The effect of different levels of nutrition at two stages of the lactation on milk production and live-weight change in Friesian cows and heifers

SUMMARY Over the 4 years 1965–8, a total of 105 mature Friesian cows and 84 Friesian heifers were fed various levels of nutrition at two stages of the lactation to study the effect on milk production. The experiments were carried out over a whole lactation at four Experimental Husbandry Farms, Boxworth, Bridget's, Great House and Trawsgoed. There were three treatment levels in early lactation (weeks 3–10) comprising 5·9, 7·8 or 9·8 kg D.M./day of concentrates for mature cows and 1·6 kg D.M./day less at each level for the heifers. In mid-lactation (weeks 12–18) the two lower levels of concentrates were fed arranged factorially with early-lactation levels. A basal forage ration usually of hay was fed to provide 85% of the basal maintenance requirements. During the remainder of the lactation all animals received the same level of nutrition. In addition to the pre-determined feed treatments, one further group of animals in each block was fed according to the milk production in the preceding week. Overall an increase in level of nutrition in early lactation produced a regular increase in milk production from successive increments with adult cows but only for the first increment with heifers. Raising feed level in mid-lactation increased milk production for all animals. There were considerable residual effects from early-lactation feeding but these were less with mid-lactation feeding. These same effects were also noted with yields of solids-not-fat and to a less extent in milk fat production. The experimental results indicated not only the mean effects of treatments but more important the interaction with individual animals. Study of the response of individual animals indicated that the effects of level of feeding varied in proportion to the potential of the cow. The presentation of mean results can therefore be misleading. The potential of a cow was indicated by milk production in the immediate post-calving period. This period could be used both in experimental designs for selecting animals in the allocation to experimental treatments and also in the practical context for rationing individuals or groups of cattle. The absolute plane of nutrition related to the potential of the animal was the most important factor in determining the efficiency of utilization of feed for milk production.