Effects of Combination of Rice Straw with Alfalfa Pellet on Milk Productivity and Chewing Activity in Lactating Dairy Cows

Animals and management

Sixteen multiparous Holstein dairy cows (670±21 kg body weight) in mid-lactation (194.1±13.6 days in milk) were used for this experiment. Animals were kept in the pen, which was installed with individual feeding gates (American Calan, Inc., North-wood, NH, USA) and moved to milking parlors for milking twice daily at 05:00 and 17:00 h. Cows were fed a TMR twice daily at 09:00 and 16:00 h ad libitum. Animals had unlimited access to fresh water and mineral block. Feed offered and orts were measured daily during the experimental period to calculate feed intake.

Experimental design and sample collection

The experiment was conducted as a randomized complete block design with two treatments in two blocks. Experimental diets offered were TMR with 50% concentrate (based on corn and soybean meal) and 50% of TH or 20% of rice straw and 30% of alfalfa pellet mixture (RSAP) (Table 1). Animals were blocked by milk yield, parity number and days in milk, and were randomly assigned to one of the two experimental diets before the preliminary period. During the 33 d experimental periods, animals were offered one of the two TMR, and dry matter intake (DMI) and milk yield were measured daily from d 19 to d 33. Milk samples were collected at morning and afternoon of d 19, d 26, and d 33 for analysis of milk composition.

Table 1

Ingredients and chemical composition of experimental diet (DM basis)

Feed and milk analyses

Samples of TMR were analyzed for dry matter, crude fiber, ether extract and ash by AOAC (1995) procedure. Neutral detergent fiber was analyzed according to Van Soest et al. (1991) and heat stable α-amylase (Sigma, St. Louis, MO, USA) was used during analysis. Particle size distribution of TMR was measured using the Penn State Particle Separator (PSPS; 19-, 8-, and 1.18-mm sieves) as described by Kononoff et al. (2003a), and all feed samples were sieved in triplicate. Geometric mean length (X_gm) and standard deviation (S_gm) were calculated as outlined by ASAE (2001) (S424) (Table 2).

Table 2

Particle size distribution for timothy base TMR and rice straw base TMR as measured by the Penn State Particle Separator

Milk samples were stored at 4°C and preserved with Broad Spectrum Microtabs II (Advanced Instruments, Inc., Norwood, MA, USA), and sent to the Korea Animal Improvement Association Milk Testing Laboratory (An-sung, Korea) for milk fat, milk protein, lactose and solid not fat analysis by using an infrared analyzer (Foss electric, Hillerød, Denmark).

Chewing activity

Chewing activity was recorded continuously using previously installed infrared digital recording camcorders (Digite, Seoul, Korea) without blind spot. Total chewing, eating and ruminating times were observed during 24 hours in the last five days of the experimental period. Data were expressed as daily eating, ruminating, or total chewing time by calculating the sum of eating and ruminating time during 24 hours. Chewing activity per kg DMI was calculated by dividing total minutes by DMI.

Statistical analyses

Data were analyzed as a completely randomized block design using MIXED procedure of SAS version 9.2 (SAS Institute, 2008). The statistical model included the fixed effect of diet and the random effect of block. The estimation method used was the restrictive maximum likelihood and the degrees of freedom method used was Kenward-Rogers. Comparison test was determined using PDIFF option and significance was declared at p≤0.05. A trend was considered to exist if 0.05<p≤0.10. All means presented are least squares means.

Intake, milk production, and milk composition

Dry matter intake, milk yield and milk composition are summarized in Table 3. The DMI did not significantly differ for cows fed TH or RSAP, but tended (p≤0.10) to increase in RSAP. Milk yield, 4% fat corrected milk (FCM) and milk compositions were similar between the groups.

Table 3

Dry matter intake, milk production and composition of cows fed experimental diets

Usually, increasing the dietary forage to concentrate ratio reduces DMI due to filling effect of forages (Moorby et al., 2006; Yang and Beauchemin, 2007). But just as in this study, DMI was not affected when forage particle size was increased (Krause et al., 2002; Beauchemin et al. 2003; Kononoff and Heinrichs, 2003a; Yang and Beauchemin, 2009). In the case of early lactating dairy cows, DMI was increased by reducing forage particle size (Kononoff and Heinrichs, 2003b). The non-significant differences in DMI also reflected in similar milk yield, 4% FCM and milk composition in cows fed with TH or RSAP. These results are similar to some studies where reducing forage particle size did not affect milk yield and composition (Beauchemin et al., 2003; Kononoff and Heinrichs, 2003b; Rustomo et al., 2006; Yang and Beauchemin, 2009; Kammes and Allen, 2012), but are in contrast to others reporting a linearly reducing milk yield and milk fat when alfalfa hay was gradually replaced with the alfalfa pellet (Khafipour et al., 2009). However, in the current study, we compared two diets using different roughage sources but having similar nutritional value meeting the requirement of lactating cows. This suggests that a proper combination of rice straw and alfalfa pellets can replace TH without decreasing of milk yield and composition.

Chewing activity

Time and time per kg DMI for eating, ruminating and total chewing are presented in Table 4. No significant differences on eating, ruminating and total chewing time (min/d or min/kg of DMI) were detected. Although there were no measurements of ruminal parameters, visible signs of metabolic disorders and difference of chewing activities were not detected in the cows.

Table 4

Chewing activity of cows fed experimental diets

Chewing activities of cows were affected by body size (Bae et al., 1983), breed (Welch et al., 1970), fasting (Welch and Smith, 1968), forage intake (Welch and Smith, 1969a), forage quality (Welch and Smith, 1969b), forage maturity (Lippke, 1980), particle size (Yang and Beauchemin, 2009) and fibrousness characteristics (Balch, 1971). In the current study, body size, breed, fasting and feed intake were controlled in homogeneous conditions, but there were forage quality, particle size and fibrous characteristics differences between TH and RSAP. However, significant differences were not detected in chewing characteristics, even though there were particle size differences between TH and RSAP. This re-validates our previous findings (unpublished) where effect of a diet containing a small amount of rice straw was not different to a diet containing large amount of TH with regard to total chewing and ruminating time in goats.

As rice straw was used after threshing the rice grain, it obviously possessed a low degradation rate of nutritive components, starch, protein and lipid, and was highly lignified due to late harvesting time compared to other forage sources which are grown primarily as feedstuff for animals. In addition, rice straw contains more silica than other cereal straws (Van Soest, 2006). Silica content in rice straw is an important factor in structural strength and digestibility (Van Soest and Jones, 1968; Smith et al., 1971; Bae et al., 1997; Agbagla-Dohnani et al., 2012), but the relationships between silica content and degradability of morphological fractions are still unclear (Ghasemi et al., 2013).

Balch (1971) reported straw showed longer eating, ruminating and total chewing time than other hay, silage and concentrate. Woodford and Murphy (1988) observed a significant reduction of the time spent ruminating and chewing, ruminal fluid outflow and pH when alfalfa hay was gradually replaced with alfalfa pellets. Khafipour et al. (2009) reported that replacing of 16% of DM of alfalfa hay with alfalfa pellets increased lipopolysaccharide in rumen fluid inducing subacute ruminal acidosis. However, both studies (Woodford and Murphy, 1988; Khafipour et al., 2009) were conducted comparing alfalfa with alfalfa pellets, whereas, in the current study, we used different roughage sources having different physical characteristics. Thus, although alfalfa pellets, which has a small particle size, have less effect on chewing stimulation, coarse-textured rice straw with alfalfa pellets stimulates chewing activity in dairy cows even though the quantity of rice straw was 40% of the TH.