Effects of Particle Size of Alfalfa-Based Dairy Cow Diets on Chewing Activity, Ruminal Fermentation, and Milk Production

Abstract

Effects offorage particle size measured as physically effective NDF and ratio of alfalfa silage to alfalfa hay of diets on feed intake, chewing activity, particle size reduction, salivary secretion, ruminal fermentation, and milk production of dairy cows were evaluated using a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. The diets consisted of 60% barley-based concentrate and 40% forage, comprised either of 50:50 or 25:75 of alfalfa silage:alfalfa hay, and alfalfa hay was either chopped or ground. Various methods were used to determine physically effective NDF content of the diets. Cows surgically fitted with ruminal and duodenal cannulas were offered ad libitum access to these total mixed diets. The physically effective NDF content of the diets was significantly lower when measured using the Penn State Particle Separator than when measured based on particles retained on 1.18-mm screen. Intake of DM was increased by increasing the ratio of silage to hay but was not affected by physically effective NDF content of diets. Eating time (hours per day) was not affected by the physically effective NDF content of diets, although cows spent more time eating per unit of DM or NDF when consuming high versus low alfalfa hay diets. Ruminating time (hours per day) was increased with increased physically effective NDF content of the diets. Rumen pH was affected more by changing dietary particle size than altering the ratio of silage to hay. Feeding chopped hay instead of ground hay improved ruminal pH status: time during which ruminal pH was above 6.2 increased and time during which ruminal pH was below 5.8 decreased. Milk production was increased by feeding higher concentrations of alfalfa silage due to increased DM intake, but was not affected by dietary particle size. Feed particle size, expressed as mean particle length or physically effective NDF was moderately correlated with ruminating time but not with eating time. Although physically effective NDF and chewing time were not correlated to mean rumen pH, they were negatively correlated to the area between the curve and pH 5.8, indicating a positive effect on reducing the risk of acidosis. Milk fat content was correlated to rumen pH but not to physically effective NDF or chewing activity. These results indicate that increasing physically effective NDF content of the diets increased chewing activity and improved rumen pH status but had limited effect on milk production and milk fat content.

Effect of forage particle length on rumen fermentation, sorting and chewing activity of late-lactation and non-lactating dairy cows

“…In spite of large differences in dietary forage particle length, no statistical differences were observed in DMI (Table 4). Failure to detect differences in DMI has been reported in cows averaging 189 6 38 DIM (Beauchemin et al, 2003); 153 6 7 DIM (Leonardi and Armentano, 2003); 189 6 39 DIM (Yang and Beauchemin, 2006); and 175 6 21 DIM (Nasrollahi et al, 2012). In contrast, other studies with cows averaging 19 6 4 DIM (Kononoff and Heinrichs, 2003) and 81 6 15 DIM (Teimouri Yansari et al, 2004) observed an increase in DMI when forage particle length was reduced (reported DIM were at the beginning of the experiments).…”

The effect of partial replacement of corn silage on rumen degradability, milk production and composition in lactating primiparous dairy cows

“…Likewise, Zebeli et al (2006) observed that milk parameters are less sensitive to the effects of dietary peNDF than are other variables, such as ruminal pH, chewing activity, and fibre digestibility. L o w milk fat content was consistent with low mean rumen pH (5.50) and low ratio of acetate to propionate (range of 1.7 to 2.0) (Yang and Beauchemin, 2003). In the current study, the daily mean ranged from 6.24 to 6.42 and from 4.00 to 4.50 for rumen pH and acetate/propio n a t e, respectively (Gencoglu and T u r k m e n , 2006).…”

“…The requirement for peNDF of dairy cows was determined by Mertens (1997), who suggested that should be 22% of ration DM to maintain an average ruminal pH of 6.0 and 20% of ration DM to maintain the milk fat percentage of early to Midlactation Holstein cows at 3.4%. Based on measurements using the PSPS, several studies reported that increased intake of peNDF increased milk fat content (Yang et al, 2001;Kononoff and Heinrichs, 2003) and decreased milk protein content (Kononoff and Heinrichs, 2003), but others did not find any effects of peNDF on milk composition (Beauchemin et al, 2003;Kononoff et al, 2003b). Results obtained from the current study showed that cows fed with the CSW and CSWA diets had higher peNDF than CS and CSA (Table 2) but the peNDF did not affect the milk fat percentage.…”

Meta-analysis of 0 to 8 h post-prandial evolution of ruminal pH

“…Also, high global correlations linked threshold-related variables and mean pH (Table 4). Beauchemin et al (2003) found much lower correlations between mean pH and time under pH 5.8 or area under pH 5.8, but they used fewer observations, from a single study. It is noteworthy that they used continuous measuring of ruminal pH, whereas our study is mostly based on measurements with time intervals of more than 30 min.…”