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Animal Nutrition and Farm Systems Review Symposium Review|Articles in Press

A review of once-a-day milking in dairy cow grazing systems

Open AccessPublished:February 09, 2023DOI:https://doi.org/10.3168/jdsc.2022-0293
A review of once-a-day milking in dairy cow grazing systems
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      Highlights

      • •
        Milking OAD during the whole lactation is practiced in about 10% of New Zealand herds.
      • •
        A OAD milking production system reduces milk production per cow, but improves cow fertility and quality of life for the farmer and farm staff.
      • •
        Cows suitable for OAD can be produced by sires selected on a OAD selection index.

      Abstract

      Twice-a-day (TAD) milking during the whole lactation is practiced in about 55% of New Zealand herds and once-a-day (OAD) milking during the whole lactation in about 10% of herds. The remainder of farmers use a mixture of TAD and OAD. Results from long-term comparisons show that over a full-lactation cows milked OAD, on average, had lower yields of milk (27%), fat (23%), and protein (24%) and higher percentages of fat and protein than cows milked TAD, but cows milked OAD for the entire lactation had better reproductive performance. Herds of cows milked OAD have higher mean 3-wk submission rate, 6-wk in-calf rate, and conception to the first service, and lower not-in-calf rate than the herds of cows milked TAD for the entire lactation. Farmers that have adopted OAD milking have culled cows that are unsuitable for OAD, and used sires selected on a OAD selection index to produce cow replacements that are more suitable for OAD milking. This OAD index includes the same traits that are included in the New Zealand national selection index with different relative economic weights on these traits plus including udder support, front teat placement, milking speed, and body capacity. A pasture-based milk production system based on OAD can be an alternative for many dairy farmers to maintain or increase farm profitability, with the additional benefits of better cow fertility and flexibility of using labor.

      Graphical Abstract

      Figure thumbnail fx1
      Graphical AbstractSummary: Once-a-day (OAD) milking during the whole lactation is practiced in about 10% of New Zealand herds, and there are also farmers milking OAD in Ireland and Australia. This study provided an updated review on OAD milking in dairy grazing systems. Cows milked OAD for the entire lactation had lower yields of milk, fat, and protein than cows milked TAD, but cows milked OAD had better reproductive performance. The main reasons for farmers adopting OAD milking production systems are improvement of quality of life for the farmer and farm staff, reduction of farm costs, and improvement of cow fertility and animal welfare. Farmers can increase farm productivity and profitability by culling cows not suitable for OAD and producing heifer replacements from the best cows for OAD mated to bulls selected on a OAD selection index.
      Dairy farming in New Zealand is pasture based with most cows calving in spring. Twice-a-day (TAD) milking during the whole lactation is practiced in about 55% of New Zealand herds and once-a-day (OAD) during the whole lactation in about 10% of herds, with the remainder of the farmers using a mixture of TAD and OAD (
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      ).
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      Livest. Prod. Sci. 1999; 59: 77-94
      https://doi.org/10.1016/S0301-6226(98)00204-8
      summarized short-term experiments comparing OAD and TAD and found that cows milked OAD produced, on average, 13% less milk than cows milked TAD.
      • Rémond B.
      • Pomiès D.
      Once-daily milking of dairy cows: A review of recent French experiments.
      Anim. Res. 2005; 54: 427-442
      https://doi.org/10.1051/animres:2005040
      summarized experiments carried out in France and found that milk yield was reduced by 25% when cows were milked OAD for periods ranging from a few days to 2 to 3 mo, but milk losses and health hazards were higher when cows were milked OAD during the entire lactation period.
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Once-daily milking of dairy cows: An appraisal.
      Proc. N.Z. Soc. Anim. Prod. 1998; 58: 36-40
      and
      • Rémond B.
      • Pomiès D.
      Once-daily milking of dairy cows: A review of recent French experiments.
      Anim. Res. 2005; 54: 427-442
      https://doi.org/10.1051/animres:2005040
      identified individual differences in milk losses and suggested that there is an opportunity for selecting cows that are tolerant to OAD milking.
      • Stelwagen K.
      • Phyn C.V.C.
      • Davis S.R.
      • Guinard-Flament J.
      • Pomiès D.
      • Roche J.R.
      • Kay J.K.
      Invited review: Reduced milking frequency: Milk production and management implications.
      J. Dairy Sci. 2013; 96 (23548302): 3401-3413
      https://doi.org/10.3168/jds.2012-6074
      did a more extensive review on OAD miking considering short-, medium-, and long-term effects on OAD on milk production, milk composition and processability characteristics, energy balance, reproductive performance, and health and welfare of dairy cows. They reported that OAD milking reduces milk yield by approximately 22%, depending on stage of lactation, breed, and parity, and it may adversely affect lactation length and persistency. One conclusion of that study was that OAD milking fits well with more extensive dairy production systems, particularly those based on grazed pasture. The objective of the present study was to provide an updated review on OAD milking in dairy grazing systems, with focus on OAD as a production system; that is, milking cows OAD during the whole lactation and over multiple lactations.
      A summary of results from studies evaluating the effect of OAD during the whole lactation is presented in Table 1. The experiment of
      • Claesson O.
      • Hansson A.
      • Gustafsson N.
      • Brännäng E.
      Studies on monozygous cattle twins. XVII. Once-a-day milking compared with twice-a-day milking.
      Acta Agriculturae Scandinavica. 1959; 9: 38-58
      https://doi.org/10.1080/00015125909433307
      with twin cows in Sweden found that the average milk yield of cows milked OAD was reduced by about 50% in the first lactation and by about 40% in the second lactation in comparison with their twins milked TAD. A similar experiment carried out by
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      in New Zealand with few cows showed that cows milked OAD produced less milk, fat, protein, and lactose per cow than cows milked TAD.
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      Anim. Res. 2004; 53: 201-212
      https://doi.org/10.1051/animres:2004014
      reported that cows milked OAD produced less milk with higher concentrations of fat and protein with no differences in lactose concentration and SCC and were milked for 12 d fewer, compared with cows milked TAD. The trials conducted in New Zealand by
      • Cooper C.V.
      • Clark D.A.
      Once-a-day milking systems to improve productivity.
      Aust. J. Dairy Technol. 2001; 56: 181
      ,
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      , and
      • Dalley D.E.
      • Clough J.W.
      • Hofman L.A.
      • Phyn C.V.C.
      • Clark D.A.
      Jersey cows milked once-a-day can produce 1200 kg milk solids per hectare.
      Proc. N.Z. Soc. Anim. Prod. 2008; 68: 96-97
      found that cows milked OAD produced less milk (19 to 31%) and milk solids (fat plus protein) per cow (14 to 30%) than their TAD counterparts. Jersey (J) cows were less affected by OAD than Holstein-Friesian (F) and crossbred Holstein-Friesian × Jersey (F × J) cows. Milk per hectare was less for the OAD than TAD counterparts because the greater stocking rate for the OAD herds did not fully compensate for the milk loss per cow. Recent analyses of commercial herds by
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      showed that F × J crossbred and J cows were less affected than F cows by OAD milking with a reduction in yield traits of 19.0%, whereas in F cows the reduction ranged between 19% to 25%.
      • Jayawardana J.M.D.R.
      • Lopez-Villalobos N.
      • McNaughton L.R.
      • Hickson R.E.
      Fertility of dairy cows milked once a day or twice a day in New Zealand.
      J. Dairy Sci. 2022; 105 (36153161): 8911-8923
      https://doi.org/10.3168/jds.2021-20946
      reported levels of milk production for both TAD and OAD herds that were higher than those reported by
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      and that cows in OAD herds produced less milk solids than cows in TAD herds. The reduction of milk production in OAD milking is hypothesized to be the result of a combination of acute and long-term alterations in mammary functions of OAD milking cows.
      Table 1Mean values for lactation yields of milk, fat, protein, lactose, and milk solids (kilograms of fat and protein) from dairy cows milked once a day (OAD) or twice a day (TAD) during the whole lactation
      StudyYears of studyBreed
      SRW = Swedish Red and White; F = Holstein-Friesian; J = Jersey and F × J = crossbred Holstein-Friesian × Jersey.
      		Milking frequencyDIMMilk (kg/cow)Fat (kg/cow)Protein (kg/cow)Lactose (kg/cow)Milk solids (kg/cow)Milk solids (kg/ha)
      • Claesson O.
      • Hansson A.
      • Gustafsson N.
      • Brännäng E.
      Studies on monozygous cattle twins. XVII. Once-a-day milking compared with twice-a-day milking.
      Acta Agriculturae Scandinavica. 1959; 9: 38-58
      https://doi.org/10.1080/00015125909433307
      		1SRWTAD2803,525140121182261
      OAD2801,792736490137
      Δ (%)−49−48−47−51−47
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      		1TAD2534,320208162217370
      OAD2512,810144110136254
      Δ (%)−1−35−31−32−37−31
      • Cooper C.V.
      • Clark D.A.
      Once-a-day milking systems to improve productivity.
      Aust. J. Dairy Technol. 2001; 56: 181
      		1F × JTAD2693,543177131171307922
      OAD2552,42712293115215753
      Δ (%)−5−31−31−29−33−30−18
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      Anim. Res. 2004; 53: 201-212
      https://doi.org/10.1051/animres:2004014
      		1HolsteinTAD3057,323315225342540
      OAD2935,114236167234403
      Δ (%)−4−30−25−26−32−25
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      		4FTAD2444,2341871492053361,051
      OAD2302,914131106138237879
      Δ (%)−6−31−30−29−33−29−16
      JTAD2422,8391621161412781,045
      OAD2292,21112994107222979
      Δ (%)−5−22−20−19−24−20−6
      • Dalley D.E.
      • Clough J.W.
      • Hofman L.A.
      • Phyn C.V.C.
      • Clark D.A.
      Jersey cows milked once-a-day can produce 1200 kg milk solids per hectare.
      Proc. N.Z. Soc. Anim. Prod. 2008; 68: 96-97
      		3JTAD/OAD2743,1961891363251,277
      OAD2692,5921631172801,219
      Δ (%)−2−19−14−14−14−5
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      		1FTAD2756,013240198274438
      OAD2754,437195157201352
      Δ (%)−26−19−21−27−20
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      		5FTAD3,824167137304
      OAD2,879136109244
      Δ (%)−25−19−20−20
      F × JTAD3,446169131300
      OAD2,787143110254
      Δ (%)−19−15−16−15
      JTAD2,929162119281
      OAD2,427137101239
      Δ (%)−17−15−15−15
      • Jayawardana J.M.D.R.
      • Lopez-Villalobos N.
      • McNaughton L.R.
      • Hickson R.E.
      Fertility of dairy cows milked once a day or twice a day in New Zealand.
      J. Dairy Sci. 2022; 105 (36153161): 8911-8923
      https://doi.org/10.3168/jds.2021-20946
      		1F, F × J, and JTAD4,860231186243417
      OAD3,201169131158300
      Δ (%)−34−27−30−35−28
      1 SRW = Swedish Red and White; F = Holstein-Friesian; J = Jersey and F × J = crossbred Holstein-Friesian × Jersey.
      Research on the effect of OAD milking on cow fertility has been limited. Few studies have reported differences of reproductive performance between cows milked OAD and TAD during the entire lactation (Table 2).
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      reported that cows milked OAD conceived 3 d earlier and took 5 d less from calving to conception than cows milked TAD. Compared with herds milked TAD, herds milked OAD had a higher (7.3%) percentage of cows inseminated in the first 21 d from the start of mating (SR21), and a higher percentage of cows that conceived in the first 21 d from the start of mating (PR21).
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      used data from commercial herds and found that percentages of cows that calved in the first 3 wk (CR21) and 6 wk (CR42) of the subsequent calving season were 5.0% higher in herds milked OAD compared with herds milked TAD.
      • Hemming N.V.
      • McNaughton L.R.
      • Couldrey C.
      Brief Communication: Reproductive performance of herds milked once a day all season compared with herds milked twice a day all season.
      N. Z. J. Anim. Sci. Prod. 2018; 78: 170-172
      also found that herds milked OAD had better fertility performance; a 7.7% higher mean SR21, 7.9% higher mean conception to first service, 10.4% higher mean PR42, 4.8% overall pregnancy rate, and 4.3% higher CR42 than TAD milking herds. The same trends were reported by
      • Jayawardana J.M.D.R.
      • Lopez-Villalobos N.
      • McNaughton L.R.
      • Hickson R.E.
      Fertility of dairy cows milked once a day or twice a day in New Zealand.
      J. Dairy Sci. 2022; 105 (36153161): 8911-8923
      https://doi.org/10.3168/jds.2021-20946
      and they reported that the intervals from start of mating to first service and start of mating to conception were significantly shorter in cows milked OAD compared with TAD.
      Table 2Mean values for reproductive performance traits
      SMCO = start of mating to conception (d); SR21 = cows inseminated in the first 21 d from the start of mating; PR21 = cows conceived in the first 21 d from the start of mating; PR42 = cows conceived in the first 42 d from the start of mating; PRFS = cows that conceived to their first service; OPR = overall pregnancy rate at end of the breeding season; CR21 = cows that calved in the first 21 d from the planned start of the calving; CR42 = cows that calved in the first 42 d from the planned start of the calving.
      from dairy cows milked once a day (OAD) or twice a day (TAD) during the whole lactation
      StudyYears of studyBreed
      F = Holstein-Friesian; J = Jersey; and F × J = crossbred Holstein-Friesian × Jersey.
      		Milking frequencySMCOSR21PR21PRFSPR42OPRCR21CR42
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      		4FTAD28.279.337.467.3
      OAD26.189.741.869.8
      Δ (%)−713124
      JTAD28.490.139.367.6
      OAD23.894.450.475.1
      Δ (%)−1652811
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      		1FTAD635073
      OAD734090
      Δ (%)16−2023
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      		8F, F × J, and JTAD5982
      OAD6487
      Δ (%)86
      • Hemming N.V.
      • McNaughton L.R.
      • Couldrey C.
      Brief Communication: Reproductive performance of herds milked once a day all season compared with herds milked twice a day all season.
      N. Z. J. Anim. Sci. Prod. 2018; 78: 170-172
      		 3F, F × J, and JTAD76.964.482.483.9
      OAD84.674.887.288.2
      Δ (%)101665
      • Jayawardana J.M.D.R.
      • Lopez-Villalobos N.
      • McNaughton L.R.
      • Hickson R.E.
      Fertility of dairy cows milked once a day or twice a day in New Zealand.
      J. Dairy Sci. 2022; 105 (36153161): 8911-8923
      https://doi.org/10.3168/jds.2021-20946
      		 1F, F × J, and JTAD2777.846.454.167.485.85982.4
      OAD21.983.856.362.875.990.165.687.7
      Δ (%)−1982116135116
      1 SMCO = start of mating to conception (d); SR21 = cows inseminated in the first 21 d from the start of mating; PR21 = cows conceived in the first 21 d from the start of mating; PR42 = cows conceived in the first 42 d from the start of mating; PRFS = cows that conceived to their first service; OPR = overall pregnancy rate at end of the breeding season; CR21 = cows that calved in the first 21 d from the planned start of the calving; CR42 = cows that calved in the first 42 d from the planned start of the calving.
      2 F = Holstein-Friesian; J = Jersey; and F × J = crossbred Holstein-Friesian × Jersey.
      The overall results indicate that cows milked OAD have better reproductive performance than cows milked TAD. Cows milked OAD are inseminated earlier, become pregnant sooner in the mating season, and calve earlier in the next season than cows milked TAD. The reduced negative energy balance during the early lactation is hypothesized to be the reason for the improved reproductive performances of OAD milking cows than the TAD milking cows (
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      ).
      A limited number of studies have reported the long-term effect of OAD milking on incidence of metabolic disorders, clinical mastitis, and lameness.
      • O'Driscoll K.
      • Gleeson D.
      • O'Brien B.
      • Boyle L.
      Effect of milking frequency and nutritional level on hoof health, locomotion score and lying behaviour of dairy cows.
      Livest. Sci. 2010; 127: 248-256
      https://doi.org/10.1016/j.livsci.2009.10.006
      evaluated the effect of milking frequency (OAD vs. TAD) at 2 nutritional levels on hoof health, locomotion, and lying behavior of cows. Cows milked OAD had lower sole lesion and white line disease scores, but higher heel erosion scores than cows milked TAD. There was an interaction between stage of lactation and milking frequency; cows milked OAD had higher overall locomotion scores than TAD cows, but this was reversed later in lactation. The conclusion of this study was that in general OAD milking resulted in improvements to hoof health and locomotion ability.
      Long-term effects of OAD milking on SCC and clinical mastitis were reported in some studies (
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      ;
      • Lacy-Hulbert S.J.
      • Dalley D.E.
      • Clark D.A.
      The effects of once a day milking on mastitis and somatic cell count.
      Proc. N.Z. Soc. Anim. Prod. 2005; 65: 137-142
      ;
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      ). In the study by
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      with only 12 cows per milking frequency, SCC were significantly lower for the TAD milking group throughout lactation, even though there appeared to be no difference in the incidence of infection measured at the end of lactation.
      • Lacy-Hulbert S.J.
      • Dalley D.E.
      • Clark D.A.
      The effects of once a day milking on mastitis and somatic cell count.
      Proc. N.Z. Soc. Anim. Prod. 2005; 65: 137-142
      reported the effect of OAD milking for complete lactations on mastitis and milk quality. Prevalence of IMI was not significantly or consistently higher for cows milked OAD compared with TAD. The SCC for uninfected cows milked OAD was approximately double that for TAD milked cows, although this difference was only significant after the first 1 to 2 mo of lactation had elapsed. Cows with minor or major pathogen infections also showed an approximate doubling of the SCC if milked OAD. The conclusion of this 4-yr study was that milking OAD consistently increases the individual cow SCC but does not significantly increase prevalence of clinical mastitis.
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      analyzed herd-test records from commercial herds and confirmed no significant differences for SCS between herds that have adopted OAD and TAD milking for the entire lactation. It seems that once the cows and farmers adapt into OAD milking under grazing conditions with low levels of production, udder health is not affected.
      Information about greenhouse gas (GHG) emissions in OAD milking systems is scarce, and this area needs further research. Greenhouse gas emissions can be evaluated in 2 ways, either looking at the total emissions of a farm or looking at the emissions per unit of product produced (efficiency). The impact of OAD milking on greenhouse gas emissions depends on which metric is used. In terms of efficiency per unit of product OAD milking would be expected to lead to higher emissions per unit of product, due to the negative impact of OAD milking on milk production. The impact of OAD milking production systems on total farm GHG emissions was evaluated by the Biological Emissions Reference Group (
      • Reisinger A.
      • Clark H.
      • Abercrombie R.
      • Aspin M.
      • Ettema P.
      • Harris M.
      • Hoggard A.
      • Newman M.
      • Sneath G.
      Future options to reduce biological GHG emissions on-farm: Critical assumptions and national-scale impact.
      New Zealand Agricultural Greenhouse Gas Research Centre, Palmerston North2018
      https://www.mpi.govt.nz/dmsdocument/32128/direct
      ) as a strategy to reduce biological GHG emissions. The Biological Emissions Reference Group concluded that from a climate change perspective, a OAD milking production system would reduce GHG emissions of the farm by 5% only to the extent that animals consume less feed, due to lower overall milk production. However, a life cycle assessment is required to comprehensively assess the full impact of OAD compared with TAD milking systems on carbon footprint at a farm and product level. The Biological Emissions Reference Group (
      • Reisinger A.
      • Clark H.
      • Abercrombie R.
      • Aspin M.
      • Ettema P.
      • Harris M.
      • Hoggard A.
      • Newman M.
      • Sneath G.
      Future options to reduce biological GHG emissions on-farm: Critical assumptions and national-scale impact.
      New Zealand Agricultural Greenhouse Gas Research Centre, Palmerston North2018
      https://www.mpi.govt.nz/dmsdocument/32128/direct
      ) indicated that apart from reduced feed demand as a result of lower milk production, OAD also has other impacts on the environment, for example, electricity savings from one less milking per day, reduced cowshed effluent, less water used for wash-down, less vehicle running for bringing the cows in, and fewer tanker loads of milk transported on the road. However, milking cows OAD means the cows will spend longer in the paddock, resulting in urine being deposited directly on pasture, which may limit the indirect emission benefits and reduces options to manage manure emissions and nitrate leaching. There are also complex interactions between genetic merit of the cows, stocking rate, reproductive performance of the herd, and cow longevity that affect milk solids production per cow and hectare with consequent effects on productivity, profitability, and GHG emissions of the production system. These need to be considered in a lifecycle analysis.
      Few studies have reported on farm profitability of OAD milking compared with TAD milking systems.
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      performed an economic evaluation of TAD and OAD milking using data generated from a trial comparing OAD and TAD at 2 nutritional levels. The stocking rates of the OAD groups were increased to produce the same amount of fat supplied by the farm under the milk quota system imposed by the European Union at that time. The results showed that farm profit was reduced for OAD compared with TAD milking by 24% and 59% at the high and low nutritional levels, respectively. This reduction was caused by reductions in milk revenue and increases in total costs. The same authors performed simulation scenarios and concluded that OAD will only suit the goals of some dairy farmers, creating flexibility on the use and requirement for labor.
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      analyzed commercial herds that have adopted full-lactation OAD. On average, there was an 11% decrease in total farm milk solids production, but after 3 yr of OAD milking, production reached previous TAD production. The decrease in total farm milk solids production was influenced by the pre-OAD level of milk solid production (kg of milk solids per cow), with a smaller effect of OAD in herds producing ≤300 kg of milk solids per cow and a greater effect in herds producing 351 to 400 kg of milk solids per cow. Further economic analysis (
      • Edwards J.P.
      A comparison of profitability between farms that milk once or twice a day.
      Anim. Prod. Sci. 2018; 60: 102-106
      https://doi.org/10.1071/AN18528
      ) reported average milk solids production per hectare decreased by 13% after adopting OAD; however, farm working expenses per hectare did not decrease, resulting in a decrease in profitability per hectare. Further analysis of a subset of 33 OAD herds, with at least one season of pre-OAD data, grouped into quartiles on the basis of their pre-OAD labor efficiency, indicated that operating profit per hectare of quartile 1 (least efficient) increased by 23% after adopting OAD, with quartile 2, 3, and 4 decreasing by 1%, 10%, and 32%, respectively. Quartile 1 herds had the largest increase in cows per full-time equivalent, highlighting the importance of labor efficiency and cost reduction to profit when milking OAD. The author indicated that profitability can be maintained or increased after adopting OAD. In agreement with
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      and
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      ,
      • Edwards J.P.
      A comparison of profitability between farms that milk once or twice a day.
      Anim. Prod. Sci. 2018; 60: 102-106
      https://doi.org/10.1071/AN18528
      ), the decision to change from TAD to OAD milking requires a calculation of the trade-off between economic and lifestyle goals. The balance of the economic factors associated with OAD milking, such as lower milk production, labor requirement, potentially lower health costs associated with improvement on lameness and fertility, and better use of capital investments on the farm, must be set against the increased flexibility and time saving that may be achieved with OAD milking.
      Dairy farming is a labor-intensive industry, with the milking process taking 43–58% of a standard 40-h week on TAD farms (
      • Edwards J.P.
      • Kuhn-Sherlock B.
      • Dela Rue B.T.
      • Eastwood C.R.
      Short communication: Technologies and milking practices that reduce hours of work and increase flexibility through milking efficiency in pasture-based dairy farm systems.
      J. Dairy Sci. 2020; 103 (32505396): 7172-7179
      https://doi.org/10.3168/jds.2019-17941
      ). Milking OAD allows farmers to significantly reduce time spent in the cowshed (18–35% of a standard 40-h week). Farmers cite several benefits from changing to OAD milking. These include ease of attracting labor, reducing labor costs, an alternative option when feed shortfalls occur, herd expansion, allowing time to build capital, utilizing farmland with hilly terrain or long walking distances, and herd health and management (
      • Bewsell D.
      • Clark D.A.
      • Dalley D.E.
      Understanding motivations to adopt once-a-day milking amongst New Zealand dairy farmers.
      J. Agric. Educ. Ext. 2008; 14: 69-80
      https://doi.org/10.1080/13892240701820611
      ). The number of farmers practicing OAD milking as system was about 200 in Ireland in 2021 (
      • Teagasc
      Once a Day Milking Conference 2021.
      https://www.teagasc.ie/news–events/national-events/events/oad-conference.php
      Date: 2021
      Date accessed: June 6, 2022
      ) and 631 in New Zealand in 2015 (
      • Edwards J.P.
      Comparison of milk production and herd characteristics in New Zealand herds milked once or twice a day.
      Anim. Prod. Sci. 2018; 59: 570-580
      https://doi.org/10.1071/AN17484
      ). However, the evidence provided by dairy farmers that have adopted grazing systems in New Zealand, Ireland, and Australia supports the statement that “OAD is not for everyone, but it is an option” (
      • Millerick C.
      • Millerick L.
      Farmer perspective – Making the decision to go once a day, current performance and future plans for their 125 cow crossbred herd in Tipperary. 2020 OAD Conference.
      Teagasc, 2020
      https://www.teagasc.ie/media/website/publications/2020/Catherine-Millerick-Once-a-Day-Milking-Conference-2020.pdf
      Date accessed: May 29, 2022
      ; p. 15). Each farm system has unique factors that may increase or decrease that individual farm's suitability to OAD milking.
      All the experiments that have evaluated the effect of whole lactation OAD (
      • Claesson O.
      • Hansson A.
      • Gustafsson N.
      • Brännäng E.
      Studies on monozygous cattle twins. XVII. Once-a-day milking compared with twice-a-day milking.
      Acta Agriculturae Scandinavica. 1959; 9: 38-58
      https://doi.org/10.1080/00015125909433307
      ;
      • Holmes C.W.
      • Wilson G.F.
      • MacKenzie D.D.S.
      • Purchas J.
      The effects of milking once daily throughout lactation on the performance of dairy cows grazing on pasture.
      Proc. N.Z. Soc. Anim. Prod. 1992; 52: 13-16
      ;
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      Anim. Res. 2004; 53: 201-212
      https://doi.org/10.1051/animres:2004014
      ;
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      ;
      • O'Brien B.
      • Gleeson D.E.
      • Shalloo L.
      Evaluation of on-farm labour saving strategies for optimisation of herd size that could be managed by one operator. Project number 5521.
      Teagasc, Ireland2009
      https://t-stor.teagasc.ie/bitstream/handle/11019/828/O%27Brien%2CB-EOPR_5521.pdf?sequence=1&isAllowed=y
      Date accessed: October 12, 2022
      ) and the data set analyzed by
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      show individual variation in the response to OAD milking. This indicates that there are genetic opportunities to select more suitable cows for OAD milking. Similarly, the differences observed among breeds in OAD performance relative to that of TAD performance are indicative of a genetic basis for the variation in the OAD yield response (
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once-versus twice-daily milking of pastured dairy cows.
      J. Dairy Sci. 2006; 89 (16606757): 1854-1862
      https://doi.org/10.3168/jds.S0022-0302(06)72254-8
      ;
      • Lembeye F.
      • Lopez-Villalobos N.
      • Burke J.L.
      • Davis S.R.
      Estimation of genetic parameters for milk traits in cows milked once- or twice-daily in New Zealand.
      Livest. Sci. 2016; 185: 142-147
      https://doi.org/10.1016/j.livsci.2016.01.022
      ).
      On a physiological basis,
      • Stelwagen K.
      Effect of milking frequency on mammary functioning and shape of the lactation curve.
      J. Dairy Sci. 2001; 84: E204-E211
      https://doi.org/10.3168/jds.S0022-0302(01)70219-6
      proposed that milk yield is a function of the number of secretory cells present in the udder and the metabolic activity of these cells. Both of these processes, alone or in combination, determine the milk yield potential of the mammary gland.
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Once-daily milking of dairy cows: An appraisal.
      Proc. N.Z. Soc. Anim. Prod. 1998; 58: 36-40
      and
      • Stelwagen K.
      Effect of milking frequency on mammary functioning and shape of the lactation curve.
      J. Dairy Sci. 2001; 84: E204-E211
      https://doi.org/10.3168/jds.S0022-0302(01)70219-6
      concluded the short-term (i.e., weeks) effects of OAD on milk secretion are mediated via an up- or downregulation of cellular activity, whereas the long-term (i.e., months) effects are more likely related to changes in cell number.
      • Davis S.R.
      • Farr V.C.
      • Copeman P.J.A.
      • Carruthers V.R.
      • Knight C.H.
      • Stelwagen K.
      Partitioning of milk accumulation between cisternal and alveolar compartments of the bovine udder: Relationship to production loss during once daily milking.
      J. Dairy Res. 1998; 65 (9513051): 1-8
      https://doi.org/10.1017/S0022029997002562
      proposed the first insight on the anatomical differences in the mammary gland between cows that are more or less tolerant of OAD milking. They suggested that the ability of the alveolar compartment to drain into the cistern is an important parameter and offers a possible explanation for the observation that cows that store a smaller proportion of their milk in the mammary cisternal compartment have greater milk losses when milked OAD.
      Livestock Improvement Corporation (LIC) introduced a OAD index in 2003 for the genetic selection of cows and bulls as parents of cow replacements more suitable for OAD milking (
      • McPherson A.W.
      • Pryce J.E.
      • Winkelman A.M.
      The genetic improvement of cows for once-a-day (OAD) milking.
      in: The Once-a-Day Milking Conference, Hamilton, New Zealand. 2007: 44-48
      https://www.dairynz.co.nz/media/917742/8_the_genetic_improvement_of_cows_for_oad_milking.pdf
      Date accessed: May 29, 2022
      ). The OAD selection index was reviewed in 2019 (
      • LIC
      Once-a-day selection index.
      https://www.lic.co.nz/products-and-services/artificial-breeding/alpha/once-day-milking/
      Date: 2019
      Date accessed: May 29, 2022
      ). This new OAD selection index includes the same traits that are in the national selection index, with different relative emphasis, plus udder support, front teat placement, milking speed, and body capacity (Table 3).
      Table 3Relative emphasis of traits included in the national selection index (breeding worth) and the selection index for once-a-day milking (OAD SI) in New Zealand dairy cattle
      Trait1Breeding worthOAD SI
      Milk1211
      Fat2624
      Protein1720
      Live weight1210
      Fertility145
      SCS68
      Survival8
      BCS
      Milking speed5
      Capacity4
      Udder support11
      Front teat placement2
      Once-a-day milking has been adopted as a milk production system by a small proportion of farmers in Ireland, Australia, and New Zealand. A much higher proportion of farmers use OAD milking for a portion of the milking season. Reduction in milk production per cow is variable and depends on level of production of the herd (feeding level), breed, and individual variation, and some cows are only slightly affected. Individual variation in adaptability to OAD milking provides the opportunity to breed more suitable cows. There is now good evidence that herds that milk OAD have superior reproductive performance than herds milked TAD. Some farmers claim that by reducing operating costs and selecting the right cow for OAD, farm profitability can be maintained or increased after adopting OAD. Better herd fertility can create an opportunity to reduce replacement rate, reduce replacement costs, and increase rate of genetic gain of the herd. The benefits of OAD on the lifestyle and health of farmers needs to be considered in the economic evaluation of OAD production systems.

      Notes

      This study received no external funding.
      No animals were used in this review, and ethical approval for the use of animals was thus deemed unnecessary.
      The authors have not stated any conflicts of interest.

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      Article info

      Publication history

      Published online: February 09, 2023
      Accepted: November 6, 2022
      Received: June 21, 2022

      Publication stage

      In Press Corrected Proof

      Footnotes

      Presented as part of the Midwest Branch Symposium: Joint ADSA Midwest Branch/Forages and Pastures Symposium: Grazing to Improve Profitability of Midwest Dairy Farms held in June 2022 as part of the 2022 ADSA Annual Meeting.

      Identification

      DOI: https://doi.org/10.3168/jdsc.2022-0293

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