Effects of feeding silage and extending lactation on the pastoral dairy farm : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University, Palmerston North, New Zealand
It is a common practice in the New Zealand seasonal dairying system to dry-off the herd at an earlier date in order to prevent excessive loss of body condition and average pasture cover. Thus, short lactation length is one of the main reasons for the low milk yield per cow in New Zealand. An experiment was carried out in April and May 1995 (54 days) at the Dairy Cattle Research Unit (DCRU), Massey University in order to measure the effects of extending the lactation, and feeding silage on the dairy farm system. On the 4th April, 54 of the lower yielding cows of the herd (118 cows) were dried-off and divided into two equal herds (D or control system). The remaining 64 cows were also divided into two equal herds, and milked for another 54 days (M system). Each of the four herds was grazed on a self-contained farmlet, at 2.9 cows/ha stocking rate. D herds received only grazed pasture (16 kg dry matter (DM)/cow/day allowance), while M herds received pasture (30 kg DM/cow/day allowance) plus silage (5.5 kg DM/cow/day). All of the replicated farmlets were feed budgeted to common targets of 2,000 Kg DM/ha pasture cover and condition score 5.0 at 29th May. At the end of the experiment the M system had produced 57.7 kg milksolids (MS, fat+protein) per cow, but had lower (P<0.01) average pasture cover (by 584 kg DM/ha) and body condition scores (by 0.33 units/cow) than the D system. The target conditions were achieved by the D system, but not by the M system (deficits of 400 kg DM/ha pasture cover and 0.38 units CS/cow). When the feed required to overcome the deficits (when compared with the D system) in pasture cover and condition score of the M system was added to the silage fed, and these were all expressed in terms of their "pasture equivalences", a total marginal response to the silage feeding and extra days in milk of 116 g MS/kg equivalent pasture DM was calculated. Findings of this and previous farm system studies show that milk production response to late lactation (autumn) supplementary feeding is higher than was commonly believed, provided that it is associated with extra days in milk. Nevertheless, feed planning and management must be specially vigilant to ensure that the extended lactation does not cause reduced body condition score and pasture cover at the start of the next season.