Bovine mammary glands were inoculated intracisternally with a streptomycin-resistant (SR) strain of Corynebacterium bovis to determine the number of colony-forming units (CFU) required to induce colonization and to maintain persistence of C bovis colonization throughout lactation and involution. Streptomycin resistance was used as a strain marker. Uninfected quarters in cows during midlactation were challenge exposed with successively higher numbers of SR C bovis until all quarters became colonized. Inoculum containing 790 CFU of SR C bovis established colonization in only 7 of 38 quarters. Colonization persisted in only 4 of these quarters by 23 days after inoculation. Eleven quarters were reinoculated with higher numbers of SR C bovis, and all became colonized by the time challenge-exposure inoculum contained 8 X 10(4) CFU. Colonization persisted throughout the 93-day experimental period. Somatic cell counts were significantly (P less than 0.01) higher in SR C bovis-colonized quarters after inoculation than before. Sixteen additional quarters were inoculated with a mean number of 8 X 10(4) CFU of SR C bovis 7 days before suppression of lactation. All quarters became colonized, and SR C bovis was shed during the experimental period; throughout the nonlactating and peripartum periods, high numbers of SR C bovis in pure culture were shed from 13 of 16 quarters.

This study aimed to evaluate the effect of different dry period lnghts (DPLs) on the udder health and fertility during the subsequent lactation. The impact of subclinical mastitis (SCM) and clinical mastitis (CM) on the reproductive efficiency were also investigated. Holstein-Friesian cows (n=894) were included in the study of udder health, of which only multiparous cows (n=499) were included in the investigation of the impact of different DPLs on the udder health and reproductive efficacy in the subsequent lactation. Cows were classified according to the DPLs into 3 groups: Short (SDPL, <40 d), Traditional (TDPL, 40-60 d) and Long (LDPL, >60 d). A limit of 200,000 somatic cell/mL milk was established to separate between healthy and mastitic udder status. Accordingly, samples with 500,000-1,000,000 cell/ml were referred to cows affected with SCM and samples with >1,000,000 cells/ml were mentioned to cows affected with CM. A higher proportion of infected udder was detected in cows with LDPL (39.19%) Moreover, a higher proportion of SCM was recorded for cows with LDPL (17.57%) compared with that recorded for cows with SDPL (8.0%) and TDPL (6.13%). A higher proportion of CM was recorded for cows with a long dry period (LDP, 8.11%) compared with that recorded for cows with SDPL (4.0%) or with TDPL (4.8%). Cows with SDPL showed the best intervals reproductive indices compared with that recorded for both TDPL and LDPL. Furthermore, LDPL was found to be associated with significantly lower CR (33.11±2.91%), lower PR (50.39±3.97%) and higher NSPC (1.98±0.37) compared with values that recorded for either SDPL or TDPL. Cows with either SCM or CM showed the longest interval reproductive indices, less CR and PR and number of inseminations to become pregnant compared with healthy udder cows. A lower proportion of affected udder was recorded for Primiparous cow (24.3%) compared with that showed by multiparous cows (32.46%). Cows affected with mastitis during the voluntary waiting period (VWP) showed longer intervals to the first detected estrus and first services while those affected during the service period (SP) showed longer calving to conception intervals, lower CR and lower PR especially when the SCC exceed 500,000 cell/ml milk. Cows experienced udder infection during the SP showed the lowest PR (32.54% & 36.44%) and required more NSPC. In conclusion, a significant linkage among different dry period lengths and both the incidence of mastitis and fertility were recorded, with the best results were recorded for cows with TDPL and SDPL. Extending the dry period above 60 days increased the incidence of both clinical and subclinical mastitis and exerted a negative impact on the reproductive performance. The occurrence of mammary infection during the VWP increased the calving to first estrus and first service intervals, while its occurrence during the SP prolonged the days open, and extremely reduced the conception and pregnancy rates.

A retrospective study was employed to investigate the effect of dry period length on reproduction, incidence of reproductive and metabolic disorders and milk production in Holstein cows belonging to a commercial dairy. Over a 5 year period (2000- 2005), data about reproductive performance, postpartum and metabolic disorders were collected on 1914 multiparous Holstein cows. Out of the obtained data production performance were available only for 793 cows. According to the obtained data the dry period was categorized into 10 groups of different lengths. Reproductive performances including the interval to 1st service, service period, number of inseminations per conception, day’s open, calving interval and percentage of pregnant cows within 100 days in milking (DIM) were recorded as a function of dry period length. The incidence of postpartum reproductive and metabolic disorders included retained fetal membranes (RFM), endometritis, cystic ovarian disease (COD), mastitis, milk fever (MF), ketosis and abomasal displacement were recorded as a function of dry period length. Milk production was also studied in relation to dry period length. Statistical analysis of the obtained data was performed.The most important notifiable results were: cows with dry period less than 28 days showed the best reproductive performance and the highest incidence of abomasal displacement among all groups. In general, the incidence of MF and RFM were higher in short dry period cows, while the incidence of ketosis was higher in cows with long dry period length. A highly significant difference was recorded between daily milk yield of cows with dry period less than 64 days (27.23 kg) and those of cows with dry period > 64 days (25.20 kg).Finally, it is recommended to keep the dry period of 40-60 day lengths to obtain optimum reproduction, health and production of Holstein cows.

The twinning rate in a herd of Holstein dairy cattle and its effect on lactation and calf performance was investigated by using records of 5815 calving events. Data from twin calving Holstein cows in (TEC-DAP) farm in Al-Fayum Governorate between January 1997 and April 2008 were compared to those giving singles to study the differences in subsequent milk yield, previous and subsequent lactation and dry period length, as well as calf performance. The obtained average twinning rate was 1.4% during the period of the study. Cows giving twins had a significantly (p<0.01) lower daily, peak and 305-d milk yields than those with singles. There was no significant difference (p>0.05) in previous and subsequent lactation and dry period length between cows calving twins or singles. Calves born as twins were significantly (p<0.005) lighter at birth and weaning time than single calves, whereas total birth weight and total weaning weight were significantly (p<0.005) increased for twins than singles. Daily body weight gain from birth to weaning was significantly lower (p<0.005) for twin than single calves. Twinning in dairy cattle has a negative depressive effect on subsequent milk yield. Calf weight produced at weaning per cow calving can be increased in cows producing twins relative to cows producing singles. Alleviation of twinning constraints including dystocia, reduced calf survival and low reproductive performance requires improved management practices and early diagnosis of cows gestating twins in order to provide higher nutritive requirements in the last trimester of gestation and proper timing of drying off, and for higher assistance requirements at parturition. Thus, due to the increased disadvantages which did not offset the additional returns earned by calves, twinning in dairy cattle via selection or artificial induction appears not to be desirable.

Naturally acquired gram-negative bacterial intramammary infections (n = 160) were studied in 99 cows over a 2-year period. Escherichia coli, Klebsiella spp, Serratia spp, Enterobacter spp, and unidentified gram-negative bacteria were isolated from 28.8, 39.4, 9.4, 5.0, and 11.2%, respectively, of infected mammary glands. A majority (61%) of intramammary infections were first detected during the nonlactating period. Gram-negative bacteria isolated during the first half of the nonlactating period were predominantly Klebsiella spp, Serratia spp, and Enterobacter spp. Onset of E coli intramammary infections was more prevalent during the second half of the nonlactating period and during the first 7 days of lactation. The majority (59%) of infections were <28 days in duration, but Klebsiella spp and Serratia spp infections were of significantly (P <0.05) greater duration than infections with E coli. The greatest percentage (47%) of gram-negative bacterial intramammary infections were first detected during the summer.

Effects of placing intracisternal bead devices (ICB) into teat cisterns of 6 dairy cows, from the end of lactation through parturition, were studied. Lacteal secretion samples were collected weekly from each mammary quarter during the nonlactating period to monitor composition changes in ICB-fitted and nonfitted quarters. In quarters remaining uninfected (n=15), there were significantly higher mean somatic cell counts (P less than 0.05), percentage of neutrophils (P less than 0.019), and cell viability (P less than 0.038), but significantly lower percentage of macrophages (P less than 0.013) in ICB-fitted quarters compared with those in nonfitted quarters. The ICB had no significant effect on mean weekly values for percentage of lymphocytes, pH, lactoferrin, citrate, citrate/lactoferrin molar ratio, serum albumin, alpha-lactalbumin, and N-acetyl-beta-D-glycosaminidase. In infected quarters (n=9), pH of mammary secretions was significantly (P less than 0.004) higher in ICB-fitted quarters, but concentrations of lactoferrin (P less than 0.004), alpha-lactalbumin (P less than 0.013), and N-acetyl-beta-D-glucosaminidase (P less than 0.028) were significantly lower, compared with those in nonfitted quarters. Coagulase-negative staphylococci comprised approximately 90% of all infections. Over the nonlactating period, 16.4 and 41.5% of samples from nonfitted and ICB-fitted quarters, respectively, contained coagulase-negative staphylococci. Microscopic examination of ICB from uninfected quarters revealed a thin coating of plaque with adhering neutrophils, macrophages, and multinucleated giant cells. Microscopic examination of plaque on devices from ICB-fitted quarters harboring coagulase-negative staphylococci revealed numerous adherent cocci and neutrophils.

A total of 5844 normal lactation records on 1483 Holstein-Friesian cows were collected from El-Alamiah dairy farm in Egypt through the period from 1996 to 2018 to study the effect of the length of dry period on the subsequent lactation performance by evaluating the performance of milk production traits, lifetime traits and some welfare factors of Holstein-Friesian cows, raised in Egypt, to determine the best length of dry period. The milk production traits studied were total milk yield (TMY, kg), 305 days milk yield (305-d MY, kg) and lactation length (LL, day). The lifetime performance traits under study were complete lactation number (CLN, no.), productive life length (PL, month), longevity length (Lon, month), lifetime total milk yield (LTY, kg) and lifetime daily milk yield (LDY, kg). Welfare factors studied were mastitis and lameness scores.  TMY, 305 d-MY and LL tended to increase with increasing DP length up to 90 d then decreased thereafter. While the lowest TMY and 305 d-MY (6470.76 and 5435.25 kg, respectively) and the shortest LL (305.81 d) were obtained when DP was below 31. Cows had DP category of 61 to 75d produced the largest amount of milk (34506.39 kg) in a longest Lon and PL (90.56 and 62.65 mo., respectively) and attained the biggest number of CLN (4.474 lactations). All lifetime traits tended to increase with increasing DP up to 61 to 75d then decreased thereafter. The 61 to 75 d DP had the largest mastitis number (0.3532), while DP category of 76 to 90d was associated with the highest lameness number (0.7976). However, no trends were observed in these traits with different DP length categories. The correlation coefficients between DP and all productive traits were significantly negative and ranged between -0.064 to -0.038. DP had no significant correlations with the health traits. Generally, the dry period of 61-75 days is the most optimum for Holstein Cows raised under subtropical warm climate. However, more studies to confirm these results under the Egyptian conditions are required.

The effect Of bovine mammary secretion during the nonlactating period and of antibiotic preparations on bovine polymorphonuclear neutrophil (PMN) phagocytic function and morphology were evaluated in a series of in vitro multifactorial experiments. Benzathine cloxacillin (CL), benzathine cephapirin (CE), sodium novobiocin (NO), and a combination of dihydrostreptomycin with procaine penicillin G (DP) were prepared in the presence and absence of a peanut oil aluminum monostearate vehicle. The PMN were isolated from bovine blood, and the effect of each antibiotic preparation on PMN function and morphology was evaluated in a buffer, fat, skim, and a combination of fat with skim from bovine mammary secretion during the nonlactating period. The fat and skim were diluted with buffer to approximate their concentration in mammary secretion. Phagocytic functions of PMN were monitored by fluorescent microscopy, which made it possible to estimate both ingestion and intracellular killing of bacteria by PMN. Changes in PMN morphology were monitored by transmission electron microscopy. The ability of PMN to ingest and kill Staphylococcus aureus ATCC 25923 was significantly decreased by fat, skim, CL, CE, NO, and DP. Effects of some antibiotics on ingestion and killing of bacteria by PMN were influenced by the addition of vehicle and by interactions with mammary secretion. Neutrophil morphology was altered by fat, skim, CL, CE, NO, and DP. The detrimental effects of CL, CE, NO, and DP on PMN morphology were influenced (some significantly) by the presence of vehicle and interactions with mammary secretion. There were significant correlations among secretion- and antibiotic-induced changes in PMN ingestion of bacteria, PMN killing of bacteria, and PMN morphology.

The effects of 2 antibiotic preparations administered intramammarily on phagocyte recruitment, function, an morphology were evaluated at the beginning of the nonlactating period. Twelve cows with no clinical or micro biologic evidence of mastitis were assigned to 1 of 2 treatment groups. At the end of lactation, 1 of the antibiotic preparations was infused in a fore- and hind quarter of each cow; the remaining quarters were untreated controls. One group was given benzathine cephapirin; the second group was given sodium novobiocin. Secretion samples were collected from 1 treated and 1 control quarter at 16 hours, and from the remaining 2 quarters at 64 hours after treatment. Total and differential somatic cell counts were determined, and morphology of mammary polymorphonuclear neutrophils (PMN) and macrophages was observed by transmission electron microscopy. In vitro ingestion and killing of Staphylococcus aureus by mammary PMN and macrophages were assessed by fluorescent microscopy, using acridine orange stain. Cells resident in a fixed volume of secretion were incubated with a known concentration of S aureus. Total cell and PMN concentrations were higher in treated than in control quarters. Neutrophils were the predominant cell type in both treated and control quarters over the sampling period. As measured in this study, in vitro ingestion and killing of S aureus by individual PMN from treated quarters was reduced. Antibiotic treatment also increased the proportion of morphologically abnormal phagocytes. There were significant correlations among PMN ingestion, killing, and morphology. However, increased PMN concentrations tended to compensate for the reduced phagocytic function of individual cells. Therefore, efficacy of antibiotic treatment of nonlactating cows may depend, at least in part, on increased PMN concentration, which may tend to compensate for reduced phagocytic function. Compared with PMN, macrophages appeared to have only a minor role in phagocytosis of bacteria.

In the conditions of the Republic of Belarus there was studied the preventive efficiency of various forms of a complex additive Felutsen against polymicroelementoses of calf-bearing dry cows and its influence on some of biochemical blood indexes. Research results proved high prophylactic efficacy of various forms of the additive Felutsen against polyhypomicroelementoses of calf-bearing dry cows. Restoration of a microelement homeostasis of cows made it possible to normalize the functional activity of liver, to prevent development renal insufficiency and dystrophic changes in bone tissue. The most expressed metabolic changes in blood of calf-bearing dry cows were stated after application of the carbohydrate-mineral additive Felutsen-briquette universal. There was given the analysis of structure of studied forms of complex additive Felutsen; indexes of trace element metabolism in cows; indexes of protein metabolism and level of nonprotein nitrogen; indexes of blood characterizing the functional condition of liver and carbohydrate metabolism of cows; indexes of trace element metabolism in cows after the termination of application of the additive.