Understanding the Key to Successful Reproduction
Estrus Detection Aids
Many
estrus detection aids have been developed to improve estrus detection and AI
service rate in dairy cows. These aids are effective if used to enhance an
estrus detection program, but should never fully replace visual detection of
estrus.
Use
of tail paint or chalk can increase estrus detection efficiency (Senger, 1994).
Tail paint was originally developed as an estrus detection aid for use in dairy
herds managed using grazing based systems (Macmillan and Curnow, 1977), and has
been shown to be an effective estrus detection aid and for practical breeding
management in New Zealand (Ducker et al., 1983; Kerr and McCaughey, 1984)
Detail Oestrus Activity Tail Paint (FIL Industries Ltd, Mount Maunganui, New
Zealand) is water-soluble and latex based, and is applied in a strip 5 cm wide
by 20 cm long over the coccygeal vertebrae of the tail head. Once dried, the
paint hardens and, according to the manufacturer, remains intact for up to six
weeks unless removed by mounting activity of a herdmate during standing estrus.
Use
of pressure-activated heat mount detectors can increase estrus detection
efficiency (Senger, 1994). These devices are affixed to the tail head of
individual cows, and are activated by direct pressure from a herdmate during
mounting events. Commercially available devices include Kamar heat detection
patches and Bovine Beacon. Although false positives can occur, these devices
are generally useful as estrus detection aids. Although primary and secondary
indicators of behavioral estrus are the best methods for determining timing of
AI, breeding to an activated Kamar device can yield acceptable results (Nebel
et al., 1994).
Androgenized
marker animals also have been shown to improve both estrus detection efficiency
as well as the accuracy of estrus (Sawyer et al., 1986). This is especially
true for smaller herds in which the sexually active group may include only one
or two animals per day. In many cases, androgenized marker animals are fitted
with marking devices or used in conjunction with tail chalk or paint. The use
of Synovex-H (Syntex Laboratories, Inc., Palo Alto, CA) is a convenient method
for androgenizing marker animals. Yearling freemartin heifers weighing 800 to
1,000 pounds are commonly used as marker animals, however, lactating cows
should never be treated with Synovex-H because milk from treated animals can
not be sold for human consumption. Older, dry cows also have been used and are
good marker animals because their pecking order within the herd is already
established. Over-conditioned animals, animals with poor feet or legs, and
those animals at the bottom of the herd pecking order should be avoided.
Treated animals are usually effective for about six months after implantation.
Although animals can be retreated after their effectiveness begins to wane,
most producers choose to treat a new animal. About 80% of treated freemartin
heifers respond to treatment, and those animals that do not respond should be
eliminated.
Surface
applied or implantable pressure sensors also have shown promise for providing
accurate daily estrus detection (Senger, 1994). For example, the HeatWatchÒ system (DDx Technology) provides
continuous information on mounting activity. When HeatWatchÒ was compared with visual estrus
detection (Walker et al., 1995), efficiency of estrus detection was greater
with HeatWatchÒ (91% vs.
51%) with similar accuracy (96% vs. 94%).
Because these types of mounting detectors require physical interaction
among cows, the best results are achieved when cows are housed in groups, such
as, in free stalls, pastures, or lots, compared with cows housed in stanchions
or tie-stalls or in poor environmental conditions.
Farris
(1954) first showed that estrus behavior in dairy cattle is accompanied by an
increase in physical activity. Kiddy (1977) was the first to use leg mounted
pedometers to determine if physical activity related to estrus varied enough
compared with nonestrual activity to be useful for estrus detection in dairy
cattle and concluded that pedometry may be a useful method for estrus detection
in dairy operations. Pedometer and computer technology improvements coupled
with increases in computer software analysis programs have resulted in greatly
improved pedometry systems (Koelsch et al., 1994; Senger, 1994). Comparison
among various statistical comparison procedures that use pedometery data in
lactating dairy cows indicate that 70% of estrual periods and 99% of nonestrual
periods can be accurately predicted using currently available pedometry systems
(Koelsch et al., 1994).