Keywords: Expert judgement | commissioned research | digestibility
What data needs were addressed? Producing a country-specific estimate of cattle feed digestibility.
Why was the data needed? Prior to 2017, Latvia had no country-specific data on feed digestibility and the GHG inventory used 65%, which is the mid-range of the representative values for pasture-fed cattle in the 2006 IPCC Guidelines (Ch. 10, Table 10.2).
Methods used: commissioned research, expert opinion.
How was the data gap addressed? The government of Norway operated a grant program to reduce disparities between members of the European Economic Area. In the program agreement on national climate policy with Latvia, the pre-defined project “Development of the National System for Greenhouse Gas Inventory and Reporting on Policies, Measures and Projections” included funding for improving estimates of feed digestibility. The research was conducted by the Latvia University of Agriculture (Degola et al. 2016).
Feed samples were taken from 38 farms in different regions of the country at different growth stages over 2015. The selection of farms was undertaken to represent farms with different scales of dairy cattle production. The samples covered hay, silage, haylage and total mixed ration. The samples were analyzed at the university’s Scientific Laboratory of Agronomic Analysis. Chemical analysis of feed was conducted for dry matter (DM) %, crude protein (CP) %, insoluble protein, %, soluble protein, %, undegraded intake protein (UIP) %, crude fiber (CF) %, acid detergent fiber (ADF) %, neutral detergent fiber (NDF) %, ash %, Ca and P %, according ISO 5983, ISO 6490/2 and ISO 6491 standards. Digestibility was determined using the cellulase method and by calculation of net energy for lactation.
The average determined digestibility of forage for natural meadow hay was 52.3±4.3% and 53.8±5.2% for cereal grass hay; for grass silage with preservative 65.2±6.1%, without preservative 62.8±4.9%; and for corn silage, respectively 71.1±0.6%, 68.2±3.1%; for haylage 62.6±4.1%, for TMR 71.7±5.7%.
For the national GHG inventory, interviews were conducted with agricultural and academic experts to identify the typical feed rations for dairy cows and other cattle. This suggested that the feed ration of dairy cows consists on average of 71% grass forage and 29% concentrates based on dry matter intake. Feed ration composition for other cattle types were also estimated. The results of cattle feed quality analysis and feeding ration composition estimates were combined, leading to a feed digestibility estimate of 67% for dairy cows in 2015. Considering that the proportion of concentrates in dairy cow diet had been gradually increasing, it was decided to use a digestibility value of 66% for dairy cows in the period 2010-2014. For other cattle, a value of 65% was estimated.
Furthermore, correlation analysis between digestibility determined using the cellulose method and the calculation method found a good correlation, leading to the conclusion that it is not necessary to determine forage digestibility in the laboratory with the cellulase method, but the formula DDM, % = 88.9 (0.779 x ADF %) can be used, where the digestibility is calculated from the ADF content in feed.
Degola L, Trupa A, Aplocina E. 2016. Forage quality and digestibility for calculation of enteric methane emission from cattle. In 15th International Scientific conference “Engineering for Rural Development”: Proceedings, pp. 456-461.