms leading to this condition are unknown. We have generated a clone of 12 bovine somatic cell nuclear transfer fetuses, using nuclear donor cells, recipient oocytes, and recipient heifers with defined mtDNA genotypes, to study nuclear-mitochondrial interactions and the origins of mtDNA heteroplasmy. Embryos were reconstructed from granulosa cells with Bos taurus mtDNA type A and recipient oocytes collected from three different maternal lineages with B. taurus mtDNA type B, B. taurus mtDNA type C, or B. indicus mtDNA. Sequence differences in the control region (CR) of B. taurus mtDNAs ranged from 6 to 11 nucleotides and differences between B. taurus and B. indicus CRs from 45 to 50 nucleotides. Fetuses were recovered from recipient heifers with B. taurus mtDNA type B on Day 80 after nuclear transfer (eight B. taurus A/B, two B. taurus A/C, and two B. taurus A/B. indicus). Agarose gel analysis of the CR by polymerase chain reaction-based restriction fragment length polymorphism failed to detect nuclear donor mtDNA in 11 investigated tissues of 10 viable fetuses and in DNA samples of two fetuses in resorption (one B. taurus A/B and one B. taurus A/C). A more sensitive analysis of 1801 plasmid clones with CR inserts derived from tissues of a B. taurus A/B. indicus fetus detected no or very low levels of heteroplasmy (0.5-0.7%). However, the analyses detected considerable amounts ( approximately 2.5% and 5%) of recipient heifer mtDNA in blood samples from two fetuses. Our data do not suggest a replicative advantage of somatic nuclear donor cell mtDNA in bovine transmitochondrial clones produced with oocytes from domestic forms of the same or a different aurochs (B. primigenius) subspecies. Detection of mtDNA from the recipient animal in the circulation of two fetuses points to leakage of the placental barrier, mimicking heteroplasmy.

Bovine somatic cell nuclear transfer using recipient oocytes recovered by ovum pick-up: effect of maternal lineage of oocyte donors

The efficiency of bovine nuclear transfer using recipient oocytes recovered by ultrasound-guided follicle aspiration (ovum pick-up [OPU]) was investigated. Oocyte donors were selected from 2 distinct maternal lineages (A and B) differing in 11 nucleotide positions of the mitochondrial DNA control region. A total of 1342 cumulus-oocyte complexes (COCs) were recovered. The numbers of total COCs and class I/II COCs recovered from donors of lineage A were higher (P < 0.001) than those obtained from lineage B. Follicle aspiration once per week yielded a higher (P < 0.001) total number of COCs per session than aspiration twice per week, whereas the reproduction status of donors (heifer vs. cow) had no effect on OPU results. Of the 1342 oocytes recovered, 733 (55%) were successfully matured in vitro and used for nuclear transfer. Fusion was achieved in 550 (75%) karyoplast-cytoplast complexes (KCCs), resulting in 277 (50%) cleaved embryos on Day 3. On Day 7 of culture, 84 transferable embryos (15% based on fused KCCs) were obtained. After 38 transfers (10 single, 22 double, and 6 triple transfers), 9 recipients (8 double and 1 triple transfer) were diagnosed as pregnant on Day 28, corresponding to a pregnancy rate of 24%. The proportion of transferable embryos on Day 7 was significantly (P < 0.05) influenced by maternal lineage of oocyte donors and by the frequency of follicle aspiration. Our study demonstrates the feasibility of generating nuclear transfer embryos with defined cytoplasmic background. These will be valuable tools to experimentally dissect the effects of nuclear and cytoplasmic components on embryonic, fetal, and postnatal development.

Variance caused by cytoplasmic line and sire by herd interaction effects for milk yield considering estimation bias

A total of 138,869 lactation milk yields (305 d, milked twice daily, mature equivalent) from the first three parities of 68,063 New York Holstein cows were used to estimate variance components that were due to additive direct genetic effects, cow permanent environmental effects (cow within sire for sire model), sire by herd interaction effects, and cytoplasmic line effects. The original data were assigned to 10 random samples, which were each analyzed using an animal model and a sire model. From each sample of original data, 20 other samples were analyzed with levels assigned randomly to cytoplasmic and interaction effects (data with randomly simulated levels). Ten of those samples were analyzed with an animal model and 10 with a sire model. The models also included fixed effects of herd-year-seasons. For the animal model and sire model, average fractions of phenotypic variance and average standard errors were, respectively, for additive direct genetic effects 0.300 (0.029) and 0.228 (0.040) for original data and 0.325 (0.025) and 0.262 (0.039) for data with randomly simulated levels. For cow permanent environmental effects the respective averages were 0.242 (0.024) and 0.444 (0.014) for original data and 0.235 (0.025) and 0.492 (0.016) for data with randomly simulated levels. The averages for sire by herd interaction effects were 0.015 (0.008) and 0.018 (0.007) for original data and 0.003 (0.007) and 0.004 (0.009) for data with randomly simulated levels. For cytoplasmic line effects, the respective averages were 0.011 (0.007) and 0.043 (0.008) for original data and 0.003 (0.006) and 0.003 (0.007) for data with randomly simulated levels. The differences between estimates of variance components for original data and data with randomly simulated levels suggest that estimates of fractions of total variance caused by sire by herd interaction and cytoplasmic effects estimated with REML may be biased upward by 0.003 to 0.004.

Variances of direct genetic effects, maternal genetic effects, and cytoplasmic inheritance effects for milk yield, fat yield, and fat percentage

Milk yield, fat yield, and fat percentage during the first three lactations were studied using New York Holsteins that were milked twice daily over a 305-d, mature equivalent lactation. Those data were used to estimate variances from direct and maternal genetic effects, cytoplasmic effects, sire by herd interaction, and cow permanent environmental effects. Cytoplasmic line was traced to the last female ancestor using DHI records from 1950 through 1991. Records were 138,869 lactations of 68,063 cows calving from 1980 through 1991. Ten random samples were based on herd code. Samples averaged 4926 dams and 2026 cytoplasmic lines. Model also included herd-year-seasons as fixed effects and genetic covariance for direct-maternal effects. Mean estimates of the effects of maternal genetic variances and direct-maternal covariances, as fractions of phenotypic variances, were 0.008 and 0.007 for milk yield, 0.010 and 0.010 for fat yield, and 0.006 and 0.025 for fat percentage, respectively. Average fractions of variance from cytoplasmic line were 0.011, 0.008, and 0.009 for milk yield, fat yield, and fat percentage. Removal of maternal genetic effects and covariance for maternal direct effects from the model increased the fraction of direct genetic variance by 0.014, 0.021, and 0.046 for milk yield, fat yield, and fat percentage; little change in the fraction was due to cytoplasmic line. Exclusion of cytoplasmic effects from the model increased the ratio of additive direct genetic variance to phenotypic variance by less than 2%. Similarly, when sire by herd interaction was excluded, the ratio of direct genetic variance to phenotypic variance increased 1% or less.

Estimation of variance of maternal lineage effects among Canadian Holsteins

Bayesian posterior estimates of variances of maternal lineage effects were obtained with a procedure that used Gibbs sampling. Data were records of yield during first parity from 245,510 Holstein cows that calved in Canada between 1990 and 1994. Maternal lineages were defined by tracing the maternal ancestry of cows to common female ancestors. Traits were standardized yields of milk, fat, and protein and percentages of fat and protein. Estimates of maternal lineage variance were < 0.5% of the total variance for all traits. Effects of this size hardly affected the cow rankings for estimated breeding value. Another analysis defined maternal lineages by establishing groups of dams and their daughters in an attempt to maximize the variance of environmental effects associated with maternal lineages, but only 1.1% of the variance in milk yield was associated with effects of the dam and daughter groups. Analyses of simulated data indicated that positive estimates of maternal lineage effects were not a result of restriction of estimates to positive values and that estimates of maternal lineage variance were biased slightly downward because of incomplete pedigree information. The partitioning of maternal lineage and additive genetic variance was correct when pedigree information was complete, according to results from simulation.

Development of in vitro derived bovine embryos following pronuclear transplantation and in vitro culture

This study was designed to evaluate the survival and development of in vitro derived bovine embryos following pronuclear transplantation and in vitro embryo culture. Bovine zygotes were produced by in vitro maturation and in vitro fertilization. Pronuclei were removed by micromanipulation and either transferred back to the same cell (Group 1) or into a previously enucleated zygote (Group 2) by electrofusion. Micromanipulated and non-micromanipulated (Group 3, control) zygotes were co-cultured with oviductal cells in a sealed modular chamber filled with 5% CO2, 5% O2 and 90% N2 at 39 degrees C for 7-8 days. Fusion rates were similar for Groups 1 and 2 (90.7 and 85.1%, respectively, P > 0.05). The percentage of embryos that cleaved was not different for Groups 1 (82.0%), 2 (90.0%) and 3 (76.9%, P > 0.05). Also, the percentage of embryos developing to the compact morula or blastocyst stage was similar (25.6, 22.5 and 22.3%, respectively, for Groups 1, 2 and 3, P > 0.05). The results of this experiment are the first to demonstrate that pronuclear transfer can be carried out successfully using bovine embryos derived from in vitro oocyte maturation and in vitro fertilization. In addition, pronuclei can be transferred from one bovine embryo to another and the reconstructed embryos develop to the compact morula and blastocyst stage in vitro. This technique, used in combination with oocyte retrieval by ultrasound-guided follicular aspiration and embryo transfer, offers the potential to study cytoplasmic inheritance in cattle directly, and to evaluate the effect of cytoplasmic inheritance on traits of economic importance.

Multiple herd evaluation of the effects of maternal lineage on yield traits of Holstein cattle

Effects of maternal lineage on yield traits were examined by using animal models. Data were 6054 multiparous records of 2264 cows from six herds in North Carolina and the breeding herd of Iowa State University. Separate analyses were performed by using first lactation records from North Carolina, all records from North Carolina, and pooled records from North Carolina and Iowa. Traits were mature equivalent yields of milk, fat, and protein; percentages of fat and protein; and milk energy concentration and yield. Cattle were assigned to maternal lineages on the basis of the earliest female ancestor recorded. Fixed effects in the models were herd-year-season, parity, and maternal lineage; random effects were animal, permanent environment, and residual. All additive genetic relationships were considered. For all analyses, maternal lineage was associated with significant differences in fat percentage and milk energy concentration. Differences between maternal lineages for yield traits were not significant. Variance components were also obtained with REML using the same data and models, but with lineage as a random effect. Based on records pooled from Iowa and North Carolina, maternal lineage accounted for 2.7% of the variance in fat percentage. Otherwise, < 1.2% of the variance of any trait was associated with maternal lineage.

Relationships between polymorphism for mitochondrial deoxyribonucleic acid and yield traits of Holstein cows

Two independent data files from the breeding herd of Iowa State University and six North Carolina herds were used to examine relationships between yield traits and mtDNA polymorphism. Maternal lineages were established by tracing ancestry of cows to founder females in the herd book of the Holstein Association. Data from Iowa State University were 1476 records from 602 cows from 29 maternal lineages. The nucleotides of mtDNA encoding rRNA were sequenced. Eleven sites of polymorphism were found. An animal model for gene substitution was used to examine the relationship between sequence differences and yield traits. Traits analyzed were mature equivalent yield of milk, fat, SNF, and milk energy as well as concentrations of fat, SNF, and milk energy. Effects of sequence differences were significant for most traits. Sequence information from the D-loop was available for 12 lineages from North Carolina. The effect of polymorphism at 4 sites was examined using 1472 records from 668 cows. Traits measured were the same, except that protein replaced SNF. No significant relationships existed between any of the traits and D-loop polymorphism, but results suggested that an association might exist between polymorphism and concentrations of milk yield, fat percentage, and energy. Whenever a significant relationship was detected, the effect of mutation (rare genotype) was detrimental.

Impacts of cytoplasmic inheritance on genetic evaluations

Simulation was used to examine the consequences of ignoring cytoplasmic effects on genetic evaluations. Effects on variance component estimation, accuracy of selection, genetic trend, and selection of bull-dams were considered. Comparisons were made for sire and animal models, several levels of cytoplasmic variance, and definition of cytoplasmic effects as either fixed or random. Ten replications with approximately 9000 cows and 20,000 records were simulated for each model and level of cytoplasmic variance. Derivative-free REML was used for estimation of variance components. Ignoring cytoplasmic effects caused overestimation of heritability with an animal model. Permanent environmental variance was underestimated with an animal model and overestimated with a sire model. Results were used for simulation of large (approximately 200,000 cow) data files for analysis of effects on accuracy of selection. Accuracy of selection increased when cytoplasmic effects were accounted for properly. Improvement of predicted breeding values was greater for cows than for sires and increased as cytoplasmic variance increased. Genetic trend also increased slightly, primarily as a function of increased accuracy of bull-dam selection. Little practical difference was detected when cytoplasmic effects were considered to be fixed rather than random.

Challenges to dairy cattle management: genetic considerations

Several new technologies will be used to produce continued genetic change in dairy cattle. These technologies are categorized broadly as 1) improved modeling, selection, and evaluation methods; 2) use of new and improved reproductive technologies; 3) new developments in molecular genetics; and 4) new developments in immunogenetics. Improvements in evaluation will continue as computers become faster and have more storage capabilities. Improved mathematical models that more nearly describe the biology of lactation will maximize estimation of genetic differences and reduce residuals. New reproductive technology could allow reduction of generation intervals two- to fivefold compared with present generation intervals and, combined with genetic markers, could markedly accelerate progress. Health problems in dairy cattle are expected to increase as production increases. Thus, selection for decreased incidences of health disorders will be needed, probably by selection of sires with improved general immunocompetence. Research is in the early stages of application of techniques of molecular genetics to animal breeding. Early uses will allow detection and alleviation of genetic defects. Eventually, marker genes that directly affect production and metabolic pathways that also affect production will be subjected to selection. The ability to foresee new and potentially useful techniques will be determined by scientific advancement of areas in which researchers are engaged; thus, accurate prediction far into the future cannot be expected.