Response of Cows during Early Lactation to a Low Energy Ration for 4 Days1

Abstract

A low-energy ration was fed to 38 Holstein and Jersey cows which were between 18 and 101 months of age (4 to 64 days postpartum). The ration, primarily alfalfa hay and cottonseed meal, provided only 30% of the energy but 90% of the protein requirements for lactation. Milk production declined, but milk fat yield was relatively constant due to a dramatic increase in milk fat percentage. Solids-corrected milk yield declined from 22.5 to 19.1 kg during the 4 days of low energy intake. Blood glucose declined and blood ketones increased by day 4. Serine, alanine and glycine were reduced in plasma while valine, isoleucine, leucine and cystine were elevated by the low dietary energy. Initial (day 0) milk yield was related positively to final (day 4) production of milk, milk fat, solids-not fat and solids-corrected milk. The percentage of solids-not fat in milk was lower with increased parity. Blood glucose was lower for cows having the shortest postpartum interval. Alanine, serine and phenylalanine were higher as the postpartum interval increased. Valine, leucine, isoleucine, proline and aspartic acid in plasma declined with increasing age of cows. Glutamic acid was lower in plasma of cows with heavier initial body weight, and methionine was lower in plasma of higher producing cows. For energy restriction studies, cows should be similar in age and production level and be used at the same point of lactation.