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• Abomasal (stomach) ulcers are frequently present in milk-fed dairy calves.
• The cause for abomasal ulcers in milk-fed dairy calves is unknown, but is probably related to diet.
• Dairy calves fed milk replacer twice a day have sustained periods of low abomasal pH.
• Feeding milk replacer more frequently than twice a day may decrease the prevalence of abomasal ulceration in suckling calves.

INTRODUCTION

Abomasal ulceration occurs commonly in dairy calves and less frequently in adult dairy cows, with a prevalence of 5-76% in healthy veal calves and 1.0-2.6% in healthy dairy cows. The cause for the high prevalence of abomasal ulceration amongst suckling calves is unknown, although diet is believed to play an important role in ulcer development. Four main causes have been proposed for abomasal ulceration in suckling calves: 1) mechanical abrasion due to ingestion of coarse roughage such as straw or the presence of “hairballs”, 2) infection with bacteria such as Clostridium perfringens type A or unidentified fungi, 3) trace mineral deficiencies, and 4) concurrent stress. None of these factors or theories alone adequately explains abomasal ulcer formation in suckling calves.

We have completed a series of studies aimed at developing an effective and practical medical treatment for abomasal ulceration in suckling calves. The results of these studies indicated that fasting abomasal pH in dairy calves was low (mean 1.4), and that suckling milk replacer at 12% body weight per day divided into 2 feedings resulted in sustained periods of low luminal pH. Abomasal hyperacidity is considered to play an important role in the development of abomasal ulceration in adult cattle, as secreted acid digests the deeper layers of the stomach wall, leading to ulceration. Because sustained periods of low pH increase the likelihood of injury to the stomach wall, we hypothesized that feeding frequency would have a profound effect on mean 24 hour pH in calves fed milk replacer and thereby influence the risk of abomasal ulceration. The aim of this study was therefore to determine the effect of feeding frequency and route of administration on abomasal pH in suckling calves.

MATERIALS AND METHODS

Six male dairy calves with cannulae in the abomasal body were administered the following 6 treatments in a randomized crossover design: 24 h fasting, suckling of a high quality milk replacer (all milk protein; 12% of body weight/day) at 12 h (2x), 8 h (3x), 6 h (4x), and 3 h (8x) intervals, and esophageal intubation of milk replacer (12% of body weight/day) at a 12 h (2x) interval. Abomasal luminal pH was measured continuously for 24 h using miniature glass pH electrodes.

RESULTS AND DISCUSSION

Mean 24 h fasting abomasal luminal pH was 1.73, whereas mean 24 h pH after suckling and esophageal intubation of milk replacer every 12 h were higher at 3.44 and 3.17, respectively. Increasing the frequency of milk replacer suckling to 3x, 4x, and 8x increased mean 24 h abomasal luminal pH; however, there was no difference in mean 24 h pH between 3x (3.69), 4x (3.64), and 8x (3.67) suckling. The percentage of the 24 h recording period that abomasal luminal pH was >3.0 was 0%, 49%, 53%, 61%, 61%, and 71% for fasting, 2x esophageal intubation of milk replacer, and 2x, 3x, 4x, and 8x suckling of milk replacer, respectively.

An important goal when preventing abomasal ulceration in milk-fed calves is to increase pH and thereby inhibit the digestive activity of pepsin and chymosin (rennin), enzymes that break down protein. Chymosin is present at birth, but pepsinogen secretion occurs soon after birth, and is quantitatively more important than chymosin for protein digestion by the 3 rd week of life. Bovine pepsinogen is activated when pH <5.0; the optimal pH for activation is 2.0-2.5 but a slow activation rate is present whenever pH >3.0. Bovine chymosin has an optimal pH for activation of 3.0-3.8 with a rapid increase in activation rate as pH decreases below 4.0. These results indicate that an abomasal pH >3.0 and >4.0 will be accompanied by a slower activation rate of pepsinogen and prochymosin, respectively, thereby markedly decreasing the ability of abomasal secretions to digest protein. Because abomasal ulcers are most frequently observed in older calves where pepsinogen is the most important protein digesting enzyme, a general goal of ulcer prevention should be to have abomasal pH >3.0 for as long as possible. The results of this study indicate that suckling at 3 h intervals (8x) increases luminal pH >3.0 for the greatest percentage of the 24 h recording period.

Beef calves usually suckle 3 to 6 meals per 24 h (range 1 to 11 meals per 24 h), and in dairy calves, ad libitum suckling and twice-daily bucket feeding produce similar rates of feed consumption and growth rate.   Feeding 2, 3, or 4 meals daily of acidified milk replacer does not alter live-weight gain, heat production, or energy retention in dairy calves and there is no difference in total feed consumption, weight gain, and diarrhea incidence between twice daily suckling and ad libitum feeding in dairy calves. It therefore appears that increasing the suckling frequency in dairy calves above the industry standard of every 12 h will more closely reflect suckling behavior in beef calves, not adversely effect on growth rate, but may decrease the prevalence of abomasal ulceration by increasing mean 24 h luminal pH and percentage of the 24 h period that luminal pH >3.0.

RELEVANT PUBLICATIONS

Ahmed AF, Constable PD, Misk NA. Effect of feeding frequency and route of administration on abomasal luminal pH in dairy calves fed milk replacer. J Dairy Sci, 2002:85:1502-1508.