There is always a tendency to be lenient with sows, and especially gilts, that exhibit some type of breeding problem, usually failure to show estrus. This is particularly true when profitability is low and the cost of culling an animal prematurely weighs on the mind. But hanging on to sub-fertile sows and gilts adds to the tally of non-productive days (NPDs), reducing overall herd productivity. Strict protocols for dealing with such animals are essential if NPDs are to be minimized.
One of the most effective tools available to producers when dealing with sows and gilts that fail to show estrus is the hormone treatment PG600 (Merck Animal Health), which may be used to initiate or enhance estrus in problem sows. PG600 stimulates the ovary to produce and release follicles. It is most effective when the injection is timed to induce heat and ovulation (which should occur approximately five days after injection ) at the same time as a naturally occurring heat is expected to occur. PG600 cannot induce estrus in a sow which has ovulated within 14 days because the sow’s own hormones override the effect of PG600.
In situations where it is impossible to know the current stage of the estrus cycle, two injections of PG600 will be necessary, 12 days apart, to ensure that at least one of the injections is given at a time which will result in estrus. It should be noted that PG600 will not induce abortion in pregnant sows and so is entirely safe to use in situations where there is uncertainty about the status of a sow or gilt.
When gilts fail to show heat
One of the largest contributor to NPDs arises from gilts that fail to show estrus during the process of boar stimulation. The level of anestrus exhibited by gilts will be very dependent on the intensity of boar exposure and the quality of heat-checking routines. All too often, substandard procedures are the cause of apparent failure to show heat. Therefore, if the rate of anestrus gilts is more than two per cent, management procedures should be reviewed and improvements made.
Assuming that facilities and procedures are adequate, the protocol for dealing with gilts should focus on good boar exposure, with the use of hormone treatment as a last resort. Gilts should be heat checked each day from the start of heat stimulation. Those failing to show estrus 28 days later should be remixed with other anestrus gilts, and moved into a new pen which will help to trigger estrus.
Releasing them from their pen and allowing them to run up and down the alleyway, preferably gaining contact with other gilts and boars, for one hour a day during the first three days will also help to stimulate the onset of estrus. Daily heat checking should continue until day 49 when they should be given an injection of PG 600. Gilts which fail to come into estrus by day 61 after first boar exposure should be re-injected with PG600. Those still remaining anestrus by day 68 should be selected for culling.
Delayed post-weaning estrus
In a well-managed herd, 95 per cent of sows should show estrus by seven days after weaning, although this figure will be less for first litter sows. Those sows which fail to come into estrus by day seven may be slightly sub-fertile and suffer from reduced productivity (litter size and farrowing rate) if re-served in the period 8-14 days inclusive post weaning. If this is a problem in first litter weaned sows, the root causes, such as inadequate lactation feed intake or too low a body weight at farrowing, should be investigated and rectified.
Where the problem with young females is persistent, routine injection with PG600 at weaning has been shown to significantly enhance the percentage of sows showing heat by day seven and also subsequent farrowing rate and litter size.
Sows that fail to show heat after seven days may be mixed into pens with other anestrus sows in an attempt to stimulate them to come into estrus. They should be checked daily for estrus and those failing to show estrus by day 21 post weaning may be injected with PG600, aligning the induced estrus with the naturally occurring one at day 26. A large proportion of these sows will come into estrus on day 25-26. Sows which fail to come into estrus by day 33 should be re-injected with PG600. Those still remaining anestrus by day 40 post weaning should be culled.
Reduced fertility with returns
After breeding, a proportion of sows will return to estrus, about two-thirds of these 18-24 days later (regular returns) with the rest (irregular returns) occurring any time after 24 days. By definition, the problem with returns is not one of failure to show estrus, but the likelihood of lost days due to lower fertility. In a herd with an 85 per cent farrowing rate, the rate for first returns is likely to be about 70 per cent and for second returns 50 per cent or less. Therefore, where possible, second returns should be routinely culled unless they have to be re-served in order to meet breeding targets.
Pregnancy testing will identify sows that are not in pig, but where estrus has not been observed. Here again, a strict routine will ensure that sows do not accumulate unnecessary NPDs. Sows identified as non-pregnant during the first scan at 28-35 days should be returned to the breeding area and checked daily for estrus. Those not showing estrus by day 37 post service may be injected with PG600 to coincide the artificial and naturally-occurring estrus at day 42. Sows which fail to come into estrus by day 49 should be re-injected with PG600. Those still remaining anestrus by day 56 should be culled.