The use of frozen semen to minimize inbreeding in small populations

In this study, we compared the average coancestry and inbreeding levels for two genetic conservation schemes in which frozen semen from a gene bank is used to reduce the inbreeding in a live population. For a simple scheme in which only semen of generation-0 (G0) sires is used, the level of inbreeding asymptotes to 1/(2N), where N is the number of newborn sires in the base generation and rate of inbreeding goes to zero. However, when only sires of G0 are selected, all genes will eventually descend from the founder sires and all genes from the founder dams are lost. We propose an alternative scheme in which N sires from generation 1 (G1), as well as the N sires from G0, have semen conserved, and the semen of G0 and G1 sires is used for dams of odd and even generation numbers, respectively. With this scheme, the level of inbreeding asymptotes to 1/(3N) and the genes of founder dams are also conserved, because 50% of the genes of sires of G1 are derived from the founder dams. A computer simulation study shows that this is the optimum design to minimize inbreeding, even if semen from later generations is available.     

Estimation of relatedness among non-pedigreed Yakutian cryo-bank bulls using molecular data: implications for conservation and breed management

Background

Yakutian cattle, the last remaining native cattle breed in Siberia, are well adapted to the extreme sub-arctic conditions. Nowadays only ca. 1200 purebred animals are left in Yakutia. The semen of six Yakutian bulls was stored in a cryo-bank without any pedigree documentation because of the traditional free herding style of the population.

Methods

To clarify the genetic relatedness between these bulls and to provide recommendations to use their semen in future conservation and breed management programs, we have analysed 30 autosomal microsatellites and mitochondrial DNA sequences in 60 individuals including the six for which semen has been stored. Four relatedness estimators were calculated. In addition, we assessed the value of the cryo-bank bulls for the preservation of genetic variation of the contemporary Yakutian cattle by calculating allelic and gene diversity estimates and mean molecular coancestries.

Results

On the basis of microsatellite variability, including the Yakutian cryo-bank bulls increases the allelic variation in the contemporary population by 3% and in the male subpopulation by 13%. In terms of the mean molecular coancestries, they are less related to the contemporary cow population than the breeding bulls and therefore could be used to reduce inbreeding in the living population. Although 30 loci are insufficient to resolve definitely their relatedness categories, the data suggest four pairs of cryo-bank bulls as possible half-sibs.

Conclusions

Our results show that even relatively limited cryo-bank storage of semen can carry allelic variation through a bottleneck. We propose a breeding scheme based on the rotation of breeding females and the division of cryo-bank bulls into three groups. Thus, if molecular data (e.g. autosomal microsatellite genotypes) for the contemporary population are available and based on relatively small-scale laboratory analyses, it is possible to avoid serious mistakes in their use for breeding applications. The approach suggested here based on the use of Yakutian cryo-bank semen can be easily extended to cryo-bank materials of other animals in future breeding programs.     

Relationship between the magnitude of the inbreeding coefficient and milk traits in Holstein and Jersey dairy bull semen used in Brazil

Artificial insemination has been used to improve production in Brazilian dairy cattle; however, this can lead to problems due to increased inbreeding. To evaluate the effect of the magnitude of inbreeding coefficients on predicted transmitting abilities (PTAs) for milk traits of Holstein and Jersey breeds, data on 392 Holstein and 92 Jersey sires used in Brazil were tabulated. The second-degree polynomial equations and points of maximum or minimal response were estimated to establish the regression equation of the variables as a function of the inbreeding coefficients. The mean inbreeding coefficient of the Holstein bulls was 5.10%; this did not significantly affect the PTA for percent milk fat, protein percentage and protein (P = 0.479, 0.058 and 0.087, respectively). However, the PTAs for milk yield and fat decreased significantly after reaching inbreeding coefficients of 6.43 (P = 0.034) and 5.75 (P = 0.007), respectively. The mean inbreeding coefficient of Jersey bulls was 6.45%; the PTAs for milk yield, fat and protein, in pounds, decreased significantly after reaching inbreeding coefficients of 15.04, 9.83 and 12.82% (P < 0.001, P = 0.002, and P = 0.001, respectively). The linear regression was only significant for fat and protein percentages in the Jersey breed (P = 0.002 and P = 0.005, respectively). The PTAs of Holstein sires were more affected by smaller magnitudes of inbreeding coefficients than those of Jersey sires. It is necessary to monitor the inbreeding coefficients of sires used for artificial insemination in breeding schemes in Brazil, since the low genetic variability of the available sires may lead to reduced production.     

A comparison of Bonus and Quota mating systems for utilising the sex-determining region Y gene in terminal sire beef cattle breeding

The use of the sex-determining region Y gene in terminal sire beef cattle breeding was investigated, assuming that fertile transgenic bulls carrying this gene on an autosome can be created. The benefit of these transgenic bulls arises from having an increased proportion of calves with a male phenotype. Two mating strategies utilising the transgenic bulls were devised and compared; the Quota scheme whereby a quota of normal bulls is used alongside the transgenic bulls in a breeding nucleus, and the Bonus scheme in which a phenotypic bonus is assigned to transgenic bulls indicating the added value of their offspring. Bonus and Quota breeding schemes were comparable, in terms of the value of offspring of the bulls, for the first 6 years of selection, after which time the Quota breeding scheme was superior. For time horizons less than 10 years, and large assumed phenotypic superiorities of male calves, breeding schemes with transgenic bulls were superior to traditional breeding schemes without transgenic bulls. If the time horizon was longer, or if the assumed superiority of male calves was small, then traditional breeding schemes were generally superior to those utilising transgenic bulls. Scenarios were observed, however, where transgenic bulls were always superior to normal bulls, in terms of their value as sires. Equations were derived to predict genetic gain and the equilibrium genetic lag between normal and transgenic bulls in Quota breeding schemes.     

Simulation study on the efficiencies of MOET nucleus breeding schemes applying marker assisted selection in dairy cattle

Advantages of breeding schemes using genetic marker information and/or multiple ovulation and embryo transfer (MOET) technology over the traditional approach were extensively evaluated through simulation. Milk yield was the trait of interest and QTL was the genetic marker utilized. Eight dairy cattle breeding scenarios were considered, i.e., traditional progeny testing breeding scheme (denoted as STANPT), GASPT scheme including a pre-selection of young bulls entering progeny testing based on their own QTL information, MOETPT scheme using MOET technology to generate young bulls and a selection of young bulls limited within the full-sib family, GAMOPT scheme adopting both QTL pre-selection and MOET technology, COMBPT scheme using a mixed linear model which considered QTL genotype instead of the BLUP model in GAMOPT, and three non-progeny testing schemes, i.e. the MOET, GAMO and COMB schemes, corresponding to MOETPT, GAMOPT and COMBPT with progeny testing being part of the system. Animals were selected based on their breeding value which was estimated under an animal model framework. Sequential selection over 17 years was performed in the simulations and 30 replicates were designed for each scenario. The influences of using QTL information and MOET technology on favorable QTL allele frequency, true breeding values, polygenetic breeding values and the accumulated genetic superiority were extensively evaluated, for five different populations including active sires, lactating cows, bull dams, bull sires, and young bulls. The results showed that the combined schemes significantly outperformed other approaches wherein accumulated true breeding value progressed. The difference between schemes exclusively using QTL information or MOET technology was not significant. The STANPT scheme was the least efficient among the 8 schemes. The schemes using MOET technology had a higher polygenetic response than others in the 17th year. The increases of frequency of the favorable QTL allele varied more greatly across the 3 male groups than in the lactating cows group. The accumulated genetic superiorities of the GASPT scheme, MOETPT scheme, GAMOPT scheme, COMBPT scheme, MOET scheme, GAMO scheme and COMB scheme over the STANPT scheme were 8.42%, 3.59%, 14.58%, 18.54%, 4.12%, 14.12%, 16.50% in active sires and 2.70%, 5.00%, 11.05%, 12.78%, 7.51%, 17.12%, 25.38% in lactating cows. Supported by Key Project for Introducing Advanced International Agriculture Science & Technologies (Grant No. 2006-G48), the National Key Basic Research and Development Program of China (Grant No. 2006CB102107) and National Key Technology Research and Development Program of China (Grant No. 2006BAD04A01).     

Testicular development and its relationship to semen production in Murrah buffalo bulls

The objectives of this study were to determine the relationship of age and body weight to testicular development and to establish norms for breeding soundness evaluations of Murrah buffalo bulls. Testicular measurements of 133 Murrah buffalo bulls of various ages were recorded with a caliper and a tape. Semen was collected twice a week for 5 weeks from groups of bulls which were 25-36 (n=17), 37-48 (n=16), 49-60 (n=14), of >60 (n=10) months of age. After examining volume, sperm concentration, and progressive motility semen was diluted in Tris-citric acid-egg yolk-fructose extender and frozen in 0.5 ml French straws. Testicular measurements of buffalo bulls were lower than those recorded for European breeds of cattle bulls. Nevertheless, like cattle bulls, scrotal circumference was highly correlated with other testicular measurements. Also, it had a significant positive relationship with semen volume and sperm concentration per ejaculate. Average sperm output per week in order of increasing age group was 15.3, 18.2, 19.8 and 23.6 x 10(9). Corresponding values for sperm output per week per gram of testis were 59.1, 45.8, 41.1, 36.2 x 10(6) indicating a reduction in spermatogenesis per unit of testis with advancing age. Compared to European breeds, daily sperm output in Murrah bulls was nearly 45% lower, presumably due to their nearly 40% lower scrotal circumference than Holstein bulls of the same age. These results indicate that in buffalo, as in cattle, scrotal circumference is a useful indicator of potential sperm output and may serve as an important criterion for selecting young bulls as AI sires.     

Genome-wide genetic diversity of Holstein Friesian cattle reveals new insights into Australian and global population variability, including impact of selection

Past breeding strategies for dairy cattle have been very effective in producing rapid genetic gain to achieve industry targets and raise profitability. Such gains have been largely facilitated by intense selection of sires combined with the use of artificial insemination. However, this practice can potentially limit the level of genetic diversity through inbreeding and selection plateaus. The rate of inbreeding in Australia is increasing, primarily as a result of semen importation from a small number of prominent bulls from the USA. The effect of this genetic influx in the Australian dairy cattle population is poorly understood both in terms of diversity and local adaptation/divergence. This study uses 845 genome-wide SNP genetic markers and 431 bulls to characterize the level of genetic diversity and genetic divergence within the Australian and international Holstein Friesian dairy population. No significant differences in genetic diversity (as measured by heterozygosity [H(o)] and allelic richness [A]) were observed over the 25-year time period (1975-1999) for bulls used in Australia. The importation of foreign semen into Australia has increased the effective population size until it was in effect a sub-sample of the global population. Our data indicate that most individuals are equally closely related to one another, regardless of country of origin and year of birth. In effect, the global population can be considered as one single population unit. These results indicate that inbreeding, genetic drift and selection has had little effect at reducing genetic diversity and differentiating the Australian Holstein Friesian population at a genome-wide level.     

Influence of sire and sire breed (Gyr versus Holstein) on establishment of pregnancy and embryonic loss in lactating Holstein cows during summer heat stress

Heat stress has negative effects on pregnancy rates of lactating dairy cattle. There are genetic differences in tolerance to heat stress; Bos taurus indicus (B. t. indicus) cattle and embryos are more thermotolerant than Bos taurus taurus (B. t. taurus). In the present study, the effects of sire and sire breed on conception and embryonic/fetal loss rates of lactating Holstein cows during the Brazilian summer were determined. In Experiment 1, cows (n=302) were AI after estrus detection or at a fixed-time with semen from one Gyr (B. t. indicus) or one Holstein sire (B. t. taurus). Pregnancy was diagnosed 80 days after AI. In Experiment 2, cows (n=811) were AI with semen from three Gyr and two Holstein sires. Pregnancy was diagnosed at 30-40 and at 60-80 days after AI. Cows diagnosed pregnant at the first examination but non-pregnant at the second were considered as having lost their embryo or fetus. Data were analyzed by logistic regression. The model considered the effect of sire within breed, sire breed, days postpartum, period of lactation, and AI type (AI after estrus versus fixed-time). There was no effect of the AI type, days postpartum or milk production on conception or embryonic loss rates. The use of Gyr bulls increased pregnancy rate when compared to Holstein bulls [9.1% (60/657) versus 5.0% (23/456), respectively, P=0.008; data from Experiments 1 and 2 combined]. Additionally, in Experiment 2, cows inseminated using semen from sire #4 (Gyr) had lower embryonic loss (10%) when compared with other B. t. indicus (35.3% and 40%) or B. t. taurus sires (18.2% and 38.5%, P=0.03). In conclusion, the use of B. t. indicus sires may result in higher conception rates in lactating Holstein cows during summer heat stress. Moreover, sire can affect embryonic loss and selection of bulls according to this criterion may result in higher parturition rates in lactating Holstein cows.     

Minimising inbreeding in small populations by rotational mating with frozen semen

Mating plans are investigated in order to minimize inbreeding in small populations when frozen semen is available. For a single dam line it was found that specific sire rotations minimized the asymptotic level of inbreeding when semen is used repeatedly from certain generations. When semen of N foundation (G0) sires is used rotationally over generations it is shown that the inbreeding level asymptotes to 1/(2(N+1) - 2). However, if only G0 sires are used then all genes will eventually descend from the founder sires. Inbreeding can be reduced further by using sires from generation one (G1) and later as this retains genes from the founder dams in the long-term gene pool. If semen from NG0 sires and N unrelated G1 sons is used rotationally then inbreeding asymptotes to (2(N-1) + 1)/(2(2N+1) - 2). When there are more founder dams than sires, the asymptotic inbreeding can be reduced even further by using the semen of half-sib G1 sires in rotation. Optimal rotations using full-sib G1 sires or generation 2 (or later) sires will lower the asymptotic inbreeding also, but generally not by much. It was found that when unlimited frozen semen from a specified group of sires was available, the optimal mating plan was achieved by selecting each generation the sire with the least co-ancestry with the current female of the dam line.     

Seasonal effects of semen collection and artificial insemination on dairy cow conception

The effects of four seasons of semen collection and of artificial insemination on conception in dairy cows were studied. The solstices and equinoxes (December, March, June and September) defined the beginning and/or end of each season. Semen was collected from 973 progeny-test bulls over 8 years at the two Norwegian AI stations at 60.8 degrees N and 63.4 degrees N where artificial light was used to provide a minimum photoperiod of 10 h/day. The effect of using semen of elite bulls during progeny testing and after selection as elite sires also was investigated. Norwegian Red (NRF) cows were inseminated over a 7-year period using progeny test semen and over the last 4 years of the same period using the semen of the elite sires. The probability of conception to only first inseminations for cows up to, and including, the fifth lactation was assessed by 56-day non-return rate (56d NRR) and calving rate. Two data sets were analysed which excluded cows culled within 270 days of AI or included such cows as non-calving. The reasons for culling were categorised as those for fertility problems or all other reasons. Semen was used for AI irrespective of the season in which it had been collected. Season of semen collection did not affect 56d NRR but calving rate was significantly higher (by 0.5-0.8%, approximately; P < 0.01) for semen collected in the December-March period, when photoperiod was increasing, than at other times of the year. The season in which AI was performed showed a peak of 56d NRR in spring for heifers (P < 0.01) and in summer for parous animals (P < 0.01). For calving rate, however, no seasonal peak was found in heifers, whereas pluriparous cows had much higher calving rates in summer and autumn/early winter than late winter and spring (P < 0.01). Semen of elite sires resulted in higher calving rates by 0.5 (NS) to 1.9% (P < 0.01) when used after selection than when used during progeny testing. The difference between the calving rate achieved when the semen from elite sires was used during progeny testing and after selection indicates that farmers select different classes of cows for submission to AI by progeny test bulls and sires. The 56d NRR was not as good as calving rate for assessing seasonal and other effects on conception rates.     

Implementation of advanced Optimum Contribution Selection in small-scale breeding schemes: prospects and challenges in Vorderwald cattle

Vorderwald cattle are a regional cattle breed from the Black Forest in south western Germany. In recent decades, commercial breeds have been introgressed to upgrade the breed in performance traits. On one hand, native genetic diversity of the breed should be conserved. On the other hand, moderate rates of genetic gain are needed to satisfy breeders to keep the breed. These goals are antagonistic, since the native proportion of the gene pool is negatively correlated to performance traits and the carriers of introgressed alleles are less related to the population. Thus, a standard Optimum Contribution Selection (OCS) approach would lead to reinforced selection on migrant contributions (MC). Our objective was the development of strategies for practical implementation of an OCS approach to manage the MC and native genetic diversity of regional breeds. Additionally, we examined the organisational efforts and the financial impacts on the breeding scheme of Vorderwald cattle. We chose the advanced Optimum Contribution Selection (aOCS) to manage the breed in stochastic simulations based on real pedigree data. In addition to standard OCS approaches, aOCS facilitates the management of the MC and the rate of inbreeding at native alleles. We examined two aOCS strategies. Both strategies maximised genetic gain, while strategy (I) conserved the MC in the breeding population and strategy (II) reduced the MC at a predefined annual rate. These two approaches were combined with one of three flows of replacement of sires (FoR strategies). Additionally, we compared breeding costs to clarify about the financial impact of implementing aOCS in a young sire breeding scheme. According to our results, conserving the MC in the population led to significantly (P < 0.01) higher genetic gain (1.16 ± 0.13 points/year) than reducing the MC (0.88 ± 0.10 points/year). In simulation scenarios that conserved the MC, the final value of MC was 57.6% ± 0.004, while being constraint to 58.2%. However, reducing the MC is only partially feasible based on pedigree data. Additionally, this study proves that the classical rate of inbreeding can be managed by constraining only the rate of inbreeding at native alleles within the aOCS approach. The financial comparison of the different breeding schemes proved the feasibility of implementing aOCS in Vorderwald cattle. Implementing the modelled breeding scheme would reduce costs by 1.1% compared with the actual scheme. Reduced costs were underpinned by additional genetic gain in superior simulation scenarios compared to expected genetic gain in reality (+4.85%).     

Effect of gonadotrophin releasing hormone on conception rate in repeat-breeder dairy cows

The effect of gonadotrophin releasing hormone (GnRH) on conception rate was studied in 961 repeat-breeder cows in five California dairy farms. Cows were injected with GnRH or saline at the time of the fourth insemination. All breeding was by artificial insemination (AI) using frozen semen from two bulls. Conception rate for GnRH-treated cows was higher than for controls (47.0 vs 37.7%, P < 0.01). There was no significant difference in conception rate between the two bulls or among five AI technicians. How GnRH acts upon fertility in repeat-breeder cattle has not been determined.     

Impact of genomic selection of AI dairy sires on their likely utilization and methods to estimate fertility: a paradigm shift

Breeding of dairy cattle is undergoing a paradigm shift to genomic selection of potential sires and dams. This undoubtedly will affect how bulls are managed in an artificial insemination (AI) center and impact methods to estimate their ‘fertility'. Our goal is to help decision-makers understand the contents of a straw of semen, current estimates of sire fertility, and how estimates might evolve in a genomic era. Sire fertility is estimated from outcome (pregnant or not) after 300 to > 2,000 inseminations and reported in units (U) as a sire's deviation from a population (> 500 bulls) average pregnancy rate (PR). Too often users do not recognize that imprecision of an estimate encompasses a 3-U range, or more. ‘True fertility' of the sire whose semen is inseminated influences outcome far less than ‘true fertility' of each female and a myriad of microenvironment and management factors. Further, AI centers discard substandard collections and intentionally adjust number of sperm per straw so that differences in pregnancy rates achieved by different sires are minimized! For > 80% of Holstein bulls, estimated ‘sire conception rates' are within a 5.4-U range. In the future, most sires will be 15 to 40 mo old and services will accumulate at > 1,000/mo. Estimated sire conception rates still will be a deviation from the population mean, but should be based on records for the most recent 6 or 12 mo, rather than 48 or 60 mo. Repeated ‘snap shots' every 2 mo would allow AI centers to adjust number of sperm per AI straw from genomic-sires in a timely manner, to maintain high pregnancy rates, and to meet market demands with sires producing ∼40% as many sperm as mature ‘proven sires' of yesteryear.     

Deletion/insertion polymorphism of the prion protein gene (<Emphasis Type="Italic">PRNP</Emphasis>) in Polish Holstein-Friesian cattle

The aim of the present study was to identify the deletion/insertion polymorphism of the bovine prion protein gene (PRNP) within the promoter sequence (23 bp), intron 1 (12 bp) and 3’ untranslated region (14 bp). DNA was isolated from blood of 234 randomly tested Polish Holstein-Friesian cows and from semen of 47 sires used for artificial insemination (AI) in 2004. No statistically significant differences were found in the frequency of genotypes and alleles between cows and breeding bulls in the 3 analysed polymorphic sites within thePRNP gene. Only 3 haplotypes were identified in sires and 4 haplotypes in cows.     

Phenotypic relationships between hair whorl characteristics and spermatozoal attributes in Holstein bulls

The objective of this study was to characterize facial whorl characteristics in Holstein stud bulls (n = 485) and to investigate their association with measures of semen quantity and quality. Bulls had 1 (n = 454), 2 (n = 21) or no facial hair whorls (n = 5). Some 39% of bulls had whorls in the middle of their forehead, whereas 43% had whorls very low down on their forehead. Spiral whorls were present on 77% of bulls while 22% had elongated whorls. Abnormally shaped whorls were found more often on bulls with low whorls (27% versus 17%, P = 0.01) than on bulls with high or middle whorls. Semen production data were obtained from the AI center database to provide a representative sample of each sires most recent semen production characteristics. The number of semen collections per bull averaged 38 with a range of 1 (n = 9) to 272 (n = 1). The average number of days between collections was 5 but varied from 1 to 425 days. Average age of bulls at first recorded collection was 679 days and ranged from 307 to 4555 days. There were no significant differences between black and white bulls in semen quality or quantity. Semen quality over the summer months was reduced in comparison to the winter months. Age of the bull at time of collection had no effect on any of the semen quality traits. Older bulls had larger scrotal circumference and produced more semen (P > 0.01). Bulls with whorls located in the center of the forehead were not significantly different in semen quality or quantity for the 10 traits considered when compared to bulls with whorls located outside the center. In contrast to previous research findings with Angus cattle, semen attributes were not significantly different between bulls characterized with round (or spiral) epicenters and those with abnormally shaped whorls. The difference between the two studies may be due to the fact that Angus bulls have a higher percentage of abnormal elongated whorls compared to Holsteins.     

Relationship of breeding soundness evaluation score and its components with reproductive performance of beef bulls

Angus, Polled Hereford and Santa Gertrudis bulls were subjected to a breeding soundness evaluation (BSE) just prior to being exposed to cows for 90 to 95 days in single-sire units under natural breeding conditions on pasture. Forty-eight of 55 bulls subjected to scrotal and semen evaluations passed the BSE and were considered acceptable for breeding. Of the bulls that passed BSE, 18 (six bulls from each breed) were used for breeding for each yr of the 2-yr study. Of the bulls used for breeding, breed of sire differences were significant for scrotal circumference and calving rate, while differences among sires within breed of sire were significant for secondary morphology, motility score and calving rate. The difference between means for bulls used vs bulls that failed BSE was significant for all eight traits. Correlations among various scrotal and semen evaluations were compared for bulls used vs bulls that failed BSE. Of the eight traits, only the motility score was significantly correlated with the calving rate. After the exclusion of bulls that failed to pass BSE, there remained differences (P<0.01) among bulls within breed of sire for calving rate. Thus, there is a need for an additional easy-to-use procedure that would more accurately predict the breeding performance of bulls.     

Effects of sperm concentration at semen collection and storage period of frozen semen on dairy cow conception

The present study was based on data obtained from artificial inseminations (AIs) performed with cryopreserved semen from elite bulls used in the Norwegian breeding program. Semen was diluted to standardize the number of spermatozoa to 18 million per AI dose. The aim of the study was to investigate whether the net sperm concentration at semen collection and the storage period in liquid nitrogen have any effect on probability of conception in dairy cattle. We demonstrated that the natural range of sperm concentration at semen collection within some of the bulls was associated with the probability of conception. However, no primary trend among bulls was found on the effect of sperm concentration at semen collection. This appears to be due to differences among bulls in their response to the dilution ratio of seminal plasma to extender. The effect of storage time was investigated in semen that had been stored between 1000 days and 2400 days in AI straws in liquid nitrogen at the AI center. Our findings showed that use of semen with the longest storage period, i.e. 1951-2400 days, resulted in a more than one percentage point lower probability of conception than semen with a shorter storage period. In conclusion, the net sperm concentration at semen collection, which affects the dilution ratio of seminal plasma to extender, should be considered individually among bulls to achieve optimal reproductive performance. Furthermore, this study gives support to the idea that a measurable degree of damage to the spermatozoa could occur during the preservation time in liquid nitrogen.     

Sperm morphology and fertility of progeny-tested AI dairy bulls in Sweden

Use of bull semen with high levels of sperm abnormalities, reflecting genital dysfunction, is not recommended for artificial insemination (AI) since it would most likely lead to subfertility. Sperm quality, including sperm morphology, may deteriorate with increasing age of the bull thus becoming a source of concern when using older, progeny-tested AI bull sires. Although a relationship between sperm morphology and fertility after AI in progeny-tested bull sires has been reported, it is yet unclear which sperm abnormalities are most critical. This constituted the core aim of a 22-month long retrospective study in proven (aged 60-84 months at the start of the study) AI sires of the Swedish Red (SR, n=8) and Swedish Holstein (SLB, n=4) breeds where their semen (107 freezing batches in total, built by a single ejaculate (n=3) or pooling two consecutive ejaculates (n=104) collected at 1-3 months interval), were subjected to detailed morphological examinations on wet- and dry, stained smears. Attention was paid to between- and within-bull variations with regard to presence and level of sperm abnormalities. Sperm morphology differed significantly between sires and ejaculates, with 6/12 sires having ejaculates containing >10% of morphologically deviating sperm head shapes, a commonly used threshold for young AI bulls in Sweden. However, with the exception of pear-shaped or narrow-at-the-base anomalies, the mean values for individual defects were always within the limits expected for a normal bull sire, and were therefore considered acceptable. The percentage of morphologically normal spermatozoa was positively related to fertility, whose output differed significantly among bulls. Among sperm abnormalities, the proportion of morphologically deviating sperm head shapes were negatively correlated with fertility, pear-shaped sperm heads in particular. In conclusion, the relationship between sperm morphology and fertility after AI calls for frequent (2-3 months interval) detailed assessments of sperm morphology in AI stud bull sires.     

No incidence of DUMPS carriers in Polish dairy cattle

DUMPS (Deficiency of Uridine Monophosphate Synthase) is a hereditary recessive disorder in Holstein cattle causing early embryo mortality during its implantation in the uterus. The only way to avoid the economic losses is early detection of DUMPS carriers. Because American Holstein semen has been intensively imported to Poland since 1970, there was a risk that DUMPS could have spread in Polish dairy cattle. In our study, 2209 dairy cattle of the Polish Holstein breed have been screened by the DNA test. The dominant group was young bulls entering the testing program (1171) and proven bulls (781). They represented all sires entering Polish breeding programs between 1999 and 2003. Also, 257 sire dams were included in the screening program. No DUMPS carrier has been found. Our results then indicate that the population of dairy cattle reared in Poland is free from DUMPS. Because of the economical significance of the DUMPS mutation and its recessive mode of inheritance, attention has to be paid to any case of a bull having in his origin any known DUMPS carrier. Such a bull should be tested and if positive eliminated from the active population. Also, young bulls (testing bulls) should be screened for DUMPS if in their progeny a high incidence of embryo mortality is observed and their genealogy cannot exclude their relatedness to any DUMPS carriers.