Drying-off thinner cows earlier in late lactation - is it beneficial?

Abstract

In New Zealand dairy systems, cows usually lose condition in early lactation, when their feed demand is high, to buffer milksolids (MS) production. Condition score (CS) at calving is influenced by drying-off date and CS at drying-off. In late-March, two groups of cows with average CS 4.5 were dried off early and offered normal (13 kg DM/cow/day) and high (26 kg DM/cow/day) pasture feeding allowances. Another group of average CS 4.5 was offered 26 kg DM/cow/ day and dried-off late (mid-May). Two more groups with average CS 5.1 were offered normal (26 kg DM/ cow/day) and high (52 kg DM/cow/day) allowances and also dried-off late. From late-March to mid-May, dry cows fed at the high level gained about twice as much condition as normally fed dry cows (+1.5 vs +0.7 CS). The late dried-off cows at initial CS 4.5 and 5.1 had a gain in CS (0.3 units) or maintained condition respectively under normal feeding, but gained 0.4 CS under high feeding. In late lactation, there was no significant difference in MS production (P<0.05) from high compared to normal feeding at CS 5.1, but the high fed cows produced significantly more MS than the normally fed cows at CS 4.5. In the next lactation, from calving in late-August to late-October, there was a trend for both early and late dried-off cows that had been fed at a high level in the preceding late lactation to produce more MS than those that had been normally fed (1.93 vs 1.79 kg MS/cow/day averaged across both CS groups). Drying-off date had a significant effect on MS production in early lactation (early drying-off 1.93 kg MS/cow/day vs late drying-off 1.76 kg MS/cow/day) for cows with initial CS 4.5. There was a strong relationship between CS at calving and MS production in early lactation, with 1 extra CS at calving equivalent to 0.19 kg of extra MS/day. Changes in cow body fat content during late lactation corresponded closely to changes in CS (52 kg body fat/CS unit). The results suggest that where autumn feed is limited, there is little difference in the efficiency of pasture use between normal autumn feeding of late dried-off fatter cows to allow higher autumn feeding of early dried-off thinner cows (5.0 kg MS/kg DM), compared with normal autumn feeding of early dried-off thinner cows to allow higher autumn feeding of late dried-off fatter cows (4.7 kg MS/kg DM) Keywords: cow body fat content, cow condition score, dairy cows, drying-off date, feeding level, milksolids production