As group housing systems for calves have gained popularity in recent years, interest in acidified milk systems has also been renewed. This article describes reasons for acidifying milk or milk replacer and examines research on acidified milk feeding systems.
Why the interest in acidifying milk?
Milk provides a very favorable environment for bacterial growth. As an example, in a Minnesota study the total plate count of colostrum increased from 100,000 cfu/mL to over 18,000,000 cfu/mL when stored at approximately 73°F for 24 hours (Stewart et al., 2005). Low temperature and pH slow bacterial growth. Refrigeration of milk in a calf feeder is generally not practical, but lowering the pH can control bacterial growth and enable milk to be held without refrigeration for a short time. Preserving milk in this way allows larger quantities of milk to be provided for ad libitum feeding of calves. The initial amount and type of bacteria in milk will have an effect on how long milk can be stored before bacterial populations reach levels that can affect calf health. In addition, each calf’s level of immunity will impact susceptibility to infection. Milk or milk replacer feeding systems need to be cleaned daily and acidification of the liquid feed should not be done just to minimize cleaning.
Does acidification affect the nutritive value of milk or benefit the calf?
After reviewing the published research, we conclude there is little evidence that acidification affects the nutrients in milk or milk replacer or the utilization of these nutrients by calves. Much of the research with acidified milk was published in the 1970s and 1980s and evaluated effects of adding acid to surplus colostrum and transition milk. When this milk was stored for extended periods of time (7 to 28 days) acidification prevented degradation of protein compared to allowing the milk to ferment naturally. However, most of today’s acidified milk systems are feeding milk within 3 days, and protein degradation should be minimal.
Calf performance, whether calves are fed milk or milk replacer, has generally not been affected by the addition of acid. Some studies compared ad lib feeding of an acidified feed to restricted feeding (for example 2 times a day) of a “sweet” feed or compared feeding transition milk to milk replacer. Differences in calf growth or health cannot be attributed to the acid in such a comparison, because calves had much higher nutrient intakes on the ad lib or transition milk treatments. In studies where intake and composition of the treatments were similar, no difference in average daily gain has been observed (Woodford et al., 1987; Raeth-Knight et al., 2009; Ribeiro et al., 2009; Hill et al., 2013; Todd, 2013). Overall, it appears the addition of acid is neutral in terms of calf growth, neither improving nor hindering calf performance. More normal fecal scores (Jaster et al., 1990) or increased fecal dry matter (Woodford et al., 1987) have been observed in calves fed acidified milk, but in both of these studies fecal scores were well within normal ranges and did not indicate large differences in the health of calves. In most studies calf health has not been significantly affected by acidification of milk or milk replacer.