“Breeding for reduced methane emission and feed-efficient Holstein cows: An international response"
Journal of Dairy Science Vol. 104 No. 8, 2021. This interesting article from researchers from universities in Denmark, Australia, Switzerland and Canada (University of Guelph and University of Alberta), explores the role of genetic selection of animals as a way to reduce methane emissions.Selecting for lower-methane-emitting animals is one of the best approaches to reduce methane given that genetic progress is permanent and cumulative over generations. Still, the authors say, since genetic selection requires many animals with records, and few countries actively record methane, combining data from different countries could help to expedite accurate genetic parameters for methane traits and build a future genomic reference population.
An important aspect of genetic selection is to know the impact that selecting for one trait can have in other economically important traits. They established three objectives for this study: to estimate genetic parameters of seven suggested methane traits, as well as correlations between those traits and production, maintenance and efficiency traits, using a multicountry database. The second aim was to estimate genetic correlations within parities and stages of lactation for methane. The third aim was to evaluate the expected response of economically important traits by including methane traits in the breeding goal.
The authors indicate that increases in dairy production are needed to fulfill the demand of the growing world population and that this constant increase presents long-term challenges of economic feasibility as well as environmental sustainability. Dairy (or ruminant) production leads to methane production (methane gas is naturally generated through enteric fermentation by ruminants), and this may compromise the sustainability of dairy products. According to several authors cited in the article, methane gas in livestock represents 17% of the global greenhouse emissions and 2% to 12% of feed energy losses in ruminants, making the reduction of methane emissions in livestock production one of the challenges of this century.
The authors refer to several studies done in the last decade which show that methane traits in dairy cattle have low to moderate heritability, from 0.11 to 0.33, making genetic selection a strong approach to reduce methane emissions. The authors refer that other than the need for a large number of data, there’s also a lack of consensus on the most appropriate trait to be included in the breeding goal. For example, should it be daily methane production in grams per head per day or methane yield (methane produced per kilogram of dry matter intake) or others?
For this study, data from four countries with more than 15,000 records of daily methane production per cow (grams per day) from around 3,000 cows was used. They concluded that methane is highly positively correlated with other economically important traits such as milk production, weight and feed intake. For this reason, it is important to have a trait that is adjusted for the production traits.
They say that residual methane (methane actually produced by the animal versus methane production predicted) adjusted by metabolic bodyweight (MBW) and energy-corrected milk (ECM) seems to be the best option. Moreover, residual methane is positively correlated with residual feed intake (RFI), implying that lower-methane-emitting animals are also more efficiently converting feed. The authors say that adding a negative economic value for methane could help to reduce methane substantially while maintaining an increase in milk production.
“Effects of extended voluntary waiting period from calving until first insemination on body condition, milk yield and lactation persistency.”
Journal of Dairy Science Vol. 104 No. 7, 2021. This article from researchers from Wageningen University in the Netherlands, investigated the effects of three different voluntary waiting periods (VWP) from calving until first insemination on bodyweight, body condition, milk yield and lactation persistency. It also identified the individual cow characteristics in early lactation that contributed to milk yield and persistency of cows with different VWP. The authors say that one-year calving interval is usually associated with maximized milk output, due to the calving-related peak in milk yield. However, extending the calving interval could benefit cow health and production efficiency due to fewer transition periods per unit of time.
Extending calving interval can affect lactation performance by fewer days dry per year, delayed pregnancy effect on milk yield and greater milk solids yield in late lactation. The study used 154 Holstein-Frisian dairy cows that were randomly assigned to three different VWP: 50, 125 or 200 days, and were monitored during one full lactation plus the first six weeks of the subsequent lactation or until culling.
The authors refer that it’s common to aim for a calving interval of 12 months, as calving is associated with a peak in milk yield around weeks four to seven of lactation. Around calving, however, cows experience multiple transitions, such as drying off, calving and the start of the next lactation. During these transitions, cows have an increased risk for developing diseases and disorders, which means that with a one-year calving interval, cows face these transitions every year.
On the other hand, with a one-year calving interval, it’s common to have cows still milking heavy around dry-off time, which increases the risk for udder infections in the dry period and at calving. One of the reasonings behind increasing the VWP between calving and first insemination is to reduce the number of transitions per unit of time, as well as reducing milk production at dry-off. However, the authors say cows with an extended calving interval have fewer peaks in milk yield per unit of time compared with cows with a one-year calving interval. This could result in a lower milk yield per cow per year.
They go on to explain that studies made to evaluate milk yield with longer VWP often focused on the 305-day milk yield. Cows in an extended calving interval, however, have longer lactation periods and fewer days dry per year, which both influence the average milk yield per day and per year. Because of this, they suggest (citing several other researchers) as an alternative to 305-day milk yield, milk yield could be expressed as the milk yield per day of calving interval, which would account for longer lactation periods or differences in days dry per year.
The conclusions were that for both primiparous and multiparous cows, when VWP was extended until 125 days, there was no effect on milk or fat- and protein-corrected milk (FPCM) yield per day of calving interval. For primiparous cows, extending the VWP further until 200 days still did not affect yield per day of calving interval, although, for multiparous cows, extending the VWP to 200 days resulted in a lower yield per day of calving interval.
Moreover, cows in longer VWP had lower yield at dry-off, which the authors say may benefit their udder health during the dry period and possibly also the subsequent lactation. The study also showed that multiparous cows in longer VWP had higher BCS at dry-off and in the first weeks of the subsequent lactation, which may have negative consequences in terms of metabolic health and adaptation to a new lactation. In summary, the authors say the VWP could be extended from 50 days to 125 days without an effect on daily yield per day of calving interval.
This column brings you information regarding some of the research being done around the world and published in the Journal of Dairy Science. The objective is to bring to light areas of research that may have an immediate practical application on a dairy farm, as well as research that, even though it may not have a practical impact now, could be interesting for its future potential application. The idea is to give a brief overview of select research studies but not go into detail on each topic. Those interested in further in-depth reading can use the citations to find each study.
