Dr. Chris Reynolds, Department of Animal Sciences, Ohio State University
The Jersey breed has a passionate following, and there is ample evidence that this is justified. Surveys and research have indicated that when compared with Holstein cows, Jersey cows have earlier first calving, easier calving, reduced mastitis and lameness, and greater longevity, while their temperament and size means they are friendly to both farmer and pasture. Although their total milk yield is lower, the Jersey cow typically produces more milk solids per pound of body weight (BW). Milk from Jersey cows has a higher fat (and therefore energy) content, as well as a higher milk protein content and manufacturing quality. A higher dry matter (DM) intake per pound of BW generally accompanies this higher milk energy output.
As a consequence of the above factors, it is likely that interest in the Jersey breed will continue to increase. In addition, there is currently an increase in the use of Jersey cows in cross-breeding programs. However, it is now recognized that in many ways, the Jersey cow cannot be treated simply as a mini-Holstein cow in terms of nutrition and ration formulation, but only limited scientific information is available on which guidelines for Jersey cows can be based. This article reviews some of this information.
Feed efficiency: A number of research summaries have indicated that the Jersey breed has advantages in terms of the milk solids output relative to metabolizable energy intake and the production of milk energy from forage. Her energetic advantage is largely due to a greater milk energy output relative to total maintenance requirement, which is associated with the higher solids content of her milk. These comparisons also assumed that the maintenance requirement of the Jersey cow is the same as for the Holstein cow, but there is evidence from non-lactating animals that the maintenance requirement of the Jersey cow is higher.
Intake and feed digestion: As the DM intake of Jersey cows per unit of BW is often higher than Holstein cows, their intake can not be predicted from BW and milk yield using equations developed for Holstein cows. Increased rate of passage of digesta through the gut has been observed for the Jersey cow. This may be a consequence of increased milk energy output, driving higher DM intakes or, alternatively, more effective mastication and rumination may increase the rate of passage and allow greater DM intake. Regardless, the higher intake in Jersey cows relative to her body size does not appear to reduce diet digestibility.
Milk fat composition and ration fiber content: The higher milk fat content of Jersey milk is associated with an increase in the relative proportion of shorter-chain fatty acids. These fatty acids and other medium length fatty acids are synthesized in the mammary gland, using lipogenic volatile fatty acids produced in the rumen. As the production of these precursors is promoted by forage digestion, it is generally believed that Jersey cows may need higher fiber levels in their rations. However, feeding too much fiber may impose a limit on their DM intake. Further research is needed to clarify the 'effective fiber' requirements of the Jersey cow and the consequence of errors in balancing rations for fiber, starch, or fat. Indeed, articles in the popular press have suggested that Jersey cows are more tolerant of low fiber rations than Holstein cows, and should be fed less long fiber to achieve maximal DM intake.
Milk fever and transition diets: One disadvantage of Jersey cows is that they have a higher incidence of milk fever. This has been attributed to fewer vitamin D receptors in the intestine. These receptors increase calcium absorption in early lactation via mechanisms which are inhibited by high blood pH. Therefore, it has been recommended that the cation-anion difference of transition rations for Jersey cows be adjusted for a lower target urine pH (5.8-6.2) than for Holstein cows (6.2-6.7), but the basis for these recommendations is sketchy and the potential negative effects of supplemental dietary anions on metabolism and health must also be considered.
Energy metabolism: Two calorimetric comparisons of lactating Jersey and Holstein cows from the first half of the century suggested little difference between the two breeds in terms of energy metabolism. However, more recent research conducted at USDA in Beltsville, USA indicates that:
· Relative yield potential of the two breeds was similar for the individuals studied; fat corrected milk yield per pound of metabolic BW (BW0.75) at peak lactation and DM and energy intake per kg BW0.75 were not different. Thus, the genetic merit of the cows used provided a good basis for a breed comparison.
· Metabolizable energy intake as a percentage of intake energy was not different: digestibility of energy was higher in the Jersey cows, but this was countered by slight increases in urine and methane energy losses.
· Energy balance (milk plus body tissue energy) as a percentage of intake energy also was not different between breeds; higher milk fat content for the Jersey cows was associated with greater milk energy output, but corresponding tissue energy retention was numerically lower. This was an important difference between the breeds.
· This study did not detect differences in the maintenance energy requirement of lactating animals, but higher metabolizable energy intake was required to avoid tissue energy loss in the dry Jersey cows. This may in part be due to differences in body composition, as well as a genetic difference between the breeds.
Conclusions: When compared on the basis of milk energy output per pound of metabolic body size, the energy requirements of lactating Jersey and Holstein cows are remarkably similar. Differences in milk energy output also explain differences in DM intake and body energy balance between the two breeds. Although further research is needed, factors which should also be considered when formulating rations for the Jersey cow include a higher rate of digesta passage, the higher incidence of milk fever, and the fiber content of the ration.