Nutrient digestibility

intervals and the sieving process repeated. Differences in the weight of feed particles held on each screen at each sieving would indicate the extent to which Jersey cows sorted in favour of smaller or larger particles during a meal compared to other breeds. Analysis of video recordings of cows’ eating behaviour may also be useful.

Nutrient digestibility

Studies by Blake et al. (1986) and Ingvartsen and Weisbjerg (1993) found no differences in nutrient digestibility between dairy breeds when offered corn silage and concentrate blends and a total mixed ration respectively. However, Aikman et al. (2008) found that although Jersey cows had a shorter rumen retention time than Holsteins, neutral detergent fibre (NDF) digestibility was significantly higher (p=0.008). No significant differences were found in dry matter digestibility, starch digestibility and N digestibility. (For details, see Appendix C, Table C.1). Beecher et al. (2014) reported that for all digestibility parameters (dry matter, organic matter, nitrogen, NDF and ADF), the apparent, total tract digestibility of fresh-cut perennial ryegrass pasture was higher for Jerseys than Holsteins. This was despite Jerseys having a faster gut passage rate, and may be at least partly explained by the Jersey’s larger gastrointestinal tract, and therefore larger area for nutrient absorption. Jerseys’ feeding behaviour may also contribute to higher digestibility. Firstly, Jerseys have more evenly distributed meals across each day and spend more time eating and ruminating per kilogram of dry matter eaten. This may help to maintain a more stable rumen and reduce the likelihood of ruminal acidosis. Secondly, chewing feed for longer (Prendiville et al., 2010) reduces it to smaller sized particles, so rumen microbes are provided with greater feed surface area for attachment and digestion.

Beecher et al. (2014) compared the relative abundance of several rumen microbial populations potentially involved in fibre digestion in Jerseys and Holsteins, but was unable to find any differences that would explain Jersey’s higher digestibility. King et al. (2011) reported that although many rumen methanogen library sequences were common to both breeds of dairy cattle, there were more individual sequences in the library specific to the Holstein and less found in the Jersey library, highlighting increased diversity in the Holstein library. The possible differences in rumen microbial populations are likely to contribute to the production efficiency differences between Jerseys and Holsteins.

Sears et al. (2020) found in their study of multiparous, mid-lactation cows fed a TMR that while Jerseys consumed more nitrogen than Holsteins as a percent of BW (0.15% vs. 0.09% respectively), their blood urea nitrogen (BUN) level was lower (12.6 mg/dL vs. 13.8 mg/dL), as was their urine total nitrogen (124.5 g/day vs. 145 g/day). This indicated that Jersey cows were more efficient at utilising dietary nitrogen. (For details, see Appendix C, Table C.2). Previous studies by Blake et al. (1986), Kauffman and St-Pierre (2001) and Knowlton et al. (2010) suggested that Jersey cows excreted about 30% less faecal and urinary nitrogen than Holstein cows, but that this was due largely to differences in BW and DM intake rather than differences in nitrogen utilisation efficiency.