Development and evaluation of a micropipette tip washing system.

A tip washing system has been developed for use with disposable polypropylene micropipette tips of different sizes. The primary hardware components of the system are constructed from polyvinyl chloride (PVC) and Plexiglas. The system relies on a low concentration of detergent, gravity or aspirator-assisted feed and flush of minimal volumes of distilled/deionized water, and air or oven drying of the tips. Comparative analyses of new versus washed tips in FAO/IAEA radioimmunoassay (RIA) and enzyme linked immunosorbent assay (ELISA) protocols indicated that disposable polypropylene micropipette tips of various sizes (e.g. 5-300 and 50-1000 microl) can be washed and reused at least ten times without introducing detectable variability into the results of either assay, if the tips are properly washed and dried using this system. Recovery cost of the system can be achieved after approximately eight reuses of 1000 tips, excluding technician time.

Factors affecting skim milk progesterone assay results.

Five studies were performed to determine factors affecting progesterone concentration in skim milk. Results of the first study indicated that progesterone concentration was higher in skim milk of samples kept 16 hours in an ice bath (0 C) than of those left at room temperature (21 C). In the second study, this temperature effect was found to be reversible, with skim milk progesterone concentration increasing when whole milk samples were cooled prior to centrifugation. In the third study, [3H]-labeled progesterone was used to determine the relationship between fat content of foremilk (the first milk obtained from the teats), midmilk (milk obtained midway through milking), and strippings (milk obtained immediately after milking machines have been removed) samples and temperature (4 C and 21 C) on the percentage of progesterone in the skim milk fraction. The relationship between percentage of butterfat and percentage of progesterone in skim milk was linear when the log of these variables was used for calculations. In the fourth study, assayable progesterone in the skim milk fraction of foremilk, midmilk, and strippings was affected by temperature. In the fifth study, a multiple-regression procedure was used to determine the amount of variation in percentage of radioactive progesterone in the skim milk fraction. Independent variables (whole milk butterfat and temperature of incubation [1, 3, 13, 22, 37, and 50 C]) and the natural log of each variable, were entered into a stepwise multiple-regression analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of high daytime temperatures on the intake and utilisation of water in lactating Friesian cows.

Four primiparous Friesian cows in mid-lactation and housed in climate chambers were simultaneously exposed to three sequential climate treatments: 1, a three-week period in a thermoneutral environment (ambient temperature Ta 14-21 degrees C and relative humidity r.h. 60-70%); 2, a similar period during which they were exposed to Ta max. 38 degrees C/r.h. max. 80% for up to 7 h and Ta 14-21 degrees C/r.h. 60-70% for 17 h each day; and 3, a three-week period during which they were subjected once more to the thermoneutral conditions described for 1. Water and a complete feed were constantly available. Compared with water intake (drinking water + feed water) under thermoneutral conditions cows exposed to treatment 2 significantly increased their mean intake by 12.2%; in three cows, this involved a phase-shift of greater than 20% in drinking habits from day (hot) to night (cool) time. Water balance trials conducted at the mid-point of each treatment revealed that the mean losses of water via urine, faeces, milk, sweat and saliva as a percentage of water intake changed significantly resulting in a net gain (retention) of body water. An accompanying significant increase in live weight despite a 9.1% decrease in DM intake during treatment 2 confirmed the water retention results. On return to thermoneutral conditions (3), the cows exhibited a marked weight loss and a significant increase in urinary water excretion over treatment 1 and 2 values, signifying that a large proportion of the water retained during 2 was of extracellular origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Milk production of Friesian cows subjected to high daytime temperatures when allowed food either ad lib or at night-time only.

Four lactating Friesian cows housed in climate chambers were exposed to the following sequential treatments: I, a four-week period when they were allowed constant access to an ad lib supply of a complete diet and water in a thermoneutral environment (ambient temperature (Ta) 14 to 20 degrees C and relative humidity (r.h.) 50 to 75%); II, a five-week period during which they were exposed to Ta 38.5 degrees C/r.h. 85% for 61/2 h during daytime and Ta 14 to 20 degrees C/r.h. 50 to 75% for the remainder of each day with constant access to ad lib complete diet and water; III, a four-week period under the same environment as treatment II but with access to food restricted to between 19.00 and 07.00; IV; a four-week period under the environment and feeding regime described for treatment II. The voluntary food intake (VFI) of cows subjected to II was not depressed as a result of high daytime temperature despite the fact that they exhibited daytime clinical features indicative of heat stress; this was because of a 27.8% compensatory increase in night-time feeding. Nevertheless there was an accompanying significant increase in the rate of lactation decline of 8.7% per month greater than that normally expected under the thermoneutral conditions (I). Subsequent restriction of food access to night-time (III) resulted in a significant reduction in mean VFI of 7.5%; however, the rate of lactation decline was drastically reduced to a value not dissimilar to the natural decline of 3.97% per month observed under thermoneutral conditions (I).