Introduction

The SCC ABV allows dairyfarmers to select bulls that produce daughters that are less susceptible to mastitis. This leads to the selection of more profitable dairy cows.

The SCC ABV provides a low-cost, long-tem benefit to individual dairyfarmers and the wider industry.

ADHIS will implement an ABV for Somatic Cell Count (SCC) in February 2002.

High SCC is an accepted indicator of mastitis. Genetic variation for SCC does exist. In other words some bulls produce daughters that are less susceptible to mastitis than others.

Mastitis is a common and expensive disease of the udder. Reducing the incidence of mastitis can potentially save the dairy industry millions of dollars. While most of the reduction in mastitis will come from improved management, breeding for low susceptibility to mastitis can have considerable long-term benefits.

The dairyfarmer can make a long-term difference to his herd's mastitis incidence, at little or no cost, simply by selecting high APR and good SCC bulls.

Data

ADHIS has many millions of SCC data. From about the mid 1990's all test-day records were accompanied by a SCC for that cow on that day. In other words ADHIS has a large data source for SCC analysis.

Heritability

The heritability used to calculate the SCC ABV is about 0.15 (or 15%). This is an estimate of how much of the variation of a trait is explained by genetics. In other words an estimated 15% of the variation in the Australian dairy cow population is explained by genetics, the other 85% of variation is explained by the management environment of the cow.

The heritability of SCC is lower when compared to other traits such as protein test (40%), protein kg (25%), milking speed (20%) and overall type (30%), However at 15% heritability we see considerable genetic variation and therefore benefit through genetic selection.

ADHIS will officially publish SCC ABV's for individual bulls when their Reliability reaches 50% with daughters in at least 15 Australian herds.

The Model

ADHIS use a test-day model to calculate SCC ABV's. The model uses three lactations, each with 10 stages, a total of 30 traits. The average of the 30 traits is used to calculate the SCC ABV.

Understanding the ABV

· A bull with a lower SCC ABV will lower your SCC.
· A bull with a higher SCC ABV will increase your SCC.

The average ABV of NASIS bulls born 1990 is the base and is set at zero.

The best SCC bull in the population has a SCC ABV of -60%. He will lower SCC in his progeny by 30% (half the benefit, the other half comes from the mother) and this is a $20 gain on APR.

The poorest SCC bull in the population has a SCC ABV of +60%. He will increase SCC in his progeny by 30% and this is a $20 loss on APR.

Example
· A bull with a SCC ABV of -20 is 20% lower for SCC than the base.

· He will pass half of this advantage (10%) onto the next generation (the other half coming from the dam).

· The benefit each dairyfarmer gets from selecting for lower SCC relates to their herd's SCC average. The higher your herd's SCC (e.g. Bulk Milk Cell Count) the higher the potential benefit. Herds with a very low SCC will see less benefit.

· In this example the benefit is an estimated 10% lower SCC from the bull's progeny.


SCC in the Australian Profit Ranking

Every 1% change in SCC is estimated to be worth $0.34 net profit per cow per year.

Therefore, given the best bull in the population is –60% for SCC and poorest bull is ranked at +60%, the difference in APR (dollar terms) between the best and worst bull is about $40.00 net profit per cow per year. Over many cows over many years, this starts to add up.

SCC and Interbull

Currently 13 countries participate in Interbulls' SCC international evaluation. ADHIS now has the opportunity to do likewise.

ADHIS will submit SCC ABV's to the next Interbull test-run in March 2002. Following this, we can expect that SCC ABV's will be available for overseas bulls. Similarly Australian bulls will have SCC breeding values in other countries.

Until this point, overseas bulls will have breed average for SCC ABV. In other words SCC will have no affect on the APR until Australian SCC ABV's are included in the Interbull analysis.

For more information about the SCC ABV, please call or email ADHIS.

Robert Poole
Executive Officer
Phone: 03 9642 8042
Email: rpoole@adhis.com.au