Consequences of genetic selection for increased milk production in European seasonal pasture based systems of milk production

Self Cite

The objective of this study is to quantify the milk production response per cow and per hectare (ha) for an incremental stocking rate (SR) change, based on a meta-analysis of published research papers. Suitable experiments for inclusion in the database required a comparison of at least two SRs under the same experimental conditions in addition to details on experimental length and milk production results per cow and per ha. Each additional increased SR treatment was also described in terms of the relative milk production change per cow and per ha compared to the lower base SR (b_SR). A database containing 109 experiments of various lengths with 131 comparisons of SR was sub-divided into Type I experiments (common experimental lengths) and Type II experiments (variable experimental lengths). Actual and proportional changes in milk production according to SR change were analysed using linear mixed model procedures with study included as a random effect in the model. Low residual standard errors indicated a good precision of the predictive equations with the exception of proportional change in milk production per cow. For all milk yield variables analysed, the results illustrate that while production per cow is reduced, a strong positive relationship exists between SR and milk production per ha. An SR increase of one cow/ha resulted in a decrease in daily milk yield per cow of 7.4% and 8.7% for Type I and Type II data, respectively, whereas milk yield per ha increased by 20.1% and 19.6%, respectively. Within the Type II data set, a one cow/ha increase in SR also resulted in a 15.1% reduction in lactation length (equivalent to 42 days). The low predictability of proportional change in milk production per cow according to the classical SR definition of cows per ha over a defined period suggests that SR may be more appropriately defined in terms of the change in available feed offered per animal within each treatment.

Section: Discussionsupporting

confidence: 60%

Meta-analysis of the impact of stocking rate on the productivity of pasture-based milk production systems

McCarthy

Delaby

Pierce

et al. 2011

Self Cite

“…Side effects of increasing milk yield per cow Loss of fertility and higher probability of the appearance of diseases are mentioned as side effects of increasing milk yield per cow in dairy farming (Lucy, 2001;Dillon et al, 2006). GHG emissions produced during the rearing phase of modelled replacement heifers contribute up to 20% of total GHG emissions from the modelled dairy farms.…”

Section: Allocation Methodsmentioning

confidence: 99%

“…Management and production assumptions for the modelled PU are shown in Table 1. Higher replacement rates for higher yielding dairy cows were assumed, in order to account for the higher replacement rate reported for Zehetmeier, Baudracco, Hoffmann and Heissenhuber systems with higher milk yield per cow per year (Lucy, 2001;Dillon et al, 2006). Age at first calving was set at 27 months for all replacement heifers included in the model.…”

Section: Model Overviewmentioning

confidence: 99%

Does increasing milk yield per cow reduce greenhouse gas emissions? A system approach

Zehetmeier

Baudracco

Hoffmann

et al. 2012

113

Milk yield per cow has continuously increased in many countries over the last few decades. In addition to potential economic advantages, this is often considered an important strategy to decrease greenhouse gas (GHG) emissions per kg of milk produced. However, it should be considered that milk and beef production systems are closely interlinked, as fattening of surplus calves from dairy farming and culled dairy cows play an important role in beef production in many countries. The main objective of this study was to quantify the effect of increasing milk yield per cow on GHG emissions and on other side effects. Two scenarios were modelled: constant milk production at the farm level and decreasing beef production (as co-product; Scenario 1); and both milk and beef production kept constant by compensating the decline in beef production with beef from suckler cow production (Scenario 2). Model calculations considered two types of production unit (PU): dairy cow PU and suckler cow PU. A dairy cow PU comprises not only milk output from the dairy cow, but also beef output from culled cows and the fattening system for surplus calves. The modelled dairy cow PU differed in milk yield per cow per year (6000, 8000 and 10 000 kg) and breed. Scenario 1 resulted in lower GHG emissions with increasing milk yield per cow. However, when milk and beef outputs were kept constant (Scenario 2), GHG emissions remained approximately constant with increasing milk yield from 6000 to 8000 kg/cow per year, whereas further increases in milk yield (10 000 kg milk/cow per year) resulted in slightly higher (8%) total GHG emissions. Within Scenario 2, two different allocation methods to handle co-products (surplus calves and beef from culled cows) from dairy cow production were evaluated. Results showed that using the 'economic allocation method', GHG emissions per kg milk decreased with increasing milk yield per cow per year, from 1.06 kg CO 2 equivalents (CO 2eq ) to 0.89 kg CO 2eq for the 6000 and 10 000 kg yielding dairy cow, respectively. However, emissions per kg of beef increased from 10.75 kg CO 2eq to 16.24 kg CO 2eq due to the inclusion of suckler cows. This study shows that the environmental impact (GHG emissions) of increasing milk yield per cow in dairy farming differs, depending upon the considered system boundaries, handling and value of co-products and the assumed ratio of milk to beef demand to be satisfied.

“…However, in the past two decades, interest has shifted towards the role of feed intake and its relationship with energy balance (EB), health and fertility. This shift in interest arose from the fact that current genetic selection for yield increases feed intake, but also results in a more negative energy balance (NEB) and more body tissue mobilisation during lactation (see Veerkamp et al, 1993;Dillon et al, 2006). As demonstrated by the size and direction of the genetic correlation between milk yield and feed intake and by the negative genetic correlation -E-mail: Roel.Veerkamp@wur.nl between milk yield and measures of EB, live-weight (LW; change) and body condition score (BCS; Veerkamp et al, 2003), the expected correlated response in feed intake from selection on yield alone cannot cover the extra requirements needed for the increased yield.…”

Section: Introductionmentioning

confidence: 99%

Genome-wide associations for feed utilisation complex in primiparous Holstein–Friesian dairy cows from experimental research herds in four European countries

Veerkamp

Coffey

Berry

et al. 2012

Self Cite

Genome-wide association studies for difficult-to-measure traits are generally limited by the sample size with accurate phenotypic data. The objective of this study was to utilise data on primiparous Holstein-Friesian cows from experimental farms in Ireland, the United Kingdom, the Netherlands and Sweden to identify genomic regions associated with the feed utilisation complex: fat and protein corrected milk yield (FPCM), dry matter intake (DMI), body condition score (BCS) and live-weight (LW). Phenotypic data and 37 590 single nucleotide polymorphisms (SNPs) were available on up to 1629 animals. Genetic parameters of the traits were estimated using a linear animal model with pedigree information, and univariate genome-wide association analyses were undertaken using Bayesian stochastic search variable selection performed using Gibbs sampling. The variation in the phenotypes explained by the SNPs on each chromosome was related to the size of the chromosome and was relatively consistent for each trait with the possible exceptions of BTA4 for BCS, BTA7, BTA13, BTA14, BTA18 for LW and BTA27 for DMI. For LW, BCS, DMI and FPCM, 266, 178, 206 and 254 SNPs had a Bayes factor .3, respectively. Olfactory genes and genes involved in the sensory smell process were overrepresented in a 500 kbp window around the significant SNPs. Potential candidate genes were involved with functions linked to insulin, epidermal growth factor and tryptophan.