Abstract

In the first of 2 experiments, the milk production, food conversion efficiency, and grazing uniformity of Friesians and Jerseys were compared during a grazing trial of 21 d duration in mid lactation. Four groups of each breed, consisting of 12 cows per group, were offered pasture allowances of 10, 20, 30 or 40 kg dry matter (DM)/cow/d. In experiment 2, the energy metabolism of 6 Jerseys and 6 Friesians was compared by means of open circuit calorimetry. Energy balances were established for each cow when offered pasture at ad libitum, and at 75% National Research Council (NRC) requirements. In Experiment 1, on average Friesians produced 26% more milk, 6% more milkfat, 13% more protein and 24% more lactose. At the lowest level of feeding (10 kg DM allowance/cow/d) Friesians produced more milk but less milkfat and protein than the Jerseys. Friesians consumed more pasture dry matter (av 13%), lost more live weight and had a lower food conversion efficiency (61 v 67 g milkfat/kg DM consumed) than the Jerseys. It was calculated that milkfat per ha, at a common live weight was lower for the Friesians than Jerseys particularly at high rates of stocking. Partitioning of gross energy into digestible energy or metabolisable energy was not significantly affected by breed in Experiment 2, but the efficiency of utilisation of metabolisable energy for milk and tissue (balance energy) was higher for Jerseys than Friesians (0.58 v 0.48 respectively). The results suggest that in mid lactation Friesians produce more milk and milk solids per cow than do Jerseys because of the greater feed intake of Friesians. In contrast, the higher food conversion efficiency, utilisation of metabolisable energy and dry matter consumption per unit live weight of Jerseys allows them to achieve a higher production per hectare than the Friesians. Comparisons between breeds at other stages of lactation is warranted, particularly in light of current discussions about the system of payment for milk.

HE, Meikle, GA Wickham, AL Rae, JL Dobbie, and SM Hickey

Proceedings of the New Zealand Society of Animal Production, Volume 48, , 195-200, 1988