The study examined the growth performance of pigs offered liquid feed or dry feed on either a restricted or an ad libitum basis, and whether their growth performance was further influenced by the water-to-feed ratio. The study was split into two parts to enable unrestricted (trial 1; n 5 64) and restricted (trial 2; n 5 48) feeding to be compared. Male pigs were randomly allocated to six dietary treatment groups. A standard dry pellets diet (D) was offered either as: (i) unrestricted ration (UR); (ii) restricted ration (R); or D soaked in water at a feed-to-water ratio of (iii) 1 : 1.5 restricted (1 : 1.5 R); (iv) 1 : 3 unrestricted (1 : 3 UR); (v) 1 : 3 restricted (1 : 3 R); or (vi) 1 : 3 restricted with the addition of lactic acid to adjust the feed to pH 4 (1 : 3(4) R). Liquid feeding improved (P , 0.05) average daily live-weight gain (ADG) and lean tissue growth rate (LTGR) in the 1 : 3 UR compared with DUR but did not alter feed conversion ratio (FCR). Within the R groups, ADG were greater in all of the 1 : 3 diets, whereas feed intake, and hence FCR, was lower (P , 0.001) in these groups when offered the R ration. In conclusion, liquid feeding has a beneficial influence on the performance of modern porcine genotypes during the growth/finishing phase and this is further modulated by the water-to-feed ratio.

Liquid feeding of growing pigs is believed to increase feed intake and growth performance compared to a dry diet. There is little information on the comparative feed conversion efficiency of pigs on the two forms of diet or the underlying physiological basis for the differences and how liquid diets affect the absorptive mucosa of the small intestine. This study was designed to investigate differences in feed utilisation and mucosal structure in modern genotype pigs offered equal amounts of feed in dry and liquid form. Additionally, the effect of reducing the pH of the liquid diet was considered.

The study examined the morphology of the gastro-intestinal tract (GI) of growing pigs offered dry feed or liquid feed with differing water-to-feed ratios.  Twenty male pigs were randomly allocated to one of four treatment groups; treatments included a standard dry pelleted diet (D) or the same diet soaked in water at a feed-to-water ratio of 1:1.5 (T1:1.5), 1:3 (T1:3) or 1:3 with the addition of lactic acid to adjust the feed to pH 4 (T1:3[4]).  Animals were humanely slaughtered after 6 weeks to enable sampling and histological examination (light, scanning electron (LSEM) and binocular dissection microscope) of the GI tract. Samples were taken at the 2% position (duodenum), the 20% position and 50 % position (jejunum) along the small intestines (SI).  Liquid-fed pigs were heavier (P < 0.05) and exhibited improved feed conversion ratios (FCR) when compared to D animals. These differences in live weight were attributed to alterations in the weight and volume of the stomach and SI, which were also heavier and larger in liquid-fed pigs (P < 0.05).  However, these differences were no longer apparent when intestinal weights and stomach volumes were adjusted for animal live weight. Differences in villus type between the treatments were noted throughout, particularly in the duodenum and proximal jejunum sections. Mean villus height was taller in all liquid-fed animals when compared to D pigs (P<0.05); this was particularly apparent in T1:1.5 and T1:3[4] pigs. There were no differences in crypt depths between treatment groups at the 2% and 20 % positions, but at the 50 % position the T1:1.5 group crypts were deeper (P < 0.05) than those in the D and T1:3 pigs. It is concluded that liquid feeding alters the morphology of the GI tract, which may in part, explain the differences in growth performance observed between liquid and D fed pigs.  The inclusion of organic acid in the diets of T1:3[4] pigs appeared to exert an effect on villus height and crypt depth when compared to those pigs receiving the T1:3 diet.