Short communication: Immediate and deferred milk production responses to concentrate supplements in cows grazing fresh pasture

Abstract

The objective of this study was to determine the increase in milk production from supplementation that occurred after supplementation ceased. This portion of the total response (i.e., the deferred response), although accepted, is generally not accounted for in short-term component research projects, but it is important in determining the economic impact of supplementary feeding. Fifty-nine multiparous Holstein-Friesian dairy cows were offered a generous allowance of spring pasture [>45kg of dry matter (DM)/cow per day) and were supplemented with 0, 3, or 6kg (DM)/d of pelleted concentrate (half of the allowance at each milking event) in a complete randomized design. Treatments were imposed for the first 12 wk of lactation. Treatments were balanced for cow age (5.4±1.68 yr), calving date (July 27±26.0 d), and genetic merit for milk component yield. During the period of supplementation, milk yield and the yield of milk components increased (1.19kg of milk, 0.032kg of fat, 0.048kg of protein, and 0.058kg of lactose/kg of concentrate DM consumed), but neither body condition score nor body weight was affected. After concentrate supplementation ceased and cows returned to a common diet of fresh pasture, milk and milk component yields remained greater for 3 wk in the cows previously supplemented. During this 3-wk period, cows that previously received 3 and 6kg of concentrate DM per day produced an additional 2.3 and 4.5kg of milk/d, 0.10 and 0.14kg of fat/d, 0.10 and 0.14kg of protein/d, and 0.10 and 0.19kg of lactose/d, respectively, relative to unsupplemented cows. This is equivalent to an additional 0.19kg of milk, 0.006kg of fat, 0.006kg of protein, and 0.008kg of lactose per 1kg of concentrate DM previously consumed, which would not be accounted for in the immediate response. As a result of this deferred response to supplements, the total milk production benefit to concentrate supplements is between 7% (lactose yield) and 32% (fat yield) greater than the marginal response measured during the component experiment. Recommendations to dairy producers based on component feeding studies must be revised to include this deferred response.