Calvings that are trouble-free and produce a live calf are the goal of all dairy producers. A difficult calving can result in significant economic loss. Extra labor to assist the cow, a farm call for the herd veterinarian or death of the calf reduces profits for the dairy farm. Additional costs may occur due to increased days open, lower milk yield and increased likelihood of culling of the cow.
Genetic evaluations are available in the Holstein and Brown Swiss breeds for traits related to calving ability. These traits are:
- Sire calving ease (SCE) – a sire’s ability to produce a calf that is born easily
- Daughter calving ease (DCE) – the ability of daughters of a sire to deliver a calf easily and their tendency to produce a calf that is born easily
- Sire stillbirth (SSB) – the tendency of calves from a sire to be stillborn (Holstein only)
- Daughter stillbirth (DSB) – the tendency of daughters of a sire to produce stillborn calves (Holstein only)
Both calving ease and stillbirth have direct and maternal effects. As Bennet Cassell explained, “direct” effect genes act on the calf, whereas “maternal” genetic effects, measured by daughter calving ease and daughter stillbirth genetic evaluations, are expressed by the dam of the calf.
Calving ease is reported as the percent of difficult births in first-lactation heifers. A difficult birth is a calving scored 4 or 5 on the 5-point scale used to report calving ease. Stillbirth is defined as a calf that is born dead or dies within 48 hours of birth. Calving ease and stillbirth data are collected through the Dairy Herd Information Association (DHIA) and the dairy records processing centers.
The calving ability (CA$) composite index was developed to incorporate calving ease and stillbirth traits into the Net Merit index (NM$). CA$ is the lifetime benefit of less calving difficulty and fewer stillborn calves. Higher values for CA$ are more desirable.
CA$ for Holsteins includes four traits. The relative emphasis on each trait is 25 percent SCE, 15 percent DCE, 15 percent SSB and 45 percent DSB. For Brown Swiss, only SCE and DCE are included in CA$.
The Council on Dairy Cattle Breeding (CDCB) calculates the genetic evaluations for calving ease and stillbirth as well as CA$. Although CA$ values are not published, the individual traits that comprise CA$ are reported through CDCB, artificial insemination organizations, and breed associations.