Summary

Wheat middlings have the potential to be used in growing- finishing and sow diets as a good energy source.

Sixty females and 60 castrates were used in a trial to evaluate the effect of the dietary inclusion of 26% wheat middlings and a xylanase enzyme on weight gain, feed disappearance and feed conversion efficiency for the growing and finishing periods and carcass characteristics at slaughter.

The dietary inclusion of wheat middlings had no effect on weight gain, but middlings decreased feed disappearance during the grower period and overall. The dietary inclusion of wheat middlings also improved feed conversion efficiency during the finisher period and overall.

The dietary inclusion of enzyme increased feed disappearance only for the finisher period, but it increased weight gain for both the finisher period and overall.

As expected, castrates consumed more feed, and converted feed into gain less efficiently than females for the finisher period and overall. Females had higher carcass index, yield and lean and less fat compared to castrates.

The results of the present study demonstrate the beneficial effect of including high levels of wheat middlings, a by-product readily available in Canada, in diets for growing – finishing pigs. It also confirmed the beneficial effect of enzyme inclusion and the fact that feed enzymes should be tailored to the main ingredients in the diet.

Introduction

Wheat middlings are a readily available by-product of wheat milling in Canada. After cleaning, sifting and separating, wheat is passed through corrugated rollers, which crush and shear the kernels separating the bran and germ from the endosperm. Clean endosperm is sifted and ground to flour for human consumption. Depending on the equipment and the demand, a mill may separate the remaining into middlings, bran, germ and mill run. Bran and germ are used in bakery products intended for human consumption. Mill run includes material cleaned out initially and all leftover fines, so it is pelleted and sold for cattle feeding in feedlots. On the other hand, middlings, which are medium-sized endosperm particles that contain bran, are a by-product with great potential to be offered to growing- finishing pigs and sows.

The carbohydrate composition of grains differs so wheat, barley and corn diets require to be supplemented with different feed enzymes in order to increase nutrient availability and absorption from each of these grains. For example, the pig’s own digestive process is not capable of breaking down the cell wall structures of wheat. Because these cell wall structures comprise mainly arabinoxylans, exogenous xylan-degrading enzymes should increase cell wall degradation thereby increasing nutrient exposure to endogenous enzymes. In poultry, feed enzyme supplementation improves nutrient utilization mainly by reducing digesta viscosity. Because of the higher water content of pig digesta, this effect is less relevant in pigs compared to poultry. Nonetheless, this reduction in viscosity is believed to improve dry matter flow in the intestine, increasing feed intake.

The objective of the present study was to study the effect of the dietary inclusion of a xylanase enzyme believed to have the potential to increase nutrient availability and utilization of wheat and wheat middlings-based diets.

Experimental Procedures

Sixty female and 60 castrated male crossbred pigs (C15 x Canabrid; Pig Improvement Canada) sorted by gender and weight, were randomly allocated to one of three dietary regimens (Table 1) from 32 kg until market weight (109 kg):

• A wheat-SBM-CM diet (control)
• The same diet having 25% of the wheat replaced by wheat middlings
• The same diet having 25% of the wheat replaced by wheat middlings and supplemented with 0.1% xylanase enzyme

The pigs were housed five per pen (4.6 x 1.52 m) in two semi-intensive rooms each containing 20 fully slatted floor pens. Pigs had ad libitum access to the diets in pellet form from self-feeders located in a front corner of the pen and to water from a single nipple drinker located at the back of the pen. The diets did not contain any antibiotic or growth promotants.

The grower diets were offered for a six week period and the finisher diets were offered thereafter. The pigs were individually weighed at the start of the trial and thereafter, every 21 days. Feed disappearance was calculated on a pen basis as the difference between the weight of the feed added and the weight of the feed weighed out at the end of each 21-day period.

Market weight ranges were set at 105 to 108 kg for barrows and 109 to 112 kg for females. At the time of shipping, individual pigs were tattooed according to sex and treatment.

The pigs were slaughtered following typical commercial conditions. Carcass lean, fat and yield were estimated using the Destron Grading Probe inserted at 70mm from the carcass mid-line between the third and fourth last ribs. Warm carcass weight included kidney fat (leaf lard), head, feet (without hooves) and the tail stub. Carcass index was calculated using individual carcass weight and yield.

This experiment conformed to the global experimental protocol for growth trials maintained on file by the University of Saskatchewan Animal Care Committee.

Results

The effects of dietary treatment and sex on pen average daily weight gain, daily feed disappearance, gain:feed and feed:gain ratios are summarized in Table 2. The effects of dietary treatment and sex on carcass characteristics are summarized in Table 3. There were no significant diet x gender interactions (P > 0.05)

Wheat Middlings
Daily weight gains were not affected by the dietary inclusion of wheat middlings for any period or the overall (P > 0.05). Pigs offered the diets including middlings, however, had lower feed disappearances for the grower period and overall but not for the finisher period compared to pigs offered the control diets (P < 0.05). Pigs offered the diets including middlings also had improved gain:feed and feed:gain for the finisher period and overall but not for the grower period compared to pigs offered the control diets (P < 0.05).

There was no effect of the dietary inclusion of wheat middlings in carcass characteristics (P > 0.05).

Enzyme
Pigs offered the diet containing middlings and enzyme had improved weight gains for the finisher period and overall compared to pigs offered the same diet without enzyme (P < 0.05). Feed disappearance was also higher for pigs offered the diet containing middlings and enzyme compared to the pigs offered the same diet without enzyme but only for the finisher period (P < 0.05). The dietary inclusion of enzyme had no effect in gain:feed or feed:gain ratios (P > 0.05).

There was no effect of the dietary inclusion of enzyme in carcass characteristics (P > 0.05).

Gender
As expected, castrates consumed more feed than females for both periods and overall (P < 0.05). Also castrates grew faster than females but the difference was merely numeric (P > 0.05). Females, on the other hand, converted feed more efficiently than castrates for the finisher period and overall (P < 0.05).

The differences in carcass characteristics between genders were, again, as expected. Females had higher carcass weights (due to the higher shipping weights), higher index, carcass yield and lean compared to castrates (P < 0.05). In contrast, the castrates had significantly higher fat than the females (P < 0.05).

Implications

The results of the present study demonstrate the beneficial effect of including high levels of wheat middlings, a by-product readily available in Canada, in diets for growing – finishing pigs. It also confirmed the beneficial effect of enzyme inclusion and the fact that feed enzymes should be tailored to the main ingredients in the diet.

Table 1: Diet Formulations

aProvided the following per kg of premix: vitamin A 1,650,000 IU, vitamin D 165,000 IU, vitamin E 8,000 mg, thiamin 200 mg, riboflavin 1,000 mg, niacin 7,000 mg, d-pantothenic acid 3,000 mg, vitamin B12 5 mg, biotin 40 mg and folic acid 400 mg. bProvided the following per kg of premix: copper 10 g, iron 16 g, manganese 5 g, zinc 20 g, iodine 100 mg, selenium 20 mg.

Table 2: Means for the effects of diet and sex on pen average daily weight gain (kg), feed disappearance (kg), gain:feed and feed:gain (kg:kg)

Table 3: Means for main the effect of diet and sex on ship weight (kg) and carcass characteristics