Herd Health

Cold Weather Effects on Bull Management

By Gary Rupp

Generally, bulls go through winter with minimal problems related to cold weather or nutritional stress, but the severe cold, snow and wind-chills this winter have created the possibility of frostbite and reduced body condition that could have long-term effects on the breeding season. As a rule, bulls are wintered with minimal concern about shelter or bedding and feed is provided at maintenance levels, but this year the combination of cold weather followed by extremely muddy conditions has increased energy requirements while winter feed supplies have been short. These factors make preparation for breeding season a high priority.

Scrotal frostbite can affect fertility in bulls. An older study conducted in the north central U.S. following two severe winters in 1949 and 1964 demonstrated the increased risk of testicular damage following moderate to severe frostbite. Older bulls with a more pendulous scrotum appeared to be at a higher risk of severe cold stress and had more evidence of frostbite on the skin of the scrotum. Of 6,389 bulls examined in the study following the 1964 blizzard, 14.2 percent had frostbite lesions. The damage to spermatogenic function was related to severity of the frostbite noted on examination (see table). Semen quality improved with time in some affected bulls, but those that developed testicular adhesions often had permanent damage.

Relationship Between Severity of Frostbite and Morphologic Character of Sperm Cells*

              Very Good   Good        Fair         Poor

Severity  (No.) (%) (No.) (%) (No.) (%)  (No.) (%)
Mild            6     21    13    45     5     17      5     17
Moderate  23    20    34    29    16    14     43    37
Severe       1     12     0      0      0      0       7     88

Morphologic characteristics of sperm**

            *Data on 1964 blizzard supplied by Dr. L.E. Newman, Glasgow,  Mont.

**P<0.01

Evaluation of bulls for breeding soundness and seminal quality is a good part of breeding-season management every year before natural mating, but it may be even more important following this winter. Previous studies have indicated the use of bulls with a high percentage of normal cells on morphology examination results in better reproductive rates. Evaluating bulls at least one month prior to the breeding season also permits an opportunity to re-test bulls that fail, if necessary, and better plan the breeding season.

Reference: Faulkner, et al. 1967. JAVMA 1515(5):602-605.  Y 
By Gary Rupp, Director and Professor, University of Nebraska Great Plains Veterinary Educational Center. He is actively involved in the development and support of the Cow Calf Computerized Herd Health-Management Record System.