Feeding live yeast through lactation can improve reproductive efficiency with reduced weaning to oestrus interval and reduced sow weight loss as well as improve birth weight. This article focuses on the effect of live yeast in lactation on improving weaning weight and post-weaning pig performance.
By Dr Peter Wilcock, AB Vista, Chesterfield, MO, USA
All pig producers strive for the same objective of maximising performance at the lowest cost/kg thereby producing the best return per pig. The initial focus of nutritionists is often on the sow and nursery production systems. It is in these areas where small adjustments can have dramatic impacts on lifetime performance. Weaning weight has always been important but it is becoming more critical as the number of pigs per sow per year increases, meaning more variable birth and weaning weights. With improvements in management, restocking and improved genetics there has been a steady year on year increase in the number of piglets weaned per sow per year globally over the last five years (Figure 1). Although this is beneficial from a production standpoint, one of the areas of concern with bigger litter sizes is possible lower birth weights and subsequently lower weaning weights.
Implications of weaning weight loss
Work by Kansas State University Researchers in 2009 on over 2000 pigs showed the effect of litter size on birth weight categories (%) and how the percentage of small pigs (<1.00 kg) increases with a larger litter size while the percentage of heavier pigs (> 2.0 kg) decreases (Figure 2). The results showed that, when litter size increased from 11 to 15 pigs per sow, litter weight at weaning increased but individual weaning weight reduced by 0.5 kg. Assuming that a loss of 0.5 kg in weaning weight equates to a loss on average of 2 kg at slaughter, a producer is losing out on potential income (app. £2.10 per pig) through poorer weaning weights. It is therefore a focus of swine producers to both increase the number of pigs weaned per sow per year and to maintain or improve weaning weights whilst at the same time reducing pre-weaning mortality.
Recently, more emphasis has been placed on lactation nutrition with a focus on improving weaning weight and reducing pre-weaning mortality.
In 2003, Schinckel and others at Purdue University projected growth for each of five 20 percentile groups (PCT) from birth and weaning through to the end of the nursery period at 60 days of age. The results (Figure 3) confirm that the top 80% of pigs have a similar average daily gain (ADG) up to day 60 while the bottom 20% (blue line) of the pigs have a dramatic fall off in late nursery performance with time. This difference will continue to grow over the lifetime production of the pig and it is therefore important to treat, where possible, the bottom 20% of the pigs as a separate population. A proactive approach such as treating these bottom 20% as a separate population would minimise the negative impact that they have on the production system as a whole.
Three trials looking at weaning weight impact on subsequent nursery growth showed that an extra 1 kg improvement in weaning weight improved growth through the nursery by approximately 36 g/day. In addition, an extra 1 kg at weaning resulted in 4.2 kg at 20 weeks of age as shown in Table 1. It is therefore important for pig producers to review their lactation nutrition and determine the economic feasibility of improving this nutrition to improve weaning weight with the potential return per pig.
Although there are many factors that can impact weaning weight we will focus on the use of live yeast during lactation to improve weaning weight and reduce pre-weaning mortality. Research conducted on a commercial live yeast product (Vistacell supplied by AB Vista) in USA and Europe has shown the impact that a live yeast can have on weaning weight and pre-weaning mortality.
In the US study we looked at live yeast supplementation through an 18 day lactation period. The results showed that the pre-weaning growth rates of piglets suckling on sows fed live yeast were improved by 6% over control piglets (0.30 kg extra in weaning weight). In addition, piglets on the live yeast fed sows had a reduced pre-weaning mortality compared to the control piglets born on the sows fed no live yeast. This reduced pre-weaning mortality in the live yeast fed sows resulted in an extra 0.5 pig per weaning. European work showed that for later weaned pigs (>21 days), pre-weaning growth rate was increased (+12%) and there was an extra 0.4 piglet weaned when sows were fed live yeast through the lactation period. Based on three trials the average weaning weight gain was +0.86 kg/ pig.
Overall the results showed (Table 2 and Table 3) that the use of a live yeast improved average weaning weights by 0.73 kg while increasing the number of pigs weaned by 0.42 pigs per litter. The results also indicate that the effect, as you would expect, is greater in longer lactation periods (>21 days) than shorter lactation periods (<21 days) but even the shorter lactation periods showed a positive response in early weaned piglets.
There are differing mechanistic reasons why live yeast benefits the sow and suckling piglets, but essentially the live yeast optimises sow gut health thereby improving nutrient utilisation and producing an improved milk composition and/or output.
Binding of pathogenic bacteria
Live yeast is effective in reducing the pathogenic load on the gastrointestinal tract. In an internal in vitro trial, a sample of gastro-intestinal mucosa layer from the piglet was taken and Salmonella enterica and E. coli K88 were introduced into the system with and without live yeast. In the presence of the yeast, the attachment of E. coli K88 and Salmonella enterica was reduced by 30% and 33% respectively. This will assist in promoting ‘beneficial’ bacteria in the gut and will reduce the maintenance energy cost of the pig due to better nutrient utilisation for growth.
It is suggested that the use of live yeast will also alter the gut micro-environment, increasing the presence of cellulytic bacteria in the hind gut. This will improve hind-gut fermentation and a higher production of volatile fatty acids which can be utilised as an energy source by the sow which will improve efficiency.
The use of live yeast has also been shown to improve the nutrient composition of the milk. Jurgens and others showed in 1997 that the use of live yeast in lactation improved milk protein by 7% and fat by 14%, which will translate into better pre-weaning piglet growth. In addition, live yeasts can impact the immune status of the animal and a trial conducted in the USA showed that piglets suckling from Vistacell fed sows had an improved immune status as measured by CD4 and CD8 levels. These immune factors essentially monitor the immune system of the body and react if an infection occurs, thereby providing the pre-weaning pig with an improved immune status to overcome pre-weaning disease challenges.
Live yeast added to the sow diet through the lactation stage can have a positive effect on piglet weaning weight and preweaning mortality. As the cost of live yeast is low, when spread over the numbers of pigs weaned per sow, it provides an economic solution to meet the current market needs of supporting more pigs weaned per sow per year while maintaining weaning weight. This combined production improvement makes the target of maximising meat yield per sow per year easier to achieve.