- Email: [email protected]
Multichannel Digital Recording for Oviposition in Japanese Quail
766
J . BlELY AND Y . POMERANZ
Offic. Anal. Chem. Washington, D.C. Bell, J. M., and G. I. Christison, 1972. Personal communication. University of Saskatchewan, Saskatoon, Saskatchewan. Canada Feeds Act, 1960, C 14 and Feeds Regulations 1967. Queen's Printer and Controller of Stationery. Ottawa, Canada. Pomeranz, Y., and G. S. Robbins, 1972. Amino acid composition of buckwheat. Agr. Food Chem. 20: 270-274. Pomeranz, Y., and G. S. Robbins, 1973. Amino acid
composition of maturing barley. Cereal Chem. 49: 560-565. Sure, B., 1955. Nutritive value of proteins in buckwheat and their role as supplements to protein in cereal grains. Agr. Food Chem. 3: 793-795. White, J. W., F. J. Halken and A. C. Richer, 1941. Experiments with buckwheat. Pennsylvania Agr. Experiment Station, Bull. 403: 1-62. Wyld, M. K., R. L. Squibb and N. S. Scrimshaw, 1958. Buckwheat as a supplement to all-vegetable protein diets. Food Res. 23: 407-410.
R.J.
PLANCK
Department of Zoology, University of Western Ontario, London, Ontario, Canada (Received for publication August 16, 1974)
ABSTRACT A multichannel recording system is described which offers the advantages of accuracy and low cost. The system was a commercially available digital printer and clock mechanism. Switch decoding circuitry is presented in the article. The system described will record from 200 switches connected to egg trip levers on bird cages. An example of data obtained from two Japanese quail illustrates the smooth patterns of lay seen when recorded to one minute accuracy. POULTRY SCIENCE 54: 766-771, 1975
INTRODUCTION
VIPOSITION times have been reported for birds in numerous studies of ovulation-ovipositional cycles. The need for an accurate means for determining these times has been met by a number of means, for example, time lapse photography (Arrington et al, 1962) and the use of strip-chart event recorders (Harrison and Becker, 1969). These methods generally have the problem of requiring the investigator to transcribe the visual presence of eggs, from a photograph or a tick mark, to numerical form for analysis. These methods are relatively expensive for large numbers of birds both in the labor time required for transcription and the purchase of the equipment.
O
To alleviate these problems we have been using a system for recording oviposition times of Japanese quail which provides a printed record of cage number and time of day to the minute. This system is capable of 200 channels or more at a cost of less than ten dollars per channel. MATERIALS AND METHODS The data acquisition system consists of a digital clock (Digitec Model 662, United Systems Corp., Dayton, Ohio) and printer (Digitec Model 691), switch decoding network and print buffer (Fig. 1). Recently a model from the same manufacturer is available as a combined clock and printer, however, this later model employs TTL (transistor-transistor
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
Multichannel Digital Recording for Oviposition in Japanese Quail
DIGITAL RECORDING OF OVIPOSITION
S RC UNITS
TENS
HUNDRED
I 23456789
123456789
I
MMUUi
i.
J Mil
PC
DN DBCD
I
BUFFER
CLOCK
PRINTER
logic) whereas the former system employs RTL (resistor-transistor logic). For this reason we shall not specify component part numbers but provide the logic diagrams from which either RTL or TTL could be constructed. The clock is connected to the printer using the cable provided by the manufacturer. The time of day is always present on this cable thus when a print command and switch number code is produced by the switch decoding network the printer prints the time as well as the switch number. Basically the printer must be given its data in binarycoded-decimal (BCD) form. This is produced by the clock but the switches must be decoded to decimal configuration and then to BCD. The first function of the decoding network
is shown, in part, in Figure 2. Although a great many diodes are used the construction is simplified by using standard perforated circuit board and small 1N34A glass diodes. Each diode is inserted into a hole in the board where needed and wires from the switches soldered to one end and wires from the BCD decoder to the other end. The general layout becomes a series of parallel wires on one side of the board representing decimal lines one through nine, ten through ninety and one hundred. The other side of the board has the parallel lines from the switches running perpendicular to the decimal lines. For example switch number 147 would have a diode connecting the wire from the switch to decimal lines 100, 40, and 7 on the other side of the board whereas switch 47 would only have its wire connected via diodes to decimal lines 40 and 7. All switches are also connected by an additional diode to the print command line. This method of construction has an advantage in that faulty diodes can be quickly found and assembly time is about one working day. The BCD decoder and buffer must transform the units and tens decimal lines to BCD and hold these data until the printer is finished printing. This is accomplished by the circuits shown in Figure 3a and b. The printer issues an end-of-print signal at the completion of a print cycle. This signal is used to reset the buffer flip-flops. There is no protection from concurrent ovipositions resulting in false data. However the probability of eggs occurring within one print cycle (about 300 msec.) is extremely slight. To protect against multiple entries caused by swinging of the switch wire or jamming of the switch, a parallel resistor-capacitor pair are wired in series with the switch.
DATA ACQUISITION Varying numbers of Japanese quail have been used in each of two temperature and
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
FIG. 1. Diagram of the recording system. S = individual cage switches, RC = the series filter from the switches (the resistors are 330 k ohms, the capacitors are 2.5 mF), DN = the diode network translating the 200 switches into 19 decimal lines and the print command (PC) line, DBCD = decimal to binary-coded-decimal converter, B = flip-flop buffer for each of the 9 binary lines, these are reset by the end-of-print signal (EOP) from the printer. The individual data lines from the clock to the printer are not shown separately since no modification to the factory supplied cable is necessary.
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FIG. 2. Diode decoding of individual switches to 19 decimal lines (1-9, 10-90, 100) and the print command (PC) is accomplished by this assembly. Diodes are inserted into holes and the ends soldered to either the decimal data lines or the lines from the RC filter. Typical wiring is shown for switches 1, 147, 47, 0 and 100. On the actual board switches are arrayed in ascending order.
light controlled rooms for studies of oviposition times. Cages such as that diagrammed in Figure 4 allow uninterrupted recording for up to 4 weeks. This limit is imposed by the food supply contained in a large feed hopper which also serves as part of the cage front and water is provided by automatic Hart water cups.
In one experiment we were interested in the individual variability of oviposition patterns of 84 quail under a photoperiod of 10 hours of darkness and 14 hours of light (Planck and Johnson, 1975). Since eggs did occasionally stick under the trapeze (switch trip wire), the birds were checked on an irregular basis.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
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DIGITAL RECORDING OF OVIPOSITION
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FIG. 3a. Decimal to binary-coded-decimal (BCD) conversion is accomplished by this array of diodes. IN34A diodes were used throughout the project. 3b. Buffering of the BCD data lines is accomplished by wiring each two 2-input NAND gates as a R-S flip-flop. EOP = end-of-print signal from the printer which is also wired to the other 8 flip-flop (FF) as a reset signal. Data are held (set) on the output line (P) until the printer is finished.
have been selected from the range in patterns to illustrate the smoothness of the curves generated by data from some birds. This degree of smoothness may be interpreted as a high degree of predictability of laying, given some history of the bird. Data recorded at greater than these one minute intervals could not be used as effectively to illustrate this point, and data recorded on an Esterline Angus event recorder would require a fast chart speed and many hours of labor to transcribe. The data have shown a sharp change in pattern for birds which do not completely entrain to the photoperiod occurring approximately at the light to dark transition. Wilson (1964) has suggested that this transition is important as a synchronizer for ovulationoviposition times. Data from this study substantiate that it is very likely the point in time to which the bird attempts to entrain. Some birds appear to have this ability (Fig. 5a) while others do not (Fig. 5b).
RESULTS AND DISCUSSION This recording system has been in operation for over two years with the only problems being a faulty diode in one instance and a faulty capacitor in another. Both problems were solved in a matter of minutes. The precision of recording to the minute is greater than most graphic data presentation techniques can represent. With these data however we are doing computer analysis and plotting with an incremental plotter. Examples of oviposition times are shown in Fig. 5. These
FIG. 4. Schematic of the cage used for recording oviposition time in quail. Food is supplied by the food hopper (H), water by the Hart cup (C). As an egg rolls down the sloping floor it deflects the egg trapeze (ET) which pivots in one of the mounting holes (M) in the coin switch (S) and, on the other side of the cage in a hole in the mounting bracket. The ET in turn deflects the switch trip wire (ST) and an event is recorded.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
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769
770
R. J. PLANCK
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
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20 3 0 4 0 DAYS FIG. 5. Examples of the variation among quail in oviposition patterns. The data for two quail (a and b) are shown. Each point represents the time of lay of an egg expressed as a deviation (±12 hours) from the circular mean time (Batschelet, 1965) of all eggs from that bird. Both birds were maintained in a controlled temperature room in 14 hours of light, 10 hours dark (shaded area). CMT = circular mean time.
DIGITAL RECORDING OF OVIPOSITION
REFERENCES Arrington, L. C , H. Abplanalp and W. O. Wilson, 1962. Experimental modification of the laying patterns in Japanese quail. Brit. Poultry Sci. 3: 105-113. Batschelet, E., 1965. Statistical methods for the analysis of problems in animal orientation and certain biological rhythms. AIBS Monograph (American Institute of Biological Sciences, Washington, D.C.). Harrison, P. C , and W. C. Becker, 1969. Extraretinal
771
photo control of oviposition in pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med., 132: 161-164. Planck, R. J., and H. Johnson, 1975. Oviposition patterns and photoresponsivity in Japanese quail (Coturnix cotumix japonica). J. Int. Cycle Res. 6: in press. Wilson, W. O., 1964. Photocontrol of oviposition in Gallinaceous birds. Ann. New York Acad. Sci., 117: 194-202.
Interrelationship of Dietary Silver with Copper in the Chick1
(Received for publication August 19, 1974)
ABSTRACT Adding 900 p.p.m. silver (as silver nitrate) to a practical diet for chicks significantly depressed growth, increased wet and dry heart weight to body weight ratios and markedly increased mortality during a four-week experimental period. Blood packed cell volume was not affected. Supplementing the diet containing silver with 50 p.p.m. copper prevented cardiac enlargement and mortality, but only partially corrected the growth depression. Glycogen content of the heart was not affected, but aortic elastin content was significantly reduced by silver and restored to normal by supplemental copper. Dietary silver significantly reduced the copper content of blood, spleen, brain, liver, but except for the brain, the level of copper in these tissues was restored to normal by dietary copper supplementation. No significant differences in copper content of kidney tissue were observed among the treatments. Copper content of the excreta was not significantly increased by adding dietary silver, but was greatly increased by adding 50 p.p.m. copper to the diet containing silver. POULTRY SCIENCE 54: 771-775, 1975
INTRODUCTION N experiments conducted to determine the effect of adding silver acetate or nitrate to practical diets on the performance of turkey poults, a marked deficiency of copper was observed (Jensen et al., 1974). Silver (900 p.p.m.) depressed growth rate, reduced packed cell volume, slightly reduced hemaglobin level, and caused cardiac enlargement. Adding 50 p.p.m. copper to the diet
I
1. Scientific Paper No. 4286. College of Agriculture Research Center, Washington State University, Pullman. Project 1941. 2. Current Address: College of Veterinary Medicine, Wash. State Univ. 3. Current Address: Department of Poultry Science, University of Georgia, Athens 30602.
completely reversed the effects of silver. Hill and Matrone (1964) showed that adding silver to a purified diet deficient in copper accentuated all of the symptoms of copper deficiency. In the presence of copper, silver had no effect. Using rat ceruloplasmin levels as a criterion, Whanger and Weswig (1970) concluded that of the known copper antagonists they tested, dietary silver was the strongest with dietary cadmium, molybdenum, zinc and sulfate following in descending order. The purpose of the present investigations was to determine the effect of adding a high level of silver to a practical diet on the performance of chicks and on the distribution of copper in the tissues, and to determine if added copper would prevent the effects of silver.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
R. P . PETERSON 2 AND L . S. J E N S E N 3
Department of Animal Sciences, Washington State University, Pullman, WA 99163
J . BlELY AND Y . POMERANZ
Offic. Anal. Chem. Washington, D.C. Bell, J. M., and G. I. Christison, 1972. Personal communication. University of Saskatchewan, Saskatoon, Saskatchewan. Canada Feeds Act, 1960, C 14 and Feeds Regulations 1967. Queen's Printer and Controller of Stationery. Ottawa, Canada. Pomeranz, Y., and G. S. Robbins, 1972. Amino acid composition of buckwheat. Agr. Food Chem. 20: 270-274. Pomeranz, Y., and G. S. Robbins, 1973. Amino acid
composition of maturing barley. Cereal Chem. 49: 560-565. Sure, B., 1955. Nutritive value of proteins in buckwheat and their role as supplements to protein in cereal grains. Agr. Food Chem. 3: 793-795. White, J. W., F. J. Halken and A. C. Richer, 1941. Experiments with buckwheat. Pennsylvania Agr. Experiment Station, Bull. 403: 1-62. Wyld, M. K., R. L. Squibb and N. S. Scrimshaw, 1958. Buckwheat as a supplement to all-vegetable protein diets. Food Res. 23: 407-410.
R.J.
PLANCK
Department of Zoology, University of Western Ontario, London, Ontario, Canada (Received for publication August 16, 1974)
ABSTRACT A multichannel recording system is described which offers the advantages of accuracy and low cost. The system was a commercially available digital printer and clock mechanism. Switch decoding circuitry is presented in the article. The system described will record from 200 switches connected to egg trip levers on bird cages. An example of data obtained from two Japanese quail illustrates the smooth patterns of lay seen when recorded to one minute accuracy. POULTRY SCIENCE 54: 766-771, 1975
INTRODUCTION
VIPOSITION times have been reported for birds in numerous studies of ovulation-ovipositional cycles. The need for an accurate means for determining these times has been met by a number of means, for example, time lapse photography (Arrington et al, 1962) and the use of strip-chart event recorders (Harrison and Becker, 1969). These methods generally have the problem of requiring the investigator to transcribe the visual presence of eggs, from a photograph or a tick mark, to numerical form for analysis. These methods are relatively expensive for large numbers of birds both in the labor time required for transcription and the purchase of the equipment.
O
To alleviate these problems we have been using a system for recording oviposition times of Japanese quail which provides a printed record of cage number and time of day to the minute. This system is capable of 200 channels or more at a cost of less than ten dollars per channel. MATERIALS AND METHODS The data acquisition system consists of a digital clock (Digitec Model 662, United Systems Corp., Dayton, Ohio) and printer (Digitec Model 691), switch decoding network and print buffer (Fig. 1). Recently a model from the same manufacturer is available as a combined clock and printer, however, this later model employs TTL (transistor-transistor
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
Multichannel Digital Recording for Oviposition in Japanese Quail
DIGITAL RECORDING OF OVIPOSITION
S RC UNITS
TENS
HUNDRED
I 23456789
123456789
I
MMUUi
i.
J Mil
PC
DN DBCD
I
BUFFER
CLOCK
PRINTER
logic) whereas the former system employs RTL (resistor-transistor logic). For this reason we shall not specify component part numbers but provide the logic diagrams from which either RTL or TTL could be constructed. The clock is connected to the printer using the cable provided by the manufacturer. The time of day is always present on this cable thus when a print command and switch number code is produced by the switch decoding network the printer prints the time as well as the switch number. Basically the printer must be given its data in binarycoded-decimal (BCD) form. This is produced by the clock but the switches must be decoded to decimal configuration and then to BCD. The first function of the decoding network
is shown, in part, in Figure 2. Although a great many diodes are used the construction is simplified by using standard perforated circuit board and small 1N34A glass diodes. Each diode is inserted into a hole in the board where needed and wires from the switches soldered to one end and wires from the BCD decoder to the other end. The general layout becomes a series of parallel wires on one side of the board representing decimal lines one through nine, ten through ninety and one hundred. The other side of the board has the parallel lines from the switches running perpendicular to the decimal lines. For example switch number 147 would have a diode connecting the wire from the switch to decimal lines 100, 40, and 7 on the other side of the board whereas switch 47 would only have its wire connected via diodes to decimal lines 40 and 7. All switches are also connected by an additional diode to the print command line. This method of construction has an advantage in that faulty diodes can be quickly found and assembly time is about one working day. The BCD decoder and buffer must transform the units and tens decimal lines to BCD and hold these data until the printer is finished printing. This is accomplished by the circuits shown in Figure 3a and b. The printer issues an end-of-print signal at the completion of a print cycle. This signal is used to reset the buffer flip-flops. There is no protection from concurrent ovipositions resulting in false data. However the probability of eggs occurring within one print cycle (about 300 msec.) is extremely slight. To protect against multiple entries caused by swinging of the switch wire or jamming of the switch, a parallel resistor-capacitor pair are wired in series with the switch.
DATA ACQUISITION Varying numbers of Japanese quail have been used in each of two temperature and
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
FIG. 1. Diagram of the recording system. S = individual cage switches, RC = the series filter from the switches (the resistors are 330 k ohms, the capacitors are 2.5 mF), DN = the diode network translating the 200 switches into 19 decimal lines and the print command (PC) line, DBCD = decimal to binary-coded-decimal converter, B = flip-flop buffer for each of the 9 binary lines, these are reset by the end-of-print signal (EOP) from the printer. The individual data lines from the clock to the printer are not shown separately since no modification to the factory supplied cable is necessary.
767
768
R. J. PLANCK
]
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FIG. 2. Diode decoding of individual switches to 19 decimal lines (1-9, 10-90, 100) and the print command (PC) is accomplished by this assembly. Diodes are inserted into holes and the ends soldered to either the decimal data lines or the lines from the RC filter. Typical wiring is shown for switches 1, 147, 47, 0 and 100. On the actual board switches are arrayed in ascending order.
light controlled rooms for studies of oviposition times. Cages such as that diagrammed in Figure 4 allow uninterrupted recording for up to 4 weeks. This limit is imposed by the food supply contained in a large feed hopper which also serves as part of the cage front and water is provided by automatic Hart water cups.
In one experiment we were interested in the individual variability of oviposition patterns of 84 quail under a photoperiod of 10 hours of darkness and 14 hours of light (Planck and Johnson, 1975). Since eggs did occasionally stick under the trapeze (switch trip wire), the birds were checked on an irregular basis.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
UJ O
o o
o o 0
0 0
o
o o o o
o
DIGITAL RECORDING OF OVIPOSITION
< h<
2 >3 >-
a
Q
< O UJ Q
<
JLi
5 >6 >7 >-
Q Q CD
iUk
DBCD>
FIG. 3a. Decimal to binary-coded-decimal (BCD) conversion is accomplished by this array of diodes. IN34A diodes were used throughout the project. 3b. Buffering of the BCD data lines is accomplished by wiring each two 2-input NAND gates as a R-S flip-flop. EOP = end-of-print signal from the printer which is also wired to the other 8 flip-flop (FF) as a reset signal. Data are held (set) on the output line (P) until the printer is finished.
have been selected from the range in patterns to illustrate the smoothness of the curves generated by data from some birds. This degree of smoothness may be interpreted as a high degree of predictability of laying, given some history of the bird. Data recorded at greater than these one minute intervals could not be used as effectively to illustrate this point, and data recorded on an Esterline Angus event recorder would require a fast chart speed and many hours of labor to transcribe. The data have shown a sharp change in pattern for birds which do not completely entrain to the photoperiod occurring approximately at the light to dark transition. Wilson (1964) has suggested that this transition is important as a synchronizer for ovulationoviposition times. Data from this study substantiate that it is very likely the point in time to which the bird attempts to entrain. Some birds appear to have this ability (Fig. 5a) while others do not (Fig. 5b).
RESULTS AND DISCUSSION This recording system has been in operation for over two years with the only problems being a faulty diode in one instance and a faulty capacitor in another. Both problems were solved in a matter of minutes. The precision of recording to the minute is greater than most graphic data presentation techniques can represent. With these data however we are doing computer analysis and plotting with an incremental plotter. Examples of oviposition times are shown in Fig. 5. These
FIG. 4. Schematic of the cage used for recording oviposition time in quail. Food is supplied by the food hopper (H), water by the Hart cup (C). As an egg rolls down the sloping floor it deflects the egg trapeze (ET) which pivots in one of the mounting holes (M) in the coin switch (S) and, on the other side of the cage in a hole in the mounting bracket. The ET in turn deflects the switch trip wire (ST) and an event is recorded.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
EOP>
769
770
R. J. PLANCK
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
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Q LJL
O LU
20 3 0 4 0 DAYS FIG. 5. Examples of the variation among quail in oviposition patterns. The data for two quail (a and b) are shown. Each point represents the time of lay of an egg expressed as a deviation (±12 hours) from the circular mean time (Batschelet, 1965) of all eggs from that bird. Both birds were maintained in a controlled temperature room in 14 hours of light, 10 hours dark (shaded area). CMT = circular mean time.
DIGITAL RECORDING OF OVIPOSITION
REFERENCES Arrington, L. C , H. Abplanalp and W. O. Wilson, 1962. Experimental modification of the laying patterns in Japanese quail. Brit. Poultry Sci. 3: 105-113. Batschelet, E., 1965. Statistical methods for the analysis of problems in animal orientation and certain biological rhythms. AIBS Monograph (American Institute of Biological Sciences, Washington, D.C.). Harrison, P. C , and W. C. Becker, 1969. Extraretinal
771
photo control of oviposition in pinealectomized domestic fowl. Proc. Soc. Exp. Biol. Med., 132: 161-164. Planck, R. J., and H. Johnson, 1975. Oviposition patterns and photoresponsivity in Japanese quail (Coturnix cotumix japonica). J. Int. Cycle Res. 6: in press. Wilson, W. O., 1964. Photocontrol of oviposition in Gallinaceous birds. Ann. New York Acad. Sci., 117: 194-202.
Interrelationship of Dietary Silver with Copper in the Chick1
(Received for publication August 19, 1974)
ABSTRACT Adding 900 p.p.m. silver (as silver nitrate) to a practical diet for chicks significantly depressed growth, increased wet and dry heart weight to body weight ratios and markedly increased mortality during a four-week experimental period. Blood packed cell volume was not affected. Supplementing the diet containing silver with 50 p.p.m. copper prevented cardiac enlargement and mortality, but only partially corrected the growth depression. Glycogen content of the heart was not affected, but aortic elastin content was significantly reduced by silver and restored to normal by supplemental copper. Dietary silver significantly reduced the copper content of blood, spleen, brain, liver, but except for the brain, the level of copper in these tissues was restored to normal by dietary copper supplementation. No significant differences in copper content of kidney tissue were observed among the treatments. Copper content of the excreta was not significantly increased by adding dietary silver, but was greatly increased by adding 50 p.p.m. copper to the diet containing silver. POULTRY SCIENCE 54: 771-775, 1975
INTRODUCTION N experiments conducted to determine the effect of adding silver acetate or nitrate to practical diets on the performance of turkey poults, a marked deficiency of copper was observed (Jensen et al., 1974). Silver (900 p.p.m.) depressed growth rate, reduced packed cell volume, slightly reduced hemaglobin level, and caused cardiac enlargement. Adding 50 p.p.m. copper to the diet
I
1. Scientific Paper No. 4286. College of Agriculture Research Center, Washington State University, Pullman. Project 1941. 2. Current Address: College of Veterinary Medicine, Wash. State Univ. 3. Current Address: Department of Poultry Science, University of Georgia, Athens 30602.
completely reversed the effects of silver. Hill and Matrone (1964) showed that adding silver to a purified diet deficient in copper accentuated all of the symptoms of copper deficiency. In the presence of copper, silver had no effect. Using rat ceruloplasmin levels as a criterion, Whanger and Weswig (1970) concluded that of the known copper antagonists they tested, dietary silver was the strongest with dietary cadmium, molybdenum, zinc and sulfate following in descending order. The purpose of the present investigations was to determine the effect of adding a high level of silver to a practical diet on the performance of chicks and on the distribution of copper in the tissues, and to determine if added copper would prevent the effects of silver.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 7, 2015
R. P . PETERSON 2 AND L . S. J E N S E N 3
Department of Animal Sciences, Washington State University, Pullman, WA 99163