Review: New considerations to refine breeding objectives of dairy cows for increasing robustness and sustainability of grass-based milk production systems

Abstract

Although food from grazed animals is increasingly sought by consumers because of perceived animal welfare advantages, grazing systems provide the farmer and the animal with unique challenges. The system is dependent almost daily on the climate for feed supply, with the importation of large amounts of feed from off farm, and associated labour and mechanisation costs, sometimes reducing economic viability. Furthermore, the cow may have to walk long distances and be able to harvest feed efficiently in a highly competitive environment because of the need for high levels of pasture utilisation. She must, also, be:(1) highly fertile, with a requirement for pregnancy within~80 days post-calving; (2) 'easy care', because of the need for the management of large herds with limited labour; (3) able to walk long distances; and (4) robust to changes in feed supply and quality, so that short-term nutritional insults do not unduly influence her production and reproduction cycles. These are very different and are in addition to demands placed on cows in housed systems offered pre-made mixed rations. Furthermore, additional demands in environmental sustainability and animal welfare, in conjunction with the need for greater system-level biological efficiency (i.e. 'sustainable intensification'), will add to the 'robustness' requirements of cows in the future. Increasingly, there is evidence that certain genotypes of cows perform better or worse in grazing systems, indicating a genotype × environment interaction. This has led to the development of tailored breeding objectives within countries for important heritable traits to maximise the profitability and sustainability of their production system. To date, these breeding objectives have focussed on the more easily measured traits and those of highest relative economic importance. In the future, there will be greater emphasis on more difficult to measure traits that are important to the quality of life of the animal in each production system and to reduce the system's environmental footprint.

Genomic Regions Associated With Gestation Length Detected Using Whole-Genome Sequence Data Differ Between Dairy and Beef Cattle

“…Notwithstanding this, as with any trait, cognizance of other traits needs to be considered when attempting to alter gestation length through breeding. Therefore, to aid in the genetic improvement of gestation length, breeding programs need to facilitate a balanced selection approach with other correlated traits also included in the breeding objective as exists for most populations (e.g., Miglior et al, 2005; Roche et al, 2018; Purfield et al, 2019).…”

Greenhouse gas emissions and nitrogen efficiency of dairy cows of divergent economic breeding index under seasonal pasture-based management

“…Due to its high nutritive value, milk is a key source of nutrition for the rapidly expanding global population (Mottet et al, 2018). In countries such as Ireland and New Zealand, milk production systems are predominantly based on a seasonal spring calving model where the primary feed source is grazed grass (Roche et al, 2018;O'Brien et al, 2018). Greenhouse gas (GHG) emissions associated with the production and transportation of imported feed are low in grazing systems (O'Brien et al, 2012).…”

A breeding index to rank beef bulls for use on dairy females to maximize profit

“…Modern dairy cow breeding goals almost exclusively focus on the efficiency of milk production and functionality, and even when taking beef merit into account (e.g., Ireland, Roche et al, 2018;Scandinavia, Philipsson et al, 1994), the breeding goals remain strongly dominated by milk production and cow functional traits. The gains in milk production efficiency from selecting on such breeding objectives are undisputed (García-Ruiz et al, 2016).…”