With so much time spent catching-up on things during the winter months, it’s not uncommon for producers to put their bulls on the “back burner.” Unfortunately, many bulls are nutritionally forgotten, leading to potential problems the following year. At a time when hay prices at are record highs, it’s possible that some producers might inadvertently underfeed their bulls this winter in order to save some money. But, proper nutritional management of bulls at this time of year is crucial to success during next year’s breeding season. This is particularly true for thin bulls and young bulls that just completed their first breeding season.

Have Your Checked Your ‘Battery’ Lately?
As funny as some folks think the words “bull battery” sound, they need to be taken seriously. On cow/calf operations, bulls provide half of the genetics in a calf crop. And, bull fertility far outweighs cow fertility, at least if you consider that a bull should breed about 25 to 40 cows in a season.

Thus, with over 90% of operations using only natural service to get cows pregnant (USDA survey data), nearly every operation could easily have just one poor-performing bull cause a lot of open or late bred cows.

As has been discussed in previous articles, getting cows to conceive early in the breeding season is crucial to the long-term reproductive and financial success of an operation. Otherwise, more open and late-bred cows will result in a longer calving season. And, late bred cows will produce younger and lighter weight calves next year, reducing income.

On spring-calving operations, most bulls have been pulled from the cowherd (or at least should have been) by early fall. It’s important that these bulls be given a period of post-breeding season “R & R” (rest and recuperation), particularly since it is uncommon for bulls to lose upwards of 10-15% of their body weight during a breeding season (i.e. 200 to 300 lbs on a 2,000 lb bull). Each bull in your bull battery should be evaluated annually for health and ability to breed, including structural soundness and vigor. After culls are removed, bulls should be divided into two groups: 1) older and more dominant bulls that have decent body condition, and 2) young and thin bulls. It is important to separate bulls, since these two groups have significantly different nutritional needs.

Meeting Winter Nutritional Needs
Most mature bulls in good body condition can get by on a 100% forage diet, without additional supplementation from grain. A hay diet consisting of 7% CP (crude protein) and about 50% TDN (total digestible nutrients) will meet a mature bull’s requirements, but only if he doesn’t need to gain weight. A daily intake of about 1.5-2.0% of body weight (2,000 lbs × 2% = 40 lbs/day; dry matter basis) should be targeted, and body condition should be monitored closely.

In contrast, young bulls that lost weight during the past breeding season (but are still growing) often need to gain upwards of 2 lbs/day during the off-season. Older bulls that are thin due to significant weight loss also need to put on substantial gain, commonly 1-2 lbs/day. Nutrient requirements for growing, thin, and mature bulls at varying levels of gain are included in Table 1.

Table 1. Nutrient requirements of bulls at varying levels of gain

Diet nutrient density

Body weight (lbs)

ADG
(lbs/day)

Dry Matter Intake (lbs)

TDN
(% DM)

CP
(% DM)

1,200

1.0

25

56

7.8

1,200

2.0

26

63

8.4

1,400

1.0

27

56

7.5

1,400

2.0

28

64

8.0

1,600

0.0

27

48

6.9

1,600

1.0

30

56

7.3

1,800

0.0

29

48

6.8

1,800

0.5

31

52

7.0

2,000

0.0

31

48

6.8

TDN = total digestible nutrients (energy); CP = crude protein; DM = dry matter.

Adapted from Hersom and Thrift (2008), based on Nutrient Requirements of Beef Cattle 1986 and 1996.

“High risk” bulls (young and/or thin) need a diet that consists of roughage at about 2% of their body weight (1,400 lbs × 2% = 28 lbs/day) and enough grain to make the total diet consist of about 7.5-9.0% CP and 55-65% TDN. Typically, about 3-6 lbs of most grain products will help to meet this requirement. Ultimately, proper winter nutrition will enable a producer to turn-out young bulls at the start of the breeding season with a body condition score of 5.5 to 6.5.

In addition to supplying energy and protein to bulls, there are a few trace minerals that are needed. Zinc is of particular importance since it directly affects sperm production. Based on research by John Arthington at the University of Florida, several measures of fertility can be improved via the supplementation of Zn at 60 ppm (twice the current recommendation). In addition, this research suggested a benefit in fertility if some Zn was fed in an organic form.

Prepare Bulls Early for a Busy Spring
Even though your bulls may try to convince you that they don’t have to work until turn-out, it’s important to spend considerable time during the spring to get them ready for the breeding season – especially after feeding them all winter!
Bull fertility is generally affected by four variables: 1) testicle size (scrotal circumference), 2) semen quality, 3) libido (generally not measured in the U.S.), and 4) structural soundness. The most crucial thing you can do for your bull battery’s fertility is to evaluate the semen quality on every bull about 30-60 day before breeding season starts with a Breeding Soundness Exam (BSE).

This evaluation of their reproductive capacity (via measurement of scrotal circumference and collection and analysis of a semen sample) helps to eliminate bulls that aren’t able to do their job. Numerous datasets have proven the value of a BSE, including data from the late Dr. Jim Wiltbank where semen classifications were compared to subsequent conception rates (Table 2).

Table 2. Effect of bull semen quality on conception rate

Semen classification

No. of bulls

Conception Rate

Range

Satisfactory

29

60%

14-100%

Questionable

11

48%

31-57%

Unsatisfactory

11

30%

0-69%

As summarized in “Reproductive and Nutritional Management of Beef Bulls” by Corah, Ritchie, and Selk.

Interestingly, results of a USDA survey indicate that 57% of operations that purchase bulls had a BSE conducted on newly-introduced bulls. However, only 17% of cow/calf operations had a BSE done on bulls that were already on their operation (i.e. not purchased recently). Larger herds were more likely to have a BSE done (54%) than small herds (11%). This is a great opportunity for producers to easily identify subfertile bulls that is generally not being done.

Beyond conducting a BSE, it is important to annually process bulls in order to vaccinate, control insects (particularly lice and flies), test for trichomoniasis (particularly in states with regular outbreaks), and check feet and legs prior to turn-out. It is also important to plan ahead so that bulls expected to share a pasture during the breeding season can be grouped together in advance.

Avoid Lazy, Injured, or Frostbitten Bulls
Unfortunately, in the wintertime some bulls get demoted to the poorest facilities on an operation. Yet, the design and layout of a bull pen can be critical for several reasons.

Some have suggested that bull wintering facilities should include approximately 2 acres per bull, especially if fighting is common. This may seem excessive, but an effort should be made to promote activity by bulls. This can also be done by putting substantial distance between feeders/bunks (if used), waterers, and loafing areas. If bunks are used, plenty of room (at least 2 feet per bull) should be provided.

Protection from severe winter weather (particularly wind chill) should also be provided to bulls. Extreme cold can freeze the lower part of the scrotum, leading to damage and reducing semen quality. The relationship between BSE score and severity of frostbite in bulls (Table 3) indicates how seriously frostbite can affect fertility. For instance, the percentage of bulls that had an “Unsatisfactory” BSE score increased to 26.7% when frostbite was moderate, and up to 88.7% when severe.

Table 3. Relationship between severity of frostbite and semen quality of affected bulls

Severity of Frostbite (%)

Breeding Soundness Score

Mild

Moderate

Severe

Satisfactory

89.5

48.0

2.1

Questionable

9.5

25.3

9.2

Unsatisfactory

1.0

26.7

88.7

As summarized in “Reproductive and Nutritional Management of Beef Bulls” by Corah, Ritchie, and Selk.

Tissue damage due to frostbite will appear as discoloration, a scab, and/or sloughing of the lower portion. Frostbite can be prevented by providing a shelter, windbreak, or heavy bedding (e.g. straw) for bulls to burrow into.

The Bottom Line
Even during times of high feed prices, nutritional management of bulls is critical – a bull contributes half the genetics to your cowherd and his fertility far outweighs that of any single cow. One bull that is unable to breed due to soundness, body condition, or fertility problems can cause many open or late bred cows.

After fall culling, older bulls should be separated from young and thin bulls. Mature bulls in good condition can be sustained on a 7% protein and 50% TDN forage-only diet. But, bulls that need to gain 1-2 lbs/day require at least 8% protein and 55% TDN. Give bulls plenty of room in large pens, and offer protection from severe weather to avoid frostbite. Severe frostbite will cause most bulls to become infertile. Finally, have a Breeding Soundness Evaluation performed on each bull 30-60 days before the start of the breeding season – the cost can easily be overcome by identifying just one subfertile bull.