Meta-analysis of the impact of white clover inclusion on milk production of grazing dairy cows

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Meta-analysis of the impact of white clover inclusion on milk production of grazing dairy cows

M. Dineen, Luc Delaby, T.J. Gilliland, B. Mccarthy

To cite this version:

M. Dineen, Luc Delaby, T.J. Gilliland, B. Mccarthy. Meta-analysis of the impact of white clover

inclusion on milk production of grazing dairy cows. 26. General meeting of the European Grassland

Federation (EGF), Sep 2016, Trondheim, Norway. �hal-02743236�

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

Meta-analysis of the impact of white clover inclusion on milk production of grazing dairy cows

Dineen M.

, Delaby L.

, Gilliland T.

and McCarthy B.

1

Institute of Global Food Security, Queens University Belfast, Belfast, United Kingdom;

Teagasc, Grassland Science, Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, Co.

Cork, Ireland;

INRA, AgroCampus Ouest, UMR 1348, Physiologie, Environnement et Génétique pour l’Animal et les Systèmes d’Elevage, 35590 Saint-Gilles, France;

Agri-food Biosciences Institute, Plant testing Station, Crossnacreevy, Belfast, BT5 7QJ, United Kingdom; brian.mccarthy@teagasc.ie

Abstract

There is recent interest in the introduction of white clover (WC) in Ireland to improve the efficiency of pasture-based grazing systems. After a literature review, a meta-analysis was undertaken to investigate the effect of WC inclusion in perennial ryegrass swards on milk production. For analytical purposes two databases were created, containing 15 and 20 papers, respectively, published between 1985 and 2015.

Database one, contained experiments comparing milk production from cows that grazed on grass-only (GO) and grass-clover (GC) swards. Database two contained only experiments that had GC swards to investigate the impact of varying sward WC content on milk production. In database one, the mean WC content of the GC swards was 33.6%. Mean daily milk yield was greater (P<0.001) for cows that grazed on GC swards compared with GO swards (18.8 kg vs 17.6 kg, respectively). However, stocking rate and milk yield per hectare were reduced (P<0.05) for the GC swards. In conclusion, the inclusion of WC into perennial ryegrass swards increased milk yield per cow but reduced milk yield per hectare.

Keywords: meta-analysis, white clover, dairy cow, milk production, grazing

Introduction

There is increased demand for dairy products worldwide (Delgado, 2005), which is coupled with the realisation that consumers want dairy products that are produced in a sustainable and environmentally benign manner. Traditionally white clover (Trifolium repens L., WC) was included in perennial ryegrass (Lolium perenne L., PRG) swards as a means of improving sward nutritive value and reducing nitrogen (N) use. However, intensification in the use of cheap mineral N has resulted in a reduction in the use of WC. Forage legumes, and WC in particular, can make an important contribution to the sustainability of pasture-based ruminant production systems (Peyraud et al., 2009). Therefore, the interest in using forage legumes is increasing again because they offer opportunities for sustainable pasture-based production systems by (1) increasing pasture yield, (2) substituting inorganic N-fertiliser inputs with symbiotic N2 fixation, (3) mitigating and facilitating adaptation to climate change and (4) increasing the nutritive value of pasture and raising the efficiency of conversion of pasture to animal protein (Lüscher et al., 2014).

Therefore, the objective of this study was to quantify the milk production response associated with the introduction of WC into a PRG sward.

Materials and methods

An electronic literature search was undertaken to identify papers where the effect of WC inclusion on

milk production in lactating dairy cows was studied. Two separate databases were created. In database one,

papers were selected if they contained a comparison of milk production from lactating dairy cows grazing

PRG-WC (GC) swards against PRG only (GO) swards. Experimental characteristics required were

experiment length, stocking rate, grazing cow-days ha

, WC content of the sward and milk production

results per cow and/or per ha. In experiments where a sub-factor was studied (e.g. 2 supplementation

levels or 2 post-grazing heights) or multiple years of data were reported, comparisons of milk production

Grassland Science in Europe, Vol. 21 – The multiple roles of grassland in the European bioeconomy 395 from GC and GO swards conducted under similar experimental conditions were considered independent studies. If a treatment had sward WC content below 5% in an experiment, then it was considered as a GO treatment. Each comparison of milk production from GC and GO swards was allocated by an individual experimental code (study). Database one contained 15 papers and 43 comparisons of milk production from GC and GO swards published between 1985 and 2015. Data from database one was analysed using mixed models (PROC MIXED) in SAS version 9.3 (SAS institute, Cary, NC, USA).

Terms included in the model were treatment (GC and GO) and study effect, which represented the variance between studies not accounted for by the variables in the model, as described by Sauvant et al.

(2008). In database two, papers were selected if they contained milk production from lactating dairy cows grazing on GC swards with varying levels of WC content. Database two was constructed similarly to database one. Database two contained 20 papers and 87 data points of milk production from GC swards published between 1989 and 2015. Data from database two was also analysed using mixed models (PROC MIXED) in SAS. Terms included in the model were WC content and the study effect. Database two experiments reflect the variation in milk production as WC content increases in the sward.

Results and discussion

The mean experimental characteristics and milk production per cow and per ha for database one were;

number of cows: 49, stocking rate: 3.12 cows ha

, experiment length: 119 days, N application: 139 kg ha

, WC content: 17.1%, milk yield cow

: 18.2 kg and milk yield ha

: 7,876 kg. The average effect of introducing WC into a sward on experimental characteristics and milk production per cow and per ha for database one is presented in Table 1. Mean daily milk and milk solids (fat + protein) yield per cow were greater (P<0.001) by 1.2 and 0.1 kg cow

for cows that grazed on GC swards compared with GO swards. The presence of WC in the sward did not affect fat or protein content, however, lactose content was greater for cows that grazed on GC swards. Stocking rate was reduced by 0.29 cows ha

on the GC swards, and consequently, milk and milk solids yield per ha were reduced (P<0.05) by 431 and 35 kg ha

, respectively. The mean experimental characteristics and milk production per cow and per ha for database two were; number of cows: 49, stocking rate: 2.82 cows ha

, experiment length: 148 days, N application:

76 kg ha

, WC content: 24.8%, milk yield cow

: 19.2 kg and milk yield ha

: 10,544 kg. The equations

that accounted for the greatest proportion of variation in predicted milk production per cow and per ha

according to WC content were linear, with the exception of milk solids yield and protein content per cow

and milk and milk solids yield per ha, which were quadratic (results not shown). The residual standard

error was low for milk yield (0.95), which indicates a good precision of the predictive equations. On the

basis of the predictive equations, a 10% increase in sward WC content resulted in a mean proportional

increase of 1.46 and 0.97% for daily milk and milk solids yield, respectively, whereas milk and milk solids

yield per ha were reduced by 15.3 and 12.0%, respectively. This is in accordance with Harris et al. (1997)

who stated that as sward WC content increased, daily milk yield per cow also increased. Within grazing

systems, stocking rate, milk yield per cow and milk yield per ha are closely linked (McCarthy et al.,

2011). Generally, as stocking rate increases milk yield per cow decreases and milk yield per ha increases

(Macdonald et al., 2008) and vice versa. The increase in daily milk yield per cow for cows grazing on

GC swards was partly due to the reduction in stocking rate and partly due to the presence of WC in the

sward. Using the stocking rate effect prediction equations of McCarthy et al. (2011), it was calculated

that the increase in milk yield per cow was 38% due to the reduction in stocking rate and 62% due to the

presence of WC in the sward. However, despite the increase in daily milk yield per cow, milk yield per ha

decreased with GC swards. Grazing experiments that have compared GO and GC swards, have reduced

stocking rate and N application rates on the GC swards and as a consequence GC systems had lower

levels of productivity. In the context of increased demand for dairy products, this raises the question as

to the possibilities of incorporating WC into more intensive pasture-based production systems.

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

Conclusions

Mean daily yield of milk and milk solids increased when WC was included in a PRG sward. However, due to management associated with WC swards (i.e. reduced stocking rate and N application rates) milk and milk solids yield per ha were reduced. The results raise interesting questions as to the possibilities of incorporating WC into more intensive pasture-based production systems and further research is required in this area.

References

Delgado, C.L. (2005) Rising demand for meat and milk in developing countries: implications for grasslands-based livestock production. In: McGilloway D.A. (ed.). Grassland: A Global Resource. Wageningen Academic Publishers, Wageningen, the Netherlands, pp. 29-39.

Harris, S.L., Clark, D.A., Auldist, M.J., Waugh, C.D., and Laboyrie, P.G. (1997) Optimum white clover content for dairy pastures.

Proceedings of the New Zealand Grassland Association 59, 29-33.

Lüscher, A., Mueller-Harvey, I., Soussana, J.F., Rees, R.M and Peyraud J.L. (2014) Potential of legume-based grassland-livestock systems in Europe: a review. Grass and Forage Science 69, 208-226.

McCarthy, B., Delaby L., Pierce K.M., Journot F. and Horan B. (2011) Meta-analysis of the impact of stocking rate on the productivity of pasture-based milk production systems. Animal 5, 784-794.

Macdonald, K.A., Penno J.W., Lancaster J.A.S. and Roche J.R. (2008) Effect of stocking rate on pasture production, milk production and reproduction of dairy cows in pasture-based systems. Journal of Dairy Science 91, 2151-2163.

Peyraud J.L., Le Gall A. and Lüscher A. (2009) Potential food production from forage legume-based systems in Europe: an overview.

Irish Journal of Agricultural and Food Research 48, 1-22.

Sauvant D., Schmidely P., Daudin J.J. and St-Pierre N.R. (2008) Meta-analyses of experimental data in animal nutrition. Animal 2, 1203-1214.

Table 1. Effect of introducing white clover into a perennial ryegrass sward on milk production per cow and per ha for database one data.

No. data Grass-only Grass-Clover SE

P-value

Experimental characteristics

Clover (%) 86 0.6 33.6 2.38 <0.001

Stocking rate (cows ha

) 66 3.27 2.98 0.270 <0.001

Nitrogen (kg ha

) 66 206 72 21.6 <0.0001

Grazing days ha

54 457 418 36.6 <0.001

Production per cow

Milk yield (kg cow

) 86 17.6 18.8 0.70 <0.001

Fat content (g kg

) 74 42.0 41.5 1.01 0.171

Protein content (g kg

) 74 33.6 33.9 0.61 0.194

Lactose content (g kg

) 32 44.6 45.3 0.79 0.004

Milk solids

yield (kg cow

) 82 1.31 1.41 0.046 <0.0001

Production per hectare

Milk yield (kg ha

) 54 8092 7661 775.5 0.017

Milk solids yield (kg ha

) 50 618 583 64.9 0.012

1 SE = standard error.

2 Milk solids = kg of fat + protein.