CNH Treatment Improved Bacterial Cure of CNS
The present results show that treatment with antibiotic plus CNH DCT was effective in curing CNS IMI. This is important because: (i) it provides a means for preventing deterioration in milk quality and associated economic losses; and (ii) it provides a potential means to prevent the hazard associated with routine use of high doses of antibiotic, with blanket DCT procedures, that have become the accepted tool to control IMI in Israel and other countries. Although in the present study, treatment with CNH was accompany by antibiotics, the significant improvement in bacterial cure in comparison to treatment with antibiotic alone under farming conditions provided evidence that intra-mammary CNH treatment has the potential for being developed into an effective non-antibiotic, non-hormonal DCT for bacterial cure. Nevertheless, in order to advance this potential, the benefit in using CNH over conventional antibiotic DCT should be demonstrated in a controlled study at dry-off.
A decade ago, CNS were often regarded as pathogens of minor importance [24, 25], especially in comparison with Staph. aureus, streptococci, and coliforms, which may cause severe mastitis. Nevertheless, in many countries, including Israel, CNS are the predominant pathogens associated with mastitis [24–27]. Mastitis caused by CNS usually remains subclinical or mildly clinical [28, 29], but it may decrease milk production [22, 30]. Leitner et al. [22, 31, 32] have shown that losses in curd yield caused by the use of CNS-infected milk are several times as great as the milk losses, because of simultaneous deterioration in milk quality. Thus, if milk is being allocated for cheese production, the economic burden imposed on dairies by loss in curd yield is greater than that imposed on farmers by loss of MY .
Although we cannot exclude the possibility of reinfection with the same species following its elimination, we assume that in the present study the CNS infections recorded immediately postpartum persisted in the udder through the entire lactation. This conclusion is consistent with evidence that CNS are capable of persisting in the udder for months or even throughout the lactation [28, 29, 33].
Some studies have found rather high spontaneous CNS cure rates of about 60 to 70% during the dry period , whereas others found markedly lower rates, ranging from 15.5 to 44% [16, 35]. In a broad survey of heifers in the USA and Canada it was found that quarters that were infected prepartum, mostly with CNS, and were treated with antibiotics had a 59.5% cure rate, compared with a spontaneous cure rate of 31.7% . A study on heifers in 2 research dairy herds yielded a very similar CNS cure rate . The somewhat lower cure rate obtained with antibiotic DCT in the present study may be related to the fact that our subjects were cows, or to the stricter criteria we applied to define a cure, compared with that used in standard definitions, i.e., absence of infection during the first month of lactation. Burriel  found that CNS can adhere to and produce slime in various tissues, including epithelial cells of the mammary gland. Thus, the absence of CNS from a culture of a given sample does not necessary indicate their absence from the sampled tissue . This hypothesis is supported by the findings of a large study in Norway that covered a total of 684 cows from 288 different herds in 3 Norwegian regions, DCT of infected quarters led to a 5.2:1 greater probability of the quarters being healthy within 30 ± 17 days into the next lactation than that in control (non-treated) groups. Nevertheless, the overall frequency of CNS in the sampled quarters of cured cows at the end of lactation was no different from that among of the control cows . The above findings justify our more strict criteria for defining a cure, and also emphasize that the success of the present CNH treatment in significantly improving the CNS cure rate was genuine.
In the present study none of the cows were infected with Staph. aureus, and the numbers of cows infected with coliforms and streptococci were too low to assess the efficacy of the CNH treatment in curing or preventing such infections. However, in a previous study, CNH treatment of single quarters during lactation has been shown to be effective in curing chronic and subclinical mastitis associated with these bacteria . Thus, it is worth further investigating the potential benefit of applying this method as a DCT to cure and reduce the SCC counts in herds having higher than the typical proportion of coliforms, streptococci and Staph. aureus IMI at dry-off in Israel.
DCT with CNH Increased Milk Yield
The progressive increase in MY at 2% per year in heifers or in the control cows is typical of the yearly improvement in MY attributed to genetic improvement in Israeli dairy herds . Thus, the increase in MY that was recorded in the experimental cows considerably exceeded any plausible trend. No such response was recorded in cows treated with antibiotic only, i.e., the 17 control cows and those observed in Period 2 that had joined the trial as heifers in Period 1 and 2, therefore this MY enhancement can be related exclusively to the effect of treating the cows with CNH.
Two hypotheses may account for this increase. First, it may relate to the higher cure rate and the reduction in the population of SCC that typically is negatively related to MY . However, analysis of MY as related to SCC distribution indicates that in the present case the effect of CNH treatment on lowering of SCC was far from significant, probably because the infection rate and, therefore, the SCC, were initially low and also because treatment did not affect new IMI in the subsequent lactation. Thus, in herds with poorer initial conditions, this effect would be expected to be more noticeable. The second hypothesis relates to the fact that treatment with CNH accelerated gland involution [11, 13]. Thus, this procedure probably increased epithelial cell apoptosis at the start of the dry period. As the gland parenchyma rebuilt itself during the period preceding the subsequent parturition, it may be expected that it would be composed of larger proportion of newly synthesized epithelial cells, which would be expected to enhance the gland milk production capacity . Our results suggest that this effect persisted through two subsequent lactations.