How lower-density starter diets can improve pig performance

A recent study carried out by Harper Adams and ForFarmers has found that, contrary to belief, lower-density starter diets don’t necessarily lead to lower performance.

In fact, the study showed they can deliver improved lifetime performance.

Lower-density diets have lower nutrient density – predominantly lower protein and energy. Vitamin and minerals levels remain the same.

High-density diets are often around 21% protein, but lower-density diets are lower.

See also: 4-step guide to pig feeding and rations

Farmers Weekly spoke to ForFarmers’ Dr Charlotte Evans to get an insight into the research, as well as independent nutritionist Andrew Zarkos-Smith, to find out what the practical implications are of incorporating this kind of diet on farm.

About the study

The trial was carried out at Harper Adams’ pig unit, which comprises 230 sows on a farrow-finish system.

Facilities at the university include an indoor-crated farrowing system, with milk line and specialist post-weaning accommodation to allow individual weights to be monitored more easily and (pen level) feed conversion rate to be tracked up to 40kg.

Following its latest repopulation, the unit has removed zinc from all of its starter diets ahead of the 2022 deadline. This made it the ideal environment for the trial.

Altogether, 348 piglets started the trial at birth and 216 were followed through to post-weaning in specialist accommodation (up to 40kg).

Piglets were fed on a milk replacer, as well as a supplementary pre-starter feed from seven days of age.

The ForFarmers milk replacer comprised 20% crude protein and 9.8% starch, and the pre-starter comprised 19% crude protein and 20% starch. 

The pre-starter was a highly digestible and palatable feed, designed to maximise early feed intake pre-weaning and ease the transition on to solid feed, containing processed starch to aid gut development.

The piglets were weaned at 27 days old and the pre-starter diet was fed for seven days pre-weaning.

At this point, the piglets were moved on to a choice of different starter regimes, containing highly digestible raw materials, cleaned and finely ground ingredients, and extruded soya bean meal, which maximises protein digestibility and enhances gut health.


Pigs fed the lower-density diet did perform better in terms of growth and feed efficiency, demonstrating the importance of aligning intake levels with nutrient requirements.

Pre-weaning summary

Pigs consumed an average of 1.4 litres of the supplementary milk and just over 500g of dry matter on the lower density diets – surpassing the recommended target.

Daily growth rates

  • First week post-weaning = 220g/day (feed conversion ratio – FCR – 1.07), with some pigs achieving 500g+/day
  • One to three weeks post-weaning = 496g/day (FCR 1.15)
  • Three to eight weeks post-weaning = 745g/day (FCR 1.75)

“Based on the results, we are able to deduce that if intake is high, pigs do not need a high concentration of nutrients, but if intake is low, they will require a higher concentration,” explains Dr Evans.

She adds: “It is important to remember that oversupplying nutrients can exacerbate underlying health issues and as we reduce dependence on zinc, it is important to focus on diets that support gut health and reduce undigested protein, mentoring the hindgut by matching intake with nutrient availability.

The results show the absolute potential of some of our herds.”

The numbers

  • 1.3 Reduction in the number of days it will take pigs to reach slaughter if a daily growth rate of 10g/day is achieved in the first two weeks post-weaning.
  • 9kg Average weaning weight
  • 130.3kg Average litter-weaning weight
  • 14.5 pigs Average piglets per litter

The practical implications of implementing low-density diets

Lower-density feeding has been encouraged in piglet diets in the Netherlands in a bid to reduce nutritional stress. However, in the UK, it hasn’t been widely practised.

Numerous studies concur with the ForFarmers/Harper Adams data and have shown the benefit of feeding low-density diets to piglets.

However, independent pig nutritionist Andrew Zarkos-Smith, of Zarkos-Smith Associates, warns there are a number of things to consider before implementing this type of diet on-farm.

Correct feeding programme

The first proviso is that the correct feeding programme must be implemented, and high quantities of dry feed must be provided pre-weaning.

According to Mr Zarkos-Smith, the efficacy of implementing such feeding strategies hinges around the principle that it takes around 20 days for the piglet’s gut morphology to change.

“By using a cup system in the farrowing crate, the piglet’s gut is exposed to vegetable protein and starches within a few days of birth, so it can fully digest these products at weaning and not suffer the usual weaning stresses.

Dry feed

The second is that high quantities of dry feed must be provided pre-weaning – although the specific amount will depend on the feeding system.

“In our study, we demonstrated that the variation of weaning weight reduced by 9.3% when fed high quantities of feed and the lifetime performance of the small pigs was considerably enhanced – +149 g/day from weaning to slaughter.”

Finally, producers must be willing to invest in farrowing-house management and feed systems to enhance lifetime performance.

The key thing to remember when incorporating diets like these on a farm is that if large quantities of feed are not consumed in the farrowing house, and pigs are weaned too early before the gut morphology can change, then it is not possible to reduce the nutrient density of the diet as the feed intakes post-weaning will not be high enough.

Other studies

Zarkos-Smith Associates

Independent farm research was carried out by Zarkos-Smith Associates five years ago – and repeated three years ago.

It demonstrated that farmers could completely remove zinc oxide, in-feed antibiotics, and reduce feed costs by some £150/t post-weaning, on average/poor health-status farms.

During the trial, an Opticare milk cup system to dispense supplementary milk was used. This system was developed for sows with surplus piglets/larger litters.

It works by mounting an Opticare cup in every farrowing pen. An automated pipeline system pumps milk to the cup, providing an unlimited milk source to the piglet.

After 12 days, the system can be switched from milk to liquid pre-starter – but the ethos behind it is ensuring every piglet gets the optimum amount of feed in the early stages of life.

Marius Nabuurs

Marius Nabuurs – a vet from Lelysted, Netherlands – published his book Etiologic and pathogenic studies on post-weaning diarrhoea in 1991, and his research came to the same conclusions.