Proc. Soc. Nutr. Physiol. (2006) 15
Effect of hay harvested at three different regrowth stages on rumen fermentation and chewing activity of non-lactating cows (Einfluss von Heu geerntet in drei unterschiedlichen Aufwuchsstadien auf die Pansenfermentation und die Kauaktivität von nicht laktierenden Kühen) Frigga Dohme* - Posieux
In dairy cow diets hay is often used as a source of physical effective fibre to ensure adequate rumen function. However, the physical effectiveness of forage is related to various factors (1) including particle size, botanical composition, and maturity. The objective of the present experiment was to compare the effect of hay maturity on rumen fermentation and chewing activity in cows.
Methods: Six ruminally canulated non-lactating Brown Swiss cows were used in a double 3 × 3 Latin square trial. During each experimental period consisting of a 14-d adaptation and a 7-d data collection period, cows were offered one of three hays ad libitum and 300 g/d mineral mix. The three hays (ryegrass-clover mixtures) were harvest either after 36 (H36, control), 50 (H50) or 61 (H61) d of regrowth and, therefore, differed in maturity. On the first and last day of each collection period, rumen fluid was sampled and analysed for the concentration of volatile fatty acids (VFA) and microbial counts. Ruminal pH and chewing activity were continuously recorded for 22 h/d over five days using an indwelling pH electrode and a behaviour recorder, respectively (2). For each cow, pH data were evaluated as minimum, maximum, mean pH and time period when pH was below 6.2.
Chewing activity was split into eating, ruminating and idling time. Feed intake was registered daily and feed samples were analysed according to standard procedures throughout the experiment.
Treatment comparisons were conducted by orthogonal contrasts: H36 vs. H50 and H61; H50 vs. H61.
Results: Cows fed H36 ingested more total dry matter (DM; P < 0.05) and sugar (P < 0.01) compared to cows fed H50 and H61. While NDF intake was not affected by the treatments, ADF intake was higher (P < 0.05) with hay H50 and H61 than with H36. Cows in the H36 group spent less time ruminating per day (401 vs. ø 419 min; P < 0.01), per kg DM (25.9 vs. ø 28.7 min; P < 0.01) and per kg NDF intake (60.6 vs. ø 64.8 min; P < 0.05) compared to cows in the H50 and H61 groups. By contrast, times spent eating and idling did not differ among treatments. The mean ruminal pH (6.26 vs. ø 6.40) was lower and the time when the pH was below 6.2 (502 vs. ø 184 min/d) was longer for cows fed H36 than for cows fed H50 and H61 (P ≤ 0.05). Although no significant differences occurred for total VFA production in the rumen, bacterial and protozoal counts were increased (P < 0.05) when H36 was offered instead of H50 or H61. The molar percentage of acetate tended to decrease (P = 0.07) while that of butyrate increased (P < 0.05) with H36 compared to H50 and H61.
Sugar intake was negatively correlated with the mean ruminal pH (r = -0.67; P < 0.01) and positively with the concentration of total VFA (r = 0.44; P = 0.07). Unexpectedly, a negative correlation was observed between NDF intake and mean ruminal pH (r = -0.43; P = 0.07). Chewing activity was not significantly correlated with fibre intake whereas the ruminating time was negatively correlated with the DM intake (r = -0.44; P = 0.07).
Conclusions: Increased sugar intake was associated with lower mean ruminal pH and a higher concentration of VFA. The relations between fibre intake and rumen fermentation traits remained weak or unclear. Therefore, it seems that the proportion of sugar in the diet had a larger effect on fermentation than the proportion of fibre. Neither sugar nor fibre intake were related to chewing activity. The small differences in the nutrient composition between the two mature hays may explain the lack of differences in chewing activity and ruminal pH.
1) MERTENS, DR (1997) J. Dairy Sci. 80: 1463-1481.
2) GRAF, CM, KREUZER, M and DOHME, F (2005) J. Dairy Sci. 88: 711-725.
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* Agroscope Liebefeld-Posieux, Swiss Federal Research Station for Animal Production and Dairy Products (ALP), CH-1725 Posieux
