Reproductive Performance In Dairy Herds Research Articles

Development and evaluation of predictive models for pregnancy risk in UK dairy cows

One suggested approach to improve the reproductive performance of dairy herds is through the targeted management of subgroups of biologically similar animals, such as those with similar probabilities of becoming pregnant, termed pregnancy risk. We aimed to use readily available farm data to develop predictive models of pregnancy risk in dairy cows. Data from a convenience sample of 108 dairy herds in the UK were collated and each herd was randomly allocated, at a ratio of 80:20, to either training or testing data sets. Following data cleaning, there were a total of 78 herds in the training data set and 20 herds in the testing data set. Data were further split by parity into nulliparous, primiparous, and multiparous subsets. An XGBoost model was trained to predict the insemination outcome in each parity subset, with predictors from farm records of breeding, calving and milk recording. Training data comprised 74,511 inseminations in 45,909 nulliparous animals, 86,420 inseminations in 39,439 primiparous animals, and 158,294 inseminations in 32,520 multiparous animals. The final models were evaluated by predicting with the testing data, comprising 31,740 inseminations in 19,647 nulliparous animals, 38,588 inseminations in 16,215 primiparous animals, and 65,049 inseminations in 12,439 multiparous animals. Model discrimination was assessed by calculating the area under receiver operating characteristic curves (AUC); model calibration was assessed by plotting calibration curves and compared across test herds by calculating the expected calibration error (ECE) in each test herd. The models were unable to discriminate between insemination outcomes with high accuracy, with an AUC of 0.63, 0.59 and 0.62 in the nulliparous, primiparous and multiparous subsets, respectively. The models were generally well-calibrated, meaning the model-predicted pregnancy risks were similar to the observed pregnancy risks. The mean (SD) ECE in the test herds was 0.038 (0.023), 0.028 (0.012) and 0.020 (0.008) in the nulliparous, primiparous and multiparous subsets respectively. The predictive models reported here could theoretically be used to identify subgroups of animals with similar pregnancy risk to facilitate targeted reproductive management; or provide information about cows' relative pregnancy risk compared with the herd average, which may support on-farm decision-making. Further research is needed to evaluate the generalizability of these predictive models and understand the source of variation in ECE between herds; however, this study demonstrates that it is possible to accurately predict pregnancy risk in dairy cows using readily available farm data.

Associations of a liver health index with health, milk yield, and reproductive performance in dairy herds in the northeastern United States

The objective was to evaluate a liver health index (LHI) by evaluating its association with negative health events, milk yield, and risk of pregnancy within 150 d in milk (DIM). In a retrospective cohort study, an LHI was calculated based on plasma albumin, cholesterol, and bilirubin concentrations for 265 primiparous and 611 multiparous cows 3 to 12 DIM enrolled across 72 farms in the northeastern United States. Mixed effects linear regression models were used to evaluate if (1) metritis (MET), (2) displaced abomasum (DA), (3) clinical ketosis (CK), (4) one or more of the 3 disorders (MET, DA, or CK), (5) 2 or more of the 3 disorders (MET, DA, or CK), or (6) culling within 30 DIM was associated with LHI. Mixed effects linear regression models were used to evaluate if LHI was associated with 305-d mature equivalent milk at the fourth test day (ME305; mean ± standard deviation: 114 ± 13 DIM) and a Cox proportional hazards model was used to evaluate if LHI was associated with pregnancy within 150 DIM. Cows that were diagnosed with MET, DA, CK, one or more of the disorders, 2 or more of the disorders, or were culled within 30 DIM had a lower LHI than cows that were not diagnosed with a disorder or culled. A 1-unit increase in LHI was associated with a 154 ± 38 kg increase in ME305 and a 8% increased risk of pregnancy within 150 DIM [hazard ratio (95% confidence interval): 1.08 (1.03 to 1.14)] for multiparous cows; however, we did not identify a relationship between LHI and ME305 or pregnancy within 150 DIM for primiparous cows. These results suggest that the LHI is associated with health, milk yield, and pregnancy within 150 DIM for multiparous cows and health for primiparous cows; therefore, the LHI can be used as a tool to evaluate transition cow success.

Combined use of non-laboratory methods for the practical diagnosis of endometritis in postpartum dairy cows.

Postpartum endometritis can cause subfertility in cows and reduce the reproductive performance of dairy herds. Thus, there is a critical need to improve the accuracy of the diagnosis of this disease, particularly in dairy cows. This study confirmed the effects of the combined use of two non-laboratory methods: Metricheck device (MT) and ultrasonography (UT) to detect signs of endometritis and therefore predict the likelihood of pregnancy. The reproductive tract of 67 lactating Holstein cows (25 primiparous and 42 multiparous) was observed at 4 and 6 weeks postpartum using the MT and UT. The cows with flecks and more purulent material in the vaginal discharge were defined as MT-positive, and the cows with uterine echogenic contents were defined as UT-positive. The combined definition was also used; both the UT and MT results or either the UT or MT result had to be positive for the final decision to be positive. The true-negative cows were determined as both MT-UT-negative. When comparing the diagnostic results obtained by MT and UT, 37.3% and 32.8% of the total cows showed conflicting results at 4 and 6 weeks postpartum. The proportion of non-pregnant cows until 200 days postpartum was significantly greater in both MT-UT-positive cows than in the true negative cows. The hazard ratios of pregnancy rate were 0.37 for both MT-UT-positives relative to the true negatives at 4 weeks postpartum. Similar significant differences were not detected using the MT or UT alone. These results indicate that a more severe effect on the chance of pregnancy could be detected in cows that are both MT-UT-positive compared with those positive for MT or UT alone. The combined use of MT and UT could support veterinary practitioners in diagnosing endometritis, potentially improving the accuracy of predicting subsequent reproductive performance.

Exploring the Relationship between Changes in Postpartum BCS (Body Condition Score) and Reproductive Performance in Dairy Herds

The current research aims to explore the effects of Body condition score (BCS) reduction on some reproductive factors such as re-pregnancy rate, number of inseminations per pregnancy, clinical endometritis, and ovarian activity in Holstein cows and also the effects of number of calving and its difficulty, on changes in the BCS. Data analysis with spss 21 software shows that with a further decrease in BCS first month after delivery, the percentage of non-pregnant cases in the herd and the number of cows with inactive ovaries increases significantly. The rate of endometritis significantly increases by increasing negative changes in BCS by 0.5 units or more. The number of inseminations necessary for creating pregnancy in two groups of decrease in BCS was different with a statistically significant difference. The odds ratios of developing clinical endometritis and also inactive ovaries in cows with BCS changes< 0.5 were significantly greater. In addition, odds ratios of pregnancy with finally 3 inseminations in cows with changes in BCS ≤ 0.5 were significantly different from cows with higher BCS changes. BCS changes of cows in second calving were not significantly different from cows in first calving, while the changes in calving 3 and 4 were significantly different. Easy parturition and parturition with some help was not different in BCS changes but dystocia but dystocia has been associated with significant BCs changes (P<0.05). According to these results, it can be concluded that a further reduction in BCS was associated with a reduction in the reproductive performance.

Selective use of a modified pre-synchronization-Ovsynch and resynchronization reproductive strategy in dairy herds: A field application study.

We aimed to evaluate whether a modified pre-synchronization-Ovsynch (MPO) and resynchronization method, adjusted for the timing of biweekly reproductive consulting visits, could be implemented successfully under field conditions in dairy herds. Forty-five days after calving (calving: Day 0), 1,182 cows were assigned randomly to Ovsynch, MPO or control groups. (1) Cows were administered GnRH on Day 65, PGF2α on Day 72 and GnRH 56hr later, followed by timed artificial insemination (TAI) 16hr later (Ovsynch, n=380). (2) Cows with a CL were administered PGF2α (n=204) and cows without were administered GnRH (n=199) on Day 45. Then, each cow was administered PGF2α on Day 55 (9 to 12days later), GnRH on Day 58 and underwent Ovsynch 7days later (selective MPO [sMPO] n=403). (3) The remaining cows underwent AI when oestrus was detected (EDAI, n=399). The probabilities of pregnancy per AI 30 and 45days after the first AI were higher in the sMPO group (odds ratios 1.99 and 1.92, p<.0001) than in the EDAI group. In addition, the probability of pregnancy by 105days postpartum tended to be higher (p<.1) in the sMPO group than in the EDAI and Ovsynch groups, which shortened the mean interval from calving to pregnancy in the sMPO group (3.4 and 4.2days, respectively) than in the EDAI and Ovsynch groups. In the sMPO group, the interval between the first and second treatments during pre-synchronization did not affect the probability of pregnancy per AI after the first AI. The probability of pregnancy per AI after the second AI did not differ between the Ovsynch, sMPO and EDAI groups. In conclusion, the sMPO programme, adjusted for the timing of biweekly reproductive consulting visits, followed by resynchronization, could be successfully adopted in field conditions, and is associated with good reproductive performance in dairy herds.

PSXII-23 Identification and evaluation of novel fertility traits using automated activity monitor data from commercial dairy herds

Abstract The reproductive performance of dairy herds is a determinant factor in their production efficiency and long-term profitability. While the genetic improvement of fertility in cows has been a top breeding objective, its success has been constrained by the low heritability of current traits and the negative impact of management practices on trait measurement accuracy. The recent development and adoption of automated sensor technologies, such as activity monitors, within dairy production systems have provided new opportunities to identify relevant and cost-effective phenotypes of fertility. To date, several activity-based measurements of estrus expression have been associated with fertility outcomes and may, therefore, be suitable predictors of female fertility. The objective of this study was to identify and evaluate novel estrus-related fertility traits using automated activity monitor (AAM) data from commercial dairy herds. A total of 8,730,987 records consisting of 10,529 estrus events were collected between January 2019 and March 2020 from 2,434 cows and 689 heifers of two U.S. commercial herds, where cows were fitted with collar-mounted accelerometers (Heatime, SCR Engineers Ltd., Netanya, Israel). The AAM dataset contained individual bi-hourly activity and rumination patterns, as well as computed fertility index scores, which were used to derive fertility traits related to estrus duration and intensity. The mean number of estrus events per cow and heifer was 4.06 ± 0.04 and 2.63 ± 0.07, respectively, with 1,408 of estruses resulting in pregnancy. Traditional fertility traits were calculated from the breeding record information of 3,255 animals. An estimation of the heritabilities along with genetic and phenotypic correlations between the novel estrus-related fertility traits and traditional fertility traits was undertaken using the program AIREML. Outputs from this project are expected to provide further insight on how to best use AAM measurements to improve selection for reproductive performance in commercial dairy herds.

Mycoplasma species in vaginas of dairy cows before and after exposure to bulls and their association with conception

Mycoplasma species can colonize the urogenital tract of dairy cattle. However, interrelationships between Mycoplasma spp. and reproductive performance in dairy herds are unclear. In this study, we measured apparent prevalences of Mycoplasma spp. in the vaginas of dairy cows (n = 629) pre- and post-bull exposure in dairy herds with and without Mycoplasma bovis clinical disease (n = 5 herds), and assessed associations between variables describing reproductive performance and consequent Mycoplasma spp. isolation. Mycoplasma spp. were infrequently isolated from the vagina pre- (1.9%; 12/629) and post-bull (3.2%; 20/629) exposure. Of the mycoplasmas isolated, Mycoplasma bovigenitalium was isolated most frequently (87.5%; 28/32), followed by Mycoplasma californicum (9.3%; 3/32). Mycoplasma bovis was only isolated from one cow. We were unable to provide any evidence of venereal transmission of M. bovis in cows in M. bovis-infected herds that use natural service bulls. There was an insufficient number of cows with Mycoplasma spp. in the vagina pre-bull exposure to assess effects on subsequent reproductive performance. Cows that had not conceived before post-bull exposure sampling had much greater odds (odds ratio 14.8; 95% confidence interval 4.2 to 52.3) of having a Mycoplasma sp. isolated from the vagina at this time compared with those that had conceived. Also, within those that had conceived, delayed conception increased the odds of having a Mycoplasma spp. isolated from the vagina at the post-bull exposure sampling by a factor of 1.62 for every additional week not pregnant. The likely cause of these findings is that cows that remain not pregnant for longer are more likely to be served by a bull (likely repeatedly) and subsequently become colonized with a Mycoplasma sp. (mostly M. bovigenitalium) through venereal transmission. In dairy herds that use bulls, there is a greater chance of isolating a Mycoplasma sp. (mostly M. bovigenitalium) after a period of bull breedings from the vaginas of cows that have remained nonpregnant for longer during the bull breeding period.

Associations between On-farm Welfare, Milk Production, and Reproductive Performance in Dairy Herds in Northwestern Spain

ABSTRACT This study was conducted to evaluate the relationship between on-farm welfare, milk production, and reproductive performance in dairy herds in northwestern Spain. Data on the welfare status from 31 herds were collected using the Welfare Quality® protocol. Linear regression was applied to assess associations between WQ criteria/principle scores on farm average 305-d milk production and calving to conception interval (CCI). Results indicated that milk production was associated with the absence of prolonged hunger criterion (average increase of 22.33kg per unit score). Each one unit increase in the score for good feeding was also associated with a26.49kg increase in milk production. A10 unit increase in the scores for the absence of pain (by management procedures), expression of social behaviors, and absence of injuries was associated with reductions in CCI by 1.77, 0.8, and 0.29 days. CCI also decreased by 1.08 and 0.53 days when the principles of good health and appropriate behavior increased by 10 units. This study points out associations which can help encourage the dairy cattle sector to adopt practices that promote animal welfare.

Effect of COQ9 and STAT5A polymorphisms on reproductive performance in a Holstein cow herd in Mexico.

Coenzyme Q9 (COQ9), a coenzyme Q (CoQ) precursor, is an essential component of the mitochondrial electron transport chain that drives adenosine triphosphate production. COQ9 polymorphism 18:25527339 is characterized by substitution of guanine (allele G) for adenine (allele A), which modifies the function of the protein encoded by the gene. In Holsteins, allele A has been associated with better reproductive performance in terms of the conception rate, number of services per conception (SPC) and days open (DO). The signal transducer and activator of transcription (STAT) protein is a transcription factor activated in the presence of cytokines and growth factors. STAT5A polymorphism 19:42407732 in exon 8 has been associated with higher fertility and embryonic survival rates. The objective of this study was to determine the relationship of COQ9 and STAT5A polymorphisms with reproductive parameters [calving to first heat interval (CFHI), DO and SPC]. Blood samples were taken from 112 lactating Holstein from a herd in México for allele genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). To estimate the association between reproductive parameters and genotypes, a linear mixed-effect model was performed. The COQ9 AG genotype was associated significantly with lower SPC (P<0.05) but not with DO or CFHI. No significant association with any reproductive parameter was found for STAT5A. Our findings suggest that the COQ9 18:25527339 polymorphism is a useful molecular marker for improvement of reproductive performance in dairy herds.

Association of lameness and mastitis with return-to-service oestrus detection in the dairy cow

Oestrus detection is an important part of maintaining efficient reproductive performance in dairy herds. Both lameness and mastitis are common diseases of dairy cows that may impact oestrus detection. A...

Does feeding extruded linseed to dairy cows improve reproductive performance in dairy herds? An observational study

Feeding n-3 fatty acids (FA) is often cited as a promising strategy to tackle impaired reproduction in dairy cows. However, the scientific literature shows conflicting results that may be explained by the nature of n-3 FA used, the amount supplemented and the timing of supplementation. In addition, designing a proper experimental design to study n-3 FA and reproduction is subjected to other difficulties such as the choice of the control diet or gaining enough statistical power. The objective of this retrospective observational study was to quantify the average effects of supplementing extruded linseed (EL), a feed rich in α-linolenic acid, to dairy cows on reproductive performances under field conditions in French commercial farms. Exposure measurement to EL feeding was particularly challenging as exact cow diets are not traced in farms. Therefore, to investigate the potential dose-effect relationship, we defined a proxy of EL intake per day by using deliveries of EL based feeds from 22 companies in the study period 2008–2015 in France. An artificial insemination (AI) was considered exposed only if the cow was supplemented with EL from the calving until 17 days after AI. Based on recommendations for EL use on the field, 4 exposures classes were created: [1–50] (n = 14,126 AIs), [50–300] (n = 88,261 AIs), [300–600] (n = 66,136 AIs), and [600-1500] (n = 28,287 AIs) g/cow/d. The reference population was composed of cows that did not receive any EL between calving until 17 days after AI within herds that were supplied, but not continuously during the study period (n = 226,795 AIs). Mean daily EL intake in exposed population was 337 g/cow/d (±239.4). Reproductive performance was studied on 423,605 AIs from 1096 herds and 158,125 cows using Cox models for days to first AI and days to conception, and logistic regression models for risk of return-to-service, adjusted for factors likely to influence the reproductive performance and for a herd random effect. Risk of return-to-service between 18 and 78 days after first and second AI did not differ between exposed and reference populations, Nevertheless, the effect on the days to first AI was higher with the lowest EL intake (HR: 1.14; 95% CI: 1.11, 1.17) than with higher EL intake levels (HR ranging from 1.06 to 1.07; 95% CI: 1.04, 1.09). Similarly, for the effect on the time from calving to conception from the lowest EL intake (HR: 1.19; 95% CI: 1.15, 1.23) compared to the higher EL intake levels (HR ranging from 1.08 to 1.11; 95% CI: 1.06, 1.14). This original large-scale epidemiological study provides new insights into the effects of feeding EL at a commercially sustainable level to dairy cows.

Effect of milk production on reproductive performance in dairy herds

The objective of the present study was to assess the relationship between individual cow milk yield and fertility, accounting for the contextual effect of the herd. A data set including 657,968 lactations from 677 dairy herds in Argentina from 2001 to 2012 was used. The odds of pregnancy by 100 d in milk (DIM) were assessed by a multilevel logistic model (with cow as the first and herd as the second hierarchical level), and time to pregnancy was assessed by a proportional hazards regression model. Multilevel logistic models included the fixed effects of milk yield by 80 DIM, parity, year, and calving season at cow level and quartiles of herd milk yield by 80 DIM as a contextual effect. The proportional hazards model included the effect of daily cow-level milk yield as time-dependent variable, with milk yield at herd level as the stratification variable. Cows producing 1 standard deviation over the mean milk yield of their herd had 1.3 percentage point lower pregnancy by 100 DIM (from 31.4 to 30.1%; odds ratio = 0.942) when in herds in the top quartile of milk yield, whereas they increased 0.5 percentage points (from 27.9 to 28.4%) when in herds in the lowest quartile of milk yield. Only 4% of the observed variation in pregnancy by 100 DIM was explained by the random effect of the herd. Similarly, cows producing 1 standard deviation (8 kg/d) greater than the herd mean daily milk had 1.3% lower hazard of pregnancy (hazard ratio = 0.987) at 63 DIM in herds in the top quartile of milk yield, whereas they had 14.8% higher hazard (hazard ratio = 1.148) in herds in the lowest quartile of milk yield. The magnitude of the negative association between the cow's daily milk yield and the hazard of pregnancy increased with DIM. In conclusion, the relationship between milk yield and reproductive performance is statistically significant, but the effect size is practically small and is modulated by herd production level.

The association of culling and death rate within 30 days after calving with productivity or reproductive performance in dairy herds in Fukuoka, Southern Japan.

The incidence of peripartum disorders in dairy herds negatively influences productivity and reproductive performance. Concrete data from local areas are helpful for explaining the importance of peripartum management to dairy farmers. This study was conducted to clarify the association of culling and death rate within 30 days after calving with productivity or reproductive performance in 179 dairy herds in Fukuoka, Southern Japan. A database was compiled from the records of the Livestock Improvement Association of Japan, the Dairy Cooperative Association and the Federation of Agricultural Mutual Relief Association. In this study, we created a comprehensive database of dairy farm production data for epidemiological analysis and used a general linear mixed model to analyze the association of culling and death rate within 30 days after calving with milk production or reproductive performance. The database can be used to describe, analyze and predict the risk of production. A cross-sectional analysis with contrasts was applied to investigate the association of cows served by AI/all cows, pregnant cows/cows served by AI, days open, milk yield and somatic cell counts with culling and death rate within 30 days after calving. The days open value significantly increased with increasing rate of culling and death within 30 days after calving (P for trend <0.001). No significant differences were found for the other comparisons. Our data suggest that proper feeding and management in the dry period may lead to improved postpartum reproductive performance in this dairy cow cohort.

How to train a dog to detect cows in heat—Training and success

Efficient and accurate estrus detection is a key management factor determining acceptable reproductive performance in dairy herds. Previous studies have shown that dogs can differentiate between vaginal mucus samples of cows in estrus and vaginal mucus samples of cows in diestrus with an accuracy between 40.3% and 97.0%. We set out (1) to develop a specific training protocol for training dogs to identify cows in estrus from the feed alley and (2) to determine sensitivity and specificity of trained dogs to detect cows in estrus. Six dogs were trained by means of positive reinforcement to detect cows in estrus from the feed alley following the training protocol. Four of those dogs participated in the final test after an average training time of 50h per dog. Overall, they correctly identified positive cows as being positive in 23 out of 32 cases (i.e. sensitivity of 71.9%) and falsely classified positive cows as being negative in nine cases (28.1% type II errors). Out of 128 cases 119 were correctly classified as true negative cows (i.e. specificity of 93.0%) and in nine cases negative cows were falsely identified as positive cows (7.0% type I errors). Further research is warranted to develop an optimized training protocol that allows training estrus detection dogs for practical use within an appropriate time.

Synchronisation of ovulation for management of reproduction in dairy cows

Important developments have occurred in the last two decades, since the advent of the Ovsynch protocol, on the understanding and use of synchronisation programmes for management of reproduction in dairy herds. This better understanding of oestrus cycle control associated with suboptimal reproductive performance in dairy herds has led dairy producers to quickly adopt timed artificial insemination (AI) protocols. Recent surveys have documented that fixed-time AI has become an important component of management of reproduction in high-producing herds. Furthermore, timed AI protocols have also demonstrated benefits in pasture-based milk production systems because of the ability to increase insemination rate. In general, successful use of the Ovsynch protocol requires some fundamental physiological principles to be respected, including: induction of ovulation to synchronise follicle growth in the first 2 days of the programme such that a young antral follicle is recruited; maintenance of high concentrations of progesterone during the development of the ovulatory follicle, but also effectively lyse the corpus luteum to result in very low concentration of progesterone at AI; and having a healthy pre-ovulatory follicle of moderate diameter that is highly oestrogenic and responsive to gonadotropins to synchronously ovulate 12 to 18 h after insemination. Current methods oestrous and ovulation synchronisation are still not optimal and future improvements will likely require new technologies for hormone formulation and delivery such that additional interventions are minimised to maintain acceptance by producers.

Evaluation of two dairy herd reproductive performance indicators that are adjusted for voluntary waiting period

BackgroundOverall reproductive performance of dairy herds is monitored by various indicators. Most of them do not consider all eligible animals and do not consider different management strategies at farm level. This problem can be alleviated by measuring the proportion of pregnant cows by specific intervals after their calving date or after a fixed time period, such as the voluntary waiting period. The aim of this study was to evaluate two reproductive performance indicators that consider the voluntary waiting period at the herd. The two indicators were: percentage of pregnant cows in the herd after the voluntary waiting period plus 30 days (PV30) and percentage of inseminated cows in the herd after the voluntary waiting period plus 30 days (IV30). We wanted to assess how PV30 and IV30 perform in a simulation of herds with different reproductive management and physiology and to compare them to indicators of reproductive performance that do not consider the herd voluntary waiting period.MethodsTo evaluate the reproductive indicators we used the SimHerd-program, a stochastic simulation model, and 18 scenarios were simulated. The scenarios were designed by altering the reproductive management efficiency and the status of reproductive physiology of the herd. Logistic regression models, together with receiver operating characteristics (ROC), were used to examine how well the reproductive performance indicators could discriminate between herds of different levels of reproductive management efficiency or reproductive physiology.ResultsThe logistic regression models with the ROC analysis showed that IV30 was the indicator that best discriminated between different levels of management efficiency followed by PV30, calving interval, 200-days not-in calf-rate (NotIC200), in calf rate at100-days (IC100) and a fertility index. For reproductive physiology the ROC analysis showed that the fertility index was the indicator that best discriminated between different levels, followed by PV30, NotIC200, IC100 and the calving interval. IV30 could not discriminate between the two levels.ConclusionPV30 is the single best performance indicator for estimating the level of both herd management efficiency and reproductive physiology followed by NotIC200 and IC100. This indicates that PV30 could be a potential candidate for inclusion in dairy herd improvement schemes.

Effect of widespread and limited use of sexed semen on genetic progress and reproductive performance of dairy cows

Stochastic simulation was used for studying the impacts of sexed semen on genetic progress and reproductive performance of dairy cows. Three strategies were compared: WSS (use unsexed semen in cows and heifers), SSH (use sexed semen in heifers and unsexed semen in cows) and SSCH (use sexed semen in both cows and heifers). Conception rate (CR) of unsexed semen was considered to be 35% and 65% in cows and heifers, respectively. CR of sexed semen was considered to be 15 (20% in cows and 50% in heifers), 10, 5 and 0 percentage points lower than unsexed semen. Thus, four subschemes were compared under SSCH (SSCH15, SSCH10, SSCH5, SSCH0) and SSH (SSH15, SSH10, SSH5, SSH0). Moreover, the effect was studied in four distinct paths of selection: active sires (AS), young bulls (YB), bull dams (BD) and milking cows (CW). The average genetic superiority of CW was 12% and 9.5% in SSCH15 and SSH15 strategies relative to a base scheme, respectively. The average genetic superiority of CW was 19% and 10.5% in SSCH0 and SSH0, respectively. Regression analysis showed that genetic superiority of CW increased significantly, that is, 0.5% and 0.1% per every 1% increase in CR in SSCH and SSH, respectively. The result showed that there is a significant difference between genetic superiority of cows in SSCH and SSH schemes. Widespread and limited use of sexed semen in commercial dairy herds resulted in a large genetic advantage in CW. The genetic advantage of gender control was minimal in the selection paths of AS, YB and BD. Open days and services per conception reached to 153 v. 125 days and 5 v. 2.86 under SSCH15 compared with WSS. The age at first calving increased from 774 to 790 days in SSH15 and SSCH15 strategies. Mean of parities decreased to 2.26 v. 2.42 by using sexed semen. The widespread use of sexed semen increased the age average of cows in all parities. Sexed semen increased selection intensity in the CW path, and this contributed to the genetic merit of future cows. On the other hand, sexed semen had a negative effect on the reproductive performance of dairy cows. Generally, although the effect of widespread use of sexed semen (SSCH) on genetic progress is significantly more than limited use of sexed semen (SSH), SSCH decreased reproductive performance of dairy herds dramatically, and this suggests that SSH scenarios might be more appropriate in animal breeding programs. Finally, to make a decision of which schemes are more convenient, it is necessary to compare the economic aspects of schemes.

An alternative surgical procedure for the preparation of teaser bulls

Use of surgically modified teaser bulls represents an opportunity to improve the reproductive performance of dairy herds in a cost effective manner. Use of these animals is currently not widespread. This article details a novel method for the surgical preparation of these animals in a low cost, safe and effective manner. Adoption of this technique will facilitate the increased use of teaser bulls in dairy herds.

Measuring and comparing reproductive performance in dairy herds: strengths and weaknesses of frequently used parameters

Despite previous recommendations on reproductive performance terminology in dairy cows, confusion remains over how reproductive parameters are defined and interpreted. For vets that want to benchmark and compare the performance of different herds, clarifying this confusion is important. The aim of this article is to describe a selection of reproductive performance parameters used in the UK and discuss potential pitfalls of how and when they are used.

Cash Flows of Instituting Reproductive Programs

Economic returns associated with improved reproductive performance in dairy herds depend upon a wide variety of factors, including initial level of reproductive performance, future value of milk and of the calves produced, cash cost of replacement heifers, and many other factors. A variety of synchronization programs have been developed that may help improve the overall pregnancy rate (PR) of the herd, but the profitability of each program varies. A spreadsheet model was designed to compare the potential profitability of an improved estrus-detection program, an estrus-detection program combined with presynchronization and a single timed insemination, and a program relying completely upon timed insemination. Each of these scenarios was compared to a baseline program based upon estrus-detection and AI. The baseline herd was designed to have an estrus-detection risk and conception risk of approximately 50% and 31%, respectively, consistent with herds at or slightly above average reproductive performance in the US. Each of the modeled scenarios predicted better future returns than the initial baseline program, but the two involving timed AI also incurred substantial costs upfront. Adoption of either of these programs carries significant potential risk if not properly implemented and managed. Poor compliance to either timed AI program dramatically decreases both the resulting PR and the predicted economic returns. Dairies that implement programs such as these should work diligently to ensure that compliance levels consistently exceed 90% in order to maximize the profitability of either approach.