What the Scales Told Us: Gilt Age, Weight and the Numbers Behind Better Conception Rates

By Jack Bosworth, Director, FJ Bosworth & Sons. Published 11 November 2021.

I hope everyone is keeping well.

I have written before about the decision we made in 2018 to double our herd to 540 sows. To get there at the pace we wanted, we obviously needed to select a much larger number of gilts to enter the breeding herd. With any expansion, the real challenge is maintaining the standards you set at a smaller scale.

A dip we had to work through

Our conception rates had always been around 80 to 90 per cent, often higher. The expansion saw a dip in performance that lasted longer than we would have liked.

I do not think you could pin it on any single issue. We made a lot of changes in a short space of time, and the breeding stock had to adapt to all of them at once:

• Electronic sow feeding (ESF) stations.
• Being housed in two large dynamic groups.
• A different environment from the one they had been bred and reared in.

Time and patience were needed for the animals to settle. That is not a glamorous answer, but it is the honest one.

Why we started weighing every gilt

Earlier this year we invested in electronic weigh scales so we could collect proper data on our breeding gilts. The goal was simple: gain real confidence in the right balance of weight and days age at first service, rather than relying on eye and assumption.

The numbers have been eye opening. The difference in both conception rate and liveborn per litter is genuinely vast, considering how small the difference between each category is.

What the data shows, by age at service

Age at service (days)	Conception rate	Liveborn per litter
241 to 244	71.00 per cent	13.2
250	92.31 per cent	13.3
261 to 265	80.00 per cent	15.9

A few weeks one way or the other genuinely matters. Gilts served at 241 to 244 days are not ready, and the conception rate of 71 per cent tells us that clearly. At 250 days the picture changes completely. The 261 to 265 day band has a slightly lower conception rate at 80 per cent, but a fantastic liveborn average of 15.9, on a smaller pool of animals.

What the data shows, by weight at first service

Weight at service (kg)	Conception rate	Liveborn per litter
141 to 145	92.31 per cent	11.0
161 to 170	93.94 per cent	14.0
Over 175	74.03 per cent	10.7

Conception rates are strong at both 141 to 145 kg and 161 to 170 kg, but the liveborn numbers are a different story. The heavier band is producing three more liveborn piglets per litter than the lighter band, with a marginally better conception rate alongside.

Anything served above 175 kg looks worst on both measures. Conception drops back to 74 per cent and liveborn falls to 10.7. There is a clear sweet spot, and going past it costs us output.

The headline number, and why it matters

Since we started weighing, our gilt conception rates are running at 82.97 per cent, with an average liveborn of 14.2 per litter.

That is now the number I watch, rather than continually checking what age and weight individual gilts are at service. As long as that overall average is steadily improving, which it has been, I know that Alex and Zoe are using both their stockmanship and the collected data well to find the optimum for each animal.

That is the bit that does not show up on a spreadsheet. The scales are a tool. The judgement still belongs to the people on the unit.

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About the author

Jack Bosworth is a fourth-generation farmer and Director of FJ Bosworth & Sons, an arable and pig farming business at Spains Hall, Willingale, Essex. The farm has been in the family since 1919, and Jack farms alongside his father Stuart Bosworth, who was named Farmers Weekly Pig Farmer of the Year in 2011. The business is Red Tractor assured and runs an integrated farm-to-fork model, with home-grown cereals milled on site using solar-generated electricity.

You can follow Jack’s articles on fjbosworth.com, or get in touch via the WhatsApp link on the site.