How do we get more even litters?

Two weeks ago I assessed what uneven litters might cost, writes John Gadd. The answer was “a lot”, and we’re getting more of them. So, what causes the problem?

Are genetics involved? Frankly, I don`t know. You should ask your seedstock supplier.

Is early pregnancy management involved? Definitely, as I will discuss shortly.

Is stress involved? I’m sure it is, and in a bigger way than is fully realised.

And is oestrus and service involved?  Maybe, but probably less important than the two points I’m going to concentrate on here.

Skilled management and stockmanship are critical to get the release of fertilised follicles quickly and evenly into the embryo stage, then on to steady development of the foetus. During the past 10 years, commercial breeders have been much better at stimulating the weaned sow into oestrus at the right time and in the right way, and then carrying out careful, clean and patient insemination. So I forecast that the problems influencing uneven litters could be less in this area than those below.

The key period in determining litter size starts at about 10 to 12 days after service and runs for rougly two weeks. During this time, the embryos are being transformed by a progression of blastocysts (the word blast means budding or cell development). Stressing the recently served sow can disturb the even and successful establishment of the developing embryo on to the endometrium (womb nutrient surface) in two ways, both causing a spread of weights at birth.

The first way is uneven regeneration (receptiveness) of the endometrium. After the litter is weaned, the surface of the womb takes a little time to become receptive to the filamentous blastocysts seeking to attach themselves (implantation). The time taken is affected by many forms of stress – from downright fear and aggression, through overcrowding, hunger, thirst, cold, discomfort, even down to mild anxiety.

Figure 1 shows how parts of the womb surface becoming receptive late, being held back by stressors. The blastocysts then have to compete for establishment in the reduced receptive areas. Some do well at this and grow away faster than others, which resultsb in an uneven litter. But others never do manage to find a home, then wither and die. This gives a secondary result of smaller litters and numbers born.

The solution to uneven generation is don’t stress sows and gilts during implantation, for fully a month from service to be on the safe side. Indeed, go further. Do everything you can to make the sow “feel good” both during implantation and the formative days before it. She has been through a switchback of emotions: farrowing, the effort of raising a family, losing them; and finally the excitement of re-mating. She must be emotionally and physically tired. Sows not only need a break, but need to appreciate it mentally – the feel-good factor. This must accelerate endometrial regeneration.

The second problem that must be addressed is asynchrony, the scientific term for delayed or sporadic follicle (the ovum and its encasing/protective cells) release. In this case, the endometrium may have regenerated promptly and evenly, but the timing of the release of the fertilised ovae into the womb is prolonged. Those reaching the endometrial surface sooner get the best choice of location and have a head start. Those arriving later find their nutritive plates constricted. They survive but are penalised (see Figure 2) and the result is an uneven litter.

The solution this time is to follow the guidelines published by Australian researcher Dr Paul Hughes, the leading authority on bringing the sow smoothly and gently to oestrus with correct timing and stimulation.

Of course, both procedures cost time and money to manage well, and they rely to an extent on having excellent facilities and thorough staff training. But, as my small trial reported last month suggests, there could be ample extra income at slaughter to pay for the measures likely to secure litters that are more even.

Everyone is talking these days about higher litter numbers born alive. Excellent, well done everybody! But even litters, whatever the numbers born, matter more than people realise.

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About The Author

John Gadd, who has spent 60 years' involvement in pig production, has had more than 2,800 articles about pigs published and has written three best-selling pig textbooks. With hands-on experience that includes managing a grow-out herd at 1,800ft in Banffshire, Scotland, and 20 years in the allied industries with Boots' Farm Department, RHM Agriculture and Taymix, he set up his own international pig management consultancy in the mid 1980s and has now visited more than 3,000 pig units in 33 countries as a pig management adviser. (Photo courtesy Bournemouth Daily Echo)