Effect of dietary roughage level on chewing activity, ruminal pH, and saliva secretion in lactating Holstein cows

Abstract

Increasing dietary roughage level is a commonly used strategy to prevent subacute ruminal acidosis. We hypothesized that high-roughage diets could promote chewing activity, saliva secretion, and hence more alkaline to buffer rumen pH. To verify the hypothesis, 12 multiparous Holstein cows in mid lactation were randomly allocated to 4 treatments in a triplicated 4 × 4 Latin square experiment with one cow in each treatment surgically fitted with a ruminal cannula. Treatments were diets containing 40, 50, 60, or 70% of roughage on a DM basis. Increasing dietary roughage level decreased DM, CP, OM, starch, and NE intake, increased ADF intake, and decreased milk yield linearly. Intake of NDF was quite stable across treatments and ranged from 7.8 to 8.1 kg/d per cow. Daily eating time increased linearly with increased roughage level. The increase in eating time was due to increased eating time per meal but not number of meals per day, which was stable and ranged from 8.3 to 8.5 meals per day across treatments. Increasing dietary roughage level had no effect on ruminating time (min/d), the number of ruminating periods (rumination periods per d), and chewing time per ruminating period (min/ruminating period). Ruminating time per kilogram of NDF intake and total chewing time per kilogram of ADF intake were similar across treatments (57.4 and 183.8 min/kg, respectively). Increasing dietary roughage level linearly increased daily total chewing time; linearly elevated the mean, maximum, and minimum ruminal pH; and linearly decreased total VFA concentration and molar proportion of propionate in ruminal fluid. Saliva secretion during eating was increased, the secretion during rumination was unaffected, but the secretion during resting tended to decrease with increased dietary roughage level. As a result, total saliva secretion was not affected by treatments. In conclusion, the results of the present study did not support the concept that high-roughage diets elevated ruminal pH through increased salivary recycling of buffering substrates.

Invited review: Current perspectives on eating and rumination activity in dairy cows

“…Similar effects of forage particle size on eating and ruminating time were reported by others (Yang et al, 2001b;Kowsar et al, 2008;Akbari-Afjani et al, 2014;Alamouti et al, 2014). However, increased eating time does not always eliminate the need for longer rumination time per kilogram of DM when intake of long forage particles is increased through increased F:C ratio (Jiang et al, 2017) or particle size (Zhang et al, 2010;Kammes and Allen, 2012). For example, Jiang et al (2017) fed dairy cows 4 diets that ranged from 40 to 70% forage.…”

“…However, increased eating time does not always eliminate the need for longer rumination time per kilogram of DM when intake of long forage particles is increased through increased F:C ratio (Jiang et al, 2017) or particle size (Zhang et al, 2010;Kammes and Allen, 2012). For example, Jiang et al (2017) fed dairy cows 4 diets that ranged from 40 to 70% forage. Eating time increased (min/d, min/kg of DM, min/kg of NDF) with increasing F:C ratio of the diet.…”

Effects of forage source and particle size on chewing activity, ruminal pH, and saliva secretion in lactating Holstein cows

“…Consistent with the unchanged ruminating periods and time length per period, daily ruminating time was not affected by treatment. The constant eating and periods of rumination were consistent with previous studies (Jiang et al., ; Kononoff & Heinrichs, ; Krause & Combs, ), except for the study by Krause, Combs, and Beauchemin (), which reported that daily meals and periods decreased when FPS was reduced. These differences might be attributable to a lower forage level (39.3%) and NDF content (24%), resulting in SARA.…”

“…Consistent with previous studies (Jiang et al, 2017;Yang & Beauchemin, 2009), daily variations in ruminal pH for all diets peaked just before the 05:30 and 17:30 hr feedings (Figure 1), which may be attributable to limited feed intake and less eating activity during several hours preceding the measurements. Consistent with the higher DM effective degradability of oaten hay than that of wild-rye hay (49.5 vs. 34.0%), the DMI increased from 21.1 to 22.2 kg/day when FPS was reduced.…”

“…As it was not possible to measure rate of saliva secretion during rumination, we assumed that eating and ruminating saliva secretion was similar. The assumption has been used by other authors previously (Bowman et al., ; Maekawa et al., ; Seth, Rai, Yadav, Pandey, & Rawat, ) and my previous study (Jiang et al., ). There were reports that saliva secretion rates during rumination was 1.8 times that of resting (Cassida & Stokes, ) and eating saliva secretion was 1.3–2.0 times that of resting (Beauchemin, Eriksen, Nørgaard, & Rode, ).…”