Volume 37, 84-93

Tropical Grasslands (2003) Volume 37, 84–93

The effect of frequency of pasture allocation on the milk production, pasture intake and behaviour of grazing cows in a subtropical environment

B.C. GRANZIN

NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, New South Wales, Australia

Abstract

Two studies were conducted in a subtropical environment to examine the effects on milk production and nutrient intake of Holstein-Friesian cows of offering a daily pasture allowance as various numbers of allocations within a day.
In Study 1, 24 multiparous cows [half early lactation (mean ± s.e. of 57 ± 16.2 d post-partum), half mid–late lactation (204 ± 32.9 d post-partum)] were allocated to 2 groups based on genetic merit, milk production, liveweight (LW) and days post-partum. These groups were offered a daily herbage allowance (HA) of approximately 19 kg dry matter (DM) of kikuyu (Pennisetum clandestinum) cv. Common pasture (above 5 cm from ground level). One group (KB2) received 75% of their HA at 16.30 h and the remaining 25% at 07.30 h the following morning. The other group (KB4) were offered 41.6% of their HA at 16.30 h, 16.7% at 19.00 h, 16.7% at 24.00 h and 25% at 07.30 h. Cows were allowed to regraze allocations given within 24 h (i.e. 16.30 h–16.30 h).
In Study 2, 32 cows (8 primiparous, 24 multiparous) in early lactation (133 ± 23.3 d post-partum) were allocated to 4 groups based on lactation number and criteria used in Study 1. All cows were offered a daily HA of approximately 40 kg DM of biennial ryegrass (Lolium multiflorum) cv. Concord or prairie grass (Bromus willdenowii) cv. Matua pasture. One group (RB1) received 100% of their daily HA at 07.30 h, a second group (RB2) was offered 66% at 07.30 h with the remainder at 17.00 h. A third group (RB3) was offered 44% at 07.30 h, 22% at 12.00 h and 34% at 17.00 h, while the fourth group (RB4) was offered 22% at 07.30 h, 22% at 12.00 h, 22% at 14.00 h and 34% at 17.00 h. Cows were allowed to regraze allocations given within 24 h (07.30 h–07.30 h).
Frequency of pasture allocation had no effect (P>0.05) on pasture intake, yields of milk, fat or protein, milk concentrations of fat or protein, or LW change in either study. Milk lactose concentrations of cows in KB4 were (P<0.05) higher than those of cows in KB2. In Study 1, milk fat levels of cows in early lactation (3.04 vs 3.38% for KB2 and KB4, respectively), milk yields (18.1 ± 0.30 vs 17.1 ± 0.30 L/d) and milk lactose concentrations of cows in late lactation (5.10 ± 0.013 vs 5.13 ± 0.13%) were different but not significantly so. In Study 1, frequency of pasture allocation had no effect (P>0.05) on grazing behaviour, with an average time spent grazing of 424 min/d. Seventy percent of grazing occurred between 07.00 h and 19.00 h. In Study 2, cows in RB1 and RB2 spent more time grazing (P<0.05) between 07.30 h and 12.00 h than cows in RB3 and RB4. Between 12.00 h and 14.00 h, cows in RB4 spent more time grazing and less time idle (P<0.05) than the other treatment groups. These studies indicate that the diurnal frequency of allocating pasture has little effect on the milk production, pasture intake and grazing behaviour of dairy cows grazing pastures in the subtropics.