New regulations for the use of medicated milk replacers containing neomycin sulfate (NEO) and oxytetracycline (OXY) have resulted in a need to explore the effects of amount and duration of antibiotic feeding on calf growth and health. “Previous work by our group showed removal of antibiotics from milk replacer at 14 days reduced growth compared with feeding antibiotics through 42 days,” says Noah Litherland, extension dairy scientist at the University of Minnesota.
In this study, researchers evaluated growth and health of calves fed milk replacer containing varying amounts of antibiotics for 0, 14, 28, or 42 days. Holstein heifer calves were assigned randomly to one of four milk replacer programs. All calves were fed 20 percent crude protein, 20 percent fat milk replacer at 1.3 pounds per day (as-fed powder weight) from day one to day 35 and 0.6 pounds per day from day 36 to day 42.
Four different antibiotic amounts and durations were included in the above milk replacer to yield four treatments; TRT 1 – 400 grams NEO/200 grams OXY per ton of milk replacer on day one to day 42; TRT 2 - 0 grams NEO/0 grams OXY per ton of milk replacer on day one to day 42; TRT 3 - 1600 grams NEO /1600 grams OXY per ton of milk replacer on day one to day 14; TRT 4 - 1600 grams NEO/1600 grams OXY per ton of milk replacer on day 1 to day 14 and day 16 to day 28.
Calves were fed milk replacer twice daily from day one to day 35, and once daily from day 36 to day 42. An 18 percent crude protein (as-fed) texturized calf starter was offered free-choice, along with water, throughout the study. Calves were housed in individual pens within a naturally ventilated barn.
Average daily gain and total body weight gain was lower for TRT 2 when compared with TRT 1 and TRT 4. Total starter intake and total dry matter intake was lower for TRT 2 compared with TRT 1 and TRT 4 through 42 days of age. Dry matter required for gain was higher for TRT 2 compared with all other treatments. TRT 3 increased average daily gain for days one through 14, but upon removal growth was similar to TRT 2.
Fecal scores were not different and averaged 1.3 across treatments. Severe scouring days (fecal score of four) were significantly higher for TRT 2 compared with TRT 4 through day 42. Calves fed increasing amounts and duration of NEO and OXY grew more efficiently, ate more starter, and had fewer days scouring than calves fed no antibiotics.
The future of antibiotic use in calf milk replacer is unclear. Non-medicated milk replacer additives that promote growth and health should be explored, notes Litherland. This research was presented at the American Dairy Science Association meeting this past July in Denver.