Estimation of genetic parameters and heterosis for longevity in crossbred Danish dairy cattle

Environmental impact of Holstein Friesian and 3-breed crossbred dairy cows using a life cycle assessment approach applied to individual animals

This study aimed to set up a life cycle assessment (LCA) approach at the level of individual animals to assess the effects of a 3-breed crossbreeding program on the environmental impact of cows. The study involved 564 cows, 279 purebred Holstein Friesian (HO) and 285 crossbred cows (CR), that originated from a 3-breed crossbreeding program based on the rotational use of Viking Red, Montebèliarde, and HO sires and kept in 2 dairy herds of northern Italy (224 and 340 cows/herd, respectively). The reference unit of the LCA model was the lifetime of cows, from the birth to culling or death. Data were collected at different levels: individual animal-based data referred to the whole life (birth, calving, dry, cull or death dates, and milk production); individual test-date collection of body measures and BCS, used to predict BW and to estimate energy requirements; common farm-based data concerning herd management (diets composition, and materials used). Data were used to compute DMI, milk and milk components production, gross income (GI), and income over feed costs (IOFC) pertaining to the lifespan of cows. An individual LCA-derived approach was set up to compute global warming potential (GWP), acidification and eutrophication potential (AP and EP, respectively), and land occupation (LO), which have been associated with different functional units (cow in her whole life or per day of life; kilograms of milk fat plus protein, and GI and IOFC [in euros] produced in the herd life). Data were analyzed using a generalized linear model including the fixed effects of genetic group (CR vs. HO), farm, and their interaction (genetic group × farm). Compared with HO, CR cows completed more lactations (+12%), had earlier first calving (-2 wk), yielded more fat plus protein in milk both in the lifespan (+8%) and per day of life (+4%). Concerning the environmental impact, when compared with HO herd mates, CR cows had nominal greater emissions per cow in the whole life, similar emissions per day of life and ∼3% lower GWP, AP, and EP per kilogram of fat plus protein yielded in lifespan. Income over feed costs per unit of emission tended to be ∼4% greater in CR compared with HO cows. Also, the use of land tended to be lower in CR compared with HO in most indicators considered. In conclusion, LCA could be adapted to represent individual animals. Moreover, managing dairy cows according to a 3-breed rotational crossbreeding scheme may be regarded as a strategy that can contribute to mitigate the emissions and to improve the environmental impact of dairy operations.

Lactation modeling and the effects of rotational crossbreeding on milk production traits and milk-spectra-predicted enteric methane emissions

Rotational crossbreeding has not been widely studied in relation to the enteric methane emissions of dairy cows, nor has the variation in emissions during lactation been modeled. Milk infrared spectra could be used to predict proxies of methane emissions in dairy cows. Therefore, the objective of this work was to study the effects of crossbreeding on the predicted infrared proxies of methane emissions and the variation in the latter during lactation. Milk samples were taken once from 1,059 cows reared in 2 herds, and infrared spectra of the milk were used to predict milk fat (mean ± SD; 3.79 ± 0.81%) and protein (3.68 ± 0.36%) concentrations, yield (21.4 ± 1.5 g/kg dry matter intake), methane intensity (14.2 ± 2.0 g/kg corrected milk), and daily methane production (358 ± 108 g/d). Of these cows, 620 were obtained from a 3-breed (Holstein, Montbéliarde, and Viking Red) rotational mating system, and the rest were purebred Holsteins. Milk production data and methane traits were analyzed using a nonlinear model that included the fixed effects of herd, genetic group, and parity, and the 4 parameters (a, b, c, and k) of a lactation curve modeled using the Wilmink function. Milk infrared spectra were found to be useful for direct prediction of qualitative proxies, such as methane yield and intensity, but not quantitative traits, such as daily methane production, which appears to be better estimated (450 ± 125 g/d) by multiplying a measured daily milk yield by infrared-predicted methane intensity. Lactation modeling of methane traits showed daily methane production to have a zenith curve, similar to that of milk yield but with a delayed peak (53 vs. 37 d in milk), whereas methane intensity is characterized by an upward curve that increases rapidly during the first third of lactation and then slowly till the end of lactation (10.5 g/kg at 1 d in milk to 15.2 g/kg at 300 d in milk). However, lactation modeling was not useful in explaining methane yield, which is almost constant during lactation. Lastly, the methane yield and intensity of cows from 3-breed rotational crossbreeding are not greater, and their methane production is lower than that of purebred Holsteins (452 vs. 477 g/d). Given the greater longevity of crossbred cows, and their lower replacement rate, rotational crossbreeding could be a way of mitigating the environmental impact of milk production.

Impact of Inbreeding and Ancestral Inbreeding on Longevity Traits in German Brown Cows

A recent study on the population structure of the German Brown population found increasing levels of classical and ancestral inbreeding coefficients. Thus, the aim of this study was to determine the effects of inbreeding depression and purging on longevity traits using classical and ancestral inbreeding coefficients according to Kalinowski (2002) (Fa_Kal, FNew), Ballou (1997) (Fa_Bal), and Baumung (2015) (Ahc). For this purpose, uncensored data of 480,440 cows born between 1990 and 2001 were available. We analyzed 17 longevity traits, including herd life, length of productive life, number of calvings, lifetime and effective lifetime production for milk, fat, and protein yield, the survival to the 2nd, 4th, 6th, 8th, and 10th lactation number, and the culling frequencies due to infertility, or udder and foot and leg problems. Inbreeding depression was significant and negative for all traits but for culling due to udder and to foot and leg problems. When expressed in percentages of genetic standard deviations, inbreeding depression per 1% increase in inbreeding was -3.61 to -10.98%, -2.42 to -2.99%, -2.21 to -4.58%, and 5.13% for lifetime production traits, lifetime traits, survival rates, and culling due to infertility, respectively. Heterosis and recombination effects due to US Brown Swiss genes were positive and counteracted inbreeding depression. The effects of FNew were not significantly different from zero, while Fa_Kal had negative effects on lifetime and lifetime production traits. Similarly, the interaction of F with Fa_Bal was significantly negative. Thus, purging effects could not be shown for longevity traits in German Brown. A possible explanation may be seen in the breed history of the German Brown, that through the introgression of US Brown Swiss bulls ancestral inbreeding increased and longevity decreased. Our results show, that reducing a further increase in inbreeding in mating plans is advisable to prevent a further decline in longevity due to inbreeding depression, as purging effects were very unlikely in this population.

Multibreed genomic prediction using summary statistics and a breed-origin-of-alleles approach

Because of an increasing interest in crossbreeding between dairy breeds in dairy cattle herds, farmers are requesting breeding values for crossbred animals. However, genomically enhanced breeding values are difficult to predict in crossbred populations because the genetic make-up of crossbred individuals is unlikely to follow the same pattern as for purebreds. Furthermore, sharing genotype and phenotype information between breed populations are not always possible, which means that genetic merit (GM) for crossbred animals may be predicted without the information needed from some pure breeds, resulting in low prediction accuracy. This simulation study investigated the consequences of using summary statistics from single-breed genomic predictions for some or all pure breeds in two- and three-breed rotational crosses, rather than their raw data. A genomic prediction model taking into account the breed-origin of alleles (BOA) was considered. Because of a high genomic correlation between the breeds simulated (0.62-0.87), the prediction accuracies using the BOA approach were similar to a joint model, assuming homogeneous SNP effects for these breeds. Having a reference population with summary statistics available from all pure breeds and full phenotype and genotype information from crossbreds yielded almost as high prediction accuracies (0.720-0.768) as having a reference population with full information from all pure breeds and crossbreds (0.753-0.789). Lacking information from the pure breeds yielded much lower prediction accuracies (0.590-0.676). Furthermore, including crossbred animals in a combined reference population also benefitted prediction accuracies in the purebred animals, especially for the smallest breed population.

Genetic analysis of longevity and their associations with fertility traits in Holstein cattle

The increase of longevity is intended to reduce involuntary culling rates, not extend the life span, and it reflects the ability of animals to successfully cope with the environment and disease during production. Sire model, animal model and repeatability animal models were used to estimate the (co) variance components of longevity and fertility traits. Six longevity and thirteen fertility traits were analysed, including herd life (HL), productive life (PL), number of days between first calving and the end of first lactation or culling (L1); number of days between first calving and the end of the second lactation or culling (L2); number of days between first calving and the end of the third lactation or culling (L3); number of days between first calving and the end of the fourth lactation or culling (L4); age at first service, age at first calving (AFC), the interval from first to last inseminations in heifer (IFLh), conception rate of first insemination in heifer, days open (DO), calving interval, gestation length, interval from calving to first insemination (ICF), interval from first to last inseminations in cow (IFLc), conception rate of first insemination in cow, calving ease (CE), birth weight, and calf survival. The estimated heritabilities (±SE) were 0.018 (±0.003), 0.015 (±0.003), 0.049 (±0.004), 0.025 (±0.003), 0.009 (±0.002) and 0.011 (±0.002) for HL, PL, L1, L2, L3 and L4, respectively. Strong correlations were appeared in HL and PL; the genetic and phenotypic correlation coefficients were 0.998 and 0.985, respectively. There were high genetic and phenotypic correlations which were observed in L1 and L2, L2 and L3, L3 and L4, respectively. All fertility traits of heifer showed medium to high heritability, while the cow showed low heritability. All heifer fertility traits had low genetic associations with longevity traits, ranging from -0.018 (L2 and IFLh) to 0.257 (L3 and AFC). Most of the fertility traits showed negative correlations with longevity traits in different parities, and we recommend DO, ICF, IFLc and CE as indirect indicators of longevity traits in dairy cows, but we also need to take into account the differences between parities.

Genetic Parameters for a Weighted Analysis of Survivability in Dairy Cattle

The genetic parameters for the survival of Holstein cows, analysed in nine consecutive time periods during the first three calving intervals, were estimated. The earlier the animals are culled, the more they are informationally underestimated. This undervaluing can be remedied by using a weighted analysis that balances the amount of information. If the method of estimating breeding values changes, the genetic parameters will also change. The Holstein cattle dataset from 2005 to 2017 used in this study included 1,813,636 survival records from 298,290 cows. The pedigree with three generations of ancestors included 660,476 individuals. Linear repeatability models estimated genetic parameters for overall and functional survivability. Due to weights, heritability increased from 0.013 to 0.057. Repeatability with weights was 0.505. The standard deviations of breeding values were 1.75 and 2.18 without weights and 6.04 and 6.20 with weights. Including weights in the calculation increased the additive variance proportion and the breeding values’ reliabilities. We conclude that the main contribution of the weighted method we have presented is to compensate for the lack of records in culled individuals with a positive impact on the reliability of the breeding value.

Loci Associated with Negative Heterosis for Viability and Meat Productivity in Interspecific Sheep Hybrids

Negative heterosis can occur on different economically important traits, but the exact biological mechanisms of this phenomenon are still unknown. The present study focuses on determining the genetic factors associated with negative heterosis in interspecific hybrids between domestic sheep (Ovis aries) and argali (Ovis ammon). One locus (rs417431015) associated with viability and two loci (rs413302370, rs402808951) associated with meat productivity were identified. One gene (ARAP2) was prioritized for viability and three for meat productivity (PDE2A, ARAP1, and PCDH15). The loci associated with meat productivity were demonstrated to fit the overdominant inheritance model and could potentially be involved int negative heterosis mechanisms.

Effects of transport age and calf and maternal characteristics on health and performance of veal calves

The objective of this study was to investigate effects of calf transport age (14 vs. 28 d) and calf (e.g., sex and breed) and dam characteristics (e.g., parity and ease of birth) on health and performance of veal calves until slaughter age. Calves (n = 683) originated from 13 dairy farms in the Netherlands and were transported at either 14 or 28 d of age from the dairy farm to 8 Dutch veal farms. A health assessment of calves was performed on a weekly basis at the dairy farm and in wk 2, 10, 18, and 24 at the veal farm. Body weight of calves was measured on a weekly basis at the dairy farm and upon arrival at the veal farm. At the veal farm, use of antibiotics and other medicines during the rearing period (both at herd and individual level) was recorded and carcass weights were obtained from the slaughterhouse. Body weight upon arrival (Δ = 11.8 kg) and carcass weight at slaughter (Δ = 14.8 kg) were greater, and mortality risk (Δ = -3.1%) and prevalence of animals treated with medicines other than antibiotics (e.g., antiinflammatories, multivitamins, and anticoccidial drugs; Δ = -5.4%) were lower in calves transported at 28 d compared with calves transported at 14 d. Crossbreds other than Belgian Blue × Holstein Friesian received a higher number of individual treatments with antibiotics and other medicines (Δ = 14.8% and Δ = 15.1%, respectively) at the veal farm compared with Belgian Blue × Holstein Friesian calves. These findings suggest that calves transported at 28 d were more robust compared with calves transported at 14 d.

Transcriptome-Wide Analyses Identify Dominant as the Predominantly Non-Conservative Alternative Splicing Inheritance Patterns in F1 Chickens

Transcriptome analysis has been used to investigate many economically traits in chickens; however, alternative splicing still lacks a systematic method of study that is able to promote proteome diversity, and fine-tune expression dynamics. Hybridization has been widely utilized in chicken breeding due to the resulting heterosis, but the dynamic changes in alternative splicing during this process are significant yet unclear. In this study, we performed a reciprocal crossing experiment involving the White Leghorn and Cornish Game chicken breeds which exhibit major differences in body size and reproductive traits, and conducted RNA sequencing of the brain, muscle, and liver tissues to identify the inheritance patterns. A total of 40 515 and 42 612 events were respectively detected in the brain and muscle tissues, with 39 843 observed in the liver; 2807, 4242, and 4538 events significantly different between two breeds were identified in the brain, muscle, and liver tissues, respectively. The hierarchical cluster of tissues from different tissues from all crosses, based on the alternative splicing profiles, suggests high tissue and strain specificity. Furthermore, a comparison between parental strains and hybrid crosses indicated that over one third of alternative splicing genes showed conserved patterns in all three tissues, while the second prevalent pattern was non-additive, which included both dominant and transgressive patterns; this meant that the dominant pattern plays a more important role than suppression. Our study provides an overview of the inheritance patterns of alternative splicing in layer and broiler chickens, to better understand post-transcriptional regulation during hybridization.

Analysis of Longevity Traits in Holstein Cattle: A Review

Dairy cow longevity is an essential economic trait that can supplement the breeding value of production traits, which is related to the herd time and lifetime milk yield of dairy cows. However, longevity is a relatively difficult trait to select for dairy cow breeding due to low heritability and numerous influence factors of the longevity in dairy cows. Longevity trait has been used as an important breeding target of a comprehensive selection index in many dairy developed countries; however, it has not been included in performance index in many developing countries. At present, cows in these countries are still in the primary stage of “large quantity, low quality, high cost, and low yield.” The average parity of dairy cows is less than 2.7, which is difficult to maintain the production efficiency to meet the demands of the dairy industry. Therefore, there is an urgent need to select and breed for the longevity of dairy cows. The various definitions and models (including linear, threshold, random regression, sire, and survival analysis) of longevity were reviewed and standardized. Survival analysis is the optimal model to evaluate longevity, and the longevity heritability is 0.01–0.30 by using different definitions and models. Additionally, the relationship between longevity and other traits was summarized, and found that longevity was regulated by multiple factors, and there were low or medium genetic correlations between them. Conformation traits, milk production traits, reproductive traits, and health traits may be used as indicators to select and breed the longevity of dairy cows. The genetic assessment methods, heritability, influencing factors, importance, breeding, and genetics of longevity were reviewed in the manuscript, which could provide a valuable reference for the selective breeding to extend the productive life of Holstein cattle.

Genetic basis of negative heterosis for growth traits in chickens revealed by genome-wide gene expression pattern analysis

Background

Heterosis is an important biological phenomenon that has been extensively utilized in agricultural breeding. However, negative heterosis is also pervasively observed in nature, which can cause unfavorable impacts on production performance. Compared with systematic studies of positive heterosis, the phenomenon of negative heterosis has been largely ignored in genetic studies and breeding programs, and the genetic mechanism of this phenomenon has not been thoroughly elucidated to date. Here, we used chickens, the most common agricultural animals worldwide, to determine the genetic and molecular mechanisms of negative heterosis.

Results

We performed reciprocal crossing experiments with two distinct chicken lines and found that the body weight presented widely negative heterosis in the early growth of chickens. Negative heterosis of carcass traits was more common than positive heterosis, especially breast muscle mass, which was over − 40% in reciprocal progenies. Genome-wide gene expression pattern analyses of breast muscle tissues revealed that nonadditivity, including dominance and overdominace, was the major gene inheritance pattern. Nonadditive genes, including a substantial number of genes encoding ATPase and NADH dehydrogenase, accounted for more than 68% of differentially expressed genes in reciprocal crosses (4257 of 5587 and 3617 of 5243, respectively). Moreover, nonadditive genes were significantly associated with the biological process of oxidative phosphorylation, which is the major metabolic pathway for energy release and animal growth and development. The detection of ATP content and ATPase activity for purebred and crossbred progenies further confirmed that chickens with lower muscle yield had lower ATP concentrations but higher hydrolysis activity, which supported the important role of oxidative phosphorylation in negative heterosis for growth traits in chickens.

Conclusions

These findings revealed that nonadditive genes and their related oxidative phosphorylation were the major genetic and molecular factors in the negative heterosis of growth in chickens, which would be beneficial to future breeding strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00574-2.

Genetic Parameters and Genome-Wide Association Studies of Eight Longevity Traits Representing Either Full or Partial Lifespan in Chinese Holsteins

Due to the complexity of longevity trait in dairy cattle, two groups of trait definitions are widely used to measure longevity, either covering the full lifespan or representing only a part of it to achieve an early selection. Usually, only one group of longevity definition is used in breeding program for one population, and genetic studies on the comparisons of two groups of trait definitions are scarce. Based on the data of eight traits well representing the both groups of trait definitions, the current study investigated genetic parameters and genetic architectures of longevity in Holsteins. Heritabilities and correlations of eight longevity traits were estimated using single-trait and multi-trait animal models, with the data from 103,479 cows. Among the cows with phenotypes, 2,630 cows were genotyped with the 150K-SNP panel. A single-trait fixed and random Circuitous Probability Unification model was performed to detect candidate genes for eight longevity traits. Generally, all eight longevity traits had low heritabilities, ranging from 0.038 for total productive life and herd life to 0.090 for days from the first calving to the end of first lactation or culling. High genetic correlations were observed among the traits within the same definition group: from 0.946 to 0.997 for three traits reflecting full lifespan and from 0.666 to 0.997 for five traits reflecting partial productive life. Genetic correlations between two groups of traits ranged from 0.648 to 0.963, and increased gradually with the extension of lactations number regarding the partial productive life traits. A total of 55 SNPs located on 25 chromosomes were found genome-wide significantly associated with longevity, in which 12 SNPs were associated with more than one trait, even across traits of different definition groups. This is the first study to investigate the genetic architecture of longevity representing both full and the partial lifespan simultaneously, which will assist the selection of an appropriate trait definition for genetic improvement of longevity. Because of high genetic correlations with the full lifespan traits and higher heritability, the partial productive life trait measured as the days from the first calving to the end of the third lactation or culling could be a good alternative for early selection on longevity. The candidate genes identified by this study, such as RPRM, GRIA3, GTF2H5, CA5A, CACNA2D1, FGF10, and DNAJA3, could be used to pinpoint causative mutations for longevity and further benefit the genomic improvement of longevity in dairy cattle.

Herd life, lifetime production, and profitability of Viking Red-sired and Montbéliarde-sired crossbred cows compared with their Holstein herdmates

The first 2 generations from a 3-breed rotation of the Viking Red (VR), Montbéliarde (MO), and Holstein (HO) breeds were compared with their HO herdmates in high-performance commercial herds in Minnesota. The designed study enrolled pure HO females in 2008 to initiate a comparison of 3-breed rotational crossbreds with their HO herdmates. Sires of cows were proven artificial insemination bulls selected for high genetic merit in each of the 3 breeds. The first-generation cows calved for a first time from 2010 to 2014 and had 376 VR × HO and 358 MO × HO crossbreds to compare with their 640 HO herdmates. The second-generation cows calved for a first time from 2012 to 2014 and had 109 VR × MO/HO and 117 MO × VR/HO crossbreds to compare with their 250 HO herdmates. Collection of data ceased on December 31, 2017, and all cows studied had the opportunity for 45 mo in the herd after first calving. Production of milk, fat, and protein (kg) during lifetimes of cows was estimated from test-day observations with best prediction. The lifetime profit function included revenue and cost. Revenue was from production, calves, and slaughter of cull cows. Costs included feed cost during lactation, lactating overhead cost, dry cow cost (including feed cost during dry periods), replacement cost, health treatment cost, insemination cost, fertility hormone cost, pregnancy diagnosis cost, hoof trimming cost, and carcass disposal cost. For individual cows with herd life longer than 45 mo after first calving, survival of cows was projected beyond 45 mo after first calving to estimate herd life, production, and profitability. The 2-breed crossbreds had +158 d longer herd life and the 3-breed crossbreds had +147 d longer herd life compared with their respective HO herdmates. Also, 12.4% of the 2-breed crossbreds died up to 45 mo after first calving compared with 16.3% of their HO herdmates. Furthermore, approximately 29% of both the 2-breed and 3-breed crossbreds lived beyond 45 mo after first calving compared with approximately 18% of their respective HO herdmates. On a lifetime basis, the 2-breed and 3-breed crossbreds provided +$122 and +$134, respectively, more cull cow revenue compared with their HO herdmates. For lifetime replacement cost, the 2-breed crossbreds did not differ from their HO herdmates; however, the 3-breed crossbreds had -$28 less lifetime replacement cost compared with their HO herdmates because of their younger age at first calving. The combined 2-breed crossbreds had +$0.473 (+13%) more daily profit (ignoring potential differences for feed efficiency) and the combined 3-breed crossbreds had +$0.342 (+9%) more daily profit compared with their respective HO herdmates. This resulted in +$173 more profit/cow annually for the combined 2-breed crossbreds and +$125 more profit/cow annually for the combined 3-breed crossbreds compared with their respective HO herdmates.

Using Random Regression Models to Genetically Evaluate Functional Longevity Traits in North American Angus Cattle

Simple Summary

Cattle longevity is usually defined as the duration of life of a cow from first calving to death. In addition to a longer lifespan, it is crucial that cows are productive throughout their lives. Incorporating optimal indicators of productive longevity in breeding schemes will directly improve the economic profitability of the beef cattle herd and long-term sustainability of the industry. Thus, the impact of different longevity indicators in the selection of North American Angus cattle was evaluated and optimal parameters were defined to perform the evaluations.

Abstract

This study aimed to propose novel longevity indicators by comparing genetic parameters for traditional (TL; i.e., the cow’s lifespan after the first calving) and functional (FL; i.e., how long the cow stayed in the herd while also calving; assuming no missing (FLa) or missing (FLb) records for unknown calving) longevity, considering different culling reasons (natural death, structural problems, disease, fertility, performance, and miscellaneous). Longevity definitions were evaluated from 2 to 15 years of age, using single- and multiple-trait Bayesian random regression models (RRM). The RRM fitting heterogenous residual variance and fourth order Legendre polynomials were considered as the optimal models for the majority of longevity indicators. The average heritability estimates over ages for FLb (from 0.08 to 0.25) were always higher than those for FLa (from 0.07 to 0.19), and higher or equal to the ones estimated for TL (from 0.07 to 0.23), considering the different culling reasons. The average genetic correlations estimated between ages were low to moderate (~0.40), for all longevity definitions and culling reasons. However, removing the extreme ages (i.e., 2 and >12 years) increased the average correlation between ages (from ~0.40 to >0.70). The genetic correlations estimated between culling reasons were low (0.12 and 0.20 on average, considering all ages and ages between 3 and 12 years old, respectively), indicating that longevity based on different culling reasons should be considered as different traits in the genetic evaluations. Higher average genetic correlations (estimated from 3 to 12 years old) were observed between TL and FLb (0.73) in comparison to TL and FLa (0.64), or FLa and FLb (0.65). Consequently, a higher average proportion of commonly-selected sires, for the top 1% sires, was also observed between TL and FLb (91.74%), compared to TL and FLa (59.68%), or FLa and FLb (61.01%). Higher prediction accuracies for the expected daughter performances (calculated based on the pedigree information) were obtained for FLb in comparison to TL and FLa. Our findings indicate that FLb is preferred for the genetic evaluation of longevity. In addition, it is recommended including multiple longevity traits based on different groups of culling reasons in a selection sub-index, as they are genetically-different traits. Genetic selection based on breeding values at the age of four years is expected to result in greater selection responses for increased longevity in North American Angus cattle.

Genetic analysis of functional longevity in a complete diallel crossing experiment involving four maternal rabbit lines

In a diallel cross between four maternal lines of rabbits, the four maternal lines and the corresponding crossbred females (does) were evaluated concerning functional longevity, estimating their crossbreeding components. Sixteen genetic groups were produced by using four maternal lines of rabbit (A, V, H and LP (L)). The groups were distributed over 4 Spanish farms. In all farms, the V line was present as the reference group. A total of 7,211 does' longevity records were recorded. Using a Cox proportional hazard model of fixed effects, survival analysis was performed to study longevity analysing the hazard of death or culling. Does from lines A, H and V had similar risks of death or of being culled, and they were more susceptible compared with those from line L. The lowest hazard was associated with L line does. No significant differences were found between the average of all crosses and the V line except when comparing the V line to the cross between A and H lines, favouring the former (1.30 higher risk of replacement for AH animals). Significant differences between reciprocal crosses were observed between VH and HV, in favour of HV (0.72 of relative risk of replacement) and between LH and HL, in favour of HL (0.76 of relative risk). Line V had the highest risk due to the direct genetic effects, and these differences were significant with the lines H (1.40 of relative risk) and L (1.43 of relative risk). The differences in maternal genetic effects were small and not significant except between lines H and V in favour of V line (0.75 of relative risk). The estimated direct heterosis effects do not always follow the same trend but they showed the importance of the crossing between specialized lines to produce crossbred does for intensive meat rabbit production.

Pure-breeding with sexed semen and crossbreeding with semen of double-muscled sires to improve beef production from dairy herds: Factors affecting heifer and cow fertility and the sex ratio

Using sexed semen to produce purebred replacement heifers makes it possible to mate a large proportion of dairy cows to double-muscled sires and to quantitatively and qualitatively improve beef production and increase the income from dairy herds. Net profit first depends on changes in the farm's overall fertility rate. The objective of this study was to analyze the conception rate in herds using a combination of conventional dairy semen (for pure- and crossbreeding), X-sorted dairy semen (to produce purebred replacement heifers), and conventional beef semen (for terminal crossbreeding). Data were obtained from 50,785 inseminations of 15,580 dairy cows (78% Holstein-Friesian, 15% Brown Swiss, 2% Simmental, and 5% crossbreds) from 106 dairy farms (average milk yield 35.1 ± 9.4 kg/d, with 3.76 ± 0.83% fat and 3.32 ± 0.39% protein contents). To account for the main potential confounders, we used separate generalized linear mixed-effects models for cows and virgin heifers. The results showed that the odds ratio of conception improved (1.00 to 1.34) with an increase in the average milk yield of the herd but worsened (1.12 to 0.70) with an increase in the milk yield of individual cows within herd. The summer months showed a strong reduction in the odds ratio of conception in cows (0.56 in July and August) but not in virgin heifers. Multiparous cows had a lower odds ratio of conception (0.85) than primiparous cows (1.00). The order of insemination did not affect the fertility of the cows or heifers, whereas the odds ratio of conception improved with advancing lactation (1.00 to 2.12). The Simmental cows were more fertile than Holstein-Friesians (1.37 vs. 1.00), whereas the fertility of the heifers was not affected by breed. Taking all these possible confounders into account simultaneously, in pure-breeding the odds ratio of conception using sexed semen did not differ from that using conventional dairy semen in cows (0.90 vs. 1.00) or in virgin heifers (0.95 vs. 1.00). However, crossbreeding using conventional beef and dairy semen improved the odds ratio of conception (1.10 and 1.17, respectively) in cows (1.37 using beef semen) and heifers (1.25 using dairy semen). The proportion of newborn heifer calves was ≥90% using sexed dairy semen. The combined use of sexed semen, especially on heifers, to produce purebred replacement females and beef semen to produce terminal crossbred calves was shown to have the potential to increase overall herd fertility, which could be further improved using sexed dairy semen to produce dairy crossbreds instead of purebred replacement heifers.

Genomic retained heterosis effects on fertility and lifetime productivity in beef heifers

This study evaluated the effects of three genomic indicators of heterosis on female fertility and lifetime productivity, and quantified changes over 11 production cycles in a crossbred cow herd. Pedigree-based breed composition (pBC) was determined and used to calculate retained heterozygosity for 412 replacement heifers born from 2004 to 2014 at the Lacombe Research and Development Centre (AB, Canada). Heifers were followed as cows over 1050 mating opportunities, 11 production cycles, and five parities. Heifers and their sires (51) were genotyped and these genotypes were used to predict each animal’s genomic breed composition (gBC) and three genomic indicators of heterosis: (1) retained heterozygosity (RHETg), (2) heterozygous proportion (H), and (3) retained heterosis (RHg). Correlations between pedigree and genomic breed fractions for Angus, Hereford, and Charolais were high (rp = 0.74–0.94; P < 0.001). Genomic indicators of heterosis were highly related (rp = 0.61 for RHETg vs. H; 0.71 for RHg vs. H; 0.96 for RHETg vs. RHg; P < 0.001). Each 10% change in RHETg resulted in 51 ± 20 d longer survival (P = 0.011) in the herd and 35.7 ± 15.2 kg more (P = 0.019) calf wean weight per cow exposed to breeding when summed over five parities. These differences resulted in an extra $161 per heifer in a year. Optimizing heterosis using genomic tools can be very beneficial for the cow herd if applied correctly.

Differences between performance of F1 crossbreds and Holsteins at different production levels

Crossbreeding in dairy cattle has recently become of increased interest. However, farmers in Scandinavian countries are reluctant to implement crossbreeding in their herds, and one reason is the common opinion that only herds at a poor level of management can benefit from crossbreeding. The Danish Cattle Database (SEGES, Aarhus, Denmark) provided data on 14 traits regarding milk yield, udder health, fertility traits, stillbirth, and survival. The data were collected from 103,307 pure Holstein cows and 14,832 F₁ crosses (Holstein dam and Nordic Red sire). The cows were born between 2008 and 2014 and originated from 424 herds that contributed data from at least 5 purebreds and 5 crossbreds across the years. We split the animals into 3 production levels: high, average, and low according to the herd's average production (kg) of 305-d fat plus protein in the given birth year of the cow. We estimated least squares means of breed group (purebred and crossbred) performance within each production level. Crossbred performance in 305-d fat yield in first-parity cows was greater than that of Holstein across all herd production levels; the gain was greater in high- (9 kg more than Holstein) and average-producing herds (7 kg more than Holstein) than in low-producing herds (3 kg more than Holstein). Regardless of production level or parity, crossbreds did not outperform Holstein in terms of 305-d protein yield (0 to 8 kg less). Crossbreds had relatively better udder health than Holstein in both first and second parity (up to 15% less mastitis) within any of the production levels. In terms of fertility, stillbirth, and survival, crossbreds performed better than purebreds, and improved performance was independent of herd production level. We conclude that differences in performance between F₁ crossbreds and Holstein are independent of production level.