Days Open measures overall reproductive performance for the previous 12 months. Problems with fertility and/or estrous detection increase Days Open. Projected Minimum Calving Interval is calculated by adding Days Open to the gestation length for a normal cow. It is interpreted in a manner similar to Days Open. A small portion of cows with high Days Open usually inflates the herd’s average Days Open to a small degree. If Days Open is inflated significantly by a few problem breeding cows, these cows should be culled. The culling policy for reproductive problems in the herd should be examined. Current Days Open when added to a gestation length for a normal cow will not always be equal to the Calving Interval one to two years from now. Some cows with reproductive problems are culled and never contribute to the Calving Interval. This difference is usually small, unless a significant portion of the herd is culled for reproductive problems. If most of the cull cows are removed from the herd for reproductive problems, then current Days Open plus gestation length may be larger than future Calving Interval. Of course, a serious problem exists in any herd where most of the cull cows are removed for reproductive problems. The causes of these problems should be determined by examining the indexes of reproductive efficiency as described in this IRM fact sheet. To calculate Days Open for a herd, list for each cow the number of days from calving to:
Actual Calving Interval is an indication of reproductive performance from 9 months to 2 years prior to the current date. This measure only reflects reproductive successes, however, and does not take into account reproductive failures. Cows that are culled for reproductive problems can be considered failures. Actual Calving Interval is figured by calculating the number of months between the most recent calving and the previous calving for each cow in second or later lactation. A Calving Interval is not calculated for first-calf heifers. The Calving Interval for each cow is then added together and the total is divided by the number of cows in second or later lactation. Actual Calving Interval should be interpreted according to the guidelines in Table given below. Producers with a herd having an Actual Calving Interval of under 11.7 months and a Days Open of under 85 Days should breed cows later in lactation for their first service to increase Days Open to 85-115 Days. Recent research indicates that milk production of herds with an Actual Calving Interval of under 11.7 months is significantly less than milk production of herds with a Calving Interval of 11.8-13.0 months. Similar to Days Open, Calving Intervals for commercial herds are interpreted differently than Calving Intervals for herds with registered cattle. An Actual Calving Interval of 13-13.5 months should be considered a slight to moderate problem for commercial but may be adequate for registered herds. An Actual Calving Interval of 13.6 to 14.0 months is considered a moderate problem for commercial herds and a slight to moderate problem for registered herds. An Actual Calving Interval of over 14.0 months is indicative of a severe problem in all herds.
The average DFS for a herd is influenced by a management decision of when first breeding will occur postpartum. This earliest number of days decided upon by management (DFS Goal) varies greatly between herds. Some cows can be safely bred as early as 40 days postpartum; however, highest fertility levels usually are not reached until 60 days. Many producers breed cows at their first estrus after 45 days postpartum. These producers avoid many fertility problems by having their veterinarian palpate all cows prior to 45 days postpartum to diagnose reproductive problems such as severe uterine infections. Breeding of cows with metritis can then be delayed until the uterine infection is eliminated and the uterus is healthy. The average DFS for a herd is influenced by when the ovaries of a cow begin to function again postpartum and the number of unobserved estrous periods. The average DFS for a herd is figured as follows:
1. Calculate the number of days from calving until first service for all cows inseminated.
2. Calculate the average DFS for the herd by adding together the DFS for each cow and dividing the total by the number of cows inseminated. After determining the earliest number of days postpartum that a cow can be bred in a herd (DFS Goal), the average DFS for a herd should be interpreted according to the guidelines in the table given below. Problems in herds with average DFS minus DFS Goal over 18 days can be due to cows being anestrus and/or unobserved estrous periods.
Average S/ Conc. for a herd is a measure of fertility in cows which were reproductive successes and have become pregnant. Breedings for cull cows and repeat breeder cows not diagnosed pregnant are not included in this index. Average S/ Conc. can be figured as follows:
This comparison can indicate whether overall reproductive efficiency during the last nine months is better, the same, or worse than the herd reproductive efficiency during the previous year. To compare Days Open to Actual Calving Interval (Cl), a Projected Minimum Calving Interval (PMCI) is calculated. Average Days Open is added to the gestation length, in days, for the most common breed in a herd (Brown Swiss,290 days; Holstein, 279 days; and Jersey, 279 days). This total is then divided by 30.25 days/month. For example, PMCI for a Holstein herd averaging 123 Days Open would be calculated: 123 days + 279 days= 13.3 months for PMCI. 30.25 days/month Comparisons of Cl and PMCI should be interpreted according to the guidelines in the table given below. Herd reproductive management does not need to be changed with improving reproductive efficiency, unless the number of missed estrous periods or repeat breeders still requires improvement. For herds with an unchanging level of reproductive efficiency, the effectiveness of reproductive management procedures should be evaluated if the value for Days Open indicates a problem exists. If overall reproductive efficiency has gotten worse during the last nine months, the effectiveness of management procedures concerning reproduction should be evaluated.
Estrous detection efficiency can be expressed as the percentage of Heats Detected (total estrous periods when a cow was detected in estrus). The percentage of Heats Detected can be estimated by first calculating an average breeding interval for the herd and then comparing the breeding interval to Table 6. Breeding interval is the average number of days between first breeding and the insemination resulting in pregnancy. Average breeding interval, can be calculated by the following formula: Breeding Interval = Average Days Open-DFS (S/Cone-l) An example for a herd with an average Days Open of 140, an average DFS of 2.6 would be: Breeding Interval = 140-75=41 days (2.6-1) Comparing the breeding interval to Table below, 41 days corresponds to 50% of Heats Detected. A guideline for interpreting percentage of Heats Detected is summarized in the Table below.. Producers with severe problems should improve their estrous detection program. Moderate problems may be caused by not observing estrus in certain cows. Examining records of individual cows may be useful. Anestrous cows or cows with feet and leg problems may be difficult to observe in estrus.
Herds that also have a poor level of fertility (S/Conc over 2.0) should use milk progesterone analysis to determine the accuracy of heats detected.
Some herds may have excellent estrous detection efficiency yet have poor fertility (S/Conc over 2.0), suggesting a problem in estrous detection accuracy. (Cows are thought to be in estrus when they are not.) Progesterone analysis of milk samples collected on the day of breeding can be used to determine accuracy of estrous detection.
Interpreting Reproductive Efficiency Indexes
Dr. M.A. Varner, Dr. J.L. Majeskie, and S.C. Garlichs
University of Maryland