Concentrate Intake Affects Ruminal pH and Milk Production of Lactating Cows on Pasture

This research paper aimed to assess the impact of varying levels of concentrate supplementation on production, ruminal pH and fermentation of lactating dairy cows on pasture. Supplements are often necessary in combination with pasture to maximize dry matter (DM) intake, milk production, and profitability, but the inclusion of supplements in the form of starch can potentially decrease ruminal pH and have adverse effects on rumen function. Six ruminally cannulated lactating Holstein dairy cows (three primiparous and three multiparous, weighing 543±45 kg and producing 29.7±5.7 kg milk/d at the beginning of the experiment) were assigned to a Latin rectangle design. Cows were fed 4, 8, or 12 kg DM of a corn-based concentrate mix per day. Not all cows consumed their daily allotment of concentrate mix (intake ranged from 0 to 12 kg DM/d); therefore, concentrate intake was analyzed as a continuous variable. Total DM intake increased with increasing concentrate intake, while intake of pasture decreased. Intake of NDF and ADF decreased with increasing concentrate intake, whereas intake of CP and starch plus water-soluble sugars increased. Total tract digestibility of starch plus water-soluble sugars and in situ digestibility of pasture DM decreased with increasing levels of concentrate supplementation. Milk production and yield of components increased with concentrate supplementation. Milk composition did not change with supplementation, except for percent lactose, which increased with increasing concentrate consumption. Total ruminal VFA, propionate, and butyrate concentrations increased with increased concentrate intake, but acetate to propionate ratio was unaffected. Daily mean and minimum ruminal pH decreased with increasing concentrate intake. Time and area spent below pH 5.8 increased with increasing concentrate consumption. Cows consuming increasing levels of concentrate experienced more bouts of pH below 5.8, and the bouts were more pronounced. In conclusion, the results indicate that grazing cows supplemented with high levels of concentrate have increased milk production, but might experience a substantial amount of time below pH 5.8, which could adversely affect digestibility.