Return to MARK Home Page
Adding gilts into the breeding herd is a major task in sow herd management. The magnitude of this task is highlighted by the large replacement rate that all sow herds experience. In PIGTALES REVIEW 1996, the average annual replacement percent for all US herds that were recorded in PIGTALES in 1995 was 52.6 percent. This included 367 farms with 251,095 sows. The annual replacement rate in the top ten percent of those herds, based on pigs weaned per sow per year, was 44.3 percent.
Critical to the success of adding in the necessary herd replacements is accurate estrus detection in the gilts. A recent report from Nebraska indicates that, of the several variables suggested to influence heat detection, the actual method of detection may be the most significant.
In the 1997 NEBRASKA SWINE REPORT, researchers Dr. Dwane Zimmerman and Denny Aherin reported on their study that compared accuracy and rapidity of heat detection in gilts heat checked with fence line exposure in each of three treatments. These treatments were with gilts housed in either stalls or in pens and given fence line boar exposure or with gilts housed in pens and relocated to the boar room for fence line exposure.
Twenty-four gilts, each of which had cycled two or more times, were randomly assigned to one of the three treatments. The stalls were 18 inches wide with vertical bars on 4 inch spacings on the front gates. The gilts in pens had four to the group in 6 foot by 9 foot pens that had front gates with vertical bars on 4 inch spacings. The gilts in the third group were in pens similar to those in the other pen treatment but were relocated to the boar room for fence line heat detection. After all the gilts completed one heat detection observation, they were rerandomized across treatments and again heat checked with the same procedures. All gilts were housed in the same room and not exposed to boars except during the actual heat checking process. Two boars were used on alternate days for 10 minutes of fence line exposure daily.
All but one gilt had two estrus periods during this experiment. One other gilt had a 33 day estrus cycle and the experiment was concluded before her second heat period.
The completed observations are outlined in Table 1. Detection of both first and last day of heat with in-place fence line boar exposure was essentially the same in gilts housed in pens and stalls (stalls, 67% vs. Pens,68%), but heat detection rate in gilts relocated to the boar room was higher (81%, P<.05). All gilts, regardless of how they were housed (stalls or pens) or were they were heat checked (in-place or relocated), responded during mid-estrus.
Gilts relocated for boar exposure responded more quickly to heat checking than those left in-place (1.7 min vs. 2.3 min, P<.05). Also, gilts in pens tended to respond more quickly than those in stalls (2.0 vs. 2.5 min, P<.1) when both were heat checked in-place. No difference was detected in the duration of estrus among the treatment groups. Overall, the average length of estrus was 52.1 hours.
The researchers concluded from this study that relocating gilts from their home environment to another environment for boar exposure gives a higher rate of heat detection and a more rapid estrus response than obtained in gilts heat checked in-place. Also, gilts not responding to fence line exposure should be given physical boar exposure. Additionally, method of housing gilts, ie. pens or stalls, is of much less importance than the method of exposing them to the boar. In summary, they stated that the key to achieving accurate and rapid heat detection is to provide gilts with novel stimuli, including physical contact, from a high libido boar(s) at a site other than the gilt's residence.
Table 1. Mean rate (%) of estrus detection and mean interval to estrus (min) in response to 10 min of fence-line boar exposure
detection rate %b | detection rate %c | to estrus min | |
|---|---|---|---|
a Gilts housed in stalls (S) or pens (P) and heat detected
with fence-line boar expoure (FBE) in place (IP) in gilt room
or after relocation (R) to boar room.
b Detection rate of first and last days of estrus (combined)
with FBE.
c Detection rate of second day of estrus (mid-estrus)
with FBE. Means in each column with difference superscripts differ
(e vs others, P<.05; h vs f and g, P<.05; and f vs g, P<.1).
Charles Stanislaw
Return to MARK Home Page