Milk production potential of two ryegrass cultivars with different total non-structural carbohydrate contents
The aim of the study was to compare a new Italian ryegrass (Lolium multiflorum) cultivar (Enhancer), bred to contain a high total non-structural carbohydrate content, with the cultivar, Dargle, in terms of dry matter (DM) production, nutritional value, carrying capacity and milk production. The ryegrass cultivars were sown (25 kg/ha) under supplementary irrigation in a randomized block design (7 blocks with 2 paddocks, 4.5 ha/treatment) on the 2nd May 2001 (year 1) and the 15th March 2002 (year 2) on an Estcourt soil type. Nitrogen was applied at 56 kg N/ha after each grazing. Grazing started on 26 June 2001 and the grazing cycle varied from 24 to 28 days. Pasture yield was estimated with a rising plate pasture meter. Forty Jersey cows from 50 to 150 days in milk were randomly allocated to one of the two treatments. The experimental period started on 22 August 2001 and consisted of an adaptation period of 15 days followed by a measurement period of 75 days. Pasture was allocated at 10 kg DM/cow/day above 30 mm. Cows were weighed and condition scored on two consecutive days at 14:00 at the start and the end of the experimental period. Milk production was recorded daily and milk composition was determined every 14 days. All cows were fed a flat rate of 3.6 kg DM of a dairy concentrate (120 g crude protein (CP)/kg DM, 11.5 MJ ME/kg DM) per day. The concentrate was fed in two equal portions during milking at 06:00 and 15:00. The total production of Enhancer was higher at 8438 and 9084 kg DM/ha in 2001 and 2002, respectively, compared to 7570 and 7694 kg DM/ha of Dargle. The DM and total non-structural carbohydrate content of Enhancer was higher than Dargle in 2001 but not in 2002. In 2002 the CP content of Enhancer was lower than that of Dargle. Enhancer increased 4% fat corrected milk production by 1.3 and 1.4 kg/cow/day in 2001 and 2002, respectively, and DM intake by 1.1 and 0.88 kg/cow/day compared to Dargle. The total milk production per hectare of Enhancer was 1499 kg and 2277 kg higher during 2001 and 2002, respectively, compared to Dargle. Enhancer, a high sugar Italian ryegrass, demonstrated good potential to increase milk production.