Susceptibility of the bovine udder to bacterial infection in the dry period

Abstract

The teats of 18 cows were externally exposed to infection with mastitis organisms by dipping them daily for 1 or 2 weeks in a mixed suspension of Streptococcus dysgalactiae and Str. uberis at the start, the middle or the end of the dry period. The teat sinuses of quarters which remained uninfected after external exposure at the beginning or the middle of the dry period were then infused with the same strains of streptococci. Of the 9 quarters infected following external exposure 8 occurred in animals exposed at the start and one in the middle of the dry period. Thirty-six new infections occurred after infusion of bacteria into the teat sinuses of 38 quarters. In a further trial with 10 cows, Staphylococcus aureus and Str. zooepidemicus were inoculated into the distal 3 mm of the streak canals of 5 cows immediately after drying-off and into those of 5 cows which had been dry for 28 weeks. Animals were slaughtered 48 h later and infection determined by teat puncture. Five infections occurred in cows which were at the start of the dry period and only one in the cows dry for 28 weeks. It is suggested that these differences in the rates of new infection between the early dry period and a very extended dry period are due to differences in the ease with which bacteria can penetrate the teat canal. At the later stage bacterial growth through the teat canal appeared to be inhibited.The unmilked udder is particularly susceptible to infection in the 3 weeks following drying-off (Neave, Dodd & Henriques, 1950). Indeed, rates of new infection during the dry period exceed those of lactation, which may be due to the absence of the flushing out effect of regular milking (Neave et al. 1968; Thomas etal. 1972). However, this could not account for the large difference in the rate of new infection between the early part and the later part of the dry period. This difference may be due to the higher level of exposure to bacteria at the beginning of the dry period, i.e. bacteria remaining on the teat skin from the preceding lactation period. Alternatively, progressive changes in the composition of the udder secretion during the dry period (Wheelock et al. 1967;Smith, Wheelock & Dodd, 19676) may influence the establishment of infection after bacterial penetration of the streak canal. It is also possible that changes within the streak canal, such as the formation of a natural seal, may make bacterial penetration more difficult in later stages of the dry period. The aim of the experiments described in this paper was to investigate further the changes in susceptibility to new infection during the dry period. Two experiments were carried out; the first was designed to expose the udders of dairy cows to similar numbers of pathogenic bacteria either at the beginning, the middle or towards the end of the dry period and to measure the resulting numbers of new infections. The second

Effects of continuous lactation and short dry periods on mammary function and animal health

“…Lower concentrations of natural protective factors are present in mammary secretions from glands producing large quantities of milk during late lactation (Smith et al, 1985b;Breau and Oliver, 1986); therefore, reduced milk production at dry-off for cows with SDP may provide higher concentration of these naturally protective factors. In addition, accumulation of a large volume of milk that increases the intramammary pressure and leakage of milk from the teats and facilitate bacterial penetration of the streak canal can be minimized by shortening DPL (Cousins et al, 1980;Burvenich et al, 2007). A positive correlation between the quantity of milk produced during late lactation and susceptibility to new IMI has been reported by others (Oliver et al, 1956).…”

Incidence of intramammary infections during the dry period without or with antibiotic treatment in dairy cows – a quantitative analysis of published data

“…There are two periods of elevated risk of new IMI during the dry period: the first weeks after drying-off during involution of the udder [50] and the weeks preceding calving during colostrogenesis [13,53,85]. Most of the DCT used did no longer prevent new IMI during the latter period of elevated risk, especially for long dry periods [5,58,62].…”

Reviews of the progress of Dairy Science: Mastitis control – progress and prospects

“…(ii) Placing small numbers of pathogenic bacteria beyond the teat duct after milking or in dry cows usually causes infection, although there may be differences between bacterial strains (132,81,35). This suggests that intramammary defence mechanisms are relatively inefficient against most of the common mastitis-causing pathogens although E. coli may be an exception, particularly in late lactation (83).…”

“…(iii) Experiments in which milking was suspended for a period and then reintroduced showed that flushing of the teat duct to prevent the ingress of bacteria is an important factor in reducing the incidence of intramammary infection (35,145). There are also reports that strict fore milking reduces rates of udder infection (68).…”