Waste milk is defined as milk that cannot be sold for human consumption.  Feeding waste milk to calves may cause infection to spread from your herd to your calves, for example Johne’s disease, BVD, Staph and E. coli.  Performance of calves may suffer as waste milk may not be as nutritious as calf milk replacer and may vary in nutritional composition throughout the year.  Also, changing the calf’s between waste calf and milk replacer will unsettle the gut and lead to scour.  If waste milk contains antibiotics, resistance to antibiotics can develop in the calves.

Some research on the use of waste milk

Selim and Cullor (1997) measured the number of viable bacteria and probable antibiotic residues in waste milk fed to calves.  The number of bacteria for waste milk was significantly higher than for either calf milk replacer or colostrum. Streptococcus sp. and Enterobacteriaceae were predominantly the bacteria identified. Both Staphylococcus and E. coli were also common.  When the waste milk was tested for antibiotic residues, 63% were positive for beta-lactams or tetracycline. Waste milk can contain a high number of bacteria that may be pathogenic to cattle and also to human.

Wray et al. (1990) found that antibiotic-containing milk was unpalatable and rejection rates were high in calves. Growth rates of the calves were poorer than those of calves that were fed calf milk replacer. Also, faecal E. coli were monitored for antibiotic resistance and were higher from calves fed antibiotic-containing milk.  Wray et al. (1990) and Walz et al. (1997) suggested that the high numbers of bacteria in waste milk may contribute to disease risk.  In addition, microbial load will increase further if waste milk is allowed to sit at room temperature for periods of time, for example between milkings.

Although pasteurization reduces the microbial load of waste milk, pasteurization is not sterilization. A heavy bacterial load in waste milk will not be completely eliminated by pasteurization, and it does not remove potential contamination from antibiotics in waste milk.