FEED CONVERSION EFFICIENCY, DAILY PASTURE INTAKE, AND MILK-PRODUCTIONOF PRIMIPAROUS FRIESIAN AND JERSEY COWS CALVED AT 2 DIFFERENT LIVEWEIGHTS

Pasture dry matter intake (DMI), milk yield and composition, and calcu lated feed conversion efficiencies (FCE), were monitored throughout la ctation for primiparous Friesian (n = 16; F) and Jersey (n = 16; J) co ws calved at either high (H) or low (L) calving liveweights (CLW). Hal f of the cows within each breed were differentially fed (H versus L) d uring 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 f ully fed on pasture as one group after calving throughout lactation. J cows were more efficient than F cows in converting DM into solids-cor rected milk (SCM) (1.63 versus 1.49 +/- 0.07 kg/kg DMI), milksolids (M S) (129 versus 115 +/- 5 g/kg DMI), milk fat (79 versus 67 +/- 3.8 g/k g DMI), and metabolisable energy intake (MEI) into milk energy (43 ver sus 37 +/- 1.8%). Average DMI measured during six periods across lacta tion and once after the completion of lactation, were higher for F tha n J cows (10.5 versus 8.6 +/- 0.2 kg/cow per day) but CLW had no effec t on average DMI. CLW did however, affect DMI at 215 days since calvin g (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 slight ly greater for J cows (2.66 versus 2.55 +/- 0.05 kg/cow per day per 10 0 kg LW). The HCLW cows lost LW while LCLW cows gained LW until 56 DSC (FH, -8.9; FL, 33.4; JH, -25.9; JL, 10.4 (8.5 kg LW/cow), with JH cow s losing more than FH (P < 0.01). The LCLW cows produced less (P < 0.0 1) milk, SCM, protein, milk fat, and lactose over the first 30-56 DSC. Thereafter, differences between CLW groups were not significant. Aver age daily milk yield across the whole lactation was affected by CLW (1 2.2 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, pri marily because of a greater efficiency in milk fat production. CLW red uced milk production during the early part of lactation but did not af fect DMI until mid lactation.