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Milk Progesterone for Pregnancy Diagnosis in Dairy Goats1
TECHNICAL NOTES Milk Progesterone for Pregnancy Diagnosis in Dairy Goats 1 J. A. P E N N I N G T O N 2 Department of Animal Sciences University of Wisconsin River Falls 54022 W. F. H O F F M A N Department of Agricultural Sciences University of Wisconsin Platteville 53518 L. H. S C H U L T Z Department of Dairy Science University of Wisconsin Madison 53706
S. L. SPAHR and J. R. LODGE Department of Dairy Science University of Illinois Urbana 51801 ABSTRACT
stages of pregnancy. Of 21 does diagnosed n o t pregnant with low progesterone, 19 does were not pregnant by either return to estrus or lack of parturition in the spring. All three incorrectly diagnosed does were problem breeders. Nine does with intermediate milk progesterone were classified questionable. Milk progesterone can be used to provide an early indication of the pregnancy status of does.
Factors affecting progesterone concentration in milk of lactating dairy goats and use of this milk for pregnancy diagnosis were studied. Radioimmunoassay was used to assay progesterone in milk. Mean milk progesterone (ng/ml) + standard errors of 6 pregnant does for first, composite, and last milk were 9.9 -+ 2.0, 18.2 + 3.5, and 21.7 + 4.1. Correlation between milk fat and progesterone in composite milk was low (. 11). Composite milk samples from 4 nonpregnant does were obtained daily throughout the estrous cycle. Milk progesterone (ng/ml) was 1 to 2 at estrus, rose to 5 to 12 within 2 to 5 days, reached a plateau at 15 to 25 in the middle of the estrous cycle, and then dropped to low concentrations again at 3 to 5 days before the next estrus. Milk progesterone also was used to diagnose pregnancy in 72 does. Forty-two does were diagnosed pregnant by high progesterone; 36 of these does later produced kids, and 5 other does aborted in various
INTRODUCTION
Received January 18, 1982. 1Supported in part by Cooperative Agricultural Research Project 038 between the University of Wisconsin-Madison, -Platteville, and -River Falls and the Illinois Agricultural Experiment Station. 2Department of Animal Science, Purdue University, West Lafayette, IN 47907. 1982 J Dairy Sci 65:2011-2014
Within the last few years, much research has been conducted on the use of milk progesterone for early pregnancy diagnosis in the lactating dairy cow (3, 5, 10, 12). Milk progesterone measurements for pregnancy diagnosis also have been extended to other species including the goat and the mare (2, 8, 9, 15). In the goat, palpation per rectum is not used for pregnancy diagnosis because of the relative size of the goat, and other methods of early pregnancy diagnosis have gained only limited use (4). Thus, there appears to be a need in the dairy goat industry for a highly reliable, simple test for pregnancy. Even return to estrus, which is the most used method of pregnancy diagnosis for dairy goats, is of questionable value toward the end of the breeding season as goats are seasonal breeders. A portion of goats are assumed to be pregnant because of lack of estrus until they do not produce a kid the next spring. They come into estrus primarily in the fall and then do not
2011
2012
PENNINGTON ET AL.
return to estrus later in the season even if they are not pregnant. These experiments then were to determine the efficiency of milk progesterone for pregnancy diagnosis in lactating dairy goats.
TABLE 1. Effect of method of sampling on progesterone concentration in milk. 1
Sampling method
Progesterone (ng/ml)
MATERIALS AND METHODS Animals and Method of Sampling
Does in this study were from three cooperating dairy herds. Samples (50 ml) were composite milk except as noted in Experiment 1 and were preserved with potassium dichromate (.0324 g tablet, NASCO, Fort Atkinson, WI). Samples were hand carried or shipped in cylindrical, cardboard mailing cartons via United Parcel Service to the laboratory.
First milk Composite milk Last milk
9.9 A 18.2B 21.7 B
Milk fat (%)
SE
X
SE
2.0 3.5 4.1
1.9A 3.1B 5.9C
.3 .3 .7
A'B'CMeans in same column with different superscripts differ (P<.01).
RESULTS AND DISCUSSION Experiment 1: Method of Sampling
Radioimmunoassay of Progesterone
Progesterone was assayed after ether extraction of milk as outlined by Pennington et al. (13). The antiserum $83 #5 was obtained from G. E. Abraham, Torrence, CA. All analyses were within 2 wk of sample collection. Experiment 1: Method of Sampling
Samples of first, composite, and last milk were collected from 6 pregnant does at the p.m. m~lking. Fat percentages in milk were measured on all samples by Babcock method (1). Statistical analysis was by a two-way factorial design (does × method of sampling) with comparison of means by Duncan's new multiple range test (17). Experiment 2: Day of Estrous Cycle
Milk samples were collected at the p.m. milking from 4 does on the day of estrus and from these same 4 does each day until the next estrus, Statistical analysis was by a randomized complete block design (17). Experiment 3: Pregnancy Diagnosis
Samples of composite milk were collected from 72 lactating does at 21 days postbreeding. Does were classified as pregnant, questionable, and not pregnant with greater than 10 ng, 7 to 10 ng, and less than 7 ng progesterone/ml in milk, respectively. These diagnoses were compared with return to estrus, detected abortions, and kidding results. Journal of Dairy Science Vol. 65, No. 10, 1982
Method of sampling had a significant effect (P<.01) on progesterone concentration in milk (Table 1). Correlation between fat percentage and progesterone concentration in the three milk fractions was .82 (P<.05). However, correlation between fat percentage and progesterone concentration in composite milk was .11 (P>.10). Effect of does on progesterone concentrations also was significant (P<.05). Interactions of animal and method of sampling did not affect ( P > . 1 0 ) p r o g e s t e r o n e concentration in milk. Several studies have indicated that progesterone in bovine milk is affected by milk fat percentage (6, 7, 11). Similar to results reported here in goats, the correlation between milk progesterone concentration and fat percentage in cattle is much lower in composite milk than in all three fractions of milk (11, 14). Thibier et al. (18) recently reported that progesterone in first milk from does in the luteal phase of the estrous cycle was approximately 10 ng/ml, which would agree closely with our data. Holdsworth and Davies (8) reported 52.9 ng/ml in whole milk of pregnant does. Throughout these studies, concentrations of progesterone in milk tended to be slightly lower than those for progesterone in cows' milk by a similar assay system (14). Experiment 2: Day of Estrous Cycle
Effects of does and of days in the estrous cycle on progesterone concentration in milk were significant (P<.O1). Patterns of milk
TECHNICAL NOTE
0~¢s of Estr0~ cycle cE~ 0
Estrus~
Figure 1. Milk progesterone (mean + SE) during the estrous cycle of goats.
progesterone during the estrus cycle in Figure 1 were similar to patterns of progesterone in blood and in milk (18, 19). Most milk progesterones were in the range of 15 to 22 ng/ml from day 6 to day 16 of the estrous cycle except for one goat that erratically had up to 38 ng/ml. Variation in progesterone concentration in dairy goat milk was comparable to that for lactating dairy cows (14), and data followed a similar pattern to results for both bovine milk and blood progesterone (7, 16). Experiment 3: Pregnancy Diagnosis
Progesterone concentrations in milk ranged from .5 to 34 ng/ml. For does classified as pregnant, not pregnant, and questionable by milk progesterone, milk concentrations of progesterone averaged 17.9 + .9, 3.0 -+ .4, and 9.4 + .4 ng/ml, respectively. Results of pregnant diagnosis are in Table 2. For animals classified
TABLE 2. Pregnancy diagnosis by milk progesterone on day 21. Diagnosis 1
Accuracy of diagnosis
Not pregnant Pregnant Total 2
19/21 = 90.4% 41/42 = 97.6% 60/63 = 95.2%
1Diagnosis by milk progesterone. 2Does diagnosed pregnant and not pregnant only; 9 additional does were classified questionable.
2013
as pregnant by milk progesterone, 97.6% (41 of 44) later either produced a live kid or were detected aborting. Five of these animals did abort in various stages of pregnancy. Of the 21 does diagnosed not pregnant with low progesterone, 19 does (90.4%) were nonpregnant by either return to estrus or lack of parturition in the spring. Nine does with intermediate milk progesterone were classified questionable. Seven of the nine animals classified questionable were pregnant. Of the animals diagnosed incorrectly by milk progesterone, all were problem breeders for their owners. The two animals diagnosed incorrectly as not pregnant with low progesterone had in previous gestations been unable to carry a kid and had aborted. The animal that was diagnosed incorrectly as pregnant but did not produce a kid also had been a problem breeder and had aborted. These results agree closely with results by Holsworth and Davies (8) and Pennington et al. (15). The field trial of 98 goats in the United Kingdom resulted in an 85.9% accuracy on positive diagnosis based on kidding data and 100% accuracy for 6 goats having negative results (8). Pennington et al. (15) found that 21 of 22 does diagnosed pregnant by milk progesterone were pregnant (18 kidding plus three abortions), whereas all three does diagnosed not pregnant did not kid. The accuracy of pregnancy diagnosis by milk progesterone in dairy goats appears to be higher than the accuracy of diagnosis by milk progesterone in dairy cattle in our studies (12, 13). We speculate that increased accuracy of pregnant diagnosis by progesterone in goats as compared to cattle may be from two related factors, higher fertility and decreased effect of embryonic death. Increased accuracy of pregnancy diagnosis by milk progesterone in cattle occurs as conception rates increase. The accuracy of cows diagnosed pregnant by milk progesterone is more affected by fertility than those diagnosed n o t pregnant (3, 12). In cases of multiple embryos, which are common in goats, if one embryo dies, another embryo will sustain pregnancy. Thus, less incidence of nonpregnancy results from embryonic death in the goat than in the cow. Embryonic death has been a major cause of discrepancies in diagnosis of cows pregnant by milk progesterone (3, 4, 7, 12). Journal of Dairy Science Vol. 65, No. 10, 1982
2014-
PENN1NGTON ET AL. ACKNOWLEDGMENTS
The authors gratefully acknowledge the e x c e l l e n t c o o p e r a t i o n a n d assistance o f D a n C o n s i d i n e a n d Paul A s h b r o o k , Portage, WI, a n d Bill Y o u n g , S e y m o u r , IL, f o r t h e i r assistance in collecting s a m p l e s o f m i l k f r o m goats. T h e y also are i n d e b t e d t o L i n d a Czisny, Julie Olson, a n d Clyde Cieszynski f o r t h e i r assistance in a n a l y z i n g m i l k samples. REFERENCES
1 Association of Official Agricultural Chemists. 1960. Official methods of analysis. Assoc. Offic. Agric. Chem., Washington, DC. 2 Bailes, G., and J. L. Holdsworth. 1978. Progestagens in mare's milk. Br. Vet. J. 134:214. 3 Booth, J. M. 1980. Milk progesterone pregnancy testing in cattle and other species. Page 109--117 in Proc. Ninth Int. Congr. Anim. Reprod. Artif. Insem. Vol. II, Madrid, Spain. 4 Corteel, J. M. 1977. Management of artificial insemination of dairy seasonal goats and through synchronization and early pregnancy diagnosis. Paper presented at Manage. Reprod. in Sheep and Goats Symp., Madison, WI. 5 Foote, R. H., E.A.B. Oltenacu, H. L. Kummerfeld, R. D. Smith, P. M. Riek, and R. K. Braun. 1979. Milk progesterone as a diagnostic aid. Br. Vet. J. 135:550. 6 Ginther, O. J., L. C. Nuti, M. C. Garcia, B. C. Wentworth, and W. J. Tyler. 1976. Factors affecting progesterone concentration in cow's milk and dairy products. J. Anita. Sci. 42:155. 7 Hoffman, B., and R. Hamburger. 1973. Progesterone in der Milch: Radioimmunologische Bestimmung, Beziehunger zur Gelbkorperfunktion and Milchfettkonzentration. Zuchthygiene 8:154. 8 Holdsworth, R. J., and J. Davies. 1979. Measurement of progesterone in goat's milk: An early
Journal of Dairy Science Vol. 65, No. 10, 1982
pregnancy test. Vet. Rec. 105:535. 9 Hunt, B., D. H. Lein, and R. H. Foote. 1978. Monitoring of plasma and milk progesterone for evaluation of postparturm estrous cycles and early pregnancy in mares. J. Am. Vet. Med. Assoc. 172:1298. 10 Laing, J. A., and R. B. Heap. 1971. The concentration of progesterone in the milk of cows during the reproductive cycle. Br. Vet. J. 127:XIX. 11 Oltenacu, E.A.B., and R. H. Foote. 1976. The relationship between milk progesterone for pregnant and mid-cycle cows. J. Dairy Sci. 59(Suppl. 1):100. (Abstr.) 12 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1976. Factors affecting progesterone in milk for pregnancy diagnosis in dairy cattle. Br. Vet. J. 132:487. 13 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1976. Pregnancy diagnosis in dairy cattle by progesterone concentration of milk. J. Dairy Sci. 59:1528. 14 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1981. Influences on progesterone concentration in bovine milk. J. Dairy Sci. 64:259. 15 Pennington, J. A., S. L. Spahr, J. R. Lodge, and D. Considine. 1977. Progesterone content of goat's milk and its application for pregnancy diagnosis. J. Dairy Sci. 60. (Suppl. 1):82. (Abstr.) 16 Schiavo, J. J., R. L. Matuszcak, E. B. Oltenacu, and R. H. Foote. 1975. Milk progesterone in postpartum and pregnant cows as a monitor of reproductive status. J. Dairy Sci. 58:1713. 17 Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill, New York, NY. 18 Thibier, M., D. Pothelet, N. Jeanguyot, and G. DeMontigny. 1981. Estrus behavior, progesterone in peripheral plasma and milk in dairy goats at onset of breeding season. J. Dairy Sci. 64:513. 19 Thorburn, G. D., and W. Schneider. 1972. The progesterone concentration in the plasma of the goat during the oestrous cycle and pregnancy. J. Endocrinol. 52:23.
S. L. SPAHR and J. R. LODGE Department of Dairy Science University of Illinois Urbana 51801 ABSTRACT
stages of pregnancy. Of 21 does diagnosed n o t pregnant with low progesterone, 19 does were not pregnant by either return to estrus or lack of parturition in the spring. All three incorrectly diagnosed does were problem breeders. Nine does with intermediate milk progesterone were classified questionable. Milk progesterone can be used to provide an early indication of the pregnancy status of does.
Factors affecting progesterone concentration in milk of lactating dairy goats and use of this milk for pregnancy diagnosis were studied. Radioimmunoassay was used to assay progesterone in milk. Mean milk progesterone (ng/ml) + standard errors of 6 pregnant does for first, composite, and last milk were 9.9 -+ 2.0, 18.2 + 3.5, and 21.7 + 4.1. Correlation between milk fat and progesterone in composite milk was low (. 11). Composite milk samples from 4 nonpregnant does were obtained daily throughout the estrous cycle. Milk progesterone (ng/ml) was 1 to 2 at estrus, rose to 5 to 12 within 2 to 5 days, reached a plateau at 15 to 25 in the middle of the estrous cycle, and then dropped to low concentrations again at 3 to 5 days before the next estrus. Milk progesterone also was used to diagnose pregnancy in 72 does. Forty-two does were diagnosed pregnant by high progesterone; 36 of these does later produced kids, and 5 other does aborted in various
INTRODUCTION
Received January 18, 1982. 1Supported in part by Cooperative Agricultural Research Project 038 between the University of Wisconsin-Madison, -Platteville, and -River Falls and the Illinois Agricultural Experiment Station. 2Department of Animal Science, Purdue University, West Lafayette, IN 47907. 1982 J Dairy Sci 65:2011-2014
Within the last few years, much research has been conducted on the use of milk progesterone for early pregnancy diagnosis in the lactating dairy cow (3, 5, 10, 12). Milk progesterone measurements for pregnancy diagnosis also have been extended to other species including the goat and the mare (2, 8, 9, 15). In the goat, palpation per rectum is not used for pregnancy diagnosis because of the relative size of the goat, and other methods of early pregnancy diagnosis have gained only limited use (4). Thus, there appears to be a need in the dairy goat industry for a highly reliable, simple test for pregnancy. Even return to estrus, which is the most used method of pregnancy diagnosis for dairy goats, is of questionable value toward the end of the breeding season as goats are seasonal breeders. A portion of goats are assumed to be pregnant because of lack of estrus until they do not produce a kid the next spring. They come into estrus primarily in the fall and then do not
2011
2012
PENNINGTON ET AL.
return to estrus later in the season even if they are not pregnant. These experiments then were to determine the efficiency of milk progesterone for pregnancy diagnosis in lactating dairy goats.
TABLE 1. Effect of method of sampling on progesterone concentration in milk. 1
Sampling method
Progesterone (ng/ml)
MATERIALS AND METHODS Animals and Method of Sampling
Does in this study were from three cooperating dairy herds. Samples (50 ml) were composite milk except as noted in Experiment 1 and were preserved with potassium dichromate (.0324 g tablet, NASCO, Fort Atkinson, WI). Samples were hand carried or shipped in cylindrical, cardboard mailing cartons via United Parcel Service to the laboratory.
First milk Composite milk Last milk
9.9 A 18.2B 21.7 B
Milk fat (%)
SE
X
SE
2.0 3.5 4.1
1.9A 3.1B 5.9C
.3 .3 .7
A'B'CMeans in same column with different superscripts differ (P<.01).
RESULTS AND DISCUSSION Experiment 1: Method of Sampling
Radioimmunoassay of Progesterone
Progesterone was assayed after ether extraction of milk as outlined by Pennington et al. (13). The antiserum $83 #5 was obtained from G. E. Abraham, Torrence, CA. All analyses were within 2 wk of sample collection. Experiment 1: Method of Sampling
Samples of first, composite, and last milk were collected from 6 pregnant does at the p.m. m~lking. Fat percentages in milk were measured on all samples by Babcock method (1). Statistical analysis was by a two-way factorial design (does × method of sampling) with comparison of means by Duncan's new multiple range test (17). Experiment 2: Day of Estrous Cycle
Milk samples were collected at the p.m. milking from 4 does on the day of estrus and from these same 4 does each day until the next estrus, Statistical analysis was by a randomized complete block design (17). Experiment 3: Pregnancy Diagnosis
Samples of composite milk were collected from 72 lactating does at 21 days postbreeding. Does were classified as pregnant, questionable, and not pregnant with greater than 10 ng, 7 to 10 ng, and less than 7 ng progesterone/ml in milk, respectively. These diagnoses were compared with return to estrus, detected abortions, and kidding results. Journal of Dairy Science Vol. 65, No. 10, 1982
Method of sampling had a significant effect (P<.01) on progesterone concentration in milk (Table 1). Correlation between fat percentage and progesterone concentration in the three milk fractions was .82 (P<.05). However, correlation between fat percentage and progesterone concentration in composite milk was .11 (P>.10). Effect of does on progesterone concentrations also was significant (P<.05). Interactions of animal and method of sampling did not affect ( P > . 1 0 ) p r o g e s t e r o n e concentration in milk. Several studies have indicated that progesterone in bovine milk is affected by milk fat percentage (6, 7, 11). Similar to results reported here in goats, the correlation between milk progesterone concentration and fat percentage in cattle is much lower in composite milk than in all three fractions of milk (11, 14). Thibier et al. (18) recently reported that progesterone in first milk from does in the luteal phase of the estrous cycle was approximately 10 ng/ml, which would agree closely with our data. Holdsworth and Davies (8) reported 52.9 ng/ml in whole milk of pregnant does. Throughout these studies, concentrations of progesterone in milk tended to be slightly lower than those for progesterone in cows' milk by a similar assay system (14). Experiment 2: Day of Estrous Cycle
Effects of does and of days in the estrous cycle on progesterone concentration in milk were significant (P<.O1). Patterns of milk
TECHNICAL NOTE
0~¢s of Estr0~ cycle cE~ 0
Estrus~
Figure 1. Milk progesterone (mean + SE) during the estrous cycle of goats.
progesterone during the estrus cycle in Figure 1 were similar to patterns of progesterone in blood and in milk (18, 19). Most milk progesterones were in the range of 15 to 22 ng/ml from day 6 to day 16 of the estrous cycle except for one goat that erratically had up to 38 ng/ml. Variation in progesterone concentration in dairy goat milk was comparable to that for lactating dairy cows (14), and data followed a similar pattern to results for both bovine milk and blood progesterone (7, 16). Experiment 3: Pregnancy Diagnosis
Progesterone concentrations in milk ranged from .5 to 34 ng/ml. For does classified as pregnant, not pregnant, and questionable by milk progesterone, milk concentrations of progesterone averaged 17.9 + .9, 3.0 -+ .4, and 9.4 + .4 ng/ml, respectively. Results of pregnant diagnosis are in Table 2. For animals classified
TABLE 2. Pregnancy diagnosis by milk progesterone on day 21. Diagnosis 1
Accuracy of diagnosis
Not pregnant Pregnant Total 2
19/21 = 90.4% 41/42 = 97.6% 60/63 = 95.2%
1Diagnosis by milk progesterone. 2Does diagnosed pregnant and not pregnant only; 9 additional does were classified questionable.
2013
as pregnant by milk progesterone, 97.6% (41 of 44) later either produced a live kid or were detected aborting. Five of these animals did abort in various stages of pregnancy. Of the 21 does diagnosed not pregnant with low progesterone, 19 does (90.4%) were nonpregnant by either return to estrus or lack of parturition in the spring. Nine does with intermediate milk progesterone were classified questionable. Seven of the nine animals classified questionable were pregnant. Of the animals diagnosed incorrectly by milk progesterone, all were problem breeders for their owners. The two animals diagnosed incorrectly as not pregnant with low progesterone had in previous gestations been unable to carry a kid and had aborted. The animal that was diagnosed incorrectly as pregnant but did not produce a kid also had been a problem breeder and had aborted. These results agree closely with results by Holsworth and Davies (8) and Pennington et al. (15). The field trial of 98 goats in the United Kingdom resulted in an 85.9% accuracy on positive diagnosis based on kidding data and 100% accuracy for 6 goats having negative results (8). Pennington et al. (15) found that 21 of 22 does diagnosed pregnant by milk progesterone were pregnant (18 kidding plus three abortions), whereas all three does diagnosed not pregnant did not kid. The accuracy of pregnancy diagnosis by milk progesterone in dairy goats appears to be higher than the accuracy of diagnosis by milk progesterone in dairy cattle in our studies (12, 13). We speculate that increased accuracy of pregnant diagnosis by progesterone in goats as compared to cattle may be from two related factors, higher fertility and decreased effect of embryonic death. Increased accuracy of pregnancy diagnosis by milk progesterone in cattle occurs as conception rates increase. The accuracy of cows diagnosed pregnant by milk progesterone is more affected by fertility than those diagnosed n o t pregnant (3, 12). In cases of multiple embryos, which are common in goats, if one embryo dies, another embryo will sustain pregnancy. Thus, less incidence of nonpregnancy results from embryonic death in the goat than in the cow. Embryonic death has been a major cause of discrepancies in diagnosis of cows pregnant by milk progesterone (3, 4, 7, 12). Journal of Dairy Science Vol. 65, No. 10, 1982
2014-
PENN1NGTON ET AL. ACKNOWLEDGMENTS
The authors gratefully acknowledge the e x c e l l e n t c o o p e r a t i o n a n d assistance o f D a n C o n s i d i n e a n d Paul A s h b r o o k , Portage, WI, a n d Bill Y o u n g , S e y m o u r , IL, f o r t h e i r assistance in collecting s a m p l e s o f m i l k f r o m goats. T h e y also are i n d e b t e d t o L i n d a Czisny, Julie Olson, a n d Clyde Cieszynski f o r t h e i r assistance in a n a l y z i n g m i l k samples. REFERENCES
1 Association of Official Agricultural Chemists. 1960. Official methods of analysis. Assoc. Offic. Agric. Chem., Washington, DC. 2 Bailes, G., and J. L. Holdsworth. 1978. Progestagens in mare's milk. Br. Vet. J. 134:214. 3 Booth, J. M. 1980. Milk progesterone pregnancy testing in cattle and other species. Page 109--117 in Proc. Ninth Int. Congr. Anim. Reprod. Artif. Insem. Vol. II, Madrid, Spain. 4 Corteel, J. M. 1977. Management of artificial insemination of dairy seasonal goats and through synchronization and early pregnancy diagnosis. Paper presented at Manage. Reprod. in Sheep and Goats Symp., Madison, WI. 5 Foote, R. H., E.A.B. Oltenacu, H. L. Kummerfeld, R. D. Smith, P. M. Riek, and R. K. Braun. 1979. Milk progesterone as a diagnostic aid. Br. Vet. J. 135:550. 6 Ginther, O. J., L. C. Nuti, M. C. Garcia, B. C. Wentworth, and W. J. Tyler. 1976. Factors affecting progesterone concentration in cow's milk and dairy products. J. Anita. Sci. 42:155. 7 Hoffman, B., and R. Hamburger. 1973. Progesterone in der Milch: Radioimmunologische Bestimmung, Beziehunger zur Gelbkorperfunktion and Milchfettkonzentration. Zuchthygiene 8:154. 8 Holdsworth, R. J., and J. Davies. 1979. Measurement of progesterone in goat's milk: An early
Journal of Dairy Science Vol. 65, No. 10, 1982
pregnancy test. Vet. Rec. 105:535. 9 Hunt, B., D. H. Lein, and R. H. Foote. 1978. Monitoring of plasma and milk progesterone for evaluation of postparturm estrous cycles and early pregnancy in mares. J. Am. Vet. Med. Assoc. 172:1298. 10 Laing, J. A., and R. B. Heap. 1971. The concentration of progesterone in the milk of cows during the reproductive cycle. Br. Vet. J. 127:XIX. 11 Oltenacu, E.A.B., and R. H. Foote. 1976. The relationship between milk progesterone for pregnant and mid-cycle cows. J. Dairy Sci. 59(Suppl. 1):100. (Abstr.) 12 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1976. Factors affecting progesterone in milk for pregnancy diagnosis in dairy cattle. Br. Vet. J. 132:487. 13 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1976. Pregnancy diagnosis in dairy cattle by progesterone concentration of milk. J. Dairy Sci. 59:1528. 14 Pennington, J. A., S. L. Spahr, and J. R. Lodge. 1981. Influences on progesterone concentration in bovine milk. J. Dairy Sci. 64:259. 15 Pennington, J. A., S. L. Spahr, J. R. Lodge, and D. Considine. 1977. Progesterone content of goat's milk and its application for pregnancy diagnosis. J. Dairy Sci. 60. (Suppl. 1):82. (Abstr.) 16 Schiavo, J. J., R. L. Matuszcak, E. B. Oltenacu, and R. H. Foote. 1975. Milk progesterone in postpartum and pregnant cows as a monitor of reproductive status. J. Dairy Sci. 58:1713. 17 Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill, New York, NY. 18 Thibier, M., D. Pothelet, N. Jeanguyot, and G. DeMontigny. 1981. Estrus behavior, progesterone in peripheral plasma and milk in dairy goats at onset of breeding season. J. Dairy Sci. 64:513. 19 Thorburn, G. D., and W. Schneider. 1972. The progesterone concentration in the plasma of the goat during the oestrous cycle and pregnancy. J. Endocrinol. 52:23.