Oxytocin concentrations of cattle in response to milking stimuli through lactation and mammary involution II

Patterns of oxytocin release to milking stimuli over a lactation and during mammary involution, were examined in seven Holstein cows used in the previous study. Blood samples were taken before, during and after milking or udder massage. Oxytocin as measured by radioimmunoassay increased within O to 2 min after attachment of the milking unit. Oxytocin levels fluctuated during milking and declined after the initial increase. Oxytocin often dropped below basal levels after milking. Milking-induced oxytocin release decreased as lactation advanced. The maximal increment for oxytocin release was significantly different between early and late lactation. The time taken to reach peak hormone concentrations declined across lactation. Relative amounts of oxytocin released in response to milking stimuli were significantly more in early than during late lactation. Cows released oxytocin during mammary involution with relatively large, rapid increases to udder massage. A distinct peak was observed and return to basal concentrations was rapid. The mean increment of oxytocin concentration above basal was 51.6 ±10.1 uU/ml. Maximal oxytocin levels occurred 1.6 ±.2 min (0 to 2 min) after initial stimulation. The total amount of oxytocin released in response to stimulation was 1.2 ±.1 uU/ml. In summary, a continuous or multiple release of oxytocin occurs during milking. The sensitivity of the neuroendocrine reflex for oxytocin appears dynamic. Changes in maximal concentrations and total amounts of hormone released in response to milking during lactation, and the relationship between these variables and basal concentrations suggest a gradual loss of sensitivity from the early stages of lactation to mammary involution.     

Plasma clearance and tissue uptake of native and desialylated equine gonadotropins

Equine luteinizing hormone (eLH), equine follicle stimulating hormone (eFSH) and equne chorionic gonadotropin (eCG) were desialylated and their plasma disappearance, tissue uptake and degradation determined. Both native hormones and their desialylated derivatives were radioiodinated and injected intravenously into male rats. Plasma samples were taken at different time intervals and examined for both total and trichloroacetic acid (TCA) precipitable radioactivity. Disappearance curves for each hormone consisted of two exponential components: a fast clearance followed by a slow phase. The apparent $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of the fast component for native eCG, eLH and eFSH were 18.3 min, 17.0 min and 17.1 min, respectively; this is in contrast to their desialylated derivatives which had a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 2.8 min, 4.9 min and 7.1 min, respectively. The slower component for native and desialylated eCG had at $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of 355.5 min and 171.2 respectively. After TCA precipitation more than 90 percent of the radioactivity in plasma was in the pellet, whereas in urine almost 95 percent of the radioactivity was in the TCA supernatant. Coincident with the disappearance of the hormone from the plasma its uptake and release was observed in liver, kidney, testis, and muscle tissue. Gel filtration data on plasma and urine samples indicated that the former had mostly intact hormone in contrast with the latter. Together these results indicate that eLH, eFSH and eCG disappear from the plasma of male rats in a biphasic manner with a rate slower than their desialylated derivatives.     

Physiological and pharmacological studies of oxytocin in virgin cattle III

Resting concentrations of oxytocin were measured in virgin cattle and it was determined if these animals would release oxytocin in response to milking associated stimuli. Half-life, clearance and entry rates for oxytocin were also quantified, to compare previous data from experiments carried out on lactating and nonlactating cows. Six Holstein virgin heifers received a two minute udder massage. Blood samples were taken before, at and after massage and analyzed for oxytocin by radioimmunoassay. Resting concentrations of oxytocin averaged 24.8 ±2.27 uU/ml (mean ± SE) and increased to 28 ±2.3 uU/ml at 2 min. The increase in oxytocin was clearly apparent after post-stimulation concentrations were corrected for basal (pre massage) levels. Serum oxytocin concentrations remained below baseline for 25 min post stimulation. No increase in oxytocin was seen prior to udder stimulation. Heifers were infused with 1.0 IU/min oxytocin to measure pharmacokinetic parameters. Oxytocin disappearance from sera was monitored by radioimmunoassay. A two compartment model for oxytocin elimination produced two half-life components. A rapid half-life component with a mean value of 3.07 ±.32 min and a slow half-life component with a mean of 24.3 ±2.2 min. The overall clearance rate for oxytocin was 9.4 ±.58 ml/kg min. The mean entry rate of oxytocin into the body was 231.96 ±25.96 uU/kg min. The sensitivity of the neuroendocrine reflex, eliciting oxytocin release, appears dependent upon the physiological state of the animal. Half-life and clearance measurements for oxytocin compare closely to those obtained in previous studies for cows in either early lactation, late lactation or undergoing mammary involution. It appears that the clearance and production of oxytocin are also related to the physiological state of the animal.     

Selection problems when antagonistic effects exist between production characteristics and calving difficulties

The interrelations between the different traits related to calving ease are analysed. These traits are adult size, conformation, birthweight, gestation length and calving ability of the cow.Some of these traits being antagonistic, a compromise is to be found, and this implies that constraints are to be placed on some of them. When feasible, it seems better to select directly for ease of calving than on correlated traits such as birthweight or gestation length.Type of calving is a maternally influenced trait and therefore genetic direct (D) and maternal (M) effects are to be taken into account.Mathematical expectations of variances and covariances for a maternally influenced trait such as calving performance are presented as well as the expected superiority of selected sires when selection is based on: (1) the average as sire, $\text{P}{}_{\mathrm{o}}$; (2) the average as grandsire, $\text{P}{}_{\mathrm{G}}{}_{\mathrm{o}}$ ; (3) a weighted average of both,

; (4) the optimum index $\text{I=b}{}_1\text{P}{}_{\mathrm{o}}\text{+ b}{}_2\text{P}{}_{\mathrm{G}}{}_{\mathrm{o}}$ corresponding to the aggregate genotype H = D + M.The variations (1) of the “between maternal grandsires” and “between sires” components of variance, (2) of the phenotypic correlation between the two sires' averages and (3) of the genetic superiority of selected sires are studied and illustrated for different values of the correlation between the direct and maternal effects and for different values of the variance of genetic maternal effects relative to that of the direct effects. When the maternal effects are important relative to the direct effects, and even if the two are negatively correlated, it is possible to improve both together, but then the average as grandsire has to be considered.A combination of both averages, $\text{P}{}_{\mathrm{o}}$ and $\text{P}{}_{\mathrm{G}}{}_{\mathrm{o}}$, as in the optimum index, gives the best prospects for improvement of the total genotype (D + M). Therefore, in problem breeds, extensive progeny-testing for growth, carcass composition and calving ability in their direct and maternal components ought to be carried out. By so doing, the opportunity will be given to estimate the parameters characterising the relations between these traits and then to construct a selection index optimising the correlation with the appropriate aggregate genotype.     

Some properties of lentogenic Australian newcastle disease virus

The Newcastle disease virus (NDV) occurring in Australia is apathogenic for chickens following natural infections. Some properties of the avirulent Australian V4 strain of NDV and of 12 new isolates of NDV were compared.The viruses grew to high titres following infection of chick embryos by the allantoic cavity and allantoic fluid had infectivity titres of from $\text{10}{}^{\mathrm{8·7}}\text{to}\text{10}{}^{\mathrm{9·5}}\text{EID}{}_{50}\text{0.2}\text{ml}$. With only two isolates did sufficient mortalities occur to allow calculation of mean death times and these were in excess of 140 h. Five of nine isolates failed to kill 100% of embryos when doses in excess of 10^7·9 EID₅₀ were used. When strain V4 was inoculated into the yolk sac of 10-day-old embryos, the LD₅₀ was similar to the ID₅₀ obtained with allantoic cavity inoculation, and the mean death time was 103 h.The intracerebral pathogenicity index for strain V4 was 0.91 and 1.02 in two experiments. The index was not significantly reduced when the virus was taken through a further cycle of plaque purification or when the inoculum was heated at 56°C for 30 min. Chickens with maternally derived antibody to NDV were not susceptible to intracerebral inoculation with strain V4. Chickens dying after intracerebral inoculation with strain V4 had haemorrhagic and necrotic liver lesions. The intracerbral pathogenicity indices for four other isolates varied from 0 to 0.22.The infectivity of V4 and three other isolates was relatively stable at 56°C and that of another eight isolates was labile. Haemagglutinins of all viruses studied were stable at 56°C for longer than 60 min. None of four isolates tested lost haemagglutinin activity on treatment with ether.Haemagglutination-elution patterns were variable but four isolates did not elute from chicken erythrocytes after 24 h at 4°C and strain V4 and isolate PM12 did not elute after 96 h at 4°C. Six viruses, including V4, agglutinated erythrocytes from all of six test horses. The haemagglutinin activity of the remaining viruses varied between horses.Four viruses including V4 haemolysed chicken erythrocytes. Gradient centrifugation allowed the separation of an infectious and a noniffectious haemagglutinin. Haemolytic activity was associated with the infectious haemagglutinin.     

Postinduction butorphanol administration alters oxygen consumption to improve blood gases in etorphine-immobilized white rhinoceros

Objective

To investigate the effects of postinduction butorphanol administration in etorphine-immobilized white rhinoceros on respiration and blood gases.

Impact of inclusion rates of crossbred phenotypes and genotypes in nucleus selection programs

Numerous methods have been suggested to incorporate crossbred (CB) phenotypes and genotypes into swine selection programs, yet little research has focused on the implicit trade-off decisions between generating data at the nucleus or commercial level. The aim of this study was to investigate the impact of altering the proportion of purebred (PB) and CB phenotypes and genotypes in genetic evaluations on the response to selection of CB performance. Assuming CB and PB performance with moderate heritabilities (h2=0.4), a three-breed swine crossbreeding scheme was simulated and selection was practiced for six generations, where the goal was to increase CB performance. Phenotypes, genotypes, and pedigrees for three PB breeds (25 and 175 mating males and females for each breed, respectively), F₁ crosses (400 mating females), and terminal cross progeny (2,500) were simulated. The genome consisted of 18 chromosomes with 1,800 quantitative trait loci and 72k single nucleotide polymorphism (SNP) markers. Selection was performed in PB breeds using estimated breeding value for each phenotyping/genotyping strategy. Strategies investigated were: 1) increasing the proportion of CB with genotypes, phenotypes, and sire pedigree relationships, 2) decreasing the proportion of PB phenotypes and genotypes, and 3) altering the genetic correlation between PB and CB performance (rpc). Each unique rpc scenario and data collection strategy was replicated 10 times. Results showed that including CB data improved the CB performance regardless of rpc or data collection strategy compared with when no CB data were included. Compared with using only PB information, including 10% of CB progeny per generation with sire pedigrees and phenotypes increased the response in CB phenotype by 134%, 55%, 33%, 23%, and 21% when rpc was 0.1, 0.3, 0.5, 0.7, and 0.9, respectively. When the same 10% of CB progeny were also genotyped, CB performance increased by 243%, 54%, 38%, 23%, and 20% when the rpc was 0.1, 0.3, 0.5, 0.7, and 0.9, respectively, compared with when no CB data were utilized. Minimal change was observed in the average CB phenotype when PB phenotypes were included or proportionally removed when CB were genotyped. Removal of both PB phenotypes and genotypes when CB were genotyped greatly reduced the response in CB performance. In practice, the optimal inclusion rate of CB and PB data depends upon the genetic correlation between CB and PB animals and the expense of additional CB data collection compared with the economic benefit associated with increased CB performance.     

Pharmacokinetics of IV Ketorolac in Horses Undergoing Orchiectomy

Ketorolac (KET) is a nonsteroidal anti-inflammatory drug for human use, with a potent analgesic activity, that is used in the relief of moderate-to-severe postoperative pain. The pharmacokinetics of KET tromethamine was evaluated after single IV injection at 0.5 mg/kg body weight, after intubation and 10 minutes before surgery, to six Arabian colts undergoing orchiectomy. Intraoperative cardiorespiratory variables were monitored. Blood samples were collected for 36 hours, and serum samples were analyzed by high performance liquid chromotography with ultraviolet-visible detection. During surgery, all monitored physiological parameters were stable. Intermittent positive pressure ventilation, and normocapnia were maintained throughout the procedure in all animals. No adverse effects were observed. The kinetics of KET was described by a two-compartment models, and also a noncompartmental analysis was performed. The distribution and elimination half-lives were t_1/2λ1$t_{1/2{\lambda }_1}$ 0.06 ± 0.02 and t_1/2λ2$t_{1/2{\lambda }_2}$ 0.59 ± 0.21 hours, respectively. Body clearance and mean residence time were 339.99 ± 120.19 mL/h/kg and 0.49 ± 0.22 hours, respectively. The volume of distribution at steady state and volume of distribution based on the terminal phase were 218.83 ± 134.26 mL/kg and 522.5 ± 529.3 mL/kg, respectively. The serum protein binding was 75.8 ± 2.9%. The results indicate that KET at 0.5 mg/kg IV was very rapidly eliminated and thus was likely not effective in the postoperative period. However, further studies including a control group and at higher doses are suggested to investigate the KET kinetics and the analgesic efficacy in horse and define the most appropriate dosage scheme.     

Quantification of transmission of foot-and-mouth disease virus caused by an environment contaminated with secretions and excretions from infected calves

Foot-and-mouth disease virus (FMDV) infected animals can contaminate the environment with their secretions and excretions. To quantify the contribution of a contaminated environment to the transmission of FMDV, this study used calves that were not vaccinated and calves that were vaccinated 1 week prior to inoculation with the virus in direct and indirect contact experiments. In direct contact experiments, contact calves were exposed to inoculated calves in the same room. In indirect contact experiments, contact calves were housed in rooms that previously had held inoculated calves for three days (either from 0 to 3 or from 3 to 6 days post inoculation). Secretions and excretions from all calves were tested for the presence of FMDV by virus isolation; the results were used to quantify FMDV transmission. This was done using a generalized linear model based on a 2 route (2R, i.e. direct contact and environment) SIR model that included information on FMDV survival in the environment. The study shows that roughly 44% of transmission occurs via the environment, as indicated by the reproduction ratio R^02Renvironment that equalled 2.0, whereas the sum of R^02Rcontact and R^02Renvironment equalled 4.6. Because vaccination 1 week prior to inoculation of the calves conferred protective immunity against FMDV infection, no transmission rate parameters could be estimated from the experiments with vaccinated calves. We conclude that a contaminated environment contributes considerably to the transmission of FMDV therefore that hygiene measures can play a crucial role in FMD control.

Electronic supplementary material

The online version of this article (doi:10.1186/s13567-015-0156-5) contains supplementary material, which is available to authorized users.     

Thymus atrophy during early pregnancy and its effect on a Trichinella spiralis infection in mice,including intestinal pathology and blood eosinophilia

The effects of pregnancy on the course of a $\text{Trichinella spiralis}$ infection and associated histopathological changes in thymus and small intestine were studied in outbred Swiss mice. For this purpose pregnant mice were orally infected with $\text{T. spiralis}$ on various days (1 to 8) $\text{post coitum}$. Virgin, age-matched infected and non-infected mice served as controls.Pregnancy induced a severe but reversible thymus atrophy, which was even more marked during a $\text{T. spiralis}$ infection. Thymus atrophy was most dramatic during mid and late pregnancy. During the involution phase a distinct increase in mast cells was observed.In animals infected during early pregnancy a not statistically significant inhibitory effect on worm expulsion was observed, whereas no effect was seen on the yield of muscle larvae, small intestine pathology (numbers of eosinophils, intestinal mast cells and globule leucocytes), blood eosinophilia and antibody production.Infection given during mid-pregnancy exerted an inhibitory effect on blood eosinophilia.On the basis of these results, it is concluded that although a severe atrophy of the thymus occurs during mid and late pregnancy, no effect on worm expulsion and intestinal pathology was observed when the infectious agent was given before thymus depletion started.     

Is single-step genomic REML with the algorithm for proven and young more computationally efficient when less generations of data are present?

Efficient computing techniques allow the estimation of variance components for virtually any traditional dataset. When genomic information is available, variance components can be estimated using genomic REML (GREML). If only a portion of the animals have genotypes, single-step GREML (ssGREML) is the method of choice. The genomic relationship matrix (G) used in both cases is dense, limiting computations depending on the number of genotyped animals. The algorithm for proven and young (APY) can be used to create a sparse inverse of G (GAPY~-1) with close to linear memory and computing requirements. In ssGREML, the inverse of the realized relationship matrix (H⁻¹) also includes the inverse of the pedigree relationship matrix, which can be dense with a long pedigree, but sparser with short. The main purpose of this study was to investigate whether costs of ssGREML can be reduced using APY with truncated pedigree and phenotypes. We also investigated the impact of truncation on variance components estimation when different numbers of core animals are used in APY. Simulations included 150K animals from 10 generations, with selection. Phenotypes (h² = 0.3) were available for all animals in generations 1–9. A total of 30K animals in generations 8 and 9, and 15K validation animals in generation 10 were genotyped for 52,890 SNP. Average information REML and ssGREML with G⁻¹ and GAPY~-1 using 1K, 5K, 9K, and 14K core animals were compared. Variance components are impacted when the core group in APY represents the number of eigenvalues explaining a small fraction of the total variation in G. The most time-consuming operation was the inversion of G, with more than 50% of the total time. Next, numerical factorization consumed nearly 30% of the total computing time. On average, a 7% decrease in the computing time for ordering was observed by removing each generation of data. APY can be successfully applied to create the inverse of the genomic relationship matrix used in ssGREML for estimating variance components. To ensure reliable variance component estimation, it is important to use a core size that corresponds to the number of largest eigenvalues explaining around 98% of total variation in G. When APY is used, pedigrees can be truncated to increase the sparsity of H and slightly reduce computing time for ordering and symbolic factorization, with no impact on the estimates.     

Feed evaluation for dairy cows: Tests on the system proposed in the Netherlands

The validity of the new Dutch feed evaluation system for dairy cattle was tested by using the results of energy balance experiments in Wageningen and of Scandinavian feeding trials performed by Frederiksen and Dijkstra. From the digestibility in vivo by wethers or in vitro, the metabolizable energy in the ration was predicted as well as the net energy to be produced. In the latter, the net energy for maintenance was assumed to be $\text{70}\text{kcal/kg}{}^{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}$ metabolic body weight. Prediction of energy in milk and energy balance agreed well with the results of energy balance trials with dairy cows fed on winter rations. For fresh grass a discrepancy was found which is not yet explainable, but further research on this subject is in progress. In the feeding trials, the measured average weight change agreed rather well with the predicted energy balance. Finally, the reliability of these methods for testing this new feed evaluation system is discussed.     

Estimation of direct and social effects of feeding duration in growing pigs using records from automatic feeding stations

Automatic feeding systems in pig production allow for the recording of individual feeding behavior traits, which might be influenced by the social interactions among individuals. This study fitted mixed models to estimate the direct and social effects on visit duration at the feeder of group-housed pigs. The dataset included 74,413 records of each visit duration time (min) event at the automatic feeder from 135 pigs housed in 14 pens. The sequence of visits at the feeder was employed as a proxy for the social interaction between individuals. To estimate animal effects, the direct effect was apportioned to the animal feeding (feeding pig), and the social effect was apportioned to the animal that entered the feeder immediately after the feeding pig left the feeding station (follower). The data were divided into two subsets: “non-immediate replacement” time (NIRT, N = 6,256), where the follower pig occupied the feeder at least 600 s after the feeding pig left the feeder, and “immediate replacement” time (IRT, N= 58,255), where the elapsed time between replacements was less than or equal to 60 s. The marginal posterior distribution of the parameters was obtained by Bayesian method. Using the IRT subset, the posterior mean of the proportion of variance explained by the direct effect (Prpσ^d2) was 18% for all models. The proportion of variance explained by the follower social effect (Prpσ^f2) was 2%, and the residual variance (σ^e2) decreased, suggesting an improved model fit by including the follower effect. Fitting the models with the NIRT subset, the estimate of Prpσ^d2 was 20% but the Prpσ^f2 was almost zero and σ^e2 was identical for all models. For the IRT subset, the predicted best linear unbiased predictor (BLUP) of direct (Direct BLUP) and social (Follower BLUP) random effects on visit duration at the feeder of an animal was calculated. Feeder visit duration time was not correlated with traits, such as weight gain or average feed intake (P > 0.05), whereas for the daily feeder occupation time, the estimated correlation was positive with the Direct BLUP (r^= 0.51, P < 0.05) and negative with the Follower BLUP (r^= −0.26, P < 0.05). The results suggest that the visit duration of an animal at the single-space feeder was influenced by both direct and social effects when the replacement time between visits was less than 1 min. Finally, animals that spent a longer time per day at the feeder seemed to do so by shortening the meal length of the preceding individual at the feeder.     

Quantitative studies of ovine haemonchosis. I. Relationship between faecal egg counts and total worm counts

The successful operation of parasite-control programmes based on monitoring of faecal egg counts stimulated an examination of the quantitative relationship between egg counts and worm counts of Haemonchus contortus in sheep in the Goondiwindi area of south-east Queensland. Sixty-one commercial Merino sheep were selected from flocks where outbreaks of haemonchosis had occurred. Faecal samples were collected prior to euthanasia and eggs and worms subsequently counted and differentiated.A strong relationship ($\text{r}{}^2\text{= 0.83, 71P < 0.001}$) was found between faecal egg counts and the total number of adult H. contortus. The size of the worm population, the time of year, and the ratio of male to female adult worms were minor sources of variation. The relationship was considered to be of value in the implementation of programmes for the diagnosis and control of haemonchosis in sheep flocks in the area.     

Lactation curves of friesian-bunaji crosses in NigeriaCourves de lactation de croisées frisonne-bunaji au NigeriaLaktationskurven von friesian-bunaji rinderkreuzungen in Nigeria

The validity of the gamma function to describe lactation curves of $\text{1}\text{2}$ and $\text{3}\text{4}$ bred Friesian-Bunaji crosses was investigated. The function explained 71% of the variation in yield in lactations which differed in duration, parity and season of calving. The effect of these variables on the components of the lactation curve was analysed by least-squares procedures. The goodness of fit of the function did not differ between classes of varying duration of lactation; short lactations, however, in addition to a lower persistence, also showed a low level of production. Lactation curves of first parity were flatter and also had a greatly reduced level of production compared to higher parities.Multiplying factors for estimating total lactation yield from part records were obtained from the fitted curves. The accuracy of prediction was greater when separate factors were used for each class of lactation length. The usefulness of part records in progeny testing is also discussed.     

Lack of reactivity of sera from Theileriaparva-infected and recovered cattle against cell membrane antigens of Theileria parva transformed cell lines

Sera from $\text{Theileria}$$\text{parva}$ infected, recovered and rechallenged cattle were tested in complement-dependent cytotoxicity, membrane immunofluorescence and antibody-dependent cellular cytotoxicity assays for the presence of antibodies against cell membrane antigens of $\text{T}$. $\text{parva}$ transformed cell lines.In the complement-dependent antibody-mediated cytotoxicity assay, sera from lethally infected animals were negative. Some recovered cattle showed a positive reaction, but such reactions were also observed when an eland cell line infected with $\text{T}$. $\text{taurotragi}$, and bovine lymphoblastoid cells were used as targets. Reaction was less against Ig-negative peripheral blood lymphocytes.Evidence is presented that these reactions could be evoked by attachment of immune complexes to Fc-receptors. It is concluded that cattle exposed to $\text{T}$. $\text{parva}$ infection do not develop antibodies against specific $\text{T}$. $\text{parva}$ (or $\text{T}$. $\text{parva}$-induced) cell surface antigens.     

Review: optimizing genomic selection for crossbred performance by model improvement and data collection

Breeding programs aiming to improve the performance of crossbreds may benefit from genomic prediction of crossbred (CB) performance for purebred (PB) selection candidates. In this review, we compared genomic prediction strategies that differed in 1) the genomic prediction model used or 2) the data used in the reference population. We found 27 unique studies, two of which used deterministic simulation, 11 used stochastic simulation, and 14 real data. Differences in accuracy and response to selection between strategies depended on i) the value of the purebred crossbred genetic correlation (rpc), ii) the genetic distance between the parental lines, iii) the size of PB and CB reference populations, and iv) the relatedness of these reference populations to the selection candidates. In studies where a PB reference population was used, the use of a dominance model yielded accuracies that were equal to or higher than those of additive models. When rpc was lower than ~0.8, and was caused mainly by G × E, it was beneficial to create a reference population of PB animals that are tested in a CB environment. In general, the benefit of collecting CB information increased with decreasing rpc. For a given rpc, the benefit of collecting CB information increased with increasing size of the reference populations. Collecting CB information was not beneficial when rpc was higher than ~0.9, especially when the reference populations were small. Collecting only phenotypes of CB animals may slightly improve accuracy and response to selection, but requires that the pedigree is known. It is, therefore, advisable to genotype these CB animals as well. Finally, considering the breed-origin of alleles allows for modeling breed-specific effects in the CB, but this did not always lead to higher accuracies. Our review shows that the differences in accuracy and response to selection between strategies depend on several factors. One of the most important factors is rpc, and we, therefore, recommend to obtain accurate estimates of rpc of all breeding goal traits. Furthermore, knowledge about the importance of components of rpc (i.e., dominance, epistasis, and G × E) can help breeders to decide which model to use, and whether to collect data on animals in a CB environment. Future research should focus on the development of a tool that predicts accuracy and response to selection from scenario specific parameters.     

Comparison of different methods to calculate venous admixture in anaesthetized horses

Objective

The aim of this study was to compare different methods to determine venous admixture (${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}}$) in anaesthetized horses. The first objective was to estimate ${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}}$ using jugular venous blood oxygen content (${\dot{Q}}_{\text{s}}/{\dot{Q}}_{\text{t}\text{jugular}}$), and a fixed value for the oxygen extraction (F-shunt). The second objective was to assess the influence of blood pressure and positioning on oxygen extraction. The third objective was to perform regression analysis between jugular and mixed venous blood oxygen tensions.