by Colin Holmes

Many methods and practices used on once-a-day (OAD) farms are the same as those used on twice-a-day (TAD) farms. However, there are some differences. Methods for which OAD differs from TAD will be described briefly, and methods that are believed to be even more important for OAD than for TAD, will be emphasised. Finally, some information is presented about the levels of performance that can reasonably be expected from OAD systems.

The information below has been compiled mainly from the collective wisdom of experienced and successful OAD dairy farmers, members of the Southern North Island OAD Discussion Group.

Limited data from farms using OAD systems, show that they experienced their largest losses of production in their first season on OAD, of about 15-25% in kg MS per cow and 15% in kg MS per hectare. Careful preparation during the final season on TAD should help to minimise these adverse effects in year one on OAD, including the expected increase in SCC.

Type and age of cows

• As for TAD, high BW cows are also generally best for OAD too (but see Breeding Programmes for OAD cows, in 3 below). Compared with TAD, milksolids (MS) yields per cow are generally decreased on OAD, but this decrease is smaller for Jerseys and J x HF crossbreds than for Holstein Friesians.
• Good udder conformation is especially important for OAD, because with nearly    24 hours between milkings, the udders will be full, heavy and tightly-stretched before each milking. Udders must be strongly attached to the body, with evenly-sized quarters, and well-placed teats that can be milked easily even when the udder is full. Strong, healthy udders, with low SCCs are a prerequisite for an OAD herd.
• Cows that have records showing clinical mastitis, and/or high SCC should be culled before OAD begins. One experiment shows that MS production of cows with low SCCs is likely to be less affected by OAD than that of cows with high SCCs.
• In an attempt to identify cows not suited to OAD; OAD could be used for the last months of the final TAD season, and those cows that dry themselves off quickly, and become fat when milked OAD could be culled or sold to TAD herds.

Drying-off at the end of the final season on TAD, mastitis control and culling

• Take this opportunity to eliminate/control/cull any mastitis problems, and cows with weak udders, before OAD begins.
• If there is evidence of a mastitis problem in the herd (e.g. herd SCC above 250,000), serious thought should be given to the use of DCT and Teat-Seal on all cows; and the use of Teat-Seal in the heifers, about 4 to 5 weeks before calving for their first time, should also be assessed.
• At the very least, stick to the guidelines given in the SAMM plan, with respect to treatment and culling.
• Including a high % of replacements into the herd will enable more voluntary culling; and 2-year-olds generally have lower SCC than older cows, and higher BWs. But 2-year-olds produce about 25% less per cow than mature cows, and their MS yield is decreased by OAD to a greater extent than is the yield of older cows.

Stocking rate (cows per ha) for the first season of OAD

• In the early part of the first season on OAD, it will probably be necessary to remove 5% to 10% of cows, because they are obviously unsuited to OAD (unless cows not suited to OAD had already been identified and culled in the season prior to the change to OAD). Extra cows should be calved to allow for this expected early culling, or on-selling of unsuitable cows.
• In this first season on OAD, milksolids yield per cow is likely to be lower by 10 to 25%. Consequently, at least for the first year or two on OAD, an increase in cows/ha (by 10 to 15%) is often recommended, to compensate for the expected decreases in pasture eaten per cow and milk produced per cow.
• BUT BEWARE! If the stocking rate is too high in this first season on OAD, this will cause periods of pasture deficit, with consequent decreases in pasture intake and yield per cow; in this case, milksolids yield per cow would be depressed by OAD and by underfeeding.
• Therefore, any increase in cows per hectare should be calculated carefully, to ensure that, first, there will be enough cows on-farm to enable early culling of those that are unsuited to OAD, and also to fully utilise the pasture, but, second, the farm will not be over-stocked.

Milking machine

(On OAD, the udders are likely to be very tight and full before each milking; therefore, during milking, the rate of milk flow through the milking machine will be faster than on TAD. These conditions may necessitate some changes in the machine).

•  Cup slip can be a bigger problem on OAD; seek advice from experienced OAD farmers or from milking specialists, about the type of long milk tube, milking cluster and teat-cup liner that have been found to work effectively with cows milked OAD.
• Ensure that the machine’s vacuum level is stable, and at the correct level, during the whole milking; the machine must have sufficient reserve air-flow capacity.
• The milk line, milk pump, and the milk cooler and refrigeration unit must all have sufficient capacities to cope with the faster rates of milk flow expected on OAD.

Springers and colostrum cows

• When to start OAD Collect cows and calves on the day of calving, and milk the cows OAD from then on.
• Withholding periods for colostrum cows, expressed as the number of days after calving; Fonterra’s rules state that colostrum from each cow should be withheld from the vat for at least 8 milkings, equivalent to 4 days for herds milked TAD.
• Members of the OAD Group generally withhold colostrum from the vat for 4 days (or, on OAD, 4 milkings) for cows, and for 5 days (or 5 milkings) for heifers.  (At least one OAD farmer has used the normal TAD withholding period of 8 milkings (or 8 days on OAD) for cows calved in the first week of calving, when most of the herd is producing colostrum; and he gradually reduced this down to a withholding period of 4 milkings (4 days) for cows calving in the fourth week, when most of the cows will be producing normal milk).
• During the 4 day withholding periods, the colostrum is likely to meet the new-born calves’ needs for immune proteins (i.e. in the first day of life, 4 litres of colostrum per calf, preferably from the cow’s first and second milkings).
• If colostrum is to be supplied to Fonterra; collect colostrum from the first two milkings, or days, to ensure sufficiently high concentrations of immune globulins.
• While the newly-calved cow still in the colostrum herd, check all quarters/cows with the Rapid Mastitis Test (RMT).
• Do not put a cow’s milk into vat unless RMT indicates a low SCC.
• One OAD farmer milks the main herd and switches-off the machine. The freshly calved cows are then collected and milked, followed by the colostrum & sick cows. The milking plant is then washed and finally switched-off for the day.
• It is advisable to inspect newly-calved colostrum-cows twice a day, to minimise losses e.g. from milk fever. If dusting pastures in wet weather e.g. with magnesium chloride, do it twice a day.

Milking methods mastitis and its treatment

Generally these are the same as for TAD; BUT, on OAD, there are 2 potentially important differences:

1. Just before cups-on, the udders will be even fuller and tighter than on TAD.
2. After cups-off, it will not be possible to inspect the teats/udders closely for the next 24 hours, much longer than on TAD. In addition, this longer inter-milking interval may enable mastitis infections to become more firmly established before the next milking. (see details in Appendix Two).

•  During milking MUST ensure that teat cups are aligned correctly on the teats, and that they remain firmly in place without slipping.
•  Before cup removal MUST ensure that all udders/quarters have been thoroughly milked-out and are empty.
•  After cup removal MUST look for, detect and attend to, any abnormal quarters (e.g. full/hard/hot), even if cups are removed by automatic devices.
•  Some farmers strip fore-milk from one (or two) quarters of all cows at one milking (e.g. front right), and rotate around the udder so that, after 4 (or 2) milkings, all 4 quarters of every udder have been checked for abnormalities.
•  One OAD farmer, who pressure-washes the teats/udder before cups-on, believes that this helps the cows to milk out more evenly.
•  MUST ensure that every teat is covered thoroughly with an approved teat spray disinfectant, after every milking; this is probably even more essential than it is on TAD (and discovery of a teat sanitiser that protects the teats for the full 24 hours, will be of special benefit on OAD).
•  Another OAD farmer reports good results, including reductions in clinical mastitis and animal health costs, after the installation of a new automated cluster/teat cup system. This system sanitises the skin of each teat immediately after the end of milk flow from the cow and then, after cup removal, it also sanitises the inner surfaces of each teat cup liner.
•  After every milking, the milk filter should be inspected for any abnormalities. If clots are discovered, the culprit-cows should be identified at the next milking, by inspecting fore-milk from suspect cows. Cows showing abnormalities in their milk should then be tested with the RMT (it is possible that, on OAD, infected cows produce clots that are more easily detected on the filter).

Withholding times for milk from a cow after antibiotic treatment

• if a product is not registered for OAD milking, use the number of milkings recommended for TAD (e.g. if 48 hours & 4 milkings recommended on TAD, then use 4 milkings, or 96 hours, on OAD); that is, the withholding time on OAD will be twice as long as for TAD.
• However, Pfizer Animal Health Company recently published details about 2 antibiotics, for which the recommended withholding times for OAD are not twice as long as those for TAD, as shown below:

Lincocin Forte S; 3 tubes at 24 hour intervals; withholding time for OAD = 96 hours or 4 milkings (for TAD= 60 hours or 5 milkings).

Orbenin LA; Either 3 tubes at 48 hour intervals; withholding time for OAD = 72 hours or 3 milkings (for TAD= 84 hours or 7 milkings).

OR

5 tubes at 24 hour intervals; withholding time for OAD = 96 hours or 4 milkings (for TAD= 96 hours or 8 milkings).

• Because, on OAD, antibiotics can be infused only once per 24 hours, it may be advisable to administer more than the minimum recommended number of tubes for effective treatment over a longer period (e.g. instead of 3 to 4 days recommended minimum on TAD, administer for 4 to 5 days on OAD); but seek veterinary advice before doing this.
• Even though the herd is on OAD, some vets recommend that cows being treated with antibiotic for clinical mastitis, should be milked TAD during treatment. This more frequent removal of infected milk from the quarters, and more frequent infusions of antibiotics may assist cure and recovery.
  

Management of cows in normal lactation (e.g. more than 20 to 30 days after calving)

• Just as for TAD cows, OAD cows need to eat sufficient feed to maintain themselves, and pregnancy, and to produce milk. Underfeeding will depress milk production of cows, regardless of whether they are milked OAD or TAD. Do not voluntarily underfeed cows milked OAD.
• Grazing management is generally similar to TAD; targets for pre-grazing yields and post-grazing residuals are the same as for TAD.
• Generally, most OAD farmers shift cows onto a fresh area of pasture twice a day; but some shift them only once, and claim useful advantages from this. The herd, and its water supply, should be checked twice a day.
• To ensure good milk production, cows must consume sufficient Metabolisable Energy each day. Therefore the cows must be offered enough pasture each day, and the pasture must be of high quality (i.e. high % of young green leaf, high digestibility, high MJME/kg DM). These factors are essential for all cows; but they may be even more essential for herd milked OAD, to entice cows to continue to eat large amounts of feed without the stimulation provided by the second milking. Therefore excellent management of grazing and feeding is essential for OAD cows, to ensure long productive lactations, and full utilisation of high quality pastures.
• Many herds milked OAD receive supplements; mainly silages, PKE and hay. The responses, in kg MS/ Kg DM fed as supplement, are likely to be slightly lower in cows milked OAD than in cows milked TAD.
• Mating and fertility: A 4 year trial in Taranaki comparing Holstein-Friesians and Jerseys milked either OAD or TAD showed that OAD reduced the time from calving to conception by 5 days and increased 3-week pregnancy rate by 8%, but with no change in final pregnancy rate.  The percentage of Holstein-Friesians cows treated with CIDRs was substantially reduced from 24% for TAD to 5% on OAD, but the corresponding reduction of 7% in Jerseys was not significant.
• Farms that use OAD systems also achieve better than average submission and pregnancy rates, with compact calving periods and a low percentage of empty cows from shorter that average mating periods. (See Table 2 in Appendix One).
• The majority of OAD herds use no inductions, and most use no CIDRs either.
• In a 640 cow Jersey herd in the Waikato, milking approximately half the herd OAD for 2 years, empty rates for those on OAD were 3-4%, but 8-9% for those on TAD.
• Most OAD farmers use Tail Paint to assist with detection of cows on heat; some observe cows and their tail paint for signs of heat only at the one milking per day, while some also observe the cows while they are undisturbed in the paddock.

 Genetic improvement programmes for OAD herds

Most of the group members are farming with high BW crossbred (Holstein Friesian x Jersey) cows (see below for the effects of OAD on different breeds). But some OAD herds comprise mainly Holstein Friesians or mainly Jerseys.

Most members use proven High BW sires; although some have used sires with high OAD BWs.

A successful OAD farmer, now in the 10^th year on OAD, milks Jersey cows producing 340 to 370 kg MS/cow. He uses the criteria shown below to choose sires for use via AB:

• High BW.
• Negative values for BV milk, e.g. from – 300 BV milk up to 0 BV milk (for Jerseys). Small + BV milk values can be accepted if all the traits below are very good.
• BV for udder support BV must be always positive i.e. + 0.3 or better.
• BV for SCC must always be negative e.g. BV – 0.3; and the bigger the negative value is, the better.
• BV for protein % must be positive; e.g. BV + 4 or better.
• Farmer traits BVs should all be positive, especially temperament & milking speed.

But other members have tried to use these criteria to select sires for their own herds, and have found that it is difficult to meet them all in one sire.

Yield of MS per cow for a full lactation

• This is likely to be lower than would have been expected on TAD, especially in the first and second seasons on OAD.
• Jersey cows and older cows generally show the smallest decreases; while Holstein Friesian cows and 2 year olds show the largest decreases. For example, 15% decreases in mature Jerseys; 31% decreases in 2 year old Holstein Friesians (Data from Dr A Winkelman, LIC).
• Limited evidence shows that, on OAD, decreases in yield are smaller in cows with low SCCs.
• These lower yields of MS per cow would be expected to reduce the cow’s Feed Conversion Efficiency (kg MS produced per t DM eaten). But, the normal calculations of feed required by TAD cows are likely to overestimate the energy requirement of a OAD cow by up to 5% (because OAD cows spend less time walking and standing on concrete, and more time lying on pastures. Also, they lose less body condition during lactation, and have to regain less condition before calving, a relatively inefficient cycle of loss and subsequent regain of body tissues).
• OAD cows generally do produce extra milk in response to extra feed, especially if their initial intake of ME had been limiting production. Their response, expressed as g extra milk per kg extra DM given, is likely to be slightly lower than would normally be expected from TAD cows.
• After several seasons on OAD, all unsuitable cows will have been culled, and average yield per cow will have increased. These higher yielding cows will of course require more feed, and may also be a bit thinner than they had been in the early years on OAD.

Milk composition

• Concentrations of fat and protein are usually higher by 0.1% to 0.3%, so that MS % is likely to be higher by 0.3% to 0.5%.
• But the concentration of lactose is usually lower by about 0.2%.
• The concentrations of some minor, but potentially valuable, components are also higher in OAD milk; these include immune globulins and lactoferrin.  SCC of milk is usually higher in OAD cows than in TAD cows, even in uninfected cows; e.g. by 10,000 to 50,000 in early lactation, and by 50,000 to 100,000 later.

 The lactation curve

• The difference in daily yields between OAD cows and TAD cows is largest at the peak of lactation. For healthy, well-fed cows, peak daily yields of between 1.4 and 1.8 kg MS/cow can be expected from OAD cows, whereas 1.8 to 2.2 kg MS/cow daily can be expected from TAD cows.
• Later in lactation the difference in daily yields between OAD and TAD cows is smaller.
• This effectively “flattens” the lactation curve of OAD cows when compared with TAD cows, an effect that may bring extra payment from Fonterra.

• Kg MS per cow and per hectare usually decrease in the first one or two years on OAD. Subsequently, production levels increase again, to be close to or even equal with their previous yields on TAD, after cows that do not suit OAD have been culled.
• Any reduction in Kg MS produced will reduce profit, unless expenditure is also reduced sufficiently to reduce $ costs/kg MS.
• Apart from lower yields of MS initially, and generally slightly higher SCC, all other aspects of performance per cow are improved by OAD (better BCS and fertility; more compact calving; reduced lameness; lower replacement rates possible).
• Farm data, for 2005/06 and for 2011/12, show that farms using OAD systems can be productive and profitable (see tables 1 and 3 in Appendix 1).
• All OAD farmers emphasise the value of the reduced stresses experienced in OAD milking systems. These benefit people and cows, including the employment and retention of good staff, and greater longevity of cows. OAD systems produce more MS per unit of work and stress!
• The genetic merit of cows for OAD will improve slowly, as cows that do not suit OAD are culled from the OAD herds, and High BW replacement heifers are included.

But in 2014, the High BW sires of these heifers have not been identified or proven specifically in OAD herds. This deficiency limits the rate of genetic progress in OAD herds when compared with TAD herds. However, the OAD BW now includes more data from cows milked in OAD herds, increasing its accuracy and reliability.