Bulk milk urea concentrations and their relationship with cow fertility in grazing dairy herds in southern Chile

Milk urea determination is being used as a broad indicator of protein/energy imbalance in dairy herds. The main purpose of this study was to compare blood and bulk milk urea values in grazing herds, to evaluate their seasonal variation under South Chilean conditions, and to examine their potential relationships with herd fertility. The association between herd blood urea concentration (mean of seven lactating cows) and bulk milk urea concentration (tank containing milk from the previous 24 h) was determined in 21 diary herds. Reference values, seasonal and herd variance, and the frequency of herds with values outside a range of 2.5 to 7.3 mmol/l were determined in bulk milk samples obtained monthly for a period of one year from 82 suppliers at two creameries located in southern Chile. Finally, bulk milk urea was measured every two weeks in samples from 24 herds, and the first service conception rate (FSCR) from 2153 dairy cows was determined. Mean bulk urea concentration was highly correlated with mean herd blood urea concentration (r = 0.95; p < 0.01). Mean urea concentration in the bulk milk samples obtained during one year from 82 herds was 4.9 +/- 1.2 mmol/l, with a range of 1.5 to 11.6 mmol/l. The highest values were found during spring and the lowest values during the summer. There was a high seasonal variation (CV = 13-47%) and between-herd variation (CV = 20-31%). Out of a total of 984 samples, 5.4% had urea values > 7.3 mmol/l and 3.8% had values < 2.5 mmol/l. Of the 82 herds, 27% had values outside the reference interval (2.5-7.3 mmol/l) on two or more occasions. FSCR was lower in herds when the bulk milk urea was > 7.3 mmol/l (50.7%) than in cows, where the urea concentration was < 5.0 mmol/l (73.8%) at the time of insemination. The study concluded that bulk milk urea concentrations provided information similar to herd blood urea concentrations in local grazing dairy herds. There was a high frequency of herds with abnormal values, with large variations between herds and between seasons. Increased milk urea concentrations during spring were associated with lower conception rates.     

Relationship between milk urea concentration and the fertility of dairy cows

The relationship between milk urea concentration and the fertility of dairy cows was examined in two studies. The first examined the relationship between bulk milk urea concentration and overall herd fertility, using data collected from 250 herds in the UK. There was no relationship either between bulk milk urea concentration and fertility, or between changes in bulk milk urea concentration and fertility. The second study compared the relationship between the milk urea concentration five days after service, and the fertility of individual cows on 11 UK dairy farms. There was no significant difference between the milk urea concentration of the cows that became pregnant and those that did not.     

Induction of parturition in dairy cattle and its effects on health and subsequent lactation and reproductive performance

OBJECTIVE: To determine the effect of induction of parturition on health, milk production and reproductive performance of dairy cows. DESIGN: A prospective cohort study in 62 dairy herds. PROCEDURE: Health, milk production and fertility indices were documented for 1449 dairy cows treated with dexamethasone trimethylacetate, with or without prostaglandin to induce calving. Equivalent data was collected for 603 untreated herd mates that calved at approximately the same time. RESULTS: The median interval from initial treatment to calving was 11 days. Induction was associated with a substantially lower calf survival and commercial value of surviving calves. Calf viability and value was lower when induced cows were at an earlier stage of pregnancy. Retained foetal membranes, photosensitisation and other problems were significantly more frequent in the induced group compared to the untreated group. Milk production of induced cows was approximately 4% lower than untreated ones, but the majority of reproductive indices were not significantly different between the two groups. CONCLUSIONS: The practice of induction of parturition in seasonal calving dairy herds is a reliable way of shortening the gestation period of cows. Costs associated with morbidity and mortality of induced cows and losses in lactation and calf production are offset by benefits of improved reproductive performance and more efficient management of the herd. The welfare aspects of induction on calf survival must be considered.     

Milk yield did not decrease in large herds of high-producing Holstein cows in semi-arid climate of Mexico

This study aimed to determine the trends in milk production, fertility, temperature-humidity index (THI), and herd size in dairy herds from the Laguna region in northern Mexico. Records of 16 dairy herds of Holstein cows from January 2002 to December 2016 were used. Milk production was categorized in low and high levels. Milk production and fertility were analyzed using generalized equation estimation procedures by a model of repeated measures that included the effect of year, month, and productive level, an interaction for month × productive level, and herd effect was nested in productive level. For THI, a generalized linear model that included the effects of year and month was used. Dairy herds with high levels of milk production yielded more milk than those with low levels (P?<?0.001). Milk production in 2002 and 2016 was 27.4?±?0.6 and 32.3?±?0.7 L/cow/day, respectively. Fertility fluctuated throughout the study. Dairy herds with high levels of milk production recorded higher fertility than those with low levels (P?<?0.001). From October to April, THI was <?70, whereas it was >?73 from May to September, indicating that cows were in heat stress (20 h/day). The median herd size was 995 and 2569 cows in 2002 and 2016, respectively. In conclusion, in large herds, milk production increased over the years of study, whereas fertility showed a wave cycle; nonetheless, when THI was >?73, both milk production and fertility decreased.

     

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

Background

Overall 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.

Methods

To 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.

Results

The 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.

Conclusion

PV30 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.     

Trends in the reproductive performance of Holstein dairy cows in Iran

The study was undertaken to determine the trends in the reproductive performance of Holstein dairy cows in Iran during 1994 to 2008. Reproductive performance data for 528,034 lactations of 246,132 cows in 1,822 Holstein dairy herds of Iran were used. The potential effect of calving season, herd, parity, calving year, as well as herd size and 305-day milk production on reproductive performance traits was investigated using multiple regression models. The least squares means of age at first calving decreased by 3.1 (±0.06) days per year from 806.5 (±96.3) days in 1994 to 788 (±89.9) days in 2008. The least squares means of calving interval increased 1.02 (±0.03) days per year from 394.1 (±65) days in 1994 to 413.2 (±81) days in 2008. Greater 305-day milk production was associated with an average increase of 6.55 (±0.08) days in calving interval per 1,000-kg increase in milk yield. Larger herd size was associated with an average decrease of 0.22 (±0.02) days in calving interval per 50 cows per herd. The mean number of days dry was 88.6 (±51.3) days and increased by 0.82 (±0.02) days per year. In conclusion, reproductive performance in Holstein dairy herds has generally decreased, whereas herd size and milk production have increased over time. Producers may make significant improvements in herd reproduction by reviewing management strategies including the sire selection, reproductive management, inseminator training and techniques, and improved estrous detection. Moreover, it may be advisable for the fertility traits to be included in the genetic selection indices to reduce the rate of reproductive decline.     

Effects of infection with bovine virus diarrhoea virus on health and reproductive performance in 213 dairy herds in one county in Sweden

Bulk tank milk samples, collected twice with a 1 year interval, from 213 Swedish dairy herds with no vaccination programme against bovine virus diarrhoea virus (BVDV), were tested for antibodies to BVDV using an indirect enzyme-linked immunosorbent assay. The herds were classified into four different BVDV groupings based on changes in the estimated prevalence of BVDV antibody-positive cows in the herds. The estimated mean prevalences of BVDV antibody-positive cows were maintained as > 80% in 58 (27.2%) and as < 10% in 84 (39.4%) of the herds. A recent introduction of the infection was deemed to have occurred in seven (3.3%) of the herds studied. The BVDV groups were compared with regard to parameters related to disease and fertility at herd level. Relationships were assessed using logistic and ordinary linear regression analyses. The risks for clinical mastitis, retained placenta and oestrus-stimulating treatments were higher and the calving intervals were longer in BVDV infected herds, i.e. those herds with an increasing or maintained high prevalence of BVDV antibody-positive cows.     

Fertility of dairy cows in Northern Ireland

A comprehensive database was established on the milk production and reproductive performance of dairy cows in 19 selected herds in Northern Ireland, varying in size, management system and genetic merit. Data were obtained for 2471 cows, 1775 of which calved in a second year, and 693 were culled from the herd for specific reasons. The estimated mean rate of heat detection (assessed by the interheat interval during the main breeding season) in all the herds was 71 per cent, with a range from 53 to 92 per cent The average conception rate to first insemination was 37.1 per cent (range 21 to 66 per cent). The average calving interval for the retained cows was 407.2 days (range 359 to 448 days). Twenty-eight per cent of the cows that calved were culled, with infertility being the largest single reason (26.8 per cent of the cows culled). There were major differences in reproductive performance between the herds, but heat detection rate, conception rate and calving interval did not appear to be affeded by a herd's genetic merit. The herds with shorter calving intervals were characterised by better heat detection efficiency (83 v 61 per cent, P<0.01), a shorter interval from calving to first insemination (74 v 97 days; P<0.05), a higher conception rate to first insemination (45 v 34 per cent, P>0.10) and a lower removal rate (23 v 37 per cent, P<0.01). Furthermore, the cows in these herds had lower body condition scores (BCS) in the dry period (3.0 v 3.3; P<0.05) but lost less body condition in early lactation (0.3 v 0.6 BCS units, P<0.05). These results show that dairy herd fertility in Northern Ireland is generally low and similar to that previously reported for England and the USA, but that in some herds changes in herd management practices improved the cows' fertility.     

Paratuberculosis sero-status and milk production,SCC and calving interval in Irish dairy herds

The objective of this study was to investigate the impact of paratuberculosis sero-status on milk yield, fat, protein, somatic cell count and calving interval in Irish dairy herds. Serum from all animals over 12 months of age (n = 2,602) in 34 dairy herds was tested for antibodies to Mycobacterium avium subsp. paratuberculosis using an ELISA. Herds were categorised by sero-status into positive, non-negative and negative, where a positive herd contained two or more positive cows, a non-negative herd contained only one positive cow and a negative herd contained no positive cows. Data at animal, parity and herd-level were analysed by multiple regression using general linear models. Positive herds (mean herd size = 129 cows) and non-negative herds (81 cows) were larger than negative herds (72 cows) (P < 0.01). Negative herds had the highest economic breeding index (EBI), while positive herds had the highest estimated breeding value (EBV) for milk yield. There was no significant effect of paratuberculosis sero-status at animal, parity or herd-level on milk yield, milk fat or protein production, somatic cell count score (SCCS) or calving interval. Negative herds tended to have a lower SCCS than positive and nonnegative herds (P = 0.087). This study only examined the effects of paratuberculosis sero-status but did not examine the clinical effects of Johne's disease at the farm or dairy industry levels.     

Indications and implications for testing of milk urea in dairy cattle: A quantitative review. Part 2. Effect of dietary protein on reproductive performance

dDietary protein and dairy cow fertility. Feeding more dietary protein has been negatively associated with dairy cow fertility in some but not all studies. We used meta-analysis to examine the relationship between dietary crude protein and conception rate. While a higher intake of dietary crude protein significantly lowered conception rate, the potential for feeding less degradable dietary protein to modify this relationship was not demonstrated.

dMilk urea concentrations and dairy cow fertility. The use of milk urea as an indicator of dietary energy and protein intake and as an indictor of reproductive performance has been questioned. We found that changes in urea concentration in body fluids explained only 25% (p = 0.08) of the variance in conception rate after conducting a meta-analysis of available studies.

dInterpretation of milk urea concentrations. High intakes of dietary protein may induce adaptations in urea metabolism, and the negative relationship identified between high intakes of dietary protein and fertility for Northern Hemisphere dairy herds may not necessarily apply in Australasian dairy herds. Because of the potential for cows to adapt to high protein diets, the use of a single milk urea determination on a herd will have limited value as an indicator of nutritional status and little value as a predictor of fertility.     

Indications and implications for testing of milk urea in dairy cattle: a quantitative review. Part 2. Effect of dietary protein on reproductive performance

DIETARY PROTEIN AND DAIRY COW FERTILITY: Feeding more dietary protein has been negatively associated with dairy cow fertility in some but not all studies. We used meta-analysis to examine the relationship between dietary crude protein and conception rate. While a higher intake of dietary crude protein significantly lowered conception rate, the potential for feeding less degradable dietary protein to modify this relationship was not demonstrated. MILK UREA CONCENTRATIONS AND DAIRY COW FERTILITY: The use of milk urea as an indicator of dietary energy and protein intake and as an indicator of reproductive performance has been questioned. We found that changes in urea concentration in body fluids explained only 25% (p = 0.08) of the variance in conception rate after conducting a meta-analysis of available studies. INTERPRETATION OF MILK UREA CONCENTRATIONS: High intakes of dietary protein may induce adaptations in urea metabolism, and the negative relationship identified between high intakes of dietary protein and fertility for Northern Hemisphere dairy herds may not necessarily apply in Australasian dairy herds. Because of the potential for cows to adapt to high protein diets, the use of a single milk urea determination on a herd will have limited value as an indicator of nutritional status and little value as a predictor of fertility.     

The effects of calcium supplementation of dairy cattle after calving on milk, milk fat and protein production, and fertility

AIM: To determine the effect of calcium supplementation of dairy cattle after calving on serum concentrations of calcium, magnesium, and phosphorous after calving, and on reproductive and productive performance in the following lactation. METHODS: This was a double-blind randomised clinical trial using 356 dairy cows of parity 3 or greater from six seasonally calving commercial dairy herds. Cows were randomly assigned to a treatment and control group. The treatment group received two doses of 380 ml of calcium chloride in oil (49 g of elemental calcium); the first dose was given as soon as practical after calving and the second 12 hours later. Control cows received 380 ml of a placebo using the same treatment regime. Treatment and control cows had blood samples taken during the first 7 days after calving to determine serum calcium, magnesium and phosphorous levels. Treatment and control cows were monitored throughout the lactation to measure production and reproductive performance. RESULTS: Treatment had no effect on PSM to first service intervals. Treatment significantly reduced PSM to conception intervals in only one of the four herds with data available for analysis (p = 0.09). There was no difference between treatment groups for adjusted corrected milk yield calculated from the first herd test milk yield (p = 0.93) or 305-day milk solids production (p = 0.19). CONCLUSION: Further studies are required to identify reasons for the between-herd effectiveness of calcium chloride treatment in improving fertility.     

Urea concentration in bulk milk as an indicator of the protein supply at the herd level

Levels of urea in bulk milk from 80 herds were analysed twice monthly during 1 year to study herd variations and effect of season (Experiment 1). The overall (mean ± s) was 4.7 ± 1.3 mmol/1 ranging from 1.4 to 10.0 mmol/1. Generally, the urea levels were high in summer and early autumn and during this period there were 3 peaks, the first one at the beginning of June, the second one in the middle of July and the third one at the end of September. The peaks reflected feed changes and use of fertilizers commonly practized in the area.In another study samples of bulk milk were obtained from 49 herds using single forage diets with fresh grass silage and standardized concentrate mixtures (Experiment 2). In these herds all feed components given on the day of urea sampling were weighed as accurately as possible and a sample of the silage was taken for chemical analyses and determination of in vitro digestibility. Mean level of crude protein (CP) in silage dry matter was 15.6 ± 2.2 % and average dietary digestible crude protein (DCP) per feed unit (FU) was 146 ± 16 g. In all herds the protein levels in the total daily ration were equal to or above recommended standards. Urea concentration in bulk milk was significantly affected by the GP content in silage, level of dietary DGP and amount of DCP/FU. In energy deficient herds relatively high urea values were obtained without any great surplus of protein. Yield did not significantly affect the urea concentration in bulk milk.     

Technical and Economic Effects of Culling and Reproduction Strategies in Dairy Cattle Herds Estimated by Stochastic Simulation

Abstract

The objective of this study was to create operational replacement guidelines under various conditions concerning reproductive performance, supply of replacement heifers and individual milk yield. Nine culling strategies were defined by three average insemination periods and by three discrimination policies between high- and low-yield cows. The effect of the nine culling strategies was analysed with combinations of heat detection rate and time of initiation of breeding after calving under two replacement heifer purchase policies: purchase (open herd) and no purchase (closed herd). The strategies were evaluated using a stochastic simulation model that simulated production and reproductive status in herds composed of dual-purpose cattle with additional young stock. The evaluation of the strategies was made in a situation without a milk quota under typical Danish conditions in 1993. Results showed that discriminating between high- and low-yield cows improved net revenue significantly in open herds but not in closed herds. Irrespective of the purchase policy, using longer insemination periods increased net revenue significantly in herds with poor reproductive performance; whereas net revenue in herds with good reproductive performance tended to increase by using shorter insemination periods. The culling rate is a poor figure when evaluating culling strategies and culling strategies should be assessed at herd level rather than per cow.     

Fertility, somatic cell count and milk production in Swedish organic and conventional dairy herds

The share of organic dairy production in EU is increasing and this study describes the herd structure and cow performance in organic and conventional dairy production systems in Sweden. The data included records from 2 902 718 lactations, collected in organic (n = 471) and conventional (n = 13 976) herds between 1998 and 2005. Compared with conventional herds, the organic herds were larger and increased more rapidly in size. The replacement rate was slightly lower in organic herds and fewer Swedish Holsteins were used. The statistical analysis of cow performance in the first three lactations showed lower milk, fat and protein production in organic herds, but the increase in production from first to second lactation was larger when expressed in kg milk. Fertility was better for organically managed cows compared to conventionally managed cows, but the somatic cell count (SCC) was higher. However, at a given production level the fertility was slightly worse in organic herds while there was no difference in SCC. No interactions of importance were found between production system and breed for any trait.The results showed that organic and conventional dairy production differed regarding herd structure and cow performance. However, the differences in fertility and SCC found were to a high extent explained by the lower milk yield in organic production and no breed was found to perform better in either system.     

Reproductive performance of Holstein dairy cows in Iran

The objectives of the present study were to describe the current reproductive parameters of Holstein dairy cows in Iran and to determine factors which have a significant effect on reproductive performance with emphasis on high-producing dairy cows. Five large Holstein dairy herds from the major milk production areas of Iran were selected for this study. Reproduction data including parity of dam, calving date, days to first service, days open, number of services, dry period, and occurrence of diseases for cows that calved from 2004 to 2007 were collected from the herds' databases. To determine the effects of year and season of calving, disease status, level of milk production, and parity of dam on reproductive parameters, the proc-mixed procedure in SAS software was used. Overall, data about 8,204 lactation were collected for the study. Results showed that mean (±SD) days open, calving interval, and days to first service for study herds were 134 (±89), 403 (±86), and 67 (±38) days, respectively. Conception rates at the first service and the overall service-conception rate were 41.6% and 41%, respectively. The level of milk production and diseases had significant negative effects on days open and service per conception (P < 0.05); statistical analysis showed that for every 100-kg increase in milk yield, days open will increase by about 0.3 days. However, no significant effect of level of productivity was observed on days to first service. The results of this study indicate that high milk production is a risk factor for decreasing fertility in Iran, like many other parts of the world.     

Reproductive performance and milk production of Israeli-Holstein cows with different supplementation during the dry period]

In three field trials comprising 602 Israeli-Holstein dairy cows, the effect of the dry period ration on reproductive performance, culling rate and milk production was investigated. The cows were fed in groups. The basic dry period rations consisted for two herds of medium quality cereal hay and for one herd of corn straw, which were fed ad libitum. In each herd dry cows were assigned to an experimental and control group. Cows of the experimental group were supplemented with 1.5 to 3 kg of lactating cows mixed ration (LMR), whereas in the control group the amount of supplement was increased by the factor two or 3.3. In the experimental group the amount of the supplement was calculated to achieve levels of net energy and of crude protein close to NRC requirements; in the control group the level of net energy and protein was 12 to 18% higher as compared to the experimental group. The amount of LMR supplement in the experimental group of herds A, B, C were 1.5 kg, 1.9 kg, and 3 kg, respectively. In the control groups these amounts were 5 kg, 3.8 kg, and 6 kg, respectively. The groups fed moderate amounts of LMR supplement had a higher conception rate at first insemination, a higher percentage of cows conceiving and fewer cows culled in the consecutive lactation than cows fed increased amounts of LMR supplement. The lactational incidence of reproductive disorders and the milk production were not affected by the differences in feeding during the dry period. Reproductive performance and culling rate appeared to be more favorable for cows fed moderate amounts of supplement during the entire dry period or during the last 3 to 4 weeks of the dry period.     

Informative Value of an Indirect Enzyme‐Linked Immunosorbent Assay (ELISA) for the Detection of Bovine Viral Diarrhoea Virus (BVDV) Antibodies in Milk

Bulk and individual milk samples from 117 herds located in Brittany (west France) were used to assess: (i) the performance characteristics of an indirect enzyme‐linked immunosorbent assay (ELISA) applied to individual milk for the detection of antibodies to bovine viral diarrhoea virus (BVDV); and (ii) the relationship between the bulk milk result obtained from this test and the within‐herd prevalence of antibody‐positive lactating cows. This ELISA test was based on a monoclonal antibody directed against non‐structural protein NS2‐3 of pestiviruses. At the individual level, based on 1113 matched milk/serum samples, the sensitivity and specificity of this test applied to milk, compared with the virus neutralization test on serum, were 95.0 and 97.7%, respectively. At the herd level, the relationship between the optical density percentage (OD%) of bulk milk and the within‐herd prevalence of antibody‐positive lactating cows was assessed using the receiver operating characteristics (ROC) analysis. Classes of OD% of bulk milk were determined so that they were associated with minimum intraclass and maximum between‐class variances of within‐herd prevalence of antibody‐positive cows. The ROC analysis resulted in two classes of bulk milk results corresponding to different expected levels of within‐herd prevalence. Herds with an OD% of bulk milk <75% and ≥75% had a mean observed prevalence of antibody‐positive cows of 8.9 and 60.6%, respectively. Herds with a bulk milk result <75% were expected to be BVDV free, whereas large variations in prevalence of antibody‐positive cows existed in the herds with OD% ≥75%. The test described in this study is suitable to identify herds likely to have a low prevalence of BVDV antibody‐positive cows.     

Variations with Breed,Age, Season,Yield, Stage of Lactation and Herd in the Concentration of Urea in Bulk Milk and Individual Cow’s Milk

The concentration of urea in the milk of 510 dairy cows in 10 herds was determined at regular intervals for a year. The herds contained approximately equal numbers of Swedish Red and White, and Swedish Holstein cows. The mean ± sd concentration in the samples from individual cows was 5.32 ± 1.13 mmol/1, and the mean concentration in bulk milk was 5.39 ± 0.96 mmol/1. These values indicated that on average the herds were fed too much protein relative to their intake of energy throughout the year.Herd factors had a strong influence on the milk urea concentration. The concentration was lower during the first month of lactation than later in the lactation, and lower when the cows were housed during the winter than when they were grazing. There was a weak positive relationship between the daily milk yield and urea concentration, particularly during late lactation, but there was no relationship with either breed or age. Bulk milk urea was a reliable guide to the average urea concentration of a herd.     

The effect of an outbreak of respiratory disease on herd-level milk production of Norwegian dairy farms

This study was done to evaluate the effect of an outbreak of acute respiratory disease associated with bovine respiratory syncytial virus (BRSV) on the daily milk yield per cow in Norwegian dairy-cattle farms. Retrospective data from 184 dairy herds located in two neighbouring veterinary districts during the study period (December 1994–May 1995, during which an epidemic of acute respiratory disease associated with BRSV occurred in this area) were analysed. Data on the bulk-milk deliveries and the date of the outbreak were collected at herd level, whereas information on calving dates and parity was collected at cow-level. The effect of the herd outbreaks on the daily milk yield was analysed with a repeated-measurement approach. The average daily milk loss was estimated to be 0.70 kg per cow for 7 days after a herd outbreak (compared with the period >1 week prior to an outbreak), adjusted for the herd-level lactation stage, parity and their interaction term. We consider the estimated milk loss associated with a herd outbreak of epidemic respiratory disease to be of minor importance.