A network simulation model of large herringbone and parallel milking parlors.

A network simulation model of herringbone and parallel milking parlors was built. Parlor performance was predicted based on the number of cows milked per hour and the amount of milk harvested per shift. Modeled parlors operated using a task-oriented milking routine. The simulation also modeled milking personnel, milking system vacuum pressure and pulsation ratio, and milk yield per cow per milking. The probability distributions of the model components that were used for validation were fitted from data collected from four dairies with the following parlors: double-16 herringbone, double-20 herringbone, double-35 parallel, and double-40 parallel. All fitted distributions were continuous, non-negative, and skewed to the right. The mean number of cows milked per hour (simulated and observed, respectively) was 1) double-16 herringbone, 164.8 and 164.6;2) double-20 herringbone, 207.6 and 206.6; 3) double-35 parallel, 319.2 and 320.2; and 4) double-40 parallel, 361.6 and 362.5. Mean milk yields harvested per shift were 1) double-16 herringbone, 9020 and 9030 kg; 2) double-20 herringbone, 14,800 and 14,746 kg; 3) double-35 parallel, 20,900 and 20,945 kg; and 4) double-40 parallel, 27,100 and 26,974 kg, for simulated and observed yields, respectively. Differences between simulated and observed means for either variable were not significant.

Factors affecting the performance of simulated large herringbone and parallel milking parlors.

A simulation model of double-16 and double-20 herringbone and parallel milking parlors and double-32 and double-40 parallel milking parlors was used to examine the effects of size, design, operating characteristics of the milking system, management strategies, and milk yield on parlor performance. Analysis of factorial experiments indicated that smaller parlors were more efficient. Turns per hour and milk per stall per hour for double-16, -20, -32, and -40 parallel parlors were 5.87, 5.91, 5.21, and 5.00 turns/h and 56.19, 56.46, 49.66, and 47.94 kg/h, respectively. A wider pulsation ratio (60:40 to 70:30) increased performance measures about 4%, and increased vacuum pressure (46.6 to 50.8 kPa) increased performance measures > 6%. Parallel parlors outperformed herring-bones by nearly 8%. Abbreviated milking procedures resulted in a > 6% increase in performance measures over standard milking procedures. Performance response was significantly diminished when the amount of milking labor exceeded deficit amounts (20 to 32 units per milker) for abbreviated milking procedures or standard amounts (13.3 to 16 units per milker) for standard milking procedures. When milk yield increased, turns per hour decreased, but milk per stall per hour increased.

Effectiveness of short-term cooling and vitamin E for alleviation of infertility induced by heat stress in dairy cows.

Four experiments were performed to determine whether cooling cows during final maturation of oocytes and early embryonic development or injection of vitamin E at AI prevented adverse effects of heat stress on pregnancy rates in lactating Holstein dairy cows. In Experiment 1, cows were placed in a cooling facility containing sprinklers and forced ventilation or received shade only from 2 to 3 d before until 5 to 6 d after breeding. Although cooling had no effect on detection of estrus, pregnancy rates were increased slightly for cooled cows (8 of 50 cows; 16.0%) compared with those for cows exposed to shade only (2 of 32 cows; 6.2%). In Experiments 2 through 4, cows were administered 3000 IU of vitamin E or placebo i.m. at AI during two consecutive summers and one winter in Florida. Administration of vitamin E had no consistent beneficial effect on pregnancy rates during summer or winter. Short-term cooling improved pregnancy rates slightly in heat-stressed cows, but administration of vitamin E had no beneficial effects on pregnancy rates during heat stress. Further improvements in cooling schemes during early pregnancy and delineation of antioxidant effects are necessary before such systems become practical for improvement of fertility in heat-stressed dairy cows.

Characterization of clinical mastitis records from one herd in a subtropical environment.

Patterns of occurrence and reoccurrence of clinical mastitis, duration of episodes, and number of quarters treated in a large north Florida dairy over 6.5 yr are described. Monthly incidence of milk disposal due to clinical mastitis varied within and between years and ranged from 1.3 to 4.7% of cow-days in milk. In first parity animals, 37.6% of lactations were treated for clinical mastitis, averaging 1.4 episodes per treated lactation. Almost half of these episodes occurred by d 35 of lactation. For second, third, and fourth or greater parities, 35.5, 48.1, and 56.6% of lactations were treated. These lactations averaged 2.1, 2.3, and 2.8 episodes. In parities 2, 3, and greater than or equal to 4, episodes initiated by d 35 of lactation were 28.2, 23.9, and 20.6% of parity episodes. Seventy-two percent of episodes were treated for less than or equal to 7 d. Sixty-seven percent of episodes were treated in one quarter and treatment in two, three, or four quarters accounted for 21.6, 5.5, and 5.9% of all episodes. When two quarters were treated simultaneously, udder halves (front, rear, right, left) were treated more frequently than were diagonals.

Climatic effects on occurrence of clinical mastitis.

Clinical mastitis records for 6.5 yr from a large north Florida dairy and corresponding daily weather data were analyzed. Monthly incidence of clinical mastitis was expressed as percent of cow-days in milk and graphed against monthly average daily maximum temperature humidity index values and monthly total rainfall. No trends were evident with rainfall. In 3 of 6 yr, monthly incidence of clinical mastitis increased more than 50% above annual incidence, and this followed high monthly temperature-humidity values. Least squares was used to estimate regression coefficients of temperature-humidity index categories based on 999,969 Holstein records. A temperature humidity index category represented the number of days used to calculate average daily maximum temperature-humidity index value. Sources of variation in observed occurrence of clinical mastitis were cow, parity, month, year, interaction of parity by month, and continuous effects of temperature-humidity index categories 2, 6, 15, 30, 60, each to third order and 60 by parity interaction. In all temperature-humidity index categories as the temperature-humidity index value increased, occurrence of clinical mastitis increased. When values rose from 55 to 80, twice as many for 2 d cows showed signs of clinical mastitis.

Factors affecting days of discarded milk due to clinical mastitis and subsequent cost of discarded milk.

Records of clinical mastitis for 6.5 yr from one Florida dairy with 1050 to 1350 cows milking per month were used to predict duration of occurrence of clinical mastitis and to estimate dollar value of discarded milk per lactation with occurrences of clinical mastitis. Only 6.1% of lactations accrued more than 28 d of discarded milk and were responsible for 52.7% of days of discarded milk. Accurate maintenance of herd mastitis records enables calculation of actual days of milk available for sale and provides a useful tool for culling and treating decisions. Duration of each occurrence of clinical mastitis was modeled by fixed effects of breed, season of occurrence, current lactation history of mastitis, number of quarters with clinical signs, and average maximum temperature-humidity index for the 2 d prior to the occurrence (to second order). These effects explained 1.8% of observed variation in duration of occurrence. Random effects of cow explained 5 to 6% of variation. Prediction of duration of occurrence had a mean value of 6.6 d. When economic status of individual animals is evaluated, comparison of days of milk production available for sale is preferable to total days of milk production. Estimated average cost of discarded milk for parities 1, 2, 3, 4, and 5 ranged from $29.73 to 223.98 per lactation.

Occurrence and reoccurrence of clinical mastitis.

Clinical mastitis records for 6.5 yr (July 1977 through November 1983) from a large north Florida dairy were analyzed. Observed frequencies of clinical mastitis were calculated in 7240 Holstein and Jersey lactations. Least squares analyses used Holstein and Jersey lactations greater than 200 d and limited maximum parity to 5 (6732 lactations, 5738 episodes). Solutions for number of occurrences of clinical mastitis adjusted for month of parturition and breed effects were .47, .59, .94, 1.27, and 1.50 for parities 1 through 5. Solutions for number of occurrences across lactation in Holsteins was greater than for Jerseys (1.28 vs. .63). Solutions for occurrence of first episode in Holsteins increased from .35 in parity 1 to .71 in parity 5. Occurrence of episodes two through five increased as parity increased. Similar trends were found in Jerseys with the exception of parity 2. Correlation of residuals between specific episodes increased as episode increased. From episode 2 through 5 probability of another occurrence of clinical mastitis was greater than .75. Solutions for proportion of occurrences of clinical mastitis occurring during the first 35 d postcalving were .60, .36, .31, .30, and .28 for parities 1 through 5. Clinical mastitis in first parity cows occurred primarily during the first 35 d postcalving.

Comparison of teat dips with differing iodine concentrations in prevention of mastitis infection.

Six commercial dairy herds were used to test the relative efficacy of three concentrations of iodine as a teat dip over 12 mo. Concentrations were .1, .25, and 1% iodine with free iodine contents of 3.5, 4.0, and 1.0 ppm. Two concentrations were compared in each herd. The greatest number of new infections (71) occurred in approximately 120 cows whose teats were dipped with the 1% iodine dip, and the fewest (52) occurred in a similar number of cow quarters dipped in .1% iodine; however, differences were not significant. Clinical mastitis was highest in the 1% group. If all clinical mastitis were the result of infection, even if bacteria were not isolated from the pretreatment sample or from samples collected at the start of the study and those quarters were added to the totals, then reduction of new infection with the .1% product would be significant.

Effect of overmilking on udder health.

This study evaluated the effect on udder health of extending the milking period with or without vacuum fluctuation. Eighty cows were allotted into treatment groups consisting of 1) Control milked with normal milking equipment and the milker removed as soon as milk flow ceases; 2) milked for 12 min with normal equipment; 3) milked 12 min with induced vacuum fluctuations; and 4) normal milking time with induced fluctuations. Groups 2 and 3 had more newly infected quarters than groups 1 and 4. However, there was no difference in the number of cows becoming infected. The increase in new infections is due to more quarters of already infected cows becoming infected rather than more new cows becoming infected. Extending the machine-on time appeared to increase the rate of cross infection presumably by lengthening the time of highest risk. Cows in groups 2 and 3 required more therapy of clinical mastitis which was a reflection of the higher new infection rate rather than of a change in trauma to the udder. Increasing the unit-on time had no apparent effect on external teat end condition.

Effect of drying off practices on mastitis infection.

Two methods of drying off cows, intermittent milking and abrupt cessation, were studied with data from 9254 quarters of cows on 36 New York dairy farms. Eighty percent of the cows were infused with nine different antibiotic preparations separately at drying off, and 20% served as controls. Cows dried off by intermittent milking has a similar number of quarters infected at drying off, had fewer spontaneous recoveries, had a higher rate of cure, and developed fewer new infections in control quarters in comparison with cows dried off by the stop method. Methods worked equally well in treated cows. However, intermittent milking resulted in fewer infections at subsequent calving than stop milking in nondry treated cows. Cows producing less than or equal to 4 kg of milk at drying off were more highly infected than higher producing cows. Hind quarters contained more infections at drying off, fewer responded to therapy, and more infections developed in the dry period. Cows with dry periods of less than or equal to 30 days had more infected quarters respond to therapy and had the fewest new infections in the dry period. The role of routine dry cow therapy in decreasing the number of infections in dairy herds by preventing new infections and removing old infections is demonstrated.