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• Milk yield remains an important trait that should not be overlooked when selecting for improvements in dairy cows.
• Selecting bulls based on PTA milk may increase returns over $50,000 for a herd of 100 cows.
• Index selection is a powerful tool for combining information on several traits.

INTRODUCTION

Selection is the most important tool available to improve genetics of a dairy herd. Over the years, the amount of genetic information available to use in selection decisions has increased significantly. However, many statistics can make it difficult to decide which information to use when selecting bulls to use as sires. In addition to information on milk yield and milk components, there are numerous indices that combine yield and type.

Which information is most important? The answer depends on your breeding goals and the specifics of your operation. Selection for any one trait will result in the most progress for that specific trait, but may not be the most economical decision if several traits are important.

PTA MILK VS. PTA TYPE

How can selecting for predicted transmitting ability (PTA) milk increase profits over selecting for PTA type? As an example, suppose a producer has 100 cows in his herd and each cow completes three lactations. Also assume that the producer receives $12.30 per hundredweight of milk.

First, assume the producer selects bulls based on PTA milk. If he chooses a bull that is 500 pounds greater than another bull (i.e. 5 cwt.), then the increase in gross return is 5 * $12.30, or $61.50 per daughter per lactation. Over three lactations, the increase would be $184.50 per daughter. For 100 daughters, the producer would receive a $18,450. gross return from sire selection for milk. Table 1 shows this information along with gross returns for selecting a bull that is 1000 pounds or 1500 pounds over another bull for PTA milk.

In contrast, selecting only top type bulls may yield an increase in returns at cattle sales. If a producer sells 2 or 3 more animals annually for reasons of confirmation, the gross return may be several thousand dollars over three years. Not every producer will be able to increase cattle sales, and in many situations, traits other than type will also be important (i.e. some say that red cattle are selling well, now). If the producers main revenue is in milk sales, it appears that increasing milk production by selecting higher PTA milk bulls will increase revenue more than selecting higher PTA type bulls.

INDEX SELECTION

Several indices are available to producers that allow for selection of a combination of traits as opposed to selecting for just a single trait. Net Merit Dollars (NM$) is an index that includes PTAs for milk, fat, protein, somatic cell score (SCS), and productive life (PL). The index starts with the milk-fat-protein economic index (MFP$), subtracts feed costs, subtracts mastitis and milk quality costs associated with SCS, and adds value of PL. The index gives a weighing of 10 for yield, 4 for PL and -1 for SCS. The NM$ index reflects the net contribution to income from these traits on a lactation basis.

Using our 100 cow herd example, selecting a bull with a NM$ rating 25 dollars greater than another bull indicates a 25 dollar increase in gross return per cow per lactation. That is, $25 * 3, or $75 per cow over three lactations, and $75 * 100 , or $7500 for 100 cows over three lactations.

If your breeding goals include increasing yield, increasing PL and decreasing SCS; comparing bulls based on their NM$ value may be profitable. Keep in mind that if you are selecting for NM$, you should not compare bulls based on individual traits. The index is constructed to combine economic information and weight each trait appropriately. A bull with a lower relative score for one trait will not be penalized if that trait is not as economically important as another trait in which he has a higher relative score. In general, select an index based on the goals of the herd, then allow the index to find the right bulls.