Comparison of reproductive performance by artificial insemination versus natural service sires in California dairies

This study compared the calving to conception intervals for cows in AI pens with cows exposed to natural service sires, controlling for milk production, mastitis occurrence, parity and calving month effects. Records from 10 western United States dairy herds (mean herd size = 2058 cows) were evaluated retrospectively over an 18-month period. Eight bull breeding analysis cohorts were created (the first cohort 0-50 days in milk and the remaining cohorts at 25 days in milk intervals through 226 days). The cohorts contained non-pregnant cows that were first moved into bullpens during the described cohort period. Equal numbers of non-pregnant cows only exposed to AI during the cohort period were randomly selected from the pool of eligible non-pregnant cows. An AI cow was used only once in the data analysis, but was included in a bull breeding cohort at a later date if she remained non-pregnant and was transferred to a bullpen. Univariate and multivariate survival analysis was used to compare the calving to conception intervals. Cows in AI groups had higher hazard rates for pregnancy across all cohorts. Parity and milk production were significantly associated with risk for pregnancy. In herds that practice a mixture of AI and bull breeding, overall herd reproductive performance might be improved by allowing cows more opportunities at AI prior to moving them into clean-up bullpens.     

Comparison of artificial insemination and natural service cost effectiveness in dairy cattle

Reproductive efficiency in the dairy herd is the most important factor for its economic success and a major concern for dairy farmers when using artificial insemination (AI) or natural service (NS). Our objectives were to estimate, compare and analyse the costs associated with breeding cattle by do-it-yourself (DIY) AI and NS and identify the factors that influence them, under typical dairy farming conditions in Greece. A simulation study was designed based on data from 120 dairy cattle farms that differed in size (range 40 to 285 cows) and milk production level (4000 to 9300 kg per cow per year). Different scenarios were employed to estimate costs associated directly with AI and NS as well as potentially extended calving intervals (ECI) due to AI. Results showed that bull maintenance costs for NS were €1440 to €1670 per year ($1,820 to $2,111). Direct AI costs were higher than those for NS for farms with more than 30 cows and ECI constituted a considerable additional burden. In fact, amongst the factors that affected the amount of milk needed to cover total extra AI costs, number of days open was the dominant one. Semen, feed and heifer prices had a very small effect. When, hypothetically, use of NS bulls results in a calving interval of 12 months, AI daughters with a calving interval of 13.5 months have to produce about 705 kg of additional milk in order to cover the extra cost. Their actual milk production, however, exceeds this limit by more than 25%. When real calving intervals are considered (13.0 v. 13.7 months for NS and AI, respectively) AI daughters turn out to produce more than twice the additional amount of milk needed. It was concluded that even under less than average management conditions, AI is more profitable than the best NS scenario. The efficient communication of this message should be a primary concern of the AI industry.     

Potential uses of cloning in breeding schemes: dairy cattle

Cloning by nuclear transfer has many potential applications in a dairy cattle breeding program. It can be used to increase the accuracy of selection and therefore the rate of genetic progress, to speed up the dissemination of the genes from animals of exceptionally high genetic merit to the commercial population, and to reproduce transgenic animals. Today, however, the main limitation of the use of cloning besides governmental regulations is its low success rate and consequently the high cost to produce an animal ready for reproduction. As a result cloning is mostly limited to the reproduction of animals of very high genetic merit or that carry genes of specific interest. Examples of this are top-ranked bulls which do not produce enough semen for the demand due to various reasons. A strategy that could be used by artificial insemination (AI) centers would be to create a bank of somatic cells for every bull entering AI facilities long before they are placed on the young sire proving program. The other use of cloning is to assist in the selection and reproduction of bull dams. Marker assisted selection (MAS) can substantially enhance the accuracy of selection for embryos or young animals without comprehensive performance records, and therefore can greatly increase the value of cloning such embryos or young animals.     

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.     

A definition of unknown parent groups based on bull usage patterns across herds

In genetic evaluations, the definition of unknown parent groups (UPG) is usually based on time periods, selection path and flows of foreign founders. The definition of UPG may be more complex for populations presenting genetic heterogeneity due to both, large national expansion and coexistence of artificial insemination (AI) and natural service (NS). A UPG definition method accounting for beef bull flows was proposed and applied to the French Charolais cattle population. It assumed that, at a given time period, unknown parents belonged to the same UPG when their progeny were bred in herds that used bulls with similar origins (birth region and reproduction way). Thus, the birth period, region and AI rate of a herd were pointed out to be the three criteria reflecting genetic disparities at the national level in a beef cattle population. To deal with regional genetic disparities, 14 regions were identified using a factorial approach combining principal component analysis and Ward clustering. The selection nucleus of the French cattle population was dispersed over three main breeding areas. Flows of NS bulls were mainly carried out within each breeding area. On the contrary, the use and the selection of AI bulls were based on a national pool of candidates. Within a time period, herds of different regions were clustered together when they used bulls coming from the same origin and with an estimated difference of genetic level lower than 20% of genetic standard deviation (σg) for calf muscle and skeleton scores (SS) at weaning. This led to the definition of 16 UPG of sires, which were validated as robust and relevant in a sire model, meaning numerically stable and corresponding to distinct genetic subpopulations. The UPG genetic levels were estimated for muscle and SS under sire and animal models. Whatever the trait, differences between bull UPG estimates within a time period could reach 0.5 σg across regions. For a given time period, bull UPG estimates for muscle and SS were generally larger by 0.30 to 0.75 σg than those of cows. Including genetic groups in the evaluation model increased the estimated genetic trends by 20% to 30%. It also provoked re-ranking in favor of bulls and cows without pedigree.     

Assessing the impact of natural service bulls and genotype by environment interactions on genetic gain and inbreeding in organic dairy cattle genomic breeding programs

The objective of the present study was to compare genetic gain and inbreeding coefficients of dairy cattle in organic breeding program designs by applying stochastic simulations. Evaluated breeding strategies were: (i) selecting bulls from conventional breeding programs, and taking into account genotype by environment (G×E) interactions, (ii) selecting genotyped bulls within the organic environment for artificial insemination (AI) programs and (iii) selecting genotyped natural service bulls within organic herds. The simulated conventional population comprised 148 800 cows from 2976 herds with an average herd size of 50 cows per herd, and 1200 cows were assigned to 60 organic herds. In a young bull program, selection criteria of young bulls in both production systems (conventional and organic) were either ‘conventional’ estimated breeding values (EBV) or genomic estimated breeding values (GEBV) for two traits with low (h²=0.05) and moderate heritability (h²=0.30). GEBV were calculated for different accuracies (r_mg), and G×E interactions were considered by modifying originally simulated true breeding values in the range from r_g=0.5 to 1.0. For both traits (h²=0.05 and 0.30) and r_mg⩾0.8, genomic selection of bulls directly in the organic population and using selected bulls via AI revealed higher genetic gain than selecting young bulls in the larger conventional population based on EBV; also without the existence of G×E interactions. Only for pronounced G×E interactions (r_g=0.5), and for highly accurate GEBV for natural service bulls (r_mg>0.9), results suggests the use of genotyped organic natural service bulls instead of implementing an AI program. Inbreeding coefficients of selected bulls and their offspring were generally lower when basing selection decisions for young bulls on GEBV compared with selection strategies based on pedigree indices.     

DGAT1 K232A quantitative trait nucleotide polymorphism in Polish Black-and-White cattle

The diacylglycerol o-acyltransferase 1 gene (DGAT1) was investigated in Polish Black-and-White cattle. The frequency of the K allele was 0.60, 0.68 and 0.48 for AI sires (n=150), young bulls (n=139) and cows (n=213), respectively. The method of selective genotyping for identification of the quantitative trait nucleotide was verified through identification of DGAT1 effect on milk production traits. Daughters of six heterozygous bulls were selectively genotyped based on their milk traits. The genotypic frequencies differed between high and low yield groups representing milk and fat contents. The Kruskal-Wallis test revealed a highly significant effect of DGAT1 K232A in cows with extremely low fat content and a significant effect in cows with extremely high protein content of milk. No significant effect of AI sires' genotypes on their breeding value was found.     

Linkage between amylase-1 locus and a major gene for milk fat content in cattle

Summary
Linkage between the amylase-1 ( Am-1 ) locus and a quantitative trait locus influencing fat content in milk was studied in offspring from heterozygous sires of the Swedish Red and White dairy breed. The effect on bull breeding values for fat content was estimated as interactions between sire and paternal Am-1 allele using a model eliminating the direct effects of sire and Am-1 allele. There were strong indications of linkage, confirming results of previous studies. The interaction was caused by strong associations in 7 out of 14 sire families. A test for within-family variance heterogeneity performed on the whole population of breeding bulls also supported the presence of a major gene for fat content in milk. The results indicate that there is genetic linkage between the Am-1 locus and a locus with large effect on milk fat content.     

Sustainable long-term conservation of rare cattle breeds using rotational AI sires

The development of inbreeding in rotation breeding schemes, sequentially using artificial insemination (AI) sires over generations, was investigated for a full AI scheme. Asymptotic prediction formulae of inbreeding coefficients were established when the first rotation list of AI sires (possibly related) was in use. Simulated annealing provided the optimal rotation order of sires within this list, when the sires were related. These methods were also used for subsequent rotation lists, needed by the exhaustion of semen stores for the first bulls. Simulation was carried out starting with groups of independent sires, with different sizes. To generate a yearly inbreeding rate substantially lower than 0.05% (considered to be within reach by conventional conservation schemes using frequent replacements), the results obtained showed that the number of sires should be at least 10–15 and that the same sires should be used during at least 50 years. The ultimate objective was to examine the relevance of implementing rotation in breeding schemes on the actual rare French cattle breeds under conservation. The best candidate for such a test was the Villard-de-Lans breed (27 bulls and 73 000 doses for only 340 females) and it turned out to be the best performer with an inbreeding coefficient of only 7.4% after 500 years and five different sire lists. Due to the strong requirements on semen stores and on the stability of population size, actual implementation of this kind of conservation scheme was recommended only in special (''niche'') cattle populations.     

The development of beef breeding bulls

Management of the bull battery will have a dramatic impact on profitability of the cow/calf enterprise. It is critical that young bulls be selected and developed to maximize longevity and productivity for the eventual buyer. Bulls must be structurally sound, healthy, and have adequate libido in order to service the required number of females. Once bulls complete their first breeding season, special care must be taken in order to ensure that they recover and regain needed body condition and pass a bull breeding soundness examination (BBSE). Mature bulls that have reached their genetic potential for growth require less intensive management, but the health program and annual BBSE cannot be overlooked. Mature bulls are also more likely to carry venereal disease and should be screened according to local disease incidence and state regulations. All bulls, regardless of age, should be observed early during the breeding season to ensure that they are physically capable of mounting and servicing females. The establishment of a complete management program, especially for young bulls, is essential to ensure that ranch resources are used efficiently, including maintenance of a high level of reproductive performance of the cow herd.     

Prion octapeptide-repeat polymorphism in Polish Black-and-White cattle

The study was carried out in a Polish Black-and-White cattle population, represented by 167 AI sires, 200 young tested bulls, 190 bull-dams, and 606 randomly chosen cows from commercial herds. The fragment of the bovine prion protein gene (PRNP) coding the octapeptide-repeat sequence, was identified by PCR analysis. Two different gene variants of 349 bp and 373 bp in size, produced three genotypes: PRNP 6/6, PRNP 6/5 and PRNP 5/5, respectively. Allele frequency in all examined populations, on average 0.894 for PRNP 6 and 0.106 for PRNP 5, shows a significant difference between the group of cows from commercial herds, characterised by high frequency of PRNP 5 (q = 0.137) in comparison to AI sires (q = 0.077), young tested bulls (q = 0.052) and bull-dams (q = 0.084). Moreover, both analysed female groups of bull-dams and cows from commercial herds are distinguished by the presence of PRNP 5/5 homozygous animals, which were not recorded in the AI sires and young tested bulls, and had never been recognised in earlier examined Holstein-Friesian populations. Analysis of the genetic equilibrium indicates a very high conformity between observed and expected number of animals in the separate PRNP genotype groups. However, some tendency of difference is observed in highly selected cows, qualified as bull-dams on the basis of very high level of milk performance traits.     

Epidemiology of Tritrichomonas foetus in beef bull populations in Florida

The objectives of this study were to estimate the prevalence of herd and individual bull infection with Tritrichomonas foetus in a survey of beef bulls in the state of Florida and to perform an epidemiological investigation of risk factors for the disease. Bulls were tested for T. foetus colonization by a single preputial scraping and culture. Bull infection prevalence within herds was calculated and relationships with bull, herd factors, and production measurements were determined. The survey included 1984 beef bulls in 59 herds throughout Florida; nine bulls in three small herds (<100 cows) were later excluded from the models. An overall prevalence for T. foetus-infected bulls was 6.0% (within-herd prevalence ranged from 0 to 27%). The herd prevalence was 30.4% (i.e. at least one infected bull); infected bulls were found in 11.1 and 39.5% of herds sampled in North and South Florida, respectively. The likelihood of disease was greatest in larger herds in more extensive management settings (> or = 500 cows, 53.9% prevalence; medium-sized herds of 100-499 cows, 10.0% prevalence). Tritrichomonas foetus infection was associated with several bull factors, including age, breed, herd, and herd management practices (bull-to-cow ratio, bulls per breeding group). Tritrichomonas foetus infection continues to be prevalent in beef herds in Florida that use natural service.     

Semen production in artificial insemination bulls in Norway

Semen production data from 792 Norwegian Red AI bulls, of 46 sires, were analyzed. Semen production was affected by AI center, year and season of collection, number of months the bull had been collected, and sire (each P < 0.01). Heritability for produced accepted doses was estimated to be 0.34 (+/-0.13). This should allow a successful phenotypic selection for this trait. A negative correlation between number of accepted and number of discarded doses (-0.82+/-0.11) was found. Selection based on number of accepted doses per bull will therefore result in improvement of semen quality.     

Influence of interactions between semen extender and number of spermatozoa on nonreturn rate estimates of fertility for individual Holstein bulls

The aim of the present study was to investigate the possibility of adapting sperm cell concentration per insemination unit to the intrinsic fertility of a given bull. For this purpose, split ejaculates of seven proven Holstein sires of unknown fertility were diluted in TRIS or in Laiciphos extenders. TRIS diluted doses contained either 8.12 or 16 million total sperm cells (T8, T12, T16 respectively), while the routinely-used Laiciphos units contained 16 million sperm (L16). A total of 18.068 first artificial inseminations were performed by three different AI centers. No difference in the average fertility occurred between T16 and L16 (69.2 vs 69%), but the individual bull results varied; L16 displayed lower inter-bull variability. The nonreturn rates (60 to 90 days) obtained with T8 and T12 (65.7 and 66.8%, respectively) were significantly lower than with T16 and L16 (P < 0.02). The effect of AI center was also significant (P < 0.05). Despite a highly significant effect of the sire (P < 0.001), no interaction was found between the bull and cell concentration or the AI center. The bull effect indicates that it may be worthwile especially for the bulls of the highest genetic merit to test for the appropriate lowest number of spermatozoa per unit to allow wider commercial and genetic diffusion without compromising the average nonreturn rate of the sire.     

Restriction fragment length polymorphism of a bovine T-cell receptor ß gene

Genetic polymorphism of a bovine T-cell receptor beta gene was investigated by analysing restriction fragment length polymorphism (RFLP). One locus, denoted TCRB, with four allelic variants was revealed. The relationship between alleles at the TCRB locus and bull breeding values for disease and milk production was investigated in a sample of 196 progeny-tested AI bulls of the Swedish Red and White breed. The statistical evaluation of the data revealed no convincing association between TCRB alleles and any of the traits studied.     

A description of the findings from bull breeding soundness evaluations and their association with pregnancy outcomes in a study of western Canadian beef herds

The primary objectives were to describe beef bulls considered for use and those reported as used in 205 beef herds in western Canada, and to determine whether factors typically assessed during breeding soundness evaluations were associated with reproductive success. More than 100 veterinary clinics reported 2990 breeding soundness evaluations for bulls considered for natural service in client's herds. Differences among clinics explained 5.2% of the variation in scrotal circumference (SC) and 6.9% of the variation in percentage of morphologically normal sperm of all bulls considered for use (after accounting for age, breed, body condition, significant physical abnormalities, month, and year). The percentage of morphologically normal sperm was lower in bulls with an SC ≤34 versus >34 cm (P < 0.006). This study included data from 1384 and 1370 bulls used for breeding in 2001 and 2002, respectively. Most (80%) of the bulls used were Simmental, Black Angus, Charolais, Red Angus, or Hereford, and 80% were ≤4 y of age. Before the breeding season, a veterinarian evaluated 89.5% of all bulls used in these herds. Of the bulls subjected to a breeding soundness evaluation and subsequently used, 93.1% were satisfactory. In 2001 and 2002, injuries were reported in 2.5 and 2.1% of bulls and in 16.6 and 11.4% of herds, and necrobacillosis of the foot was reported in 2.5 and 1.2% of bulls and 11.2 and 6.5% of the herds. The average number of cows exposed to each bull was 26 (both years). Cows exposed to bulls with a smaller SC were less likely to be diagnosed pregnant (P < 0.047) and had a longer median interval from first bull exposure to calving (P < 0.016) than bulls with a larger SC. In conclusion, our findings emphasized the value of breeding soundness evaluations, including measurements of SC, in fertility management of beef cattle.     

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.     

Insemination factors affecting the conception rate in seasonal calving Holstein-Friesian cows

Differences in conception rate to first service between artificial inseminations (AI) carried out by commercial AI operators (CAI) or do-it-yourself operators (DIY), between natural service (NAT) and AI, between different AI sires, and between fresh and frozen-thawed semen, on Irish commercial dairy farms, were studied using logistic regression. The study comprised 12,933 potential first inseminations from 77 spring-calving dairy herds. The data were recorded during 1999 and 2000. Amongst the total, 4,394 cows had repeated records across the two years. Adjustment variables included: herd, year, parity, calving period, calving to service interval, herd size, proportion of North American Holstein-Friesian genes, peak milk yield, semen fresh or frozen-thawed status, AI sire and a cow history variable to account for the correlation structure that may exist between performance records of cows present in both years of the study. Interactions of interest were tested but were non-significant. No significant association was observed between the category of AI operator and the likelihood of conception rate to first service (PREG1). The variation in PREG1 observed within the category of operator (CAI and DIY) was investigated using the Levene test for homogeneity of variance. There was no difference between the level of variation observed within CAI and DIY operators. There were significant differences in the likelihood of PREG1 between different AI sires. Amongst the 40 most commonly used AI sires, 3 sires had a lower likelihood of PREG1 (P < 0.05) when compared to the reference AI sire (sire with PREG1 similar to the mean of the group). There was a tendency for a reduced likelihood of PREG1 with the use of fresh semen compared to frozen-thawed semen (OR = 0.80, P = 0.067). Amongst the adjustment variables in the model, those significantly associated with the likelihood of PREG1 included the herd, calving period, calving to first service interval and peak milk yield. No significant difference in the likelihood of PREG1 was observed between AI and NAT.     

Effect of one or three timed artificial inseminations before natural service on reproductive performance of lactating dairy cows not observed for detection of estrus

The objectives were to determine the effects of one or three timed artificial insemination (AI) before natural service (NS) in lactating dairy cows not observed for detection of estrus on hazard of pregnancy, days nonpregnant, and 21-days cycle pregnancy rate. A total of 1050 lactating Holstein cows were subjected to a double Ovsynch program for their first postpartum AI. On the day of first AI (78 ± 3 days in milk), cows were blocked by parity and randomly assigned to receive either one timed AI (1TAI, n = 533) or three timed AI (3TAI, n = 517) before being exposed to NS. Cows assigned to 1TAI were exposed to bulls 7 days after the first AI. Nonpregnant cows in 3TAI were resynchronized with the Ovsynch protocol supplemented with progesterone twice, with intervals between AI of 42 days, before being exposed to NS 7 days after the third AI. Cows were evaluated for pregnancy 32 days after each timed AI, or every 28 days after being exposed to NS. Pregnant cows were re-examined for pregnancy 28 days later (i.e., 60-day gestation). Exposure to heat stress was categorized based on the first AI being performed during the hot or cool season, according to the temperature-humidity index. Body condition was scored at first AI. All cows were allowed a period of 231 days of breeding, after which nonpregnant cows were censored. Pregnancy to the first AI did not differ between 1TAI and 3TAI on Day 60 after insemination (30.8 vs. 33.5%). Cows receiving 3TAI had a 15% greater hazard of pregnancy and a 17% greater 21-days cycle pregnancy rate than 1TAI and these benefits originated from the first 84 days of breeding. These changes in rate of pregnancy reduced the median and mean days nonpregnant by 9 and 10 d, respectively. Despite the long inter-AI interval in cows subjected to 3TAI, reproductive performance was improved compared with a single timed AI and subsequent exposure to NS. In dairy herds that use a combination of AI and NS, allowing cows additional opportunities to AI before onset of breeding with bulls is expected to improve reproductive performance.