Impiego di insilati di mais nella alimentazione del suino pesante: performance e integrità delle mucose gastriche

The thesis was part of a project (Project Ager No. 2011-0280) aimed to test new feeding strategies for finishing heavy pigs able to improve animal welfare and reduce the environmental impact, without compromising growth, slaughter traits and meat quality. The thesis is composed by two feeding trials where fibrous corn silages were fed to heavy pigs and by two studies, which used experimental data from different trials to analyses the impacts of new diets based on corn silages on main meat quality traits and on the development of gastric damages (ulcers). The aim of a first feeding trial (trial 1) was to compare two dietary levels of whole ear corn silage (ES), fed in two physical forms (coarse or after wet milling), on growth, slaughter traits and stomach development of heavy finishing pigs. Fifty six “Italian Large White x Italian Duroc” (about 5 months of age and 78-80 kg of live weight (LW) were divided into pairs homogeneous and were kept in 28 pens (1.2 x 3 m, partially-slatted) equipped with two separate troughs to avoid competitions for feeding and with free access to water. Four dietary treatments resulted from the combination of two ES inclusion levels (300 and 400 g/kg DM, ES30 and ES40, respectively) and two physical forms of the silage (coarse and wet milled). Seven pairs of pigs were randomly assigned to each dietary treatment and the animals were slaughtered at an average LW of 163.0 Kg (±1.92 kg). The coarse ES had particles longer than the milled silage (4.4 vs 2.7 mm) and when it was fed to pigs the pH of fecal samples were lower (P<0.01) than that from pigs fed the milled ES, at both dietary inclusion levels (6.00 vs 6.20 for the ES30 diets and 5.97 vs 6.14 for the ES40 diets). There were no significant differences in organic matter total tract digestibility, ADG, DMI and G:F ratio among the dietary treatments (0.81, 764 g/d, 77.1 g DM/kg LW0.75, 0.266 g/g DM, on average respectively). The ES40 diets reduced the Longissimus dorsi thickness (56.4-59.8 vs 62.7-64.1 mm, P<0.011) and increased the stomach weight (0.0040 vs 0.0038 of the LW, P<0.05), while the coarse dimension of silage particles increased the DM content of the material in the stomach (from 142-171 to 179-183 g/kg DM, P<0.045) and the surface of the pyloric region (from 214-216 to 225-232 cm2, P<0.029). The two dietary inclusion levels and physical forms of ES do not differentiate growth and slaughter traits of the heavy finishing pigs. However, the coarse form of the silage modifies the development of the stomach by increasing the internal surface of the pyloric region as a possible consequence of a longer retention time in the stomach. In a second trial (trial 2) the aim was to test the inclusion of high cut whole plant corn silage (HCCS) in diets for finishing heavy pigs on digestibility, metabolic utilization, growth performance and slaughter traits. In two experiments a control diet (C, containing corn meal, barley meal, extracted soybean meal and wheat bran, 550, 250, 90 and 80 g/kg DM, respectively) was compared with a diet containing HCCS (200 g/kg on DM basis, CS) in substitution of wheat bran and part of corn meal. In a first experiment 8 barrows (134.2 ± 5.8 kg of LW) were used in two periods cross over design with periods of 21 d, included 7 d of total collection and three cycles of 24 h each in a respiratory chamber. In a second experiment 28 barrows (89.5 ± 4.9 kg LW) were divided into pairs on the basis of LW and kept in 14 partially slatted pens (1.2 × 3 m) and fed with the experimental diets (7 pens/diet) until slaughter (an average LW of 170.9 ± 6.2 kg). Diets differed for CP, NDF and P contents (137 vs 128, 138 vs 188 and 5.6 vs 5.0 g/kg DM, respectively for C and CS diets). A lower DM, OM, CP and energy CTTAD was measured for the CS diet (approximately -0.04). Overall P retention as percentage of P intake was higher for CS diet (P=0.007), while N retention was similar for the two diets (on average 38.0% of N intake). Pigs fed CS tended to have a lower retained energy (15.0 vs 17.0 MJ/d, P<0.074) and the estimated NE of corn silage was 8.47 MJ/kg DM. In the second experiment pigs fed the CS diets had a lower daily gain (700 vs 765 g/d, P<0.05), a lower LW at slaughter (167 vs 175 kg, P<0.05) and a reduction in the weight of back fat (4.5 vs 5.4 kg, P<0.05). The inclusion of silage increased the size of the stomach (779 vs 692 g, P<0.05 and 1403 vs 1168 cm2, P<0.01, respectively of weight and surface), the NDF concentration of stomach content (0.499 vs 0.289, P<0.01) and reduced the incidence of follicular gastritis (0.29 vs 1.14 n/pig, P=0.010). The inclusion of 200 g/kg DM of HCCS in diets for finishing heavy pigs lowers digestibility and energy retention, and reduces growth rate and back fat deposition, but stimulates the stomach development, its filling with fibrous materials and reduces follicular gastritis. To study the effects of dietary inclusion of corn silages on fatty acid composition of back fat and the weight loss of hams during the seasoning we used data from animals fed in a previous trial (Zanfi et al., 2014) a control diet (dry corn meal, wheat bran and soya) and a diet where wheat bran and part of the dry corn were replaced up to 300 g/kg DM with WECS (ES30 diet,). The data set included also animals of trial 2, which were fed a similar control diet and a diet containing HCCS (200 g/kg DM). The inclusion of silages did not modified the hams weight losses during seasoning, while determined a significant increase of the saturated fraction (from 40.6 to 41.9 %, P<0.05), mainly due to the increase of the C 18:0 fatty acid (from 14.3 to 15.2 %, P<0.01). The inclusion of coarse corn silages in diets for heavy pigs has no detrimental effects on the weight loss during ham seasoning (range 30-31%), while it increments the saturated fatty acids in the back fat. Finally, the macroscopic pathological examination of the internal mucosa of stomachs were analyzed together to determine the topographic distribution of gastritis lesions in pigs through an open source Geographic information systems (GIS) software analysis. The hyperplastic gastritis lesions had an average surface of 77.8 cm2 and were mainly located in an oval shaped area of the fundus region of the stomach near the Curvatura ventriculi major. The follicular gastritis lesions had generally a smaller surface (40.3 cm2) and were concentrated in two distinct small areas of the pyloric region. The GIS analysis provided the opportunity to produce useful maps showing the distribution and characteristics of gastritis in pigs. The overall results of the thesis support the possibility to utilize coarse and fibrous corn silages in feeding systems of finishing heavy pigs. Whole ear corn silage, fed coarse without milling, is a promising feed resource because it does not affect the growth performance and slaughter traits of pigs (even if at an inclusion rate of 40% DM) while it has potential advantages in terms of stomach health, back fat and ham quality and reduction of pollution and dietary costs. Whole plant corn silage should have similar dietary advantages, but requires to be used at low dietary inclusions (less than 20% DM) to minimize the negative impact on digestibility and growth rate.