Canadian Dairy Research Articles

Short communication: Evaluation of 5 different ELISA for the detection of bovine leukemia virus antibodies

Although Canadian dairy herds have been infected with bovine leukemia virus (BLV) for years, recent research has put new emphasis on the potential negative effects of this infection. Consequently, BLV control is becoming more favorable; however, BLV control cannot be successful without identifying infected animals. Bovicheck BLV (Biovet, Saint-Hyacinthe, QC, Canada) is currently the only assay licensed by the Canadian Centre for Veterinary Biologics. The first goal of this study was, therefore, to determine the reproducibility of the Bovicheck BLV assay for serum samples derived from Canadian cattle. The second goal was to evaluate and compare 5 different ELISA and determine their test characteristics using serum samples from Canadian herds. The considered ELISA were Bovicheck BLV, ID Screen BLV Competition (IDvet, Grabels, France), Idexx Leukosis Serum X2 Ab Test (Idexx Europe B.V., Hoofddorp, the Netherlands), Svanovir BLV gp51-Ab (Svanova, Uppsala, Sweden), and the Serelisa BLV Ab Mono Indirect (Synbiotics, Lyon, France). Eighty serum samples from Canadian cattle provided by Prairie Diagnostic Services (PDS; Saskatoon, SK, Canada) and an additional 80 serum samples from Canadian dairy and beef herds were used for the study. The Bovicheck BLV assay yielded the same results for all PDS-derived samples, implying a high level of reproducibility and robustness of this assay. Additionally, the comparison of the assays' results showed high agreement between assays, with Cohen's kappa values between κ = 0.91 and κ = 1. Furthermore, using original test results of the field samples as true status, relative diagnostic sensitivity and specificity were calculated. Relative diagnostic sensitivity of all tests was 100%. False-positive results were probable; therefore, the following relative diagnostic specificities were determined: 100% for Bovicheck BLV, Idexx Leukosis Serum X2, and Svanovir BLV; 95% for ID Screen BLV; and 97% for Serelisa BLV. When considering other test characteristics, ID Screen BLV is exceptional due to considerable practical advantages.

Demonstrating the Effect of Forage Source on the Carbon Footprint of a Canadian Dairy Farm Using Whole-Systems Analysis and the Holos Model: Alfalfa Silage vs. Corn Silage

Before recommending a feeding strategy for greenhouse gas (GHG) mitigation, it is important to conduct a holistic assessment of all related emissions, including from those arising from feed production, digestion of these feeds, managing the resulting manure, and other on-farm production processes and inputs. Using a whole-systems approach, the Holos model, and experimentally measured data, this study compares the effects of alfalfa silage- versus corn silage-based diets on GHG estimates in a simulated Canadian dairy production system. When all emissions and sources are accounted for, the differences between the two forage systems in terms of overall net GHG emissions were minimal. Utilizing the functional units of milk, meat, and total energy in food products generated by the system, the comparison demonstrates very little difference between the two silage production systems. However, the corn silage system generated 8% fewer emissions per kg of protein in food products as compared to the alfalfa silage system. Exploratory analysis of the impact of the two silage systems on soil carbon showed alfalfa silage has greater potential to store carbon in the soil. This study reinforces the need to utilize a whole-systems approach to investigate the interrelated effects of management choices. Reported GHG reduction factors cannot be simply combined additively because the interwoven effects of management choices cascade through the entire system, sometimes with counter-intuitive outcomes. It is necessary to apply this whole-systems approach before implementing changes in management intended to reduce GHG emissions and improve sustainability.

Producer perceptions of manual and automated milk feeding systems for dairy calves in Canada

As part of a cross-sectional survey, Canadian dairy producers were asked a set of questions to (1) determine factors that influenced them to continue using manual milk feeding (MMF) systems or to switch to automated milk feeding (AMF) and (2) investigate producers’ perceived advantages and disadvantages regarding both feeding systems. A total of 670 responses were received. Among respondents, 16% used AMF and 84% used MMF. The four most frequent factors that producers reported as important in motivating them to switch to AMF were to raise better calves, offer more milk to calves, reduce labor, and improve working conditions. For MMF farms, investment in equipment and group housing facilities, as well as farm size, were the primary reasons reported for their continued use of MMF systems. The principal perceived advantages of having an AMF were that calves are able to express natural behaviors and drink more milk without increased labor input. For MMF systems, the main perceived advantage was related to easier identification of sick calves. Results provide insights into factors affecting the choice of calf feeding methods by dairy producers, and improve understanding of producers’ needs and expectations regarding calf management and adoption of technology.

Dairy producers' attitudes toward reproductive management and performance on Canadian dairy farms

The objectives of this study were to explore Canadian dairy producers' attitudes toward reproductive performance and challenges they perceive to be related to reproduction and reproductive management practices. A survey in both English and French was developed, validated, and administered to Canadian dairy farmers between March and May 2014 to collect general farm, reproduction management, and reproductive performance data, as well as opinions and perceptions about different facets of reproduction. Associations between management practices and the perceived importance of reproduction were tested using a logistic regression model. Thematic network analysis was used to identify themes from the open-ended survey questions about challenges concerning reproduction. Finally, questions that were answered on a Likert scale were graphically represented using diverging stacked bar charts. A total of 832 questionnaires were completed online and by mail, which represents approximately 7% of all dairy farms in Canada. Respondents that ranked reproduction in lactating dairy cows as 1 of the 3 most important challenges faced on their farm (66%) were more likely to house their lactating cows in a tiestall and to have a lower herd annual 21-d pregnancy rate. Estrus detection and conception risk were 2 major themes raised and discussed by the respondents. Other concepts, including housing and milk production, were also perceived to affect estrus detection and conception risk. Whereas analysis of open-ended survey questions does not allow for quantification of the importance of different themes in the sample as a whole, it does show that respondents are aware of the multifactorial complexity of reproductive challenges on dairy farms. Improving performance was the main factor influencing decisions concerning reproduction for 80% of the respondents, and they adopted tools and technologies such as synchronization programs and automated activity monitoring systems to improve herd reproductive performance. More research is required to describe how this performance is defined and perceived by the respondents, and how it relates to the actual variability of performance (i.e., pregnancy rate) among farms.

Comparison of treatment records and inventory of empty drug containers to quantify antimicrobial usage in dairy herds

Assessment of antimicrobial use (AMU) is vital for interpreting the origin of changes in antimicrobial resistance (AMR). The objectives of the present study were to estimate the association between AMU determined using on-farm treatment records (TR) and inventory of empty drug containers (INV). Herds were selected to represent Canadian dairy farms. Producers were asked to record animal health events and treatments on a standard General Health Event form. For inventory data, 40-L receptacles were placed at various locations considered convenient to deposit all empty drug containers. Antimicrobial defined-daily dosages (ADD) were calculated for 51 Canadian herds using the 2 methods. Estimation of AMU was 31,840 ADD using the INV and 14,487 ADD using the TR, indicating that for every TR entry, 2.20 times more treatments were observed using the INV. Mastitis, reproductive conditions, and dry cow therapy were the most frequent reasons for antimicrobial therapy when assessing TR. For all antimicrobials evaluated, mean ADD was higher using the INV versus TR. Regardless, a strong positive correlation (0.80) was observed between the 2 methods, indicating that herds with increased number of ADD recorded using the INV also had increased number of ADD recorded using TR. Furthermore, a positive association was observed for the 6 most commonly used antimicrobials. In comparison to methods used in surveillance programs on AMU in livestock that assume a constant use in all herds (i.e., sales data), INV provided a herd-level specific quantity of AMU positively correlated with AMU recorded at the animal level in general. The INV was easy to implement and provided a measure of total AMU in the herd. Availability of such information would be valuable for interpreting changes in AMR at the herd level and enabling evaluation of interventions for decreasing AMR.

Producer estimates of prevalence and perceived importance of lameness in dairy herds with tiestalls, freestalls, and automated milking systems

Lameness is one of the most important welfare and productivity concerns in the dairy industry. Our objectives were to obtain producers' estimates of its prevalence and their perceptions of lameness, and to investigate how producers monitor lameness in tiestall (TS), freestall with milking parlor (FS), and automated milking system (AMS) herds. Forty focal cows per farm in 237 Canadian dairy herds were scored for lameness by trained researchers. On the same day, the producers completed a questionnaire. Mean herd-level prevalence of lameness estimated by producers was 9.0% (±0.9%; ±SE), whereas the researchers observed a mean prevalence of 22.2% (±0.9%). Correlation between producer- and researcher-estimated lameness prevalence was low (r = 0.19) and mean researcher prevalence was 1.6, 1.8, and 4.1 times higher in AMS, FS, and TS farms, respectively. A total of 48% of producers thought lameness was a moderate or major problem in their herds (TS = 34%; AMS =53%; FS = 59%). One third of producers considered lameness the highest ranked health problem they were trying to control, whereas two-thirds of producers (TS = 43%; AMS = 63%; FS = 71%) stated that they had made management changes to deal with lameness in the past 2 yr. Almost all producers (98%) stated they routinely check cows to identify new cases of lameness; however, 40% of producers did not keep records of lameness (AMS = 24%; FS = 23%; TS = 60%). A majority (69%) of producers treated lame cows themselves immediately after detection, whereas 13% relied on hoof-trimmer or veterinarians to plan treatment. Producers are aware of lameness as an issue in dairy herds and almost all monitor lameness as part of their daily routine. However, producers underestimate lameness prevalence, which highlights that lameness detection continues to be difficult in in all housing systems, especially in TS herds. Training to improve detection, record keeping, identification of farm-specific risk factors, and treatment planning for lame cows is likely to help decrease lameness prevalence.

Comparison of online, hands-on, and a combined approach for teaching cautery disbudding technique, including administration of a cornual nerve block, to dairy producers

The use of pain control for disbudding and dehorning is important from both an animal- and industry-centered perspective. Best practices include the use of local anesthetic, commonly given as a cornual nerve block, and a non-steroidal anti-inflammatory drug (NSAID). Approximately 40% of Canadian dairy producers do not use local anesthesia, perhaps in part due to lack of knowledge regarding cornual nerve block technique. Although this skill is typically learned in person from a veterinarian, alternative or adjunct methods may be useful for hard to reach producers. The objective of this trial was to determine if there were differences in the efficacy of online training, hands-on training, and a combined approach for teaching producers to successfully administer a cornual nerve block and disbud a calf less than 12 weeks of age.

Projected impact of future climate conditions on the agronomic and environmental performance of Canadian dairy farms

Climate change is expected to increase agricultural productivity in Canada and in other northern countries but this increase will likely affect the environmental performance of dairy farms, one of the most important agricultural sectors in Canada. The objective of this study was to project the impact of climate change on the agronomic and environmental performance of a virtual dairy farm in each of three climatically contrasting areas of Canada through near future (2020–2049) and distant future (2050–2079) periods, using the Integrated Farm System Model (IFSM) and three climate models (CanESM2, CanRCM4, and HadGEM2). Under future climate conditions and relative to a reference period (1971–2000), projected yields of perennial forages and warm-season crops increased, whereas those of small-grain cereals decreased slightly. Projected ammonia emissions increased on virtual farms of the three areas and in all future scenarios (+18% to +54%). Methane emissions from manure storage increased (+26% to +120%), whereas those from enteric fermentation and field manure application decreased. Projected farm N2O emissions changed only slightly relative to the reference period. Fossil fuel CO2 emissions related to field operations increased slightly, due to a larger number of forage cuts per year in future scenarios, but CO2 emissions related to grain drying decreased substantially. Projected losses of P increased on virtual farms of the three areas. The projected reactive N footprint of dairy farms in future scenarios varied more (−15% to +46%) relative to the reference period than the C footprint (−5% to +9%). Although greenhouse gas mitigation should be a priority for dairy farms under future climate conditions, it should not overshadow the need for strategies to reduce reactive N losses.

Bacteriocins of Non-aureus Staphylococci Isolated from Bovine Milk.

Non-aureus staphylococci (NAS), the bacteria most commonly isolated from the bovine udder, potentially protect the udder against infection by major mastitis pathogens due to bacteriocin production. In this study, we determined the inhibitory capability of 441 bovine NAS isolates (comprising 26 species) against bovine Staphylococcus aureus Furthermore, inhibiting isolates were tested against a human methicillin-resistant S. aureus (MRSA) isolate using a cross-streaking method. We determined the presence of bacteriocin clusters in NAS whole genomes using genome mining tools, BLAST, and comparison of genomes of closely related inhibiting and noninhibiting isolates and determined the genetic organization of any identified bacteriocin biosynthetic gene clusters. Forty isolates from 9 species (S. capitis, S. chromogenes, S. epidermidis, S. pasteuri, S. saprophyticus, S. sciuri, S. simulans, S. warneri, and S. xylosus) inhibited growth of S. aureus in vitro, 23 isolates of which, from S. capitis, S. chromogenes, S. epidermidis, S. pasteuri, S. simulans, and S. xylosus, also inhibited MRSA. One hundred five putative bacteriocin gene clusters encompassing 6 different classes (lanthipeptides, sactipeptides, lasso peptides, class IIa, class IIc, and class IId) in 95 whole genomes from 16 species were identified. A total of 25 novel bacteriocin precursors were described. In conclusion, NAS from bovine mammary glands are a source of potential bacteriocins, with >21% being possible producers, representing potential for future characterization and prospective clinical applications.IMPORTANCE Mastitis (particularly infections caused by Staphylococcus aureus) costs Canadian dairy producers $400 million/year and is the leading cause of antibiotic use on dairy farms. With increasing antibiotic resistance and regulations regarding use, there is impetus to explore bacteriocins (bacterially produced antimicrobial peptides) for treatment and prevention of bacterial infections. We examined the ability of 441 NAS bacteria from Canadian bovine milk samples to inhibit growth of S. aureus in the laboratory. Overall, 9% inhibited growth of S. aureus and 58% of those also inhibited MRSA. In NAS whole-genome sequences, we identified >21% of NAS as having bacteriocin genes. Our study represents a foundation to further explore NAS bacteriocins for clinical use.

Short communication: Prevalence of digital dermatitis in Canadian dairy cattle classified as high, average, or low antibody- and cell-mediated immune responders

Lameness is a major animal welfare issue affecting Canadian dairy producers, and it can lead to production, reproduction, and health problems in dairy cattle herds. Although several different lesions affect dairy cattle hooves, studies show that digital dermatitis is the most common lesion identified in Canadian dairy herds. It has also been shown that dairy cattle classified as having high immune response (IR) have lower incidence of disease compared with those animals with average and low IR; therefore, it has been hypothesized that IR plays a role in preventing infectious hoof lesions. The objective of this study was to compare the prevalence of digital dermatitis in Canadian dairy cattle that were classified for antibody-mediated (AMIR) and cell-mediated (CMIR) immune response. Cattle (n = 329) from 5 commercial dairy farms in Ontario were evaluated for IR using a patented test protocol that captures both AMIR and CMIR. Individuals were classified as high, average, or low responders based on standardized residuals for AMIR and CMIR. Residuals were calculated using a general linear model that included the effects of herd, parity, stage of lactation, and stage of pregnancy. Hoof health data were collected from 2011 to 2013 by the farm's hoof trimmer using Hoof Supervisor software (KS Dairy Consulting Inc., Dresser, WI). All trim events were included for each animal, and lesions were assessed as a binary trait at each trim event. Hoof health data were analyzed using a mixed model that included the effects of herd, stage of lactation (at trim date), parity (at trim date), IR category (high, average, and low), and the random effect of animal. All data were presented as prevalence within IR category. Results showed that cows with high AMIR had significantly lower prevalence of digital dermatitis than cattle with average and low AMIR. No significant difference in prevalence of digital dermatitis was observed between high, average, and low CMIR cows. These results indicate that having more robust AMIR is associated with lower prevalence of digital dermatitis hoof lesions.

Genetic analysis for quality of frozen embryos produced by Holstein cattle donors in Canada

The number of embryos produced by Holstein donors has been shown to be heritable, so it could be possible to genetically select for this trait to improve the efficiency of the assisted reproductive technology (ART) in dairy cattle. Another important parameter to consider for achieving good results from ART is embryo quality because embryos of good quality have more chance of producing live offspring. The possibility of using genetic selection for increasing the quality of embryo produced from ART has yet to be assessed. The objective of this study was, therefore, to perform a genetic analysis of embryo quality of Holstein donors in Canada using data recorded by Holstein Canada. The data set used was missing quality score data for embryos transferred fresh into a recipient, so the analyses were only performed for frozen embryos. With most traits in the Canadian dairy industry being evaluated with linear models, embryo quality was also evaluated with this class of models. However, considering the categorical nature of embryo quality, a threshold model was also evaluated. Embryo quality data were analyzed with either a univariate linear animal model or a univariate binomial threshold animal model. Genetic parameters estimated from the different models were comparable. A low heritability was found for the donor (0.04 ± <0.01) and the service sire (0.02 ± <0.01), but the repeatability estimate for the donor was higher (0.17), indicating that it was worthwhile to use a repeated records model. Overall, considering the low genetic parameters estimated, slow genetic progress is expected for the quality of frozen embryos produced by Canadian Holstein donors. Rank correlations were calculated between breeding values estimated from different models. High correlations were found between all models, indicating that no substantial re-ranking of the animals is expected from the different models. So, even though a threshold model is better suited for the analysis of categorical data, a linear model could be used for the analysis of embryo quality because it is less computationally demanding.

Whole Genome Sequencing of a Canadian Bovine Gammaherpesvirus 4 Strain and the Possible Link between the Viral Infection and Respiratory and Reproductive Clinical Manifestations in Dairy Cattle.

Bovine gammaherpesvirus 4 (BoHV-4) is a herpesvirus widespread in cattle populations, and with no clear disease association. Its genome contains a long unique coding region (LUR) flanked by polyrepetitive DNA and 79 open reading frames (ORFs), with unique 17 ORFs, named Bo1 to Bo17. In 2009, a BoHV-4 strain was isolated (FMV09-1180503: BoHV-4-FMV) from cattle with respiratory disease from Quebec, Canada, and its LUR was sequenced. Despite the overall high similarity, BoHV-4-FMV had the most divergent LUR sequence compared to the two known BoHV-4 reference strain genomes; most of the divergences were in the Bo genes and in the repeat regions. Our phylogenetic analysis based on DNA polymerase and thymidine kinase genes revealed that virus isolate was BoHV-4 gammaherpesvirus and clustered it together with European BoHV-4 strains. Because BoHV-4-FMV was isolated from animals presenting respiratory signs, we have updated the BoHV-4 Canadian cattle seroprevalence data and tried to find out whether there is a link between clinical manifestation and BoHV-4 seropositivity. An indirect immunofluorescence assay (IFA) was performed with nearly 200 randomized sera of dairy cattle from two Canadian provinces, Quebec (n = 100) and Ontario (n = 91). An additional set of sera obtained from Quebec, from the healthy (n = 48) cows or from the animals experiencing respiratory or reproductive problems (n = 75), was also analyzed by IFA. BoHV-4 seroprevalence in Canadian dairy cattle was 7.9% (Quebec: 6% and Ontario: 9.9%). Among animals from the Quebec-based farms, diseased animals showed higher BoHV-4 seropositivity than healthy animals (P < 0.05), with a significant 2.494 odds ratio of being seropositive in sick compared to healthy animals. Although there is no established direct link between BoHV-4 and specific diseases, these seroprevalence data suggest the possible involvement of BoHV-4 in dairy cattle diseases.

Nitrogen efficiency of eastern Canadian dairy herds: Effect on production performance and farm profitability.

Nitrogen efficiency (milk N/dietary N; NE) can be used as a tool for the nutritional, economic, and environmental management of dairy farms. The aim of this study was to identify the characteristics of herds with varying NE and assess the effect on farm profitability. One hundred dairy herds located in Québec, Canada, comprising on average 42 ± 18 cows in lactation were visited from October 2014 to June 2015. Feed intake was measured over 24 h. Samples of each feedstuff were taken and sent to a commercial laboratory for analysis of chemical composition. Feeding management and feed prices were recorded. Milk yield was recorded and milk samples were collected over 2 consecutive milkings. Fat, protein, and milk urea N were analyzed. Balances of metabolizable protein (MP; MP supply - MP requirements) and rumen degradable protein (RDP; RDP supply - RDP requirement) were calculated. A hierarchical cluster analysis was conducted and allowed grouping the farms by their NE. Four clusters were identified with an average NE of 22.1 (NE22), 26.9 (NE27), 30.0 (NE30), and 35.8% (NE36). Herds in clusters NE30 and NE36 were fed diets with greater concentrations of starch, net energy for lactation, and nonfiber carbohydrates than those in the other 2 clusters. Moreover, the average proportion of corn silage was lower for herds in cluster NE22 compared with NE30 and NE36 (8.23 vs. 31.8 and 31.3% of total forages, respectively). In addition, crude protein of the diets declined from an average of 16.0 to 14.9% with increasing NE among clusters. Average dry matter intake declined from 26.1 to 22.5 kg/d as NE of clusters increased. Herds in cluster NE22 had lower yields of milk (28.7 vs. 31.8 kg/d), fat (1.15 vs. 1.29 kg/d), and protein (0.94 vs. 1.05 kg/d) than the other clusters. Also, milk urea N was greater for farms in cluster NE22 (13.2 mg/dL) than for farms in the other clusters (11.4 mg/dL). Furthermore, MP and RDP balances decreased from 263.2 to -153.7 g/d and from 594.7 to 486.9 g/d, respectively, with increasing NE among clusters. Income over feed cost increased from $14.3 to $17.3/cow per day (Can$) as NE among clusters augmented. Results from this study showed that some farms were able to achieve high NE by using lower levels of dietary N and having cows with lower DMI while maintaining milk performance. These farms had a potentially lower environmental impact, and they were more profitable.

Management practices for male calves on Canadian dairy farms.

Morbidity, mortality, and antimicrobial use and resistance are major concerns in the rearing of male dairy calves, so information to support disease prevention is important. The objective of this cross-sectional study was to describe management practices associated with the care of male calves during their first days of life on Canadian dairy farms. A survey was completed by dairy producers across Canada between March 1 and April 30, 2015. The survey included 192 questions covering producer background, farm characteristics, biosecurity practices, disease prevalence, calf health, animal welfare, lameness, milking hygiene, reproduction, and Internet and social media use. A total of 1,025 surveys were completed online, by telephone, or by mail, representing 9% of all dairy farms in Canada. Five percent of respondents (n = 49) answered that they had euthanized at least 1 male calf at birth in the previous year, and blunt force trauma was commonly used in these cases. The majority of respondents always fed colostrum to male calves; however, 9% (n = 80) did not always feed colostrum. Almost 40% (n = 418) of respondents reported always dipping the navels of male calves, 12% (n = 123) vaccinated male calves, and 17% (n = 180) did not provide the same quantity of feed to male calves as heifer calves. The care of male calves differed greatly depending on the geographical region of the respondents. However, some regional effects may be confounded by economic conditions and the logistics of marketing male dairy calves in different parts of the country. Herd size was another important variable in many aspects of the management of male calves on dairy farms. Larger herd sizes were more likely to use an appropriate method of euthanasia at birth but were less likely to always feed colostrum to their male calves or feed them the same as female calves. Familiarity with the Code of Practice for the Care and Handling of Dairy Cattle (National Farm Animal Care Council) by respondents was associated with better care of male calves on dairy farms. The results of this survey suggest that the treatment of male dairy calves on Canadian dairy farms varies and that there are opportunities to improve the health management of male calves on the farms of origin.

Whole-Genome Sequence Analysis of Antimicrobial Resistance Genes in Streptococcus uberis and Streptococcus dysgalactiae Isolates from Canadian Dairy Herds.

The objectives of this study are to determine the occurrence of antimicrobial resistance (AMR) genes using whole-genome sequence (WGS) of Streptococcus uberis (S. uberis) and Streptococcus dysgalactiae (S. dysgalactiae) isolates, recovered from dairy cows in the Canadian Maritime Provinces. A secondary objective included the exploration of the association between phenotypic AMR and the genomic characteristics (genome size, guanine–cytosine content, and occurrence of unique gene sequences). Initially, 91 isolates were sequenced, and of these isolates, 89 were assembled. Furthermore, 16 isolates were excluded due to larger than expected genomic sizes (>2.3 bp × 1,000 bp). In the final analysis, 73 were used with complete WGS and minimum inhibitory concentration records, which were part of the previous phenotypic AMR study, representing 18 dairy herds from the Maritime region of Canada (1). A total of 23 unique AMR gene sequences were found in the bacterial genomes, with a mean number of 8.1 (minimum: 5; maximum: 13) per genome. Overall, there were 10 AMR genes [ANT(6), TEM-127, TEM-163, TEM-89, TEM-95, Linb, Lnub, Ermb, Ermc, and TetS] present only in S. uberis genomes and 2 genes unique (EF-TU and TEM-71) to the S. dysgalactiae genomes; 11 AMR genes [APH(3′), TEM-1, TEM-136, TEM-157, TEM-47, TetM, bl2b, gyrA, parE, phoP, and rpoB] were found in both bacterial species. Two-way tabulations showed association between the phenotypic susceptibility to lincosamides and the presence of linB (P = 0.002) and lnuB (P < 0.001) genes and the between the presence of tetM (P = 0.015) and tetS (P = 0.064) genes and phenotypic resistance to tetracyclines only for the S. uberis isolates. The logistic model showed that the odds of resistance (to any of the phenotypically tested antimicrobials) was 4.35 times higher when there were >11 AMR genes present in the genome, compared with <7 AMR genes (P < 0.001). The odds of resistance was lower for S. dysgalactiae than S. uberis (P = 0.031). When the within-herd somatic cell count was >250,000 cells/mL, a trend toward higher odds of resistance compared with the baseline category of <150,000 cells/mL was observed. When the isolate corresponded to a post-mastitis sample, there were lower odds of resistance when compared with non-clinical isolates (P = 0.01). The results of this study showed the strength of associations between phenotypic AMR resistance of both mastitis pathogens and their genotypic resistome and other epidemiological characteristics.

Prevalence of non-aureus staphylococci species causing intramammary infections in Canadian dairy herds

Non-aureus staphylococci (NAS), the microorganisms most frequently isolated from bovine milk worldwide, are a heterogeneous group of numerous species. To establish their importance as a group, the distribution of individual species needs to be determined. In the present study, NAS intramammary infection (IMI) was defined as a milk sample containing ≥1,000 cfu/mL in pure or mixed culture that was obtained from a cohort of cows assembled by the Canadian Bovine Mastitis Research Network. Overall, 6,213 (6.3%) of 98,233 quarter-milk samples from 5,149 cows and 20,305 udder quarters were associated with an NAS IMI. Of the 6,213 phenotypically identified NAS isolates, 5,509 (89%) were stored by the Canadian Bovine Mastitis Research Network Mastitis Pathogen Collection and characterized using partial sequencing of the rpoB housekeeping gene, confirming 5,434 isolates as NAS. Prevalence of each NAS species IMI was estimated using Bayesian models, with presence of a specific NAS species as the outcome. Overall quarter-level NAS IMI prevalence was 26%. The most prevalent species causing IMI were Staphylococcus chromogenes (13%), Staphylococcus simulans (4%), Staphylococcus haemolyticus (3%), Staphylococcus xylosus (2%), and Staphylococcus epidermidis (1%). The prevalence of NAS IMI as a group was highest in first-parity heifers and was evenly distributed throughout cows in parities ≥2. The IMI prevalence of some species such as S. chromogenes, S. simulans, and S. epidermidis differed among parities. Overall prevalence of NAS IMI was 35% at calving, decreased over the next 10 d, and then gradually increased until the end of lactation. The prevalence of S. chromogenes, Staphylococcus gallinarum, Staphylococcus cohnii, and Staphylococcus capitis was highest at calving, whereas the prevalence of S. chromogenes, S. haemolyticus, S. xylosus, and S. cohnii increased during lactation. Although the overall prevalence of NAS IMI was similar across barn types, the prevalence of S. simulans, S. xylosus, S. cohnii, Staphylococcus saprophyticus, S. capitis, and Staphylococcus arlettae IMI was higher in tiestall barns; the prevalence of S. epidermidis IMI was lowest; and the prevalence of S. chromogenes and Staphylococcus sciuri IMI was highest in bedded-pack barns. Staphylococcus simulans, S. epidermidis, S. xylosus, and S. cohnii IMI were more prevalent in herds with intermediate to high bulk milk somatic cell count (BMSCC) and S. haemolyticus IMI was more prevalent in herds with high BMSCC, whereas other common NAS species IMI were equally prevalent in all 3 BMSCC categories. Distribution of NAS species IMI differed among the 4 regions of Canada. In conclusion, distribution differed considerably among NAS species IMI; therefore, accurate identification (species level) is essential for studying NAS epidemiology.

Prediction of milk fatty acid content with mid-infrared spectroscopy in Canadian dairy cattle using differently distributed model development sets

The fatty acid profile of milk is a prevailing issue due to the potential negative or positive effects of different fatty acids to human health and nutrition. Mid-infrared spectroscopy can be used to obtain predictions of otherwise costly fatty acid phenotypes in a widespread and rapid manner. The objective of this study was to evaluate the prediction of fatty acid content for the Canadian dairy cattle population from mid-infrared spectral data and to compare the results produced by altering the partial least squares (PLS) model development set used. The PLS model development sets used to develop the predictions were reference fatty acids expressed as (1) grams per 100 g of fatty acid, (2) grams per 100 g of milk, (3) the natural logarithmic transform of grams per 100 g of milk, and (4) subsets of samples randomly selected by removing excess records around the mean to present a more uniform distribution, repeated 10 times. Gas chromatography measured fatty acid concentration and spectral data for 2,023 milk samples of 373 cows from 4 breeds and 44 herds were used in the model development. The coefficient of determination of cross-validation (Rcv2) increased when fatty acids were expressed on a per 100 g of milk basis compared with on a per 100 g of fat basis for all examined fatty acids. The logarithmic transformation used to create a more Gaussian distribution in the development set had little effect on the prediction accuracy. The individual fatty acids C12:0, C14:0, C16:0, C18:0, C18:1n-9 cis, and saturated, monounsaturated, unsaturated, short-chain, medium-chain, and long-chain fatty acid groups had (Rcv2) greater than 0.70. When model development was performed with subsets of the original samples, slight increases in (Rcv2) values were observed for the majority of fatty acids. The difference in (Rcv2) between the top- and bottom-performing prediction equation across the different subsets for a single predicted fatty acid was on average 0.055 depending on which samples were randomly selected to be used in the PLS model development set. Predictions for fatty acids with high accuracies can be used to monitor fatty acid contents for cows in milk recording programs and possibly for genetic evaluation.

Comparing the Impact of Saturated Fatty Acids from Different Dairy Sources on LDL Particle Size Phenotype

BackgroundLow‐density lipoproteins (LDL) constitute a heterogeneous class of lipoproteins among which small and dense LDL may be more atherogenic than large LDL particles, independent of cholesterol concentrations. The aim of this study was to examine how consumption of saturated fat (SFA) from different dairy sources modifies the LDL particle size phenotype compared with other dietary fats (monounsaturated ‐ MUFA and polyunsaturated fat‐ PUFA) and a low‐fat diet/high carbohydrate diet.MethodsA randomized crossover controlled trial was conducted in 92 men and women with abdominal obesity and relatively low HDL‐C. Subjects were assigned to sequences of 5 isoenergetic diets of 4 weeks each (Table): 1) a diet rich in SFA from cheese (CHEESE); a diet rich in SFA from butter (BUTTER); a diet rich in MUFA; a diet rich in PUFA and a low‐fat, high carbohydrate diet (CHO). All foods were provided to the participants during the experimental phases. Features of the LDL particle size phenotype (mean LDL particle size, proportion of small and large) were assessed by one dimension nondenaturing polyacrylamide gel electrophoresis.ResultsLDL particle size at baseline (mean±SD) in women was larger than in men (252.24±2.85 vs. 251.67±3.49, p=0.04), although differences were no longer significant after adjustment for waist circumference. The CHEESE diet had no significant impact on all phenotypic measures of LDL particle size compared with BUTTER, CHO, MUFA and PUFA. Consumption of the BUTTER diet significantly increased LDL mean size compared with CHO (p=0.021) and MUFA (p=0.005). The increase in mean LDL size with BUTTER was more apparent among individuals with small LDL particles at baseline than among those with large LDL (P treatment × baseline LDL size=0.047). There was no difference in the distribution of small and large LDL particles among diets.ConclusionsResults from this full‐feeding study suggest 1‐ that SFA from butter and cheese have similar effects on features of the LDL particle size phenotype, and 2‐ that consumption of SFA from butter may be associated with less atherogenic LDL particles. These data are partly consistent with the fact that consumption of cheese and butter are not associated with an increased risk of cardiovascular disease.Support or Funding InformationSource of Research Support : Dairy Research Cluster Initiative (Dairy Farmers of Canada, Agriculture and Agri‐Food Canada, the Canadian Dairy Network and the Canadian Dairy Commission). Macronutrient (% energy), calcium and sodium content of experimental diets CHEESE BUTTER MUFA PUFA CHO Lipids (%) 32.0 32.0 32.0 32.0 25.0 SFA (%) 12.6 12.4 5.8 5.8 5.8 MUFA (%) 12.5 12.3 19.6 12.6 12.6 PUFA (%) 4.8 4.8 4.8 11.5 4.8 Carbohydrates (%) 51.9 52.0 51.9 51.9 58.9 Proteins (%) 16.0 16.0 16.0 16.0 16.0 Calcium (mg/2500 kcal) 1261 811 812 812 842 Sodium (mg/2500 kcal) 2482 2480 2479 2479 2485 Fibers (g/2500kcal) 31 31 31 31 31

Comparing the Impact of Saturated Fatty acids from Different Dairy Sources on the proteome of High Density Lipoproteins

BackgroundHigh‐density lipoproteins (HDL) play different protective roles in the etiology of atherosclerosis. The anti‐inflammatory and antioxidant properties of HDL are of particular interest in that regard. Because dietary saturated fatty acids (SFAs) are known to increase HDL‐C concentrations, we investigated how consumption of SFAs from different dairy sources modifies HDL functions as reflected by changes in HDL proteomic profile compared to other dietary fats (monounsaturated ‐ MUFAs and polyunsaturated ‐ PUFAs) and a low‐fat diet/high carbohydrate diet.MethodsA randomized crossover controlled trial was conducted in 42 men and women with abdominal obesity and relatively low HDL‐C. Subjects were assigned to sequences of 5 isoenergetic diets of 4 weeks each (Table): 1) a diet rich in SFA from cheese (CHEESE); a diet rich in SFAs from butter (BUTTER); a diet rich in MUFA; a diet rich in PUFA and a low‐fat, high carbohydrate diet (CHO). All foods were provided to the participants during the experimental phases. HDLs' proteome was assessed by mass‐spectrometry (MS) after isolation of the HDL fraction by sequential ultracentrifugation after each treatment.ResultsUsing conservative analytical procedures, a total of 66 unique proteins were quantified in the HDL fraction. There was no difference between any diets in the levels of HDL proteins known to be involved in oxidative processes and acute phase response. CHEESE increased levels of HDL proteins related to immune response, namely angiotensinogen (vs. BUTTER, P&lt;0.05), and Ig gamma‐1 chain C region, platelet basic protein and vitronectin (vs. CHO diet, P&lt;0.05). BUTTER increased levels of vitronectin (vs. CHO, P&lt;0.05) but had no effect on other immune response proteins. Apolipoproteins A‐IV and C‐IV, which play key roles in cholesterol homeostasis, were significantly increased after CHEESE (vs. CHO, P&lt;0.05) but not after BUTTER.ConclusionsThis full‐feeding study suggest that SFAs from butter and cheese do not significantly influence the antioxidant and anti‐inflammatory properties of HDL compared with other dietary fats and CHO. However, immune response and cholesterol homeostasis proteins were modified by cheese but not by butter in comparison with CHO, consistent with a modest food matrix effect modifying the impact of SFAs on cardiometabolic health. Functional studies are necessary to confirm these findings.Support or Funding InformationNational Dairy Council, Dairy Research Cluster Initiative (Dairy Farmers of Canada, Agriculture and Agri‐Food Canada, the Canadian Dairy Network and the Canadian Dairy Commission). Macronutrient (% energy), calcium and sodium content of experimental diets CHEESE BUTTER MUFA PUFA CHO Lipids (%) 32.0 32.0 32.0 32.0 25.0 SFA (%) 12.6 12.4 5.8 5.8 5.8 MU FA (%) 12.5 12.3 19.6 12.6 12.6 PUFA (%) 4.8 4.8 4.8 11.5 4.8 Carbohydrates (%) 51.9 52.0 51.9 51.9 58.9 Proteins (%) 16.0 16.0 16.0 16.0 16.0 Calcium (mg/2500 kcal) 1261 811 812 812 842 Sodium (mg/2500 kcal) 2482 2480 2479 2479 2485 Fibers (g/2500 kcal) 31 31 31 31 31

Genetic analysis of groups of mid-infrared predicted fatty acids in milk

The objective of this study was to investigate genetic variability of mid-infrared predicted fatty acid groups in Canadian Holstein cattle. Genetic parameters were estimated for 5 groups of fatty acids: short-chain (4 to 10 carbons), medium-chain (11 to 16 carbons), long-chain (17 to 22 carbons), saturated, and unsaturated fatty acids. The data set included 49,127 test-day records from 10,029 first-lactation Holstein cows in 810 herds. The random regression animal test-day model included days in milk, herd-test date, and age-season of calving (polynomial regression) as fixed effects, herd-year of calving, animal additive genetic effect, and permanent environment effects as random polynomial regressions, and random residual effect. Legendre polynomials of the third degree were selected for the fixed regression for age-season of calving effect and Legendre polynomials of the fourth degree were selected for the random regression for animal additive genetic, permanent environment, and herd-year effect. The average daily heritability over the lactation for the medium-chain fatty acid group (0.32) was higher than for the short-chain (0.24) and long-chain (0.23) fatty acid groups. The average daily heritability for the saturated fatty acid group (0.33) was greater than for the unsaturated fatty acid group (0.21). Estimated average daily genetic correlations were positive among all fatty acid groups and ranged from moderate to high (0.63-0.96). The genetic correlations illustrated similarities and differences in their origin and the makeup of the groupings based on chain length and saturation. These results provide evidence for the existence of genetic variation in mid-infrared predicted fatty acid groups, and the possibility of improving milk fatty acid profile through genetic selection in Canadian dairy cattle.