Short communication: Heterosis and breed effects for milk production and udder health traits in crosses between Danish Holstein, Danish Red, and Danish Jersey.

During the last decade, the use of systematic crossbreeding in dairy cattle herds has increased in several countries of the world. The aim of this study was to estimate the effect of breed proportion and heterosis on milk production traits and udder health traits in dairy cattle. The study was based on records on milk yield (MY), protein yield (PY), fat yield (FY), somatic cell score (SCS), and mastitis (MAST) from 73,695 first-lactation dairy cows in 130 Danish herds applying systematic crossbreeding programs. Around 45% of the cows were crosses between Danish Holstein (DH), Danish Red (DR), or Danish Jersey (DJ), and the remaining were purebred DH, DR, or DJ. The statistical model included the fixed effects of herd-year, calving month, and calving age and an effect representing the lactation status of the cow. In addition, the model included a regression on calving interval from first to second lactation, a regression on the proportion of DH, DR, and DJ genes, and a regression on the degree of heterozygosity between DH and DR, DH and DJ, and DR and DJ. Random effects were the genetic effect of the cow and a residual. The effect of breed proportions was estimated relatively to DH. For MY, a pure DR yielded 461 kg milk less than DH, whereas a pure DJ yielded 2,259 kg milk less than a pure DH. Compared with DH, PY was 41.7 kg less for DJ, whereas PY for DR was 4.0 kg less than for DH. For FY, a DR yielded 10.6 kg less than DH, whereas there was no significant effect of breed proportion between DJ and DH. A DR cow had lower SCS (0.13) than DH, whereas DJ had higher SCS (0.14) than DH. There was no significant effect of breed proportion on MAST between the 3 breeds. Heterosis was significant in all combinations of breeds for MY, FY, and PY. Heterosis for crosses between DH and DR was 257 kg (3.2%), 11.9 kg (3.2%), and 8.9 kg (3.2%) for MY, PY, and FY, respectively. Corresponding figures for crosses between DH and DJ were 314 kg (4.4%), 14.3 kg (4.4%), and 10.4 kg (4.0%), whereas heterosis between DR and DJ was 462 kg (6.7%), 19.6 kg (6.7%), and 13.9 kg (5.4%) for MY, PY, and FY, respectively. Heterosis was only significant for SCS in the crosses between DH and DR. Heterosis effects for MAST were nonsignificant for all the crosses. The results obtained in this study demonstrate that in first lactation cows, there is a positive effect of heterosis on milk production traits, but limited effect on udder health traits.

Genetic parameters for handling and milking temperament in Danish first-parity Holstein cows.

The human-animal relationship in dairy cattle is reflected in the trait "temperament" in breeding programs and is mainly based on observations by farmers. However, farmers' knowledge of an individual cow's temperament decreases with an increased herd size, and this has been the case in many countries during the last decades. The aim of this study was to investigate if temperament recorded by classifiers and automatic milking systems is heritable, and estimate the genetic relationship with farmer-assessed temperament. Farmer-assessed temperament is defined as the overall assessment of the individual cows' temperament at milking and handling. Data on handling temperament were recorded by Danish classifiers from October 2016 to April 2017 on a 1 to 9 scale specially designed for this purpose. Data from automatic milking systems were recorded from January 2010 until April 2017, where connection time and number of attachments per teat were classified as milking temperament traits. Estimated heritabilities were relatively low for handling temperament (0.13) and farmer-assessed temperament (0.10). For milking temperament traits, connection time showed higher heritability than number of attachments per teat (0.36 and 0.26, respectively). The genetic correlation between farmer-assessed temperament and handling temperament was highly favorable (0.84). The genetic correlations between handling temperament and the 2 milking temperament traits, connection time and number of attachments per teat, were low (-0.02 and -0.10, respectively). Moderate genetic correlations were estimated between farmer-assessed temperament and connection time (-0.29) and between farmer-assessed temperament and number of attachments per teat (-0.37). The genetic correlations and heritabilities suggest a basis for further investigations of the possibility of including handling or milking temperament traits (or both) in the breeding program for temperament in dairy cattle.

Genetic correlations between methane production and fertility, health, and body type traits in Danish Holstein cows.

Our aim was to investigate the genetic correlations between CH4 production and body conformation, fertility, and health traits in dairy cows. Data were collected from 10 commercial Holstein herds in Denmark, including 5,758 cows with records for body conformation traits, 7,390 for fertility traits, 7,439 for health traits, and 1,397 with individual CH4 measurements. Methane production was measured during milking in automatic milking systems, using a sniffer approach. Correlations between CH4 and several different traits were estimated. These traits were interval between calving and first insemination, interval between first and last insemination, number of inseminations, udder diseases, other diseases, height, body depth, chest width, dairy character, top line, and body condition score. Bivariate linear models were used to estimate the genetic parameters within and between CH4 and the other traits. In general, the genetic correlations between CH4 and the traits investigated were low. The heritability of CH4 was 0.25, and ranged from 0.02 to 0.07 for fertility and health traits, and from 0.17 to 0.74 for body conformation traits. Further research with a larger data set should be performed to more accurately establish how CH4 relates to fertility, health, and body conformation traits in dairy cattle. This will be useful in the design of future breeding goals that consider the production of CH4.

Is rumination time an indicator of methane production in dairy cows?

As long as large-scale recording of expensive-to-measure and labor-consuming traits, such as dry matter intake (DMI) and CH4 production (CH4P), continues to be challenging in practical conditions, alternative traits that are already routinely recorded in dairy herds should be investigated. An ideal indicator trait must, in addition to expressing genetic variation, have a strong correlation with the trait of interest. Our aim was to estimate individual level and phenotypic correlations between rumination time (RT), CH4P, and DMI to determine if RT could be used as an indicator trait for CH4P and DMI. Data from 343 Danish Holstein cows were collected at the Danish Cattle Research Centre for a period of approximately 3 yr. The data set consisted of 14,890 records for DMI, 15,835 for RT, and 6,693 for CH4P. Data were divided in primiparous cows only (PC) and all cows (MC), and then divided in lactation stage (early, mid, late, and whole lactation) to analyze the changes over lactation. Linear mixed models, including an animal effect but no pedigree, were used to estimate the correlations among traits. Phenotypic and individual level correlations between RT and both CH4P and DMI were close to zero, regardless of lactation stage and data set (PC or MC). However, CH4P and DMI were highly correlated, both across lactation stages and data sets. In conclusion, RT is unsuitable to be used as an indicator trait for either CH4P or DMI. Our study failed to validate RT as a useful indicator trait for both CH4P and DMI, but more studies with novel phenotypes can offer different approaches to select and incorporate important yet difficult to record traits into breeding goals and selection indexes.

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

Crossbreeding has been shown to improve the longevity of dairy cattle in countries across the world. The aim of this study was to estimate heterosis, breed effects, and genetic parameters for longevity in crossbred dairy cattle among Danish Holstein (DH), Danish Red (DR), and Danish Jersey (DJ) breeds. Data were provided from 119 Danish commercial herds that use systematic crossbreeding (i.e., rotational crossbreeding). Additional data from 11 mixed-breed herds with DH and DJ were included to estimate reliable breed effects for DJ. Survival information on 73,741 cows was analyzed with a linear animal model using the artificial insemination-REML algorithm in the DMU package. Five longevity (L) traits were defined: days from first calving until the end of first lactation or culling (L1), days from first calving until the end of second lactation or culling (L2), days from first calving until the end of third lactation or culling (L3), days from first calving until the end of fourth lactation or culling (L4), and days from first calving until the end of fifth lactation or culling (L5). Heritabilities ranged between 0.022 and 0.090. Additive breed effects in units of days were estimated relative to DH for DR as -0.5 (L1), +10.5 (L2), +18.5 (L3), +11.9 (L4), and +28.6 (L5), and corresponding figures for DJ were +2.0, +0.5, +14.2, +27.7, and +44.0. Heterosis effects in L1 were low (1.2%) but favorable in crosses between DH and DR, whereas negative heterosis effects were estimated for crosses between DH and DJ (-2.5%) and DR and DJ (-1.2%). The largest heterosis effects for L2, L3, L4, and L5 were found in DH × DR and were favorable (+3.3, +5.7, +7.7, and +8.5%, respectively). Corresponding figures for heterosis effects in DH × DJ and DR × DJ were favorable as well: +2.3, +4.1, +5.6, and +6.2% in DH × DJ and +3.1, +7.3, +6.9, and +7.2% in DR × DJ. The favorable heterosis effects show that crossbreeding is an efficient tool for improving longevity in Danish dairy cattle.

Genetic correlations between dressage, show jumping and studbook-entry inspection traits in a process of specialization in Dutch Warmblood horses.

Sport performance in dressage and show jumping are two important traits in the breeding goals of many studbooks. To determine the optimum selection scheme for jumping and dressage, knowledge is needed on the genetic correlation between both disciplines and between traits measured early in life and performance in competition in each discipline. This study aimed to estimate genetic parameters to support decision-making on specialization of breeding horses for dressage and show jumping in Dutch warmblood horses. Genetic correlations between performance of horses in dressage and show jumping were estimated as well as the genetic correlation between traits recorded during studbook-entry inspections and performance in dressage and show jumping competitions. The information on competition comprised the performance of 82 694 horses in dressage and 62 072 horses in show jumping, recorded in the period 1993-2012. For 26 056 horses, information was available for both disciplines. The information on traits recorded at studbook-entry inspections comprised 62 628 horses, recorded in the period 1992-2013. Genetic parameters were estimated from the whole dataset and from a subset without horses recorded in both disciplines. Additionally, the genetic parameters were estimated in three different time periods defined by horses' birth year. The genetic correlation between dressage and show jumping in the whole dataset was -0.23, and it was -0.03 when it was estimated from horses recorded in only one discipline. The genetic correlation between dressage and show jumping was more negative in the most recent time period in all the cases. The more negative correlation between disciplines in more recent time periods was not reflected in changes in the correlations between competitions traits and the traits recorded in the studbook-first inspection. These results suggest that a breeding programme under specialization might be most effective defining two separate aggregate breeding goals for each of the disciplines.

Genetic association between leg conformation in young pigs and sow longevity.

Longevity is important in pig production with respect to both economic and ethical aspects. Direct selection for longevity might be ineffective because 'true' longevity can only be recorded when a sow has been culled or died. Thus, indirect selection for longevity using information from other traits that can be recorded early in life and are genetically correlated with longevity might be an alternative. Leg conformation has been included in many breeding schemes for a number of years. However, proving that leg conformation traits are good early indicators for longevity still remains. Our aim was to study genetic associations between leg conformation traits of young (5 months; 100 kg) Swedish Yorkshire pigs in nucleus herds and longevity traits of sows in nucleus and multiplier herds. Data included 97 533 animals with information on conformation (Movement and Overall score) recorded at performance testing and 26 962 sows with information on longevity. The longevity traits were as follows: stayability from 1st to 2nd parity, lifetime number of litters and lifetime number of born alive piglets. Genetic analyses were performed with both linear models using REML and linear-threshold models using Bayesian methods. Heritabilities estimated using the Bayesian method were higher than those estimated using REML, ranging from 0.10 to 0.24 and 0.07 to 0.20, respectively. All estimated genetic correlations between conformation and longevity traits were significant and favourable. Heritabilities and genetic correlations between conformation and longevity indicate that selection on leg conformation should improve sow longevity.

Analysis of competition performance in dressage and show jumping of Dutch Warmblood horses.

Most Warmblood horse studbooks aim to improve the performance in dressage and show jumping. The Dutch Royal Warmblood Studbook (KWPN) includes the highest score achieved in competition by a horse to evaluate its genetic ability of performance. However, the records collected during competition are associated with some aspects that might affect the quality of the genetic evaluation based on these records. These aspects include the influence of rider, censoring and preselection of the data. The aim of this study was to quantify the impact of rider effect, censoring and preselection on the genetic analysis of competition data of dressage and show jumping of KWPN. Different models including rider effect were evaluated. To assess the impact of censoring, genetic parameters were estimated in data sets that differed in the degree of censoring. The effect of preselection on variance components was analysed by defining a binary trait (sport-status) depending on whether the horse has a competition record or not. This trait was included in a bivariate model with the competition trait and used all horses registered by KWPN since 1984. Results showed that performance in competition for dressage and show jumping is a heritable trait (h2 ~ 0.11-0.13) and that it is important to account for the effect of rider in the genetic analysis. Censoring had a small effect on the genetic parameter for highest performance achieved by the horse. A moderate heritability obtained for sport-status indicates that preselection has a genetic basis, but the effect on genetic parameters was relatively small.

Effect of specialization on genetic parameters of studbook-entry inspection in Dutch Warmblood horses.

Recent studies on data from the Dutch Warmblood Studbook (KWPN) have shown that the ongoing specialization of horses for either dressage (DH) or show jumping (JH) has led to a decreasing genetic relationship between the two subpopulations. The aim of this study was to analyse the effect of the specialization process on the genetic parameters of traits measured in the studbook-entry inspection of KWPN during the last fifteen years. Data from 18,125 DH and 23,800 JH recorded from 1998 until 2013 were used to analyse 13 traits scored in both DH and JH. Analyses were performed in a Bayesian framework. Firstly, variance components were estimated based on the whole data set. Secondly, genetic correlations between traits measured in DH or JH were estimated using bivariate analyses. Thirdly, three time periods were defined and genetic correlations between subpopulations were estimated within each period. Heritability was moderate (0.17-0.39) for both DH and JH. Genetic correlations between traits measured in DH or JH were not different from one considering the posterior standard deviation of the estimation; however, in most of the traits, a clear trend in reduction of the genetic correlation for traits expressed in DH and JH and an increase in their posterior standard deviation for recent years was observed. These results suggest that specialization could lead to differences in traits measured in DH and JH in the recent years.

Short communication: Heterosis by environment and genotype by environment interactions for protein yield in Danish Jerseys.

Crossing of lines or strains within and between breeds has been demonstrated to be beneficial for dairy cattle performance. However, even within breed, differences between strains may also give rise to heterosis. A key question is whether an interaction exists between heterosis and environment (H × E) that is independent of genotype by environment (G × E) interactions. In this study, H × E and G × E interactions were estimated in a population of approximately 300,000 Danish Jersey cows. The cows were a mixture of pure Danish Jerseys and crosses of US and Danish Jerseys. The phenotype studied was protein yield. A reaction norm model where the unknown environmental covariates are inferred simultaneously with the other parameters in the model was used to analyze the data. When H × E, but not G × E, was included in the model, heterosis was estimated to be 3.8% for the intermediate environmental level. However, when both H × E and G × E were included in the model, heterosis was estimated to be 4.1% for the intermediate environmental level. Furthermore, when only H × E was included in the model, the regression on the unknown environmental covariate was estimated to be 0.15, interpreted as meaning that an increase of average herd-year protein yield by 1 kg of protein led to an increase in heterosis of 0.15 kg above the average heterosis for a first-cross cow. When both H × E and G × E were included in the model, the regression on the unknown environmental covariate was not significantly different from zero, meaning that heterosis was similar in all environments investigated. The genetic correlation of protein yields for different environmental levels ranged from 0.72 to 0.93, which was significantly different from unity, indicating that G × E exist for protein yield.

Short communication: a genetic study of mortality in Danish Jersey heifer calves.

The aim of this study was to estimate genetic parameters for mortality of Jersey heifer calves during the first 6 mo after birth, calculate the genetic trend of the trait, and estimate breeding values of widely used Jersey sires. More than 260,000 heifer calves were included in the study. The mortality traits included in the analysis were defined as mortality in 8 different periods from 24h after birth to age 180 d (d 1-14, d 15-30, d 31-60, d 61-90, d 91-120, d 121-150, and d 151-180) and mortality over the entire period. A linear model was used for estimation of genetic parameters, breeding values of sires, and genetic trend. Fixed effects included in the model were herd-year class, month of birth, parity of mother, and whether the calf was sold to another farm in the first 6 mo. Both direct and maternal genetic effects were included in the model; however, the maternal genetic effect was very small and not significant. The mortality rate was highest in the first month after birth (7.8%). Total mortality in the first 180 d was 12.5%. Direct heritabilities of mortality were quite low, ranging from 0.002 to 0.03 on the observable scale and 0.025 to 0.076 on the underlying scale. Maternal heritabilities were even lower. The genetic correlation between mortality from d 1 to 14 and d 1 to 180 was estimated to be 0.88, although by definition, these 2 traits share the same observations for many records. No clear genetic trend existed over the last 20 yr; however, considerable genetic variation exists. The best and the worst sires differed by about 8% in their estimated breeding values of mortality in the first 180 d. Based on the results obtained in this study, genetic selection for reducing calf mortality should be possible.

Short communication: Is crossbreeding only beneficial in herds with low management level?

The economic benefit of crossbreeding has been well known for many years within dairy production. However, in most countries with an intensive dairy production, an extended use of systematic crossbreeding has not occurred. This may be due to the myth that heterosis is expressed mainly in low-producing herds. The aim of the study was to investigate the effect of heterosis with different management levels in Danish Jersey herds. More than 300,000 records of 305-d milk, fat, and protein yield from first-lactation Danish Jersey cows with different contributions from original Danish and US Jersey were analyzed using an animal model. The herds were distributed in 5 management groups based on production level. First, the results showed a large increase in additive genetic variance from the herds with lowest production level to the high-producing ones, and second, heterosis for all 3 production traits were lowest within the low-intensity management group and tended to be highest in the intermediate management groups. The results, therefore, support that crossbreeding is a breeding system that should be considered valuable for all management levels.

Short communication: Born to be a loser cow?

Over the last few years, an increasing awareness has arisen in Denmark of the existence of cows with a generally lowered health and production status, referred to as "loser cows." A previous study has estimated that the overall prevalence of loser cows in Danish Holstein herds is 3.2%. The aim of this study was to estimate genetic and phenotypic parameters for the loser cow state and the underlying traits: lameness, hock lesions, other cutaneous lesions, and condition of hair coat. Records on 6,098 cows were analyzed with an animal model including fixed effects of herd, season of scoring and location of scoring, age at first calving, lactation stage, and parity in addition to additive genetic effects and permanent environmental effects. The heritability of the loser cow score was 0.08 and for the underlying traits the heritability ranged from 0.05 to 0.12. The genetic correlations between various pairs of traits included in the loser cow score ranged from 0.04 to 0.68 and the phenotypic correlations ranged from 0.09 to 0.21. The genetic and phenotypic correlations between the loser cow score and the underlying traits ranged from 0.25 to 0.89 and 0.20 to 0.85, respectively, supporting the concept of the loser cow score. The traits included in the loser cow score are easy to assess and all showed genetic variation. They are therefore suitable for inclusion in a total merit index aimed at breeding for more robust cows.

Estimation of genetic parameters for young stock survival in beef x dairy crossbred calves.

Young stock survival is a trait of crucial importance in cattle breeding as calf mortality leads to economic losses and represents an animal welfare issue. The aim of this study was to estimate genetic parameters and sire breeding values for young stock survival in beef x dairy crossbred calves. Two traits were analysed with a univariate animal model: young stock survival between 1 to 30 days and 31 to 200 days after birth. Breed combinations with Belgian Blue sires outperformed all other sire breeds. The lowest survival rates were found for breed combinations with Jersey dams or Blonde d'Aquitaine sires. The results showed low but significant heritabilities (0.045 to 0.075) for both survival traits. Differences in breeding values between sires ranged from -2.5% to 3.5% and from -5.4% to 4.7% survival from 1 to 30 days and 31 to 200 days, respectively. Based on these findings, we concluded that it is feasible to breed for improved young stock survival in beef x dairy crossbred calves. This will hopefully contribute to increasing the survival rate of the calves and reduce economic losses for the farmers.

Invited review: crossbreeding in dairy cattle: a Danish perspective.

The value of crossbreeding in livestock species has been known for a long time; it has been used heavily within beef cattle, pig, and poultry production systems for several decades. This has not been the case for dairy production but lately there has been increased interest in crossbreeding dairy breeds. This review focuses on the practical and theoretical background of crossbreeding and describes the gain to be expected using systematic crossbreeding in dairy production. In Denmark, 24% of dairy farmers would consider starting crossbreeding programs within their herd. Evidence for the value of crossbreeding is documented with special emphasis on results from a Danish crossbreeding experiment. This experiment included 1,680 cows from 3 breeds and their crosses. In general, at least 10% heterosis can be expected for total merit, mainly due to increased longevity and improvement of functional traits. A minor part of heterosis for total merit is due to heterosis for production traits. For production, there is evidence of recombination loss using continued crossbreeding programs, which does not seem to be the case for longevity and total merit. However, recombination loss should be investigated more carefully as crossbreeding is becoming more popular. A prerequisite for crossbreeding to be beneficial on a long-term basis is that genetic gain within the parental breeds not be reduced. As long as the crossbred cow population constitutes less than 50% of the whole population, and young bulls can be tested through crossbred offspring, this prerequisite can be fulfilled. Crossbreeding can increase dairy income substantially, especially in management systems requiring a high level of functional traits.

Technical note: assessment of recovery site of mobile nylon bags for measuring ileal digestibility of starch in dairy cows.

The objective of this study was to evaluate recovery site of mobile nylon bags for measuring ileal digestibility of ruminally undegraded starch in dairy cows. Eight feed samples of untreated and treated concentrates were examined. Three lactating cows equipped with rumen fistula and duodenal and ileal cannulas were used in the experiment. The mobile nylon bags containing intact feeds or residues after a 12-h ruminal incubation were pretreated using a 2-step procedure to simulate abomasal digestion before insertion through the duodenal cannula. To assess the effect of hindgut fermentation on starch digestibility, approximately half of the bags were collected from the ileum and half from the feces. The results indicate that feed samples should be preincubated in rumen before insertion into duodenum, and that samples with relatively high fractions of rumen-undigestible starch should be collected from the ileum instead of from feces.

Short communication: genetic correlation between test-day electrical conductivity of milk and mastitis.

Electrical conductivity (EC) of milk is an indicator of mastitis. If EC shows genetic variation and is genetically correlated to mastitis, it could be used in a breeding program that includes selection for improved mastitis resistance. In this study, daily records of EC and mastitis from about 1,500 Holstein cows were analyzed. A bivariate animal model was used for estimation of (co)variance components, including fixed effects of age of calving, herd-test-day, and days in milk, in addition to random additive genetic effects and permanent environmental effects. For EC, the estimated heritability was moderate (0.22 to 0.39), whereas for mastitis, the heritability was low (0.013). The genetic correlation between EC and mastitis was estimated to be 0.75, and genetic improvement of mastitis resistance should be feasible through selection for reduced EC.

Caspase-2 promotes cytoskeleton protein degradation during apoptotic cell death.

The caspase family of proteases cleaves large number of proteins resulting in major morphological and biochemical changes during apoptosis. Yet, only a few of these proteins have been reported to selectively cleaved by caspase-2. Numerous observations link caspase-2 to the disruption of the cytoskeleton, although it remains elusive whether any of the cytoskeleton proteins serve as bona fide substrates for caspase-2. Here, we undertook an unbiased proteomic approach to address this question. By differential proteome analysis using two-dimensional gel electrophoresis, we identified four cytoskeleton proteins that were degraded upon treatment with active recombinant caspase-2 in vitro. These proteins were degraded in a caspase-2-dependent manner during apoptosis induced by DNA damage, cytoskeleton disruption or endoplasmic reticulum stress. Hence, degradation of these cytoskeleton proteins was blunted by siRNA targeting of caspase-2 and when caspase-2 activity was pharmacologically inhibited. However, none of these proteins was cleaved directly by caspase-2. Instead, we provide evidence that in cells exposed to apoptotic stimuli, caspase-2 probed these proteins for proteasomal degradation. Taken together, our results depict a new role for caspase-2 in the regulation of the level of cytoskeleton proteins during apoptosis.