FEED-UTILIZATION BY THE DAIRY-COW OVER MULTIPLE LACTATIONS - A REVIEW

Compared with the intensive research into the effects of short term variation of feeding the dairy cow, that into multi-lactation feeding is very modest. The evidence is conflicting regarding cumulative beneficial effects on milk production from a single increment in plane of nutrition repeated lactation by lactation: some experiments do, others do not, show a positive build-up of milk production over at least a double lactation. The general concensus of evidence is that liveweight stabilizes at a level commensurate with plane of nutrition but interpretations differ regarding the course of liveweight change over successive lactations of underfeeding. Evidence is uniform on residual effects on resumption of normal intakes after a lactation of underfeeding: milk yield is reduced for a lactation and body reserves are re-established. This effect constitutes a change in partition of nutrients between milk and body, a change that is in fact initiated in the later phases of the lactation of underfeeding itself. Neither diet composition in ad lib. feeding regimes nor system of allocation of compound feeds with ad lib. forage allowance had specific multi-lactation effects. Variation in rations applied over multiple lactations did not produce definitive effects on milk composition beyond those observed in the short term, and did not affect calving interval; but some health disorders were associated with protracted intensive feeding.