Smith, Geoff2016-12-092016-12-092015https://hdl.handle.net/10182/7638The objectives of this research were to (1) quantify milk production and urinary N excretion from dairy cows grazing irrigated lucerne (Medicago sativa L.) and perennial ryegrass (Loluim perenne L.)-white clover (Trifolium repens L.) pastures at different stages of lactation and herbage allowances, (2) determine herbage production and composition of irrigated lucerne and perennial ryegrass-white clover pastures managed under irrigation, and (3) model the productivity and profitability of using lucerne on an irrigated dairy farm in Canterbury New Zealand. The first experiment measured milk production, milk composition and N excretion of dairy cows fed pure lucerne (L), perennial ryegrass/white clover pasture (G) or a temporal sequence where lucerne was offered in the morning and perennial ryegrass-white clover pasture in the afternoon (GL). Three trials were conducted in early and mid-lactation (November and then January). Milksolid (MS) production was unaffected by pasture treatment in all three trials, averaging, 2.31, 1.90, and 1.68 kg MS/cow/d for early lactation, mid lactation (November) and mid lactation (January) respectively. Although milk yield was higher in L than G during Mid-Nov lactation (22.7 vs 20.2 litres/cow/day respectively) this was offset by lower milk protein percentage in L (3.67% versus 4.03% for G) so that total milksolid production was similar across treatments. It was believed the lack of difference was due to similar estimated DM intake and diet metabolisable energy (ME) between L and G. Despite no differences in milk production, there was consistently higher urine N concentration and estimated urinary N output g/day in L (359 to 408 g/d) and GL (234-312 g/d) than G (146 to 263 g/d). The second experiment measured dry matter (DM) intake, diet composition, milk production and milk composition of cows in mid lactation (October) fed G and L at 20, 30, 40, 50 and 60 kg DM/cow/d above ground level. Milk yield and milksolids production increased with herbage allowance in both G and L treatments but was unaffected by pasture treatment or by the interaction of pasture treatment and herbage allowance. The average marginal response (kg milk per extra kg DM eaten) was 0.63 for L and 0.56 for the G. The increase in milk production in both G and L treatments with herbage allowance was due to an increase in DM intake from low to high herbage allowances. Cows feeding on both L and G at the lowest herbage allowance (20 kg DM/cow/d) substituted lower DM intakes and low feed value by mobilising energy reserves which helped maintain milksolids production. Post grazing herbage mass increased with increasing herbage allowance as utilisation of above ground dry matter decreased from 81-42% in L and 78-46% in G. The third experiment measured apparent DM intake, diet composition, milk production and botanical composition in the re-growth from different herbage allowances in the second experiment. Cows were fed a constant herbage allowance of 30 kg DM/cow/d above ground level. Herbage allowance from the second experiment and subsequent post grazing herbage allowance had no effect on milksolids production in either L or G when grazed at a constant herbage allowance. The lack of an effect of previous post grazing herbage mass may be due to the differences in DM intake and diet quality being negligible between G and L, or that energy may have been partitioned away from milk production to liveweight gain. The fourth experiment measured seasonal and annual herbage DM production, herbage quality and botanical composition of G and L under irrigation. The total annual DM production was non-significant in L (18,483 t DM/ha) and G (17,626 t/DM/ha) under full irrigation. However, herbage growth rates in L were greater than in G from November- March averaging 18.6 kg DM/ha/d more. The herbage quality of G was fairly consistent throughout the year (11.8 to 12.7 MJ ME/kg), while L quality declined considerably (12.2 to 9.2 MJ ME/kg DM) with an increase in herbage mass during times of peak growth in summer. The effect of incorporating lucerne into an irrigated dairy farm was modelled using FARMAX Dairy Pro. Data from experiment 1 to 4 was incorporated into the model and the effect of different proportions of lucerne on farm (0 to 50%) and stocking rate (3.6 to 4.2 cows/ha) on profitability was modelled. The most profitable system at a $6.50/kg MS was 40% lucerne on the milking platform. This system did not have the highest milk production per ha but the lowest cost per kg MS ($3.6/kg MS). Herbage production increased from 17.3 t DM/ha at 0% to 17.6 t DM/ha at 50% lucerne. The increased herbage production at 3.6 cows/ha allowed more feed to be conserved over summer and used in spring and autumn. This resulted in less purchased feed required, decreasing cost per kg MS. Also contributing to the lower cost per kg MS in the high proportion lucerne systems was the lower N use which reduced from 259 kg/ha to 173 kg/ha. Results shown that despite there being no difference in diet quality or milk production between lucerne and perennial ryegrass-white clover, there could still be some advantages of using lucerne with greater diet selection and liveweight gain at certain herbage allowances. Lucerne could also have some advantages for increasing overall herbage production and shifting the growth curve to allow more feed to be conserved in summer, reducing purchased feed on the shoulders of the season and reducing costs per kg MS.enhttps://researcharchive.lincoln.ac.nz/pages/rightslucerneperennial ryegrassmilksolids productiondry matter intakenitrogen partitioningurinary nitrogen excretionherbage allowanceherbage dry matterdry matter productionherbage qualityfarm systemsMedicago sativairrigated lucerne productionThesisANZSRC::070106 Farm Management, Rural Management and AgribusinessANZSRC::070105 Agricultural Systems Analysis and ModellingANZSRC::070305 Crop and Pasture Improvement (Selection and Breeding)Q112910724