Effects of increasing diet fermentability on intake, digestion, rumen fermentation, blood metabolites and milk production of heat-stressed dairy cows

Abstract

Heat stress is a major problem for dairy cows in hot climates, thus coping strategies are essential. This study evaluated the effects of increasing diet fermentability on intake, total tract digestibility, ruminal pH and volatile fatty acids (VFA) profile, blood metabolite profile and milk production and composition of lactating dairy cows managed under conditions of ambient heat stress. Nine multiparous cows (650 ± 56 kg BW; mean ± SD) averaging 102 ± 13 days in milk and producing 54 ± 6 kg/day were randomly assigned to a triplicate 3 × 3 Latin square. During each 21-day period, cows were offered one of three total mixed rations that varied in diet fermentability. The three levels of diet fermentability were achieved by increasing the proportion of pellets containing ground wheat and barley in the dietary DM from 11.7% (low), to 23.3% (moderate), and 35.0% (high) by replacing ground corn grain. Each period had 14 day of adaptation and 7 day of sampling. The ambient temperature–humidity index ( ≥ 72) indicated that the cows were in heat stress almost the entire duration of the study. Also, rectal temperature of cows was elevated at 39.2°C, another indication of heat stress. Increasing diet fermentability linearly decreased dry matter intake (22.8, 22.5, 21.8 kg/day for low, moderate and high, respectively; P ≤ 0.05) but increased non-fibre carbohydrate digestibility (P ≤ 0.05) and tended to increase digestibility of DM (P = 0.10) and crude protein (P = 0.06). As a result, the intake of digestible DM was not affected by the treatments. The production of 3.5% fat corrected milk (32.6, 33.7, and 31.5 kg/day) was quadratically (P ≤ 0.05) affected by diet fermentability with lower production for the high diet compared with the other two, which were similar. Rumen pH (ruminocentesis) and proportions of butyrate and isovalerate linearly decreased whereas propionate proportion linearly increased with increasing diet fermentability (P ≤ 0.05). The rumen concentration of NH3-N (11.0, 9.0, and 8.7 mg/dL) and blood concentration of urea linearly decreased with increasing diet fermentability (P ≤ 0.05). The activity of alkaline phosphatase increased (65.1, 83.2, and 84.9 U/l) and concentration of malondialdehyde decreased (2.39, 1.90 and 1.87 µmol/l) linearly with increasing diet fermentability (P ≤ 0.05), which indicated possible attenuation of the effects of oxidative stress with increasing diet fermentability. Overall, a modest increase of diet fermentability improved nitrogen metabolism, milk protein production and oxidative stress of heat-stressed dairy cows, but a further increase in diet fermentability decreased milk yield.

The effects of the ratio of pellets of wheat and barley grains to ground corn grain in the diet on sorting and chewing activities of heat stressed dairy cows

“…The research was part of a larger project, and full details of experimental set‐up, cow management and housing condition were reported previously (Nasrollahi et al., 2019). Briefly, nine multiparous lactating Holstein dairy cows (650 ± 56 kg BW; mean ± SD ) averaging 102 ± 13 days in milk (DIM) and producing 54 ± 6 kg of milk daily were used in a replicated 3 × 3 Latin square design with 21 day periods.…”

“…The percentage of corn and pellets in the diet was fixed at 35% of diet DM and the three diets were formulated to have similar protein (CP = 14.5% of DM) and energy (NEL = 6.46 MJ/kg of DM) contents with a similar forage to concentrate ratio (40:60). Information on diet ingredients and chemical compositions were reported in companion paper (Nasrolahi et al., 2019). The study was conducted from May 2015 to August 2015.…”

“…To measure fermentability, an in situ experiment was conducted on pellet and corn grain samples of present experiment and relative data were reported in previous companion paper (Nasrollahi et al., 2019). Concisely, the in situ experiment was conducted on two nonlactating cannulated Holstein cows.…”

“…Increasing diet fermentability is suggested as a favourable way for improving productivity of heat stressed dairy cows but too much diet fermentation can cause rumen acidosis (Nasrollahi et al., 2019; Kadzere et al., 2002; West, 2003). The effect of diet fermentability on the increasing risk of acidosis might be dependent on feeding behaviour.…”

“…Increasing diet fermentablity is usually achieved through modification of grain source with expected different rumen fermentability, and it might be possible that the discrepancy among the results can be related to the severity of the modification. Using the pellets of barley and wheat grain is known as a successive way of increasing diet fermentablity up to a severe condition (Li et al., 2012; Nasrollahi et al., 2019), but the effects on feeding behaviour were not evaluated. Therefore, the objective of the present study was to investigate the effect of the ratio of pellets of wheat and barley grains to ground corn grain on sorting index and chewing behaviour in heat stressed dairy cows.…”