Evaluation of test characteristics of 2 ELISA tests applied to bulk tank milk and claw-trimming records for herd-level diagnosis of bovine digital dermatitis using latent class analysis.

Bovine digital dermatitis (DD) is an infectious claw disease with a negative effect on animal welfare and production. Treponema spp. is the main causative agent, and infected animals produce specific antibodies. Our aim was to estimate sensitivity (Se) and specificity (Sp) of 2 ELISA research tests, Medicago's ELISA test and GD Animal Health's in-house ELISA test, for detection of DD-associated Treponema antibodies in bulk tank milk. We used bulk tank milk samples from 154 Norwegian dairy cattle herds, 96 from an expected high-prevalence region and 58 from a low-prevalence region. Both tests were evaluated separately against herd-level (aggregated) claw-trimming records extracted from the Norwegian Dairy Herd Recording System using latent class models in a Bayesian analysis. Cutoff values were selected using an explorative approach, and both noninformative priors for all parameters and informative ß priors for distribution of Se and Sp of claw trimming were explored. The estimated (median) true herd-level prevalence of digital dermatitis varied between 24 and 30% in the high-prevalence region and between 3 and 6% in the low-prevalence region. For Medicago's ELISA test, an Se (95% posterior credible interval) of 0.57 (0.32; 0.94) could be achieved without compromising Sp, and for GD Animal Health's in-house ELISA test, an Se of 0.60 (0.37; 0.92) was achieved. Our study showed that both ELISA tests can detect antibodies against DD-associated Treponema spp. in bulk tank milk. However, neither of the 2 ELISA tests produced satisfactory sensitivity without compromising specificity. Based on these results, inspection at claw trimming in a chute is necessary for surveillance and control of DD at the herd level in Norway, although these ELISA tests of bulk tank milk might be a useful supplement.

A cohort study of the effect of Streptococcus agalactiae on milk yield and somatic cell count in Norwegian dairy cows.

The primary objective of the present study was to estimate the effect of Streptococcus agalactiae intramammary infection on milk production and somatic cell count (SCC) in Norwegian dairy cows. A secondary objective was to assess differences in the effect of common Strep. agalactiae sequence types (ST) found in Norwegian dairy herds. We performed a cohort study combining registry data with sequence-type data from Strep. agalactiae isolates. Herds in which Strep. agalactiae had been detected in individual animals (bacteriological culture or quantitative PCR) between 2012 and 2015 were included. We accessed monthly test-day milk yield records for the entire period to compare milk yield and SCC between cows that were Strep. agalactiae positive and all other cows, within each herd. The study sample consisted of 150 herds, 15,757 cows, 30,850 lactations, and 204,126 test days. We evaluated the effects of Strep. agalactiae on test-day milk yield and SCC using mixed linear regression models, controlling for clustering by herd, cow, and lactation. Multilocus sequence typing of Strep. agalactiae was available for isolates from 86 herds. Additional models were fit to a subset of herds (n = 59) in which ST1, ST23, ST103, and ST196 had been found, to compare the effects of ST on milk production and SCC. In the period 3 to 2 mo before diagnosis, Strep. agalactiae-positive cows produced an average of 1.3 kg more DIM-adjusted milk/d than their negative herd mates. At the time of diagnosis, production was on average 0.13 kg less DIM-adjusted milk/d in Strep. agalactiae-positive cows than in negative cows; 2 to 3 mo after diagnosis, they produced 1.24 kg less DIM-adjusted milk/d than negative cows. Losses persisted for the rest of the investigated period. Cows with ST23, ST103, and ST196 followed a similar pattern as the overall analysis with respect to milk production, whereas ST1-affected cows produced similar amounts of milk before diagnosis as the negative cows. Cows with ST1 experienced the largest milk loss 1 to 2 mo after diagnosis but then recovered to some extent; for cows with ST103, the severe milk loss persisted for the rest of the investigation period. The cow-associated ST103 elicited a lower response in peak SCC compared with ST23, ST103, and ST196. The results indicate an effect of Strep. agalactiae on milk production and SCC. Production was lowest 2 to 3 mo after a positive sample. Peak SCC was reached the month before diagnosis, with notable differences between sequence types.

Latent class analysis of real time qPCR and bacteriological culturing for the diagnosis of Streptococcus agalactiae in cow composite milk samples.

Streptococcus agalactiae (S. agalactiae) has re-emerged as a mastitis pathogen among Norwegian dairy cows. The Norwegian cattle health services recommend that infected herds implement measures to eradicate S. agalactiae, this includes a screening of milk samples from all lactating cows. The performance of the qPCR-test currently in use for this purpose has not been evaluated under field conditions. The objective of this study was to estimate the sensitivity and specificity of the real-time qPCR assay in use in Norway (Mastitis 4 qPCR, DNA Diagnostics A/S, Risskov, Denmark) and compare it to conventional bacteriological culturing for detection of S. agalactiae in milk samples. Because none of these tests are considered a perfect reference test, the evaluation was performed using latent class models in a Bayesian analysis. Aseptically collected cow-composite milk samples from 578 cows belonging to 6 herds were cultured and tested by qPCR. While 37 (6.4%) samples were positive for S. agalactiae by bacteriological culture, 66 (11.4%) samples were positive by qPCR. The within-herd prevalence in the six herds, as estimated by the latent class models ranged from 7.7 to 50.8%. At the recommended cut-off (cycle threshold 37), the sensitivity of the qPCR was significantly higher at 95.3 (95% posterior probability interval [PPI] [84.2; 99.6]) than that of bacteriological culture at 58.2 (95% PPI [43.8; 74.4]). However, bacterial culture had a higher specificity of 99.7 (95% PPI [98.5; 100.0]) compared to the qPCR at 98.5 (95% PPI [94.6; 99.9]). The median estimated negative predictive values of qPCR was consistently higher than those of the BC at all estimated prevalences, and the superiority of the qPCR increased with increasing within-herd prevalence. The median positive predictive values of BC was in general higher than the estimates for the qPCR, however, at the highest prevalence the predictive ability of both tests were similar.

Factors associated with the number of calves born to Norwegian beef suckler cows.

A retrospective cohort study was performed to evaluate factors associated with the number of calves born to Norwegian beef suckler cows. Production data from 20,541 cows in 2210 herds slaughtered over a three-year period (1st of January 2010 to 23rd of January 2013) were extracted from the national beef cattle registry. This study's inclusion criteria were met for 16,917 cows (from 1858 herds) which gave birth to 50,578 calves. The median number of calves born per cow was 2 (min 1, max 18). Two multilevel Poisson regression models with herd random effects showed that early maturing breeds (Hereford and Aberdeen Angus) gave birth to more calves than late maturing breeds (Charolais and Limousin) in four out of five areas of Norway. The significant breed-region interaction indicated that the coastal South East region of Norway, which has a relatively long growing season and gentle topography, yielded the highest number of calves born for all but one breed (Simmental). Cows that needed assistance or experienced dystocia at their first calving produced fewer calves than those that did not: incidence rate ratio 0.87 (95% confidence interval (CI) 0.84-0.91) for assistance and 0.70 (95% CI: 0.66-0.75) for dystocia, respectively. Cows in larger herds (>30 cows) produced 11% more calves in their lifetime compared to cows in smaller herds (≤30 cows) (P<0.001). The herd random effects were highly significant, suggesting that unmeasured factors at the herd level were responsible for a large amount of the unexplained variation in the number of calves born. The large inter-herd variation indicate systematic differences in herd level factors influencing the number of calves born to each cow.

A cross-sectional study of factors associated with birth weights of Norwegian beef calves.

A cross-sectional study was performed to evaluate factors which influence birth weights of beef suckler calves in Norway. Data were from a national beef cattle registry, and lifetime production data of cows slaughtered between January 2010 and January 2013 were included in the study population. The study population consisted of 20,541 cows and 53,819 calves. The analysis was performed on the subset of singleton calvings from which birth weights were recorded. The study sample consisted of 9903 cows with birth weights available for 29,294 calves. The mean birth weight was 43.47kg (95% CI 43.40; 43.53). Two multilevel linear regression models were built; the first was for all calves and included parity of dam as one of the explanatory variables (with herd and cow as random effects), the second model was for calves born to primiparous dams only where age of first calving was included as an explanatory variable (with a random herd effect). The multilevel regression models estimated that female calves were 2.3kg lighter than males (95% CI 2.2-2.4, P<0.001), that calves of Norwegian Red, Charolais, Aberdeen Angus and "Other" born in the western part of Norway were lighter than from all other regions, and that calving in the autumn yielded lighter offspring than calving other parts of the year. Furthermore, calves born from primiparous cows were heavier than calves from older cows. Herd explained a large proportion of the variation in birth weights (40% and 37%, in the full and heifer models, respectively), and both the herd and cow random effects were highly significant. In conclusion, birth weights of beef calves in the Norwegian Beef Cattle Recording System were influenced by sex of the calf, breed of the dam, parity, age at first calving, calving season, cow, herd and region.

Ewe characteristics associated with neonatal loss in Norwegian sheep.

A case-control study was conducted to identify ewe characteristics that affect the risk of a ewe losing at least one lamb during the first 5 days post lambing. Data were from a national sheep registry, and only ewes that lambed in the spring of 2010 belonging to flocks that reported disease events were included. Ewes registered with abortion or stillbirth were excluded. Cases (n=4850) and controls (n=85,354) from 1153 flocks were studied using logistic regression models, accounting for within flock correlation. The odds of losing at least one lamb increased substantially when litter size exceeded two. For example, in 3-year-old ewes, the odds were 6 times greater for those with 3 lambs than for those with 1 lamb. However, the effect of litter size depended on the age of the ewe; for example for ewes giving birth to triplet lambs, the odds of losing at least one lamb were 2.7 times greater in 1-year-old ewes than in 3-year-old ewes. Dystocia was associated with increased risk of losing at least one lamb, but the effect varied by litter size. In ewes with single lambs, the odds of lamb loss were 5 times greater in those that experienced dystocia than in those that did not, while within subgroups of ewes with twins, triplets or >3 lambs, the corresponding odds ratio (OR) of losing one or more lambs was 2.2, 1.5 and 1.3, respectively. Compared with ewes of the Norwegian White breed, ewes of old Norwegian breeds were less likely to lose lambs (OR=0.8). We also examined the effects of several diseases experienced by the ewe during pregnancy or shortly postpartum on the risk of subsequent neonatal lamb loss. Significantly increased risk was found for ewes with abdominal hernia (OR=2.5) and for ewes treated for moderate to severe clinical mastitis (OR=1.6) when compared with ewes without these disorders. In conclusion, our large study population allowed for a detailed analysis of the combined effect of important ewe factors that affected survival of their lambs in the early neonatal period.

Housing conditions and management practices associated with neonatal lamb mortality in sheep flocks in Norway.

A study was conducted in order to obtain information about sheep farms in Norway and to identify housing and management characteristics that were risk factors for neonatal mortality of lambs 0-5 days of age. A questionnaire was submitted to sheep farmers, who provided demographic data and information on sheep housing conditions and feeding and management practices. Our description of farms is based on the questionnaire responses received from 2260 farmers. Data on lamb mortality during the preceding lambing season were available for those flocks that were enrolled in the Norwegian Sheep Recording System. Some flocks where the number of lambing ewes was less than 20 or greater than 400 were excluded. The total number of flocks included in the analysis of neonatal mortality was 1125. An increase in the mean number of live-born lambs per ewe per flock was associated with increasing neonatal mortality. Factors independently associated with increased neonatal survival were continuous monitoring of the ewes during the lambing season, active support to ensure sufficient colostrum intake of the lambs, feeding a combination of grass silage and hay compared with grass silage alone, and supplying roughage at least twice per day versus only once. Increased survival was also observed in flocks where the farmer had at least 15 years of experience in sheep farming. Flocks in which the Spæl breed predominated had lower odds for neonatal deaths compared to flocks in which the Norwegian White breed predominated. In conclusion, measures in sheep flocks targeted at feeding practices during the indoor feeding period and management practice during lambing season would be expected to reduce neonatal lamb mortality.