BACKGROUND
Postweaning diarrhoea (PWD) remains an important problem in pig production, especially when antimicrobial growth-promoting strategies such as medicinal zinc oxide and prophylactic antibiotics are restricted. Nutritional manipulation of cereal and protein sources is one of the main non-antimicrobial approaches used to reduce dysbiosis, diarrhoea, and the postweaning growth check. Rice is of particular interest because of its high starch content, low non-starch polysaccharides, and prior evidence of good performance in young pigs. At the same time, animal proteins are often considered more digestible and less likely to aggravate intestinal dysfunction than vegetable proteins. This study tested whether extruded rice of different grain types, combined with either animal or vegetable protein sources, would influence growth, diarrhoea-related outcomes, faecal shedding of β-haemolytic Escherichia coli, and total tract digestibility in newly weaned pigs.
METHODS
The experiment used 84 entire male Large White × Landrace piglets, approximately 24 days old and weighing 6.7 ± 0.13 kg at the start. The study ran for 21 days and used a 3 × 2 factorial design with three cereal types and two protein sources. The cereal treatments were medium-grain extruded rice (cultivar Amaroo), long-grain extruded rice (cultivar Doongara), and wheat. Each cereal was combined with either animal protein sources or vegetable protein sources, producing six diets: MGAP, MGVP, LGAP, LGVP, WAP, and WVP. Diets were formulated to be isonitrogenous and isoenergetic, contained no antimicrobial compounds, and included titanium dioxide as an inert marker for digestibility calculations. Pigs were housed in pens of four for the first 7 days after weaning and then individually for the last 2 weeks to allow collection of faeces from the pen floor. Faecal swabs were collected on arrival and on days 2, 5, 6, and 8 after weaning to score β-haemolytic E. coli from 0 to 5. Clinical diarrhoea was monitored daily, and affected pigs were treated with intramuscular Trisoprim-480. Digestibility of dry matter, starch, energy, and crude protein was determined from pooled faeces collected on days 18–21. Treatment effects were analysed using two-way ANOVA, and p < 0.05 was considered significant.
KEY RESULTS
In the first week after weaning, there were no significant differences among treatments for average daily gain (ADG), showing that the piglets adapted similarly across the six diets. Across weeks 2 and 3, cereal type had no significant main effect on growth, feed intake, or feed conversion ratio. In contrast, protein source had a marked effect: pigs fed animal proteins were heavier at the end of the experiment than pigs fed vegetable proteins (11.8 vs. 10.4 kg, p = 0.01). They also grew faster (317 vs. 242 g/day, p < 0.001), ate more feed (580 vs. 500 g/day, p = 0.007), and had a better FCR (1.87 vs. 2.31, p = 0.028). The number of antibiotic treatments for clinical diarrhoea was statistically similar across treatments (p > 0.05), although both rice-based diets with vegetable proteins appeared to require fewer treatments than the wheat-based diets. For faecal E. coli, there was a trend for protein source, with pigs fed animal proteins having a higher score than pigs fed vegetable proteins (0.63 vs. 0.43, p = 0.057). There was also a tendency for a cereal × protein interaction (p = 0.069), driven by greater scores in LGAP and WAP. In the detailed treatment means, the faecal swab scores were 0.5, 0.7, 0.6, 0.3, 0.8, and 0.3 for MGAP, MGVP, LGAP, LGVP, WAP, and WVP, respectively.
Digestibility outcomes showed clearer diet effects. The CTTAD of dry matter, energy, and crude protein differed significantly by cereal type, protein source, and their interaction. For dry matter, MGAP and LGAP had the highest values at 0.92 and 0.92, compared with 0.85 for WAP, while the vegetable-protein diets were lower at 0.83, 0.82, and 0.80 for MGVP, LGVP, and WVP, respectively (cereal × protein p < 0.001). For energy, MGAP and LGAP again were highest at 0.92 and 0.91 versus 0.83 for WAP, with the vegetable-protein diets at 0.82, 0.81, and 0.80 (p < 0.001). Starch digestibility was very high in all diets, ranging from 0.989 to 0.999, but was higher in both rice-based diets than in wheat-based diets (p < 0.001), and the cereal × protein interaction was significant (p = 0.016). Crude protein digestibility showed a significant interaction as well (p = 0.016): WVP had the highest value at 0.76, whereas MGVP and LGVP were 0.67 and 0.66, respectively; animal-protein diets were 0.79, 0.78, and 0.78 for MGAP, LGAP, and WAP. Overall, rice-based diets improved digestibility of DM, starch, and energy relative to wheat, while animal proteins generally improved digestibility compared with vegetable proteins.
CLINICAL IMPLICATIONS
Although this is a livestock study rather than a human clinical trial, the findings have practical relevance for nursery pig nutrition and gut-health management. The main message is that extruded rice, whether medium-grain or long-grain, performed as well as wheat as the sole cereal in the first 3 weeks after weaning, supporting its use as a high-quality cereal for young pigs. However, protein source mattered more than cereal type for postweaning growth: animal proteins consistently improved ADG, feed intake, FCR, and final body weight compared with vegetable proteins. Vegetable proteins showed a trend toward lower faecal β-haemolytic E. coli scores, suggesting a possible benefit for gut microbial balance even though this did not translate into fewer antibiotic treatments. The digestibility data indicate that cereal and protein choices interact, particularly for dry matter, energy, and crude protein, and these interactions should be considered when formulating postweaning diets. In settings where antimicrobial use is restricted, combining extruded rice with carefully selected protein sources may help maintain growth while supporting gut health and nutrient utilization in weaned piglets.