Gholamreza Ghorbani Kharaji
Isfahan University of Technology, Iran
Title: Variability in susceptibility to acidosis among high producing mid-lactation dairy cows
Biography
Biography: Gholamreza Ghorbani Kharaji
Abstract
Lactating dairy cows (n=78, days in milk=103±26.5; body weight=630±76.8 kg) were fed a high-concentrate diet consisting of 35% forage and 65% concentrate. Cows were adapted for 14 d and then were sampled for 10 d. Although all cows were fed the same diet, rumenocentesis pH and minimum reticuloruminal pH values ranged from 5.05 to 6.98 and 4.78 to 6.08, respectively, and the acidosis index ranged from 0 to 28 pH×min/kg of dry matter intake (DMI). Cows were classified according to rumenocentesis pH as tolerant (pH≥ 6.0; n=26), marginal (5.8≤pH<6; n=21), and susceptible (pH<5.8; n=31). Cows were also classified according to reticuloruminal pH as susceptible if duration of an acidotic condition (pH<5.8) exceeded 330 min/d (an average of 920 min/d; n=9) and tolerant if the acidotic condition persisted <330 min/d (an average of 78 min/d; n=5). The classification based on rumenocentesis pH revealed that DMI during first 2 h after morning feeding decreased with increasing SARA (Subacute Ruminal Acidosis) susceptibility. This result was associated with greater daily DMI of tolerant cows which also were of greater body weight. Sorting against long particles and in favor of fine particles during the morning feeding (0 to 6 h) also increased with increasing SARA susceptibility. However, when cows were classified according to reticuloruminal pH, DMI and sorting activity were not significant. Milk fat percentage was greater in tolerant cows, whereas total yield and yield of other components was not significant. The proportions of isovalerate and valerate were correlated with increased SARA susceptibility in cows classified according to rumenocentesis pH. These results indicate that substantial variation exists in SARA susceptibility among high producing, mid-lactation dairy cows, and that cows characterized as tolerant to the high-grain diet exhibit greater DMI and milk fat percentage, but decreased sorting behavior and proportion of isovalerate in the rumen.