Milksolid production and nitrogen partitioning of dairy cows grazing high and low diversity pasture mixes: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours

Abstract

Research was conducted to examine the effects of a diverse pasture mix including lotus, chicory and plantain with high sugar ryegrass and white clover on dry matter intake, milk yield and nitrogen (N) partitioning of lactating dairy cows. This diverse pasture mix (HSD) was compared against low diversity pasture mixes containing high sugar ryegrass and white clover (HS) or ryegrass and white clover (RG). The experiment was conducted at Lincoln University, New Zealand using three groups of 12 cows in late lactation over a 10 day period. There was no significant difference (P = 0.472) between dry matter intake for the three treatments; however there was a significant difference (P = 0.064) in N intake with the HSD cows consuming 645.5 g/d compared to 754.4 and 707.1 g/d for HS and RG treatment cows respectively. The cows grazing the HSD pasture had a greater milk yield (P = 0.002) of 16.89 Lid compared to 14.70 and 15.18 Lid for HS and RG respectively. There was no significant difference (P = 0.330) in milksolids yield for the three treatment. There was however a significant difference (P = 0.012) in milk protein yield for the HSD cows of 0.333 kg/d compared to 0.305 and 0.311 kg/d for HS and RG respectively. The increased milk protein yield resulted in a greater (P = 0.003) N output in milk of 112.1 g/d for the HSD cows compared to 101.8 and 104.8 g/d for HS and RG respectively. Urinary N excretion was lower (P < 0.001) for the HSD cows at 353.8 g/d compared to 426.6 and 438.3 g/d for HS and RG respectively. These results suggest that lotus, chicory and plantain provide a valuable addition to pasture mixes and can contribute to the goal of reduced nitrate leaching and nitrous oxide emissions from dairy farming systems. This is most likely due to the action of CT as well as a lower CP content and a higher WSC content.