Methods of collection and lipid composition of teat canal keratin in dry and lactating cows

Relationship between previous history of Streptococcus uberis infection and response to a challenge model

Streptococcus uberis is the most common cause of clinical mastitis at calving in pasture-based dairy cows. Results of experimental inoculations were compared with cows' previous history of infection to help define a model for susceptibility to Str. uberis mastitis. Cows used had either no apparent history of intramammary infection (IMI) by Str. uberis or other major mastitis pathogens throughout their productive lifetime ('apparently uninfected'; AUI), or had a confirmed history of Str. uberis IMI ('historically infected'; HI). Cows were exposed to Str. uberis in sequential steps: dipping of the teat end (DIP; n=53 cows); a teat canal inoculation (TCI; n=33 cows); and, finally, intramammary inoculation challenge (IC; n=7 cows). Only cows that remained free of infection at each step progressed to the next phase. Infection rates were similar between AUI or HI cows following the DIP (9 and 17% respectively), or the TCI (75 and 68% respectively). Physical and biochemical traits of cows were examined. Analysis of traits prior to inoculations implied that HI cows produced more milk fat, while AUI cows tended to have longer teat canals. Analysis of traits for cows that became infected following DIP, implied that there was a positive association with milk fat production and negative association with somatic cell count (SCC), while there was a positive association with the duration of p.m. milking, and negative association with SCC in those cows that became infected following TCI. Only AUI cows became infected following the IC inoculation. Similarity in response to experimental inoculation between the two groups suggests that the current dip or teat canal inoculation (using a 3-mm depth of inoculation) models are not good predictors of natural resistance to Str. uberis. However, a population of cows was identified that remained uninfected after DIP, TCI and IC, and may comprise a resistant phenotype.

Influence of pulsationless milking on teat canal keratin growth and turnover

In two separate experiments, the effects of pulsationless milking and milking vacuum on the rate of keratin removal from the teat canal were determined. Sixteen cows were milked with or without pulsation for either a single milking or for eight milkings. Milking without pulsation removed 10% of keratin present before milking, significantly less than milking with pulsation, which removed 32%. After eight milkings (4 d) without pulsation, up to 20% more keratin had accumulated within the teat canal but the rate of keratin regeneration reduced significantly upon return to pulsation milking. In a second experiment, ten cows were milked at 45 or 55 kPa and without pulsation. Only the absence of pulsation significantly reduced keratin loss during milking. Keratin loss during milking appears to be controlled by liner compression rather than by the rate of milk flowing through the teat canal. Pulsationless milking may increase penetrability of the teat canal to bacteria by reducing the natural rate of keratin removal during milking and reducing the rate of keratin regeneration.

Physical characteristics of the bovine teat canal and their influence on susceptibility to streptococcal infection

Physical characteristics of the bovine teat canal were examined for their influence on susceptibility to intramammary infection. All quarters of 18 cows were inoculated with 2 x 10(5) cfu Streptococcus agalactiae (Trial 1) and 20 cows with 10(5) cfu Str. uberis (Trial 2) 3-4 mm into the teat canal every 3 d for 12 d. Incidence of quarter infection was similar for both pathogens, 30/72 (42%) in Trial 1 and 32/80 (40%) in Trial 2. Logistic regression analysis showed that probability of infection by Str. agalactiae increased significantly with an increase in quarter peak flow rate (P < 0.05) whereas probability of infection increased for Str. uberis with a decrease in teat canal length (P < 0.05). A significantly higher (P < 0.001) incidence of infection by Str. uberis was observed in quarters that contained a low wet weight (< 1.8 mg) of removable keratin compared with those that contained > 1.8 mg keratin, but there was no correlation between weight of keratin and length of the teat canal. Infections by Str. uberis took significantly less (P < 0.05) time to show a rise in somatic cell count above 7.5 x 10(5) cells/ml than Str. agalactiae. The results provide evidence that these pathogens use different mechanisms to pass through the teat canal.

Influence of pulsationless milking on teat canal keratin and mastitis

Twenty-four Holstein cows, producing at least 21 kg of milk/d, were used in two replicate experiments to determine the effect of presence or absence of pulsation on loss of teat canal keratin during machine milking. Left quarters were milked without pulsation and right quarters were milked with pulsation. On d 0 and 10, keratin was collected from one left and from one right teat canal of each cow prior to milking and from the remaining two teat canals after milking. Milk was collected for assessment of SCC and bacteriological status on d 0 and approximately every 3 d until d 18. Quantity of keratin recovered before milking on d 10 did not differ between teats milked with or without pulsation, but loss of keratin because of milking was greater from teats milked with pulsation. By d 7, 30% (12 of 43) of quarters milked without pulsation had become infected, but no (0 of 47) quarters milked with pulsation were infected. By d 14 to 16, new infections had increased to 68% (28 of 41) of quarters milked without pulsation and 2% (1 of 43) in quarters milked with pulsation; mean SCC in pulsationless quarters increased sevenfold relative to pulsation quarters. Protein and water content of keratin did not differ because of treatment, and changes in lipid composition were minor. Histological analysis of the teats of 4 cows indicated that the mean diameter of the teat canal, within 2 h after milking, was greater without pulsation than with pulsation (680 vs. 483 microns).

Increased susceptibility to intramammary infection following removal of teat canal keratin

Influence of teat canal keratin on susceptibility to intramammary infection was investigated in lactating Jersey cows. In each of two replicate trials, keratin was removed from the left teats of 20 cows immediately before milking. Immediately after milking, all teats were exposed to bacterial challenge by immersion in a suspension of Streptococcus agalactiae (5 x 10(7) cfu/ml). Bacterial challenge was repeated after the next four milkings. Foremilk samples were obtained for 8 d after keratin removal to determine infection status. A mammary quarter was classified as infected based solely upon the bacteriological criteria outlined by the National Mastitis Council. The rate of infection in quarters from which keratin was removed was greater than that in control quarters. Infection rates were 26.3% for keratin-removed quarters and 8.3% for control quarters in trial 1 and 13.5 and 0%, respectively, in trial 2. When more stringent criteria (recovery of greater than 100 cfu of S. agalactiae/ml in three or more successive milk samples and a SCC of greater than 10(6)) were used to identify a subset of infections that were clearly intramammary, infection rates were 9.3% for keratin-removed quarters and 1.4% for control quarters. Thus, partial removal of keratin from the teat canal compromised the ability of the teat to prevent passage of bacterial pathogens from the external environment into the mammary gland.

Effect of clinical and subclinical mastitis on lipid composition of teat canal keratin

Two experiments were conducted to investigate lipid composition of teat canal keratin when different conditions of bacterial colonization and quarter inflammation were present. In Experiment 1, 11 multiparous cows with subclinical mastitis (bacteria present but no visible inflammation) in at least one quarter were selected for study. Quarters that were sampled and found negative for bacterial growth were classified as control. In Experiment 2, 10 multiparous cows with clinical mastitis in one or more quarters were selected. Milk samples from inflamed quarters were cultured to identify mastitis pathogens; these quarters were classified as clinical; all other quarters were classified as control. Teat canal keratin was collected from all quarters just before an a.m. milking, samples were weighed, and lipid determinations were conducted by TLC. Keratin from subclinical quarters compared with keratin from control quarters did not differ in either neutral lipid or fatty acid composition. Total lipid was significantly higher in keratin from teats of clinical quarters than in keratin from control quarters (27.8 vs. 21.5 microgram/mg). Neutral lipid composition of keratin was similar between teats from clinical quarters and teats from control quarters. In Experiment 2, quarter foremilk samples were also obtained to determine lipid composition. The FFA in milk from clinical quarters contained fewer short-chain fatty acids, whereas polyunsaturated fatty acids were significantly higher in milk from clinical quarters.

Lipid composition of teat canal keratin collected before and after milking from Holstein and Jersey cows

In three experiments, keratin was collected from individual teats of 40 Holstein and 20 Jersey cows immediately before and after milking. In Experiments 1 and 2, keratin collected from teats of 20 Holstein cows before milking was compared with keratin collected after milking. In Experiment 3, keratin was collected from two teats of 20 Jersey and 20 Holstein cows before milking and compared to the other two teats of the same cows after milking. All three experiments yielded similar results. In Holsteins, keratin weight before milking was 1.6 times greater than keratin weight after milking (3.1 vs. 1.9 mg). In Jerseys, only small amounts of keratin were removed during milking (3.5 mg before vs. 3.1 mg after) In Holsteins and Jerseys, neutral lipid concentration was 1.6 times greater after milking than before, suggesting that when keratin was removed during milking, only moderate amounts of lipid were removed. In Holsteins, total lipid collected per teat was similar before or after milking (59.2 vs. 48.5 micrograms). Results demonstrate that keratin collected after milking had a different lipid composition than keratin collected before milking.

Regeneration of teat canal keratin in lactating dairy cows

This study was designed to determine the regeneration rate of teat canal keratin in two groups of 10 lactating Holstein cows. The weight of keratin obtained upon successive collections of keratin was determined. Intervals between successive collections were varied between 8 and 72 h. Following initial collection, the quantity of keratin removed was regenerated within 1 to 2.5 d. The rate of keratin regeneration per teat was approximately 1.5 mg of wet weight or .6 mg of dry weight per 24 h. The concentration (microgram lipid/mg keratin, wet weight) of lipid in keratin samples collected during regeneration was almost twice that present initially or after regeneration was complete. With the exception of free cholesterol, composition (%) of lipid components of keratin did not differ between samples collected initially, those collected early in the process of regeneration, and those collected after the mass of keratin removed had been replaced. Although data suggest that keratin matures during the process of regeneration, maturation appears complete by the time mass of keratin is fully regenerated. Additionally, the quantity of keratin recovered at initial sampling was inversely correlated with milk production. We hypothesize that as milk production increases, more keratin is lost during milking.