Human breastmilk is great for human babies, and cows milk is great for calves! There are many benefits to extended bf (breastfeeding beyond 12 months). Cows milk is vastly inferior to your breastmilk. If you are happy with your breastfeeding relationship continuing, then go for it! I recommend a book called 'Mothering Your Nursing Toddler' by Norma J. Bumgarner.