Pasture dry matter intake (DMI), milk yield and composition, and calculated feed conversion efficiencies (FCE), were monitored throughout lactation for primiparous Friesian (n = 16; F) and Jersey (n = 16; J) cows calved at either high (H) or low (L) calving liveweights (CLW). Half of the cows within each breed were differentially fed (H versus L) during the 8 weeks before expected calving date to produce CLWs of 404 (FH), 354 (FL), 334 (JH), and 277 (JL) ± 14 (SED) kg. Animals were fully fed on pasture as one group after calving throughout lactation. J cows were more efficient than F cows in converting DM into solids-corrected milk (SCM) (1.63 versus 1.49 ± 0.07 kg/kg DMI), milksolids (MS) (129 versus 115 ± 5 g/kg DMI), milk fat (79 versus 67 ± 3.8 g/ kg DMI), and metabolisable energy intake (MEI) into milk energy (43 versus 37 ± 1.8%). Average DMI measured during six periods across lactation and once after the completion of lactation, were higher for F than J cows (10.5 versus 8.6 ± 0.2 kg/ cow per day) but CLW had no effect on average DMI. CLW did however, affect DMI at 215 days A95076 Received 21 December 1995; accepted 12 July 1996 since calving (DSC) when LCLW cows consumed more DM (FH, 11.3; FL, 12.0; JH, 9.4; JL, 10.2 (0.4 kg DM/cow per day). Liveweight-corrected DMI were slightly greater for J cows (2.66 versus 2.55 ± 0.05 kg/cow per day per 100 kg LW). The HCLW cows lost LW while LCLW cows gained LW until 56 DSC (FH, FL, 33.4; JH, JL, 10.4 ( 8.5 kg LW/cow), with JH cows losing more than FH (P < 0.01). The LCLW cows produced less (P < 0.01) milk, SCM, protein, milk fat, and lactose over the first 30-56 DSC. Thereafter, differences between CLW groups were not significant. Average daily milk yield across the whole lactation was affected by CLW (12.2 versus 11.0 (0.6 kg/cow per day; HCLW versus LCLW). LCLW cows had higher concentrations of milk protein (38.5 versus 36.1 ± 0.8 g/1000 g) and milk fat (57.1 versus 54.1 ± 1.5 g/1000 g). It was concluded that J cows were more efficient converters of pasture DM into MS, primarily because of a greater efficiency in milk fat production. CLW reduced milk production during the early part of lactation but did not affect DMI until mid lactation.
