Early lactation pasture allowance and duration: the effect on yield of milk fat and protein

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Early lactation pasture allowance and duration: the effect on yield of milk fat and protein

E. Kennedy, Luc Delaby, J. Roche, Brendan Horan, E. Lewis

To cite this version:

E. Kennedy, Luc Delaby, J. Roche, Brendan Horan, E. Lewis. Early lactation pasture allowance and

duration: the effect on yield of milk fat and protein. 26. General meeting of the European Grassland

Federation (EGF), Sep 2016, Trondheim, Norway. �hal-02741532�

Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy 403

Early lactation pasture allowance and duration: the effect on yield of milk fat and protein

Kennedy E. ¹ , Delaby L. ³ , Roche J. ² , Horan B. ¹ and Lewis E. ¹

1 Teagasc, Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland;

2 Down to Earth Advice Ltd, P.O. Box 12520, Chartwell, Hamilton, New Zealand; ³ INRA, AgroCampus Ouest, UMR Pegase, 35590 Saint-Gilles, France; emer.kennedy@teagasc.ie

Abstract

Early spring pasture growth can be low, resulting in a pasture availability deficit. The objective of this experiment was to investigate if different pasture allowances offered to early lactation grazing dairy cows for varying time durations influenced yield of milk fat and protein. The two year experiment offered cows one of four pasture allowances (PA; 60, 80, 100 or 120% of intake capacity) for either 2 or 6 weeks.

Once the 2- and 6-week time durations had elapsed, the treatments were offered 100% of intake capacity.

During the first 2 weeks of the experiment yield of milk fat and protein increased linearly with increasing PA (1.73, 1.77, 1.84 and 1.98 kg cow ^-1 day ^-1 ; 60, 80, 100 and 120% PA, respectively). At the end of the 6 weeks there was an effect of the interaction between pasture allowance and duration on yield of milk fat and protein on milk solids yield. All 2-week cows had similar cumulative milk yields for the first 6 weeks of the experiment (78 kg); although they were similar to the 100x6 cows they were different to all other 6-week treatments. The 60 and 80% 6-week cows produced similar yields of milk fat and protein to each other (70 kg), but lower than the 100 and 120% 6-week cows, who differed significantly from each other (80 and 87 kg, respectively). This suggests that in early lactation the effect of PA yield of milk fat and protein depends on the severity and duration of the reduction in feed allowance.

Keywords: pasture allowance, early lactation, dairy cow

Introduction

Low over-winter pasture growth in Ireland (Hurtado-Uria et al., 2013) can result in low pasture availability during early spring, which is a challenge in intensive grazing systems. In anticipation of quota removal in 2015 Irish herd sizes started to increase and it is envisaged that this increase will continue.

As land is frequently limited stocking rates on farms have increased, which may further exacerbate the problem of low pasture availability in spring. Restricting pasture allowance (PA), by altering post-grazing height, for a ten-week period in early lactation has previously been shown to reduce immediate milk production but cumulative milk production was unaffected (Ganche et al., 2013). The objective of this experiment was to investigate if different PA offered for varying time durations to grazing dairy cows during early lactation influenced yield of milk fat and protein.

Materials and methods

The study was carried out over a two year period; from March 25 to November 27, 2014 and March 9 to November 23, 2015. Each year 96 dairy cows (41 primiparous and 55 multiparous in year one (Y1); 24 primiparous and 72 multiparous in year two (Y2)) were assigned to a randomised complete block design with a 4×2 factorial arrangement of treatments. Cows were balanced on calving date, breed, lactation number and production variables from the two weeks prior to the start of the experiment. Cows were then randomly assigned to one of four PA (60, 80, 100 or 120% of intake capacity; IC) for either 2 or 6 weeks. Once the 2- and 6-week time durations had elapsed, the treatments were offered 100% of IC. Intake capacity was calculated using the equation of Faverdin et al. (2011) based on age, parity, days in milk, bodyweight (BW), body condition score (BCS) and potential milk yield. Pastures were

>80% perennial ryegrass. Fresh pasture areas were offered after each milking while treatments were being

404 Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy imposed and on a 24-hour basis thereafter. Pre- and post-grazing sward heights were measured daily using a rising plate meter. Herbage mass (HM; >3.5 cm) was measured twice weekly by cutting 6 strips (120 m ² ) per grazing area. Treatment groups grazed adjacent to each other to ensure similar HM was offered. Pasture allowance (>3.5 cm) for the 60, 80 and 120% treatments were calculated based on the IC of the 100×6 treatment. As HM was similar between treatments daily area allocations were different between treatments. Milk yield was recorded daily and milk composition was measured weekly. Data were analysed using covariate analysis and mixed models in SAS v9.3. Terms for year, parity, breed, PA, duration and the interaction of PA and duration were included. Pre-experimental values were used as covariates in the model.

Results and discussion

The mean PA for the 60, 80, 100 and 120% treatments for weeks 1 and 2 were 8.0, 10.7, 13.4 and 16.0 kg DM cow ^-1 day ^-1 , respectively (P<0.001). This resulted in post-grazing heights (PGH) of 2.4, 2.9, 3.5 and 4.1 cm, respectively (P<0.001). The mean PA and PGH during weeks 3-6 were 9.1, 12.1, 15.1, 18.2 kg DM cow ^-1 day ^-1 and 2.5, 3.1, 3.8, 4.3 cm for the 60, 80, 100 and 120% 6-week treatments. Pasture allowance and PGH for the 2-week treatment, which was grazed as a single herd during weeks 3-6, were 14.8 kg DM ha ^-1 and 3.7 cm, respectively.

There was no effect of duration or breed on yield of milk fat and protein during the first two weeks of the experiment, there was an effect of year as production was higher in the second year of the study due to a more mature herd profile. During the first 2 weeks of the experiment there was a linear increase with increasing PA (1.73, 1.77, 1.84 and 1.98 kg cow ^-1 day ^-1 ; 60, 80, 100 and 120% PA, respectively; Table 1).

There was a significant effect of the interaction between PA and duration on yield of milk fat and protein during weeks 3-6 (P<0.001). Average daily yield of milk fat and protein during this period was similar for the 2-week treatments (1.86 kg cow ^-1 day ^-1 ) indicating no carryover effect of PA offered during the first two weeks of the experiment. Although the two-week treatments were similar to the 100×6 cows they were different to all other 6-week treatments. As expected, because of PA treatments still being imposed, there were differences among the 6-week treatments. The 60×6 and 80×6 treatments had similar yield of milk fat and protein to each other (1.66 kg cow ^-1 day ^-1 ), but were lower than the 100×6 (1.91 kg cow ^-1 day ^-1 ) and 120×6 (2.08 kg cow ^-1 day ^-1 ) treatments, which were significantly different to each other.

There was a significant effect of the interaction between PA and duration on the cumulative yield of milk fat and protein for the first six weeks of the experiment (P<0.001). Six week cumulative yield of milk fat and protein was similar for all 2-week treatments (78 kg cow ^-1 ) and they were similar to the 100×6 cows (80 kg cow ^-1 ) but different to all other six-week treatments. The 60x6 and 80×6 were similar (70 kg cow ^-

1 ) but lower than the 100×6 and 120×6 (87 kg cow ^-1 ), which also differed from each other (P<0.01).

Table 1. Yield of milk fat and protein of early lactation dairy cows offered 1 of 4 pasture allowances for either 2 or 6 weeks. ^1,2

Treatments Significance

60×2 80×2 100×2 120×2 60×6 80×6 100×6 120×6 SED PA D PA×D Brd Wks 1 and 2 (kg d

) 1.75 1.78 1.82 1.95 1.72 1.76 1.86 2.02 0.045 0.001 0.624 0.630 0.840 Wks 3 to 6 (kg d

) 1.84

1.86

1.82

1.92

1.62

1.70

1.91

2.08

0.042 0.001 0.241 0.001 0.557 Cumulative wks 1-6 (kg cow

) 76

77

77

80

68

71

80

87

1.8 0.001 0.362 0.001 0.670 Cumulative 33 wks (kg cow

) 351

338

323

343

329

340

344

374

10.3 0.104 0.250 0.064 0.530

1

Pasture allowance (PA) 60%, 80%, 100% or 120% of intake capacity; D = duration; SED = standard error of the difference; Brd = breed;

2

Superscripts denote significant differences between treatments with regard to the PA×D interaction.

Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy 405 When cumulative yield of milk fat and protein production for the entire experimental period (33 weeks) was examined there was a tendency (P=0.064) for an interaction between PA and duration. The cows assigned to the 120×6 treatment tended to have a higher yield of milk fat and protein production when compared to all other treatments. No differences were observed between any of the other treatments.

Conclusions

Although early lactation yield of milk fat and protein is reduced when PA is restricted there is little effect when cumulative lactation yield of milk fat and protein is considered compared to cows offered 80% or 100% of IC, however offering 120% of IC for six weeks in early lactation tended to increase yield of milk fat and protein. All other variables such as cow BW and BCS and fertility need to be considered in order to obtain a complete picture of the residual effects of altering PA in early lactation.

Acknowledgements

The authors wish to thank the Moorepark farm staff and technicians for their care of the experimental animals and assistance with experimental measurements. This experiment was funded by Teagasc Core Funding and the Irish Dairy Levy.

References

Faverdin P., Baratte C., Delagarde R., and Peyraud J.L. (2011) GrazeIn: a model of herbage intake and milk production for grazing dairy cows. 1. Prediction of intake capacity, voluntary intake and milk production during lactation. Grass and Forage Science 66, 29-44.

Ganche E., Delaby L., O’Donovan M., Boland T.M., and Kennedy E. (2013) Direct and carryover effect of post-grazing sward height on total lactation dairy cow performance. Animal 7, 1390-1400.

Hurtado-Uria C., Hennessy D., Shalloo L., Schulte R.P.O., Delaby L., and O’Connor D. (2013) Evaluation of three grass growth

models to predict grass growth in Ireland. The Journal of Agricultural Science 151, 91-104.