Expert opinion


Replacement gilts – age at first service – new advice

I am sure you have seen the interesting report on age at first service by JSR Genetics revealing that age at first service – in terms of numbers born alive and returns to service – takes precedence over bodyweight and fat P2 level. They claim that 240 days old shows the best response and is most cost effective, with bodyweight and fat cover far less important within quite wide boundaries.

For the past ten years best opinion has been not to grow the gilt too rapidly between final selection, say at 100 kg at 180 days old, and first service at 225/230 days at 125/130 kg. This six week period  was said to be a sufficiently-long induction period to strengthen her immune competence,  which is still a desirable factor today.

240 days extends this by ten to 14 days, which from the immunocompetence viewpoint is probably beneficial as it allows more time for a 14-day challenge period and then a 28 to 35 day fortification period which the specialist pig vets advise. I strongly suspect that this two-stage induction protocol helps boost immunity to PRRS, as those farmers who have adopted it seem less plagued by this troublesome disease.

My suggested weight for age table based on 240 days is given below.

Table 1. Gilts: Suggested typical weights for age for modern high lean gain European breeds. Gilt growth rate = Aim to achieve 100 kg in 170-180 days, gilt growth rate at 550 g/day, rising to 600 g/day towards puberty.*

100 kg              180 days 25th or 26th week 6.5 months + old
104 kg 187 days week 27  
108 kg 194 days week 28 7 months old
112 kg 210 days week 29  
116 kg 209 days week 30  
120 kg 216 days week 31  
125 kg 223-225 days       week 32 8 months old

* Consult your seedstock supplier for actual targets

But what about cost?

Of course this will cost more, especially when a gilt developer diet is used, as it should be for these latest hyperprolific gilts.

Higher numbers born
But when you take into account higher numbers born alive and fewer returns at first litter as well as less of a second-litter fallaway and a longer SPL (Sow Productive Life) then the extra cost is repaid fivefold (Gadd, in press). A gilt developer diet is quite different to the conventional grower diet many producers are still using to grow-on their replacement gilts.

A good pig nutritionist can design one on a daily intake basis to achieve from selection at 100 kg to the 240 day first-service date, in cooperation with the seedstock house you have chosen. Important as genotypes do differ between lines.

Weight suggestions
Thus my weight suggestions in Table 1 might vary (usually downwards) a little according to the 'brand' of gilt you have chosen and the gilt developer diet and daily feed scale designed for them.

Sounds complex, but with the right advice it is simple enough as it looks as if we need to worry less, within the bounds of common sense of course, about weight and fat cover in future.


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    Michael Mc Keon, Teagasc, Ireland

    John, Our experience in Ireland over the last 10 years would also agree with delaying gilt service until 240 days to achieve higher born alive. This is espicially borne out where units are been restocked as the oldest gilts (first ones selected for service pool formation) have generally the highest born alive.

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    Pavel Kerber

    Hello Mr. Gadd. What do you advice for DanBred gilts? I was trying to find a recommended growth curve for gilts from DanBred but could not get one. We have bought gilts for two farms. They were delivered at age from 150 days (weight 110kg) to 210 days (weigth 135 kg). They are growing very fast- almost 1 kg a day, being fed only 2,5 FU a day, in age from 25-32 weeks. They are hungry all the time. In order to slow down their growth we fed them only 2,5 FU and they ended up with less backfat-13 mm - at age of 34 weeks. Our goal is to serve them at age of at least 238 days, second or third heat, 16 mm and at least 135 kg. But if we wanna achieve 16 mm of backfat the gilts will be a monsters weighing well over 170 kg. What do you suggest? What is smaller evil? Thank you Pavel

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    John Gadd

    Sorry to be so long in replying, Michael.
    The gilt pool is the right place to carry out the 14day challenge period followed by the 4 week (6 week if PRRS is in the area, I guess quiet/consolidation period (no challenges) which satisfies the 240 day service date target at 135 kg. A gilt pool also encourages the breeder to give the gilt at this time more space - proximity stress is a real problem I suspect during the consolidation period . I see them packed in so tight everywhere I go - not good. I have a lot of problems convincing breeders to set a gilt pool up on cost grounds but those with spare cattle courts have no problem in joining the 'gilt pool brotherhood'.
    Is it coincidence that those I've recorded so far are getting their sows to last 2 litters longer?
    A few (ie 4) swallows don’t make a summer but in a couple of years time I should have enough evidence to support the premise that a well-planned gilt pool might do just that?
    By the way Teagasc has done some fine work over the years - very practical/cost-concious stuff. Keep it up!

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    John Gadd

    Pavel. Sorry to be so long in replying.
    I’m not dodging the issue here but I must redirect you to Danbred ( whom I consider one of the 5 best pig breeding companies in the world) for advice on their own genotypes. They know their own genelines best.
    My only comment is not to fuss too much about the gilt’s backfat at service. It seems to have little effect on numbers born, the spread being only about 0.4 piglets difference between 11mm P2 and 20mm.(Walling 2009). Your 13mm is fine by me.
    As to your growth rates, these `new` latest-model gilts can/will grow well over 1100 g/day which I think is too fast, as faced with these monsters the breeders reaction is to get them served quick before they get any bigger! Remember my tongue-in-cheek analogy which is going the rounds of pig producers at present, of the giltt having the body of a gorgeous 20 year-old young woman and thus ready for service - but inside she has the breeding hormone make-up of a 12 year old schoolgirl !
    My own advice with these outwardly precocious ladies is to hold growth back to 550 to 600/g/day when they arrive at 100 kg or so and rise to 750g/day at flushing/before service. I used dried sugar beet pulp to provide a feeling of satiety and dull those hunger-grizzles. Straw bedding in giltpool yards helps, too. They should have a gilt developer diet during this whole period. This will allow the schoolgirl inside to catch up with the young woman hormonally and ensure good ovulation at 240 days and subsequent evenly-placed implantation 3 weeks later to help with nice level and heavy birthweights.

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