Effect of maize stalk processing methods on fattening bulls and on diet digestibility

The experiment was conducted to determine the effect of maize stalk processing methods on fattening bulls and on diet digestibility. Thirty crossbred bulls were randomly divided into six groups that were fed cut stalk, rolled cut stalk, baled stalk, stalk pellets, stalk blocks, stalk sticks, respectively. The results showed: 1. feed intake was highest in the last three maize stalk groups, lowest in the cut stalk group, 2. the digestibility of the stalk pellet was lower than the other forms, 3. daily gains were highest in the stalk block and stalk stick groups, lowest in the cut stalk group.


INTRODUCTION
In the northern regions of China most ruminants rely generally on maize stalk as a roughage source.Due to its loose texture, poor palatability and low nutritive value (Ranjhan and Pathak, 1979), many processing methods have been developed to improve its intake and digestibility.In recent years, numerous stalk processing enterprises have emerged to market stalk products in different physical forms such as stalk pellets, blocks, and compressed bales.The objectives of this experiment were to study the effect of maize stalk processing methods on fattening bulls and on diet digestibility and to provide technical references both for selection of stalk products for fattening-bull breeders and for determination of processing methods for stalk processing enterprises.

Experimental animals
Thirty crossbred bulls (Simmental×Chinese Yellow cow, 18 months old and 336±20.5 kg liveweight) were divided into 6 treatments.They were housed individually and fed twice daily (08.00 and 16.00) .

Experimental diets
The experiment was conducted with a randomized block design involving six experimental diets.For the experiment, the nutrient content of the diet complied exactly with the Feeding Standards for Beef Cattle in China (2004).All diets contained 5.5 kg maize distiller's grain and 3.92 kg concentrate mixture.They were supplemented with maize stalk in different physical forms.The six maize stalk forms (Table 1) were: 1. stalk compressed bale (SCB): maize stalks were cut and rolled, then compressed into bales; 2. stalk pellets (SP): maize stalks were cut and crushed, then extruded into pellets; 3. stalk blocks (SB): maize stalks were cut and extruded into blocks; 4. stalk sticks (SS): maize stalks were cut and extruded into columns; 5. cut stalk (CS): maize stalks were cut only; 6. rolled and cut stalk (RCS): maize stalks were cut, and rolled into fi laments.The fi rst four maize stalks were made using new processing methods, the last two are commonly used by farmers.The stalk above was from Jidan 136 variety maize.

Measurements and sampling
Feeding trial.The experimental periods were 90 d; 10 d were for dietary adaptation.The feeding procedure was: maize stalks were soaked in 0.5% NaCl solution for 12 h, then mixed with concentrate and maize distiller's grain fed at a fi xed level, stalk pellets, stalk blocks and stalk sticks were fed at a restricted level avoiding excess intake by the animals, and cut stalk, rolled and cut stalk, and stalk bales were fed ad libitum.To monitor performance, feed intake of each group was measured daily and body weight was measured once every 15 d prior to feeding in the morning.
Digestion trial.Total faeces were collected to determine apparent digestibility of nutrients over 6 days (from days 31 to 36).During the collection period, the feeds offered and refused and faeces were recorded daily.Samples of feeds and faeces were taken daily and then pooled for the whole collection period.Dry matter content of feeds offered and refused and of faeces from individual bulls was determined daily.Samples of feeds, refusals and faeces were analysed for crude protein (CP), ether extract (EE), crude fi bre (CF), nitrogen-free extractives (NFE) and ash.

Statistical analysis
The results were analysed with one-way ANOVA by SPSS (Statistical Analysis Software, SPSS Institute Inc., USA).Means values were compared using a least signifi cant difference test.

RESULTS
The results of the feeding trial are summarized in Tables 2 and 3.The maize stalk processing methods had a signifi cant effect on the growth performance of fattening bulls.Feed intake (DMI) and nutrient ingestion in groups SP, SB and SS were highest, followed by groups SCB and C2, lowest in group C1.The average daily gain in groups SB and SS was similar, but signifi cantly higher than in groups SCB, SP and C2 (P<0.05), and higher than in group C1 (P<0.01).Furthermore, the average daily gain of groups SCB, SP and C2 groups was higher compared with group C1 (P<0.05).The digestibility coeffi cients are shown in Table 4.The digestibility of DM, CP, CF and NFE in group SP was signifi cantly lower (P<0.01)than in other groups, in which no differences were found in the digestibility of any nutrients.

Table 1 .
Processing methods and physical forms of maize stalks ND: not determined SU X.-X.ET AL.

Table 2 .
Feed intake and nutrient ingestion in cattle fed different forms of maize stalk

Table 3 .
Average daily gain of cattle fed different forms of maize stalk

Table 4 .
Digestibility of feed in cattle fed different forms maize stalk, % AB P<0.01