Browsing Animal & Grassland Research & Innovation Programme by Funder "Agriculture Victoria Research"
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Forage type influences milk yield and ruminal responses to wheat adaptation in late-lactation dairy cowsThe effects of different wheat adaptation strategies on ruminal fluid pH, dry matter intake (DMI) and energy-corrected milk (ECM) were measured in 28 late-lactation dairy cows. Cows were fed either perennial ryegrass (PRG) hay or alfalfa hay and had no previous wheat adaptation. Wheat was gradually substituted for forage in 3 even increments, over 6 or 11 d, until wheat made up 40% of DMI (∼8 kg of dry matter/cow per day). We found no differences in DMI between adaptation strategies (6 or 11 d) within forage type; however, cows fed alfalfa hay consumed more overall and produced more ECM. The rate of ruminal pH decline after feeding, as well as the decrease in mean, minimum, and maximum ruminal pH with every additional kilogram of wheat was greater for cows fed alfalfa hay. Cows fed alfalfa hay and on the 6-d adaptation strategy had the lowest mean and minimum ruminal fluid pH on 3 consecutive days and were the only treatment group to record pH values below 6.0. Despite ruminal pH declining to levels typically considered low, no other measured parameters indicated compromised fermentation or acidosis. Rather, cows fed alfalfa hay and adapted to wheat over 6 d had greater ECM yields than cows on the 11-d strategy. This was due to the 6-d adaptation strategy increasing the metabolizable energy intake in a shorter period than the 11-d strategy, as substituting wheat for alfalfa hay caused a substantial increase in the metabolizable energy concentration of the diet. We found no difference in ECM between adaptation strategies when PRG hay was fed, as there was no difference in metabolizable energy intake. The higher metabolizable energy concentration and lower intake of the PRG hay meant the increase in metabolizable energy intake with the substitution of wheat was less pronounced for cows consuming PRG hay compared with alfalfa hay. Neither forage type nor adaptation strategy affected time spent ruminating. The higher intakes likely contributed to the lower ruminal pH values from the alfalfa hay treatments. However, both forages allowed the rumen contents to resist the large declines in ruminal pH typically seen during rapid grain adaptation. Depending on the choice of base forage, rapid grain introduction may not result in poor adaptation. In situations where high-energy grains are substituted for a low-energy, high-fiber basal forage, rapid introduction could prove beneficial over gradual strategies.
Manipulation of the pre-partum diet of dairy cows to promote early adaptation to perennial ryegrass herbageThe diet of dairy cows in Ireland traditionally changes abruptly from predominantly pasture silage before calving to grazed perennial ryegrass immediately after calving. This potentially leads to problems with adaptation of microbes in the rumen with consequences of reduced intake and ultimately lower milk production. This experiment aimed to determine if introducing first-lactation dairy cows to perennial ryegrass herbage in the final weeks of pregnancy, thus eliminating a major dietary change at calving, could improve the adaptation process, potentially increasing dry matter intake (DMI) and milk production in early lactation. Three weeks prior to their expected calving date, 14 spring calving dairy cows were assigned to one of two treatments (n = 7): pasture silage pre-partum and perennial ryegrass herbage post-partum, or perennial ryegrass herbage both pre- and post-partum. Treatment diets were fed for 11 (±7) d pre-partum and for 14 (±0) d post-partum. For both treatments, DMI increased post-partum, but there was no difference between treatments, pre- or post-partum (5.9 and 8.8 kg DM/cow per day, respectively). There were no differences in milk yield or composition between the treatments. Body condition score declined following parturition but there were no differences between treatments. Plasma non-esterified fatty acids, glucose and β-hydroxybutyrate were also unaffected by treatment but did indicate a state of negative energy balance in early lactation. The results of this experiment suggest that pre-partum adaptation to perennial ryegrass herbage would not benefit milk production in first-lactation dairy cows in early lactation in Irish dairy farms employing this system.