Risk factors for new intramammary infections during the dry period in untreated dairy cows from herds using selective dry cow therapy.

This study aimed at investigating risk factors for new intramammary infections (IMI) during the dry period in untreated cows from herds using selective dry cow antibiotic therapy (DCT). A total of 980 uninfected quarters in 347 untreated cows from 28 herds using selective DCT were included in a prospective survey. A herd-level questionnaire and an individual cow-level recording sheet were implemented to collect data on putative risk factors. Quarter milk samples were taken at drying-off and on day 3 after calving to assess the occurrence of new IMI during the dry period. A multivariate model including a herd effect as random and a cow effect as repeated was run at the quarter level. Interactions between risk factors and the cow infection status at drying-off (cow infected in at least one quarter v. uninfected) were checked. Three risk factors were found significantly associated with the risk for new IMI without interaction (P < 0.05): cows infected in at least one quarter at drying-off (v. uninfected cows) (relative risks (RR) = 1.58); long preceding lactation (>355 days v. shorter length) (RR = 1.62); long dry period (>65 days v. shorter length) (RR = 1.46). One risk factor acted only in interaction with the cow infection status at drying-off: in cows uninfected at drying-off, the risk for new IMI was significantly higher in cows with short teats (RR = 1.21) when compared with cows with long or normal teats, while the reverse relationship was observed in cows infected at drying-off. Risk factors can be translated in recommendations, for instance to have dry periods not longer than 2 months. Moreover, as suggested by our results, the efficacy of selective DCT towards the prevention of new IMI would be improved if all infected cows were detected and treated. Criteria to accurately identify these infected cows should be therefore further investigated.

Between and within subject correlations and variances for certain semen characteristics in fertile men.

Between subject and within subject variances and correlations for different semen characteristics have been determined for a population of 315 fertile men who provided one or more ejaculates within an abstinence period of 1 to 5 days. The semen characteristics measured were sperm count, semen volume, pre-freeze motility and post-thaw motility. An approach via a decomposition of the variance or via a decomposition of correlation leads essentially to the same conclusions i.e. the within subject factors are not negligible but are less important than the between subject ones. Thus there is broad evidence for overall differences in the quality of the ejaculate from one subject to the other but not for different ejaculates of the same subject.

Within-subject variability and the importance of abstinence period for sperm count, semen volume and pre-freeze and post-thaw motility.

The within-subject variability of semen sperm count (n), volume (v), total number of spermatozoa (N) and pre-freeze (mo) and post-thaw (m1) motility was studied on 564 ejaculates from 98 normal subjects after an abstinence ranging from 1 to 5 days. After logarithmic transformation of n, v and N, the within-subject variances for each variable were found to be similar for all subjects; the within-subject centered distributions were nearly normal and 95% confidence intervals were calculated. These three variables appeared to increase linearly with the length of abstinence. For both mo and m1, the within-subject variances were also similar for all subjects and this without logarithmic transformation. Their respective within-subject centered distributions were normal; mo and m1 were not influenced by the length of abstinence during the period studied.

Fecundability, coital frequency and the viability of Ova.

Summary An extension of Barrett and Marshall's model expressing fecundability as a function of coital pattern is proposed. In particular, this extension includes the probability that the ovum remains alive. The extended model has been applied to Barrett and Marshall's data, a series of cycles for which basal body temperature curves and the date of coitus have been recorded. It was thus possible to estimate the daily probabilities of fertilization and, under certain assumptions, the proportion of lost ova. This proportion was estimated to be above 50 per cent, and increases with age. The increase of fecundability with frequency of intercourse is more moderate than that predicted by Barrett and Marshall's model.