Ontario Dairy Herds Research Articles

Analytic Validation of an Infrared Milk Urea Assay and Effects of Sample Acquisition Factors on Milk Urea Results

The objective of this study was to determine if milk samples, as they are routinely collected by Ontario Dairy Herd Improvement, would yield accurate milk urea results with an infrared assay. This investigation involved analytic validation of the infrared assay and assessment of the effect of DHI routine sample acquisition factors on milk urea results.Analytic validation of an automated milk urea assay was performed by assessing the relative accuracy and precision of milk urea results produced by the Fossomatic 4000 Milk Analyzer, an infrared method of analysis, compared with the Eurochem test, an accepted reference method. Results indicated that, when interpreted at the group level, milk urea results between the infrared method and the reference test were in good agreement. The two tests shared a similar and high level of precision.Milk urea concentrations obtained from composite (metered) milk samples, and not quarter stripping samples, were most representive of concurrent serum urea concentrations. The addition of bronopol preservative did not result in a numerically important change in milk urea concentrations. Storage of preserved metered milk samples for up to 4 d at either room temperature or by refrigeration, or for up to 3 d by freezing, did not result in changes in milk urea concentrations.We concluded that milk samples, as they are routinely collected and handled by DHI, are suitable for measurement of milk urea concentrations with the infrared method of analysis if data are interpreted at the group level.

Milking Management and Bulk Milk Iodine Concentrations in Ontario Dairy Herds

The role of hygiene in the prevention of new intramammary infections has been well understood since the late 1950's. In 1965, Newbould reviewed the literature on disinfection in the prevention of udder infections.1 Throughout the next decade, numerous disinfectant products were approved and marketed. Even though significant extension education efforts were mounted, in 1981 a formal observational study reported that the implementation of proper milking management methods on Ontario dairy farms had not kept pace with the current knowledge on mastitis control.2 Barely 50% of herds were using post-milking teat dipping. Since that time, there has been relatively little published regarding implementation of recommended mastitis control practices.3 During the same time period, the iodine content of fluid milk has been questioned. The concentration of iodine has been reported for raw farm milk4 and for retail milk samples.5 Some evidence of samples with high milk iodine content was documented in these reports. Even though iodine is essential, it is a potentially harmful dietary element, and cause for public concern. The impact of pre-milking teat disinfection on the iodine content of milk has been studied.6 However, recent literature is lacking on the prevalence of elevated iodine in the farm-gate milk supply. The objective of this project was to determine the current status of the Ontario dairy industry for frequency of use of various milking management procedures, and to study the association between the use of these practices and bulk milk iodine concentrations.

Results of an Observational Study Describing the Relationship Between Milk Urea Concentrations and Feeding Management and Performance in Ontario Dairy Herds

A 13-month observational study of 60 Holstein herds in Ontario, Canada was performed to describe the relationship between milk urea nitrogen (MUN) concentrations, as measured by routine DHI testing, and nutritional management in commercial dairy herds. A second objective was to determine if MUN concentrations, as measured by routine DHI testing, were associated with performance in commercial dairy herds. Measures of performance included reproductive performance, production, and efficiency (cost) of production.

Factors affecting reproductive performance in Ontario dairy herds

Data were collected on reproductive, health and production events in 45 dairy herds in southwestern and eastern Ontario, Canada, from July 1990 to July 1993. Mean and median days in milk at first estrus, at first service, and at conception were 85.1 and 83.9, 94.0 and 88.9, and 126.3 and 115.5 d, respectively. The mean estrus detection rate was 48.3%, with a minimum of 28.4% and a maximum of 64.2%. The mean overall conception rate was 46.7%, with a minimum of 29.8% and a maximum of 70.7%. The most commonly used used therapeutic agents were GnRH (11.5% lactational incidence risk) and PG (13.1% lactational incidence risk). Estrus management accounted for the largest portion of PG use in the herds studied (69.4%). Results of a two sample t-test indicated no significant difference in reproductive performance among herds housed in free-stall compared with those housed in tie-stall barns. Multivariate linear regression models of 3 reproductive performance measures indicated that cows with ovarian cysts and/or increased peak milk production had significantly longer calving-to-first estrus and calving-to-conception intervals as well as lower conception rates than average producing cows without cysts. Cows with metritis were found to have significantly shorter calving-to-conception intervals but no detectable difference in conception rate or calving-to-first estrus interval than their herdmates. As lactation number increased reproductive performance improved. Cows that were observed in estrus earlier conceived earlier. Animals receiving uterine infusions had significantly longer calving-to-conception intervals and lower conception rates than their herdmates. There was no detectable difference in reproductive performance for cows treated with GnRH or PG compared with the nontreated cows. An increased estrus detection rate was associated with shorter calving-to-conception intervals and lower conception rates. Based on the range of performance in the study herds, the factors with the greatest potential influence on calving-to-conception interval in the average herd were the estrus detection rate and conception rate.

Trends in milk component production in dairy herds in Ontario: 1985–1994

The objectives of this study were to investigate the dynamics of milk component production in dairy herds in Ontario, Canada, over time and to assess the impact of changes to the allocation of milk quota and payment systems on component production. The data consisted of monthly production records from all of the approximately 11 000 farms that shipped milk in Ontario between March 1985 and July 1994.Farm mean yields of milk and milk components have increased over the past decade. The mean fat percentage among the farms increased from 3.85% in 1985 to 3.99% in 1994; protein percentage remained relatively constant at 3.30% in 1985 to 3.32% in 1994. The percentages of protein and fat showed a seasonal pattern. Relatively high component percentages were observed during the fall of each year, and low component percentages were observed during the summer months. Mean fat and protein percentages did not appear to change in response to changes in the allocation of quota or pricing systems. Farms with high (or low) relative protein percentage in one year tended to maintain high (or low) relative protein percentage in the subsequent year, suggesting that herd level factors are related to protein percentage. Key words: Milk components, time trends, dairy

Evaluation of Overall Reproductive Performance of Dairy Herds

Reproductive efficiency was assessed in 106 commercial dairy herds in Ontario. Herds that were similar in historical calving interval or projected calving interval varied widely in reproductive culling rate. The correlation between the reproductive culling rate and the historic calving interval and between the reproductive culling rate and the projected calving interval were −0.23 and were not significant. The coefficient of variation associated with the reproductive culling rate (75.7%) was much higher than that of the historical calving interval (3.8%) or the projected calving interval (4.5%). The repeatability of the reproductive culling rate (0.26) was much lower than that of the historical calving interval (0.81) or the projected calving interval (0.60) because culling rate was not only influenced by the overall herd reproductive performance, but also by the differences in the maximal allowable days open for rebreeding and the estimation of which cows were culled for reproductive failure. Additionally, a high coefficient of variation for the reproductive culling rate is unavoidable because this variable has a binomial distribution and a low mean value (7.5%). These disadvantages are not sufficient to exclude this measure from a comprehensive assessment of overall herd reproductive performance. The projected calving interval and the reproductive culling rate can be combined into the adjusted calving interval and thus interpreted jointly. On 40.5% of the farms providing data for this study, fertility assessment based on the projected calving interval indicated better reproductive performance than that based on adjusted calving interval. Hence, the assessment of herd fertility on the basis of projected calving interval can lead to a different and erroneous conclusion regarding the level of herd fertility than that obtained with the evaluation based on adjusted calving interval.

Evaluation of Five Cowside Tests for Use with Milk to Detect Subclinical Ketosis in Dairy Cows

The objective of this study was to evaluate the characteristics of five ketone tests for use with milk to detect subclinical ketosis [defined as >1200 µmol of β-hydroxybutyrate (BHBA)/L of blood] in dairy cows. The tests studied were the Ketolac® BHB strip to detect BHBA (Hoechst, Unterschleiβheim, Germany) and four tests based on sodium nitroprusside to detect acetoacetate (Rothera tests) [Ketostix® strip (Bayer, Etobicoke, ON, Canada), Bioketone powder (Societé d’ Analyses Biopharmaceutiques, Laval, QC, Canada), KetocheckTM powder (Great States, St. Joseph, MO), and Utrecht powder (University of Utrecht, Utrecht, The Netherlands)]. Milk samples (n = 529) from 266 cows in 25 Ontario dairy herds were used for this investigation. The Ketolac® BHB strip at 50 and 100 µmol of BHBA/L of milk showed sensitivities of 92 and 72%, respectively. This test was more sensitive for subclinical ketosis than were any of the Rothera tests. The sensitivities of the Rothera tests were 43, 33, 28, and 5%, respectively, for Utrecht powder, Bioketone powder, KetocheckTM powder, and Ketostix® strip. The Rothera tests were highly specific, as was the Ketolac BHB strip at 200, 500, and 1000 µmol of BHBA/L of milk (specificity, >97%). The prevalence of subclinical ketosis was highest during the first 6 wk of lactation, and a peak was detected during the 2nd wk of lactation. Of the tests evaluated in this study, Ketolac® BHB strip was the most useful to monitor subclinical ketosis in dairy herds.

Severe acute bovine viral diarrhea in Ontario, 1993-1995.

In 1993, noncytopathic bovine viral diarrhea virus (BVDV) strains with enhanced virulence caused unprecedented outbreaks of severe acute bovine viral diarrhea (BVD) in dairy, beef, and veal herds in Ontario (Canada). Fever, pneumonia, diarrhea, and sudden death occurred in all age groups of cattle. Abortions often occurred in pregnant animals. Gross lesions in the alimentary tract were similar to those associated with mucosal disease, especially in animals >6 months of age. Cattle of all age groups had microscopic lesions in the alimentary tract similar to those seen with mucosal disease. The epidemic peaked in the summer of 1993, with 15% of all bovine accessions from diseased cattle presented to the diagnostic laboratory being associated with BVDV. The virus strains involved in the outbreak were analyzed using monoclonal and polyclonal antibodies and the polymerase chain reaction. The virus isolates from these outbreaks of severe disease were determined to be type 2 BVDV. Type 2 BVDV has been present in Ontario at least since 1981 without causing widespread outbreaks of severe acute BVD, which suggests that type 2 designation in itself does not imply enhanced virulence. Cattle properly vaccinated with type 1 BVDV vaccines appear to be protected from clinical disease.

Comparison of rebreeding policies for Ontario dairy herds

Net-revenues of rebreeding policies that differed in the maximum allowable days after calving for breeding were compared using data generated by a dynamic stochastic simulation model of Ontario dairy herds. Such comparisons benefit farmer decision support, as rebreeding decisions are important management choices. Rebreeding up to 168 d after calving only was least optimal. Hence, the rebreeding period should not be too short. At average and high herd fertility, a rebreeding policy under which cows with a mature equivalent milk production level lower than 80%, between 80 and 100%, and greater than 100% of the herd average were not rebred, bred up to 168 d after calving, and bred up to 250 d after calving, respectively, resulted in higher net-revenue than rebreeding policies that used a single cut-off for all cows. Differences in net-revenue between the optimal and the least optimal policy were $217.90 and $114.40 per cow per year for the lowest and highest simulated reproductive performance, respectively. At low herd fertility, rebreeding up to 364 d postpartum was optimal. However, at this level of performance emphasis should be given to improving fertility, rather than choice of rebreeding policy. Key words: Dairy cattle, simulation, economics, insemination policy, rebreeding policy

Associations Between Winter Herd Management Factors and Milk Protein Yield in Ontario Dairy Herds

A questionnaire was used to investigate associations between farm management practices in winter and milk protein yield. The questionnaire was completed by 500 dairy producers in Ontario, Canada in March 1994. A high positive correlation (0.96) existed between herd mean for protein yield per day per cow and herd mean for milk yield per day per cow. Therefore, most management practices that were associated with the farm mean for protein yield per day per cow were also associated with the farm mean for milk yield per day per cow. After adjustment for farm mean milk and fat yields, farms that housed dry cows as a separate group had higher mean protein yields than did herds that housed dry cows with the milking herd or the bred heifers. A positive association existed between herd mean for days of lactation and protein yield. Because of the correlation between milk and protein yields, these associations were of small magnitude. Thus, the potential benefit of progressive practices in herd management are primarily related to increased yields of milk and milk components in general rather than specifically to an increase in protein yield.

Estimation of Economic Values of Indices for Reproductive Performance in Dairy Herds Using Computer Simulation

Relationships between measures for reproductive performance and net revenue were studied using data that had been generated by a stochastic model in a computer simulation program for Ontario dairy herds. These measures included projected calving interval, involuntary culling rate, and adjusted calving interval. Adjusted calving interval was calculated by dividing the projected calving interval for pregnant cows by the fraction of the cows that were not culled for reproductive failure. The regression of adjusted calving interval on net revenue had an R2 of 0.72, which was higher than the R2 of 0.59 obtained by the regression of projected calving interval on net revenue. Hence, the estimation of financial losses from suboptimal reproductive performance was more accurate when adjusted calving interval was used as a measure of this performance than when projected calving interval was used. This difference is because projected calving interval did not consider cows that were culled for reproductive reasons, but those cows contributed to a reduction in profit because of suboptimal reproductive performance. The highest R2 (0.78) was obtained with a model that included projected calving interval and involuntary culling rate. However, use of that model might not be practical because herd operators differ in their ability to distinguish between involuntary and voluntary culling. The mean reduction in net revenue from a 1-d increase in adjusted calving interval was estimated at $4.7 (Canadian) per cow. This economic value was not significantly affected by level of adjusted calving interval, carcass price, feed costs, cost of a replacement heifer, or milk price.

Reasons that Dairy Cows Leave Home

Approximately 100,000 dairy cows are culled from dairy herds enrolled in milk recording through Ontario Dairy Herd Improvement (DHI) each year. The impact that these animals have on herd performance parameters, through their inclusion or exclusion, has been well established. As each cow removal is recorded, the producer is asked to designate one of 13 potential reasons for the cull. Once a year, a summary of all removals, including the removal reason and the days in milk (DIM) at removal, is provided to each producer. Questions have been raised about the utility of the removal report, and the validity of the information that it contains. The objective of this retrospective study was to validate, if possible, the reasons for removal and to suggest alternative strategies to recording and reporting dairy herd removal information.

Associations between farm management practices, productivity, and bovine leukemia virus infection in Ontario dairy herds

The objective of this study was to investigate the associations between herd-level bovine leukemia virus (BLV) status and herd-level management and production variables. The study population consisted of 1330 cows sampled from 102 Ontario dairy herds. The individual-cow prevalence of BLV infection in the population (based on AGID testing) was 23%, with 69.6% of herds having one or more positive animals. The herd-level explanatory variables were divided into two datasets containing winter housing variables and all non-seasonal variables, and summer housing variables and all non-seasonal variables. In both datasets, multivariable analyses found a negative association between herd-level milk production and BLV status, and positive associations between weaning age and purchasing animals from outside sources, and BLV status. Housing pre-weaned calves in hutches or separate calf buildings in either season was associated with an increased risk of BLV. The model containing winter housing variables also included positive associations between contact with older animals and BLV status, and between BLV status and the facilities used to house dry cows in the winter.

Relationship of production to reproductive performance in Ontario dairy cows: Herd level and individual animal descriptive statistics

Data were collected on reproductive, health and production events in 45 dairy herds distributed throughout southwestern and eastern Ontario. The data were collected between July 1990 and July 1993. The herds were serviced by 11 different veterinary practices. Herd size ranged from 19 to 231 lactating cows, but 90% of the herds consisted of fewer than 125 milking cows. Mean and median actual milk yields per cow per day were 46.0 and 52.3 lbs, respectively, with a minimum of 21.3 and maximum of 67.8 lbs. Mean and medium adjusted corrected milk yields were 56.0 and 62.3 lbs, reflecting mean and median average days in milk of 199.0 and 198.5 d, respectively. Mean and median days in milk at the first estrus were 85.1 and 83.9 d, respectively, at first service 94.0 and 88.9 d, and at conception 126.3 and 115.5 d. Mean and median percentages of days open > 120 were 27.7 and 23.1%, respectively. The mean estrus detection rate was 48.3%, with a minimum of 28.4% and a maximum of 64.2%. The mean first service conception rate was 48.2%, with a minimum of 27.0% and maximum of 72.1%. The mean overall conception rate was 46.7%, with a minimum of 29.8% and a maximum of 70.7%. Mean and median lactation lengths were 341.1 and 338.5 d and the mean and median average dry days were 62.0 and 67.0, respectively. The mean lactational removal rate was 20.6%, with a range of 4.3 to 40.5%. Reasons for culling were available for 1381 cows. Low production accounted for 23.7 % of the cullings; reproductive reasons, 20.6 %; dairy sales, 13.4%; mammary problems, 12.8%; and lameness, 9.9%. Lactational incidence rates for diseases were lower than previously reported for Ontario dairy herds. The most commonly used therapeutic agents were GnRH (10.5%) and PGF (11.7%).

Efficacy of Monensin in the Prevention of Subclinical Ketosis in Lactating Dairy Cattle

A field study was conducted to evaluate the efficacy of a monensin controlled release capsule (Rumensin CRC) for the prevention of subclinical ketosis in lactating dairy cattle. A total of 1011 cows from 25 Holstein dairy herds in southern Ontario were enrolled in this trial. Allotment of treatment and placebo capsules were randomised within farm and the capsules were administered approximately 21 days prior to expected calving date.

The prevalence of anti-bovine leukemia virus antibodies in dairy cows and associations with farm management practices, production and culling in Ontario

Samples and data from a serum bank involving 998 cows from 268 dairy herds in Ontario were used to estimate the prevalence of dairy cows with anti-bovine leukemia virus (BLV) antibodies, and to investigate associations between BLV serological test results and farm management practices, selected production indices, and culling. Sera were tested for anti-BLV antibodies by the BLV agar-gel immunodiffusion test. Data matched with the serum bank consisted of production records from the Ontario Dairy Herd Improvement Corporation, including breed-class average for milk, calving interval and somatic cell counts. Also matched with the serum bank were farm management data that had been collected by a mail survey during a previous cross-sectional study. The individual-cow prevalence of BLV seropositivity was 24.2%; herd prevalence was 47%. All analyses were adjusted for herd size. The odds of a herd having at least one seropositive cow were increased (relative to other categories) if cows calved in separate calving pens and if calves were raised in calf hutches in the winter months, and were decreased for farms on which cows calved in separate pens in the summer. No significant associations were detected between BLV seropositivity and milk production, somatic cell counts, age at disposal and culling. BLV-seropositive cows had a slight, statistically significant, increase in calving interval, after accounting for age and milk production in the most recent lactation.

Interrelationships among health problems and milk production from consecutive lactations in selected Ontario Holstein cows

Clinical health problems and milk production data from Holstein cows from 34 commercial south-western Ontario dairy herds, for which two subsequent lactations were available, were investigated. Associations of health problems and milk production from a previous lactation with the occurrence of health problems in the following lactation were investigated using a stepwise logistic regression procedure. Milk fever, teat injuries and mastitis were the only problems that were associated with previous milk production. Retained placenta, mastitis and ovarian cysts in a lactation were predictors of the same events happening in the subsequent lactation. Long lactations without ovarian problems increased the risk of udder oedema occurring during the following lactation. Reproductive infectious problems showed less capacity to predict health problems in the subsequent lactation than did non-infectious problems. Lactations with low milk production and older animals increased the risk of difficulty at the following calving.

Interrelationships of health problems and age on milk production in selected Ontario Holstein cows

The interrelationships of common clinical health problems with milk production in Holstein cows from 34 commercial south-western Ontario dairy herds were investigated. The data used were from 1588 lactations. Analyses were conducted on a data file containing all lactations and on a data file containing only lactations having 305 days in milk (305-d) standardized production. Stepwise multiple linear regressions (controlling for herd) were used to estimate the effect of health problems and age on milk production. The effects were investigated with respect to milk production of concurrent and subsequent lactations. Age was associated with a decrease in milk quality and an increase in risk of health problems and total milk produced. Milk fever, retained placenta, abortion and udder problems were detrimental to milk production. Metritis and ovarian cysts had a positive effect on concurrent milk production through an increase in days in milk and ovarian cysts also had a direct effect. The positive effect of ovarian problems on total milk yield in the concurrent lactation was followed by a detrimental effect on milk production in the subsequent lactation. Using only standardized milk production measures introduced a bias in the results, because the effect of short lactations was ignored.

Heifer Fertility and Its Relationship with Cow Fertility and Production Traits in Holstein Dairy Cattle

Breeding receipts from three AI units were merged with Ontario Dairy Herd Improvement Corporation and Record of Performance production records. Data comprised 53,705 heifer, 41,253 lactation 1, 14,688 lactation 2, and 3054 lactation 3 records by daughters of 2150 sires represented in 15,877 herd-year-seasons of birth. Three measures of heifer fertility, three measures of cow fertility, and three measures of production were investigated. Measures of heifer fertility were ages at first and last breeding and number of inseminations per conception. Cow fertility traits were days from calving to first breeding, days open, and number of inseminations per conception. Production traits were breed class average milk, breed class average fat, and fat percentage. Relationships among these nine traits for the first three lactations were estimated using a maximum likelihood multiple-trait procedure. The linear mixed model for each trait included fixed effects of herd-year-season of birth and genetic groups of sire and the random effect of sire. Transformations of the data for non-normality had no influence on the estimates of genetic and phenotypic parameters. The heritability of .12 for age at first insemination, which was higher than other heifer fertility traits, indicated that selection would result in genetic response. Genetic and phenotypic correlations between heifer fertility and cow fertility and production traits in all three lactations were not different from zero.There was no genetic antagonism between fertility and subsequent production traits.

An Analysis of the Relationships Among Stayability, Production, and Type in Canadian Milk-Recording Programs

Sire proofs for stayability to 17, 30, 43, and 55 mo of productive life were related to official production and type proofs in three milk-recording programs: 1) Ontario and Quebec Record of Performance, 2) supervised Ontario Dairy Herd Improvement and Quebec Dairy Herd Analysis Service, and 3) owner-sampler Dairy Herd Analysis Service. Simple correlations among all stayability traits and most production and type traits were significant and positive for the Record of Performance data set. Milk, fat yield, and a few type traits were positively correlated with stayability to 17 and 30 mo of productive life for the supervised data set. Only milk and fat yield had significant relationships with early stayability for the owner-sampler data. Highest multiple squared correlations in the Record of Performance analyses resulted when milk yield, final class or general appearance, and rump were included in the regression equations. For the supervised analyses, multiple squared correlation was highest when dairy character and feet and legs or mammary system were included in the prediction of stayability to 17 and 30 mo and when mammary system alone predicted stayability to 43 mo. For the owner-sampler analyses, only fat yield was included when predicting stayability to 17 and 30 mo.