The effect of timing of maize silage supplementation and pasture allocation on milk production and nitrogen losses of dairy cows in late lactation: A dissertation submitted in partial fulfillment of the requirement for the Degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

This study compared the effect of the timing of maize silage supplementation and fresh pasture allocation on milk solids production and N losses of dairy cows. The seven day trial was conducted in late lactation (autumn), using four groups of six lactating Friesian x Jersey cows in a 2 x 2 factorial design. Cows were offered new pasture allocations of 13kg DM, above a post-grazing residual of 1480 kg DM/ha, after the morning or evening milking, and 3 kg DM maize silage after the morning or evening milking. The experimental period took place over seven days with a lead in period prior. Animals were offered the same pasture allowance, and the chemical composition was the same for the pastures with the exception of ADF% (P<0.05) which increased from 21.2 to 22.0% as the day progressed. Total daily dry matter intake (x = 12.9 kg DM/cow/day) and milk production (x = 13.5 L/cow/day, x = 1.37 kg MS/cow/day) were not affected by timing of pasture allocation and maize silage supplementation. Milk fat % was significantly increased (P<0.05) by feeding maize silage in the (6.19%) relative to the evening (5.66%). MUN was greater (P<0.05) when fresh pasture was allocated in the morning (1.39 mmol/L), compared to the evening (1.57 mmol/L). Urine N% was greater (P<0.01) in AM than PM pasture allocation and for PM than AM maize allocation (P<0.05), and also total N excreted. Total urinary output was significantly (P<0.01) affected by timing of maize silage supplementation and timing of fresh pasture allocation. Urinary output was greater in cows fed maize silage AM (163.3 g/d) compared to PM (126.9 g/d) and cows offered fresh pasture allocations AM (164.7g/d) compared to PM (124.5 g/d). Fecal N% (x = 3.03) was not significantly (P>0.05) affected by treatment. The results of this study indicate that a simple change in the time of day supplement is feed can have a large impact on the N losses from a dairy system, while maintaining the same level of milk production.