While most reduction in mastitis comes from management, genetic variation for mastitis resistance does exist and some cows and bulls produce daughters that are less susceptible to mastitis than others. The Mastitis Resistance ABV is expressed relative to an average of 100 with higher breeding values indicating healthier cows. To breed replacements with improved mastitis resistance, choose bulls from the Good Bulls Guide with a Mastitis Resistance ABV of more than 100.

While most improvement in herd reproductive performance comes through improved management, genetic variation for fertility does exist and some bulls produce daughters that are more likely to become pregnant earlier. The Daughter Fertility ABV reflects the percentage of an animal’s daughters pregnant by six weeks after the mating start date compared to the average. For year round calving herds, this is equivalent to the percentage of their daughters pregnant by 100 days after calving. Daughter fertility is included in each of the three indices, with a higher weighting in the HWI. To improve fertility in your herd, select animals with a Daughter Fertility ABV of more than 105.

The Heat Tolerance ABV allows you to identify animals with greater ability to tolerate hot, humid conditions with less impact on milk production. To improve heat tolerance in your herd, select animals with a Heat Tolerance ABV of greater than 100. Allow for the lower reliability of the Heat Tolerance ABV by using a team of bulls.