Detection of Estrus in Dairy Cows by Electrical Measurements of Vaginal Mucus and by Milk Progesterone P. G A R T L A N D z ,J. S C H I A V O 2, C. E. H A L L 3, R. H. F O O T E 2 , and N. R. S C O T T l Departments of Animal Science 2 and Agricultural Engineering ~ , and The New York State College of Veterinary Medicine 3 Cornell University, Ithaca, NY 14853 INTRODUCTION ABSTRACT
Electrical resistance (ohms) of mucus were analyzed in 20 postpartum Holstein cows by use of a probe inserted into the anterior vagina every other day for 30 days. Composite milk samples were taken on the same day, and progesterone was determined by radioimmunoassay. Cows were observed twice daily for standing estrus and reproductive organs palpated weekly per rectum (rectal palpation). Fifteen cows which were cycling showed increasing progesterone 6 to 7 days after the onset of estrus with values of 8.1 to 10.0 ng progesterone/ml milk on days 10 to 17. Concentrations had declined rapidly 2 days before onset of the next estrus. Progesterone in milk was affected by cow and by day of the cycle. Electrical resistance followed a similar cyclical pattern, but variability was large and only cows differed. The correlation between milk progesterone and mucus resistance was .22. Progesterone concentrations for four cows with follicular cysts fluctuated randomly with a mean of 2.6 ng/ml. Mean resistance of vaginal mucus was 44 g2 for both cycling and cystic cows, indicating that a single measurement of electrical resistance every 2nd day was unreliable in distinguishing physiological states. One cow had high progesterone in milk on days 19 to 25 and was diagnosed pregnant by rectal palpation 3 wk later. Cows were not seen in estrus 28% of the time when milk progesterone and rectal palpation indicated they were in the follicular phase of the estrous cycle and were cycling.
Received November 6, 1975.
Many difficulties are encountered in detecting estrus by visual observation alone, especially in large herds (9, 14). This study compares two methods in addition to visual observation. One method was based upon the progesterone content of milk which monitors the function of the corpus luteum. The success of this technique has been reported by several workers (4 to 7, 12). A second method involved measuring electrical resistance of vaginal mucus associated with changes in estrogen concentrations preceding ovulation. While there is some disagreement about the repeatability of the measurements, the method has been recommended for determining the best time to breed (2, 3, 8, 10, 11, 13). Palpations of the reproductive organs per rectum also were performed further to characterize the reproductive status of cows.
MATERIALS
AND METHODS
Twenty postpartum Holstein cows in the University herd had composite milk samples for progesterone analysis taken every other day for 30 days at the same time electrical resistance of the mucus was determined. A probe of the same design used by Metzger et al. (8) was inserted into the anterior vagina to measure mucus resistance. Milk samples were refrigerated immediately upon collection and subsequently were frozen in a methanol-solid carbon dioxide bath. Then they were stored in the freezer at --20 C until assayed. Progesterone in milk was determined by a radioimmunoassay procedure (1) which was validated in this laboratory for milk, following an extraction procedure (12) suitable for this fluid. An examination per rectum was performed each week, and ovarian structures, uterine size, and uterine tone were assessed. Cows were observed twice daily for standing estrus. Due to the 2-day sampling interval, some cows came into estrus on the day they were 982
DETECTION OF ESTRUS IN COWS 12
_--
10
E
o W-6
65 .-~
0
o 60 o
o. •"
4
55 u Z so ~ 45 N 40 uN 1
3
5
7
9
11
13
15
17
19
21
'35 ~
DAYS
FIG. 1. Means _+ SE for progesterone in milk and resistance of vaginal mucus in 15 cycling dairy cows with estrus occurring on days 0 to 1 and 20 to 21. The +SE is for milk progesterone and --SE for resistance.
probed and milk was collected. Others came into estrus on the alternate day. For purposes of analysis, data were grouped by 2-day intervals, with days 0 to 1 c o m b i n e d as the day of estrus. To compare cows with different cycle lengths, cows were put on a 21-day cycle basis by combining the first 14 to 15 days after estrus with the 5 to 6 days preceding the n e x t estrus. Progesterone in milk and electrical resistance measurements for cycling cows were subjected to standard analysis of variance and correlation techniques. Cows were r a n d o m and days fixed. RESULTS
Fifteen out of 20 cows tested appeared to be cycling normally. Progesterone in milk in these
983
COWS rose sharply 6 to 7 days after the onset of estrus, reached a plateau on days 10 to 11, remained near this plateau for 7 to 8 days, and then declined rapidly about 2 days before the next estrus (Fig. 1). Differences a m o n g days and cows were significant (P
Electrical resistance (ohms) of mucus were analyzed in 20 postpartum Holstein cows by use of a probe inserted into the anterior vagina every other day for 30 days. Composite milk samples were taken on the same day, and progesterone was determined by radioimmunoassay. Cows were observed twice daily for standing estrus and reproductive organs palpated weekly per rectum (rectal palpation). Fifteen cows which were cycling showed increasing progesterone 6 to 7 days after the onset of estrus with values of 8.1 to 10.0 ng progesterone/ml milk on days 10 to 17. Concentrations had declined rapidly 2 days before onset of the next estrus. Progesterone in milk was affected by cow and by day of the cycle. Electrical resistance followed a similar cyclical pattern, but variability was large and only cows differed. The correlation between milk progesterone and mucus resistance was .22. Progesterone concentrations for four cows with follicular cysts fluctuated randomly with a mean of 2.6 ng/ml. Mean resistance of vaginal mucus was 44 g2 for both cycling and cystic cows, indicating that a single measurement of electrical resistance every 2nd day was unreliable in distinguishing physiological states. One cow had high progesterone in milk on days 19 to 25 and was diagnosed pregnant by rectal palpation 3 wk later. Cows were not seen in estrus 28% of the time when milk progesterone and rectal palpation indicated they were in the follicular phase of the estrous cycle and were cycling.
Received November 6, 1975.
Many difficulties are encountered in detecting estrus by visual observation alone, especially in large herds (9, 14). This study compares two methods in addition to visual observation. One method was based upon the progesterone content of milk which monitors the function of the corpus luteum. The success of this technique has been reported by several workers (4 to 7, 12). A second method involved measuring electrical resistance of vaginal mucus associated with changes in estrogen concentrations preceding ovulation. While there is some disagreement about the repeatability of the measurements, the method has been recommended for determining the best time to breed (2, 3, 8, 10, 11, 13). Palpations of the reproductive organs per rectum also were performed further to characterize the reproductive status of cows.
MATERIALS
AND METHODS
Twenty postpartum Holstein cows in the University herd had composite milk samples for progesterone analysis taken every other day for 30 days at the same time electrical resistance of the mucus was determined. A probe of the same design used by Metzger et al. (8) was inserted into the anterior vagina to measure mucus resistance. Milk samples were refrigerated immediately upon collection and subsequently were frozen in a methanol-solid carbon dioxide bath. Then they were stored in the freezer at --20 C until assayed. Progesterone in milk was determined by a radioimmunoassay procedure (1) which was validated in this laboratory for milk, following an extraction procedure (12) suitable for this fluid. An examination per rectum was performed each week, and ovarian structures, uterine size, and uterine tone were assessed. Cows were observed twice daily for standing estrus. Due to the 2-day sampling interval, some cows came into estrus on the day they were 982
DETECTION OF ESTRUS IN COWS 12
_--
10
E
o W-6
65 .-~
0
o 60 o
o. •"
4
55 u Z so ~ 45 N 40 uN 1
3
5
7
9
11
13
15
17
19
21
'35 ~
DAYS
FIG. 1. Means _+ SE for progesterone in milk and resistance of vaginal mucus in 15 cycling dairy cows with estrus occurring on days 0 to 1 and 20 to 21. The +SE is for milk progesterone and --SE for resistance.
probed and milk was collected. Others came into estrus on the alternate day. For purposes of analysis, data were grouped by 2-day intervals, with days 0 to 1 c o m b i n e d as the day of estrus. To compare cows with different cycle lengths, cows were put on a 21-day cycle basis by combining the first 14 to 15 days after estrus with the 5 to 6 days preceding the n e x t estrus. Progesterone in milk and electrical resistance measurements for cycling cows were subjected to standard analysis of variance and correlation techniques. Cows were r a n d o m and days fixed. RESULTS
Fifteen out of 20 cows tested appeared to be cycling normally. Progesterone in milk in these
983
COWS rose sharply 6 to 7 days after the onset of estrus, reached a plateau on days 10 to 11, remained near this plateau for 7 to 8 days, and then declined rapidly about 2 days before the next estrus (Fig. 1). Differences a m o n g days and cows were significant (P
