Title: Similar milk yields for two systems.
Source: New Zealand Dairy Exporter, 01/06/2012, Vol. 87 Issue 11, p114-115, 2p, 1 Color Photograph, 1 Chart
Organics
A Massey University trial comparing production from an organic and a conventionally farmed farmlet showed the first grew less pasture/ha in every year.
This was probably largely due to the application of much less nitrogen (N)/ha because low-cost forms of N permissible for organic systems were not widely available.
So the organic farmlet was managed under a lower stocking rate even though it did offer more imported feeds.
In 20082011 total feed offered/cow was higher for the organic herd. In these years both herds produced similar yields of milksolids (MS)/ cow but the organic farmlet still produced less MS/ha because of its lower stocking rate.
In 2003-2008 MS/cow from the organic herd was lower (measured from milk into the vat - herd test values indicated similar production/cow) than from the conventional herd; therefore, with its lower stocking rate, the organic farmlet produced considerably less MS/ha.
The trial began in 2001 when an organic farmlet of 20ha and a conventional farmlet of 22ha were established at Massey's Dairy Cattle Research Unit, No 3 Dairy.
The Tokomaru Silt Loam soils are heavy and liable to pugging in wet conditions, despite mole-and-tile drains.
Previously the farm has grown 11-12 tonnes of dry matter (DM)/ha/year with no N applied.
Initially both herds were high breeding worth (BW) Holstein Friesian (HF) cows, originating from the previous comparison of heavy HFs, with a high percentage of overseas genetics, and light HFs (with a high percentage of New Zealand genetics). But from 2003, HF/Jersey crossbred cows were introduced into both herds to make up 40% and 60% of the conventional and organic herds respectively by 2010/11.
Both herds had similar age structures in 2001/02 but by 2010/11 the organic herd had a higher percentage of two and three-year-olds (51%) than the conventional herd (40%). These two factors resulted in the herds becoming lighter over the 10 year period, from 530kg liveweight (LWT) for both herds in 2001/02, down to 460 and 470kg LWT for the organic and conventional herds respectively in 2010/11.
Both herds were stocked at a similar rate at the start, with the same planned start of calving (PSC) date. But with little or no N applied, the organic farmlet grew less pasture, especially in late winter/ early spring. So from 2003 the organic farmlet was operated at a lower stocking rate and with a later PSC date than the conventional farmlet.
Milk data
Milk production and composition was measured by collecting the milk from each herd separately in two milk vats at each milking. The milk data given was derived from Fonterra's milk dockets, and excluded any milk discarded from cows with high somatic cell counts (SCC)/mastitis and milk used to raise replacement heifer calves. Under organic systems calves are reared on milk for a longer period than in conventional systems. Both herds were also herd-tested monthly as well as being weighed and condition-scored after the afternoon milking.
Pasture growth was estimated from weekly platemeter measurements on every paddock. Pasture composition (for nutritive value) was measured on samples of pasture taken monthly, from paddocks that were about to be grazed by the cows.
The main results for the two farmlets in two periods 2003-2008, the first five developmental years after full organic certification, and 2008-2011, when the two systems had been fully developed, are shown in Table 1.
The conventional farmlet grew more pasture in every year, by 2t DM/ha and 0.7t DM/ha in the two periods.
Assuming that the extra N applied was the sole cause of the extra pasture grown, these correspond to about 12 and 18kg extra DM grown/kg extra N applied. This assumption is unlikely to be true.
Pastures for both farmlets in both periods were of similar high nutritional quality, with annual averages of 11.7- 12.1 megajoules of metabolisable energy (MJ ME)/kg DM, and 22.6-23.4% crude protein (CP) in the DM.
In both periods the organic farmlet had a slightly lower stocking rate but also imported slightly more feed/ha.
Estimated pasture utilisation (t DM/ha eaten / t DM grown x 100%) was similar for both farmlets in 2003-2008 (81 and 83%) but was lower for the organic farmlet in 2008-2011 (82% vs 73%).
From 2003-2008 the organic herd had higher SCC and sold less MS/cow. The organic herd was offered more imported feed/cow but despite this, it was offered less total feed/cow. The large difference between the organic and conventional milk sold/cow data can be explained reasonably and credibly as follows:
The additional milk for calves equates to 8 kg MS/cow, and milk withheld from the vat for somatic cell and mastitis cows 12-27kg MS/cow. If you add to this the impact of less pasture available per cow of 20-40 kg MS/cow they add up to the 40-70kg MS/ cow difference.
With its lower yield of MS/cow in the vat and its lower stocking rate the organic farmlet produced considerably less MS/ha than the conventional farmlet.
Similar yields
But from 2008 - 2011, even though the organic herd contained a higher percentage of two and three-year-olds (51%) than the conventional herd (40%), yields of MS/cow (both milk in the vat and at herd test) and SCC were similar for both herds. With its lower SCC, less milk from the organic herd was withheld from the vat in this period than in 2003-08. For the organic herd, the larger amount of total feed offered/cow (6.0 versus 5.4t DM/cow), and its lower stocking rate, probably contributed to its higher yield of MS/cow than in 2003/08, and to its lower pasture utilisation (73% versus 82% for the conventional herd). Another contributing factor to the organic herd's higher MS/cow was a higher % MS in its milk, probably due to its higher percentage of crossbred cows.
However the organic herd was stocked at a lower rate, resulting in a lower yield of MS/ha than the conventional herd.
In both periods 2005-2008 and in 20082011, average body condition scores (BCS) were slightly lower for the organic herd at 3.7 than the conventional herd at 3.9.
The results for 2008-2011 show that, as would be logically expected, organically farmed cows can produce as much MS/cow as conventional cows if they are equally healthy, fertile and well fed.
It is also logical to expect that organic farms should be able to produce as much MS/ha if they are both able to offer equal amounts of high quality feeds/ha. This wasn't proven in 2008-2011 even though both farmlets offered the same amounts of total feed (13.3t DM/ha). With its lower stocking rate, the organic farmlet ate a lower percentage of the pasture grown (estimates of 73% versus 82%) and despite its larger amount of imported feed offered/ ha, it's likely that the organic farmlet's herd ate less total feed/ha.
It is possible that, if both farmlets had used the same stocking rate in 2008-2011 and had offered equal amounts of total feed/ha, both farms might have produced equal amounts of MS/ha. But equality of production may not have maximised profit for both farmlets and the probable environmental advantages of a lower stocking rate and less N applied/ha on the organic farmlet must also be taken into account.
Control of mastitis in organic herds is always likely to be difficult because of the restrictions on use of antibiotics.
But the results for 2008-2011 and experiences of other farmers indicate that it's not impossible, and that organic cows can be managed to maintain a low SCC.
It is also likely to be more difficult to offer equal quantities of feed on organic farms because of the greater difficulties of sourcing organically certified N and feeds.
The present data suggests that organic farms that apply little or no N are likely to grow less pasture than conventional farms that apply average rates of N.
So, for systems that operate without N and without additional imported supplementary feeds organic farms are likely to produce less MS/ha than conventional farms. For organic farms to produce yields of MS/ha equal to those produced by otherwise comparable conventional farms, on which N and imported feeds are used, they would either have to identify alternative 'organic' N fertilisers to increase pasture growth, and/ or feed extra organic supplementary feeds.
Profitability would depend on the effects of organic management on costs, the value of organic milk, and farm efficiencies. It wouldn't necessarily be maximised even if MS/ha on organic farms could be made to equal that on conventional farms.
The probable environmental advantages of the lower stocking rate and less N applied/ha on the organic farmlet suggest that if, in future, limits on cows farmed / ha and kg N applied/ha are introduced for environmental reasons, organic systems may look attractive to more farmers.
This is the second of a series of four articles on results of the organic versus conventional trials conducted at Massey University. The article was written from data compiled by Stijn Voets, an intern from The Netherlands, under the supervision of Professor Nicola Shadbolt and Dr Colin Holmes.
Table 1: Main results for conventional and organic farmlet
Table 1: Main results for conventional and organic farmlet
Payout 2003-2008 Organic 2008-2011 Organic Conventional Conventional Cows/ha 2.37 2.28 2.44 2.21 Planned start of calving (PSC) 28/7 5/8 27/7 5/8 Kg milksolids (MS) sold/cow 389 325 366 354 Kg MS sold/ha 919 742 893 785 Average somatic cell count (SCC) 160,000 194,600 115,000 " 116,000 Liveweight(LWT), kg/cow 526 525 474 462 Kg nitrogen (N) applied/ha 135 24 107 Pasture grown, tonnes of dry matter 12.0 10.0 11.1 10.4 (DM)/ha/year Total feed offered, t DM/cow/year 5.3** 5.1** 5.4 6.0 Includes pasture grown + imported feeds.
For 2005-2011; Imported feeds* offered * t DM/ha 1.8** 2.2** 2.2 2.9 Total feed offered; t DM/ha 12.68 11.74 13.29 13.28 * Imported feed includes grazing-off for dry cows and imported supplements. ** These values are for the period 2005-2008 so don't include 2003-2005.
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