Quantitative trait loci exploration and characterization of gestation length in Holstein cattle.

Gestation length (GL) is a moderately heritable trait in cattle with economic and management implications. This study aimed to characterize the gestation length of an Argentinian Holstein cattle population, understand contributing factors, and explore the GL effect on production performance. Further objectives were to estimate direct and maternal heritabilities for this trait and to identify genomic regions affecting it. Data consisted of GL records from 45,738 births corresponding to 17,004 Holstein cows and heifers. The effects of age and calving season over GL were analyzed using a Student's t-test for homoscedastic samples. The effects of the GL category (GL shorter than 1.5 SD, within ±1.5 SD, and longer than 1.5 SD from the mean) on production performance were studied by analysis of variance. A single-step genome-wide association study was performed using the BLUPF90 suite of programs with genotypes from 654 Holstein animals on 40,339 SNP. The results showed that the younger the age at calving, the shorter the GL. Moreover, gestations ending in warmer seasons were, in general, statistically shorter than those ending in colder seasons for both heifers and cows. Regarding the effect of GL on production performance, cows with gestation periods within ±1.5 SD from the population mean exhibited the highest 305-day cumulative milk, fat, and protein productions. Direct and maternal heritabilities for GL were 0.42 and 0.03, respectively. We detected a SNP suggestively associated with direct gestation length at 57.7 Mb on Bos taurus autosome 18, a locus included in a region described in the literature as associated with the trait. The information obtained on the environmental and genetic factors affecting GL in Argentinian Holstein cows contributes to characterizing the population in pursuit of improving the performance of national dairy cattle breeding systems.

Risk evaluation of nonvaccinated, weaned calves transported through areas under systematic foot and mouth disease (FMD) vaccination.

The recurrence and persistence of foot and mouth disease (FMD) could be the consequence of cyclic and massive transportation of calves. For this reason, in South America, vaccination strategies related to livestock dynamic are being promoted. In order to aid the evaluation of such strategies, a method for predicting the risk of transportation of nonvaccinated weaned calves was developed; this method combines expert opinion and empirical evidence using Bayesian estimators. It was applied through Monte Carlo simulation to data of Argentina under four hypothetical vaccination schemes: E1, extended vaccination season of 1/6 of the population of calves each month from July to December without second round vaccination (SRV); E2, extended irregular vaccination from July to December with SRV applied to 70% of the calves resembling the scheme applied in Argentina in 2001; E3, vaccination in November and December without SRV; and E4, vaccination concentrated in November. E1 resulted in probability of transporting non vaccinated calves (tnvc) reaching its maximum in the following year in May with mean=0.0250 and percentile 95% (P95)=0.0404; for the same month tnvc estimates for the other schemes were E2: mean=0.0071; P95=0.0162; E3: mean=0.0017; P95=0.0042 and E4: mean=0.0001; P95=0.0004. Bonferroni multiple comparison for simultaneous assertions for May showed that E4 resulted the best scheme, E1 the worst, and E2 and E3 are intermediate with nonsignificant difference observed between overall (p<0.05). Results were consistent with historical records and quantification for future needs for re-vaccination was made possible. While the ratio "total vaccinated"/"total estimated existences" will give a biased vision of vaccination coverage under the situation of extended vaccination campaigns, a model as the one developed here could allow a more accurate assessment and the design of mitigation plans.

Effect of somatic cell count level on functional longevity in Valle del Belice dairy sheep assessed using survival analysis.

The objectives of this study were to evaluate the effect of somatic cell count (SCC) on functional longevity and to estimate the heritability of functional longevity using survival analysis in Valle del Belice dairy sheep. A total of 4,880 lactations of 2,190 ewes from 11 flocks were used. In this study, SCC was considered as an indication of subclinical mastitis. In case of clinical cases, identified by the technicians at milking time, test-day weights and milk samples of those ewes were not considered. Somatic cells were analyzed as counts, without any transformation, and were grouped in 3 classes based on the observed SCC maximum (mxSCC). The mxSCC classes, expressed as 10(3) cells/mL, were classified as 1 if mxSCC or= 1,000. An increase in SCC was associated with an increased hazard of being culled. Ewes in the highest class of SCC on a test-day had a 20% higher hazard of being culled than those in the lowest class. Therefore, SCC played a role in culling decisions of Valle del Belice dairy sheep farmers. The heritability estimate for functional longevity was 7% on the logarithmic scale and 11% on the real scale, indicating that selection for this trait is possible in sheep. The flock-year-season effect explained 19% of the variation on the logarithmic scale and 27% of the variation on the real scale.

Short communication: casein haplotype variability in sicilian dairy goat breeds.

In the Mediterranean region, goat milk production is an important economic activity. In the present study, 4 casein genes were genotyped in 5 Sicilian goat breeds to 1) identify casein haplotypes present in the Argentata dell'Etna, Girgentana, Messinese, Derivata di Siria, and Maltese goat breeds; and 2) describe the structure of the Sicilian goat breeds based on casein haplotypes and allele frequencies. In a sample of 540 dairy goats, 67 different haplotypes with frequency >or=0.01 and 27 with frequency >or=0.03 were observed. The most common CSN1S1-CSN2-CSN1S2-CSN3 haplotype for Derivata di Siria and Maltese was FCFB (0.17 and 0.22, respectively), whereas for Argentata dell'Etna, Girgentana and Messinese was ACAB (0.06, 0.23, and 0.10, respectively). According to the haplotype reconstruction, Argentata dell'Etna, Girgentana, and Messinese breeds presented the most favorable haplotype for cheese production, because the casein concentration in milk of these breeds might be greater than that in Derivata di Siria and Maltese breeds. Based on a cluster analysis, the breeds formed 2 main groups: Derivata di Siria, and Maltese in one group, and Argentata dell'Etna and Messinese in the other; the Girgentana breed was between these groups but closer to the latter.

Bayesian reanalysis of a quantitative trait locus accounting for multiple environments by scaling in broilers.

A Bayesian method was developed to handle QTL analyses of multiple experimental data of outbred populations with heterogeneity of variance between sexes for all random effects. The method employed a scaled reduced animal model with random polygenic and QTL allelic effects. A parsimonious model specification was applied by choosing assumptions regarding the covariance structure to limit the number of parameters to estimate. Markov chain Monte Carlo algorithms were applied to obtain marginal posterior densities. Simulation demonstrated that joint analysis of multiple environments is more powerful than separate single trait analyses of each environment. Measurements on broiler BW obtained from 2 experiments concerning growth efficiency and carcass traits were used to illustrate the method. The population consisted of 10 full-sib families from a cross between 2 broiler lines. Microsatellite genotypes were determined on generations 1 and 2, and phenotypes were collected on groups of generation 3 animals. The model included a polygenic correlation, which had a posterior mean of 0.70 in the analyses. The reanalysis agreed on the presence of a QTL in marker bracket MCW0058-LEI0071 accounting for 34% of the genetic variation in males and 24% in females in the growth efficiency experiment. In the carcass experiment, this QTL accounted for 19% of the genetic variation in males and 6% in females.

Effects of diseases on reproductive performance in Swedish Red and White dairy cattle.

The objectives of this study were to evaluate the effect of diseases on days open (DO), days to first breeding (DFB) and days from first breeding to conception (DFBC) using survival analysis models, and to assess the significance of the sire component and its possible confounding effect. The data consisted of a random sample of 20% of all herds enrolled in Swedish recording system and using 100% artificial insemination with at least 15 Swedish Red and White cows calving in 1991. The follow-up period was from 45 to 145 d after calving. After editing, the data sets had 23,927, 28,197, and 22,089 cows for days open, days to first breeding, and days from first breeding to conception, respectively. The Cox models included parity, calving season, cow milk production and age at first calving as fixed effects, and herd and sire as random effects. Ten disease groups were considered as possible risk factors for the reproductive traits. Disease groups were treated differently if they occurred before or after 45 d postpartum. Diseases occurring in the first 45 d after calving were treated as time-independent covariates and diseases occurring after day 45 were treated as time-dependent covariates for days open and days to first breeding. The percentages of censored cows were 35% for days open, 19% for days to first breeding, and 33% for days from first breeding to conception. Days open increased in cows with dystocia, stillbirth, retained placenta, metritis, or other diseases occurring in the first 45 d after calving, and in cows with metritis, mastitis, or other diseases occurring after 45 d. Days to first breeding increased in cows with stillbirth, retained placenta, milk fever, mastitis, foot and leg problems, or other diseases occurring before day 45, and in cows with metritis, mastitis, foot and leg problems, or other diseases occurring after 45 d. Days to first breeding decreased in cows treated for ovulatory dysfunctions either before or after 45 d. Days from first breeding to conception increased in cows with dystocia, stillbirth, retained placenta, metritis, or ovulatory dysfunctions occurring before first breeding, and in cows with mastitis occurring after first breeding. Although the additive genetic components were significant for all traits considered, the sires did not act as confounders because only a small amount of variability for the traits considered in this study was explained by the sires, with estimated heritabilities of 2% on the logarithmic scale and from 3 to 4% on the real scale.

Effect of lameness on culling in dairy cows.

The purpose of this study was to assess the effect of lameness on dairy cow survival. Cox's proportional hazards regression models were fitted to single-lactation data from 2520 cows in 2 New York State dairy herds. Models were controlled for the time-independent effects of parity, projected milk yield, and calving season, and for the time-dependent effects of lameness and culling. Other common diseases were found to be nonconfounding and so were not included in any of the final models. Survival was measured as the time from calving until death or sale. Cows were censored if they reached the start of the next lactation or end of the study, whichever occurred first. All models were stratified by herd. For all lameness diagnoses combined, survival in the herd decreased for those cows becoming lame during the first half of lactation, with a hazard ratio of up to 2 times that of a nonlame cow. Foot rot diagnosed during the second or third months of lactation decreased survival during the same time period (hazard ratio=5.1; 95% confidence interval=1.6 to 16.2). Sole ulcers diagnosed in the first 4 mo of lactation decreased survival in several subsequent periods in which the strongest association was between diagnosis in the third and fourth months of lactation and exit from the herd during that same period (hazard ratio=2.7; 95% confidence interval=1.3 to 6.0). Foot warts were not associated with decreased survival in this analysis. Lameness was never associated with increased survival in any of the models.

Dam-related effects on heart girth at birth, morbidity and growth rate from birth to 90 days of age in Swedish dairy calves.

We investigated the effects of dam-related factors (such as calving performance, milk leakage, diseases, milk production, and somatic-cell count (SCC)) on heart girth at birth and the incidence risk of diarrhoea and respiratory disease during the first 90 days in Swedish dairy calves. The effects of these dam-related factors and environmental and management-related (but not dietary) factors on the calves' growth rate during the first 90 days of life also were analysed. The study used nearly 3,000 heifer calves born in 1998 on 122 farms in the south-west of Sweden. Individual health records were kept by the farmers and visiting project veterinarians. The calf's heart girth was measured at birth and weaning. We used generalised linear mixed models for the size of the calf at birth and growth rate. Variables associated with the heart girth at birth were breed, calving performance, mastitis in the dam in the last 49 days before calving, milk production and parity. Variables associated with the growth rate were breed, calving performance, disease in the calf during its first 90 days of life, heart girth at birth, and housing of calves. The effect of the dam on the relative risk of diarrhoea and/or respiratory disease in the calf was evaluated by a generalised linear mixed model with a logit link. Morbidity in the dam during late pregnancy, retained placenta and SCC were associated with the relative risk of respiratory disease in the calf. None of the explanatory variables (other then breed) was associated with the relative risk of diarrhoea.