The effects of breeding and selection on lactation in dairy cattle

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Source: John B Cole, Bayode O Makanjuola, Christina M Rochus, Nienke van Staaveren, Christine Baes, The effects of breeding and selection on lactation in dairy cattle, Animal Frontiers, Volume 13, Issue 3, June 2023, Pages 62–70, https://doi.org/10.1093/af/vfad044

Implications
  • Genetic selection to increase milk yield has been very successful.

  • Genetic selection can be used to alter the shape of the lactation curve, manufacturing properties of milk, and composition associated with human health.

  • Mid-infrared spectral data has potential for enabling low-cost, high-throughput phenotyping.

  • There remains a disconnect between farmers’ investments in improved milk properties and payment for that milk.

Introduction

Lactation is a dynamic process of milk production to provide nutrition and immune benefits to the offspring while ensuring maintenance requirements of the mother are met (Darmon, 2009; Strucken et al., 2015). In dairy farming, milk is also the main product marketed for human consumption (Darmon, 2009) which is why farmers have worked to increase milk production over time. Milk production of domesticated dairy cows can reach 30–50 L per day or 6,000 to 12,000 Lover a lactation compared to 8–10 L per day and <1,000 L over lactation in feral cows (Webster, 1995). Milk production in cows follow a dynamic curve starting with an initial rapid increase in milk yield in early lactation (approx. 0–45 days-in-milk, [DIM]), followed by a peak (approx. 46–55 DIM), and then a slow decline in milk yield during late lactation (approx. 56–340 DIM) (Strucken et al., 2015). Factors such as peak milk production, persistency and lactation length determine how the total amount of milk produced is distributed over lactation (Muir, 2004).

Since 1960, the amount of milk produced per cow has almost tripled (Figure 1) which is due in part to genetics (reviewed by Strucken et al., 2015; Miglior et al., 2017; Brito et al., 2021). Selection for production traits in Canada initially focussed on milk yield and milk fat yield (reviewed by Miglior et al., 2017). However, as technology developed also selection started to focus on milk protein yield and the shape of the lactation curve. In particular, the lactation curve, persistency (e.g., persistency of production or rate of decline), week of peak yield and peak yield were considered (reviewed by Miglior et al., 2017). Different milk production traits are now considered in selection indices worldwide to provide a balanced breeding goal where milk production is no longer the sole objective but also includes, for example, health and fertility traits (Miglior et al., 2017; Cole and VanRaden, 2018).

Figure 1.

The size of the US (left) and Canadian (right) national dairy herds in millions of cows (left y-axes) and the average milk production per cow in kg/y (right y-axes) between 1970 and 2020 for US and Canadian herds (data from United States Department of Agriculture, Economic Research Service & Agriculture and Agrifood Canada, respectively). Canadian data reflects only animals on herd recording.

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