Dietary Yeast as an Alternative for Nursery Pigs

As the world moves away from pharmacological zinc oxide, do we have other options?

By Brenda Christensen, Dr. Elijah Kiarie & Dr. Lee-Anne Huber

Weaning is a difficult transition for piglets.

Removal from the sow, mixing with other pigs, changes in diet composition and form, and fading maternal immunity all contribute to reduced feed intake and increased susceptibility to enteric disease. Typically, low feed intake immediately after weaning is the main driver of the post-weaning growth lag.

With the removal of in-feed antibiotics as growth promotors, zinc oxide (ZnO), fed at high inclusion levels (>150ppm), became an attractive strategy to overcome the post-weaning growth lag. Feeding ZnO increases the hunger hormone, ghrelin, which promotes feed intake. However, feeding zinc above the requirements of pigs increases zinc excretion in the manure, which ends up accumulating in water and soil. Additionally, high levels of zinc can promote the development of antibiotic resistant bacteria in the intestine. Thus, the European Union banned the use of high levels of ZnO (>150ppm) in feed as of June 2022, and Canada may soon impose a similar ban. To remain competitive, producers are trying to find suitable alternatives.

Feeding yeast may be an alternative to ZnO. There are many yeast products on the market including living microorganisms (yeast probiotics), inactive yeast (yeast prebiotics) or inactive yeast with its metabolites, and growth medium (yeast postbiotics). We are interested in yeast postbiotics since this product can provide nutrients for the beneficial microorganisms living in the host gut and stimulate immune cells to help the host fight infections.

The purpose of this study was to compare the efficacy of a postbiotic yeast additive, HY40, against ZnO when fed to nursery pigs. Pigs were fed their respective diets from weaning (21 days of age) until 42 days after weaning. Diets were corn-, soybean meal-, and wheat-based, and were formulated to meet or exceed nutrient requirements. Pigs were provided either a control diet, which did not c¬ontain additional ZnO or HY40 (control), or a control diet supplemented with +HY40, +ZnO, or both (HY40+ZnO). Diets were fed in two phases (phase I for 14 days and phase II for 28 days) with ZnO included at 3,000ppm and HY40 included at 0.5 per cent; these inclusion levels were halved in phase II. Fourteen days after weaning, jejunal tissue samples were collected for determination of jejunal histomorphology (villus height and crypt depth) measurements.

Pigs fed diets with HY40 or ZnO were heavier than their respective controls by the end of the nursery period (Table 1). However, only +ZnO pigs were heavier by the end of phase I. This is due to the increased feed intake during phase I, for those pigs given diets with ZnO. Feed intake was increased during phase II, for pigs fed diets with HY40 or ZnO. During phase II, pigs provided diets with HY40 or ZnO had increased average daily gain versus their respective controls. This did not result in improved feed efficiency. Feeding diets with ZnO diets did result in greater fecal zinc excretion throughout the experimental period than those fed diets without ZnO (Figure 1).

As mentioned previously, ZnO increases feed intake immediately after weaning and throughout the nursery period, which was observed in this study. The increase in feed intake corresponded to increased average daily gain and bodyweight throughout the study. However, HY40 did not work through the same mechanism. In the jejunum, which is the main site of nutrient absorption in the small intestine, the crypt depth was reduced for pigs fed diets with HY40, indicating less cell turnover and therefore less tissue damage (Table 1). This also corresponded to an improved villus height to crypt depth ratio, an indicator of surface area available for nutrient absorption (Table 1). Furthermore, HY40 contains high amounts (40 per cent) of immune modulating components (i.e., β-glucans and mannooligosaccharides), which can assist in reducing inflammation and bind to pathogenic bacteria preventing invasion in the intestine. We also saw an improvement in immune indicators in jejunal tissue (data not shown).

Further work still needs to be done on HY40 to determine its effects at different inclusion levels and during different periods of the production cycle. However, this research has shown that HY40 is effective at improving growth and nutrient absorption capacity in the intestine. As the European Union moves away from current dietary strategies targeted at the post-weaning period, global efforts are aiming to develop effective, environmentally sustainable alternatives. It is possible that yeast additives such as HY40 will play a part in replacing pharmacological ZnO in nursery pig diets in the future. BP

Dr. Lee-Anne Huber is an assistant professor and Dr. Elijah Kiarie is an associate professor in the department of animal biosciences at the University of Guelph in Ontario. Their research focuses on swine and monogastric nutrition, respectively. Brenda Christensen is a doctoral student working with Drs. Huber and Kiarie. This research was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) alliance programs, Ontario Agri-Food Innovation Alliance, AB Agri Ltd and DCL Nutrition.

For more information see: Christensen et al. (2022). Growth performance, immune status, gastrointestinal tract ecology and function in nursery pigs fed enzymatically treated whole yeast without or with pharmacological levels of zinc. J. Anim. Sci. 100: 1-14. https://doi.org/10.1093/jas/skac094