Somatic Cells in Milk-Physiological Aspects and Relationship to Amount and Composition of Milk.

Somatic cells in milk include epithelial cells from the gland and leukocytes from the blood. Epithelial cells are elevated in very early and late lactation. Leukocytes increase during mastitis infection or injury. They have phagocytic properties and combat invading organisms. Mean somatic cell counts of each milking over a 1-month period for cows with no udder infection, non-pathogens, or pathogens, were 169,500, 225,800, and 997,800 cells per ml, with coeffecients of variation of 94, 66, and 82%. Advanced age, late lactation, and a previous history of mastitis are related to elevated cells. Milk loss in subclinical mastitis is related to somatic cell counts. On a quarter basis, loss started at 500,000 cells per ml, progressed to 7.5% at 1 million, and 30% at 5 million. In cell counting programs associated with monthly testing of individual cows, those cows with two cell counts over 1 million cells per ml produced over 1,000 pounds of milk per lactation less than other cows in the same lactation whose cell count never exceeded 500,000 per ml. Use of cell counting on an individual cow basis improves its usefulness as a management tool for the dairyman compared to bulk tank counts. Literature data suggest the following changes in the milk composition from quarters definitely positive to mastitis screening tests based on somatic cell counts compared to normal quarters (values represent percent of normal): total solids (92), lactose (85), fat (88), total protein (100), caseins (82), whey protein (162), chloride (161), sodium (136), potassium (91), pH (105), lipase activity (116), and acid degree value (183).

N-Acetyl-B-D-glucosaminidase activity and somatic cells in goat milk.

N-Acetyl-B-D-glucosaminidase activity, somatic cell count, and udder infection status were determined in milk of nine Saanen goats. Plasma enzyme activity was also measured. Individual half udder milk samples were taken for 12 d over a 3-wk period and animals were bled weekly. Three of the 18 udder halves were infected with coagulase-negative staphylococci over all 12 sampling d. The N-acetyl-B-D-glucosaminidase and somatic cells in milk were significantly elevated in samples where minor pathogens were isolated. Plasma enzyme was variable among goats but not within goats or across weeks. Greater daily variation was seen in somatic cell count as compared to milk enzyme activity. Correlation between milk N-acetyl-B-D-glucosaminidase and somatic cell count was .54.

N-Acetyl-B-D-glucosaminidase in milk and blood plasma during dry and early postpartum periods.

Milk and plasma N-acetyl-B-D-glucosaminidase activity was determined for cows during the dry and early postpartum periods. Milk samples were taken from individual quarters of 12 cows from 7 d preceding dry off until calving. Weigh jar milk samples were taken daily for 28 d postpartum from 9 of the 12 cows. Somatic cell concentration was also measured in the postpartum samples. N-Acetyl-B-D-glucosaminidase activity of mammary secretions was significantly elevated in the dry period. Activity in mammary secretions was significantly higher than blood plasma concentrations during the dry period, which suggests that the enzyme present in mammary secretions comes mainly from within the gland. Milk enzyme concentrations declined sharply by 4 d postpartum and gradually declined through 28 d postpartum. Activity was still slightly elevated at 28 d postpartum as compared with normal lactation. Greater daily variability was seen with somatic cells than with N-acetyl-B-D-glucosaminidase. However, somatic cells were more responsive to clinical infections postpartum, showing significant elevations in both clinical episodes. The enzyme was elevated in one clinical case, but relatively unchanged in the other. Plasma levels were constant throughout both trials.

Mastitis therapy for cows elevated somatic cell counts or clinical mastitis.

Intramammary treatment with a broad spectrum antibiotic was evaluated for cows treated after a single high monthly somatic cell count of for cows with clinical mastitis. Forty-three quarters of 36 cows were treated after a high somatic cell count, and 56 quarters of 48 cows were treated after clinical symptoms. There was no significant decrease of cell count in response to treatment in the high somatic cell group. Organisms were isolated from 70% of the pretreatment quarter samples, but only 13% of the isolates were major pathogens. Bacteriological cure rate for major and minor pathogens combined was 23.3%. Treatment costs (antibiotics and discarded milk) were $38.19 per animal treated. Organisms were isolated from 70% of the pretreatment quarter samples of the clinical group. Forty-nine percent of the isolates were major pathogens. Bucket and quarter somatic cell counts decreased following treatment. Production rose posttreatment almost back to normal. Bacteriological cure rate was 21.6% for major and minor pathogens combined with 37% of the cured quarters becoming reinfected with minor pathogens during the monitoring period. The predominant minor pathogens isolated micrococci and coagulase negative staphylococci. The predominant major pathogens were Streptococcus uberis and coliforms.

Effect of infection status on quarter milk production and composition following omitted milking.

Sixteen cows in middle to late lactation were milked for 3.5 days at 12-h intervals except for a 24-h interval between third and fourth milkings. A cowside quarter milking unit was used. Quarters were classified by infection status. Milk chloride, lactose, somatic cell concentrations, N-acetyl-B-D-glucosaminidase activity, and cell differential counts were determined. Following the omitted milking, concentrations of milk chloride and somatic cells were elevated and lactose concentration reduced in infected quarters. In uninfected quarters, chloride concentration increased, and lactose concentration decreased after the 24-h interval. The milk N-acetyl-B-D-glucosaminidase activity was elevated only in quarters infected with major pathogens. Changes of milk secretion induced by an omitted milking are affected by infection status, and additional secretory cell damage in quarters infected with a major pathogen may result from an omitted milking.

Use of a combination of propylene glycol and niacin for subclinical ketosis.

Twenty-six cows that developed positive milk tests for ketosis in early lactation were randomly assigned to one of three groups: control, propylene glycol (125 ml/d), or 125 ml of propylene glycol plus 12 g of niacin daily. Treatments were administered for 7 d. Changes in milk production, milk composition, and feed intake were similar for all three groups. None of the cows in any of the groups developed clinical ketosis. During the 14-d monitoring period from the start of treatment there were similar increases in blood glucose in all groups. Declines in plasma beta-hydroxybutyrate and free fatty acids over the period were also similar for all treatments. Results reinforce the concept that optimum feeding and management reduces the need for additives for ketosis control.

Relationship of insulin concentration to blood metabolites in the dairy cow.

Jugular blood samples were taken at regular intervals from 31 ketosis-prone cows from 2 wk prepartum to 7 wk postpartum. Eleven cows exhibited elevated blood ketones and depressed blood glucose indicative of subclinical ketosis. There were no significant differences between means of normal and subclinically-ketotic cows in serum insulin or blood metabolites prior to calving. However, in early lactation, those cows which developed ketosis showed depressed serum insulin, blood glucose, and plasma triglycerides with elevated ketones, acetate in blood, and free fatty acids and cholesterol in plasma. Milk production was also lower in ketotic cows. Correlations within cow between serum insulin and glucose, total ketones, acetate of blood and free fatty acids, triglycerides, and cholesterol in plasma were .014,--.307, .080,--.421, .413, and -.002 for normal cows and .348, -.425, -.324, -.317, .298, and -.131 for subclinically-ketotic cows. It is suggested that low insulin during ketosis is a reflection of depressed blood glucose and, consequently, adipose lipolysis and hepatic ketogenesis are accentuated while acetate utilization and hepatic triglyceride release are depressed.

Blood and liver metabolites in fed and fasted diabetic goats.

Two trials were to study alloxan diabetes in goats. The data were grouped: 1) normal fed goats (10); 2) 48-h fasted goats (5); 3) fed goats sampled 96 h after alloxan treatment (5); and 4) goats treated with alloxan following a 48-h fast and sampled 96 h after alloxan treatment with continued fasting (3). Groups 1 and 4 exhibited the following means: serum insulin 43.9, 16.4, 9.4, and 6.7 muU/ml; blood glucose 55.0, 47.3, 219.6, and 485.6 mg/100 ml; blood ketones 4.3, 2.6, 36.6, and 28.6 mg/100 ml; blood acetate 4.7, 4.0, 42.7, and 4.9 mg/100 ml; plasma-free fatty acids 1.8, 10.0, 14.4, and 40.5 mg/100 ml; and plasma triglyceride 13.3, 7.0, 47.6, and 12.2 mg/100 ml. Liver samples from five fed goats before and 12 days after alloxan treatment exhibited the following means: phospholipid 27.5 and 26.1 mg/g; triglyceride 21.2 and 98.9 mg/g; and percent lipid 7.2 and 14.4. The diabetes was accompanied by fatty liver development and probably reduction in utilization of acetate and triglyceride in the fed animals.

Effects of feeding oleic acid or hydrogenated vegetable oils to lactating cows.

In feeding trials to clarify the mechanism by which unsaturated oils depress milk fat percentage, oleic acid at 250 or 500 ml per cow per day did not reduce milk fat percentage significantly. At 500 ml these changes were significant (control, oleic): rumen acetate 61.6, 60.3%; rumen propionate 19.4, 21.0%; milk fat content of 18:1 trans fatty acid 3.0, 8.0%; and of 18:2 cis fatty acid 2.2, 1.4%. Feeding hydrogenated vegetable oil containing 13% trans acid at 454 g per cow per day decreased slightly milk fat percentage and elevated plasma cholesterol 190 to 245 mg/100 ml and 18:1 trans fatty acid in milk fat 4.2 to 6.2%. Hydrogenated vegetable oil containing 49% 18:1 trans acid at 454 g daily decreased milk fat 3.9 to 3.1%. Milk fat triglycerides decreased in short chain fatty acids and increased in 18:1 trans 2.6 to 11.2%, 18:1 cis 22.9 to 29.0%, and 18:2 trans .2 to 1.8%. Milk phospholipids decreased 14.1 to 9.6% in 14:0 fatty acid and increased .3 to 3.1% in 18:1 trans and 20.5 to 31.4% in 18:1 cis. Blood cholesterol esters were increased 152 to 195 mg/100 ml. The data lend support to the concept that trans acids or compounds produced in the rumen during their formation from polyunsaturated fatty acids are responsible for the milk fat depression from unsaturated oils.

Oral nicotinic acid as a treatment for ketosis.

Changes in blood metabolites and milk production were measured in eight cows with subclinical or clinical ketosis following treatment with daily doses of 12 g nicotinic acid fed with the concentrate mixture. Ketotic cows displayed a positive milk ketone test, reduced milk production and feed intake, hypoglycemia, hyperketonemia, and elevated free fatty acids in plasma. The milk ketone test was negative in all cows 5 to 9 days following initiation of treatment. After 7 days of treatment, milk production and glucose in plasma were increased while there were decreases in plasma beta-hydroxybutyrate and free fatty acids. No relapses occurred.

A combined resorcin-crystal violet-periodic acid-Schiff stain.

Resorcin-crystal violet followed by the periodic acid-Schiff (PAS) reaction can be used to stain elastic fibers and membranes greenish-yellow, while coloring PAS-positive materials pink to purple. Other tissue components are left unstained.

Effects of administration of nicotinic acid on glucose, insulin, and glucose tolerance in ruminants.

Effects of nicotinic acid on glucose metabolism were studied in a series of experiments with goats. Oral administration of single doses of nicotinic acid (6.5 to 17.0 g) elevated blood glucose, impaired glucose tolerance, and elevated insulin. The magnitude of the effects was related positively to nicotinic acid dosage. Maximum effect occurred 2 to 3 days after administration. Blood glucose was elevated, with or without glucose administration, despite markedly elevated insulin. However, exogenous insulin given 48 h after nicotinic acid still reduced blood glucose although the response was delayed and was less than in control animals. A lactating cow given 160 g nicotinic acid exhibited alterations in glucose metabolism similar to control animals. These studies demonstrate that nicotinic acid, in addition to previously reported effects on lipid metabolism, also has significant effects on carbohydrate metabolism.

Dynamics and significance of coagulase-negative staphylococcal intramammary infections.

Cows (n = 139) were sampled within 17 d postpartum and monthly thereafter to examine dynamics of mammary infections and relationships between infection status, milk yield, SCC, NAGase activity, and chloride concentration. Forty-eight and 67% of cows and 19.5 and 30.5% of quarters were infected at first test and lactation end, respectively, with 51% of all infections present at first test. Coagulase-negative staphylococci accounted for 67 and 65% of first test and total infections with 85% persisting to lactation end. Animals with coagulase-negative staphylococci infections had significantly elevated quarter SCC and NAGase activity and a decrease of 821 kg mature equivalent lactation milk production compared with uninfected animals. Clinical cases with no bacterial isolation or major pathogen infections were associated with significant elevations in bucket and quarter milk SCC, NAGase activity, chloride concentration in quarters, and a decrease of 1153 kg mature equivalent lactation milk production as compared with uninfected animals. Correlations between milk production and in SCC and ln NAGase and between ln SCC and ln NAGase were -.15, -.25, and .55 (-.23, -.28, and .41 for first lactation only).

Factors related to milk loss in quarters with low somatic cell counts.

Relationship between milk production and milk composition was studied through comparisons of udder halves within cow. Cows were milked by milking unit for separate quarters of udder. Six trials had six cows per trial. Trial length was 3 d, and milkings were at 12-h intervals. Foremilk samples were taken aseptically for bacterial analysis. Milk weights by quarter were recorded, and samples by quarter were analyzed for concentrations of lactose, somatic cells, and chloride. Milk cell differential counts and N-acetyl-B-D-glucosaminidase activity also were determined. Eighty-four percent of quarter milk samples contained less than 400,000 cells/ml. Differences between right and left udder halves with respect to all measurements were computed. For halves of udders within-cow correlation coefficients for differences between production and log(base 2) somatic cell count, lactose, chloride, bacterial presence, neutrophil percent, lymphocyte percent, macrophage percent, and N-acetyl-B-D-glucosaminidase activity were -.16, .23, -.31, .09, .12, .01, -.14, and -.41. Regression coefficients of milk production (kg) on somatic cell count log(base 2) cells per milliliter, lactose (%), chloride (mg/100 ml), and N-acetyl-B-D-glucosaminidase (nmol/min per ml) were -.12, .57, -.05, and -.46. From negative correlations between production and concentrations of chloride, somatic cells, and N-acetyl-B-D-glucosaminidase activity, differences between udder halves in production may be related to changes of the blood-milk barrier, leukocyte diapedesis, and loss of integrity of secretory cells.

Comparison of pregnancy diagnosis by milk progesterone on day 21 and day 24 postbreeding: field study in dairy cattle.

Milk samples collected at 21 and 24 d after breeding were used to diagnose cows as pregnant, questionable, or not pregnant with high, intermediate, or low progesterone in the milk. Total agreement of pregnancy diagnosis in cows by milk progesterone at 21 d postbreeding and diagnosis by return to estrus or palpation of reproductive organs was 85.8% (77.4% on pregnant progesterone diagnosis and 97.2% on not pregnant progesterone diagnosis). Total agreement of diagnosis by progesterone at 24 d postbreeding and diagnosis by estrus or palpation was 88.4% (83.5% on pregnant progesterone diagnosis and 95.3% on not pregnant progesterone diagnosis). Although total accuracy of cows diagnosed both pregnant and not pregnant by milk progesterone on d 24 postbreeding was greater than diagnosis on d 21 postbreeding when cows in estrus by d 24 were deleted from the data, other comparisons for effect of day on accuracy of diagnosis were not different. Total accuracy of diagnosis on d 24 was not increased by using milk progesterone on both d 21 and 24. Samples collected on the day of breeding indicated that 18 of 960 (1.9%) had intermediate or high progesterone. Fourteen (1.5%) additional cows had progesterone above levels expected for a cow in estrus.

Changes in bovine milk secretion following intramammary infusions of concanavalin A, oyster glycogen, or water.

Effects of sterile intramammary infusion of Concanavalin A on milk secretion were contrasted with infusion of oyster glycogen or water. Twenty-four cows were infused intramammary with 100 mg Concanavalin A, oyster glycogen in 20 ml water, or with 20 ml water alone. Concentrations of lactose, somatic cells, immunoglobulins G and A, serum albumin, and activity of N-acetyl-B-D-glucosaminidase were determined in milk. Blood N-acetyl-B-D-glucosaminidase activity and concentrations of blood immunoglobulins G and A and serum albumin were determined. Oyster glycogen and concanavalin A caused inflammation in treated quarters; peak elevations of milk somatic cell counts, serum albumin, immunoglobulin G concentrations, and N-acetyl-B-D-glucosaminidase activity were at 12 to 36 h following treatment. Milk production and lactose concentration were reduced by oyster glycogen and Concanavalin A. Selective indices of relative accumulation of milk immunoglobulins decreased following Concanavalin A and oyster glycogen, whereas the N-acetyl-B-D-glucosaminidase activity selective index generally remained unchanged. Inflammation reduced the selective accumulation of immunoglobulins, and absence of change in the N-acetyl-B-D-glucosaminidase selective index indicated that blood is not a major source of milk N-acetyl-B-D-glucosaminidase.

Relationship of milking rate to somatic cell count.

Information on milking rate, monthly bucket somatic cell counts, mastitis treatment, and milk production was obtained from 284 lactations of Holstein cows separated into three lactation groups. Significant correlations between somatic cell count (linear score) and other parameters included production in lactation 1 (-.185), production in lactation 2 (-.267), and percent 2-min milk in lactation 2 (.251). Somatic cell count tended to increase with maximum milking rate in all lactations, but correlations were not statistically significant. Twenty-nine percent of cows with milking rate measurements were treated for clinical mastitis. Treated cows in each lactation group produced less milk than untreated cows. In the second and third lactation groups, treated cows had a shorter total milking time and a higher percent 2-min milk than untreated cows, but differences were not statistically significant. Overall, the data support the concept that faster milking cows tend to have higher cell counts and more mastitis treatments, particularly beyond first lactation. However, the magnitude of the relationship was small.

Iodine in field milk samples and effects on mastitis organisms.

Bulk tank milk samples collected from 175 dairy herds throughout Wisconsin averaged 466 micrograms of iodine per liter with 11% of the samples containing greater than 1000 micrograms per liter. From questionnaires on feeding and management, use of iodine supplements in feed was associated with increased iodine in milk. One gram of ethylenediamine dihydriodide was fed daily for 2 wk to dairy cows with a history of mastitis. Milk iodine increased from 210 to 6225 micrograms per liter. There was no significant effect on somatic cells, mastitis organisms, or incidence of clinical mastitis.

Calcium redistribution into subcutaneous fat at parturition in the dairy cow.

Blood samples and subcutaneous fat biopsies from six dairy cows at -14, 0, 14, and 28 days of parturition were analyzed to test the hypothesis that movement of calcium into subcutaneous fat contributes to hypocalcemia of parturient paresis. Plasma and subcutaneous fat calcium decreased while plasma free fatty acids increased at parturition. No trends were significant in magnesium or total lipid content of subcutaneous fat. Calcium content of subcutaneous fat was related positively to calcium concentration in plasma.