In fl uence of forage type on feed intake , chewing activity and rumen pH in goats

This study was conducted to investigate the effects of forage type on feed intake, chewing activity and rumen pH in goats. Neutral detergent fi bre (NDF) concentration in dry matter (DM) was 44.86, 64.92 and 77.91% for lucerne hay (LH), maize silage (MS), and wheat straw (WS), respectively. In Experiment 1, three fi stulated goats were used to measure the degradation kinetics of MS, LH and WS. Effective ruminal degradability of DM, and NDF was higher for LH compared with MS and WS. In Experiment 2, six yearling Saanen × Guanzhong goats (32.3 ± 1.6 kg) fi tted with ruminal cannulas were used in a replicated 3×3 Latin square design. MS diet contained 32% NDF from MS. In the other two diets, 60% MS NDF was substituted by NDF from LH and WS, respectively. When expressed as min per day, LH tended to increase time spent in chewing. However, when expressed as min per kg forage NDF intake, WS increased chewing time. Average rumen pH was lower for goats fed LH diet than MS and WS diet. These results suggest that NDF effectiveness to stimulate chewing and maintain rumen pH increases as NDF concentration increases and ruminal degradability decreases in forages.


INTRODUCTION
Forage fi bre stimulates chewing and then secretion of salivary buffers which neutralize fermentation acids and maintain rumen pH.Physically effective fi bre has been defi ned as that portion of the diet stimulates chewing activity and salivary buffer production (Mertens, 1997).NRC for dairy cows (2001) recommended minimum concentration of forage NDF (FNDF) to maintain the ruminal and cow health.The recommendation originates from experiments using diets containing high quality forages.Low quality forages, such as wheat straw and rice straw, have been widely used to alleviate the shortage of high quality forages in developing countries.NRC (2001) recommendations do not account for differences in forage quality.There is little information available documenting the relative physical effectiveness among different forages.Therefore, the objectives of present study were: 1. to evaluate physical effectiveness differences between high and low quality forages, and 2. to investigate relationship among physical effectiveness and degradation characteristics of NDF.

Forage preparation
Lucerne hay (LH), maize silage (MS) and wheat straw (WS) were chopped by the same cutter with the same theoretical length of cut.Samples were sieved and sequentially through screens with the following aperture sizes: 19.00, 8.00, 1.18 mm, and bottom pan.

Experiment 1
Three fi stulated into rumen goats were fed the diet containing 60% maize silage and 40% concentrate.Samples of dried forages were ground through a 1 mm screen and material less than 75 μm was removed by hand sieving.Approximately 2.0 g of DM of test forage was weighted into nylon bags (6 cm × 9 cm) with a pore size of 50 μm.The bags were placed into rumen on 09.00 and were removed after intervals of 0, 6, 12, 24, 48, or 72 h and washed in cold running water until the washing ran clear.
Degradability coeffi cients were calculated according to Bowman and Firkins (1993): P = A, when 0 < t < L; and P = A + B (1 -e -C (t-L) ), when t > L Effective ruminal degradability was calculated using the equation of Wang et al. (2004): where: t -incubation time, L -discrete lag time, P -the cumulative amount degraded at time t, A -the readily soluble fraction, B -the fraction potentially degraded in the rumen, C -the constant rate of degradation of B, D -the effective ruminal degradability, K -ruminal outfl ow rate.
A nonlinear regression method of SAS (1990) was used to estimate degradability coeffi cients of DM, and NDF of forages.

Experiment 2
Six yearling Saanen × Guanzhong goats (32.3±1.6 kg) fi tted with ruminal cannulas were used in a replicated 3×3 Latin square design.The silage diet contained 32% of DM from MS NDF.In the other two diets, 60% MS NDF was substituted by LH NDF and WS NDF, respectively.Goats were fed a TMR three times daily at 08.00, 13.00 and 18.30 h.
Experimental treatment periods were 13 d for dietary adjustment followed by 5 d of data collection.Diets were mixed daily.Dry matter intake was measured from 14 to 17 days of each period.Goats were monitored for chewing activity for a continuous 24-h period on the fi rst day (d 14) at each collection period according to Krause et al. (2002).Rumen samples were taken on d 18 of each period, and were fi ltered through four layers of cheesecloth.Rumen liquid pH was immediately determined.
Dietary and faecal samples were dried at 55°C for 48 h and ground through a 2 mm screen.Dry matter (DM) and nitrogen content of diets were analysed according to the procedures of the AOAC (1990).Fibre analysis was performed as described by Clark and Armentano (1993).
Data were analysed as a replicated 3×3 Latin square design using the GLM procedures of SAS (1990).The statistical model included period, goat, and dietary treatment.Means were separated by Duncan's multiple range tests.

RESULTS AND DISCUSSION
Concentrations of NDF and ADF were greatest for WS, intermediate for MS, and least for LH (P<0.05;Table 1).In contrast, the ratio of ADF to NDF was greatest for LH, intermediate for MS, and least for WS (P<0.05).The results were supported by NRC (2001).Previous studies have shown physical effectiveness of forage NDF is highly related to particle length (Krause et al., 2002).In present experiment, the proportion of particles size of three forages did not differ (P>0.05) because the samples were sieved through the same screens.Soluble fraction of DM did not differ for MS and LH but was less (P<0.05) for WS (Table 3), which is supported by the work of Bourquin and Fabey (1994).Soluble fraction of NDF did not differ (P>0.05)among forages, and was close to zero.Effective ruminal degradability of DM and NDF (P<0.05) for LH was higher than MS and WS, which is consistent with other study (Bourquin and Fahey, 1994).
Goats fed the WS diet ate less (P<0.05)DM compared with those fed MS and LH diet (Table 4).FNDF intake was signifi cantly higher (P<0.05) for goats fed LH diet than that of goats fed WS and MS diet.These results agree with previous study (Haddad and Husein, 2001).Chewing activity and rumen pH were measures of the physically effectiveness of NDF.When expressed as min per day, LH tended to increase (P=0.12)time spent in chewing.However, when expressed as min per kg FNDF intake, chewing time was greatest for goats fed WS diet, intermediate for MS, and least for LH (P<0.05).Average rumen pH was lower (P<0.05)for goats fed LH diet than MS and WS diet.This might be partially explained by the lower chewing time per kg FNDF intake.Based on the data on chewing activity and rumen pH, both fi bre of MS and WS were similar physical effectiveness, but LH fi bre was less effectiveness.Previous researches have shown that WS is more effectiveness to stimulate chewing and maintain rumen pH than LH in cattle (Shain et al., 1999) and in sheep (Haddad and Husein, 2001).Our results tend to support this conclusion.In present study, physical effectiveness measured chewing time and rumen pH increases as forage NDF concentration increases and ruminal degradability decreases.These results are consistent to others.Welch and Smith (1970) reported that rumination time increases as forage quality decreases.Mertens (1997) reviewed several studies and concluded that physical effectiveness linearly increases as the NDF concentration in forages increases.

CONCLUSIONS
Based on the data of these two experiments, physical effectiveness increases as forage NDF concentration increases and ruminal degradability decreases.Therefore, in order to maintain rumen health, forage NDF recommendations in dairy ruminant diets containing low quality forages can be properly decreased on the basis of NRC ( 2001) recommendation.

Table 1 .
Chemical composition of maize silage, lucerne hay and wheat straw SEM -standard error of means; n=12; 2 NDF -neutral detergent fi bre 3 ADF -acid detergent fi bre; a, b, c row means with common superscripts do not differ (P>0.05)

Table 2 .
Ingredient and nutrient composition of experimental diets

Table 3 .
Degradation kinetics of dry matter and neutral detergent fi bre of maize silage, lucerne hay and wheat straw

Table 4 .
Effects of forage type on feed intake, chewing activity and rumen pH in goats FNDF -neutral detergent fi bre from forage a,b row means with common superscripts do not differ (P>0.05)