FERTILITY-ASSOCIATED ANTIGEN ON BULL SPERM INDICATES FERTILITY POTENTIAL

A 30-kDa heparin-binding protein named fertility-associated antigen (F AA) was identified in sperm membranes of beef bulls with greater ferti lity potential. In a survey of 2,191 beef bulls, 88% had FAA present i n sperm membranes (FAA-positive), and 12% were FAA-negative. In the fi rst study, 54 Santa Gertrudis and 51 Santa Cruz bulls were grouped (1 to 14 bulls per group) according to FAA profiles and were bred to 2,40 3 cows at ratios of 1 bull: 25 cows. Fertility for 14 groups of FAA-po sitive bulls averaged 88%, whereas three groups of FAA-negative bulls impregnated 79% of the cows. Thus, FAA-positive bulls were nine percen tage points more (P < .01) fertile than FAA-negative bulls. In the sec ond study, 2-yr-old Santa Cruz bulls (n = 26) were grouped according t o FAA profiles and serving capacity. The fertility of the group of 12 high-serving-capacity, FAA-positive bulls was 87% of 270 cows. The gro up of six FAA-negative bulls with high serving capacity impregnated 78 % of 143 cows. Among the groups of bulls with high serving capacity, F AA-positive bulls were nine percentage points more (P < .05) fertile t han FAA-negative bulls. The group of eight FAA-positive bulls with low serving capacity impregnated the least(P < .01) percentage (69%) of 2 38 cows. Serving capacity of bulls should be considered when optimizin g fertility potential. Among bulls with acceptable physical characteri stics and serving capacity, determination of FAA profiles in sperm can be used as a tool to identify subfertile bulls.