Cow’s milk contains a certain amount of nitrogen in the form of urea. Not essential to the composition of milk, this N represents so much waste, as it derives from protein in the feed that the animal failed to utilize.
The goal of the present project was to improve the efficiency of utilization of feed protein by increasing the C:N ratio of the feed to a level more nearly in line with the animals’ requirements. The approach was two-fold. The dairy ration was supplemented with molasses as a source of readily available carbohydrate, while the portion of high-protein grain in the diet was reduced.
Ms. Myers enlisted the cooperation of three dairy farmers and their herds. The animals of one herd were given a daily supplement of liquid molasses that averaged 4 lbs each, while their daily grain supplement was limited to 1% of body weight. A second herd was divided in two, half the animals receiving an average of 2½ lbs molasses/head/day, and the other half 1½ lbs/head/day. All animals in this herd received daily grain supplements amounting to 1.3% of body weight. The third herd received no molasses supplement, but did receive grain supplements of 1.65% of body weight/day. All three herds grazed on similar pastures, samples of which tested between 25 and 34% crude protein. They were also fed corn silage. During July and August of 1999, when the area was severely afflicted by drought, the experimental herds were grazed on alfalfa, and fed fermented haylage as well.
The experiment was run for six months, from April to September, 1999. Records were kept of milk production, milk urea nitrogen, percent butterfat, percent solids not fat, and body score (a subjective assessment of the animals’ body fat).
Results: The herd fed 4 lbs molasses/head/day showed an increase in milk production over the previous year, until the drought took hold. Levels of urea N in the milk were little changed. Reproductive efficiency was not impaired. This herd experienced fewer hoof problems, possibly because of the high biotin content of the molasses. Levels of butterfat in the milk were slightly elevated, compared to the year preceding; levels of other solids were less consistent. A substantial saving in grain expenses was realized.
The animals given lesser levels of molasses did experience diminished reproductive efficiency, and a number of the cows developed cysts. Milk production was inconsistent compared to the year preceding. Percent butter fat in the milk rose, percent non-fat solids showed little change. Because the data are incomplete a comparison of urea N in the milk is not possible.
Milk production in the control herd was inconsistent compared to the year preceding, except that production was decidedly off during the worst of the drought. Fat and non-fat solids likewise showed little if any change. Urea N data are incomplete, and consequently do not admit of comparison.
Conclusions: Protein utilization was much improved only at the highest level of molasses supplementation, but butterfat was higher in the milk of both herds receiving molasses. Molasses supplementation may have contributed to a diminution in hoof problems. Body scores of all animals fell within the acceptable range.
This experiment showed that it is possible to reduce the need for grain by supplementing the diet with molasses, and that this can be done without incurring negative consequences for milk production or quality, or herd health. What, however, in the molasses was responsible for this salutary effect—whether carbohydrate, N, vitamins, or minerals—remains an open question. The price of molasses varies. At $82/ton for molasses, corn must be above $2.70/bushel to make the molasses worthwhile. At $62/ton, corn must be above $2.00/bushel.