Glossary of Dairy and Dairy Genetics

AIPL Animal Improvement Programs Laboratory. Remember, not all labs have microscopes or test tubes. A laboratory at USDA is a research unit. AIPL does research on dairy performance records, and the methods used to analyze the records. AIPL is part of BARC (Beltsville Agricultural Research Center) which is part of ARS (Agricultural Research Service), one of the three agencies of the REE (Research, Extension and Education) area of USDA, and the principal research agency of USDA.
DHIA Dairy Herd Improvement Associations were organized in the early 20th century. Their mission was to improve dairy production through better breeding. By keeping performance records on many cows, DHIA provide farmers with the information they needed to decide which cows were the best cows for breeding. Today in the U.S., 32 DHI affiliates manage data collection and milk component testing.
DRPC Six Dairy Record Processing Centers are contracted by DHIA affiliates to manage data. Centers are located in North Carolina, Pennsylvania, Wisconsin, Utah, California, and Texas. The DRPC prepare reports for producers, and compile data to forward to AIPL
Heritability The degree to which the phenotype (expression of a trait that you can measure, or describe like how much milk, or what color hair) of an animal is likely to predict the expression of that trait in the offspring of the animal. How likely is it for a cow that produces a lot of milk to have a daughter that produces a lot of milk?
PTA Predicted Transmitting Ability is the predicted difference of a parent animal's offspring from average, due to the genes transmitted from that parent. Each PTA is given in the units used to measure the trait. The PTA for milk is reported in pounds or kilograms, the PTA for productive life is reported in months.
Reliability Sometimes called repeatability,
SCS Somatic Cell Score is calculated from the Somatic Cell Count (SCC). When milk is produced, a small number of cells, are also transferred to the milk (along with the proteins, fat, water, and minerals that make up milk). Although all milk contains some of these cells, milk quality is affected if they are present in very high numbers. Milk processors limit the amount they will allow in milk they buy from farmers. Also, knowing the SCS for an individual cow can help the farmer tell if the cow is healthy because irritation in the udder can cause higher SCS. Health management has the biggest effect on SCS, but just like some people inherit a higher chance of getting ear infections, cows can inherit traits which cause higher SCS. Next to traits like milk or protein production, SCS has a low heritability.
Statistical Analysis A way of using mathematical formulas to make predictions. For example: sports ‘stats' use a players actual performance numbers to predict how they will perform in future situations. A ‘model' is an equation that explains the type of prediction being made.
A simple model might be used to predict how many home runs a player will hit after the All Star Break, based on how many they hit in the first half of the season. By plugging the numbers for an individual player, we can make a prediction: If Sammy Sosa hit 30 HR in the first half of the season, he will hit 60 HR for the season.
A more complex model for the same problem might also include adjustment factors for who his opponents are, where games are held, or even his health or age.
An even more complex model might also use the past performance of other players in similar situations to help improve the accuracy of the prediction.