• Evaluation of the n-alkane technique for estimating the individual intake of dairy cows consuming diets containing herbage and a partial mixed ration

      Wright, M.M.; Auldist, M.J.; Kennedy, Emer; Dunshea, F.R.; Galvin, N.; Hannah, M.C.; Wales, W.J.; DJPR; Victoria; Dairy Australia (Elsevier BV, 2020-07)
      Estimation of dry matter intake (DMI) using the n-alkane technique was evaluated in lactating dairy cows fed fresh herbage and a partial mixed ration (PMR). Four dietary treatments were investigated in a 2 × 2 factorial experiment using 16 Holstein-Friesian dairy cows. Dietary treatments were combinations of low and high amounts of fresh herbage (8 or 14 kg DM/cow per day) and PMR supplement (6 or 12 kg DM/cow per day). The pre-experimental period was 14 days followed by a 10-day experimental period. Cows were housed in individual metabolism stalls to allow for accurate measurement of DMI and total fecal output. Fecal n-alkane recovery rates were calculated to determine the most accurate corrections for incomplete fecal n-alkane recovery. The n-alkane technique accurately estimated DMI when corrected for incomplete fecal recovery using both published recovery rates and recovery rates calculated in this experiment. The most accurate application of recovery rates was with those calculated for each combination of dietary treatments, compared with using an average recovery rate. This research has important implications for the future use of the n-alkane technique, especially in PMR feeding systems. The discrepancy between estimated (when treatment recovery rates were applied) and measured herbage DMI increased with the amount of herbage offered but was not affected by amount of PMR. It was also found that the recovery rates of all natural n-alkanes increased as the amount of herbage increased. This research demonstrates that the n-alkane technique can be used to accurately estimate individual cow intake when fresh herbage and PMR are offered separately, evidenced by strong Lin’s concordance estimates.
    • Forage type influences milk yield and ruminal responses to wheat adaptation in late-lactation dairy cows

      Russo, Victoria M.; Leury, B.J.; Kennedy, Emer; Hannah, M.C.; Auldist, M.J.; Wales, W.J.; Agriculture Victoria Research; Dairy Australia; Teagasc; The University of Melbourne (Elsevier, 2018-08-23)
      The 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.